canbaufo

Oh boy, I'll try to make it a relatively short story with the main question...well, at least before the end anyway. Mechanic friend chased his tail thinking my miss was spark related (I mislead him because I saw arcing plug wires in the dark). He swapped wires, plugs, opti, coil, ICM, bypassed MSD, etc, etc, etc... to no avail. After running 10 gallons of gas through the car during all of that troubleshooting he finally decided to check fuel pressure. It was around 20 PSI.

So he bypassed my inline booster fuel pump and found good pressure at the rail on just the in-tank pump. He fired it up ...still missing. He plugged in a noid-type test light on injector wires and sometimes it lights up and sometimes not. Seems to do better with front injectors but nothing is consistent. So he feels very strongly the PCM is bad ...as he's seen injectors not get a pulse signal due to bad PCM's many times before. But then I have to ask myself, "what are the odds of an inline fuel pump and a PCM going bad at the same time?"

I've read up on this a bit and I believe the more likely culprit is a shorted or faulty injector. Low fuel pressure is a known issue that existed through 10 gallons of troubleshooting run time. Cause and effect theory here: Low fuel pressure is not going to kill a PCM, but injectors??? ..um, yeah I think some of them could die in a 20 PSI environment if subjected long enough (oh they were of course...).

Early on in his troubleshooting something he noted was the front four cylinders were running hot and the back four were running cold (feeling the headers as a reference). My theory is that there was more fuel pressure getting to the front four injectors since the fuel has to "turn around" in the front half of the rail ...so most of them perhaps survived. But the rear four injectors perhaps not. Remember that 10 gallons of gas has passed through the engine while it was only getting 20 PSI (yes, I'm very worried).

Can a noid light be thrown off if there is one or more injectors bad? I'm thinking yes, as they are all on the same circuit? ..or at least each side is?? This is the main thing I'm getting at if people don't want to read the rest below, starting with the next paragraph. I know there's probably a write up but I already have hours upon hours of researching the wrong things due to misdiagnosis (eg. I learned all about Opti choices and replacement ). If someone can answer this and maybe point me to the most efficient (and hopefully relatively easy) way to test injectors I would really appreciate it.

I've lost interest in the car in the last few years so forgive my ignorance. I saw arcing plug wires in the dark where the car was being stored a few months ago and believed it to be the cause of the miss. I do most of my own work now but it was stored away from home (away from my tools) and missing kinda bad; so I took it to him for new wires, painting of bumpers, and an AC charge to prepare it for a sale. I recently completely rebuilt my Powerdyne with top notch (928 Motorsports) cogs, internal belt, bearings, impeller shaft, etc. and was waiting on him to finish the other stuff before putting the blower back on (to get the car ready for me to sell). Now I have $2,500 in the car recently and no resolution of the miss....and the nicely rebuilt Powerdyne is still sitting in a box

He's super overwhelmed with a full time job (60 hours) and running this shop on the side with his son and another guy. He's honest but I'm nervous about his ability to diagnose this and/or devote appropriate time to it ..understandably so after all of this. I'm also very worried about some things I observed when I was at the shop. It blew at least one header gasket and I could tell the exhaust coming out of it was very "gassy" (just thinking if the combustion environment was poor enough that it blew a header gasket ...what else is wrong?). I'm worried that 10 gallons passing through the engine at 20 PSI has washed out the rings, polluted the oil with excessive fuel, etc....by the way the oil was rather old when the car arrived at his shop anyway. I saw smoke coming from the tailpipes and may have just been paranoid but I thought it might even have a blueish tint. If so, doesn't that mean my longblock is shot? If you're getting blue smoke out of the exhaust on old shot oil, even if you put new (non polluted) oil in that doesn't mean your rings are going to start sealing efficiently ...right?

I'm considering abandoning this nightmare and offering the car to him for next to nothing (he has a long history with the car and me). It's in very good condition and only has 67K miles. The mod list is super long but the main mods are in my sig. Not including the purchase price I probably have about 30K in this car over the years. Recently I decided I would spend around 2K to get the car ready for a sale of around 7K (just being realistic about the soft market for LT1 cars). I've paid him $1,500 for the work he's done and that even includes re-painting the front and rear clips (and he only asked for $1150). With the blower rebuild, money to him and parts I'm out of $2,500 so far and probably need new injectors (and/or a PCM ...car was jumped a lot on old battery when it first arrived at his shop). He's a nice guy but I need to get on with things somehow and pick a direction. This has been going on for a click over 4 months now! I took my car into his shop thinking I'd get it back in a week or two. Now it's been this long and I'm concerned the rings or who knows what else may be trashed. Arrrrrghhhhh ......

Injuneer

Have to admit, I haven’t read past the first few paragraphs. But the first thing to do with a misfire or rough engine is 1) check the fuel pressure and 2) scan it for codes. Appears he waited way too long for step #1. Has he done step #2? This is basic. People rag on me for posting those two steps in response to most "my car is running poorly” threads. But it's the best way to approach the problem.

There is a code for faulty injector circuits. Has he verified reliable 12 volts on the pink wire at each injector connector with the key on? Has he verified the resistance of each injector? Has he examined the injector wiring for damaged insulation, corroded contacts, etc.. Has he shaken the wiring while using the ‘noid light? Has he tried a different 'noid light?

The PCM had an individual driver for each injector. In the 20+ years I've been helping people with the LT1 on sites like this, I can’t remember more than one or two verified cases of PCM failure of that nature. Most failures are due to bricking the PCM while programming.

Running injectors at low fuel pressure will not hurt them. There's basically an electromagnetic coil that lifts something (pintle, disc, ball, etc.) to open the injector. Less pressure means less work to open it.

The theory about the higher pressure at the front four injectors due to the fuel having to turn a corner has little basis with respect hydraulic fundamentals. The rail bore diameter is made large to keep velocity low and minimize loss of pressure from the inlet end to the outlet end. Yes, pressure drops along the way in the straight sections due to friction, but velocity and pressure loss is kept low due to the large diameter. Yes, as flow changes direction pressure is lost in each turn. But flow can only exist if the upstream pressure is higher than the downstream pressure. There are far too many people using the stock rails in very high HP applications, and front injector pressure being greater than rear injector pressure is not experienced.

It appears from your description, but not verified, that the car may have sat for an extended period. Was it started regularly to circulate oil and fuel? Was the fuel treated with stabilizer? Was any effort made to clear the fuel system before trying to start it? Have the injectors been cleaned? Have the fuel lines and rails been flushed? Has he pulled the fuel rails up and observed the injector flow and spray pattern? Noticed the question about blue smoke. The longer the engine sat unstarted, the more likely the rings could be gummed up.

Next step would seem to be a data log using Scan9495. I can review the data log for you.

https://www.camaroz28.com/forums/com...95-lt1-874306/

canbaufo

Wow Fred, thank you. Actually I was hoping you'd be responding to this thread. I've literally been putting off looking because I've become anxiety-ridden over this...and I thought it would be good to wait for responses anyway. OK, I need to give you background and reiterate my most basic observation (that low fuel pressure is now a known problem that was present until he bypassed the inline booster pump). Nothing technical here but only common sense telling me that the car running with very low fuel pressure during troubleshooting (to the extent of using about 10 gallons of gas) likely led to whatever else is wrong. I have an adj FPR and he said I have "good pressure" at the injectors. I asked him if the adj FPR might be thrown off since it was adjusted for both pumps running in line and he said "it doesn't care what's behind it, it's still regulating the same pressure at the rail". Which makes sense to me as long as there's excess pressure to bleed off regardless of whether one pump is running or two. I know this is long, but I'm a layperson and figure the more info you have the better ...hoping something jumps out as a red flag (like rear four cylinders being dead, as an example).

The car has always been garage kept (so corrosion should not be an issue) and was moved to another garage away from home in good running condition last summer. I started it every 2-3 weeks and took it around the block to full operating temp each time. I think once it sat for about two months, the longest period while there. I started it up and did my typical drive to operating temp without any issues. Then about 2-3 weeks after that I took it for a maintenance run and it developed a very faint miss, much akin to a plug wire being loose on a plug. I'd give it more gas while driving it (means less vacuum and more fuel pressure as a result) and the miss would smooth out. I figured it needed plugs, as it had been awhile anyway and needed some anyway ...so I decided when I'd have time I would change at least most plugs and see if it helps. I drove it gently two more times over the following month and the miss very progressively got worse (my theory is either the inline pump was slowly dying and/or I suppose it's at least possible the injectors were dying too). Once the miss became worse I decided to tackle the plugs. I changed the 6 easiest (all but back two on passenger side) and the miss did not improve at all. Then I observed the plug wires (and they were quite old) and noted some faint blue arcing in the dark. By the way, yes, it had fuel stabilizer in it. Apparently had a bad battery but I didn't know because it was on a smart tender. He had jumped it a few times during troubleshooting and then later told me it needed a battery. Not sure how many times it was jumped, but we did get a new battery in there somewhat early in this whole process.

I already had plans to have the A/C fixed and some paint work done at his shop ...so I decided to let him tackle the wires...this is why it wound up at his shop. Oh the irony of all of this ...years ago I decided to replace my fuel pressure gauge with a wideband. Should have made room for keeping the pressure gauge. I thought the wideband reading lean might indicate a fuel pressure issue ...or rich maybe a firing issue (I now realize this isn't always the case). Since it ran rich I thought it was more likely a spark issue than fuel pressure. Now in hindsight I realize even low fuel pressure can cause a rich reading since the fuel doesn't atomize properly without enough pressure. Never, ever get rid of a fuel pressure gauge.

You asked if he scanned....I need to read back through the nearly 300 texts and will tell you what I can but I do know one of the first things he scanned and found was a -40 (yes, negative 40 ...didn't say if C or F) reading coming from the front water temp sensor (the one that the PCM uses for feedback). We replaced both temp sensors and even the plug for the front sensor and he got a better reading. At that point it started idling better but still had a bad miss. At the time he said "heavy gas smell, seems to be choking on fuel, no backfires though". Then later on he said "opti spark is my call, four cylinders dead ... 5,7,6,8 dead". His explanation of "dead" at the time was that the rear four cylinders were "running cold" and he had little to no heat at the headers. He said he had a couple hours in dealing with the sensor and "getting engine light to stay out" ...not sure what he did there.

Reading through the plethora of texts and doing my best to convey what's pertinent, sorry...this has been so stressful. He did say the injectors passed the resistance test, but at the time said it wasn't much of a test really. At the time he said the pulse was good too (I guess this is what is now fidgety with the noid light as described). Maybe he didn't check all of them at that time, I am not sure.
As I read through the texts I see that many times he mentioned the back four cylinders basically not running. He said he was puzzled because there was spark and pulse ...at this point he still hadn't checked fuel pressure but had mentioned it was something he needed to do.

He checked grounds and reseated them, installed an opti and took it off and put my old one back on, swapped coil and ICM with ones he had at the shop, bypassed my MSD, etc ...all to no avail. Then finally he checked fuel pressure and was like "20 freaking pound of pressure ...I can't believe it" ...and thought he had found the problem well enough that we know knew what it was. He bypassed the inline booster fuel pump and found "good pressure" at the rail (I haven't asked what "good" is) and was bummed to find it still missing. Then he did the noid light check and found it fickle, so he assumes it's the computer. He's said all along the PCM is suspect. I think it's a very slim chance, especially based on what you've told me here.

With regard to the rear four cylinders being dead; I did a search on that and found someone with a C5 that had the same problem. They found the PCM to ground wire was chafed and that caused the rear injectors to stay on all the time, flooding the engine with fuel. Just thought I'd throw that out there. He said all grounds were checked and re-seated ...I don't know if he probed them for voltage or whatever (remember, I'm just a layperson).

Will try to answer the most critical questions you asked about injector testing and other. He did tug and pull on injector wires gently while we watched noid light, no rhyme or reason could be detected. I do not know if he verified the resistance for EACH injector or only a few...but he did do that check at least in some capacity. He hasn't tried another noid light but feels that one's good based on other use. I do not believe he has done the 12V pink wire injector test, but all of them will light up the noid at some point (if that makes it a moot point, I have no idea). I don't believe the injector wiring has been thoroughly checked over. He said if there was an issue there "it would be somewhere in this harness". I think he's mostly just relying on the noid light to tell him something. He did a compression check and said that was good too, but I don't know if he checked all cylinders.

I don't think he has lifted the rail to see the spray pattern of the injectors. No, the lines have not been flushed and injectors have not been cleaned. The car really didn't sit that much IMO, but maybe every 2-3 weeks up to operating temp isn't really enough.

Let me reiterate that low fuel pressure is now known to be a condition it was toubleshooted (ran with) for most of this process. I can't help but think in terms of cause and effect that somehow that contributed to what the mystery miss is. I don't know what he scanned with but at least know he scanned it once and found the -40 degree reading at the front water temp sensor ...and he did something else to make a check engine light go off, apparently.

Sounds like the easiest course of action (which is what he needs as he's very busy) would be to try the Scan9495 you're talking about. I appreciate the offer and will see if there's a way we can do that. Oh boy...looking below I see tons of related posts about noid lights and injector issues.

I only want to sell this car and I'm afraid I'm going to have more money in it than I'll get out of it if I go much further. $2,500 deep so far here recently. Should I just sell the car as is?? I don't want to part out...no space or time for that. Just rebuilt my supercharger last Fall and wanted to reinstall it while fixing a few minor things up and now this....

canbaufo

Didn't mean to scare you away, was just hoping any and all background might make something obvious or appear to be a likely culprit.

Ultimately I want to see the car back in it's former glory before selling it. Need the money for the car in running condition vs non running condition too ...so my nerves are a little shot, sorry.

Considering it's had 10 gallons of fuel ran through it at 20 PSI fuel pressure while running it at no load during troubleshooting (while missing) ...is it likely that my rings are damaged? I'm concerned that the oil was overly polluted with gasoline (at one point he admitted the plugs were dripping in gasoline when he pulled them out). I'll soon do my own oil quality check and/or see if the oil level is literally too high because it's now gassed up.

Finally with regard to worrying about the state of the longblock, consider that during troubleshooting it at least blew one header gasket (the driver side, if not both). I'm thinking "if the state of the running condition was so bad that it blew a header gasket even with no actual load on the engine, what else is wrong"?

I'm going to go check it out and scan some in a day or two (I at least have a Scanmaster in dash) and see if I can find anything else like a blown head gasket. If I see something major like that or the oil quality is basically more like gasoline I think I'm out and will choose to sell the car as is. Will be a real shame if this is how 20 years with that car ends.

Any advice is appreciated. Sorry for the long posts, but if you can make time to review the previous (huge) one just for some insight I'd greatly appreciate it.

Been awhile since these pics but it's still in comparable shape:

https://www.camaroz28.com/g/album/8139214

Injuneer

OK.... taxes filed and Professional Engineer continuing education units completed. This is going to seem disjointed, but I keep going back and forth to read what you posted, and I'll spot something in a paragraph I hadn't noticed before.

Low fuel pressure reduces fuel flow. If the pressure is 20psi, vs 43.5psi stock (no vacuum), the fuel flow is only 68% of what it should be. If the PCM is in open loop, and does not warm up enough to put it into closed loop, and the PCM long term fuel trims (LTFT) have been cleared, the engine is going to run lean in open loop. Once the engine reaches ~140-degF, and the O2 sensors are showing activity, the PCM will switch to closed loop.

The coolant temp sensor problem (water pump) could explain the rich condition, but ONLY if there was sufficient pressure to supply the rich fuel mixture that the PCM is programmed to supply when the engine is cold.

In closed loop, the PCM will see the lean readings in the O2 sensors, and will start to add fuel using the LTFT's. The most it can add is 25%, which is almost enough to make the fuel "whole". It can then use the short term fuel trims (STFT) to add more fuel. The LTFT's are stored, and when you restart the car again, as long as power to the PCM has not been lost, the LTFT's will continue to add fuel, but the STFT's cannot add fuel until the PCM enters closed loop.

The info on the FPR is correct.... if it's set to maintain 43.5psi (no vacuum) it simply stays closed until the pressure in the system exceeds 43.5psi. If the pump can't produce 43.5psi, it's going to dead end the system, no return.

With the S/C, do you have an FMU? If not, is the system adding fuel based on the tune? Do you have a 2-bar MAP sensor? Keep in mind the job of the FPR is not to maintain the rail pressure. It's job, since it is vacuum (or boost) compensated, is to keep the DIFFERENTIAL pressure (rail pressure minus intake manifold vacuum) at 43.5psi.

If you have a misfire, and the fuel is not burning, or it's not burning because of poor atomization, the O2 sensor will read "lean". The O2 sensor can only "see" oxygen. There is no way that having unburned fuel in the exhaust can cause an O2 sensor to read "rich".

Running lean does not explain the wet plugs - makes it hard to rationalize the conflicting issue of low fuel pressure. It would also not cause fuel contamination of the oil, unless the cylinders were seriously misfiring. If the rear 4 injectors were not firing, there's no unburned fuel to wash down the cylinder walls. All you need to do to check the oil for fuel contamination is pull the dipstick and smell it. If the engine hasn't been run hard, just some idling and light loads, even with a bit of fuel in the oil, it's not likely to damage the rings or cylinder walls.

I don't know the internal wiring of the PCM. Whether one of the PCM grounds being lost would cause the 4 rear injectors to not fire is a possibility, but only if the two PCM grounds are kept separate internally. Don't know. And a C5 is not an LT1. Whole next generation of PCM. While the resistance of the injectors is a simple check, it's important because the wrong resistance will set codes, and may pull enough current to burn out a driver. But if the circuit voltage is wrong, the PCM should set DTC 18 and deactivate the injector. The comment on the "chafed" ground make me wonder if some mice have been at work, and maybe there are some other wiring issues.

As far as "blowing" a header gasket, is it possible you have a clogged cat (if you even have a cat)? That would explain a lot of things, particularly with the S/C. Did it experience any backfires during all the time idling for diagnostic work?

Use the Scanmaster. It can show you codes, it can show you if the coolant temp sensor is giving a rational reading, along with many other sensors. Scan9495 may turn up soe issures as well.

ACE1252

If he isn't scoping the secondary ignition(or other electronics), it could lead to a lot of guess work as to what is going on. You can see quite a bit about what is going on with the spark/fueling by looking at the firing pattern/sparkline of the secondary ignition. Have a look at this as a starting point....scannerdanner's youtube channel is a treasure trove for those wanting to know how to diagnose engine problems like a pro.

Current clamping the primary ignition coil/ignition feed circuit can show you a lot as well. It's how I verified a cylinder miss on my 2005 Frontier V6(and which one it was). It only once threw a code for a misfire. Misfire would come and go. Current clamping the ignition circuit and looking at all the ignition current waveforms verified that #3 was missing/having issues. I had either a bad coil or plug. I changed them both at the same time since I had to pull the intake to get the coil pack out.....in fact I changed them all out on that side as a preventive maintenance move(135K+).

Search Scannerdanner misfire on youtube and watch the videos. You'll learn a lot.

canbaufo

Sorry, I failed to mention I use an open loop tune (I disabled the parameters that enable closed loop). The car ran much smoother without a "lean cam surge" condition at low loads when I tuned out closed loop. Ran it that way for many years, no issues ...I leaned out the fuel tables some to compensate for constant open loop running and have a wideband permanently mounted (usually runs 14.0:1 when putting around).

No FMU, it is tuned to provide good fueling for 42.5# injectors. Typically use an inline booster fuel pump with stock intank fuel pump, but right now inline pump is bypassed and he said it has good pressure. MAP is the factory 1994 sensor.

Very good info, noting this before I go over there to scan. Thank you.

No cat. No backfiring. Just very concerned that merely running it at no load popped a gasket, makes me wonder what else is wrong.

Some more things are occurring to me as I think through the ordeal and I must reiterate the simplest observations in case this is all being over-thought:

- I am using Ford/SVO/Bosch 42.5# injectors, which may be even more sensitive to low fuel pressure, or more prone to failure in such conditions.

- The ONLY known problem so far is that low fuel pressure was present for a significant period of troubleshooting run-time. Bad PCM doesn't logically coincide with a failed inline fuel pump, but failed injectors certainly could. This miss started as very faint like a plug wire loose on a plug and got progressively worse. This makes me feel like a few injectors were going one by one until a few were out (or maybe only one being out can affect the pulse signal for all)??? Can a bad injector cause the pulse/trigger signal to get fouled up for any and all???? (noid light test)

- The fact that plugs were pulled and dripping in fuel makes me feel like one or more injectors are STUCK OPEN. An observation that supports this theory is that it had had a tremendous amount of fuel to drink during troubleshooting run-time. I could see it using a ton of fuel if you have big 42# injectors stuck open. I am not sure if he checked that fuel pressure was maintained after shutting off the engine (could indicate injectors stuck open if it suddenly drops).

- I feel very sure that initially the only thing wrong was low fuel pressure due to no power going to inline pump or failed inline pump (no confirmation of which yet). Cause and effect, the low fuel pressure hurt something or caused a problem. Without being able to diagnose it hands-on at the moment, common sense tells me it's possible that injectors have been fouled up by running at low pressure for too long. You said less pressure means less work to open injectors, so perhaps they were too easy to open for too long and are now stuck open.

- You said there's an individual driver for each injector. Would I be correct in assuming it's likely only one would go out if that was the issue?

Thanks so much for your input and you too ACE1252! I'm heading over to review the Scanmaster and look things over and will let you all know my findings.

Injuneer

You seem convinced you damaged the injectors due to low fuel pressure. There's apparently nothing I can add to change your mind.

canbaufo

No. My mind is wide open. Just wanted to answer your questions and be clear that low fuel pressure is the only diagnosis of anything that was wrong thus so far (other than a bad water pump temp sensor connector, that has been repaired). After five long months believe me, I am not "convinced" of anything.

I'm articulating every "theory" possible because frankly, I'm not sure my mechanic friend has the time or interest in diving into a true diagnosis. He would rather try new injectors or try a new PCM and see what happens. Therefore I need to at least take a shot at speculating as to what the most likely culprit may be ...as I once again may have to resort to trial and error, which thus so far hasn't been kind.

I appreciate any and all input. Thank you and please don't give up on this.

canbaufo

Finally some real data here! I checked it out myself and sure enough when I checked the DTC part of the Scanmaster is had thrown CODE 18! I did a little quick research and found this post that I've quoted too:

"What happens with code 18 is the PCM detects a fault in the two injector circuits and shuts off the bank affected, causing your car to run on 4
cylinders. Power for the injectors goes through the ignition switch from a pink wire to a fuse block then to the injectors. If the connection is bad the PCM will detect it as a fault and set DTC code 18. These are the possible causes: a grounded circuit, open circuit, a circuit shorted to voltage, an injector that is shorted, open, or has low resistance. The injectors should measure at least 11.6 ohms. The engine should be cold when checking injector resistance."

I confirmed that the rear 4 cylinders are cold to the touch while the front 4 are nice and hot (header primaries).

Sadly, my fears about severe fuel contamination of the oil are also confirmed. The dipstick measures way-overfilled and the consistency seems to be about 50/50 gas and oil ...virtually no viscosity.

He said he will do some testing on the wires and ohms testing of the injectors. He may have missed code 18 because he put a new battery in. Perhaps not long after the battery install he scanned it and the PCM hadn't had enough time to set a code. I verified this possibility myself by disconnecting the negative battery cable, then reconnecting to scan again immediately; code 18 was not present.

Injuneer

Except the two injector circuits are not divided by bank.

Fuse #9 - #2/#3/#5/#8

Fuse #10 - #1/#4/#6/#7

And, neither of those separates the engine into front and rear cylinders.

The description of DTC 18 you found would appear to be for a 1993, the only year with batch-fire injection (not full sequential like 1994-1997). It fires an entire bank of the engine at the same time using a driver for each bank.

If you look at the 1994 factory service manual, page 6E3-A-50, which documents DTC 18, you see:

“The PCM continuously monitors the voltage of EACH injector driver circuit. When the PCM detects a voltage that is out of range, (grounded circuit, open circuit, a circuit shorted to voltage, an injector that is shorted, open, or has a low resistance), a DTC 18 will set and the driver will be disabled.”

“Action Taken (PCM will default to): The PCM will disable driver on THE PARTICULAR INJECTOR THAT HAD THE FAULT. DTC 18 will be stored in the PCM memory but will not turn “ON” the Malfunction Indicator Lamp (MIL).”

For the back 1/2 of the engine to be cold the PCM would have to have sensed four defective circuits.

canbaufo

Great information, thank you. Yes, it was only a quick search so it must have been a discussion about a 1993 model. I can definitely tell you the rear four cylinders were cold and the front four were nice and hot.

One unexpected observation this time; stone cold it fired right up and idled great for about 10 seconds before it started missing.

What if anything do the new observations lead you to suspect? It doesn't look likely that he'll be able to utilize Scan9495, although he may not realize I have an ALDL cable that will attach to a laptop. I didn't note anything else in the Scanmaster readings that appeared to be relevant (but didn't observe long because I didn't want to run the engine long). I cycled through everything and noted that left pulse and right pulse were about the same (~1.8 or so at no load light throttle if memory serves me).

He's pretty much ready to do an ohms test on injectors and blame the issue on the PCM if they check out. I sense there's potentially plenty more to it than that.

Thanks for the FSM information.

I now know only five things with certainty:

1. Low fuel pressure was a condition it ran with for a significant period of time during troubleshooting.
2. Oil is contaminated with a significant amount of gasoline.
3. Code 18 has been set by the PCM
4. The rear four header primaries are cool enough to rest your hand on while the engine is running, while the front four are very hot like normal.
5. Noid light is not consistent, especially on rear four injectors

Injuneer

With only 4 cylinders firing, the engine has got to sound terrible. Surprised is even starts. With the back 1/2 of the engine not firing, there are three cylinders in sequence that don’t fire.

NOT FIRING - 8, 6, 5, 7

FIRING ORDER - 1 - 8 - 4 - 3 - 6 - 5 - 7 - 2

Injuneer

The possibilities for the rear four cylinders not firing:

- 4 dead, plugged or stuck open injectors. Swap injector positions front to rear to see if problem (cold exhaust) follows injectors. Just one injector stuck open could flood cylinder and then oil with fuel. Observe spray pattern. Observe fuel pressure leak down rate.

- 4 dead injector drivers. Possibility of the internal ground split (2 ground wires to PCM) affecting those 4 drivers). But as noted earlier, I have no idea what the internal wiring of the PCM is. I'll see if GaryDoug knows or can check this out on his LT1 PCM simulator setup. Or, out in left field idea - swap harness connectors for injectors #3 and #5, and for #4 and #6. See if problem (cold exhaust) follows harness connectors. Firing injectors out of sequence has surprisingly little effect on engine smoothness. I've run my engine with the injector timing 180-deg out of phase. On a cold engine, may cause occasional stumble, hot engine, no perceptible difference, because the fuel vaporizes on the hot valve. That's why the batch fire engines run just fine (although slightly dirtier and less fuel efficient).

canbaufo

Great info. Yes, it runs that kind of bad. When fired up stone cold it actually ran fine for around 10 seconds. I'm assuming this is due to "not being flooded yet" during cold start up.

Fantastic ideas! I'm checking with PCM4Less to get their input on the possible causes of driver issues, but if you can get info from GaryDoug that would be awesome. Swapping middle harness connectors is an easy try for sure. Throughout the day today I've been wondering what the rear four cylinders have in common (like a common ground or circuit) and thought it to be a strong probability as the issue....whatever the common thing is. I was obsessed with the idea that low pressure hurt the rear four injectors at first, but the more I think about it it really doesn't make much sense that the rear four would go bad. Seems a circuit or ground issue is more likely.