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Bad PCM or Bad Injectors throwing off noid light??? ...opinions wanted ..NIGHTMARE!

LT1 Based Engine Tech 1993-1997 LT1/LT4 Engine Related

Bad PCM or Bad Injectors throwing off noid light??? ...opinions wanted ..NIGHTMARE!

Old 01-25-2019, 11:11 AM
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Re: Bad PCM or Bad Injectors throwing off noid light??? ...opinions wanted ..NIGHTMAR

See photo below for my 25 year old fuel pressure test gauge. Simple, doesn't even have a pressure release valve. Just need to wrap a cloth around the connector as you unscrew it.

A test gauge will include a pin as part of the connector that will depress the valve core, so it can read the pressure. Technically, you could hook up the gauge connector with no core present, than turn the key to run to build the pressure. Would be a bit messy disconnecting the gauge, because there would be some fuel leaking out.

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Old 01-26-2019, 03:29 PM
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Re: Bad PCM or Bad Injectors throwing off noid light??? ...opinions wanted ..NIGHTMAR



Thanks for the pic and feedback. I am going to post a couple pics here and detail a couple of things I observed. The L - shaped fitting appears to be installed directly onto the Schrader valve to me. I can't unscrew it from the valve where it meets it, as the top part will bump the intake. So it appears I have to take the top of the "L" off and then unscrew from the Schrader. I can barely even get a hand back there, much less two wrenches (which I'd need to hold it steady and not twist-crack the rail. I might be better off using a fuel line disconnect to pull the rail off ...crazy to pull a rail off and put it back on just to check FP though and the disconnect tool was awkward for me last time I used it. Another idea is to use some bolt blaster on it and gently attempt to get parts of it to turn. I cannot even remove the vacuum line from the AFPR, as it feels glued on and is jammed against the L-shaped thing. I was freezing in that unattached garage and had to get home.

After priming the fuel system with the key twice I felt around the area where it goes into the Schrader and it seems there's slight seepage, mechanic may have installed it without plumbing tape.

Perhaps the most relevant thing I noticed on this visit was that after priming the fuel system with the key twice I removed the gas cap and absolutely no pressure escaped (yes, it was on tight too). Perhaps a vehicle that's been sitting won't necessarily build pressure in the fuel tank merely from two key-on primes though.

One or both of the fuel pumps sounds horrible. Probably the inline one that he bypassed, yet left power hooked up to ...so I assume if it was a good pump it isn't now after being run dry. This situation is so depressing. Thanks for your help.
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Old 01-26-2019, 08:03 PM
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Re: Bad PCM or Bad Injectors throwing off noid light??? ...opinions wanted ..NIGHTMAR

Too risky to work under the cowl, trying to keep wrench pressure from breaking the valve off the line. I've pulled the rails without disconnecting the fuel lines. There's a metal clamp that holds the two hard lines that the quick connects attach to. That clamp is attached to one of the intake bolts. (Caution - this is all from memory 20 years ago when I still had stock setup). But the clamp is held tight on the hard lines by a single (I think Torx) screw. Problem is the head of the screw points downward, so you need a short Torx socket to access the screw head. Once itís loose, the rails can be lifted with the lines intact.

The 90į elbow on the Schrader valve is probably a -4AN swivel fitting. Commonly used to turn the connection to the side so a hose, gauge, pressure sensor, etc. can be attached without pointing up and hitting the cowl. The silver piece probably adapts the -4AN fitting to provide a 1/8Ē NPT female thread for a pressure sensor or gauge.

As far as tank pressure, the fuel pump pressures the lines, not the tank. The only time you may see pressure in the tank is when the fuel starts to warm up and the fuel vapor pressures the tank. There is a very low pressure white plastic pressure/vacuum relief valve near the rear axle that protects the tank from excessive pressure or vacuum:

courtesy of Shoebox

http://shbox.com/1/fuel_pump_wiring.jpg

I see you have an Aeromotive fuel pressure regulator. Those frequently fail.

Still not not sure how fuel pressure would cause only four rear cylinders not to receive fuel, but worth checking the pressure anyway. I donít think you should believe anything the mechanic told you.
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Old 01-26-2019, 10:53 PM
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Re: Bad PCM or Bad Injectors throwing off noid light??? ...opinions wanted ..NIGHTMAR

Awesome info and I appreciate it. Yes, I really kind of felt like "no way" when trying to imagine removing the fitting to access the Schrader. Well, when the time comes I'll just remove it all either the way you described or with the disconnect tool. Obviously I need to ditch that fitting and get a cap for the Schrader...and a core for it if it's missing. Between the cold and a few things going on, looks like I'm paused for a couple weeks or so....yet again. Thanks Fred
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Old 02-06-2019, 10:57 PM
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Re: Bad PCM or Bad Injectors throwing off noid light??? ...opinions wanted ..NIGHTMAR

I found that unfortunately I do not have clips on the injectors. So I decided to change the spark plugs to check their condition and to simply have clean plugs in that might help me determine if the injectors are leaking. The idea was to put clean plugs in and prime the fuel system several times (just the key on test to power up the fuel pumps), then pull the plugs out and see if any fuel was present. I primed it four times and pulled a couple of the rear plugs (5 and 7) to find nothing. But maybe the fuel just can't make it that far even if the injectors are leaking a bit.

The picture attached shows two of the OLD plugs that I removed. The blackish one on the left is from cylinder #3 and the cleaner looking one on the right is from #5. #3 smelled of gas and number 5 sort of smelled like oil, but it may have been in my head out of paranoia. #3's header primary gets hot, #5's does not, looking at the plugs alone I would have thought the opposite. So after checking the new plugs for fuel as I described in the first paragraph, I put them back in and started the car. It really didn't want to start. I opened the throttle and it coughed and sputtered and started up as usual missing horribly, then came the strong gas smell. To me it acted flooded from the four fuel pump primes (since opening the throttle while cranking was the only way it would start).

It took me so many hours to safely get the lowered car's passenger side off of the ground and the R&R of plugs #6 and #8 (Hooker LT's in the way) that I ran out of time before attempting to pull the fuel rail. I hope to go back tomorrow. Sure wish I had reused injector clips.

Last edited by canbaufo; 02-06-2019 at 10:59 PM.
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Old 02-12-2019, 09:37 PM
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Re: Bad PCM or Bad Injectors throwing off noid light??? ...opinions wanted ..NIGHTMAR

Pulled the rail today and boy were you right about clips, those injectors stayed in the intake....so there wasn't going to be any key-on or spray pattern testing. Now that I think about it, Woodbridge Dynotech removed those clips back in 2002 when the 42# injectors were first installed (I wouldn't have omitted them). I don't see how he checked fuel pressure, as the L-shaped attachment on the end of the Schrader is jammed against the vacuum line of the AFPR right where the line attaches to it (and the rubber line end turns / is-tweaked a bit on the end of the AFPR, I just disconnected the vacuum line at the intake and left it on the AFPR as I removed the rail). Maybe he tapped into the end of the L-fitting somehow, who knows. I pulled one rear and one front injector out of the intake and they looked the same, the tiny holes in the bottom looked clean and the O-rings (top and bottom) are in excellent condition.

I had to go home so I took the rail with me and made little "condoms" for the tops of the injectors and left them in the intake. I took two more pics of the rail unattached but it doesn't show things differently enough (with the AFPR and weird fitting) to be worth posting here. However, I did take a pic of the FP gauge I've borrowed ...as I'm curious if it will work with the GM Schrader. Forgive me, I've never done this before. Can I take the weird end off of the hose and attach one of those other ends? I've yet to remove the L-fitting to see if there's a valve core (soaking in PB overnight), just trying to prepare ahead a bit. Want to get everything worked out with the FP gauge and rail / Schrader before I go back across town to the car.



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Old 02-12-2019, 11:36 PM
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Exclamation Re: Bad PCM or Bad Injectors throwing off noid light??? ...opinions wanted ..NIGHTMAR

Fred, I went downstairs to check out the AFPR / rail assembly a bit more and a MAJOR light bulb went off. As I said earlier, the vacuum line won't even come off of the AFPR as currently installed. I blew into the manifold-end of the vacuum line and could hear a minor leak coming out of the AFPR-end of the line (right where it connects to the AFPR). I spit on it and proceeded a bit more but couldn't detect exactly where the audible air leak was coming from. Then I started thinking about how you said these AFPR's often fail. I looked for fuel in the vacuum line but can't tell if any has been in it or not. I sure wish I had thought to pull the AFPR vacuum line from the manifold when the rail was on the car to see if fuel was coming out of it. For reasons I am about to convey I strongly suspect the diaphragm of the AFPR may have failed causing two problems, improper pressure and fuel leakage into the backside of the intake, potentially causing severe flooding of the rear-most cylinders of the engine.

Thinking back on a recent visit that I had primed the fuel system I thought I noted fuel seeping from the general Schrader area, but it was a damp day and I wasn't sure if it was possibly just condensation. Looking at the first picture below, and considering that I have now noted a leak in the vacuum line that is jammed up against the L fitting that attaches to the Schrader, it now appears perhaps fuel was leaking through the diaphragm of the AFPR, out of the leak in the vacuum hose, and onto the L-fitting / Schrader valve.

Now, looking at the second picture below, note the fuel rail assembly flipped upside down with the vacuum line defaulting to it's typical place where it plugs into the intake. It is MUCH closer to the REAR FOUR cylinders than the front. If there is leakage into that vacuum line, it may explain why my oil is being polluted so QUICKLY and severely, perhaps much more so than a dribbling few injectors might cause. It may also explain the mysterious "rear four cylinders" miss.

Finally, take a look at this random post (FPR failure on a different vehicle), very familiar as far as the description of the odors and fuel contamination of the oil (post #6):

https://www.bimmerforums.com/forum/s...5#post29717405

Obviously once I re-install the assembly one of the first things I'll be checking out is the AFPR functionality with line on and off and how it affects FP, check to see if fuel is leaking from the vacuum line , etc.




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Old 02-14-2019, 09:39 AM
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Re: Bad PCM or Bad Injectors throwing off noid light??? ...opinions wanted ..NIGHTMAR

Any comments on my last post above are appreciated. If there's a practical way to test the diaphragm operation of the AFPR while it's uninstalled that would be nice. I will probably take the rail and gauge pictured above to the mechanic family member I borrowed the gauge from and see if he can help me with connecting the gauge (or a different one) properly.
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Old 02-14-2019, 10:45 AM
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Re: Bad PCM or Bad Injectors throwing off noid light??? ...opinions wanted ..NIGHTMAR

Everything you said made sense. The Aeromotive AFPR is highly failure prone, and has been for 20 years. Pulling a vacuum on the diaphragm, via the hose connection should reveal a leak, if it will not hold the vacuum. Wouldn't show whether the unit is calibrated correctly though. Worth trying if you have a vacuum pump.
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Old 02-14-2019, 01:03 PM
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Re: Bad PCM or Bad Injectors throwing off noid light??? ...opinions wanted ..NIGHTMAR

Thanks for the tip on a vacuum pump, if my mechanic relative has one we'll try that. I still have the OEM FPR but it's been sitting in a box in my garage since 2002. If I confirm the AFPR is bad can I get the calibration at least very close on a replacement unit by having the adjustment screw set at the same number of turns? My understanding of the Aeromotive AFPR (from memory) is that boost is offset on a 1:1 ratio, in other words if I'm making 6-PSI of boost the AFPR makes another 6-PSI of fuel pressure. Does the OEM FPR do the same or is it static once at 0 vacuum and above? I'm curious because I might consider reusing the OEM, at least for troubleshooting purposes. Thanks a lot for the replies, it's encouraging knowing I may be heading in the right direction. My word, if this is all the problem has been after all of this (bad AFPR) I think it's a travesty what I've been through with the former mechanic. Here I am just a lay person and may have found the issue with my first real troubleshooting attempt.... arrghh.
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Old 02-14-2019, 01:11 PM
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Re: Bad PCM or Bad Injectors throwing off noid light??? ...opinions wanted ..NIGHTMAR

Also, the fired mechanic's son at one point admitted to me that he seemed to remember the leak down rate of FP was in his opinion maybe a bit too fast. I also think back to how the miss first developed (very progressive, started out super faint). I suppose a gradually (worsening) failing AFPR diaphragm could cause the progressively more severe miss symptom. Finally, I also remember vapor coming from the open breather I have on the passenger side valve cover, which is in a similar orientation front to back as the vacuum nipple for the AFPR.
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Old 02-14-2019, 03:37 PM
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Re: Bad PCM or Bad Injectors throwing off noid light??? ...opinions wanted ..NIGHTMAR

Both the stock fuel pressure regulator and the Aeromotive AFPR will have the same 1:1 relationship on boost. Stock FPR will produce 43.5 PSI without the vacuum line attached. If you apply 6 PSI to that via the vacuum line, you will see 49.5 PSI. I used the stock FPR to boost the pressure to ~80-90 PSI when spraying nitrous with the NOS 5176-EO dry kit.

Just keep in mind, a 1:1 regulator does not increase the fuel flow through the injectors enough, by itself, to insure adequate fuel for 6 PSI of boost. 6 PSI of boost should increase HP by about 40% (less the HP lost turning the blower). A 6 PSI fuel pressure increase over stock only increases the fuel flow by 6.7%. That's why an FMU will have a 6:1 or 7:1 ratio. Of course the tuner has other ways to increase fuel flow on boost.
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Old 02-14-2019, 07:21 PM
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Re: Bad PCM or Bad Injectors throwing off noid light??? ...opinions wanted ..NIGHTMAR

Thanks for the info, I enriched my fuel mostly via the PE vs RPM table. Well here we have it ladies and gents ....Aeromotive has logged yet another failure. I visited my mechanic-relative and we used a vacuum pump on the AFPR. It fell off instantaneously, I mean really just immediately. In a recent earlier post in this thread I stated that I could hear a leak at the AFPR-end of the vacuum line when blowing into the other end of the line with my mouth. I was fooled by the sound of it, as it was really the AFPR itself leaking and it just sounded like the end of the vacuum line. I can now confirm this by holding my ear to the fuel return line as I blow into the vacuum line. Just using my lungs I can get air to pass the diaphragm of the AFPR in BOTH directions (yes, blow and suck). So if I can suck air through the line imagine what several units of vacuum can pull through; I would imagine a significant amount of fuel is the answer. In fact, when I first started doing the mouth/lung test I could hear a burbling / bubbling sound ...must have been some residual fuel. Mechanic-relative said he feels it's pretty safe to assume the AFPR is shot. He showed me how to hook up the FP gauge and got rid of the swivel attachment.

So at this point, I feel it is probably unnecessary and a waste of effort to reinstall the AFPR for additional troubleshooting. Mechanic-relative said the Aeromotive may be rebuildable, and that he probably wouldn't risk using the old OEM one that's been sitting for years. Probably best to just buy another Aeromotive and set the adjuster to the same length as the old one to get myself pretty close on whatever the old (unknown) pressure was, then adjust in fine increments only if necessary. Whatever the old pressure was, I doubt it had been set significantly greater or less than 43.5 (???). It's just a mild 355 with 42# SVO's and the PCM is tuned for the bigger injectors.

In 2002 Woodbridge Dynotech had difficulty tuning my car with the stock engine and 6-PSI. They chased their tails for nearly 3 months, as the dyno graph got wavy above 5K no matter what they tried. I finally suggested valve float as a possibility and they checked it out and found spring pressures to be inadequate, so they put in new springs and the issue was resolved. Unfortunately my then cabin-mounted FP gauge didn't read in fine increments and the FP just looked like "40-ish" to me for years. Then the FP gauge was recalled and I replaced it with a wideband. Even after the mild-355 build the AFPR was never touched, just a PCM reflash. I retuned it many times to enhance driveability using the fuel tables and disabling closed loop, all low load cam surge vanished and it was very pleasant to drive. Laptop and backups are now dead/gone and I'll have to tune with the AFPR only. So this is why I feel like I need to go with the darned Aeromotive again ….argggh.

Based on the info presented, is it likely safe to assume the AFPR is dead? Perhaps the OEM FPR would be sufficient for troubleshooting. As things have been going it's probably not wise to try however, lol.

Best plan, new Aeromotive adjusted like old one and reinstall / test FP?

Right now the extra inline fuel pump is bypassed, so the intank pump (which is OEM ...I know, "barf") is the only fuel volume I'm getting. Assuming it's in proper working condition, will the stock intank pump flow enough volume for 42# injectors to at least work properly during low load conditions? I assume yes but just thought of this. Of course if I get the car running right I will be reinstalling the supercharger and a new inline booster fuel pump (since he bypassed the booster pump but LEFT THE POWER HOOKED UP TO IT!). If it wasn't bad it sure is now, don't think they like to be run dry!

I've also considered trying to drain the exhaust system of fuel that may be present, could it get hot and explode? Maybe not, since at least half the cylinders have been firing, giving the exhaust some heat and hopefully sufficient evaporation of fuel.

Well to add even one more concern to the list, I'm wondering if out of caution I should do something to help insure that the rings of the rear 4 cylinders (in particular) will seal upon what may be their first firing in quite some time. I've heard of people putting some transmission fluid or something like that in the spark plug holes to aide with this, should this be done regardless or just wait to see if I'm getting a ton of blue smoke first?

Sorry for all of the questions, just trying to cover the bases for what might happen here. The main questions pertain to the AFPR. Thanks!

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Old 02-16-2019, 09:21 AM
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Re: Bad PCM or Bad Injectors throwing off noid light??? ...opinions wanted ..NIGHTMAR

Got too wordy again in that last post but I appreciate feedback if time permits. The main thing is moving forward appropriately with regard to the AFPR for now.

I'm going to hook the vacuum line from the AFPR up to a vacuum port from another vehicle and listen to the operation of the diaphragm as a confirmation (should hear a fluttering noise or obvious leak).

I now remember another "tell" from when I was removing the rail. Even with the battery disconnected I kept hearing this very faint sound like a faucet being turned on and off intermittently, but very irregularly. This was after the car had sat for a week without running, so even then apparently the diaphragm of the AFPR was allowing some pressure to seep through (which by then couldn't have been a lot of pressure). I thought it was happening due to me fiddling with the fuel line disconnect tool but then I sat back and listened to observe the faucet sound doing it's own thing.

When I popped the supply and return lines off there obviously wasn't a ton of pressure, didn't have a ton of fuel to soak up.

In summary, the plan is to test the AFPR diaphragm on a vacuum port from another vehicle as a confirmation. Then order a new Aeromotive and install it with the same visual adjustment as the old one. I will still test FP even if it runs great, just to see how the factory in tank pump is doing (if working properly it is plenty of volume for low load running of the 42# injectors, correct)? If there is a better plan please let me know opinions.

The Schrader valve did not have a core but my mechanic relative supplied one that fits, but told me it's from an unknown source and to be wary of it. I have learned that regular tire cores should be avoided due to the rubber seat disintegrating in fuel. The one I'm using is tapered and not a rubber seat, but I don't know what it's made of. I think I will use it for testing FP only, then obtain a metal -3AN cap for the Schrader, because I can't find an OEM valve core anywhere as of now!

Last edited by canbaufo; 02-16-2019 at 09:24 AM.
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Old 02-16-2019, 09:38 AM
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Re: Bad PCM or Bad Injectors throwing off noid light??? ...opinions wanted ..NIGHTMAR

I have to admit I only scanned post #43 around midnight last night, planning on read it this morning, and I still need to go through the two latest posts. How did you apply vacuum to the AFPR? Did you manage to remove the old vacuum hose elbow, that you said was cracked?

And, why would you buy another Aeromotive AFPR? Why not just get a stock, non-adjustable replacement? Beside the seemingly high failure rate of the Aeromotive, are you planning to “tune” the system playing with the fuel pressure? Nothing wrong with an AFPR when used for the right reason. I run my fuel system at 58 PSI, but I have an outboard Weldon AFPR. Yes, requires modified fuel rails, and I have mine modified to run in parallel, rather than in series. I also have a fuel pressure sensor attached to the passenger side rail, and a gauge in the dash. Not suggesting you modify the rails, just asking why an AFPR, and pointing out the need for a reliable AFPR if you have a need for one.
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