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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 02-16-2019, 09:54 AM
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Re: Bad PCM or Bad Injectors throwing off noid light??? ...opinions wanted ..NIGHTMAR

Look for a Schrader valve core with a viton seal, suitable for gasoline or diesel. They are out there.

EDIT

Amazon listing shows the AC Delco cap/core (GM calls it a pressure relief valve) part #12570619 fits a 94 Camaro Z28. Seems over-priced at $19+...... I think Rock Auto sells it for $16 and change.

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Old 02-16-2019, 03:02 PM
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Re: Bad PCM or Bad Injectors throwing off noid light??? ...opinions wanted ..NIGHTMAR

3rd paragraph of post #43 probably explains it, (reason for maybe going with Aeromotive again) sorry, too much info posted!

He removed one of the elbow-ends of the vacuum line when he attached the vac pump to it. I think I tricked myself into thinking the line itself leaked, as the sound seemed to come from the elbow / end of the line but it was really passing through the attached AFPR. The vac dropped so fast it had to be the diaphragm failing, a line wouldn't drop the vac that quickly unless it had a visible hole. I'll confirm with another vacuum source.

Thanks so much for the valve core info, I may as well use the right thing if it's available.
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Old 02-18-2019, 04:39 PM
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Re: Bad PCM or Bad Injectors throwing off noid light??? ...opinions wanted ..NIGHTMAR

Originally Posted by Injuneer View Post
Look for a Schrader valve core with a viton seal, suitable for gasoline or diesel. They are out there.

EDIT

Amazon listing shows the AC Delco cap/core (GM calls it a pressure relief valve) part #12570619 fits a 94 Camaro Z28. Seems over-priced at $19+...... I think Rock Auto sells it for $16 and change.
Many thanks again. After looking at the pictures of the correct core, the one my mechanic-relative provided me looks identical (tapered light blue seal/seat and it's definitely not rubber, feels like hard plastic). In the interest of safety and $aving$ I plan to use the valve core he gave me and use a quality brass or other-metal -4AN cap, which should have been OEM anyway in case of a valve core failure! Not sure where to find one locally but we have a Fastenal and they may have it. Very hard to confirm the -4AN on the internet. Appears to be 3/8". I assume thread tape must be used for a cap alone to not leak fuel, not sure if they're sealing type threads or not.

I tried using a vacuum source from another vehicle to confirm the leaking diaphragm of the AFPR but couldn't discern the noise intelligibly. Seemed to hear a leak but I may have merely been hearing the engine run through the vacuum line. Mechanic-relative used a proper vacuum gauge and we watched it fall off immediately, plus I am sure I was able to blow some air through the diaphragm before (now I can't however ...it may be sealing intermittently). I just want to confirm that the AFPR is bad some other way before I order another one (and as stated before, I guess I'll stick with the darned Aeromotove to try to approximate the unknown setting of the old one since I can't tune with a laptop anymore).
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Old 02-18-2019, 06:09 PM
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Re: Bad PCM or Bad Injectors throwing off noid light??? ...opinions wanted ..NIGHTMAR

Well this just became slightly more complicated. I did a search for a new Aeromotive AFPR out of curiosity, they are now a totally different style than whatever model is attached to my rail (no numbers anywhere). So now there's no way for me to set a beginning baseline "guess-adjustment" on a new unit compared to the old unit as an apples to apples comparison.

I guess I would start at the baseline 43.5 PSI with the line off (and plugged) and see how it goes, making fine incremental adjustments only if necessary. Although I'd have no idea where to begin with the adjustment setting (maybe approx 15% above the low end of the range of adjustment)? 43.5 may be a good place to start because I believe I saw upper 30's to 40 or so at idle / low-load back when I had a cabin-mounted FP gauge; and that makes sense with some vacuum bringing the 43.5 PSI down a bit.

Open to suggestions as to either re-using my OEM FPR that's been sitting in a box forever, trying a different brand AFPR, or going with Aeromotive's current LT1 style AFPR that is too different from mine to draw adjustment comparisons between. Sorry I've posted so much, after 1.5 years I'm just really ready to see some light in the tunnel of this laborious project.

Last edited by canbaufo; 02-18-2019 at 07:14 PM.
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Old 02-19-2019, 05:33 PM
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Re: Bad PCM or Bad Injectors throwing off noid light??? ...opinions wanted ..NIGHTMAR

My takeaways from #43::

- you appear to have verified failure of the Aeromotive

- you are running the PCM in open loop, and plan to tune using the AFPR. I have limited experience with boost, and no experience with tuning open loop using an AFPR. I have no idea how that will work out.

- decent LT1 tuners seem difficult to find. Might be worthwhile to pursue best way to tune for low boost on ltxtech.com. This site gets no help on forced induction from members any more. If you post on ltxtech.com, keep it brief and to the point. No history dating back to 2002. Just say you're starting over. There is an LT1 tuner who is a sponsor on ltxtech.com, Moe Bailey, under the name Moehorsepower.com. He gets good reviews, but it would be mail order - I think he's in Texas.

- stock fuel pump will easily support 300+ HP. As long as you don't exceed that level of demand, doesn't matter what size the injectors are. Don't hammer it with 6 PSI boost.

- how much fuel is left in the exhaust will depend on how long it’s been sitting and how warm it has been.

- the excess fuel getting by the rings should have been diluting the oil, and it should smell of fuel. Obviously should be changed. Worn rings would show up with compression/leakdown test.

I'll read #44 later. I need to eat.


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Old 02-19-2019, 10:23 PM
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Re: Bad PCM or Bad Injectors throwing off noid light??? ...opinions wanted ..NIGHTMAR

Gasoline is a non-compressible fluid. When you open quick connects, it only takes a few drops to relieve the pressure, not a lot of flow.

You should just get the AC Delco Schrader core and brass cap kit. I researched the Schrader valve, and it has a 45 taper. I have used the -4AN swivel fitting on the Schrader valve, and it worked fine, no leaks. But the -AN spec is a 37 taper. The AC Delco cap will provide the best seal, and shouldn’t need Teflon tape on the threads. In retrospect, in the 20+ years I've been dealing with these cars, I have never heard of a failed valve core causing an engine fire. The factory plastic cap is just a dust cover.

At this point I have no idea who makes an AFPR for the factory rails, other than Aeromotive. You might want to check with Racetronix to see what they sell. They are definitely LT1 fuel system experts. If you don't mind the extra work, install the old factory regulator in the rail before you reinstall them. Install, then measure the pressure to see if it is working right. A damaged diaphragm will cause the pressure to drop rapidly after the pump primes and shuts off. But a leaking check valve in the fuel pump, leaking injector(s), or a leaking fuel line will also produce rapid pressure loss. With the 50kPa MAP at idle, you would see about a 7 PSI pressure drop when the vacuum line is reconnected... 43.5 —-> 36.5 PSI.

It would be interesting to see how your former mechanic “bypassed” the inline pump.

Let me know if I missed anything.

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Old 02-20-2019, 03:39 PM
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Re: Bad PCM or Bad Injectors throwing off noid light??? ...opinions wanted ..NIGHTMAR

Wow, I can't thank you enough for reading through all of that and the responses. Sorry the excessive info is dilutive to some extent, I have a difficult time being articulate enough without overdoing it (it's a fine line seemingly). Just FYI he bypassed the pump by hooking the fuel lines up to a pipe in lieu of the pump, but left the power to the pump on, wonderful. Before ever going on any real (high loads) drive I'll of course replace the inline booster pump and confirm/adjust fuel pressure.

I have no need or desire to do any tuning, other than getting the new FPR to provide at least roughly the same PSI that the Aeromotive AFPR was providing prior to failure. The PCM is already tuned for the combo I have (works great with or without the supercharger since without the blower there's less FP due to the AFPR vacuum/boost line not being pressurized with boost). Since there's no longer any block learning and no O2 sensor feedback, all I need is for the fuel pressure to be fairly close to what it was before to be in the right state of tune. This is a little more critical than usual because it's an open loop tune (no fuel trims / adds). I'm guessing I can play around with an AFPR setting and get close enough. I have a pillar-mounted wideband gauge to aide with this. The OEM FPR may be just fine at it's factory setting but it is very old and I hesitate to chance it (plus I can't adjust if I find out I need to). Bottom line, I only need the new AFPR to make whatever FP the old AFPR did before it failed and the tune will be fine.

Maybe the LT1-specific Aeromotive is preset to get pretty close to 43.5 PSI out of the box. Based on what I observed back when I had a pillar-mounted FP gauge I think my Aeromotive was actually set pretty close to the stock 43.5 PSI anyway. I've never adjusted an AFPR, so I don't know where the starting point is or a good way to get there quickly. I assume if they're built for 40-70 PSI, then I'd want to start not far off of the bottom of the adjustment (example only).

Not sure of the taper angle of the valve core. I already have a good plastic "dust cap" for the Schrader, maybe I should just order a proper GM valve core and call it done. Unless there's a rea$onable kit that already includes a brass cap (might be what you meant), I'll be looking.

I don't seem to be capable of conveying any of this with brief posts, my apologies for that but many thanks for all of the input!
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Old 02-20-2019, 04:10 PM
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Re: Bad PCM or Bad Injectors throwing off noid light??? ...opinions wanted ..NIGHTMAR

The taper I was referring to is the angle of the truncated dome at the top of the fitting, not the taper of the valve core. The seal is formed by the mating tapered surfaces of the Schrader fitting and the cap.
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Old 02-20-2019, 10:05 PM
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Re: Bad PCM or Bad Injectors throwing off noid light??? ...opinions wanted ..NIGHTMAR

Originally Posted by Injuneer View Post
The taper I was referring to is the angle of the truncated dome at the top of the fitting, not the taper of the valve core. The seal is formed by the mating tapered surfaces of the Schrader fitting and the cap.
Roger that. Do you think the light blue plastic seat of the valve core I have is likely to be Viton since it looks exactly like the pic of the GM version and is obviously not rubber? It fits like a glove in the Schrader, with the relief valve at the right height. Splitting hairs here a bit, seems logical to either use it and obtain a brass cap for the Schrader or get the proper GM valve core and use the plastic "dust cap" that I already have.

If you have time to opine on my previous post I value your opinions highly. Thanks for the tip on the other AFPR vendor. Have to consider it, as it sickens me to give Aeromotive more of my money after their product (and my ex-mechanic) may have washed out my piston rings. Have read through many old posts (including yours) of other failures and it's absurd!

I should insist on Aeromotive taking mine back and that they issue a free replacement, but I'm already way behind schedule on this project.

I wonder just how many engines have been washed out due to their product, disgusting.

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Old 02-21-2019, 11:06 AM
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Re: Bad PCM or Bad Injectors throwing off noid light??? ...opinions wanted ..NIGHTMAR

I'll try to make this my last post for awhile until I try something and report back. I'm concerned about possibly having the rear 4 cylinders fire up for the first time in a long time after all of this run time while flooding. When I changed the oil last May about 6 quarts came out and it was heavily diluted with gas. The "new" oil is a 10/30 full synthetic and slightly diluted but nothing like the old oil from last May.

​​​​​​ I know a leak down test should be done, but basically if these rings won't seal I won't be re-ringing it anyway (too expensive and too much work) and will sell as is. So any tricks to prevent blowing the rings or getting them to seal is what I'm after. I've heard of using transmission oil or something similar in the spark plug holes possibly helping. Perhaps I should change oil yet again and go a little thicker or use dino oil. I'm open to ideas. Not sure if I should go ahead and use some type of fluid in the spark plug holes to try to prevent a sealing problem, or should I only do that if I observe blue smoke from the exhaust. Just nervous about it firing up and blowing rings.
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Old 02-21-2019, 05:45 PM
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Re: Bad PCM or Bad Injectors throwing off noid light??? ...opinions wanted ..NIGHTMAR

If the rings are worn, nothing you can squirt in the cylinders is going to restore them. Not sure what you mean by “blowing the rings”. I would change the oil if there is any smell of gasoline. Actually, I would do it no matter what, but you know long it's been in the engine, how much it’s been run, etc.

Use the correct 5W-30 or 10W-30. Heavier oil may cover up bearing issues briefly, but I don’t see it improving worn rings performance. Synthetic vs. conventional is simply a matter of cost, and how many miles you might put on it. Since you need to do the compression/leakdown test, I'd lean toward conventional. Synthetics are good for longer change intervals.... worthwhile if the car gets driven a lot between changes.
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Old 02-21-2019, 08:35 PM
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Re: Bad PCM or Bad Injectors throwing off noid light??? ...opinions wanted ..NIGHTMAR

"Blowing the rings" as in maybe they'll fail to seal because of however I might improperly go about firing it up under these circumstances (example, start it with the gas-diluted oil and maybe they'll fail to seal, whereas if I had changed oil first they would have sealed). The mechanic relative I borrowed the FP gauge from told me Dex III or something similar in the plug holes might help. Said to crank it 30 seconds or so with plugs out of the holes until excess spits out of the holes to get the cylinders coated nicely. He may have thought I have a stuck ring, as from what I'm reading the Dex III could help with that. I also see it can be useful for a "wet test vs dry test" to confirm a compression change when it's added (meaning the rings are shot if there's higher compression with the wet test).

After some Googling it looks to me like Dex III, Restore or Rislone can all be used as a "band aid" for smoking rings when mixed in oil, but nothing more than a patch-fix. I thought it sounded to good to be true but one never knows. I thought it might be possible that a fluid introduced to the cylinder bore might help a ring expand and re-seal, looks like no Bueno. Now, one thing that seems contradictory to all of this is the fact that all engines have at least some level of blowby, as in no ring seals absolutely perfectly. So let me ask this, if my rings weren't sealing with a super thinned out gas-diluted oil mixture, could they possibly seal with good new oil? I fear the answer is NO, "once the seal is broken it's broken".

Thanks yet again for the insight, I wasn't looking forward to changing the plugs again just to lube the cylinders.

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Old 02-21-2019, 11:22 PM
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Re: Bad PCM or Bad Injectors throwing off noid light??? ...opinions wanted ..NIGHTMAR

I have no idea what happens when you add something like ATF. I see people recommending something like that to loosen stuck rings, on engines that have sat unused for a long time. No idea how that works. Stuff like Rislone that claims to add a layer of “chemical polymer” to rings and cylinder walls is “snake oil”.

Oil splashed on the cylinder walls does not seal the rings. It lubricates the ring/wall interface. The ring spring tension holds the rings against the wall so they seal. Wear the surface of the rings down, the diameter drops and spring tension is reduced. Overheat the rings because of poor oil film, and spring tension is lost.

Correct, all rings allow some blowby. When an engine is running with the correct A/F ratio, and firing correctly, the blowby is combustion gasses - CO2 (maybe a tiny bit of CO) and water vapor - minimum fuel.... that's allmost all been vaporized and burned. The PCV system pulls the water vapor out of the crankcase to prevent condensation of water, which contaminates oil and encourages the formation of acids.
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Old 02-22-2019, 09:28 AM
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Re: Bad PCM or Bad Injectors throwing off noid light??? ...opinions wanted ..NIGHTMAR

Canbaufo, just a word of encouragement to ignore the fear of rings failing on your repair. Consider that in a two stroke engine the only lubrication the rings/pistons get is the fuel with a little oil mixed into it. The LT-1 has its weaknesses (optispark anyone!) but the rings are not one of them.

Good luck solving the misfiring problem!
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Old 02-22-2019, 12:03 PM
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Re: Bad PCM or Bad Injectors throwing off noid light??? ...opinions wanted ..NIGHTMAR

Washing the rings due to pouring so much excess fuel into a cylinder that it washes the oil off the cylinder wall and dilutes the oil to the tune of a full extra quart in the crankcase is not a problem unique to the LT1..... kinda applies to all engines. That appears to be his situation, due to the failed diaphragm in the Aeromotive fuel pressure regulator. The situation was worsened by the car being held captive by a "mechanic" who couldn't figure out why the back four cylinders were so cold when the engine was running. Took two pages of posts to get him to take the car back from the hack mechanic.
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