LT1 trouble shooting help

[liquidroam]

So as many of you know I was running around to all of the LT1 knowledgeable (or sometimes just anyone) getting help to get my engine back in shape over the weekend at Hallett. First off thank you as always for the assistance everyone is always willing to give. Unfortunately I was not successful and have not been successful up to this point. Below is what I have done up to this point and what I felt in the car.

It ran great Friday morning. Midway through the session right after lunch I just started loosing power. At first I thought I was just not carrying enough corner speed and subsequently exiting at a lower RPM. It got worse fast though. We had noticed after session one that my water pump had started to leak from the weep hole so I planned on changing it that night. when I started loosing power I assumed that the Opti had gone bad from water getting inside or something.

Replaced those that night. On Saturday for warm up..... same problem. Also the plug wires where on their last leg so went ahead and put news ones on as well. I checked all the spark plugs that night and gaped them. A few looked a bit too white but they did not correlate with the dead cylinders that I had.

We found out that the back three cylinders on the driver side were not doing anything. We determined this by pulling the injector plug on each cylinder one at a time and then replacing it to see if engine reacted. I know I had air because..... well I have no reason to think it would not be getting air. I know it had spark because after replacing the opti i pulled a spark out of one of the dead cylinders and had Tyler turn the car over. Shocking the crap out of myself confirmed that we had spark. Last but far from least I know that the injectors were at least firing because you could feel it and Tyler put a screw to each one and against his ear and could hear them. I at the time what I did not know is whether or not fuel was actually making it through. I ended up find out that Curtis had injectors in his trailer so i put those on. Still no fix.


Back here I ran a compression test. Every cylinder was between 125 and 135psi. Measured fuel pressure at idle with vacuum line pulled from the FPR, 42. With Vacuum line on and on the road, 34-38 WOT.

I am hopefully going to be pulling the codes this weekend, so hopefully that sheds some light. That being said, at this point if anyone has ideas I am all ears. :D


BTW is Curtis on this forum? If so what is his username, I have some injectors that I need to mail back to him.

[Fbody383]

You did measure fuel pressure and check the fuel regulator not leaking? Might not hurt to pull the fuel rails and make sure there is nothing in them.

[ShadowBolt]

From what I have seen the fix for a LT1 is an LS1 swap. In the Ford camp we are working the 4.6 and the 5.0 hard to get to the current CMC numbers. The LS1's are just coasting at CMC power levels. If I could drop an LS1 in the 55 I would be all over it. I know this is not the answer you are looking for but I would not spend much money on trying to fix a LT1.

JJ

[MikeP99Z]

Pcm?

[Trublu]

Check the float bowl levels

[liquidroam]

PCM?

I do not think that is bad but I should know this weekend since I am going to trying to pull codes.

[liquidroam]

Check the float bowl levels

????? Float bowls... we are not talking carbs here. Maybe I about to look really dumb but I did not think I had float bowls with EFI.

[Trublu]

????? Float bowls... we are not talking carbs here. Maybe I about to look really dumb but I did not think I had float bowls with EFI.

They are hard to find....

[liquidroam]

They are hard to find....

Touche

[Sook]

Were the dead cylinder's exhaust tubes getting hot? I've been fooled by the injector test before.

Disassemble the whole intake path, I had a MAF clogged with rubber at cresson. How are the O2 sensors? Maybe lost a sensor and is in limp mode?

Skipped timing chain??

[Sook]

The LT1 beat me last year. Once they start acting up it's hard to figure out the problem (within CMC rules). I was always finding broken things but they would never solve the problem.

[Pranav]

Lift the Fuel rail above the intake with the injectors and lines still attached, disconnect the coil connector (the control/thin wires, not the plug wire) to stop spark, and see if all of your injectors are spraying correctly while cranking the motor over with the ignition on. Keep all ignition sources away from the engine bay so put the vape and cigarettes away and make sure all of your spark plug wires are still connected with the coil disabled by disconnecting small low voltage connector.

If you see an injector that is not firing, it is either clogged or not getting a signal to fire; swap it to another position to verify the issue.

Autozone also has a Noid light set on loan a tool that you can plug into each injector connector to verify it is getting voltage to the injector (can't check with a voltmeter because it is a PWM signal).


I know clogged injectors were an issue for you in the past from your donor motor, but if you used the old/donor fuel rail with your good injectors from your original motor, the old fuel rail WILL shed varnish and clog up the good injectors.

All post-filter fuel injector/rail/hose parts need to be cleaned if they came off a non running car. This was an issue for me in the past as I even did my injectors and rail, but the supply hose kept shedding varnish and clogging my injectors.

[liquidroam]

Were the dead cylinder's exhaust tubes getting hot? I've been fooled by the injector test before.

Disassemble the whole intake path, I had a MAF clogged with rubber at cresson. How are the O2 sensors? Maybe lost a sensor and is in limp mode?

Skipped timing chain??

Got it... ya there may be a sensor issue. I am hoping codes can point me in the right direction. If that is the case. I did not even think about the timing chain but that could make sense.

[liquidroam]

Lift the Fuel rail above the intake with the injectors and lines still attached, disconnect the coil connector (the control/thin wires, not the plug wire) to stop spark, and see if all of your injectors are spraying correctly while cranking the motor over with the ignition on. Keep all ignition sources away from the engine bay so put the vape and cigarettes away and make sure all of your spark plug wires are still connected with the coil disabled by disconnecting small low voltage connector.

If you see an injector that is not firing, it is either clogged or not getting a signal to fire; swap it to another position to verify the issue.

Autozone also has a Noid light set on loan a tool that you can plug into each injector connector to verify it is getting voltage to the injector (can't check with a voltmeter because it is a PWM signal).


I know clogged injectors were an issue for you in the past from your donor motor, but if you used the old/donor fuel rail with your good injectors from your original motor, the old fuel rail WILL shed varnish and clog up the good injectors.

All post-filter fuel injector/rail/hose parts need to be cleaned if they came off a non running car. This was an issue for me in the past as I even did my injectors and rail, but the supply hose kept shedding varnish and clogging my injectors.

Ya, good call on the fuel rail. Man that just sounds like an accident waiting to happen. Lol.....

[Pranav]

Lol you can take some baggies or something and cover up the injectors so the fuel doesnt go everywhere.

[liquidroam]

Lol you can take some baggies or something and cover up the injectors so the fuel doesnt go everywhere.

Ah great now I am building a weak compression chamber. Boom!!! See ya'll on the other side.

[Fbody383]

Sean reminded me we had a similar issue at Houston in January. Before we started swinging parts we borrowed Casey's laptop and his scanning software. We found that the PCM engine temp signal was sketchy - you could wiggle it and see it drop out. I think we changed pigtail and sender.

[39PitCrew]

Sean reminded me we had a similar issue at Houston in January. Before we started swinging parts we borrowed Casey's laptop and his scanning software. We found that the PCM engine temp signal was sketchy - you could wiggle it and see it drop out. I think we changed pigtail and sender.

Yep. That's what we did. Computer was jumping back and forth between open loop and closed loop because the
temp it was seeing was jumping between -40F and ~210F which really messed with the timing. Turned out to
be a damaged wire a couple inches from the factory connector. The insulation had been cut and the wire was
all corroded about an inch in each direction. Eventually the wire had broken inside the insulation.

[liquidroam]

Was hoping to be able to hook it up today but nice, waiting the cable. Should know being in Wednesday or Thursday, will know more then.

[Supercharged111]

Are you using all OEM ignition components? Any aftermarket bits are garbage. ICMs especially, Blow Reilly's will sell you the same POS for a 93-97 LT1 and GM spec'd 3 different ICMs: 93, 94-95, 96-97. They all have different curves and none of them match the aftermarket stuff from what I've read. Now an ICM is more of an item that either works or it doesn't, so doubtful it's the smoking gun for this but I am inclined to leaning toward wiring or electrical/engine management if the compression is solid. We had an LT1 here that also had a bad pigtail for the coil so the car would just randomly die and gave no indication on the scanner WTF was going on.

[Sook]

ICM issues are what led to us doing the LS1 swap. I never figured out why but the car was eating them every two sessions. The ACDelco ones would last longer. They all exhibit the same symptoms though, I would loose ignition for a few seconds once, then about 10-30 minutes of track time later it would go out completely. It was a contributing factor to the grass fire at TWS (along with leaking oil and my stupidity of putting in the grass). The last time it happened the car back fired horribly, ringing ears and all. Did it again when I tried to fire it at the shop.

I wanted to try this kit, but adjustable timing is against the rules.
https://www.jegs.com/i/MSD-Ignition/121/83811K/10002/-1

I just now found the piece parts I *think* you need to eliminate the ICM by itself. Not sure on the rules status of it but in the spirit of the CMC rules I'm going with illegal. If I had found them earlier maybe I would have tried them out.

Pig-tail
https://www.jegs.com/i/MSD-Ignition/121/8876/10002/-1

Digital ignition
https://www.jegs.com/i/MSD-Ignition/121/6425/10002/-1

- Josh

[marshall_mosty]

Check the float bowl levels

Isn't that something that's only legal to do in Colorado at the moment??

[Pranav]

ICM issues are what led to us doing the LS1 swap. I never figured out why but the car was eating them every two sessions. The ACDelco ones would last longer. They all exhibit the same symptoms though, I would loose ignition for a few seconds once, then about 10-30 minutes of track time later it would go out completely. It was a contributing factor to the grass fire at TWS (along with leaking oil and my stupidity of putting in the grass). The last time it happened the car back fired horribly, ringing ears and all. Did it again when I tried to fire it at the shop.

I wanted to try this kit, but adjustable timing is against the rules.
https://www.jegs.com/i/MSD-Ignition/121/83811K/10002/-1

I just now found the piece parts I *think* you need to eliminate the ICM by itself. Not sure on the rules status of it but in the spirit of the CMC rules I'm going with illegal. If I had found them earlier maybe I would have tried them out.

Pig-tail
https://www.jegs.com/i/MSD-Ignition/121/8876/10002/-1

Digital ignition
https://www.jegs.com/i/MSD-Ignition/121/6425/10002/-1

- Josh

I wonder if this and and good clean Opti is all that's needed to make an lt1 run right?

ICMs gave me some trouble too early on.

[Supercharged111]

Isn't that something that's only legal to do in Colorado at the moment??

Looks like your options are expanding.

[liquidroam]

So i was finally able to get the computer to read the PCM using a pretty basic program call Scan9495. It was extremely easy to use. The issue I was running into was simply that whoever wired the car did not care to reconnect the serial data wire so it was cut in the middle of the wiring. That took a while of banging my head against the wall thinking I had done something wrong with the software. I grabbed a few screen shots of the data. What stands out to people. I expected to have several fault codes. Unfortunately I thought it would save the list of the codes but it did not. I will screen shot those while it is logging tomorrow.

http://www.aicmctexas.com/attachment.php?attachmentid=1799&stc=1

[Supercharged111]

Are you open loop? Because fuel trim values of 128, IIRC, equate to 0% being added or subtracted, and LTFTs are applied regardless of temperature, MAP, or throttle position.

[Sook]

Your O2 sensors are wildly different as well. Might be normal, but I doubt it.

[liquidroam]

These are the DTCs that are showing. The program is setup to look at an automatic transmission so ignore the transmission codes. the two codes that stand out to me are 16 and 48. That is the MAF and Distributor code. I did put an extra MAF on that I had last week just in case, all of the connections internally appeared to be good. I am assuming that the distributor code is telling me that something is wrong with the OPTI. I ran it long enough this morning long enough to go into closed loop. I did notice that the O2 sensors look a bit off. LT and ST look like it is trying to compensate for something that is going on with bank 1 which is the same bank that we originally diagnosed as not firing on the back 3 cylinders. I will add a screen shot of the most recent scan.

http://www.aicmctexas.com/attachment.php?attachmentid=1800&stc=1

I noticed that it is hard to see. code 16 is "distributor ignition system (low resolution pulse)"

[liquidroam]

This is when it was in closed loophttp://www.aicmctexas.com/attachment.php?attachmentid=1801&stc=1

[liquidroam]

ingore code 16. After clearing the codes it did not come back while running. Looks like it is down to the MAF. It is throwing the code and never changes from 470.62. I have two MAF sensors and both respond the same so I am assuming it is all in the wiring. Already found a broken ground wire for it but still getting the same feedback so i assuming there is more to the story.

Update: I have the MAF situation taken care. The wiring turned out to be all sorts of jacked up and the connector it self was not in good shape. A wiggle of the 12v wire at the base of the connector and it shut the entire car off.so now the connector is replaced and functioning g properly along with a solid ground situation. The the LT looks good but the ST for Bank1 is all jacked up. I think it is a relsut of a bad O2 sensor. And so it is trying to compensate by running g really far. Send the injectors out to get cleaned and flow tested. And then testing the P2 situation when they get back.

[liquidroam]

Lol you can take some baggies or something and cover up the injectors so the fuel doesnt go everywhere.


Pranav clear your inbox, it won't let me PM you.

Below is what I was trying to send

Do you have someone that you know and trust for cleaning injectors/ fuel rails?

I have found a ton of people that do and most are $17 -$19 a piece. Not bad high or low but it feals like a reasonable ball park.

[Pranav]

Yeah injector RX has done mine.

I still have my clean rail and injectors for sale if you want.

I ran mine full of sta-bil before pulling them.