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Need help with my LT1

Old 10-21-2018, 04:43 PM
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Re: Need help with my LT1

Originally Posted by Injuneer View Post
Clear the codes. Pull the “PCM BAT” fuse in the box under the hood for 30 seconds. Then crank the engine (fully charged battery) for an extended period. Then check for codes. DTC 16 will set under those conditions. And, while cranking the engine, watch the tach to see if it jumps up a couple hundred RPM. In the data log, there was an RPM reading when you first started cranking the engine, but as I recall (I am not in a location where I can access your file) the RPM reading disappears. I'll check that tomorrow morning.
Okay, I pulled the fuse for a few minutes and put my charger on the battery so it wouldn't die for extended cranking. I did not see the RPM jump, in fact I didn't see it move at all. Looking at the scanner the RPMs were between high 150s and low 170s but mostly in the 160s. The scanner does not show any DTC codes.I attached the file from the scan. Thanks again for the help. It will be nice to figure out what the problem is eventually.
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Old 10-22-2018, 08:25 PM
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Re: Need help with my LT1

I bought a 94 z28 and it ran like trash until I did plugs but the day after the car lost all throttle and backfired really loud. I’m at a loss it tries to start but ends up falling on its face and backfired and smokes. I don’t know what to do?!?
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Old 10-22-2018, 10:50 PM
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Re: Need help with my LT1

Originally Posted by 94fbodyz View Post
I bought a 94 z28 and it ran like trash until I did plugs but the day after the car lost all throttle and backfired really loud. I’m at a loss it tries to start but ends up falling on its face and backfired and smokes. I don’t know what to do?!?
You need to start you're own, new thread on this forum. Not fair to hijack someone else's thread and cause confusion.

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Old 10-22-2018, 11:13 PM
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Re: Need help with my LT1

Originally Posted by sactodreamer View Post
Okay, I pulled the fuse for a few minutes and put my charger on the battery so it wouldn't die for extended cranking. I did not see the RPM jump, in fact I didn't see it move at all. Looking at the scanner the RPMs were between high 150s and low 170s but mostly in the 160s. The scanner does not show any DTC codesi.I attached the file from the scan. Thanks again for the help. It will be nice to figure out what the problem is eventually.
The RPM is in the log, so the Opti is working. In the brief first log, it appeared the RPM disappeared, but apparently you just stopped cranking the engine.

After you cleared the codes, DTC 16 would have come back while (extended) cranking. DTC 42 will also set while cranking. DTC 64 will not reset, if active, until the vehicle is fully warmed up. Question is why did 16, 36, and 42 set previously and remain as stored codes? Something happened to the Opti.

I went back and looked at a few data logs that actually show cranking. All of them started very rapidly, but in the 2 or 3 lines of data, the high MAP, “0” MAF, and long injector pulse widths were similar to yours.

Next checks:

- do you have spark at all the plugs?

- what is the fuel pressure with the engine cranking (but not running)?

- can you check for injector pulse, with a ‘noid light or a stethoscope?

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Old 10-25-2018, 11:04 PM
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Re: Need help with my LT1

Originally Posted by Injuneer View Post


The RPM is in the log, so the Opti is working. In the brief first log, it appeared the RPM disappeared, but apparently you just stopped cranking the engine.

After you cleared the codes, DTC 16 would have come back while (extended) cranking. DTC 42 will also set while cranking. DTC 64 will not reset, if active, until the vehicle is fully warmed up. Question is why did 16, 36, and 42 set previously and remain as stored codes? Something happened to the Opti.

I went back and looked at a few data logs that actually show cranking. All of them started very rapidly, but in the 2 or 3 lines of data, the high MAP, “0” MAF, and long injector pulse widths were similar to yours.

Next checks:

- do you have spark at all the plugs?

- what is the fuel pressure with the engine cranking (but not running)?

- can you check for injector pulse, with a ‘noid light or a stethoscope?

Ok, thanks, I'll check those and report back.
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Old 10-27-2018, 12:54 PM
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Re: Need help with my LT1

I put a noid on all of the injectors and it flahed. I checked one spark plug wire for spark and got nothing so I checked for spark at the coil and got nothing. Bad coil?

I have to get a fuel pressure tester to check it. That'll probably be Monday.

If the coil was the issue the whole time, would it have acted like it did (bogging) before it got to this point of not running?
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Old 10-27-2018, 04:25 PM
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Re: Need help with my LT1

Hi Sacto,

Just a thought (while waiting for the Injuneer) but what coil do you have? Earlier you said that the old opti was MSD, is the coil also MSD? I had serious trouble with a MSD coil not making good connection with the stock GM coil wiring plug (it fit a little loose and the pins didn't always connect causing an intermittent problem). I changed back to a Delco coil and have had no problems since.
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Old 10-27-2018, 04:44 PM
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Re: Need help with my LT1

Originally Posted by squarehead View Post
Hi Sacto,

Just a thought (while waiting for the Injuneer) but what coil do you have? Earlier you said that the old opti was MSD, is the coil also MSD? I had serious trouble with a MSD coil not making good connection with the stock GM coil wiring plug (it fit a little loose and the pins didn't always connect causing an intermittent problem). I changed back to a Delco coil and have had no problems since.
I haven't pulled it out yet to see what brand it is, but it isn't red so it's probably not a MSD brand. As of right now I'm planning on replacing the coil on Monday either way.
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Old 10-28-2018, 12:42 PM
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Re: Need help with my LT1

Changed the coil........didn't fix it.
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Old 10-29-2018, 01:45 PM
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Re: Need help with my LT1

Originally Posted by Injuneer View Post
Next checks:

- do you have spark at all the plugs?


No and not at the coil. I slapped a new coil in and still nadda.

Originally Posted by Injuneer View Post
- what is the fuel pressure with the engine cranking (but not running)?
Fuel pressure is at 40 when priming and during engine cranking and 36 after priming.

Originally Posted by Injuneer View Post
- can you check for injector pulse, with a ‘noid light or a stethoscope?
All injectors tested with a noid and the all get pulses.

Thanks again for the help.
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Old 10-29-2018, 02:52 PM
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Re: Need help with my LT1

Time to have the ICM tested at a parts store.
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Old 10-29-2018, 03:34 PM
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Re: Need help with my LT1

Originally Posted by Injuneer View Post
Time to have the ICM tested at a parts store.
OP, do this. Also use a heat gun on it if you can to bring it up to engine temp artificially.....ICM's can test "good" when room temp...its when they heat up that issues happen with them.

If it tests good cold...try heating it up and then re-testing

If you wind up replacing it, get a AC Delco. More $ than off brand ones but worth it IMHO
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Old 10-29-2018, 05:42 PM
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Re: Need help with my LT1

ICM tested bad. I bought a new one and it's running again. Thank you! However it seems to be running the same (bogging) as it did before it quit running. I'll hook up the laptop, record it driving, and post it.
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Old 10-30-2018, 12:07 AM
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Re: Need help with my LT1

Originally Posted by Chimera96 View Post
OP, do this. Also use a heat gun on it if you can to bring it up to engine temp artificially.....ICM's can test "good" when room temp...its when they heat up that issues happen with them.

If it tests good cold...try heating it up and then re-testing

If you wind up replacing it, get a AC Delco. More $ than off brand ones but worth it IMHO
The engine wasn’t starting....... cold.
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Old 10-30-2018, 02:59 PM
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Re: Need help with my LT1

Originally Posted by Chimera96 View Post
If it tests good cold...try heating it up and then re-testing
Originally Posted by Injuneer View Post


The engine wasn’t starting....... cold.
My comment, after you recommending OP test his ICM, was "if" it did test good "cold" than heat it up to test it ideally under use temperature.

But yeah Fred since it tested bad cold...it was dead. Good recommendation to the OP to test it
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