4586

The 95 LT1 drive-line is in a street rod, was running fine, took it in for frame bracket welding. Battery was not disconnected during weld.

Now car won't run get moments where it spits and sputters. Now getting Code 18 related to injector wiring.

Have 12v with key on to each injector
they ohm out fine
spark good to each spark plug
great fuel pressure

Using a noid, sometimes I get the light sometimes I don't...in other words signals from PCM are not consistent. So I am assuming that the lack of signals to injectors are the concern.

Took a formally dean PCM that I got up and running down there today..same problem. Do have an unmolested PCM arriving tomorrow...hope to have it flashed early am and down there around lunch time to try again.

Next:

Will check each pcm to injector wire also, but something is disrupting the ground signals to the injectors.

Don't know a whole bunch about the opti's but if the optical sensor is bad..could it cause the hit/miss grounds for each injector and how do I check the opti with basic tools?

Thanks

4586

Just found this....might be on to something:

https://www.camaroz28.com/forums/lt1...t-help-701338/

ACE1252

Sounds like something certainly happened during the welding. If the ground for the welder was not very close to the weld point, it may have caused the electricity to move through paths you don't want it to go(through sensors and modules). It's always recommended to disconnect both battery cables when welding on a car. There is also something in the back of my head telling me that there is a risk damaging or exploding the battery if it's not disconnected during welding. It may relate to where the ground clamp is located in relation to the weld. Under some circumstances, the welder might try to "overcharge" the battery, but I think you'd really have to screw up in where you put the welder ground clamp, in relation to the weld point for that to even come close to happening.

Are you sure it didn't melt some wiring somewhere? On the other side of the body, inside the car, under the carpet maybe(if welding was done directly to the car body and not just the frame)?

Here is good video on how to troubleshoot the opti. It gives a good starting point, but sometimes you have to dig deeper with an oscilloscope or ignition scope.


These are for a 1996, but should help.

Index of /1996_Z28_Factory_Manual_Snapshots/No_start

You can download a '94 factory service manual here(other years are here too)....they have loads of troubleshooting charts.

https://www.mediafire.com/?40mfgeoe4ctti

4586

ACE1252...Thanks for responding..running down to the car again today to try a few more things including a fresh PCM. A lot of great reference material for me to study. Thanks again..

4586

Update:

Went back down with another PCM..no difference, even installed a new ICM.

The injectors ohm at 12 straight across.

Cranking the engine injectors do not light up a noid consistently...hit and miss.

BUT...if we spray starting fluid to the air intake it starts and the noid lights start flashing and the car runs with short spurts of start fluid. Stop spraying and the car shuts down which makes me think it's a fuel delivery problem.

Occasionally we get "initial" start bursts like it's getting fuel. Didn't have a fuel pressure tester available today but a couple days ago..it was at about 42lbs cranking.

Going to manually clean the injectors tomorrow but was wondering if it's possible to have too much fuel pressure for these LT1's?

Been running a Ford inline frame mounted E2000 pump...how much pressure can the LT1 handle?

I'll know tomorrow if the injectors are opening...like I mentioned it ran great until the frame was welded.

Thanks
`

Injuneer

The stock Multec injectors can have problems at maybe 65 psi and above. But DTC 18 is only set by electrical problems. PCM has no way to know the pressure, whether the injectors are flowing or not.

Are you using the stock fuel pressure regulator setup?

4586

Yes..stock regulator..

ACE1252

Are you sure that its not just because the cranking RPM is so slow? The pulses will get much faster at idle speed. To know for certain what is going on there, you would need to scope an injector along with either the high res or the low res opti signal. I think the low res would be the easiest to see(much less counting of the pulses compared to high res). That way you could see if the injector is firing once every couple of revolutions of the crank(or one cam revolution). I don't think it's doing double pulsing or any kind behavior such as that during cranking.

If you want to get into some advanced electrical troubleshooting....this guys channel is awesome. He knows his stuff.

https://www.youtube.com/user/ScannerDanner

GaryDoug

Check the voltage at one of the injectors while cranking to make sure it isn't dropping too much. Might be borderline in that case, leading to some injectors working poorly or not at all.

4586

Found the problem and up and running, went back down there after cleaning the injectors and noticed that the fuel pressure shot way up. When the guys were working on the shocks they decided to bolt down the fuel lines and the longer the car set the more the return link became kinked.

Straightened the line and the fuel pressure went back to normal and the car started.

Thanks for the help.

ACE1252

Right on, glad you found the issue.