I have a LT1 in my 94 Z28 and it's only running on 7 cylinders at the moment. I took it to my mechanic and after a few tests he determined that the #3 injector was not getting a signal.

What I need to determine now is if it's the computer or harness. Any ideas?

I am going to clean and check the harness plugs and look for obvious damage. What should I do next?

Thanks!

 

Key on/engine not running, check the pink wire at the injector to make sure it is supplying +12V. Power is always present at the injector, the PCM supplies the ground to open the injector. If you have +12V on each pink wire, pull the connector off, and measure the resistance across the pins of the injector. Should be in the range of 12-15 ohms. If it is OK, it would appear to narrow it down to a faulty ground wire to the injector, or a PCM fault. Did the mechanic use a set of 'noid lights to determine that #3 was not firing?

 

Thanks for the help! I was raised in NJ but escaped 10 years ago. I will give NJ the point for better food than Kansas, but no vehicle inspections and 1/2 price car insurance make up for it for me.

Yes, he used a noid light.

It was not blinking, but he does not know if the signal is leaving the PCM but not getting to the injector (wire fault) or the PCM is not sending it (PCM fault).

I will try the tests you mention and see if I can nail it down to the + or - side. I am thinking if the + is not there than it can't be the PCM.

Looks like Autozone wants about $140 for the PCM. The local Chevy dealer wants $75 to tell me if it's the PCM or harness. If I can't figure anything out I might just buy the PCM. Worst case I will get stuck with a spare for $65. Thanks again!

 

Don't waste your time buying a PCM. I have yet to see an OBDI PCM be faulty. It's either the socket or the wiring. Just ohm it from contact to contact.

 

Well Speedy, I should have waited a bit longer I guess. I got the PCM after reading your post and just wanted to let you know it looks like your right. It did not make any difference.

I remember when I was looking at cars I thought about getting a Camaro from the 70s but decided I really wanted the computers and fuel injection. The only problem I have had with the 94, comptuers and fuel injection.

 

You should be getting an SES light, and DTC 18 for the injector circuit fault.

 

You should have Waited?????? You said you bought it AFTER reading my post. How much later does it get????????

So in any regard, what was the outcome of the testing????

Let's remember that when the PCM sees what it thinks is an injector fault like DTC 18. It disables the output. So it appears that the injector drive from the PCM is dissabled.

What the PCM is looking for is certain voltage at its driver circuit before it activates the injector. In other words, it has a driver circuit and a monitor circuit (for simplicity) on the same connection for the injector.

Unfortunately a DTC 18 will NOT set an SES as was previously mentioned.

 

Sorry, typo. I read the post after I bought the PCM obviously.

In the middle of working on the miss the tranny lost 3rd and 4th. So thanks all for the help but I am afraid this story has to be put on hold until the larger problem gets funded. Now let's see what can go to eBay...