summers_Z28

94 camaro z28 -350 lt1 4l60e auto

Original Problem:
had the car in school to look at the heating & air conditioning. When cold, car would start, run for a bit, then die and wouldn't start. Replaced Distributor after following trouble tree (took to a shop).

New Problem:
After the shop replaced the distributor it had the same problem except now the timing seemed too advanced (he says the timing on the lt1s can't be adjusted)

What's been done:
Distributor (Warranty)
PCM (Warranty)- he thought this was the problem, because on the scan tool it wasn't showing any rpm, Timing advanced / retard. After this still had same problem but ran a little better.
Knock Sensor - Put in a used, known good one, helped a little bit, but still ran bad and would die.
Checked the pig tail connector from the distributor to the connector into the wiring harness - 3 /4 wires came back OL when you'd play with them. Replaced the bad wires. That solved the dying issue.

What it's doing now
When at idle it runs fine, but when you put it in gear and step on the gas a little bit it starts knocking really bad, like the timing is way too advanced.
On the scan tool the ECT is showing -40, so I need to have the wires checked and possibly replaced but I don't think that is the issue with the knocking.
Any suggestions?

KW Baraka

Where did you get this PCM from.....GM dealership?

And who 'tuned' the PCM?

KW

summers_Z28

The PCM is from A street Auto ( a local parts store). The one I got on warranty was programmed @ O'reilly's auto parts. The one we took off was programmed by A st Auto and it ran good on the car for a few months.

Injuneer

If the splined shaft that drives the Optispark distributor is not correctly indexed to the teeth in the cam sprocket, it will throw the timing off. In THEORY it can only be assembled one way, but unforunately, based on the feedback I see here and on similar websites, about 10% of the installs are not indexed correctly.

Fix the ECT. Shoebox has a way to check it:

4th Gen LT1 F-body Tech Articles

Have you been scanning it for codes? A faulty coolant temp sensor (the one in the water pump housing for the PCM) should set a code. So should problems with the harness for the Opti. It sounds like neither you, the school or the shop has scanned it.

The PCM may be richening the mixture for a very cold condtion. If the engine warms up, but the PCM can't tell, because of the faulty ECT, it may be running so rich that it stalls. This is more likely than the Opti. Appears you may possibly have paid for a part you didn't need, and then they screwed it up by not indexing it correctly...... just a possibility, based on the limited data you have supplied so far.

summers_Z28

I'm thinking about maybe putting the old distributor back on and see if that does anything.. It didn't have this pinging problem until after we replaced the distributor, then we found the wires on the pigtail connector to have an issue. I'm just wanting to hear any ideas because I'd prefer not to have to pay him for replacing the distributor 2 times.

summers_Z28

We scanned it at school and the shop had a scan tool up to it as well. The only codes was one for the ECT, one for the MIL (check engine light blown), and another code for the High / low Resolution, which would be the signal from the optical sensor inside the distributor.

Injuneer

You don't need to reinstall the old Opti unless you plan to tell the shop to take then new one back. If you want to keep the new one, you just need to check whether the splined shaft is installed correctly.

http://shbox.com/1/93-94_opti.jpg

The misaligned shaft would throw the timing off.

summers_Z28

I'm not sure what they did.. but they called me yesterday and told me that they went to start it up to look at scan data and that the pinging is not there anymore..and that they are seeing an advance / retard, rpm, ect, knock sensor on the scan tool etc etc.. But now they're saying that it is misfiring..lol.. Thinking I may take it somewhere else if I feel I can't live with the misfire it's having