MeenZ28

How likely is my ECM toast?

For background - Car is a 1992, 305 TPI w/ 700R-4. Basically stock. Plugs, wires, coil, and injectors have all been replaced in the last 2 months.

Here's the situation. Last Monday on the way to work, I took off from a red light (nothing harsh, normal driving), the car stalls out in motion and I have to coast it into a parking lot. Try starting it again and It'll start but won't stay running. Towed it home. Won't start at all now. Checked the DTCs. Only one code - 42. I read this is the EST circut (The communication between the ICM and the ECM). Based on this I've checked the wiring all the way from the ECM all the way back to the distributor. No breaks or cuts or burns. So I replaced the distributor & ICM - no change. Still won't start.

Being logical, I'm thinking the ECM bricked.... is this something that happens? Or should I be looking at something else?

bigal55

iTrader: (1)

How did you check the DTCs? If you have a code 42, you have an ignition problem. Have you checked for spark? You can disconnect the ECM from the distributor via the four pin connector at the distributor. The ICM will still fire the coil but the car will not start due to injectors not firing. Let us know what you find.

MeenZ28

Sorry for the delay responce.
I checked the code the same way i always do, jump the terminals on the diagnostic port with a paper clip and counted the times the CES light flashes. Course the code is gone now that ive disconnected the battery. Still no start.

I verified visually i DO have spark. Pulled plug wire #1 and poped a spare plug in it laying on the strut tower. Yup, sparking. Timing is correct. #1 is at tdc with the timing mark on the crank at 0. I rotated the distributor so The rotor is pointing to the #1 terminal... But still no start. I have fuel, the injectors are from Southbay and have less than 100 miles on them. Pump is working. I can hear it prime with the key to on and i have pressure at the rails verified by pressure gauge at the shrader valve... Soooooooo what is this car's problem?

bigal55

iTrader: (1)

Good you have fuel pressure and new injectors, pump runs. Concentrate on the code 42 problem. Follow this troubleshooting chart to help in your diagnosis. HTH!

MeenZ28

Helpful chart cept, car wont start. Says to let engine idle and see if the code comes back. If the car wont start i dont think i can follow this...

Scorpner

iTrader: (4)

IMO, the first step in the diagram is to verify that code 42 is still valid. In other words, that the problem still exists. It won't hurt to ohm out the suggested items to see if anything is off.

MeenZ28

True. Since the ECM is sitting on the passenger side floor at the moment shouldn't hurt to check. I'll try that tonight and report back. thank you.

Dyno Don

iTrader: (7)

To be sure you have fuel, spray some starting fluid in the throttle body.
If it starts, you're not getting fuel thru the injectors.

bigal55

iTrader: (1)

Just start where you have verified code 42, no need for you to do step 1 as you have verified code 42 already.
The ECM will not pulse the injectors if it doesn't receive pulses from the distributor. To verify this, do as Dyno Don suggests and spray starting fluid into the throttle body to see if it will fire. Follow the steps in the chart to find the cause of your problem. GL!

MeenZ28

Someone on another board mentioned the starter fluid thing too. I'll try that tonight after work too.

ASE doc

A quick note on checking spark. It is not a valid test on any high KV ignition, such as HEI, to test spark using a spark plug laid against engine or body ground. Just because the system can produce a spark across a clean plug gap sitting in open air doesn't mean it can produce enough KV to start the engine. To properly test the HEI system, you need to do a KV test.

Use either a KV tester, or a screwdriver inserted into a plug boot and held 1/2-1" away from a good engine ground. The HEI should produce 40KV and be able to jump up to a 1" gap with a loud snapping arc.

MeenZ28

I didn't know that. Thank you. I'll try that tonight too.

MeenZ28

I did what you sugested ASE Doc, and there was a noticable strong spark from the screwdriver to ground. So im not worried there. The starter fluid didn't help. Didnt get a chnce to check the ecm as i ran out of daylight. Ill have to wait till saturday to do that as i have family plans tomorrow....

MeenZ28

That walk threw doesn't work for me. I believe thats geared toward the 86-89 Camaros. The wires and pinouts on my ECM are differant (there is no white wire at D4 - there is no wire period).

I'm done. I think it's time to take it somewhere.

m16a2r

Vats chip is bad? Also not sure if the car has cam position sensor, my LS1 (different generation I know, just throwing it out there) didn't want to start when it was unplugged. Also oil sending unit would prevent start if bad I think.

MeenZ28

VATS has been bypassed many many years ago. Not the problem.
I don't think the TPIs have a cam position sensor. Someone correct me if I'm wrong.

bigal55

iTrader: (1)

Maybe this will help.

bigal55

iTrader: (1)

Follow the troubleshooting chart by wire color and then reference to the pin number, in the diagram, for the 730 ECM.