Audax

For a first time I want to say hello for everybody here.
This forum is very helpful for me in last time, and now i want ask for help.
My friend ask me to find a problem with his car. And after 3 days I decided what main problem is ECU.
How I found it?
The Vette run pretty good. starts and stop engine in normal order. But if you stop engine after 20-30 minute, go shopping, and try to start - you cannot do this. You need to wait until eng. is cooling down.
For a first time i thought it wiring, injectors and etc. BUT! I was make obstacles when its happened and cool ECU by pressed air. And car go !
We make order from ebay used ECU from C4.
I want to ask you about some issues in replacing. Can we change the ECU in this vehicle, or we met problems? (immobilizer, etc)...

hcbph

Welcome to the forum.

I'm no expert but there's a lot of info required before someone more knowledgeable than I will be able to help.

Year, model, engine and transmission in the car. Is this an ongoing problem or did it start suddenly? Had any work been done on the car prior to the problem developing? When you say the car won't start when hot - does the engine turn over and not start, not turn over or what? Is it consistent or occasional?

Have you checked for error codes? How exactly did you come to the decision it's the ECM?

It might be the ECM, might be the distributor or several other areas that could cause problems but without more details it's all pure guesses.

Audax

Thanks for fast reply)
About car - She is 1993, eng. - 5,7 LT1. Targa body. For additional info, she has a non-adjustable suspension.

This problem appears every time after this sequence:
1.start as normal.
2. keep running to 227F and fan begins. Meaby several times.
3. Stop engine
3.5 (if you try start immidiatly after stop - its run)
4. Wait a 15 minutes
5. Trying to spin crank. And you haven't signals from ECU: Positive wire from ECU to injector has no signal. Fuel pump doesn't starts after you turn on ignition.
That's it.

I screw out some bolts from ECU's body, and blow there a cooled air for a 2-3 min.
6. Try to start, and its run properly.

Audax

Sorry. And I forgot to say. We send after this the ECU to repair shop. They clean up the PCB (microscheme) and solded some of terminals.
It was a 16'th june.
After it the Vette runs one day as normal. But symptoms back yestarday.

dizwiz24

sounds like might be an optispark issue also (if ecm doesnt fix it).

those are well known to work when cold and fail when hot

Audax

As my friend say - he replace an opti in this year.
now we awaiting for order of ECU.

ddahlgren

The only thing I can think of is to make sure the new ECU is flashed to what your car has for equipment trans gears etc..

Audax

Ou! the ECU needs to be flashed ?

ddahlgren

I have a 91 L98 and mine has a removable prom that can be swapped and had thought the LT1 cars there is no such thing and had to be flashed with the correct code for engine and equipment. I might be all wrong there but lacking a replacement for an identical engine trans gears etc. it would certainly be something to confirm. I can't imagine a ECU out of a 6 speed manual trans knows anything about an auto trans just as a start.

WVZR-1

The '93 is still an ECM with a removable PROM so "flashing/programming" isn't a requirement. Just requires the PROM from the original. It ran for a day so we'll assume that was accomplished. The OP might check to see if the PROM is seated correctly, check for a loose connection at one of the four ECM connections OR MAYBE bent pins from a poor attempt at connections. The bent pins happen frequently.

Kevova

The PROM or Programmable Read Only Memory or commonly called "chip" is the program for ECM. In some cases there can be different ecms for automatic and manual transmissions. The 92-93 lt1 used same ecm, whether in the corvette or f body manual or automatic ,the prom contained all the required programing for the application. OBD2 required tamper proof ecm leading to reflashing. In the early 90's GM started using the reflashable ecms so as to be compliant with OBD2 for the 1996 model year.

Audax

1. As I understand right, i might change the microcontrollers between our ECU and that we ordered in last month?
P.S. if we coudn't start in simple way of course.

2. Do I need use antistatic equip/UV cover when i change the MK? (in early 90th i met the MK's what afrait UV light, and loose programm).

Audax

We ordered the same ECU as car has. (i hope, what it the same )