Help! Possible ECM problem on 1988 ???

[keremarsan]

Hi !

After trying to start the car without fuel pump and with accelerating ( something never to do , I learned it with very bad way , don't do this !!!! ) , since I have some strange problems,

even the fuel pump is changed and work perfect now, this electronic problem continues :

My car
1) Can not show the fuel consumption
2) Can not show the Range ( indicates zero )
3) Can not decrease the iddle ( fixed at 1100-1200 RPM ) and irregular sound on iddle.
4) No error code stored

If I connect ALDL A to B

5) it can not begin the diagnosis.


If I start the car with ALDL A to B connected :

My car

RETURNS to NORMAL operating conditions
1) Show the consumption
2) Indicated the Range
3) Can decrease the iddle to 700 RPM

from New Page 3 , I get the information that the A5 pin of ECM ( brown -white cable ) has a possible short to ground problem.

I can use the car as ALDL conncected , but , more strange, the car can begin to diagnosis when the car is running and I understand that this time the car is totally normal and when I disconnect the ALDL , continues to run normally for a certain time, then same problem return ( I understand that the problem returns because suddenly the car again can not shows the consumption and range = 0 and iddle RPM rise to 1100)

I think to change the ECM ,

Can anybody experienced the same problem ? Where is this cable ( brwn - white ) comes from before reaching the ECM ??

I looked the ECM wiring, everything seems clear, but on the firewall part,
these cables are in dusty condition.

My car has now 74400 original miles.

All information is appreciated

Thank you

and I want to say hello to all vette lovers

from Istanbul / Turkey

kerem

 

[Hib Halverson]

I'm going to try and help here but please understand there might be a problem with translation or language barrier.

First, when you are trying to use flash code diagnostics you need to jump the diagnostic pint of the DLC to ground then turn the key on but do not start the engine. It won't work with just the pins jumped and the key off.

If you start the engine with the jumper in place you put the system in to system into the "field service mode" and when it's in that mode, driveability might be different.

As for pin 5 on the ECM, (bwn/wht) it goes to the service engine light and from there it goes to the inj 1 fuse.

One suggestion I have is that, if you don't have a factory service manual, you order one from one of the U.S. Corvette parts vendors, such as Corvette Central.

 

[keremarsan]

Sure,

I now that I must to connect A to B and turn the key to ignition , but when I do that, nothing, steady service engine soon lamp .
Normally it must to flash tree time code 12 then if there is , other codes then finish with tree times 12. it does not that.

I say on my problem : No code stored , because, when the car is running erraticly, I don't get service engine soon lamp.

Maybe the car can not show the error code. To test that, I dicconnected the mas air flow sensor connection and I started the car , few seconds after, I get the Engine Service Soon Lamp ON. So the car can store codes. But it can not flash them ......

thanks for reply,

 

[keremarsan]

Thanks Again Hib,

I tried another thing,
On chevythunder, they say , if ALDL grounded, I don't get flash ESS lamp, turn key off and disconnect the all 2 conncetion from the ECM ,

Then turn the key ON, if there is Engine service soon lamp , short ground to A5 cable
if NO Engine service soon , replace the ECM and check the PROM.

I have done this, and I don't get SES lamp ON, so the ECM is faulty I think.......

Thanks for help

 

[Hib Halverson]

If the ECM was faulty, it's possible the car could stil run ok but I'm not for sure on that.

You see, If you key-up but don't start and you don't have the pin A to pin B jumper in place, the SES will stay on.

I'd make sure that pin A, the DLC ground pin, is actually grounded.

To do that, connect Pin B to a known-good ground such as one of the ground connections under the dash or a long jumper to the neg. battery terminal, turn the key on and see if the SES flashes. Also, you could use a DMM to check the ground pin by connecting the meter between Pin A and a known-good ground. You should see no or extremely low resistance.

If you go through all that and you're still concluding that ECM needs to be replaced, I'd reseat the PROM and if that still doesn't get the SES to flash then, I guess, you need a new engine controller.

Good luck!

 

[keremarsan]

Dear Hib,

I have the ECM at home now,

I disconneted the PROM from ECM

What I must to check now, can you help me ?

 

[Hib Halverson]

Make sure the contacts in the socket and the chip are clean. Spray them with electrical contact cleaner if they are not, then push the PROM back in until it locks securely.

There are no tests you can perform on the ECM.



If the PROM is seated and you're diagnostic result is still "replace ECM" then, I'd follow the recomendation in the factory service manual or, if you don't have the FSM, that web site you're using.

 

[keremarsan]

Thanks a lot,

I will put the ECM on car and see what happens ,

Ecklers has the ECM but don't have the street runner prom for 1988 automatic, I will maybe order both .... when they have both in the same time.

Thanks, I will reply you the result

 

[keremarsan]

Problem is still here

There is one thing maybe a guideline : When the car has done this first, the average fuel cunsomption was 12,8 litre/100 . While the problem is here, instant fuel consumption is 0 ( zero/100 ) but the average consumption indicates 12,8/100 , value of the day she did that first, something like average consumption is stored and nevere changes.......

I will chnage the ECM

thank you very much again Hib