Hi Everyone!!

I have a '98 Blazer and I believe I have a problem with my ECM. The truck will run fine for about 15 to 20 min and then just crap out. It will restart for a few seconds then crap out again and It will continue to do this until I leave it off for a long while then it goes back to working for 15 to 20 then cutting off every few seconds....I had this sort of problem before in a '88 Z24 and that was the case....I'm not getting ANY fault codes.....Any ideas would be awesome....Thanks Everyone

 

It's not quite that easy. Not saying it isnt the PCM but really it is rare for these to fail.
Fuel pumps on these are a problem. Do you hear the fuel pump at key on? Then you need to check fuel pressure at key on - not running. 60 psi and holds above 50 for ten minutes.
THEN check spark for blue strong spark.. While it's in its 'being difficult' mode.

If it does happen to be FP, Delphi or Ac Delco only! Or you WILL do it again.

 

[quote=pettyfog;517492]It's not quite that easy. Not saying it isnt the PCM but really it is rare for these to fail.
Fuel pumps on these are a problem. Do you hear the fuel pump at key on? Then you need to check fuel pressure at key on - not running. 60 psi and holds above 50 for ten minutes.

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I just changed the fuel pump 6 mo ago....I would think that would "work" or "not work"......As I said b4....The truck starts and runs fine for 15 to 20 min then dies....Thanks why Im thinking I have a bad capacitor or something in the ecm.. because when bad capacitors heat up they fail

 

I'm actually an elect engineer by former vocation, so I got what you mean. Thing is, just like any computer, almost all the caps are in the power supply circuits.
So.. dont worry about fuel pressure, just check if pump runs, first, then check for blue spark. If those happen the PCM may still be at fault but you'll have someplace to start.

 

In the early stages of failure, fuel pumps can be very erratic. What you're experiencing is a very common symptom of a failing fuel pump. If this is an aftermarket fuel pump, after 6 months it isn't all that surprising.

If this happens when the OBDII system switches to closed loop operation, it could indicate a problem with oxygen sensors not reporting correctly. During warm up, (open loop) the PCM ignores oxygen sensor data. As pettyfog mentioned, it's extremely rare for the PCM to fail.

Check fuel pressure and leakdown first and post the results.

 

That O2 sensor might be the issue....I recently removed the cat and cut the o2 sensor off.....how do i remedy that without having to buy a new cat???

 

The downstream oxygen sensor, (after the converter) has absolutely no affect on engine performance. It monitors the efficiency of the converter, that's it. Without the sensor, the SES light will come on and a DTC will be set in memory.

Both front sensors affect engine performance when the PCM is operating in closed loop operation only.

 

I think this is closely related: I'm trying to find the 5 vref wire coming out of my ecm. Do I just match the color to the grey wire at the TPS?

 

What year, make, model, engine, transmission, 2WD or 4WD? What problem/symptom are you having?

 

Thanks for your prompt response.

91 Blazer S10, 4.3l, 5speed, 4x4, "Z".

The vehicle started choking and bucking, surging about 3 wks ago. It would do it and then come out of it while I was driving....acting like it would die but didn't at first. When this happened the ces light would come on. When it cleared up, the lite would go out.

One night while driving home it started this and eventually died. It was 2 1/2 hrs. before it started, and I made it home. It is giving me trouble codes 22 and 34 (tps and map low voltage). I checked before the trouble lite came on and stayed on, for the 5v at the sensors and it was there. When it finally was undriveable I checked again and it was not there at the sensors. I have the ecm out and sprayed electronic contact cleaner on the contacts, but wanted to check to see it the 5v was coming out of the ecm. And, do a continuity test on the wire itself to see if there is a short. That's why I asked "which wire". Thanks for any help you can share.