Electronic spark control module

[Layne02]

87 Sierra Classic, rebuilt motor while back and been fighting some kind of timing issue. Idles bad, wants to stall in gear, popping through exhaust.

Replaced distributor , ignition module and pickup coil, plugs , wires , coil.

Now I am wondering about this electronic spark control module. Didnt know what this thing was til now. I unplugged it while it was running and made no change . So does that mean it isnt working? And what does it do that ignition module doesnt do?

Thanks

 

[1987 GMC Jimmy]

87 Sierra Classic, rebuilt motor while back and been fighting some kind of timing issue. Idles bad, wants to stall in gear, popping through exhaust.

Replaced distributor , ignition module and pickup coil, plugs , wires , coil.

Now I am wondering about this electronic spark control module. Didnt know what this thing was til now. I unplugged it while it was running and made no change . So does that mean it isnt working? And what does it do that ignition module doesnt do?

Thanks

It's there to relay the need to make incremental adjustments to the timing. It works in conjunction with the knock sensor to know when there's spark knock that can be remedied by a slight retardation in timing. The ignition control module controls injector pulse and actual spark generation as opposed to spark timing. If there was a problem in this ESC circuit, you'd more than likely get a Code 43 unless there was something wrong with your ECM. Are you getting any SES lights aside from when you unplug things? Is your SES light self-testing when you turn the key on? Where specifically did you set your timing at, and when you did, did you make sure to unplug the EST bypass single wire connector at the driver side firewall when you set the timing, reconnect it when you were done, and reset the ECM by disconnecting a battery lead for thirty seconds? The way I see it, there are a multitude of things that could be wrong here, but we need to answer these aforementioned questions so we can either resolve the issue or proceed further.

 

[Layne02]

Well, i did unplug the advance wire, and plugged it back in ,BUT, i cannot get the timing set to zero. When trying to set it ,
It needs advancing more to get it to zero but when i do it starts to die. Its weird, it runs ok as long as distributor is centered but if I advance or retard it a few degrees ,it dies.
It does give me a code 34. I have also gotten a code 42. Its got me stumped. I've rebuilt several carbureted motors and they are simple. Not use to all these sensirs and codes. Any ideas on what to check?

 

[1987 GMC Jimmy]

You left the bypass unplugged while you attempted to adjust the timing? I'm not saying you didn't; it just sounded like you plugged it back in before you started turning the distributor. The sensors and the OBD1 system in general are fairly simple. Once that bypass wire is unplugged, it's supposed to react to changes just like a standard HEI or point breaker distributor would. It shouldn't be doing that is essentially what I'm saying. Also, Code 34 is MAP sensor low voltage. Check the vacuum line going to the sensor, and check the EGR valve just to be safe. You can test the EGR by depressing the plunger, capping your finger over the nipple, letting go of the plunger, and seeing if it holds. If it does, it's good. If not, it's bad. If it's a newer style EGR, the plunger is going to be encased, but there'll be access holes. In that case, you may have to remove it and test it using an instrument to push the plunger, but the test will still work. I might look for other vacuum leaks while you're at it. If your emissions sticker is still there, that's a good tool to use for that. If any thing's rotting or disconnected, repair it, but you can also spray a combustible aerosol like starting fluid around potential vacuum leak areas when the vehicle is running, and a change in idle will indicate a vacuum leak in the area where you sprayed. The TBI base gasket is also a potential leak site, as is the throttle shaft area on a high mileage unit. The only way to fix the shaft is put a bushing in there. All of that stuff is just the cheap attack of that Code 34. Unfortunately, it sounds like your MAP sensor is on the way out, too, granted you don't have a wiring problem.

 

[Layne02]

I had the advance unhooked when timing it, honestly I didnt notice a huge difference in idle from when it was plugged and when it was unplugged.

The map sensor is new, I even hooked old one back up to no difference, egr is new, tb is rebuilt one with new bushings and new gasket, i will check around for leaks.

So if no vacuum leak is found, are you thinking electrical ? Everything is plugged in, not exactly sure where I should look.

Thanks for your time and advice on this.

 

[1987 GMC Jimmy]

Hold on a second. How many miles are on the engine? Going back and looking at what you said, it kinda sounds like your timing chain is stretched or something chipped, especially since it can't handle a timing adjustment. It should just change how it runs in terms of speed and quality, especially starting to ping when you advance too much. The backfiring and stumbling are symptoms of that, too. There are a couple things you can do to check. I'll attach a video or two that can explain it better than I can.

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As far as the MAP code goes, does it run any better with it unplugged? It sounds like the sensor is good, and if the little vacuum line's good, it's electrical. There are a series of tests you can do here. You need a handheld vacuum pump w/ a gauge, though. Also, before you do these, check to make sure the ground strap between your firewall and the passenger side cylinder head is tightly connected and intact. And go over the other vacuum stuff, too, like you said. By the way, ignore the OBDII trouble codes on this link I'm attaching.

http://troubleshootmyvehicle.com/gm/4.3L-5.0L-5.7L/how-to-test-the-map-sensor-1

 

[Layne02]

I rebuilt motor, timing chain is new. I feel pretty confident everything is correct as far as rebuild is concerned.

I will check grounds tomorrow.

I did unplug the MAP sensor and it ran better, little stronger , so not sure where that leaves me.

I have changed almost everything on it except that spark module.

It seems like its something small, it starts up and runs and revs up too good for much to be wrong.

 

[1987 GMC Jimmy]

To me, it seems most logical that a timing chain issue would happen either when the motor was totally fresh due to a defective part or when it was super tired due to age and wear. If it was a 50,000 mile motor, I wouldn't suspect it as much. Not saying that's it by any means, but it's not something I would completely toss out of my basket, especially if things persist with no headway. That's just weird that it wants to die whenever you adjust the timing. So when exactly does it run poorly? Is it idling better, and it just shows out under throttle or is it doing something else? I would try to make headway on the MAP sensor stuff, too, but I'm not sure if that's causing any of your problems. One time my MAP sensor hose melted, and that's the worst my Jimmy ever ran. It was awful. You've covered a lot of ground. If I think of anything else worth trying, I'll let you know.