Truck just quit on me

[1987 GMC Jimmy]

Any developments? Your old module is likely fine if you have spark and injector pulse. Those cheaper modules are bad news, by the way. I had one fail in May, and it took an injector with it. Is the spark white and not yellow? If your spark is good, my question is if there’s enough fuel. I would test this in a pinch by disconnecting the injectors and spraying starting fluid in there while turning the key to see if it fires. The only other thing I can think of at the moment would be a timing issue.

 

[Jppr26]

So it acts like it will start up, almost like an old carburetor truck would on a cold day, wants to fire but just never catches. Almost like it is the timing but how would it just change on me out of nowhere

 

[1987 GMC Jimmy]

By the way, I’d clean those distributor cap contacts to make sure you’re getting the best spark possible. A loose timing chain could have caused it to jump timing, probably nothing else besides that since you haven’t had the distributor out. When it starts and with the EST bypass disconnected, I watch how the timing mark behaves to see if it jumps around when you blip the throttle and let go, but you could also remove the cap and see how much slack is in it by turning the engine manually till the rotor catches and then turning it other way. You then gauge how long it took to get the chain to engage. Here’s a better explanation of the procedure:

http://www.misterfixit.com/chanslop.htm

 

[Camar068]

Here’s a better explanation of the procedure:

Very nice quick troubleshooting. Guessing you could do that with newer vehicles by watching the rockers.

 

[Jppr26]

I haven’t gotten to check the cam chain yet but I did dump some gas down the throttle body and cranked the engin over, and nothing new still acts like it wants to start when I pump the throttle but won’t fire up. I have been confused while looking under my distributor rotor, what I have don’t match the pics in my Chilton book here is pics of what I have. Is it a HEI? What is this I’m pointing at? And how do I remove it

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[1987 GMC Jimmy]

It’s not HEI in the conventional sense. TBI has a somewhat different system. What you’re pointing at is the pickup coil. You have to remove the distributor to remove it. Here’s a test procedure for the high energy coil and pickup coil.

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[chengny]

So it acts like it will start up, almost like an old carburetor truck would on a cold day, wants to fire but just never catches. Almost like it is the timing but how would it just change on me out of nowhere

What kind of got skimmed over (and remains unanswered) was Jesse's question regarding the color of the spark across the electrodes. It was buried within the text of post 16:

Is the spark white and not yellow?

A healthy spark manifests itself as a bright blue/white arc that jumps across the electrode gap and emits an audible snap.

If what you see is a feeble yellow trickle of light that momentarily bridges the gap - that is not a healthy spark and it won't fire the engine.

This is what you want to see:

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[Jppr26]

Spark is a fat blue.
I hope you guys don’t think I’m asking stupid questions, I’m not a great mechanic, but can usually figure stuff out, electrical stuff gets over my head kinda quick, an all I got is a Chilton manual.

 

[chengny]

Spark is a fat blue.
I hope you guys don’t think I’m asking stupid questions, I’m not a great mechanic, but can usually figure stuff out, electrical stuff gets over my head kinda quick, an all I got is a Chilton manual.

Stupid questions? Sheeiit, you should see some of the questions that come in. At least you're actively trying to figure this out and have done your homework. It's not unusual to get requests for help that include a description of the problem that goes something like this - "My engine doesn't run, what could be the problem?" - and that's it.

Anyway, you are getting a nice, robust, blue spark at the plugs. If that is the case, it kind of begs the question; Why are you tearing into your distributor? Ignition system would seem to be okay.

You have also verified fuel supply:

So I’m getting fuel and spark, I checked with an old plug that I had, I’m gong to pull the plugs tonight and check them

You confirmed that by - with the engine cranking - you can see fuel spraying from the injectors. Correct? Don't rely just on fuel pump operation as an indication that fuel is actually being delivered to the intake manifold. It has to spray from the injectors.

Since you have noted a good spark and witnessed fuel spraying from the injectors, it would be time to look at the engine management system.

The first check is that the ECM is getting voltage and is operational. Easy, just turn the ignition switch to the RUN position and verify that the SES (service engine soon) light on the dash illuminates - and stays illuminated as long as the key is in RUN.

Assuming the SES warning lights up, the next diagnostic would be to check for any stored DTC's - and also that communication with the ECM can be established:

Take a regular paper clip and form it into a "U" shape with a sharp bend - so that the two legs are only about 1/4" apart.

Locate the ALDL (assembly line diagnostic link) connector. It should be under the dash on the LH side of the steering column.

Using the diagram below, locate the "A" & "B" terminals. There should be tiny letters under each terminal.

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Turn the ignition switch to RUN and use the paper clip to jump terminal A to B. Be ready to count flashes of the SES light.

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After code 12 is displayed 3 times (one flash/pause/two flashes), if any other DTC's are present they will be flashed in a similar manner (also 3 times). The list of DTC's in use in 1987:

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[Snoots]

I'll tell you a little story.

This will be short.

Check the distributor pins by doing this . . .

Remove each connector at the distributor one at a time
Be certain that the pins are locked into place by pressing backwards on them with a piece of wood

I had a terrible time with one that always looked good but wouldn't fire.
I found that once the connector had been installed, one of the pins had broken lock tabs and would push out leading to a 'no connection here' issue.
There was absolutely no way to see this.
A buddy of mine came over and found it in 15 minutes. He had seen it before too.

Worth a shot.

 

[Jppr26]

I have ses light, code 12 only, fat blue spark, fuel squirting it, I even poured some gas down the throttle body.
I never seen a pickup coil befor, and was wondering if that’s could be the issue, I’m gong to check my timing tonight I would really like to know where chengny got those computer command troubleshooting guides

 

[chengny]

I have ses light, code 12 only, fat blue spark, fuel squirting it, I even poured some gas down the throttle body.
I never seen a pickup coil befor, and was wondering if that’s could be the issue, I’m gong to check my timing tonight I would really like to know where chengny got those computer command troubleshooting guides

http://www.mediafire.com/file/i59ns...Fuel_and_Emissions_Including_Driveability.pdf
And a lot more:

http://67-72chevytrucks.com/vboard/showthread.php?t=545416

Compliments of hatzie.

 

[Jppr26]

So I just got done checking my timing, checked the crank mark to where the distributor should be, that looked good, I decided to check it with a timing light, that’s where it got interesting. Now I’ve never messed around with a timing light much at all, like ever, but I was getting some very random flashes, that would almost make me thing that spark is not being delivered at the proper times, making me wanna lean to the pickup coil being the issue. Or something else?

 

[Jppr26]

So I did the steps to check my pickup coil and my ignition coil, as shown above from 1987 GMC Jimmy and it all checks out perfectly. While sitting in the engin bay fusterated and looking at my distributor cap for ***** and giggles I checked for resistance on the center coil pin to the rotor. Nothing. Rotated the center spring pin a few times and Whamo, maxed out the needle, spun it a few more times and nothing. Now this cap has maybe 1000 miles on it and is only about 6 months old, so I just assumed it was fine, but I’ll get a new one tomorrow and I’ll know for sure.

 

[1987 GMC Jimmy]

That’s interesting. I’d be interested to hear what a new cap does when tested this way. For future reference, the test procedure doesn’t mention twirling and gently tugging on the pickup coil lead while you test it, but you’re supposed to, and your reading is supposed to stay constant. If it fluctuates, that’s no good. It’s a huge pain to do by yourself with the pickup installed, at least it is for me, but definitely doable.