1987 TBI wont start, no spark, but has fuel

[Alex Meador]

hey everyone I'm new to the forums but ive been doing a lot of reading to try and tackle this problem. I've owned my Sqaure body for about 6 months now and its run great since day 1. until 4 weeks ago i noticed that the engine started to have a bit of a stumble under acceleration so i replaced the coil and plug wires and it appeared to remedy the situation. until 2 weeks ago i was able to drive my truck from off the street into my driveway but then 30 minutes later i went to start it and it would crank over but not start. I've done as much diagnose as i can and still cant track it down:

I've replaced the following:
coil
plug wires
whole new distributor so (ICM, pick up coil, rotor, and cap)

I am getting fuel out of my injectors and i hear my fuel pump priming so i dont think thats the problem, I am getting 12v to the ignition wire to the coil but I am not getting any spark from the coil itself, I also check and I have a solid ground from my distributor to the engine with no resistance.

any help would be awesome as I would love to be able to drive the truck for the michigan winter that has already started

 

[1987 GMC Jimmy]

Did replacing the distributor completely fix your problem initially? I'd take the ICM out and have it tested. A partial failure like that is not out of the question. Everything good with your ECM? You get the orange light every time you turn the key to "ON?" Any codes?

 

[4WDKC]

Did replacing the distributor completely fix your problem initially? I'd take the ICM out and have it tested. A partial failure like that is not out of the question. Everything good with your ECM? You get the orange light every time you turn the key to "ON?" Any codes?

He said he is seeing the injectors spraying, the ICM tells the ecm when to fire the injectors. Check the wires from the ICM to coil for damaged wires or pins in the connectors, do you still have your old coil laying around?

 

[1987 GMC Jimmy]

I know. I'm almost certain people have come on here in the past with halfway failed modules. They were seeing injector pulse but no spark and/or spark with no injector pulse, which replacing the ICM remedied the problem.

 

[fmxr47]

I remember having a similar issue on my 90 OBS tbi350 oil pressure sender I thought fixed mine but it’s been a long time ago.


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[Alex Meador]

hey guys sorry for a delay in response, so to answer the first question when i was trying to solve the stuttering of the engine I replaced just the coil and plug wires and it appeared to solve the issue for the most part. now that the engine stopped turning on I put in the new distributor to help fix it. I just did a contunitiy test on the connectors going from the coil to the distributor and I found that I have a good connection from the pink 12v wire but no connection with the signal/pulse yellow wire so fingers crossed I finally found the bandit, tomorrow I'm gonna go get a replacement wire and I'll see if that fixes it

 

[Alex Meador]

Great news the new wire harness fixed the engine! I think the timing may be a tad off from the new distributor but I'll be fixing that this weekend hopefully, unfortunaetly once I got the engine running again I could hear that the stumbling that the engine was doing previously has seemingly comeback. It doesnt look or sound like a full missfire as the engine doesnt shake and its not consistent so I'm beginning to think its a fuel issue, any suggestions on where I may go next?

 

[fmxr47]

Don’t forget to unplug the one wire when setting timing, I think it’s white? I really can’t remember.


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[MrMarty51]

Get the timing set first then see what it does. If the misfire is still there then see what a compression test tells You.
Welcome to the forum Alex.

 

[MrMarty51]

Don’t forget to unplug the one wire when setting timing, I think it’s white? I really can’t remember.


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I believe it is tan with a black stripe, Do not remember where it is located on the V model of trucks though.

 

[fmxr47]

Tan! Yes, that rings a bell, I only know it from my 90 OBS which was mounted to the firewall


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[Cuba]

To be 100% sure about the fuel on a TBI system, you'll need to install an in line gauge. Once in, you can leave it there.

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Disregard the yellow jumper wire, I was doing some testing.

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[Alex Meador]

Thanks for all of the replies and help! I was able to get the timing happy again, I think the previous owner has done some dabbling in the wiring cause the Tan and black wire appear to be replaced with a green one but I was able to figure it out by looking at where all of the wires plug in. The truck runs great and I was able to take it out for a couple snow donuts in a parking lot to really prove it was fixed. I think ultimately my goal is going to be pulling the original 350 SBC and putting a built 454 in and replace the ECM and Distributor with a holley sniper kit and MSD ignition so that I can eliminate some of these problems from happening in the future!

 

[MrMarty51]

Thanks for all of the replies and help! I was able to get the timing happy again, I think the previous owner has done some dabbling in the wiring cause the Tan and black wire appear to be replaced with a green one but I was able to figure it out by looking at where all of the wires plug in. The truck runs great and I was able to take it out for a couple snow donuts in a parking lot to really prove it was fixed. I think ultimately my goal is going to be pulling the original 350 SBC and putting a built 454 in and replace the ECM and Distributor with a holley sniper kit and MSD ignition so that I can eliminate some of these problems from happening in the future!

That TBI 350 will run for a very long while if it is taken care of. It will drink a whole lot less fuel too.
The 87 K1500 that I once had would get 17 to the gallon, I will guarantee You will never get that from a BB.
The four barrel sniper system might be a nice upgrade for the 350 though, someone in here has one for saloe for 500 bucks, You might want to check that out.

 

[stefan79moros]

You need to change the modulator in the distributor when it gets hot it will not allow the truck to start another words once it cools down it should start again


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