1987 GMC 350 TBI Problems, please help!

[Barney313]

Ok folks, I am begging for help. I have an 87 GMC V1500 350 TBI that I cannot make any progress with. The problems started a few months ago when my son called and said it had quit on him while driving down the road. We drug it to the house and no spark at all, plenty of fuel. I pulled Code 32. OK, EGR, maybe, so I replaced the EGR with the correct one, along with the EGR solenoid. Surprise, surprise, no spark. Started backtracking and talking to friends, replaced the electronic spark control and got spark back. Pulled the wire at the booster and got the timing dead on 0 degrees, reconnected the wire and drove the truck, within 6 miles, it was spitting and sputtering again. OK, more "advice" led to a new TPS, a new ECM, a completely new distributor even though the module was only 6 months old, and still same issue. Drove it to the gas station after my last round of parts replacement and guit on the way back, again, set a code 32 and just died. No spark. I am out of ideas and money and no, I am not buying Auto Zone parts, mainly Rock Auto and BWD electronics, but I really need some help. Any advice? I have heard of fuel pumps on other threads, but i am getting a fine spray at the injectors, so I am clueless. Thanks for your advice!

 

[89Suburban]

Did you replace the coil?

 

[89Suburban]

Oil pressure switch, ign switch?

 

[Barney313]

Help!

Yep, brand new coil (external) and the oil pressure is showing 40+ lbs on the gauge. Is there another switch that I need to look at? Thanks!

 

[Jims86]

Oil pressure switch, ign switch?

Ign switch is a likely culprit, worn out, runs till the circuit heats up a little, then poof.
Oil,pressure would only effect fuel. First thing is first though. If you have a volt meter or test light, turn the ignition on( try to start the truck first to see if it runs of course) if not, prpbe the large gauge pink wire to the coil to see if you get battery power...if not, problem is at the ign switch, or the power feed from the fuse dist panel.

 

[MrMarty51]

While it was running, was it doing anything weird, like, maby a carbed engine with the choke partially engaged ??? if so, then I would be thinking about the o2 sensor.

 

[Barney313]

good point on the Ig switch, I can handle that and see what happens, Thanks Jim. Marty, it kind of bogging down and acting a little sluggish off and on, but was not setting any O2 codes?

 

[89Suburban]

Oil,pressure would only effect fuel.

Yup, my bad.

 

[chengny]

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CHART C-4A - IGNITION SYSTEM CHECK



Test Description :

1.Checks for proper output from the ignition system. The J26792 (ST-125) spark tester requires a minimum of 25,000 volts to fire. This check can be used in case of an ignition miss because the system may provide enough voltage to run the engine but not enough to fire a spark plug under heavy load.
1A. If the engine will start with the connector disconnected, it indicates the problem is related to the EST circuit. The problem would usually be a grounded EST line or no ground to the ECM.

2.Normal reading during cranking is about 8-10 volts.
3.Checks for a shorted module or grounded circuit from the ignition coil to the module. The distributor module should be turned off so normal voltage should be about 12 volts. If the module is turned "ON", the voltage would be low but above 1 volt. This could cause the ignition coil to fail from excessive heat. With an open ignition coil primary winding, a small amount of voltage will leak through the module from the "Bat." to the tach. terminal.
4.Checks the voltage output with the pick-up coil triggering the module. A spark indicates that the ignition system has sufficient output, however intermittent no-starts or poor performance could be the result of incorrect polarity between the ignition coil and the pick-up coil. The color of the pick-up coil connector has to be yellow if one of the ignition coil leads is yellow. If the ignition coil has a white lead, any pick-up coil connector color except yellow is OK.
5.Checks for an open module or circuit to it. 12 volts applied to the module "P" terminal should turn the "ON" and the voltage should drop to about 7-9 volts.
6.This should turn off the module and cause a spark. If no spark occurs, the fault is most likely in the ignition coil because most module problems would have been found before this point in the procedure. A module tester could determine which is at fault.

 

[Barney313]

Well Jim and Marty, ghost in the machine I guess. So I replaced the ignition switch, only 14 bucks for BWD switch, no problem. Went to start it, nothing. Got irritated and reached under the hood and unplugged the timing advance connector and tried again, it started, ran like crap but started. plugged the advance wire back in, smoothed out a little bit and as the ECM got it's bearings back it ran a little better. Sounds good so far right? Anyway, moved it over to the garage and shut it off, came back about 30 minuted later and the seat belt buzzer was going off, no key in the switch, nothing. Plugged the seat belt in, still buzzing. Got the keys, restarted it, buzzer went off and life if good. All this to say, it seems I have an electrical problem messing with the entire truck. Other than tracing wires one at a time, any suggestions on where I should start? Can you guys think of a common place that might cause the ignition system to get screwey and then make the freaking seat belt buzzer go crazy. I am pulling my hair out! Thanks in advance!

 

[foamypirate]

Well Jim and Marty, ghost in the machine I guess. So I replaced the ignition switch, only 14 bucks for BWD switch, no problem. Went to start it, nothing. Got irritated and reached under the hood and unplugged the timing advance connector and tried again, it started, ran like crap but started. plugged the advance wire back in, smoothed out a little bit and as the ECM got it's bearings back it ran a little better. Sounds good so far right? Anyway, moved it over to the garage and shut it off, came back about 30 minuted later and the seat belt buzzer was going off, no key in the switch, nothing. Plugged the seat belt in, still buzzing. Got the keys, restarted it, buzzer went off and life if good. All this to say, it seems I have an electrical problem messing with the entire truck. Other than tracing wires one at a time, any suggestions on where I should start? Can you guys think of a common place that might cause the ignition system to get screwey and then make the freaking seat belt buzzer go crazy. I am pulling my hair out! Thanks in advance!

Bad grounds can make electrical systems do weird things as the current finds it's own path to ground (often through other circuits). I would start by making sure your battery cables are in good shape, checking the ground strap from the firewall to the back of the passenger cylinder head, and the ground strap from the frame to the bellhousing on the drivers side are good. From there, I would check any other grounds you can find (there is one up inside the dash area on the drivers side. It's a tab bolted down with 6 prongs sticking off of it for different circuits to attach to.

 

[Barney313]

Bad grounds can make electrical systems do weird things as the current finds it's own path to ground (often through other circuits). I would start by making sure your battery cables are in good shape, checking the ground strap from the firewall to the back of the passenger cylinder head, and the ground strap from the frame to the bellhousing on the drivers side are good. From there, I would check any other grounds you can find (there is one up inside the dash area on the drivers side. It's a tab bolted down with 6 prongs sticking off of it for different circuits to attach to.

Awesome, thanks for the suggestion! Headed out to trace grounds now.

 

[Jims86]

Barney...not for nuthin, but did the new dist come wit new cap and rotor? this is sounding like a cap button problem, and running like crap is sim ilar sounding to a cracked cap or moisture, or even carbon tracking. spark not going where its supposed to.
Also, if the coil wire is old, and not carrying spark, the spark will usually find its way to the coil body, and not the dist.

 

[Barney313]

OK, grounds are good under the hood, took the whole dash apart and found the 6 prong ground, five of them are great, one is empty and I cannot find anything else that looks like it is missing. Spent most of the day taking years worth of extra abandoned wire out and cleaning things up. Will try to post again after I get things buttoned up.

Jim: Nothing is for nothing at this point, thanks for asking. Yep, the whole distributor was new, not saying it can't be the cap/rotor, I will check it out later and look for any signs or arcs. The wire set is all new as well, all 8MM BWD wires as well. Got so much money in this thing already I hope I wind up finding the cause. If not, I am gonna have a 87 Sierra for sale! Thanks gents!

 

[Barney313]

One more stupid question. When I pulled the instrument panel out, there is one instrument panel light right between the speedo and fuel gauge has a pretty good size black / green wire on it that runs to nowhere? Any of you guys ever seen that before and have any idea where the other end goes? The wire is connected to the bulb socket and "almost" makes contact with the back of the printed circuit board and the other end is hanging free? Doubt it matters, but at this point, no stone unturned...