Frustrated 87 GMC owner!

[SirRobyn0]

@eric 87 I'm trying to feel what your feelings are for this and I'm struggling to do so. Maybe it's just me, I want to help but I'm genuinely unsure what direction you'd like to go in so I'm going to try to give you my thoughts in pieces.

Back in the day when we'd get a TBI rig in doing this one of the first things we'd do is unplug the IAC valve and then plug the passage in the throttle body and set the minimum idle to spec, which I'd have to look up that spec as it's been a long time but I think it's something like 500 RPM. Anyhow then we'd see if the truck still acted up. If yes, then it's likely to be something mechanical on the truck. If no then it's likely to be computer related.

Maybe this has all been checked before and if so just ignore this:
EGR valve, if leaking can cause high idle and stalling. Would need to remove the EGR valve flip valve upside down, pour water in one of side of the passage and see if it leaks into the other side.

Brake booster leaking.

Often over looked is the charcoal canister, on these truck sometimes they will crack or rupture and leak vacuum like crazy.

So those are my thoughts on your issue this time around.

Any luck with the electrical stuff?

You said "Either way this thing is getting tiring. This part of car ownership but I prefer the fun part of adding to make it better and nice routine maintenance. Chasing problems not so much." If you think this is bad, you should try being a mechanic especially if your customer does not understand that some problems are difficult and time consuming to find and likes to call up or come down to yell at you. We have all been in your shoes either with our personal vehicles, customers or both. It sucks but if you stick with it one way or another you'll get it nailed down and it'll feel good when you do.

 

[WP29P4A]

I would pause the multi directional search and check the least expensive most simple and obvious potential cause of the problems you are experiencing. Have you verified that all the grounds are in place and the connections are not rusted or corroded? Lots of people think they are smarter that the engineer that designed their truck and believe that if they remove emissions equipment or thermostat it will run better, that same thought process makes them believe that grounds are not important.

My son had most of the problems that you do. I cleaned up all the ground connections, connected the one from the firewall to the back of motor that was just dangling, replaced the pollick valve (dual tank switch valve) redid the fusible links at the starter, replaced all the starter connectors and adjusted the idle screw on the throttle body. No more stalling, no more surging at cold idle, and it starts perfect every time now. It was running rough on one tank but not the other and would fill the left tank when he was using the right tank and the vapor canister would leak gas. Yes, we followed forum advise and checked all that vacuum stuff first before we cleaned up the electrical issues.

I just watched some frustrated guy on the Dodge Charger site I spend time on, spend six months chasing down all the ideas everyone was giving him. They were telling him to remove the whole wiring loom from his car to find the short he thought he had. I made a video for him to show him I could duplicate his problem exactly by removing the ground on my car, he installed proper grounds and for the first time since he bought the car he was able to start and drive the car, guy was so happy he said he was almost brought to tears, he was so excited.

For what it's worth that is my two cents, just for the record, I have been in the low voltage industry for more than 40 years and have owned several dodge and chevy vehicles from the 70's and I do custom electrical work on my clients classic vehicles from a 41 ford pick up to a $70,000. 2006 jeep rock crawler with dual computers to control the corvette crate motor and trans, while the stock computer controls the dash systems. I've seen a few things. lol

 

[Goldie Driver]

I would pause the multi directional witch hunt and check the least expensive most simple and obvious potential cause of the problems you are experiencing. Have you verified that all the grounds are in place and the connections are not rusted or corroded? Lots of people think they are smarter that the engineer that designed their truck and believe that if they remove emmissions equipment or thermostat it will run better, that same thought process makes them believe that grounds are not important. My son had most of the problems that you do. I cleaned up all the ground connections, replaced the pollick valve (dual tank switch valve) redid the fusible links at the starter and adjusted the idle screw on the throttle body. No more stalling, no more surging at cold idle, and it starts perfect every time now. It was running rough on one tank but not the other and would fill the left tank when he was using the right tank and the vapor canister would leak gas.

I just watched some frustrated guy on the Dodge Charger site I spend time on, spend six months chasing down all the ideas everyone was giving him. I made a video for him to show him I could duplicate his problem exactly by removing the ground on my car, he installed proper grounds and for the first time since he bought the car he was able to start and drive the car, guy was so happy he said he was almost brought to tears, he was so excited.

For what it's worth that is my two cents, just for the record, I have been in the low voltage industry for more than 40 years and have owned several dodge and chevy vehicles from the 70's and I do custom electrical work on my clients classic vehicles from 41 ford pick up to a $70,000. 2006 jeep rock crawler with dual computers to control the corvette motor and trans, while the stock computer controls the dash systems.

Have you been able to solve the classic Mopar headlight dim at idle?

Dodge trucks from the 70s are horrible about it- but not the vans - - and the 2 69 Chargers I had experience with (college buddy who's Dad owned them) did it as well.

81 and up for the trucks- whenever the body style changed- dont seem to do it.

 

[Bruce Wingate]

Electrical gremlins are tough. I have a carb'ed 350 with HEI ignition and it has cut out on my twice with a sudden stumble and die like it ran out of fuel quickly. Nice strong crank but no spark. Turns out it was the battery connector to the distributor that was very loose - it fell off when I just brushed against it. I'm in the process of fixing that, doing a tune up and then testing it out.

As frustrating as it is, I would chase down the engine's electrical gremlins before doing major changes there. Adding a new(ish) and unknown carb or engine to the mix will just give you one more series of problems to track down if a similar problem persists.

Also, if you were willing to drop 6k on an engine, have you thought about going for a modern EFI conversion like Holley Sniper or Edelbrock Pro Flo 4? Still pricey but about half the cost and if your engine is solid, it is just a matter of changing the intake manifold and wiring in the power and the fuel pumps.

 

[WP29P4A]

Have you been able to solve the classic Mopar headlight dim at idle?

Dodge trucks from the 70s are horrible about it- but not the vans - - and the 2 69 Chargers I had experience with (college buddy who's Dad owned them) did it as well.

81 and up for the trucks- whenever the body style changed- dont seem to do it.

I have always made sure grounds are good and use a heavy duty alternator and battery with the highest amp hour rating, with the best CCA I can fit in the car. Not much problem with dim lights, but when you short something it sure lets you know in a spectacular flashy way.

 

[Doppleganger]

Mine didn't have TBI but had the ongoing runability issues. Looking back, I think it was a vacuum leak at the base of the carb (main issue anyways). When it stalled, I hit the hazards and had none. When I finally got home, I got under the dash and found a w@d of solid core wires the size of a volleyball, with a lamp cord (no joke) going to where the blower used to be. I gutted the truck and started over.

An Edelbrock ProFlo4 EFI was one of the first things I decided on. I like carbs fine but read the reviews or what fellas on here who have it think.

And yeah......the wife is definitely a keeper. I have one like that too.

 

[eric 87]

@eric 87 I'm trying to feel what your feelings are for this and I'm struggling to do so. Maybe it's just me, I want to help but I'm genuinely unsure what direction you'd like to go in so I'm going to try to give you my thoughts in pieces.

Back in the day when we'd get a TBI rig in doing this one of the first things we'd do is unplug the IAC valve and then plug the passage in the throttle body and set the minimum idle to spec, which I'd have to look up that spec as it's been a long time but I think it's something like 500 RPM. Anyhow then we'd see if the truck still acted up. If yes, then it's likely to be something mechanical on the truck. If no then it's likely to be computer related.

Maybe this has all been checked before and if so just ignore this:
EGR valve, if leaking can cause high idle and stalling. Would need to remove the EGR valve flip valve upside down, pour water in one of side of the passage and see if it leaks into the other side.

Brake booster leaking.

Often over looked is the charcoal canister, on these truck sometimes they will crack or rupture and leak vacuum like crazy.

So those are my thoughts on your issue this time around.

Any luck with the electrical stuff?

You said "Either way this thing is getting tiring. This part of car ownership but I prefer the fun part of adding to make it better and nice routine maintenance. Chasing problems not so much." If you think this is bad, you should try being a mechanic especially if your customer does not understand that some problems are difficult and time consuming to find and likes to call up or come down to yell at you. We have all been in your shoes either with our personal vehicles, customers or both. It sucks but if you stick with it one way or another you'll get it nailed down and it'll feel good when you do.

I know I can be all over the place with my thinking at times. Spending money on a new carb, intake and distributor taking it back to basics seems to be the easy fix. Then to add more confidence into what I own and dependability I thought lets go full on and replace engine and just know that even with new there can be problems but the odds greatly go down.
These are last resorts in order.

Now I did say I was going to look for electrical. I went looking. MY SES light bulb had gone out. I took the gauge cluster out the other night. Replaced two bulbs then thought why not all of them.
I fiddled around looking under the dash and engine compartment. I had mentioned I believe the engine died on me going down the road at 40mph steady. I lost power even to radio but when I coasted into a driveway put in park it cranked. THought what can cause this but then to start up? Well lets pull out the part gun once more since my gauge was dropping to 8 at times. I bought myself a new alternator and installed yesterday. Thinking was it will be used no matter what I do in the future.
New bulbs in dash and alternator installed. I started the truck and the SES light was brightly lit. I spent 20$ awhile back on the OBD1 code reader which is really just a plastic case that house two pins like a paper clip.
I got a code 42 .
With said purchase I got a book with the codes in it.
EST short or open circuit
DIS which it doesn't have
Fuel cutoff relay open circuit or ground.
It might be the later but since there was just a new distributor put in checked the plugs to the ignition module. Need to clear the codes again and restart. Maybe there is a short since that is the EST part of the equation.
Checked all the plugs and wires to components. Noticed the plug going into the alternator looked a bit black and crusty.
Anyway since the module is 35$ and I thought the coil looked original to truck I may run and get them today.
If I can get this figured out I will keep the TBI as is since it has really ran better when the gremlins aren't acting up.
If I can't fix it then I may opt for the carb conversion. But if I do that I found another option.

JEGS 8758K3: Crate Engine Conversion Kit - JEGS

Get the Best Performance with JEGS Crate Engine Conversion Kit 8758K3 parts at JEGS. Shop Now at the Guaranteed Lowest Price!

www.jegs.com

This is the sort of engine I want. Nothing in the performance builds. Just a nice steady engine that is dependable. I figure if I go the carb swap route by the time I am done it would be about a grand. Might as well spend another 1600 for an engine.
Having said that I hope to find the issue with this one.
Oh I know how frustrated I get and know how much pressure it must be when someone things you are a wizard.
I have called the guy at the shop and he has probably cussed me when he gets off the phone but he has been helpful telling me what to look for. ALso said he may have pulled on something when laying across engine to cause something to wiggle loose.

I appreciate the help. To clarify I prefer to go with what I have if I can find the issue. Code 42 now. 305 TBI.

 

[eric 87]

Electrical gremlins are tough. I have a carb'ed 350 with HEI ignition and it has cut out on my twice with a sudden stumble and die like it ran out of fuel quickly. Nice strong crank but no spark. Turns out it was the battery connector to the distributor that was very loose - it fell off when I just brushed against it. I'm in the process of fixing that, doing a tune up and then testing it out.

As frustrating as it is, I would chase down the engine's electrical gremlins before doing major changes there. Adding a new(ish) and unknown carb or engine to the mix will just give you one more series of problems to track down if a similar problem persists.

Also, if you were willing to drop 6k on an engine, have you thought about going for a modern EFI conversion like Holley Sniper or Edelbrock Pro Flo 4? Still pricey but about half the cost and if your engine is solid, it is just a matter of changing the intake manifold and wiring in the power and the fuel pumps.

Well I was thinking the Sniper and others were overkill for a stock 87 305 that is solid as of now but came with 180 hp at best. And the cost of those are typically more than all the parts for a carb conversion. Along with the conversion I have thought about also getting a wiring harness from Painless or American autowire for an 86 so it has no computer in the harness. Then I can redo the wiring and all the grounds through the entire truck. Bad thing is that leaves me with my old Ford f150 which is telling me it wants to be retired with each increasing clatter and my 69 firebird which I do use and not let sit and be pretty only in the garage. But while I have regular tags and drive it I hate to use it as the ONLY car for an extended period while I work on my truck. I mean if I rewire then of course I want to clean the engine bay and maybe make it pretty as new and run the wires so they are out of the way and protected etc.

So for now I am hoping to work out the bugs. Next cheapest route is the carb conversion. But for practical purposes if I go that far why not replace with
https://www.jegs.com/i/JEGS/059/8758K3/10002/-1

It is a case of an annoying problem frustrating me to that point of replacing a good engine! SO I hope to have turkey in my mouth and a wrench in my hand unless I get it figured out today.

 

[eric 87]

I would pause the multi directional search and check the least expensive most simple and obvious potential cause of the problems you are experiencing. Have you verified that all the grounds are in place and the connections are not rusted or corroded? Lots of people think they are smarter that the engineer that designed their truck and believe that if they remove emissions equipment or thermostat it will run better, that same thought process makes them believe that grounds are not important.

My son had most of the problems that you do. I cleaned up all the ground connections, connected the one from the firewall to the back of motor that was just dangling, replaced the pollick valve (dual tank switch valve) redid the fusible links at the starter, replaced all the starter connectors and adjusted the idle screw on the throttle body. No more stalling, no more surging at cold idle, and it starts perfect every time now. It was running rough on one tank but not the other and would fill the left tank when he was using the right tank and the vapor canister would leak gas. Yes, we followed forum advise and checked all that vacuum stuff first before we cleaned up the electrical issues.

I just watched some frustrated guy on the Dodge Charger site I spend time on, spend six months chasing down all the ideas everyone was giving him. They were telling him to remove the whole wiring loom from his car to find the short he thought he had. I made a video for him to show him I could duplicate his problem exactly by removing the ground on my car, he installed proper grounds and for the first time since he bought the car he was able to start and drive the car, guy was so happy he said he was almost brought to tears, he was so excited.

For what it's worth that is my two cents, just for the record, I have been in the low voltage industry for more than 40 years and have owned several dodge and chevy vehicles from the 70's and I do custom electrical work on my clients classic vehicles from a 41 ford pick up to a $70,000. 2006 jeep rock crawler with dual computers to control the corvette crate motor and trans, while the stock computer controls the dash systems.

Well I suspected I had to have a burned out SES bulb since it had flickered a couple times months back. Pulled the dash and replaced bulbs in the cluster. Also thought what can cause the gauge to drop to 8 ? Why when I hit my brakes does the gauge go down. Often the best it would do is 12.5 on the gauge. When I put in the new bulbs I noticed if I had my headlights on and put the four way flashers on they had a weird sort of flash. As if real slow and not in a steady flash. Turn off the headlights and they flashed as they should. Something is not right somewhere. As far as the engine grounds I have pretty much checked them all and they seem good and solid. I wonder if I have something going on in the wiring under the dash since it quit going down the road. Could ignition.....see I don't know where to begin to look.
Anyway I replaced the Alternator as well thinking maybe the regulator was acting up. Started the truck with the new bulb and I get a code 42 flashing.
EST ground short of open circuit
DIS which doesn't apply to my truck
Fuel cutoff relay circuit open or ground

I think either the first or the last on that list. Something killed the truck I still have the idle issues. But when it is running down the road it is better than it ever has been.
I don't think it is a throttle body issue so much as a wiring issue somewhere. But if I get rid of the computer out of the truck I don't have to worry about 80% of the wiring. That was my thinking on the conversion to carb.

 

[eric 87]

@ WP29P4A

Curious is there any diagram that shows where all the grounds are on the entire truck? Without all the other wiring in the diagram lol. I know what the ground symbol looks like on a diagram if I have to use that but to simplify or speed up the process I was wondering if there is one just for the grounds? Is there such a thing. If not maybe I will do it one day.

 

[WP29P4A]

The main grounds are simple, you have the fat ground cable from the negative battery post going to the front of the motor (attached to head or block) the negative cable should have a second smaller wire going to the chassis of the truck, attached somewhere close to the battery. Then you should have another ground wire going from the back of the engine to the firewall. If the bed on the truck has rubber between the mounts for isolation it will also have a ground strap from the bed to the frame. (if the grounds connect to the frame and not the bed it may not need the ground strap from bed to frame.

The secondary grounds are all close to components. the tail light will have a ground close by, the headlights are grounded close by, probably to the radiator support. The dash with have multiple grounds near the e-brake assembly. Most vehicles from that era also have a ground from the steering column to the dash.

Sorry the pictures are grounds on my Charger and not truck, I can post pics tomorrow when my son comes over with his 87 GMC.

 

[WP29P4A]

FYI, most intermittent issues with starting and stalling will be electrical connections, its the heat and cool cycles along with moisture that create the intermittent adventures. An old mechanic back in the late 70's (before carbs had electrical wires) told me that 90% of all carburator problems are electrical. Meaning, most times the problem is ignition/electrical not the carb.

 

[WP29P4A]

The easy way to test the grounds after visual verification is to use a test light, extend the ground wire on your test light so you car reach the whole truck. Connect the end with the clip to the negative terminal on the battery. (the negative wire from battery to engine needs to be connected for this test). With the clip connected to the battery negative terminal, touch the different areas of the truck with the tip of test light, frame, radiator support, fender, etc. If the test light lights up you have a lack of ground to that area of the truck.

Keep in mind, electricity flows in a circle, it leaves the positive terminal on the battery and wants to return to the negative terminal, if it does not make it back to the negative terminal.(NOTHING WORKS)

Electricity and water will always try to find the path of least resistance.

 

[WP29P4A]

Well I suspected I had to have a burned out SES bulb since it had flickered a couple times months back. Pulled the dash and replaced bulbs in the cluster. Also thought what can cause the gauge to drop to 8 ? Why when I hit my brakes does the gauge go down. Often the best it would do is 12.5 on the gauge. When I put in the new bulbs I noticed if I had my headlights on and put the four way flashers on they had a weird sort of flash. As if real slow and not in a steady flash. Turn off the headlights and they flashed as they should. Something is not right somewhere. As far as the engine grounds I have pretty much checked them all and they seem good and solid. I wonder if I have something going on in the wiring under the dash since it quit going down the road. Could ignition.....see I don't know where to begin to look.
Anyway I replaced the Alternator as well thinking maybe the regulator was acting up. Started the truck with the new bulb and I get a code 42 flashing.
EST ground short of open circuit
DIS which doesn't apply to my truck
Fuel cutoff relay circuit open or ground

I think either the first or the last on that list. Something killed the truck I still have the idle issues. But when it is running down the road it is better than it ever has been.
I don't think it is a throttle body issue so much as a wiring issue somewhere. But if I get rid of the computer out of the truck I don't have to worry about 80% of the wiring. That was my thinking on the conversion to carb.

Keep in mind that computer you want to eliminate also controls the distributer.

 

[SirRobyn0]

I know I can be all over the place with my thinking at times. Spending money on a new carb, intake and distributor taking it back to basics seems to be the easy fix. Then to add more confidence into what I own and dependability I thought lets go full on and replace engine and just know that even with new there can be problems but the odds greatly go down.
These are last resorts in order.

Now I did say I was going to look for electrical. I went looking. MY SES light bulb had gone out. I took the gauge cluster out the other night. Replaced two bulbs then thought why not all of them.
I fiddled around looking under the dash and engine compartment. I had mentioned I believe the engine died on me going down the road at 40mph steady. I lost power even to radio but when I coasted into a driveway put in park it cranked. THought what can cause this but then to start up? Well lets pull out the part gun once more since my gauge was dropping to 8 at times. I bought myself a new alternator and installed yesterday. Thinking was it will be used no matter what I do in the future.
New bulbs in dash and alternator installed. I started the truck and the SES light was brightly lit. I spent 20$ awhile back on the OBD1 code reader which is really just a plastic case that house two pins like a paper clip.
I got a code 42 .
With said purchase I got a book with the codes in it.
EST short or open circuit
DIS which it doesn't have
Fuel cutoff relay open circuit or ground.
It might be the later but since there was just a new distributor put in checked the plugs to the ignition module. Need to clear the codes again and restart. Maybe there is a short since that is the EST part of the equation.
Checked all the plugs and wires to components. Noticed the plug going into the alternator looked a bit black and crusty.
Anyway since the module is 35$ and I thought the coil looked original to truck I may run and get them today.
If I can get this figured out I will keep the TBI as is since it has really ran better when the gremlins aren't acting up.
If I can't fix it then I may opt for the carb conversion. But if I do that I found another option.

JEGS 8758K3: Crate Engine Conversion Kit - JEGS

Get the Best Performance with JEGS Crate Engine Conversion Kit 8758K3 parts at JEGS. Shop Now at the Guaranteed Lowest Price!

www.jegs.com

This is the sort of engine I want. Nothing in the performance builds. Just a nice steady engine that is dependable. I figure if I go the carb swap route by the time I am done it would be about a grand. Might as well spend another 1600 for an engine.
Having said that I hope to find the issue with this one.
Oh I know how frustrated I get and know how much pressure it must be when someone things you are a wizard.
I have called the guy at the shop and he has probably cussed me when he gets off the phone but he has been helpful telling me what to look for. ALso said he may have pulled on something when laying across engine to cause something to wiggle loose.

I appreciate the help. To clarify I prefer to go with what I have if I can find the issue. Code 42 now. 305 TBI.

I guess for me one of the things is that I could not consider an engine replacement over a runabilty issue simply because I don't have that kind of money to throw at a truck unless I really had too. Get that code 42 sorted out. That is very likely your stalling issue.