87 Buick V8 307 Stalling after driving 20-30 Minutes

Tore

Not-quite-so-new-guy
Jan 8, 2024
27
0
1
Got a 1987 Buick Regal Limited and keeps stalling after warming up. After stalling let rest a few mins and fires right back up and can go maybe a mile and stall out again. Manual fuel pump was replaced ~9 months ago. Changes out throttle position senor. All new wires and spark plugs along with distributor cap and coil. Help! Thanks
 

57 Handyman

Master Mechanic
Feb 6, 2017
339
389
63
Definitely heat and/or fuel-related! Next time this happens, open the gas cap and listen for a whoosh sound. This would indicate a need to replace the cap. Next, candidate is the insulation under the carb which would contribute to fuel starvation due to fuel-boiling and evaporation.
 

MrSony

Geezer
Nov 15, 2014
6,831
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Des Moines, Iowa
My guess is the ignition module. iirc the factory .080 gap for olds engines was killing modules trying to fire it. Change the module, and get some spark plugs with a .045 gap and see if that helps. Dont forget to clean off the old thermal paste and apply some new. It should come in a packet with the new module. just a thin smear.
 
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Clone TIE Pilot

Comic Book Super Hero
Aug 14, 2011
3,861
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Galaxy far far away
Get a HEI spark tester and see if you have spark when your car stalls. Avregular dpark tester won't do on a HEI system, you must use a HEI tester.
 

69hurstolds

Geezer
Supporting Member
Jan 2, 2006
8,198
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Did you check/readjust the new TPS? It shouldn't cause your issue, but it won't help your carb feedback to the ECM if it's too far off.

To me, if it repeats like this, it doesn't sound like a carb problem or a dirty fuel sock. Very unlikely since it seems fairly repeatable.

Although you haven't done much diagnostics at this point, I tend to agree with MrSony on VERY LIKELY the ignition module. Your 87 307 uses a 7 pin module. And as stated, you need THERMAL paste as a heat sink seal between the distributor housing and the bottom of the ignition module. If some paste is left under the old unit that isn't full of dirt, you can re-use it. It doesn't go bad as it's not like a greased bearing. You don't need much. Make sure if you put new on it, that it's THERMAL paste. It can be dielectric thermal paste, but make sure it's for heat sink application. Or you'll fry the new one, too. If it's dry underneath the module, that's a problem.

Carry a friend and a timing light with you. The timing light means you don't have to disconnect anything to test for spark. As soon as it dies, get to the side of the road if possible, have a friend crank it after you hook up the leads to the timing light, any cylinder will do, doesn't matter which spark plug wire but preferably #1. Have them crank it over ASAP and check for spark by seeing if the timing light will flash when cranking. If none, it's the ignition module AND/OR coil. I've heard of coils conking out after they get warm. Kinda rare, but possible. If you DO have spark, then it may be time to focus on the fuel. If it does crank and fire up, then check the timing mark and see if it's steady or fluttering around. If it flutters badly, it may be a timing chain telling you it may be going bye bye. If it's original, it has nylon gear teeth which are notorious at that age of breaking off and ruining people's fun. If you get it back to the house and it's running, do a timing check on it and make sure it's at 20 degrees with the A&B terminals on the ALDL under the dash jumpered to lock timing while you check it. With the terminals grounded you should see 20 degrees BTDC. And it should be pretty steady.

If you put new plugs in it and set them to proper gap, the 87 307 uses a 0.060" gap. You can use that and shouldn't be a problem, but probably better to again probably reset those to 0.045 to 0.050" max. JMO. It'll run just fine that way and not overtax the ignition system.

Again, try the 7 pin module. Various GM p/ns, but also you can get Standard LX315.

You didn't say WHEN you changed the coil. Was it before the issues or after? As far as any coil change, you HAVE to make sure the polarity is right. Not all HEI coils interchange. Did you just buy a coil from AutoZone or something and let some counter jockey without experience make the call? Depending on what's in the computer, they MIGHT have gave you the wrong coil. Just feeling out possibilities. Still got the receipt or box it came in? Part number? This can help me determine if you got the correct one.

For your 307, 12498336 is the GM part number you seek (or aftermarket equivalent, like Standard DR-32). RED AND WHITE wires. If there's a yellow wire in there, it's the wrong one.
 
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Tore

Not-quite-so-new-guy
Jan 8, 2024
27
0
1
Did you check/readjust the new TPS? It shouldn't cause your issue, but it won't help your carb feedback to the ECM if it's too far off.

To me, if it repeats like this, it doesn't sound like a carb problem or a dirty fuel sock. Very unlikely since it seems fairly repeatable.

Although you haven't done much diagnostics at this point, I tend to agree with MrSony on VERY LIKELY the ignition module. Your 87 307 uses a 7 pin module. And as stated, you need THERMAL paste as a heat sink seal between the distributor housing and the bottom of the ignition module. If some paste is left under the old unit that isn't full of dirt, you can re-use it. It doesn't go bad as it's not like a greased bearing. You don't need much. Make sure if you put new on it, that it's THERMAL paste. It can be dielectric thermal paste, but make sure it's for heat sink application. Or you'll fry the new one, too. If it's dry underneath the module, that's a problem.

Carry a friend and a timing light with you. The timing light means you don't have to disconnect anything to test for spark. As soon as it dies, get to the side of the road if possible, have a friend crank it after you hook up the leads to the timing light, any cylinder will do, doesn't matter which spark plug wire but preferably #1. Have them crank it over ASAP and check for spark by seeing if the timing light will flash when cranking. If none, it's the ignition module AND/OR coil. I've heard of coils conking out after they get warm. Kinda rare, but possible. If you DO have spark, then it may be time to focus on the fuel. If it does crank and fire up, then check the timing mark and see if it's steady or fluttering around. If it flutters badly, it may be a timing chain telling you it may be going bye bye. If it's original, it has nylon gear teeth which are notorious at that age of breaking off and ruining people's fun. If you get it back to the house and it's running, do a timing check on it and make sure it's at 20 degrees with the A&B terminals on the ALDL under the dash jumpered to lock timing while you check it. With the terminals grounded you should see 20 degrees BTDC. And it should be pretty steady.

If you put new plugs in it and set them to proper gap, the 87 307 uses a 0.060" gap. You can use that and shouldn't be a problem, but probably better to again probably reset those to 0.045 to 0.050" max. JMO. It'll run just fine that way and not overtax the ignition system.

Again, try the 7 pin module. Various GM p/ns, but also you can get Standard LX315.

You didn't say WHEN you changed the coil. Was it before the issues or after? As far as any coil change, you HAVE to make sure the polarity is right. Not all HEI coils interchange. Did you just buy a coil from AutoZone or something and let some counter jockey without experience make the call? Depending on what's in the computer, they MIGHT have gave you the wrong coil. Just feeling out possibilities. Still got the receipt or box it came in? Part number? This can help me determine if you got the correct one.

For your 307, 12498336 is the GM part number you seek (or aftermarket equivalent, like Standard DR-32). RED AND WHITE wires. If there's a yellow wire in there, it's the wrong one.
For spark plugs I gaped to 0.060 and replaced coil after the issue.

My neighbor is a retired NAPA guy with 30+ years.

Think I am going to try the ignition module and see how it goes.
 

69hurstolds

Geezer
Supporting Member
Jan 2, 2006
8,198
17,600
113
For spark plugs I gaped to 0.060 and replaced coil after the issue.

My neighbor is a retired NAPA guy with 30+ years.

Think I am going to try the ignition module and see how it goes.
You should be fine with the factory recommended 0.060". I just wouldn't go over that. They changed that I believe in 1985 but never updated the underhood labels for 85 model year. Since the coil was an afterthought to the party and didn't hurt or help, it doesn't appear the coil has much to do with your issue. So it's even more likely the module is the issue.

No disrespect at all to your retired NAPA neighbor as I'm sure he has skills, but I've gone a whole lot longer than 30 years' experience with mainly Oldsmobile parts. He's likely had to deal with nearly every make and model on the planet. I like to say I have 45+ years' experience concentrated on Oldsmobiles, but I also could have 1 years' experience 45 times. And I'm STILL learning new things. And I STILL make mistakes. And so could the guy putting a coil in a NAPA box at the factory, which is now probably in Indonesia or whatever.

I'm not saying your guy wouldn't know, but then again, we don't know what he does or does not know when it comes to nuances about Oldsmobile stuff. None of us here know what parts you were working with to even help you try to figure it out. So with that, we're on this side of the internet with little to no parts information. So this isn't a slam on you or your neighbor. Think of us as new detectives trying to look at the crime-scene evidence and trying to figure out what you got, when you installed it, and all the events leading up to now to try and isolate the issue long-distance. The help you end up with is dependent upon the information you make available.
 
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69hurstolds

Geezer
Supporting Member
Jan 2, 2006
8,198
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And here again, no disrespect for your skillset, but here's some service manual information that may be helpful if you (or anyone else) isn't fluent in tackling module replacements.

n_Engine%20281.jpg


n_Engine%20282.jpg
 
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Tore

Not-quite-so-new-guy
Jan 8, 2024
27
0
1
You should be fine with the factory recommended 0.060". I just wouldn't go over that. They changed that I believe in 1985 but never Since the coil was an afterthought to the party and didn't hurt or help, it doesn't appear the coil has much to do with your issue. So it's even more likely the module is the issue.

No disrespect at all to your retired NAPA neighbor as I'm sure he has skills, but I've gone a whole lot longer than 30 years' experience with mainly Oldsmobile parts. He's likely had to deal with nearly every make and model on the planet. I like to say I have 45+ years' experience concentrated on Oldsmobiles, but I also could have 1 years' experience 45 times. And I'm STILL learning new things. And I STILL make mistakes. And so could the guy putting a coil in a NAPA box at the factory, which is now probably in Indonesia or whatever.

I'm not saying your guy wouldn't know, but then again, we don't know what he does or does not know when it comes to nuances about Oldsmobile stuff. None of us here know what parts you were working with to even help you try to figure it out. So with that, we're on this side of the internet with little to no parts information. So this isn't a slam on you or your neighbor. Think of us as new detectives trying to look at the crime-scene evidence and trying to figure out what you got, when you installed it, and all the events leading up to now to try and isolate the issue long-distance. The help you end up with is dependent upon the information you make available.
Yes sir...
 

Tore

Not-quite-so-new-guy
Jan 8, 2024
27
0
1
And here again, no disrespect for your skillset, but here's some service manual information that may be helpful if you (or anyone else) isn't fluent in tackling module replacements.

n_Engine%20281.jpg


n_Engine%20282.jpg
None taking.. I know the basics of how things work and how to replace basic parts myself. Had this car for about years now so new to 307 olds engine so anything helps. Thanks
 

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