87 Buick V8 307 Stalling after driving 20-30 Minutes

Tore

Not-quite-so-new-guy
Jan 8, 2024
29
2
3
Do you just have a code reader or a scanner that displays both codes and live data? An analog dwell meter displays fuel mixture solenoid dwell time which tells you if the ECM is responding rich or lean as well as RPM and voltage. An OBD1 scanner like a old Alltest Brainmaster displays the previous 3 features as well as live sensor data which makes TPS adjustment easier. On top of that a Mityvac is very handy for testing vacuum parts. It takes a lot of specialized tools to work on smog controlled cars which includes modern ones. Without at least a analog dwell meter you are working blind on CCC cars.

I have all 3 tools above. Analog dwell meters and OBD1 scanners are pretty much only available used these days. The advantage of a analog dwell meter is you can watch the needle sweep to get a better view of the solenoid dwell.
Just code reader. Was looking at the alltest Brainmaster but unsure what model and connection for my car.
 

69hurstolds

Geezer
Supporting Member
Jan 2, 2006
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Just code reader. Was looking at the alltest Brainmaster but unsure what model and connection for my car.
Connection is OBD1 for 82 and later. I think 81 the connector was a bit different IIRC. Until they came out with OBD2. There are some scanners that can do 1 and 2, but you need to only be concerned with OBD1. Simplistic system compared to today's stuff, but as stated, it can be troublesome to tune without the right test tools.

FWIW, you can adjust dwell of the mixture control solenoid with a digital meter, but it's WAY tougher, IMO. An analog set on 6 cyl mode lets you see the sweep and a way easier to read. It's like watching a movie on a gameboy screen vs a 72" TV. It's the only time IMO that analog wins over digital.
 
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69hurstolds

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Supporting Member
Jan 2, 2006
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Fuel pressure is good. On the upper side of the stock range but good. TPS reading 0.85 V is high if you're at the recommended 450 rpm for measuring the TPS.

According to the service manual, TPS should be 0.40-0.42V @ 450 RPM with ILC retracted. Computer might think your engine needs more fuel because it "sees" the primaries as more open than they were. It's weird because IIRC, the computer won't throw a Code 21 (misadjusted TPS) until it hangs over 1 V for 10 seconds. Could be wrong on that. The ECM coolant sensor (it's the front driver corner one on the intake, not the other one just inboard of it), baro sensor, VAC, and O2 sensors can mess with your too as these sensors are all intertwined with how well the vehicle runs. This is why any vacuum leaks are so important to fix on these CCC cars.

You can get an idea of what max reading will be if you have the car engine off, ignition on, and take the carb to full throttle position. TPS voltage should go to 4.x volts (approaching reference signal of 5V). It should be somewhere north of 4 but the closer to 5 the better. Due to resistance, you may not see 5V, as most are a little less. But that's ok.

All that said, your TPS voltage alone LIKELY isn't the cause of your issues you describe. Usually timing and driveability issues come from vacuum leaks and other ill-adusted junk. Your readings don't seem THAT far off, although it WILL probably not be optimum. I have a gut feeling there's something else involved.


How to adjust TPS- from 84 Cutlass CSM. Other years and E2ME/MC are the same procedure since they share the same type of primary bits.
n_Engine%20179.jpg

n_Engine%20180.jpg



Just to make sure of something...assuming your VAC sensor on the passenger side fender well (behind the coolant overflow tank) is the orignal or if it was swapped out with a new one, it's an actual VAC (aka D/P) sensor and not a MAP sensor? If you're not getting a code, it's probably ok. Just asking. If they were swapped up, they do the opposite on voltage sensing so you would sure as heck get a code thrown.

1707747818123.png


This is not to say to simply fire the parts cannon at it. Sometimes these issues take seemingly forever to find and diagnose. Far be it from me to claim any expertise in chasing down glitches in a CCC system. It's got wires and electrical junk in it and I'm not great with it.

Can't recall if the carb was ever messed with or not. Was thinking about the M/C solenoid itself. While unlikely, it might be good to check the M/C solenoid resistance at the terminals.
 
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Tore

Not-quite-so-new-guy
Jan 8, 2024
29
2
3
Fuel pressure is good. On the upper side of the stock range but good. TPS reading 0.85 V is high if you're at the recommended 450 rpm for measuring the TPS.

According to the service manual, TPS should be 0.40-0.42V @ 450 RPM with ILC retracted. Computer might think your engine needs more fuel because it "sees" the primaries as more open than they were. It's weird because IIRC, the computer won't throw a Code 21 (misadjusted TPS) until it hangs over 1 V for 10 seconds. Could be wrong on that. The ECM coolant sensor (it's the front driver corner one on the intake, not the other one just inboard of it), baro sensor, VAC, and O2 sensors can mess with your too as these sensors are all intertwined with how well the vehicle runs. This is why any vacuum leaks are so important to fix on these CCC cars.

You can get an idea of what max reading will be if you have the car engine off, ignition on, and take the carb to full throttle position. TPS voltage should go to 4.x volts (approaching reference signal of 5V). It should be somewhere north of 4 but the closer to 5 the better. Due to resistance, you may not see 5V, as most are a little less. But that's ok.

All that said, your TPS voltage alone LIKELY isn't the cause of your issues you describe. Usually timing and driveability issues come from vacuum leaks and other ill-adusted junk. Your readings don't seem THAT far off, although it WILL probably not be optimum. I have a gut feeling there's something else involved.


How to adjust TPS- from 84 Cutlass CSM. Other years and E2ME/MC are the same procedure since they share the same type of primary bits.
n_Engine%20179.jpg

n_Engine%20180.jpg



Just to make sure of something...assuming your VAC sensor on the passenger side fender well (behind the coolant overflow tank) is the orignal or if it was swapped out with a new one, it's an actual VAC (aka D/P) sensor and not a MAP sensor? If you're not getting a code, it's probably ok. Just asking. If they were swapped up, they do the opposite on voltage sensing so you would sure as heck get a code thrown.

View attachment 234986

This is not to say to simply fire the parts cannon at it. Sometimes these issues take seemingly forever to find and diagnose. Far be it from me to claim any expertise in chasing down glitches in a CCC system. It's got wires and electrical junk in it and I'm not great with it.

Can't recall if the carb was ever messed with or not. Was thinking about the M/C solenoid itself. While unlikely, it might be good to check the M/C solenoid resistance at the terminals.
Yeah its frustrating!! Checked the carb again when it stalled and not spraying then literally a minute later starts spraying. Got a OBD1 scanner coming see what that tells me. A
 

Tore

Not-quite-so-new-guy
Jan 8, 2024
29
2
3
Yeah its frustrating!! Checked the carb again when it stalled and not spraying then literally a minute later starts spraying. Got a OBD1 scanner coming see what that tells me. A
Thanks for the info also.
 

69hurstolds

Geezer
Supporting Member
Jan 2, 2006
8,324
17,981
113
NO spray? It's either a failed (or missing) carb plunger pump check ball that won't seat right, a worn/split carb plunger pump diaphragm. Possibly an outside chance of a very low float level issue or combination thereof. Something is hindering the carb plunger pump.
 

86 Salon

Apprentice
Mar 14, 2021
77
86
18
Yeah its frustrating!! Checked the carb again when it stalled and not spraying then literally a minute later starts spraying. Got a OBD1 scanner coming see what that tells me. A
When you say the carb isn't spraying, are you saying that when you open and close the throttle, no fuel is coming out of the accelerator pump squirters? If so, the float bowl is empty so you either have a supply issue to the fuel pump or a bad fuel pump. What does your fuel pressure read when you crank the car after it stalls?
 

Tore

Not-quite-so-new-guy
Jan 8, 2024
29
2
3
When you say the carb isn't spraying, are you saying that when you open and close the throttle, no fuel is coming out of the accelerator pump squirters? If so, the float bowl is empty so you either have a supply issue to the fuel pump or a bad fuel pump. What does your fuel pressure read when you crank the car after it stalls?
Correct. I have not checked fuel pressure after stall because by the time I hooked it up to test pressure it would be back to normal. As I said after a minute of sitting it purs like a kitten until going down road for another mile or so.
 

86 Salon

Apprentice
Mar 14, 2021
77
86
18
Correct. I have not checked fuel pressure after stall because by the time I hooked it up to test pressure it would be back to normal. As I said after a minute of sitting it purs like a kitten until going down road for another mile or so.
Keep the fuel pressure gauge attached while driving. Get a long enough hose and put the gauge on the windshield so you can see it while driving.
 

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