Cees Klumper
Active Member
- Joined
- Nov 4, 2019
- Messages
- 189
- Reaction score
- 134
- Points
- 43
- Location
- De Luz, CA (near Camp Pendleton)
- Vehicle Year
- 1990
- Make / Model
- Bronco II XLT
- Transmission
- Automatic
Hey 2.9 community - I need your help with a very elusive intermittent stall. Symptoms:
- without any warning, the car (1990 Bronco II, California ECU) stalls when driving slowly, maybe 5-10 MPH. It restarts fine then runs like nothing happened
- it is progressively getting worse. A few months ago, at idle sometimes (once every 100 miles?) it would start idling poorly, and sometimes the check engine light would come on briefly. Engine would recover and all would be well again for the next 100 miles
- more recently, in the past couple of weeks, it would suddenly stall out while driving at low RPM/speed
- just now, it stalled while pulling into our apartment complex, while going 5-10 MPH. Restarting it for the first time was difficult, and it stalled again repeatedly while looking for a parking spot. This was after at least 30 miles driving around town running errands, with 0 problems.
Troubleshooting I've done:
- codes: only code thrown so far was oxygen sensor. So I replaced that, no change
- I swapped out the ECU with a spare California (same spec) one - no change. I had already replaced the two condensors with new ones
- swapped out the Idle Air Control valve with new Motorcraft - no change
- put in a new Motrocraft ignition control module - no change
- checked the throttle position switch (which is relatively new Motorcraft) - resistance values are fine
- bypassed the fuel cutoff switch in the cabin, passenger footwell - no change
- swapped out the Mass Airflow Sensor - no change
- checked fuel pressure at normal idle - checks out fine. I have not tried checking fuel pressure when the engine stalls, since it happens so infrequently I have not been able to recreate the problem while testing
- replaced the plugs, no change. Old ones looked good and evenly worn, nothing out of the ordinary
- the engine has a relatively new coil and plug wires
- checked the fuel pressure modulator, seems A-OK, holds vacuum. I replaced it with a good new one a few years ago when the old one had ruptured dumping fuel into the intake
- I wiggled all electrical connections/plugs under the hood to see if I could replicate the issue. Yesterday I thought I had it - when I manipulated the connector on the alternator, the engine started idling poorly - I installed a new (aftermarket) alternator last year and the connector doesn't fit all that well, so it was loose and when I touched it it temporarily disturbed the connection causing the engine to falter. I cleaned the connector and reinstalled it with a triewrap around it, so that it is now super-tight. So that doesn't seem like it's it either.
- checked for vacuum leaks, none to be found (and none that could be that dramatic and only so intermittent)
- replaced the EGR valve
- checked the battery, it's in great condition. Starter motor spins like a top so it doesn't seem low-voltage related
- checked the brake booster one-way valve, seems perfectly fine
- the in-tank fuel pump is relatively new, but I have not checked the electrical connections / plug at the pump (no access panel, and it's a pain to drop the tank for this. But, also, since the stalling is so sudden, as if I turn off the ignition, I don't think it's the fuel supply also because when I start it up again, there is a strong smell from the exhaust, as if there's extra fuel being burned off. This to me points more to the ignition than to the fuel being the problem).
So far, it has only happened at idle, or close to idle, not when driving at any speed over say 10 mph - which must be a clue of some sort, I just don't know what to make of it. Also, it is progressively getting worse. But, like today, it was totally absent for the whole day and many short trips to here and there under the exact same conditions that it later decided to stall/difficult restart.
The entire exhaust system is new, less than 5K miles, including the CA compliant catalytic converter. It passed smog with very good values a few months ago.
I am down to the following possibilities, but would very much appreciate any other thoughts:
- could it be the distributor - a bad/loose connection inside? Something that is interrupting the spark? Should I replace the distributor? AFAIK it's the original one, and the engine has 245K miles
- wiring loom - some partially broken wire that under some conditions causes the engine to die? Tough to diagnose since the problem is so intermittent, and only at/slightly above idle
- maybe the capacitor that is attached to the coil?
- possibly it's the ignition switch in the steering column, or the wiring/connector to it?
- bad connection to the fuel pump, at the tank? I can cut out an access panel, am tired of dropping the tank every time I need to replace a hose or e.g. the vent connector I did a few months ago to pass smog. Maybe the fuel pump itself is going bad? It's maybe 5 years old, the previous owner put it in new before he sold the truck to me. But then why is it not happening when driving at speed.
- could it be that both ECUs are bad? But then having the exact same issue, developed at the same time? Seems quite unlikely
I will pull the codes again, retry manipulating that alternator connector; I guess I can try manipulating the big plug that attaches to the ECU in the cabin to see if maybe that replicates the issue. Investigate the ignition switch / wiring in the steering column. This engine runs really well and strong - when it runs which is 90% of the time. I replaced the heads two years ago, replaced the fuel injectors with OEM rebuilts, all vacuum hoses and many other parts. It feels like it is a simple issue, nothing major, just very hard to diagnose.
- without any warning, the car (1990 Bronco II, California ECU) stalls when driving slowly, maybe 5-10 MPH. It restarts fine then runs like nothing happened
- it is progressively getting worse. A few months ago, at idle sometimes (once every 100 miles?) it would start idling poorly, and sometimes the check engine light would come on briefly. Engine would recover and all would be well again for the next 100 miles
- more recently, in the past couple of weeks, it would suddenly stall out while driving at low RPM/speed
- just now, it stalled while pulling into our apartment complex, while going 5-10 MPH. Restarting it for the first time was difficult, and it stalled again repeatedly while looking for a parking spot. This was after at least 30 miles driving around town running errands, with 0 problems.
Troubleshooting I've done:
- codes: only code thrown so far was oxygen sensor. So I replaced that, no change
- I swapped out the ECU with a spare California (same spec) one - no change. I had already replaced the two condensors with new ones
- swapped out the Idle Air Control valve with new Motorcraft - no change
- put in a new Motrocraft ignition control module - no change
- checked the throttle position switch (which is relatively new Motorcraft) - resistance values are fine
- bypassed the fuel cutoff switch in the cabin, passenger footwell - no change
- swapped out the Mass Airflow Sensor - no change
- checked fuel pressure at normal idle - checks out fine. I have not tried checking fuel pressure when the engine stalls, since it happens so infrequently I have not been able to recreate the problem while testing
- replaced the plugs, no change. Old ones looked good and evenly worn, nothing out of the ordinary
- the engine has a relatively new coil and plug wires
- checked the fuel pressure modulator, seems A-OK, holds vacuum. I replaced it with a good new one a few years ago when the old one had ruptured dumping fuel into the intake
- I wiggled all electrical connections/plugs under the hood to see if I could replicate the issue. Yesterday I thought I had it - when I manipulated the connector on the alternator, the engine started idling poorly - I installed a new (aftermarket) alternator last year and the connector doesn't fit all that well, so it was loose and when I touched it it temporarily disturbed the connection causing the engine to falter. I cleaned the connector and reinstalled it with a triewrap around it, so that it is now super-tight. So that doesn't seem like it's it either.
- checked for vacuum leaks, none to be found (and none that could be that dramatic and only so intermittent)
- replaced the EGR valve
- checked the battery, it's in great condition. Starter motor spins like a top so it doesn't seem low-voltage related
- checked the brake booster one-way valve, seems perfectly fine
- the in-tank fuel pump is relatively new, but I have not checked the electrical connections / plug at the pump (no access panel, and it's a pain to drop the tank for this. But, also, since the stalling is so sudden, as if I turn off the ignition, I don't think it's the fuel supply also because when I start it up again, there is a strong smell from the exhaust, as if there's extra fuel being burned off. This to me points more to the ignition than to the fuel being the problem).
So far, it has only happened at idle, or close to idle, not when driving at any speed over say 10 mph - which must be a clue of some sort, I just don't know what to make of it. Also, it is progressively getting worse. But, like today, it was totally absent for the whole day and many short trips to here and there under the exact same conditions that it later decided to stall/difficult restart.
The entire exhaust system is new, less than 5K miles, including the CA compliant catalytic converter. It passed smog with very good values a few months ago.
I am down to the following possibilities, but would very much appreciate any other thoughts:
- could it be the distributor - a bad/loose connection inside? Something that is interrupting the spark? Should I replace the distributor? AFAIK it's the original one, and the engine has 245K miles
- wiring loom - some partially broken wire that under some conditions causes the engine to die? Tough to diagnose since the problem is so intermittent, and only at/slightly above idle
- maybe the capacitor that is attached to the coil?
- possibly it's the ignition switch in the steering column, or the wiring/connector to it?
- bad connection to the fuel pump, at the tank? I can cut out an access panel, am tired of dropping the tank every time I need to replace a hose or e.g. the vent connector I did a few months ago to pass smog. Maybe the fuel pump itself is going bad? It's maybe 5 years old, the previous owner put it in new before he sold the truck to me. But then why is it not happening when driving at speed.
- could it be that both ECUs are bad? But then having the exact same issue, developed at the same time? Seems quite unlikely
I will pull the codes again, retry manipulating that alternator connector; I guess I can try manipulating the big plug that attaches to the ECU in the cabin to see if maybe that replicates the issue. Investigate the ignition switch / wiring in the steering column. This engine runs really well and strong - when it runs which is 90% of the time. I replaced the heads two years ago, replaced the fuel injectors with OEM rebuilts, all vacuum hoses and many other parts. It feels like it is a simple issue, nothing major, just very hard to diagnose.
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