2006 V6 Random stalling mystery

[Ishkabibble]

I've been having this random stalling issue for about a year now. About once a week, sometimes more, sometimes less, my car will stall out at random times out of the blue. It will be running perfectly fine with zero problems and then it will simply shut off. No sputtering, no coughing, rough idle, knocking - nothing. It just stops and I have to find a safe spot to ditch, or just sit in traffic while the car sorts itself out. This happens at traffic lights or at low speeds 30-40 mph, but never at high freeway speeds. When I try to restart it will crank but not start. There is electric power. I have to wait a minute or two and try again several times before the car will start again, and when it does it runs perfectly fine as if nothing has happened. There are never any codes or faults triggered by this. Gas tank is full, all fluids full, the car is bone stock and well-maintained. No bolt-ons or flash tunes. The only other clue is that the tachometer is acting funny and reading near or below zero when idling normally. Sometimes it reads correctly for a time, then goes wonky again. The gas gauge is a little off, too, with the 50 mile low fuel warning coming at around 1/4 tank instead of 1/8 tank like before. The fuel pump seems to be operating normally. Mileage is about 115k miles of regular driving. I don't race.

I have taken the car to two dealerships and two independent mechanics, and no one was able to find anything wrong. It presents with a serious case of repairman syndrome, where they were never able to replicate the problem even after keeping the car for two weeks each time and driving it every day. I know they drove it because I reset the trip odo and checked the fuel levels. Diagnostic computers never detected any fault codes or stored faults. I replaced the fuel filter and crank sensor. Mechanics cleaned the throttle body thoroughly and all sensors seem to working fine. I have spent periods of time driving like a bat out of hell to see if I could break whatever was failing, but no such luck. Wtf?

Has anyone here experienced this? I hope someone can give me a clue because this has become kinda ridiculous, and I don't want to just start throwing parts at it because that can get expensive real quick. I love my car, but I can't depend on it like I should.

 

[DieHarder]

I've been having this random stalling issue for about a year now. About once a week, sometimes more, sometimes less, my car will stall out at random times out of the blue. It will be running perfectly fine with zero problems and then it will simply shut off. No sputtering, no coughing, rough idle, knocking - nothing. It just stops and I have to find a safe spot to ditch, or just sit in traffic while the car sorts itself out. This happens at traffic lights or at low speeds 30-40 mph, but never at high freeway speeds. When I try to restart it will crank but not start. There is electric power. I have to wait a minute or two and try again several times before the car will start again, and when it does it runs perfectly fine as if nothing has happened. There are never any codes or faults triggered by this. Gas tank is full, all fluids full, the car is bone stock and well-maintained. No bolt-ons or flash tunes. The only other clue is that the tachometer is acting funny and reading near or below zero when idling normally. Sometimes it reads correctly for a time, then goes wonky again. The gas gauge is a little off, too, with the 50 mile low fuel warning coming at around 1/4 tank instead of 1/8 tank like before. The fuel pump seems to be operating normally. Mileage is about 115k miles of regular driving. I don't race.

I have taken the car to two dealerships and two independent mechanics, and no one was able to find anything wrong. It presents with a serious case of repairman syndrome, where they were never able to replicate the problem even after keeping the car for two weeks each time and driving it every day. I know they drove it because I reset the trip odo and checked the fuel levels. Diagnostic computers never detected any fault codes or stored faults. I replaced the fuel filter and crank sensor. Mechanics cleaned the throttle body thoroughly and all sensors seem to working fine. I have spent periods of time driving like a bat out of hell to see if I could break whatever was failing, but no such luck. Wtf?

Has anyone here experienced this? I hope someone can give me a clue because this has become kinda ridiculous, and I don't want to just start throwing parts at it because that can get expensive real quick. I love my car, but I can't depend on it like I should.

You have an intermittent issue. Likely electrical and heat related since it only happens sitting in traffic or at low speeds. Unfortunately, this can be one of the most difficult type of problem to diagnose. Just me thinking out loud the most likely way to repeat symptoms is to have the car idle until it fails while connected to a scan tool or computer that captures various Mode data. I believe several members can recommend scan tools/software they find useful and may help in this situation.

In the meantime here's some troubleshooting recommendations from the manual: https://iihs.net/fsm/?d=8
and Intermittent Diagnostics: https://iihs.net/fsm/?d=8&f=Intermittent Diagnostic Techniques.pdf

Do you have a Volt/Ohm meter? You might want to check running voltage across the battery. Should be 14.5 - 14.7 vdc. If not clean any grounds you can get to in the engine bay and recheck. If still not consider replacing the battery cables.

Since the gas gauge/tact started acting up I'd check/clean electrical connections for the gauges; then check fuel system relays (including the FPDM (fuel pump driver module) in the trunk and grounds for the system. Mine also failed once exhibiting the exact behavior you described (would crank but not start).

After that, you can try disconnecting/cleaning other connections in the engine bay (most likely problem area since it's heat related) and keep a log of which ones you've touched but it's time consuming and more akin to getting lucky vs narrowing down the problem at hand.

 

[86GT351]

You have an intermittent issue. Likely electrical and heat related since it only happens sitting in traffic or at low speeds. Unfortunately, this can be one of the most difficult type of problem to diagnose. Just me thinking out loud the most likely way to repeat symptoms is to have the car idle until it fails while connected to a scan tool or computer that captures various Mode data. I believe several members can recommend scan tools/software they find useful and may help in this situation.

In the meantime here's some troubleshooting recommendations from the manual: https://iihs.net/fsm/?d=8
and Intermittent Diagnostics: https://iihs.net/fsm/?d=8&f=Intermittent Diagnostic Techniques.pdf

Do you have a Volt/Ohm meter? You might want to check running voltage across the battery. Should be 14.5 - 14.7 vdc. If not clean any grounds you can get to in the engine bay and recheck. If still not consider replacing the battery cables.

Since the gas gauge/tact started acting up I'd check/clean electrical connections for the gauges; then check fuel system relays (including the FPDM (fuel pump driver module) in the trunk and grounds for the system. Mine also failed once exhibiting the exact behavior you described (would crank but not start).

After that, you can try disconnecting/cleaning other connections in the engine bay (most likely problem area since it's heat related) and keep a log of which ones you've touched but it's time consuming and more akin to getting lucky vs narrowing down the problem at hand.

Working at a dealer even with some of the best Techs I have ever worked with, intermittent can drive them crazy. Especially on newer modules where there are multiple modules/computers that have to talk to each other for proper operation of the vehicle.

 

[Ishkabibble]

You have an intermittent issue. Likely electrical and heat related since it only happens sitting in traffic or at low speeds. Unfortunately, this can be one of the most difficult type of problem to diagnose. Just me thinking out loud the most likely way to repeat symptoms is to have the car idle until it fails while connected to a scan tool or computer that captures various Mode data. I believe several members can recommend scan tools/software they find useful and may help in this situation.

In the meantime here's some troubleshooting recommendations from the manual: https://iihs.net/fsm/?d=8
and Intermittent Diagnostics: https://iihs.net/fsm/?d=8&f=Intermittent Diagnostic Techniques.pdf

Do you have a Volt/Ohm meter? You might want to check running voltage across the battery. Should be 14.5 - 14.7 vdc. If not clean any grounds you can get to in the engine bay and recheck. If still not consider replacing the battery cables.

Since the gas gauge/tact started acting up I'd check/clean electrical connections for the gauges; then check fuel system relays (including the FPDM (fuel pump driver module) in the trunk and grounds for the system. Mine also failed once exhibiting the exact behavior you described (would crank but not start).

After that, you can try disconnecting/cleaning other connections in the engine bay (most likely problem area since it's heat related) and keep a log of which ones you've touched but it's time consuming and more akin to getting lucky vs narrowing down the problem at hand.

Thanks for taking the time to respond. I have tried driving with a scanner attached to the port, and the car actually stalled twice on two different days. The scanner detected nothing. The battery is strong, and there is no corrosion on the contact points or ground points. I don't have a volt meter, and I wouldn't know what measurements I need to look for. I'm not sure this is heat related issue as I just tried to start it in the garage from cold and it won't. When I put it in the garage yesterday it was running perfectly.

The problem is getting worse. It is stalling more frequently, and in the past few days has acted hinkey on startup a couple of times, where it will start roughly and struggle to come to a smooth idle. Also, it has happened a couple of times that the car will initially run fine, but after a few minutes will struggle to maintain an even idle, alternating between bogging and revving to keep itself going. Ultimately it will stall, and when I try again a few minutes later it runs perfectly. And again, no codes thrown at all.

I am going to take it in soon to a good mechanic, again. My daughter's boyfriend is a journeyman tech at a Benz & BMW shop with a brilliant master mechanic, and the shop next door to them are general mechanics. He was the one who lent me the scanner and also brought the shop's more sophisticated diagnostic computer to my house to check each of the car's systems. All systems read normal. I was hoping to get some possible clues from the community since the car itself is giving no definitive indicators. I guess they are going to have to do some old school troubleshooting.

 

[DieHarder]

Thanks for taking the time to respond. I have tried driving with a scanner attached to the port, and the car actually stalled twice on two different days. The scanner detected nothing. The battery is strong, and there is no corrosion on the contact points or ground points. I don't have a volt meter, and I wouldn't know what measurements I need to look for. I'm not sure this is heat related issue as I just tried to start it in the garage from cold and it won't. When I put it in the garage yesterday it was running perfectly.

The problem is getting worse. It is stalling more frequently, and in the past few days has acted hinkey on startup a couple of times, where it will start roughly and struggle to come to a smooth idle. Also, it has happened a couple of times that the car will initially run fine, but after a few minutes will struggle to maintain an even idle, alternating between bogging and revving to keep itself going. Ultimately it will stall, and when I try again a few minutes later it runs perfectly. And again, no codes thrown at all.

I am going to take it in soon to a good mechanic, again. My daughter's boyfriend is a journeyman tech at a Benz & BMW shop with a brilliant master mechanic, and the shop next door to them are general mechanics. He was the one who lent me the scanner and also brought the shop's more sophisticated diagnostic computer to my house to check each of the car's systems. All systems read normal. I was hoping to get some possible clues from the community since the car itself is giving no definitive indicators. I guess they are going to have to do some old school troubleshooting.

Sounds like you're in good hands. Only other recommendation would be to search online/Utube for areas/issues/symptoms to look into when troubleshooting. Since it's getting worse that may actually be a good thing. Once it fails completely you have a better chance of identifying the culprit/subsystem at fault.