Sorry in advance, this is going to be long...
So the issue is that occasionally my 2003 MCS will act like I have lifted off the gas pedal. It doesn't give any codes, no check engine light. It only lasts for a couple seconds at a time. Then it comes back to normal. It has done this before, I was on a long drive here in south Texas. I replaced my bpv cause I was having issues related to that, and after thinking back on it, this hasn't happened since then. It then started doing it again about a month ago, it got so bad, again while on a long drive, that I had to pull over on the side of the interstate and it would stall out. I was able to limp it to a gas station and topped off the tank and it ran fine. So at that point I was thinking fuel issue. I replaced the fuel pump and fuel filter, runs fine, right up until yesterday. Super hot day compared to the last few days, 103* at the time it happened this time. Driving through town it started doing it again. Now I did notice that when at idle it would start idling rough and the oil pressure light would come on, when I lightly tap the gas pedal it would go out. I checked my oil level when I got home and it is good. I tried to replicate it today, but couldn't get it to do it again. Got to thinking about it and remembered I have been having issues with my A/C dragging down my engine, and with it being so hot yesterday I probably had my A/C on. So I went back out and turned my A/C on and sure enough at idle it was making the oil pressure light come on again. So my question is, what is going on? I am not sure if my A/C was on the other times when it was cutting out or not. Is it something with my A/C? Or is it a fuel issue again? Maybe the sensor in the gas pedal? BPV? I am at a complete loss here, and I have to make this same long drive again twice next week, even if it means dealing with the cutting in and out. Still no codes.
Thanks in advance.
Dustin W.

 

Has nobody come across this issue before?

 

Not with my Mini.

In fact not with any car I can recall. Well, sort of but the problem was a bad VarioCam solenoid/actuator.

What is a "bpv"?

No active codes but are there any pending codes?

I was going to offer the behavior suggested a fuel pump problem but you replaced the fuel pump and the behavior is still present.

If you tell me the behavior only appears if the fuel level gets down below a certain point, but still plenty above a truly low fuel condition, and goes away after you refill the fuel tank I'm thinking there's a problem with the fuel lines in the tank and the fuel pump is having trouble getting enough gasoline to keep the fuel lines to the engine full and under sufficient pressure if the fuel level gets too low.

This can also be due to a fuel pressure regulator that is intermittently failing and allowing fuel pressure to drop.

It might be interesting to monitor short term fuel trims and see what they look like when the symptoms appear. If the trims go big positive percentage that is a sign the engine controller is having to add fuel which suggests a fuel starvation problem.

For the A/C to affect engine speed/behavior is odd. With modern cars the engine controller has a target idle speed and regardless of the reason if the idle speed drops by too much the engine controller will attempt to adapt and bring the idle speed back up to where it should be.

Now it could be the A/C load is too high and the engine controller can't adapt. Does the A/C blow reasonably cold air?

Are you sure the battery and alternator are good? If the alternator can't supply enough power the engine can run crummy. A battery voltage gauge is useful to keep an eye on the voltage. If it drops close to or under 13V that's a sign of an alternator or voltage regulator problem.

(I had a car in which over maybe 20 miles of driving the battery voltage would drop from around 13.5V to 12V. Bad alternator.)

 

 

 

Thanks for the ideas guys. I dont think its the apternator, it is showing around 13.5V while driving, the battery is not even a year old, and none of the lights dim or anything when it happens. As far as scanner goes, i have a bosch obd 1150. It might not be able to go deep i guess, but it diesnt find any codes and says the MIL should be off.

 

Just figured I would update, just drove 360 miles with no issue, I let it go below 1/4 tank to see if that caused any isuesi. But no problems at all.