I have a 2003 x50 with modifications, and 44k miles. Most of the time I drive the car it's completely fine. Then other times I can be driving around town or on the high way and the car goes into limp mode under normal driving. Dash lights up, etc, and the car essentially turns off. After 24 hours or so not driving the car it is essentially no issues again, but I'm trying to figure out why this can happen or why it does. The modifications are upgraded fueling, turbos, engine internals, and the car was dyno tuned. Any feedback would be appreciated.

 

Does it always take 24 hours for the engine to recover? Or is the engine fine after just a moment or two or until the engine cools down some or does it really take 24 hours to recover?

In this 24 hours do you do anything special, special like connect a battery charger/maintainer?

Impossible to know for sure what's going on absent any active or pending error codes.

One suspect is the alternator. If the alternator stops producing enough electrical power the car will run off battery power but not for long. The engine starts to run rough, a number of error warnings appear, warning lights come on, then the engine dies. I've seen an alternator that does this then "recover" after just turning off the engine for a few minutes. The battery recovers too and in say 10 minutes the engine starts ok and even runs ok for a few minutes until the behavior reappears.

Another explanation is a fuel supply/pressure problem.

IOWs, an intermittently bad fuel pump or a flaky relay could be the culprit. Hard to believe though it would take a full 24 hours for a fuel pump (or fuel pump relay) to recover from whatever ails it.

Does the behavior occur at any particular spot in the road that is say on a particularly rough patch of road/pavement?

I could like -- even more than a fuel pump/fuel pump relay -- a crankshaft position sensor. If this is loose or just intermittently bad... You can I believe check this is secure and even replace it. I don't think the sensor is that expensive and with the engine cold not that hard to get at. The car probably needs to be on a lift though and a wheel might need to be removed to get more room.

I take it the CEL is off and there are no pending error codes?

There is the possible explanation of a bad E-Gas or throttle body.

You can do an E-Gas calibration and afterwards check for any E-Gas/throttle body error codes. Not sure if these would be in the OBD2 error code realm and obtainable by an off the shelf OBD2 code reader or if you would need something like Durametric or a Porsche diagnostic computer to obtain these codes.

 

Well there are many possibilities. I would start by getting the codes read. Then I would contact your tuner.

 

Its not always 24 hours. I just notice after a day or so it doesn't happen. It typically has to sit for some time, because just an hour or so doesn't seem to be enough. The problem persists. Thanks for the insight!

 

no codes

 

I don't know if this is you issue, but....My car had an issue where it would just die when you were driving along. It would splutter, and then cut out.

We traced it to a loose hose on the fuel pump in the tank.
Popped the hose back on, fitted a new hose clip, and all has been fine since.

 

PM sent John

 

Check fuel pressure for sure while it's doing this! Mine went intermittent and would be fine after sitting a bit and acted just like this.

 

Fuel for sure - ECU sensing lean and killing spark. Let us know what u find.

 

Thanks for all the feedback. Looks to be more common than I thought. I'll post when I find out later this week. This is why I love 6SpeedOnline!

 

any modifications done to the fuel pump? i'd probably test the fuel pressure, ones the car dies, tap the fuel pressure tester next to the fuel filter. try to crank it, see where the pressure is.

 

Yes. It has upgraded fueling. Has evoms gt700 fueling.