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  • Diagnosis Help :P0171 & P0174 (Rough Idle & Loss of Power then Car Died)

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Repair Questions and Answers.

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 #396005  by ANDREWT360
Hey Folks,

Hoping you can all guide me in the right direction. 300M 2004 with 240K KM on it, timing belt changed at recommended interval (160K), fuel pump recently changed at ~200/220K and confirmed working(i hear it priming on start).

I was driving when i suddenly felt a rough idle and loss of power, was able to get it pulled over. Let the vehicle rest for 15 minutes, when I tried to start again it would not start.

Originally I thought it could be the ignition coils but heres why I'm leaning towards a fuel delivery issue. I have in the past say 1-2 years ago on infrequent occasions (say 1-2/yr) experienced struggling start issues, this was remedied by priming to fuel pump via key turns multiple times, after which vehicle would start and everything would work fine (after a few revs). Pretty sure that means leaky injector.

With that being said, I am now presented with this problem where the vehicle will not start. Although when I use the above tactic and prime the fuel system I can achieve start which then results in a very rough idle and shortly after dies.

This must be a dead fuel injector, do you agree? If so, how can I go about diagnosing which one it is?

Is there other things I should consider as the fault?

Appreciate your responses soon as I am hoping to get this fixed by the end of the weekend (fingers crossed).

Thank you all as always!

User avatar
 #396006  by FIREM
:usflag Confirm fuel pressure at fitting on fuel rail. Just because you hear the pump there is a remote chance there is no flow or pressure.
Check for spark, pull a coil, connect an old plug or a screwdriver and crank checking for good spark.
Chances of all 6 injectors failing at once slim to none unless there is no fuel or severely contaminated fuel.
Check all fuses and the ASD Relay also.
Link to more information: viewtopic.php?t=37718
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 #396007  by LUNAT1C
One or two faulty injectors won't cause a no-start. They can be checked using a multimeter to confirm continuity. When I had a failed injector on my Jeep, it only caused a misfire, which then resulted in a similar rough idle and loss of power. But, it started every time with no struggle.

Like Bob said, check for fuel pressure at the fuel rail. I would suspect there is low pressure if you need to cycle the key few times to build pressure, and then it dies once that built up pressure is consumed. Sounds to me like a weak fuel pump, even though that is rare. Do all of the checks Bob noted before getting too deep into it.
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 #396011  by hrmwrm
check for fuel pressure.
check for power to injectors and coils.
check for any codes stored.
don't think it would even stumble with a bad crank sensor.
probably a fuel or even a map problem, not delivering fuel.
i would think it might even be pump gone bad.
regulator is built into the pump as ours is a 1 line system so could even be it.
did they replace the pump or the whole module?
filter is built into the module, which if plugged would shorten the life of a new pump.
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 #396063  by MoPar~Guy
A year ago during early spring my '04 M stalled in traffic. It had been raining and generaly very damp/wet at that time.

I knew that my gas filler pipe was rusted because every time I put gas in, the car would stink of gas for a while. I would get home and use a hose and just point it up under the rear fender and shoot away for a minute.

When the car stalled I managed to get it started again and I parked it for an hour, let it cool down and let traffic get light before I continued home. During the next few days there were sporadic episodes of the car not starting. Some thought it was the camshaft position sensor - I swapped that from another M and did still experience one or 2 episodes so it likely wasn't that.

I then theorized that I had water in the gas tank because of the leaky / rusty filler neck. I took the pipe out, it was generally very rusty, I cut the last foot or two of the pipe off and I bought RADIATOR HOSE to go from the tank to the pipe. I could not find any local source of gasoline-compatible fuel line that was 1.25 inch diameter that wasn't krazy expensive for 2 or 3 feet of length, so I went with this really durable/high-pressure radiator hose and ever since then I've had no gas smell after putting gas in the tank, and the car has never stalled since then.

BTW, this car also must have a problem with the drain-back valve in the fuel pump, because when I start the engine I have to keep the key in the ignition position for a few seconds before I turn to the start position to turn the engine over. The few seconds allows the pump to come on and pressurize the line. If I don't do that then the engine will just turn over but won't start.

(note that the car never put out any codes or CEL when these issues happened)