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Discussion Starter #1
Hi All,
My 2000 p38 dse is starting and running very smoothly at lower revs, but surges at 4000 revs ,losing power then coming back in again when going uphill, showing the engine warning light on the dash, which goes out when the revs drop and the car is running smoothly again. Snap on diagnostics show 2 faults- RPM SENSOR 129, & INJECTION BEGIN CONTROL 144. Has anyone experienced similar, please? I am wondering whether replacing the no 4 injector, with the wire on will cure the problem on its own, or should I also replace the crank position sensor? Any thoughts would be much appreciated!
 

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do you have plenty of power on flat grade and struggle going uphill? Does it like to slowly decrease in speed while going uphill? Any hesitation for the automatic kickdown should you floor it? Especially uphill? Any of those symptoms “could” point towards your throttle position sensor. Even if you do have power uphill it could still be a faulty TPS.. when I had extreme power loss & especially uphill, replacing my TPS solved everything. OEM from dealer. The aftermarket from autozone did NOT work properly for me. Their could definitely be something else going on so don’t quote me.
 

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do you have plenty of power on flat grade and struggle going uphill? Does it like to slowly decrease in speed while going uphill? Any hesitation for the automatic kickdown should you floor it? Especially uphill? Any of those symptoms “could” point towards your throttle position sensor. Even if you do have power uphill it could still be a faulty TPS.. when I had extreme power loss & especially uphill, replacing my TPS solved everything. OEM from dealer. The aftermarket from autozone did NOT work properly for me. Their could definitely be something else going on so don’t quote me.
Also I did NOT have any codes at all for TPS but I promise my TPS was the culprit 110%
 

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Discussion Starter #4
Thanks RoverRain, the symptoms differ from your description; the car idles very smoothly, increasing the revs by depressing the accelerator pedal, even when static, results in the revs " jumping about " from above 3500 to 4500. the rev counter needle surges,and drops, as do the revs.It was possibly misleading of me to talk about going uphill, but that is when the effect is greatest as I depress the accelerator pedal. Steady motoring on the flat, below 40 mph, with only gentle acceleration does not produce the problem. I hope this clarifies the nature of the fault, and thanks again.
 

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I think, but as the flags next to a posters avatars have stopped working so we don't know where someone is any longer, RoverRain is in the US. In which case it won't be relevant as the diesel was never exported to the US so he will be talking about a similar fault on a V8.
 

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Thanks RoverRain, the symptoms differ from your description; the car idles very smoothly, increasing the revs by depressing the accelerator pedal, even when static, results in the revs " jumping about " from above 3500 to 4500. the rev counter needle surges,and drops, as do the revs.It was possibly misleading of me to talk about going uphill, but that is when the effect is greatest as I depress the accelerator pedal. Steady motoring on the flat, below 40 mph, with only gentle acceleration does not produce the problem. I hope this clarifies the nature of the fault, and thanks again.
Ahh i see. I’m not well informed on this topic nor do I have any experience with the diesel model BUT nonetheless in my general opinion it does sound like a communication issue. The fact that going uphill effects anything at all makes me even more inclined regarding component communication. Despite my previous described symptoms my 4.6 p38 always idled flawlessly. If you can’t develop any logical leads I do know the following, idle air control valve, throttle position sensor, crankshaft position sensor, and mass airflow sensor ALL will communicate active info to the computer/becm. A fault anywhere between could trigger communication errors easily effecting pedal response/surging miscalculated revs. Again I’m not saying that’s your problem but IF I was throwing parts at it I’d start their just because it is reasonably possible. Then reset adaptive settings with rovacom. Disconnecting those wires could also make it run funny so just keep the rovacom in mind.
 

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If this engine has a power control valve to reroute air to the combustion chambers for higher rpm power, you may have an issue there. I have frequently seen "sympathetic" codes set by something simple going wrong, and confusing the PCM. Try clearing ALL of the codes, then duplicate the issue setting the codes. Usually the first code set will begin the troubleshooting. Let's start there. Ray
 

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One other thing to check here, depending on mileage, would be the fuel filter, and fuel pressures. Over 4000 rpm requires the fuel pump to provide maximum pressure to the injectors. A failing pump or dirty filters can limit fuel supply. The resulting engine issues can then set unrelated codes due to confusing parameters being noted. Ex. dirty filters or failing pump can set codes for MAF, TPS, rpm, and O2 sensor failures.
 

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It sounds like a discrepancy between the injector timing and the crank sensor timing? Does the injector light flash up on the dash at any point. Normally very briefly.
And issues starting with anything less than a quarter tank of diesel? ;)
 

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Discussion Starter #10
One other thing to check here, depending on mileage, would be the fuel filter, and fuel pressures. Over 4000 rpm requires the fuel pump to provide maximum pressure to the injectors. A failing pump or dirty filters can limit fuel supply. The resulting engine issues can then set unrelated codes due to confusing parameters being noted. Ex. dirty filters or failing pump can set codes for MAF, TPS, rpm, and O2 sensor failures.
I did fit a new fuel filter when the problem first appeared, - no change, however, a couple of days ago I took it on a test drive up and down hills and a long flat section to try to get it hot and see whether there was any improvement, and there was, so I began wondering if dirty fuel was the cause....? I now have a bottle of injector cleaner to put in the tank to see if it improves further, the plan is to repeat the previous route and see whether it gets any better!
 

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Discussion Starter #11
It sounds like a discrepancy between the injector timing and the crank sensor timing? Does the injector light flash up on the dash at any point. Normally very briefly.
And issues starting with anything less than a quarter tank of diesel? ;)
I also think this could be the right direction to follow.. this model is 2000, so it doesn't have an injector light but an engine pictogram, which does light up when it behaves erratically , then goes out when the revs stabilise...?
 

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I also think this could be the right direction to follow.. this model is 2000, so it doesn't have an injector light but an engine pictogram, which does light up when it behaves erratically , then goes out when the revs stabilise...?
There are no issues when there is only a quarter tank of fuel...
 

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Discussion Starter #13
Update, Ran the vehicle along the previous route having put a bottle of injector cleaner in the fuel, gradual improvement, smoothing of the revs around 3750-4000. took it to my local mechanic who put the snap-on fault reader on it, then we got a fault for the MAP sensor, which wouldn't clear. I installed the map sensor from my other P 38, which gave better readings, ran the car, took it back to the mechanic who was then able to clear the fault. Now the only fault code remaining is RPM sensor, which also won't clear. I have ordered a new RPM sensor!
It'a definitely improving gradually all the time when it's being driven, the revs don't jump about so much, even when the engine warning light comes on. Thank you all for your help! I will let you know the results when the new rpm sensor is installed.
 
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