Power drops

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ocm1uk

Member
Posts
26
Location
East Sussex
Okay, so I've discussed this slightly on another thread so thought I should start a relevant one.
My p38 2.5 diesel loses power in the first 10 miles or so after starting from cold. I've replaced the in tank pump, fuel filter and the top bit it screws into. I've also replaced the spill pipes. The problem occurs when cruising along at low speeds, up to about 50, the power just drops off momentarily, sometimes slightly longer. The engine light flashes on intermittently as well. Also when running along at a constant speed when I lift my foot off the throttle the the engine light will flash on and then go off. Any other ideas would be most welcome.
 
Wammers what would it show up as in diag, as I am trying to learn what mine is telling me, mind mine is a rovacom light so different screens.
 
brianp38dse said:
Wammers what would it show up as in diag, as I am trying to learn what mine is telling me, mind mine is a rovacom light so different screens.
Click to expand...

Every time the Mil lamp comes on whilst driving a fault will be logged. Usually if the Mil lamp comes on in overrun or coming out of cruise it is a quantity servo fault, usually feedback pot. As this develops the car will start to stall at lights or when coming to a halt or sometimes with steering input whilst turning or setting off at low speed. It can be held off by raising the idle speed slightly. But will eventually need a refurbed injection pump. But if it is an intermittent number four injector there should be a timing fault logged. The engine will go to limp mode and the Mil will be lit whilst the fault is present.
 
Thanks that's cleared things up a bit, Ive had the light come on when lifting of but the other day it was like someone had cut ignition, dropped it down a couple of gears then eventually came back to life and ran fine, plugged it in cleared faults and will check again to see what comes back.
but looks like pump rebuild time, I have a spare pump but it is unknown I think it might have 130k on it so more than mine.
 
brianp38dse said:
Thanks that's cleared things up a bit, Ive had the light come on when lifting of but the other day it was like someone had cut ignition, dropped it down a couple of gears then eventually came back to life and ran fine, plugged it in cleared faults and will check again to see what comes back.
but looks like pump rebuild time, I have a spare pump but it is unknown I think it might have 130k on it so more than mine.
Click to expand...

When the engine shuts down the fuel quantity servo actually stops it by going to a zero fuel position. The stop solenoid is just a back up to this. If the ECU loses contact with the quantity servo through faulty feedback pots, it does not know the quantity servos position so will drop the stop solenoid and stop the engine. Wipers and pots wear mostly around the idle point as they are constantly moving on the tracks to adjust fuel for various engine loads to maintain idle RPM. When you lift off and the quantity servo goes to idle position, if the wipers lose contact with the pot even momentarily the Mil lamp will flick on. If this has been going on for some time unattended to, eventually in some instances the wipers will lose contact and not remake soon enough and the ECU will drop the stop solenoid and stop the engine. This is the main reason for the shut down whilst driving some experience. There can of course be other reasons but if the Mil has been flashing on liftoff that will be the most likely.
 
Last edited:
Thanks again Wammers that explains it nicely so it looks like full pump rebuild or can you just get that bit done,
sorry to Op for hijacking his thread but hope it helps. with his fault
 
Thanks to all for the input. Mine doesn't shut down completely, it just drops off. It will often happen cruising along where it will drop to idle, then if I lift off completely and then re accelerate it picks up.
 
Just spoke with a guy at pf jones. Apparently there are 4 possibilities of pump for my p38. If I buy a used one from eBay and use it temporarily until I get mine back will that work or will I have BeCM issues?
 
Before you replace injection pump, check shutoff solenoid wire - they just snap giving the same symptoms.
 
Most places do the pumps on an exchange basis and will refund when they get the old one back, you don't really want to be messing about keep swapping pumps as I gather it can be tricky to set up right it's not just unbolt, bolt in job.
 
N2O said:
Before you replace injection pump, check shutoff solenoid wire - they just snap giving the same symptoms.
Click to expand...

I'll look at that tonight.

brianp38dse said:
Most places do the pumps on an exchange basis and will refund when they get the old one back, you don't really want to be messing about keep swapping pumps as I gather it can be tricky to set up right it's not just unbolt, bolt in job.
Click to expand...

I don't want to do it at all
to be honest, trouble is I can't have it off the road to long.
 
ocm1uk said:
Thanks to all for the input. Mine doesn't shut down completely, it just drops off. It will often happen cruising along where it will drop to idle, then if I lift off completely and then re accelerate it picks up.
Click to expand...

If that is the case you need diag on it to check the throttle potentiometer for linearity. That could be losing contact causing your trouble.
 
ocm1uk said:
Just spoke with a guy at pf jones. Apparently there are 4 possibilities of pump for my p38. If I buy a used one from eBay and use it temporarily until I get mine back will that work or will I have BeCM issues?
Click to expand...

Pump not reliant on BECM. No problems there.

You need some timing tools but it is fairly simple. The ally casing is weak as butter though so I wouldn't want to be changing it that often. And it is a bit of hassle having to unbolt all the injector pipes so not quick. Afternoon job.
 
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