A little help please p38 running wild

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Mdean22

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Sorry My first post is just about a problem I have. But thanks in advance to anyone who can help.

Firstly I have a 1998 p38 diesel, the car is an auto and has done 180k miles with full service history. Had regular oil changes and been maintained regardless of the cost it's been in the family for over 10 years.

Basically the car will start but revs by itself at full revs. We have had it on a diagnostic machine and no fault codes were found. Its not the turbo as we have since disconnected that and the car does the same thing. I don't let the car run with it screaming because i know it won't be doing it any good. So simply start it until see revs rise and then switch it off.

Hopefully this is a common problem and an easy fix we can't keep throwing money at it and I don't want to scrap it.
 
Hiya mate pop over to the introduce yourself section and say hi there the locals will get bouncy if you ask for help without telling us who you are :)
 
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Mdean22 said:
Sorry My first post is just about a problem I have. But thanks in advance to anyone who can help.

Firstly I have a 1998 p38 diesel, the car is an auto and has done 180k miles with full service history. Had regular oil changes and been maintained regardless of the cost it's been in the family for over 10 years.

Basically the car will start but revs by itself at full revs. We have had it on a diagnostic machine and no fault codes were found. Its not the turbo as we have since disconnected that and the car does the same thing. I don't let the car run with it screaming because i know it won't be doing it any good. So simply start it until see revs rise and then switch it off.

Hopefully this is a common problem and an easy fix we can't keep throwing money at it and I don't want to scrap it.
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First of all what diag did you use on it? If CPS has failed it will run at about 3000 RPM on start up. If the quantity servo feedback circuit has failed you may get high RPM on start up but the ECU should close the stop valve if that happens.
 
Littelwill said:
Ahh didnt read that bit good point..:eek:
Click to expand...

Also if the turbo was causing the high RPM through oil ingestion the engine would not stop when switched off. Well not until the sump was empty or it blew up, which i think would occur considerable quicker than the empty sump would. :D:D
 
Hi thank you for the replys it's been on a snap on solus and a autel maxidas. With no joy, it switches off with no issues and doesn't run away, I've taken the air manifold off and it doesn't look like oil has been getting in. We have fired it up and restricted the air intake to try calm the engine down and play with the throttle but that hasnt made a difference. Could the fuel pump be stuck wide open?
 
Mdean22 said:
Hi thank you for the replys it's been on a snap on solus and a autel maxidas. With no joy, it switches off with no issues and doesn't run away, I've taken the air manifold off and it doesn't look like oil has been getting in. We have fired it up and restricted the air intake to try calm the engine down and play with the throttle but that hasnt made a difference. Could the fuel pump be stuck wide open?
Click to expand...

Yes the fuel quantity servo could have failed or it's return spring snapped. But that should show up on proper diag.
 
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Intercooler has oil in it but most do nothing out of the ordinary. Can you take the lid off the top of the fuel pump to have a look at its workings? I know fuel pumps are a pain and need to be timed up so don't want to mess with it to much
 
Mdean22 said:
Intercooler has oil in it but most do nothing out of the ordinary. Can you take the lid off the top of the fuel pump to have a look at its workings? I know fuel pumps are a pain and need to be timed up so don't want to mess with it to much
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Just the top yes but not the mid section. Take top off, with ignition off small wiper on right should be on it's stop towards engine. Pull relay 12 before switching on. When ignition is turned on it should go to roughly mid point. DO NOT turn the engine over. If it is flopping about the return spring has failed.
 
Why can you take the mid section off? I thought you'd only mess with timing if you took complete pump off?
 
Also what does relay 12 do? Could I open up turn ignition on and blip throttle to see if it's moves fully open?
 
Mdean22 said:
Also what does relay 12 do? Could I open up turn ignition on and blip throttle to see if it's moves fully open?
Click to expand...

Fuel pump relay. Unless you want diesel all over the place when you switch on pull it. Don't know if that would work to be honest you can try it though. My guess is that it will already be fully open. The servo is connected to a sleeve below that slides along the piston. The piston has an hole in it, when the cam moves the piston the hole becomes uncovered and stops delivery of fuel. Obviously the position of the sleeve determines how much fuel is injected so throttling the engine. The ECU sets the position of the servo according to throttle request. A feedback pot tells the ECU that the servo is in the correct position. If feedback fails the ECU shuts the engine down. Feedback fail cannot be your problem or the engine would shut down. So i can only think it is a mechanical fail of the quantity servo only thing that can fail and cause that as far as i am aware is the return spring. You could try some better diag, Nanocom or similar and read the throttle pot output i feel sure the ECU should know if the engine is revving it's balls off and the throttle demand is idle.
 
Mdean22 said:
Why can you take the mid section off? I thought you'd only mess with timing if you took complete pump off?
Click to expand...

It's not timing to alter if you take the mid section off and don't get it back correctly, it's fuel quantity and you have enough problems with that already.
 
Little update, we have swapped the fuel pump with a tested pump and now the car won't start, the i tank pump is pushing fuel through but the new pump is not working. We have cracked the fuel pipes to the injectors and no fuel is coming through at all.
 
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