P38A head repair,power loss

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rover75lover

rover75lover

Active Member
Posts
210
Location
newport.wales.uk
1996,p 38 ,auto,diesel 2.5 ,auto.

My p 38 finally boiled once too often and was getting air into the system,getting to "normal" temperature in 5 mins of idling so the head had to come off.
Loads of visible cracks so had it pressure tested and it failed .
Got another head ,had it pressure tested,all good so had the valves and seats done and a very slight skim.
got it all back together and now at least it stays a lot cooler and drives for over 20 minutes before getting to "normal" and it stays there so all good.
Only thing is I've lost all power ,top speed now is just about 55 mph and it seems the throttle works to half way but no more.
took the air filter hose off and its drawing in air ok,so i disconnected the hose at the manifold and had a friend rev it to 3000 rpm but theres no gush,whoomph from the hose. Is the turbo gone?
 
Sounds like turbo is not right, pull of the inlet hose to it and check it spins ok, also check that the waste gate actuator rod is not seized.
 
Is the map sensor 3.2mm hose from the inlet to map sensor by the fuel filter plugged in? Is no4 injector ok?
A boost gauge if only temporarily t-pieced into the map sensor line would show if it's boosting.
Mines a manual flat out 1500rpm nothing then at 2k spikes to 20psi then settles about 16-17.

Get a hand on the hose to the intake and get someone to floor it quick and hard to the floor to about 4K you should feel the hose pressurise
 
thanks for all the replies,i have a few health problems so couldnt do anything last night but will try later to try and sort things out later on,at least now with your help i have a few things to look at.
It just seemed strange for it to happen after id done the head,I was really concerned id got the valve timing incorrect,even after using the bmw camshaft holding tool etc,its funny what worries an old man,lol. I dont think its valve timing though as its start so well,idles great and i know it sounds strange it idles smoothly.
Thinking about it ,it feels as though the throttle doesn't work after half way like it used to. In the old days id have said the throttle was being stopped by the carpet,mat underneath it., I know its fly by wire but it feels like it.
Think your correct though as the turbo doesn't seem to be working as top speed is down,when i boot it theres no push back to the seat bit and she black smokes like never before,so im thinking its getting enough fuel but no where near enough air so to speak. Simple terms i know but thats what it feels like.
Just odd as it happens after the head off and yesterday she flew through her mot especially on the emmisions . Not bad for a 1996 vehicle having no mot faults and NO advisories.
Thanks to all you great folks who are so willing to lend me your experience with p 38's its MUCH appreciated
 
check all turbo hoses to and from the intercooler are connected and havn't blown off also hose from turbo to intercooler.
 
Look inside the hoses have a habit of delaminating inside and blocking up as pressure increases, had it on mine.
 
Ongoing Update,
Wammers was correct the hose wasnt split but blocked solid and I couldnt even blow through it. I replaced it but although better the motor isnt right.
Ive now taken the turbo off and it was seized. Played with it and Ive now manged to get it to spin.
Ill probably find a secondhand replacement for two reasons
The original one is plasterd inside with engine oil so I assume that the turbo seals are leaking.
As its jammed once ,id always be worried it might jam again ,shatter and go through the engine.

I still find it odd though that it jammed,seized after id changed the head etc . Thinking on it though perhaps a hard piece of carbondislodged and jammed it or perhaps a bit of swarf etc might have tried to get through
 
turbo wouldnt spin so got it off
I had another turbo here so swapped it over ,joy of joy,my motor now has its power back.
She idles lovely and pulls like a trooper up to 3200 then it sort of stone walls and i loose power and my revs go down.
Any one have any ideas?
 
rover75lover said:
turbo wouldnt spin so got it off
I had another turbo here so swapped it over ,joy of joy,my motor now has its power back.
She idles lovely and pulls like a trooper up to 3200 then it sort of stone walls and i loose power and my revs go down.
Any one have any ideas?
Click to expand...

Any black smoke anywhere? Is the pipe collapsing?
 
no black smoke ,i havent established if any pipes are collapsing but when stood it will rev to 4200 but gets awful fussy and then starts smoking before cuting down,have to lift my foot off the accelerator then gently put it down to get here to rev back up again
 
just disconnected the small pipe that goes from the inlet manifold to the electrical unit on the filter head. everything is exactly no difference still revs to 4200 standing then stops revving and drops the revs same as with the hose connected
 
rover75lover said:
just disconnected the small pipe that goes from the inlet manifold to the electrical unit on the filter head. everything is exactly no difference still revs to 4200 standing then stops revving and drops the revs same as with the hose connected
Click to expand...

Clean out the MAP sensor, if the pipe was blocked odds on that is also. Contact cleaner and blow out gently with air. May need to repeat several times. Don't poke inside it with anything sharp. If you can't clean it fit a new one. Also check connector under manifold that pressure pipe goes onto is clear. Sounds like MAP sensor is not working. Good diag would find the problem.
 
changed the map sensor for another known good one and no difference ive attatched the nanacom and I get

ecu no faults found

water temp 88.95
air 23
boost 103.46
ambient 103.46
throttle potential o.00
throttle potential volts 0.4

she was idling on the above

on the fuelling it gives
start fuel 32
fuel quantity 63
fuel quantity current 6.25
fuel quantity compared 2650

On one of the revs up when she cut out reving at 4200 and dropped back she started to only fire on some cylinders but came back to normal at idle
 
rover75lover said:
changed the map sensor for another known good one and no difference ive attatched the nanacom and I get

ecu no faults found

water temp 88.95
air 23
boost 103.46
ambient 103.46
throttle potential o.00
throttle potential volts 0.4

she was idling on the above

on the fuelling it gives
start fuel 32
fuel quantity 63
fuel quantity current 6.25
fuel quantity compared 2650

On one of the revs up when she cut out reving at 4200 and dropped back she started to only fire on some cylinders but came back to normal at idle
Click to expand...

Is the boost pressure rising as engine revs are increased and is the lift pump working?
 
Last edited:
wammers said:
It's a diesel. ;)
Click to expand...
I know, I was just thinking that as the revs build and the turbo spools up, the pressure increase could cause more air to escape thus making it super rich? If the head has been off, it could be a gasket on the inlet tract not sealing properly?
 
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