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Pete
Pete, Car Enthusiast
Category: UK Car
Satisfied Customers: 24657
Experience:  Over 17 years experience diagnosing and repairing automobiles.
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Mate, I'm a mechanic also, I have an E28 520i in the

Customer Question

Hi mate, I'm a mechanic also, I have an E28 520i in the workshop at the mo with the m20b20 engine. The car came in with symptoms of a lack of power above 4000rpm. This problem seems to be engine temp related, when its cold ish, it seems to pull fine but the hotter it gets the worse the problem, to the point where if you keep pushing it it will barely rev past 2k under no load. I have checked the cam timing and ignition timing and fixed a number of tiny air leaks which has not surprisingly smoothed the idle. I have had the TPS off and apart to clean which was full of oil. Someone has been at it before because the plastic tabs were damaged. I have set the TPS up so that it clicks the idle switch at the throttle idle position. Still the same problem! !!! Any ideas? Was thinking water temperature sensor could be to blame because if it's telling the ecu the engine is cold when it's hot I guess I will over fuel? Cheers, Tom.
Submitted: 1 year ago.
Category: UK Car
Customer: replied 1 year ago.
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Expert:  Pete replied 1 year ago.

My name is ***** ***** I am a professional here at Just Answer. I noticed that your question was not getting a response and thought I would see if you still need help with this.I apologize for the delay and I hope I can still assist you with this here.

My info is limited on your model here but I see no one else has responded and thought I would see if I can help here.

The engine coolant/water temperature sensor can cause a fault like this here as I have seen before needing replaced.I would start with this and see if this resolves the fault here.If this does not work I would have the exhaust tested to see if there is excessive back pressure from a restricted exhaust component needing replaced to correct this here as this will also cause this like a restricted catalytic converter,resonator or muffler.

If more help is needed, use the reply tab to continue our conversation. If no further assistance is needed, kindly rate my service.You can rate at any time and we can continue to work on your question as this will not close out your question.Thanks Pete.

Customer: replied 1 year ago.
Hi Pete, thanks for your reply, I will take your advise on the water temp sensor, though having driven it more whilst really focusing on the nature of the fault, I'm now not totally convinced that it is water temp related. There are multiple temp senders dotted around the thermostat area and by a process of elimination I have figured out which ones do what. One of them kills the engine if you disconnect it while it's running so I'm guessing thats the one linked to the ecu, though I was quite surprised that a lack of water temp signal would kill engine???? (Wiring loom is a mess and has been messed about with).
I have a throttle postition switch on order because if you hold your foot down foot down flat to try and push through the restriction, it will start to jerk forward as though it wants to break through and it feels electrical. Also I see no black or dark smoke out the back when this is happening which would suggest that it's not over fueling.
With regard to the blocked cats or silencer suggestion, the whole exhaust system looks to be about the only brand new thing on the car so I think that's fairly unlikely, and remember the fault is intermittent and mainly happens when hot. If anything was blocked, it would be consistent I would imagine.
Im thinking this is fuel starvation or possibly a sticky diaphragm for the vacuum advance.
So many potential issues but none of them blindingly obvious. This is a friends car and he is skint, otherwise I would just replace everything step by step but I'd also like to think we can just figure it out!
Thanks for your help Pete.
Expert:  Pete replied 1 year ago.

Your welcome

If the engine wiring is damaged or has been tampered with I would inspect this to see if any faults are found with wiring needing repaired.I have seen engine wiring issues cause this type of fault here in some cases as well.I would probably start with this here myself with checking this wiring.

If more help is needed, use the reply tab to continue our conversation. If no further assistance is needed, kindly rate my service.You can rate at any time and we can continue to work on your question as this will not close out your question.Keep in mind in some cases it can be difficult to fully diagnose or help repair your vehicle without seeing it and I work on delivering the best possible answer from what I see to work with.Thanks Pete.

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