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BMW 3-Series (E90 E92) Forum > E90 / E92 / E93 3-series Powertrain and Drivetrain Discussions > N55 Turbo Engine Tuning and Exhaust Modifications - 335i Tuning > How to know if HPFP, LPFP or injectors are failing?



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      01-21-2022, 12:42 AM   #1
TheGoodTheBadTheUgly
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How to know if HPFP, LPFP or injectors are failing?

As the title says I want to know how I can diagnose or have some clue that could point me towards which component is failing.

I know I have a problem with my fueling systen because whenever I cold start my car it will have some very very long and slow cranking and sometimes it will cause misfires until I clear the codes. The crank length and symptoms seem to be worse on days that are colder. I live in Canada and we are having very cold days so I noticed that the colder it is the worst the symptoms.

The car usually gets to start but it will make weird noises at the begining and will have some bad vibrations until a few seconds after its started.

I usually have some codes for lean gas mixture entering the downpipe and I can usually have other codes linked to the HPFP.

So I logically thought it might be the HPFP, but once the car is started for a few minutes and that I clear the codes, I monitor the rail pressure and its well over 2500 PSI sustained under load which would suggest that it is healthy. Is it possible that the HPFP is failing and has a bad time supplying fuel on startup but then works well and meets the rail pressures it should or is it a problem with the LPFP or injectors?

I am pretty positive I need to get a new HPFP but I am just confused as to how it struggles on startup and then works perfectly fine.
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Last edited by TheGoodTheBadTheUgly; 01-21-2022 at 12:49 AM..
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      01-21-2022, 01:56 PM   #2
njang92
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Log your cold start and watch your fuel pump pressures. Should be able to connect to MHD Adapter in auxiliary mode and start the log then turn your engine on.
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      01-21-2022, 03:49 PM   #3
TheGoodTheBadTheUgly
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Quote:
Originally Posted by njang92 View Post
Log your cold start and watch your fuel pump pressures. Should be able to connect to MHD Adapter in auxiliary mode and start the log then turn your engine on.
Will do thanks.

I'm worried that too long cranks would prevent the oil pump from building enough pressure leading to a seizure problem. Is this possible?
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      03-16-2022, 04:05 AM   #4
Tkenupp
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Quote:
Originally Posted by TheGoodTheBadTheUgly View Post
Will do thanks.

I'm worried that too long cranks would prevent the oil pump from building enough pressure leading to a seizure problem. Is this possible?
Not at all, one recommendation while replacing the oil filter housing gasket is to take off the fuel pump fuse and crank the car before starting it to create oil pressure.
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