Misfiring..LPFP?

The_E92_Fan · 11-03-2017, 01:08 PM

Im running stage 1 aggressive MHD on my 2010 335i. Ive noticed misfires lately at high rpm in higher gears. I decided to take a log, which i posted before, but it brings up a question.

At what LPFP psi will the N54 motor start misfiring due to a weak LPFP?

For example, at the top of 2nd, 3rd, and 4th (the only gears i went through during the log) my LPFP was hitting as low as 49 psi. I didn't get misfires during that run, but i have before at the top of any gear. My HPFP stayed at 1800 psi.

arhoads335i · 11-03-2017, 01:50 PM

should be 50+ psi but mine goes lower than that and I don't have misfires so id look elsewhere

CoffeeBean · 11-03-2017, 01:55 PM

LPFP pressure won't cause misfires if the HPFP pressure is still good. Read the codes on MHD, it'll tell you which cylinder(s) are misfiring. Then check the plug(s) and/or change the coil(s). Rule those 2 out first. By the way, if your LPFP is hitting 49 and you don't plan on ever going to upgraded turbos, just replace it with a new OEM pump. Mine was hitting low 40's and now doesn't drop out of the 60s on Stage 2+.

The_E92_Fan · 11-03-2017, 06:21 PM

On the misfires, i was getting them only for a few days. they have since gone away, probably only momentarily. I supposedly have a stage2 fuel it pump (previous owner), but i seriously doubt it based on my log. I will in fact go with upgraded turbos in a few years. My concern is that i don't actually have that stage 2 pump, or that its dying. I want to run the E40 tune soon to hit the 1/4 mile and i don't think my LPFP can handle it. Is there a way to check what pump i have without having to open the gas tank?

CoffeeBean · 11-04-2017, 11:10 AM

There's no way to know without looking at it. It's not hard to pull up the back seat, open the cover and pull it out. (don't try it with a full tank). They make removal tools for the top cover, but I was able to carefully get it loose by using the top (rounded) end of a ratchet extension and tapping the other end with a hammer. Make sure you alternate back and forth on the clips like you would when tightening lug bolts.

11-03-2017, 01:08 PM	#1
The_E92_Fan V8 Bait 207 Rep 769 Posts Drives: your mom Join Date: Jun 2016 Location: your moms house iTrader: (0)	Misfiring..LPFP? Im running stage 1 aggressive MHD on my 2010 335i. Ive noticed misfires lately at high rpm in higher gears. I decided to take a log, which i posted before, but it brings up a question. At what LPFP psi will the N54 motor start misfiring due to a weak LPFP? For example, at the top of 2nd, 3rd, and 4th (the only gears i went through during the log) my LPFP was hitting as low as 49 psi. I didn't get misfires during that run, but i have before at the top of any gear. My HPFP stayed at 1800 psi. __________________ Broke AF
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11-03-2017, 01:50 PM	#2
arhoads335i Captain 180 Rep 772 Posts Drives: 2015 435i grand coupe xdrive Join Date: Jan 2017 Location: Philadelphia, PA iTrader: (3) Garage List 2008 BMW 128I [0.00]	should be 50+ psi but mine goes lower than that and I don't have misfires so id look elsewhere __________________ 2015 435i grand coupe xdrvie (current) 2006 F250 powerstoke CCSB (current) 2014 M235i Black on Red (SOLD) / 08 e90 335i MT Pure Stage 2 High flow (SOLD) 08 128i 6MT (SOLD) / 08 335i 6MT Pure stage 1 (SOLD)
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11-03-2017, 01:55 PM	#3
CoffeeBean Lieutenant 226 Rep 554 Posts Drives: 640i M-Sport GC Join Date: Aug 2012 Location: AL iTrader: (2)	LPFP pressure won't cause misfires if the HPFP pressure is still good. Read the codes on MHD, it'll tell you which cylinder(s) are misfiring. Then check the plug(s) and/or change the coil(s). Rule those 2 out first. By the way, if your LPFP is hitting 49 and you don't plan on ever going to upgraded turbos, just replace it with a new OEM pump. Mine was hitting low 40's and now doesn't drop out of the 60s on Stage 2+.
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11-03-2017, 06:21 PM	#4
The_E92_Fan V8 Bait 207 Rep 769 Posts Drives: your mom Join Date: Jun 2016 Location: your moms house iTrader: (0)	On the misfires, i was getting them only for a few days. they have since gone away, probably only momentarily. I supposedly have a stage2 fuel it pump (previous owner), but i seriously doubt it based on my log. I will in fact go with upgraded turbos in a few years. My concern is that i don't actually have that stage 2 pump, or that its dying. I want to run the E40 tune soon to hit the 1/4 mile and i don't think my LPFP can handle it. Is there a way to check what pump i have without having to open the gas tank? __________________ Broke AF
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11-04-2017, 11:10 AM	#5
CoffeeBean Lieutenant 226 Rep 554 Posts Drives: 640i M-Sport GC Join Date: Aug 2012 Location: AL iTrader: (2)	There's no way to know without looking at it. It's not hard to pull up the back seat, open the cover and pull it out. (don't try it with a full tank). They make removal tools for the top cover, but I was able to carefully get it loose by using the top (rounded) end of a ratchet extension and tapping the other end with a hammer. Make sure you alternate back and forth on the clips like you would when tightening lug bolts.
	Appreciate 0 Quote