Fuel pressure related to ambient temp?

drwillb · 10-16-2018, 10:42 AM

My fuel pressure is running low and I need to replace components but, as you all know, diagnosing which pump is going bad is not easy without a lower pressure sensor. I have both pumps and the filter/regulator on hand but haven't gotten around to installing any of them. However, I did make an interesting observation over the last couple of weeks.

FP_H seems to be linked to environmental temperature. When the temps were in the low 70s, I was running 7 or 8 for pressure as indicated by JB4 phone app. Lately, 70s temp makes the pressure dip to 6. With temps in the high 60s, pressure ran at 8 or 9, somtimes 10. Temps at low 60s gave pressure of 9 or ten. You can see the trend. Two days ago, I was out before 7am and the temp was in the low 40s. This gave me a pressure of 12-13. Same thing this morning.

These readings weren't just for the first couple of minutes during warmup. The numbers hold for at least 20 minutes and then drop. Again, this is temp related. The colder it is outside, the longer the reading is stable and the less the pressure drop when it occurs.

Kinda makes me think this is low pressure pump related since the fuel temp would be a factor vs. engine block temp that would rise to a predictable and steady temp within a few minutes.

drwillb · 10-22-2018, 07:17 AM

Today's morning temp was 34 degrees. FP_H was a solid 14.

The car ran hard this morning. No hiccups, just smooth power to redline.

I didn't mention this above, but I have a 2012 135, N55, FBO except for DP, and PS1 set to 17psi to 6k rpm.

10-16-2018, 10:42 AM	#1
drwillb BMW Fan 289 Rep 838 Posts Drives: e30 M3, e30 M3, e46 M3 Join Date: Aug 2008 Location: northern NJ iTrader: (4)	Fuel pressure related to ambient temp? My fuel pressure is running low and I need to replace components but, as you all know, diagnosing which pump is going bad is not easy without a lower pressure sensor. I have both pumps and the filter/regulator on hand but haven't gotten around to installing any of them. However, I did make an interesting observation over the last couple of weeks. FP_H seems to be linked to environmental temperature. When the temps were in the low 70s, I was running 7 or 8 for pressure as indicated by JB4 phone app. Lately, 70s temp makes the pressure dip to 6. With temps in the high 60s, pressure ran at 8 or 9, somtimes 10. Temps at low 60s gave pressure of 9 or ten. You can see the trend. Two days ago, I was out before 7am and the temp was in the low 40s. This gave me a pressure of 12-13. Same thing this morning. These readings weren't just for the first couple of minutes during warmup. The numbers hold for at least 20 minutes and then drop. Again, this is temp related. The colder it is outside, the longer the reading is stable and the less the pressure drop when it occurs. Kinda makes me think this is low pressure pump related since the fuel temp would be a factor vs. engine block temp that would rise to a predictable and steady temp within a few minutes. __________________ 2012 135i Mods: air scoops, CP, K&N filter, PS1, ADE FMIC, BMW PE, JB4, 1M front body, full M3 suspension front and rear, M3 brakes front and rear, M3 rear subframe and LSD Owned so far: 88 M3 x 2, 95 325is, 95 M3 x 2, 06 Mini Cooper S, 08 335 xi, 09 Z4 35i, 01 M3, 12 135i Last edited by drwillb; 10-22-2018 at 07:14 AM..
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10-22-2018, 07:17 AM	#2
drwillb BMW Fan 289 Rep 838 Posts Drives: e30 M3, e30 M3, e46 M3 Join Date: Aug 2008 Location: northern NJ iTrader: (4)	Today's morning temp was 34 degrees. FP_H was a solid 14. The car ran hard this morning. No hiccups, just smooth power to redline. I didn't mention this above, but I have a 2012 135, N55, FBO except for DP, and PS1 set to 17psi to 6k rpm. __________________ 2012 135i Mods: air scoops, CP, K&N filter, PS1, ADE FMIC, BMW PE, JB4, 1M front body, full M3 suspension front and rear, M3 brakes front and rear, M3 rear subframe and LSD Owned so far: 88 M3 x 2, 95 325is, 95 M3 x 2, 06 Mini Cooper S, 08 335 xi, 09 Z4 35i, 01 M3, 12 135i
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