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Discussion Starter · #1 ·
My 2001 m3 has a misfire with no codes thrown, I notice increased fuel consumption and a rough start-up idle at times. I am original owner, the car has 200K plus on odometer, no intake leaks (confirmed with smoke test), throttle bodies cleaned as well as the idle control valve, vanos done, recent new plugs, fuel filter, fuel pump and air filter. Car has original MAF and pre/post O2 sensors (I plan to change pre O2 sensors soon).

In looking at the fuel trims I see negative trim values as follows LTB1 -5.4 and LTB2 - 3.9 on average which improve ny a few points with car at WOT and hot, but do not get to zero.

I tested the fuel pressure today and found some results that I am trying to understand as follows.

With fuel pressure gauge hooked up, turn key and get an initial pressure reading of 73 psi which is just within spec. but then in 5 seconds drops down to 62psi (with multiple runs to confirm).

Start car and the PSI jumps back up to 70 PSI then oscillates back and forth from 73-68 PSI with engine surging in attempt to find stable idle.

In about 10 seconds the engine idle starts to run smooth and the pressure stays at 62psi engine running (not in spec).

Shut car down and the pressure goes down to 58 psi immediately.

Over the next 30 minutes the pressure drops down to zero - will not hold pressure.

Hoping for some help in confirming that these symptoms indicate a failed fuel pressure regulator and that it also is likely the cause of the misfire and perhaps the negative trims.

Any words are greatly appreciated.
 

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In looking at the fuel trims I see negative trim values as follows LTB1 -5.4 and LTB2 - 3.9 on average
Need to see the total fuel trim = short + long. LTFT alone doesn't mean much in this case.
Start car and the PSI jumps back up to 70 PSI then oscillates back and forth from 73-68 PSI with engine surging in attempt to find stable idle.
the fuel pressure should bot oscillating like this. OEM pump or aftermarket?
Shut car down and the pressure goes down to 58 psi immediately.
Over the next 30 minutes the pressure drops down to zero - will not hold pressure.
I don't care much if the pressure leaking after engine turned off. Why care?
 

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My 2001 m3 has a misfire with no codes thrown, I notice increased fuel consumption and a rough start-up idle at times. I am original owner, the car has 200K plus on odometer, no intake leaks (confirmed with smoke test), throttle bodies cleaned as well as the idle control valve, vanos done, recent new plugs, fuel filter, fuel pump and air filter. Car has original MAF and pre/post O2 sensors (I plan to change pre O2 sensors soon).

In looking at the fuel trims I see negative trim values as follows LTB1 -5.4 and LTB2 - 3.9 on average which improve ny a few points with car at WOT and hot, but do not get to zero.

I tested the fuel pressure today and found some results that I am trying to understand as follows.

With fuel pressure gauge hooked up, turn key and get an initial pressure reading of 73 psi which is just within spec. but then in 5 seconds drops down to 62psi (with multiple runs to confirm).

Start car and the PSI jumps back up to 70 PSI then oscillates back and forth from 73-68 PSI with engine surging in attempt to find stable idle.

In about 10 seconds the engine idle starts to run smooth and the pressure stays at 62psi engine running (not in spec).

Shut car down and the pressure goes down to 58 psi immediately.

Over the next 30 minutes the pressure drops down to zero - will not hold pressure.

Hoping for some help in confirming that these symptoms indicate a failed fuel pressure regulator and that it also is likely the cause of the misfire and perhaps the negative trims.

Any words are greatly appreciated.
When was last time the fuel filter and regulator was changed?
 

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Discussion Starter · #4 ·
Thank you for the replies,
Need to see the total fuel trim = short + long. LTFT alone doesn't mean much in this case.
I will post up first thing in the morning OBDfusion logs for cold start idle, straight highway run and warm idle.
the fuel pressure should bot oscillating like this. OEM pump or aftermarket?
The fuel pump replaced 1.5 years ago was OEM. I am unsure why the pressure goes to the correct 73 PSI pressure initially and then drops in 5 seconds prior to starting and also of the oscillation when searching for stable idle?
I don't care much if the pressure leaking after engine turned off. Why care?
I was under the impression that the pressure was to hold after the car was shut off?
When was last time the fuel filter and regulator was changed?
The fuel filter and air filter were replaced within 6 months as PM. The fuel regulator valve has never been changed.
 

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Discussion Starter · #5 ·
Trim values have gotten better strangely over the last 2 days, I still feel a misfire and my Foxwell 510 tells me the misfire moves around to different cylinders.

I did run Liquid moly injector cleaner last tank of gas.

The gas for this test was straight 93, not sure if that helped the trims improve as I was seeing -6 for a few days prior to testing fuel pressure. Files attached as follows:

So grateful for any diagnostic interpretation info.

Cold Start Idle
Warm HWY Cruise
Warm Idle
Warm Post HWY Diagnostic Report
 

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Thank you for the replies,

I will post up first thing in the morning OBDfusion logs for cold start idle, straight highway run and warm idle.

The fuel pump replaced 1.5 years ago was OEM. I am unsure why the pressure goes to the correct 73 PSI pressure initially and then drops in 5 seconds prior to starting and also of the oscillation when searching for stable idle?


I was under the impression that the pressure was to hold after the car was shut off?


The fuel filter and air filter were replaced within 6 months as PM. The fuel regulator valve has never been changed.
Years ago I had a MIL light traced to a bad fuel pressure regulator..it’s part of the fuel filter assembly on my 03M3 vert. It’s rather large compared to old-school fuel filters, not to mention the sintered-bronze metal plug inserts you used to see on Rochester quadrajet carbs. Those went away with in-line filters and larger fuel filters and independent-of-fuelpump pressure regulators.
one other problem could be the vacuum line from the fuel pressure regulator to the engine. These cars are like 20 years old and rubber/plastic doesn’t like age or ozone or UV.
 

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Discussion Starter · #7 ·
Years ago I had a MIL light traced to a bad fuel pressure regulator..it’s part of the fuel filter assembly on my 03M3 vert. It’s rather large compared to old-school fuel filters, not to mention the sintered-bronze metal plug inserts you used to see on Rochester quadrajet carbs. Those went away with in-line filters and larger fuel filters and independent-of-fuelpump pressure regulators.
one other problem could be the vacuum line from the fuel pressure regulator to the engine. These cars are like 20 years old and rubber/plastic doesn’t like age or ozone or UV.
Thank you for the reply, I am going to have another look and will change out the inexpensive vacuum line as pm. I am considering purchasing a pressure regulator but hoping for some feedback on the data in my last post prior to ordering a new regulator which is still low cost at ~$55.
 

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Thank you for the reply, I am going to have another look and will change out the inexpensive vacuum line as pm. I am considering purchasing a pressure regulator but hoping for some feedback on the data in my last post prior to ordering a new regulator which is still low cost at ~$55.
Yes, I was somewhat chagrined to pay over $80 I think for the fuel filter regulator assembly from the BMW dealer a few years ago ( too lazy to pull the 2” thick paper file and thumb through it!) but I will say it was trivial if tedious to change it out under the car. Only thing I really did was to clamp both fuel lines or plug them on either end of the assembly to minimize fuel spill. In my case the replacement was pm after a fuel pump replacement but I haven’t had any fuel oroblems since.
 
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