Rich idle, lean WOT

[JuCo]

Hey All,

99 M3 with Stage 2 Technique Tuning.

I'm looking to solution a problem I've been experiencing with the car. I just haven't taken any time to look into it or research much, the issue: At idle the car runs extremely rich the smell of un-burnt fuel can be smelt quite a bit, however when giving it any bit of gas it goes lean quickly. Would this be caused by a vacuum leak? Bad O2 sensor? Bad MAF?

I'm open to any feedback to get my car back to being enjoyable before I upgrade in the near future.

thanks in advance, Justin

[MikeE36]

Hey All,

99 M3 with Stage 2 Technique Tuning.

I'm looking to solution a problem I've been experiencing with the car. I just haven't taken any time to look into it or research much, the issue: At idle the car runs extremely rich the smell of un-burnt fuel can be smelt quite a bit, however when giving it any bit of gas it goes lean quickly. Would this be caused by a vacuum leak? Bad O2 sensor? Bad MAF?

I'm open to any feedback to get my car back to being enjoyable before I upgrade in the near future.

thanks in advance, Justin

Hey Justin,

Are you running a stock fuel pressure regulator? A boost leak would usually slow Lean at idle and Rich in boost, but you have the opposite. Assuming your fuel pump is OK (which I assume by it being rich at idle and overfueling), I think your pressure just may be too high (bad FPR). Do you have a stock FPR, or aftermarket? Any gauge on it?

Mike

[JuCo]

Hey Mike,

Thanks for the quick reply. I am running the stock FPR. No gauge. It has never been replaced. I was about to add that to a list of possible culprits. If this is indeed the issue what paths for replacement would take? I plan of upgrading my setup in the future and would want something capable of supporting 600whp.

[MikeE36]

Hey Mike,

Thanks for the quick reply. I am running the stock FPR. No gauge. It has never been replaced. I was about to add that to a list of possible culprits. If this is indeed the issue what paths for replacement would take? I plan of upgrading my setup in the future and would want something capable of supporting 600whp.

The stock FPR is capable of supporting 600whp no problem, but with a high volume fuel pump, they tend to "overpressurize" the system at idle due to the factory FPR orifice not being large enough to bypass sufficient fuel and keep pressure in check. This can result in a slightly rich idle, but can be tuned around by your tuner, and usually is. The *ideal* setup is an aftermarket FPR that can keep fuel pressure perfect at idle, even with a large fuel pump like a walbro 400lph. If you are OBD1, it will require you chopping off the end of the fuel rail and welding it shut, then running your return line to the aftermarket FPR, then out to the stock hardline. If you are OBD2, you will be bypassing your stock proportioning valve underneath the driver side frame rail near the fuel filter with the same scenario (but no chopping of fuel rail - return line will go through the aftermarket FPR, then to the return hardline).

Hope that helps!

Mike

[JuCo]

Good to know. I am OBD2. Being that the FPR isn't an expensive fix this seems like it could be replaced, however the upgrade sounds like it would be worth it. Thanks for the details on the setup Mike.


What are the majority of members here making 400-600whp running? Anyone got any photos of their current setup they wouldn't mind sharing? I'm a visual person.

[MikeE36]

Good to know. I am OBD2. Being that the FPR isn't an expensive fix this seems like it could be replaced, however the upgrade sounds like it would be worth it. Thanks for the details on the setup Mike.


What are the majority of members here making 400-600whp running? Anyone got any photos of their current setup they wouldn't mind sharing? I'm a visual person.

Here is the install I did on my dad's 1997 M3/4/6 GT35R car. Previously was a TTS2 setup, and had constant off-idle and stomp AFR problems where it would stumble all over the place. After going to the aeromotive, driveability has never been better. Off idle torque and response is dramatically better.







I don't have any pics of bypassing the stock piece, but I can get some in the AM.

Mike

[chikinhed]

If the vacuum line to the FPR falls off or has a leak you will be rich at idle and lean at WOT.

Sent from my GTX3582R

[Irish M5]

F

[IR M5]

What do your AFRs look like at idle and WOT. You do have a wideband, right?

[JuCo]

What do your AFRs look like at idle and WOT. You do have a wideband, right?

At idle is 10-11 and when gas is applied it goes 15-17.

[Butters Stoch]

Aeromotive #13109

[bimmerbumm193]

I just had the same exact thing happen, super rich at idle which slopes up to 14 at WOT. My tuner told me to look for boost leaks and check the line to the FPR. I had the FPR line going to the small barb on the side of the turkey neck adaptor that snaps into the bottom of the OBD1 manifold. I have been since told that that barb doesnt receive full vac or pressure, although I dont know why, you can blow right through it?? I Teed the FPR line into the bypass valve line but have not yet been able to test the car yet. But I have also heard its not good to Tee these lines together, is this true. If not where do you get the vac sources from, tap more barbs into manifold?

[JuCo]

Here is the install I did on my dad's 1997 M3/4/6 GT35R car. Previously was a TTS2 setup, and had constant off-idle and stomp AFR problems where it would stumble all over the place. After going to the aeromotive, driveability has never been better. Off idle torque and response is dramatically better.







I don't have any pics of bypassing the stock piece, but I can get some in the AM.

Mike

Hey Mike, can you get some pics of by passing the stock unit. Does this throw any cell codes?

[bimmerbumm193]

Has this been resolved? I installed an aeromotive fpr and it still does the same exact thing, rich at idle and slopes up lean at WOT on dyno. I will be starting my own thread. Hope you get yours resolved, keep us posted!

[JuCo]

No not resolved yet, I looked over the car, the lines seemed to be ok. Since you replaced your FPR unit and it didn't resolve the issue I'm a bit worried it might not resolve mine. I'm also on a upgrade path and will most likely replace the walbro unit with the larger 450lph model however I'd like to sort the car out before I make too many changes. I'll let you know as I go along. Do you think you could share some photos either here or in a PM of your FPR setup and how you ran the lines, placed the unit etc..

[BadBoostedBmwM3]

I just had the same exact thing happen, super rich at idle which slopes up to 14 at WOT. My tuner told me to look for boost leaks and check the line to the FPR. I had the FPR line going to the small barb on the side of the turkey neck adaptor that snaps into the bottom of the OBD1 manifold. I have been since told that that barb doesnt receive full vac or pressure, although I dont know why, you can blow right through it?? I Teed the FPR line into the bypass valve line but have not yet been able to test the car yet. But I have also heard its not good to Tee these lines together, is this true. If not where do you get the vac sources from, tap more barbs into manifold?

I don't either, but I originally had my BOV hooked up there. And, it was slow to function or non-existent.

[IR M5]

Did you ever get this sorted out? My TT Stage 2 is running pig rich at idle.

[MisterM52]

was there any fix to this issue? I am having this same problem since a week or so ago after I fixed some vaccume leaks using my smoke machine. And now I get 10 - 11 idle and around 17 - 22 WOT!

Fuel Pressure Regulator?
Fuel Pump?
Injectors?
Spark Plugs?
Coils?
MAF?

[bmw328m52]

I experienced something similar when I had a torn line going from ICV to throttle elbow. Car ran pig rich at idle and when I gave it gas I'd be in the 15-17afrs. Currently car runs great outside of boost but I'm still a little rich at WOT cuz of my fpr. From what I hear, your fuel pressure should be 44psi at idle so I'd put a gauge to the rail.

[Butters Stoch]

I experienced something similar when I had a torn line going from ICV to throttle elbow. Car ran pig rich at idle and when I gave it gas I'd be in the 15-17afrs. Currently car runs great outside of boost but I'm still a little rich at WOT cuz of my fpr. From what I hear, your fuel pressure should be 44psi at idle so I'd put a gauge to the rail.

Torn line from ICV should be lean condition at idle and cruise , then rich in boost.
So, that's interesting.

[bmw328m52]

Torn line from ICV should be lean condition at idle and cruise , then rich in boost.
So, that's interesting.

Never mentioned anything under boost. Only when I got on the gas in cruise it was lean AF. Didn't really change my idle but it fluctuated a Lil more.

[Anandkumar2288]

Hi
I recently started spoting same issue. Checked the vaccum with Torque bluetooth OBD 2 scanner. Vaccum/Boost showing at -29.92 in hg. From start to end its steady at -29.92. Is that bad reading. Pls help if any issue that fig pointing to.

[fmaybach37]

From the grave.. is there any answers to this common problem?