Fuel Stutter on GR's

[toomes]

The GR fuel system is know for its limitations at roughly about stage 2. The design now incorporates a balance hose between the feed fuel damper and the FPR (located on the return line). This causes as hesitation at around 2500 RPM when the car starts looking for fuel during spool, some are worse than others. My car in particular was almost unnoticeable until my upgrades to the fuel system began...

1. Fuel Injectors were upgraded to FIC900cc top feed.
2. Fuel Pump was upgraded to a DW65C.

Immediately after scaling the injectors in AccessTuner, the stutter became greatly exaggerated and was tuned around as best as possible, but it was apparent that it would need to be resolved. Long story short, I drove it like this for 3 weeks or so...then Wicked Big Meet happened. We were on the way back and I would see my AFR leaning out like crazy...the AP was telling me that bank 1 (front O2) was adding 25% fuel and then BAM CEL. P0171, Fuel System Too Lean (Bank 1).

Breakdown:

• My original thought, was that I blew out a gasket at the cylinder head.
• What died so fast? MAF? Front O2? Vacuum leak? Definitely not a vacuum leak that I could find, I went through the engine bay with a fine-tooth comb.
• MAF swap - happening today.
• Gasket leaking at passenger side cylinder head? Had it swapped at Kizen for a new one.

At this point I want to blame mechanical, but...the car is fine at 3000RPM steady throttle (5%) or so at cruise. +/- 5%.:roll:

 

[HolyCrapItsFast]

I would think that the current condition would exist from the beginning after the initial tune and not worsen three weeks in.

I would prescribe the usual first and then look at the tune a little more in depth... Things like fuel pressure, Boost leak test, O2 sensor... That sort of thing.

Toomes... do you have a wideband and does it match the AP?

 

[toomes]

I have a wideband that I will probably install this weekend. Upon resetting the ECU, the issue comes back immediately - it is not the tune. It is definitely mechanical or a leak. I swapped MAF sensors at lunch today, no change. On to the O2 sensor.

 

[HolyCrapItsFast]

The reason I ask is because when the o2 sensor is bad it will show on the wideband as an opposite result. Usually in this situation the ecu reads the o2 as lean and adds fuel in response when in actuality it shouldn't. The wide band will go rich. I'm wondering if this is happening.

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[toomes]

Thanks George, I will check it out and report back.

 

[HolyCrapItsFast]

Not in this case I don't believe. 25% trims and lean code three weeks after the fact is not condusive to a tuning issue but a hardware issue IM(Edumacated)O

 

[Vermont]

Not in this case I don't believe. 25% trims and lean code three weeks after the fact is not condusive to a tuning issue but a hardware issue IM(Edumacated)O

George is right, not a tune issue here, but the issue with the GR stumble is most defiantly a tune issue (which is what I think reks and fuji were referring to right?), reason I say tune issue is I had the stumble when stock, went stage 1 and it went away. I didn't get the stumble back until just recently when I did the turbo swap, since I have been lazy and have not finished my tune I know for a fact that my timing is not how it is supposed to be. In conclusion I would have to say it is a timing issue, whether from poor smoothing or from the engine just not liking a certain amount at that rpm and load (maybe asking to much from the engine for the conditions?).

On the other hand this issue sounds kind of like a front O2 sensor issue. If the front O2 is all messed up and reading rich, it will then pull fuel like crazy causing you to go deadly lean. I had the exact opposite of this with my GR after I swapped my up-pipe. There front O2 was reading lean and so the ecu kept on adding more and more fuel until my wide band was pegged at 10.0:1 under CL and idle :shock:. Was so rich it caused rich miss fires and stumbling. I swapped out the front O2 and everything was hunky dory. I would suggest being very very careful when installing the O2 sensor. These suckers are super delicate and even a little bit of PB blaster on them or wrenching too hard will kill them (ask me how I know ). You might want to also check the front O2 wire leading up the passenger side head to the right near the passenger side strut tower. Make sure the wire is connected properly and not split. The best way to remove the O2 sensor is honestly to unplug the wire from up top, feed it all the way down and then pull the whole up-pipe off. Yes I know you can get too it from the fender but honestly When putting in the new sensor you run the risk of damaging it and being right back in the same situation, just $200 poorer.

 

[toomes]

Crazy!! Yeah my stumble was not present prior to the injectors and the fuelpump and then the shit hit the fan, I am just going to buy a new front O2 tomorrow despite everything and try that along with looking for leaks since it will be easy. Thanks guys, I will keep you posted.

 

[HolyCrapItsFast]

Yeah I agree that the stumble is tuning but the fuel trims indicate another problem all together. I think he needs to address that first and then revisit tuning for stumble.

Hey toomsey! if you get the wide band hooked up, even temporarily, all you have to do is verify if the wide band matches the AP. If it does then you don't need a new O2 sensor and I would start looking for leaks. This way you don't have to spend money prematurely on a sensor that may not be bad.

 

[Vermont]

Yeah I agree that the stumble is tuning but the fuel trims indicate another problem all together. I think he needs to address that first and then revisit tuning for stumble.

Hey toomsey! if you get the wide band hooked up, even temporarily, all you have to do is verify if the wide band matches the AP. If it does then you don't need a new O2 sensor and I would start looking for leaks. This way you don't have to spend money prematurely on a sensor that may not be bad.

Agreed!

I honestly don't know of a way to verify that an O2 is bad with out a wide band, and I wouldn't just go and buy one, them suckers are super expensive.

 

[holyscoobysnacks!]

Yep holy! I'm dealing with that on an 04 that don't wanna trim correctly and just dump fuel. It's got all sorts of stupid grounds and god knows how many boost leaks. We're about to tear it apart and rebuild it from the ground up.

Which the Stutter on my 04 got worse since we attempted tuning it Rek

 

[HolyCrapItsFast]

Agreed!

I honestly don't know of a way to verify that an O2 is bad with out a wide band, and I wouldn't just go and buy one, them suckers are super expensive.

I have discovered a way to test it. You have to remove it but it is easy from there. You simply remove the sensor and let it hang. Go turn on the car but don't start it and observe the free air AFR on the accessport or on romraider. It should be full lean. Now get a rag and soak it with brake cleaner and wrap the sensor with the soaked rag. It should go full rich and stay there. If it doesn't or does but then goes lean again, the sensor is bad. :tup:

 

[Vermont]

I have discovered a way to test it. You have to remove it but it is easy from there. You simply remove the sensor and let it hang. Go turn on the car but don't start it and observe the free air AFR on the accessport or on romraider. It should be full lean. Now get a rag and soak it with brake cleaner and wrap the sensor with the soaked rag. It should go full rich and stay there. If it doesn't or does but then goes lean again, the sensor is bad. :tup:

+1 :tup:

That is a very good idea. I had heard about doing that before (probably from you) but had totally forgotten about it.

 

[toomes]

Well, it turns out, the fuel pump was not 100% installed! It's crazy how it took a while for it to rear its head up. The sleeve was not installed onto the feed pipe and it also only had 1 o-ring instead of two. Now that that is taken care of - back to the tuning

 

[HolyCrapItsFast]

Glad it got worked out :tup:

 

[Td_d]

I have discovered a way to test it. You have to remove it but it is easy from there. You simply remove the sensor and let it hang. Go turn on the car but don't start it and observe the free air AFR on the accessport or on romraider. It should be full lean. Now get a rag and soak it with brake cleaner and wrap the sensor with the soaked rag. It should go full rich and stay there. If it doesn't or does but then goes lean again, the sensor is bad. :tup:

Nice one, George - as always, pragmatic!


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[toomes]

I did not install this myself, I have had very little time in my life lately to dedicate to this car with my new position at work and being addicted to Diablo 3 again... LOL!! I had a tech install it from my local tuner, who couldn't believe he forgot it. We were rushing for WBM that day, it was just an oversight. It currently has 2 orings but no sleeve on it because I did not have the stock pump parts with me at the time we diagnosed it. Seems to be doing okay just in that condition. I will probably try to tackle it this weekend if I feel up to it.