High AFRs at 30lbs on my stage II

GNDriven

Active Member
I am about to start diagnosing a potential problem and would like to see if anyone has seen this before or has some thoughts. I am seeing AFRs in the high 11, low 12 :jawdrop: when I crank the boost up to 30lbs. I have made three passes and the MPH is consistently in the low 150s.
Injectors = 120lb Precision
Fuel System = dual feed, Fuelab high volume pump, Fuelab regulator.
Fuel management = Classic Fast - I have the VE numbers at 140 in the upper boost/rpm part of the map.

I am going to verify the regulator is tracking with the boost, but just wondering if I am out of injector or something. The fuel pump claims it can support 1400hp. Injector/HP calculator says 120lb injector can support 1000hp at 85% duty cycle, so maybe I am close to those limits. Does anyone think so?

Thanks,
 

Mike E

Mr. Badwrench
I assume you have XFI with a 3 bar map. What lower amount of boost do you see correct AFR's at. Meaning: is it 2lbs. that makes the difference or is it 10? What is the target A/F in the top row of the table? When you data log, what duty cycle does it get to? Is it trying to add fuel?
What fuel are you running?
 
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Eticket

Well-Known Member
Yeah.. those VE numbers feel high, but there might be other things in your software/setup affecting it. Of course like Bison said - you could be outta pump or having pump issues.
 

Dusty Bradford

Well-Known Member
Log the fuel pressure.

If your pressure tracks along with boost up to a certain point but then you begin seeing some separation then you are out of pump....which is also my guess.


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GNDriven

Active Member
I am running race gas VP116.
Mike E - good question, I have the classic fast not XFI, I will look at the log and see what boost level it starts to go lean.
I'll look at the logs tonight and provides some answers
 

ttypewhite

Well-Known Member
Your setup is very similar to mine. You are definitely not out of injector. Sounds like the fuel pump is up for the task at hand. Is this a street/strip car? if it is, my recommendation is a Racetronix double pumper. I had a noisey Weldon 2025A pump behind my car and it worked well, but my injector duty cycle was high (98% at 30psi running 154mph). I tore the whole system out of my car and replaced it with the Racetronix double pumper, Racetronix wiring harness and their line kit. I had a chance to run it at the track and data log some runs. My injector duty cycle is at 68% and I have the ability to drive this car anywhere with no fuel controllers or a constant humming noise coming from the back of the car. I too have the Old Classic FAST as well.
 

Mike E

Mr. Badwrench
Something to think about. I have a fuellab pump also and they put a link to this video on yellowbullet a while back. I'm not sure how this would show up in tuning, but if your pump is sucking aerated fuel it would kill actual fuel volume all over and you would probably have high VE numbers to compensate. I put a 1/2" stainless return to the bottom of the cell on mine and it seems to be fine. I'm sure this would be an issue with any pump, not just fuelab.

 

GNDriven

Active Member
So I checked on my fuel return. My fuel cell return port has a diffuser looking cap were the return line goes. It converts the main stream into three streams. The middle stream does have decent velocity coming out but does not look to be penetrating the fuel very deep. It did not appear to be churning the fuel enough to make bubbles or aerate the fuel.
I manually turned up the fuel regulator to from 45psi to 65psi to see what the return fuel looked like entering the fuel cell and I did not observe a difference.

Next I am going to pull the FAST WB sensor and make a test pass using a hand held WB unit to verify the FAST WB is still working properly. It is 10 years old.
 
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turbobitt

Well-Known Member
I manually turned up the fuel regulator to from 45psi to 65psi to see what the return fuel looked like entering the fuel cell and I did not observe a difference.
I would check the flow at 85 psi since your issue is at 30 psi boost. You may be surprised how fast the pump decays. Also, check for pinch points of the fuel line. Chassis flex can do some bad things.
AG
 

Chuck Leeper

Toxic old bastard
Staff member
So I checked on my fuel return. My fuel cell return port has a diffuser looking cap were the return line goes. It converts the main stream into three streams. The middle stream does have decent velocity coming out but does not look to be penetrating the fuel very deep. It did not appear to be churning the fuel enough to make bubbles or aerate the fuel.
I manually turned up the fuel regulator to from 45psi to 65psi to see what the return fuel looked like entering the fuel cell and I did not observe a difference.

Next I am going to pull the FAST WB sensor and make a test pass using a hand held WB unit to verify the FAST WB is still working properly. It is 10 years old.

This: I am running race gas VP116.
And this: It is 10 years old.
 

GNDriven

Active Member
I don't have the correction turned on. I've always been so close and had no need to use the correction factors. Until now.
 

GNDriven

Active Member
Got motivated from a good day of sunshine and had a Buick friend come over to help me step through my high AFR issue. I think he just really wanted to see what a stage II on 30psi feels like lol. Anyway, we made a few test runs and took good notes. The AFRs started going up up sharply at 24 psi. It was pointing to a fueling issue. We did some tests and decided to switch the fuel pump over to its high setting (it has internal speed control). We then made another couple of test runs. This time the AFRs were bottomed out at like 9.1. So I pulled 5 % fuel and retest. The AFRs were holding low around 9.3. I did not get to pull any more fuel out and retest, but now I know it was the pump being ran in the low setting that was not keeping up at the higher boost levels. I did try this already before I posted on here, but I must have pulled the wrong log and convinced myself that I still had high AFRs even with the fuel pump in the high mode. I am glad we stepped back through it and now I know I can get on to putting this thing in the 8s.
 

Mike E

Mr. Badwrench
So how fast had you been with the pump on low speed? Do you know which model you have?

You can use a hobbs switch and a relay to have it automatically switch from low to high. I use my xfi and a relay to switch mine at anything greater than 100kpa and 50%tps.
 

GNDriven

Active Member
I have the 424 1800hp one. I went 9.14 at 152 on the low speed :nailbiting:. AFRs got to like 11.8:eek: Don't tell Chris, he may void my 100k mile warranty! I just put a toggle switch on it last night and so now I can just switch it to low speed when I'm street driving. aWhat lead me to the pump speed, was with the pump running, engine off, I cranked up the fuel pressure on the regulator to see how far it would go. At 65 psi the gauge needle would start bouncing very rapidly. It went up to 80psi, but the needle was crazy. So I then switched the pump to the high setting, and boom the needle on the gauge was rock steady at 80psi. I feel a little stupid but I was just mislead by a marketing guy saying "this pump is so badass that you prob won't ever need to run it in the high speed mode" WRONG.
 
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