surging at part throttle
03-21-2003, 01:21 PM
#1
Three Wheelin'
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Join Date: Jul 2002
Location: Connersville IN
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surging at part throttle
Car surges at part throttle and will sometimes buck. Runs good to certain rpm at times and then it's like it hits a brick wall. Once the boost comes on all is good. idles like it has a big cam in it.when slowing down in gear it will pop alot. any more ideas? 
03-21-2003, 01:42 PM
#2
Do you have an MAF? My car used to surge and buck after I installed my big turbo. I helped ease the problem by twisting my MAF sensor, so that the sensor was on the outside of the bend (higher air velocities). I later fixed the problem altogether by having a custom MAF pipe made up, to move my MAF sensor so that it sits as far away from the turbo inlet as possible, right after the air filter.
Do you have any kind of a/f controller in the car? You may need to hook up a wideband O2 sensor, check those a/f ratios and do some tuning.
Do you have any kind of a/f controller in the car? You may need to hook up a wideband O2 sensor, check those a/f ratios and do some tuning.
03-21-2003, 05:57 PM
#4
Race Director
"Car surges at part throttle and will sometimes buck. Runs good to certain rpm at times and then it's like it hits a brick wall. Once the boost comes on all is good. idles like it has a big cam in it."
You've got too much fuel in the areas where you're experiencing the stumbling. The K27 has more lag than stock and at certain operating zones, it will actually have less flow than stock. Meanwhile your chips are notorious for being too rich in the mid-range, a double whammy! Easy troubleshooting step is to turn down the fuel-pressure, if you have adjustable FPR. Then you would know for sure if you're too rich or too lean when that happens.
Another troubleshooting step is to turn down the boost. Does this still happen? Then install your stock chips and see if the stumbling goes away. Most likely you've got too much fuel in the mid-range.
"What do you mean by twisting afm?"
I remember corresponding with Ian when he was installing his MAF. I'm assuming you have the stock AFM which isn't plagued by the low-flow/idle problems that Ian and big MAF users have. Apparently there's some stalling of the sensor where air-flow isn't sufficient; could be caused by some reversion or interference from the compressor blades. Sporadically, the MAF-sensor would output zero-voltage (no flow) and cause stumbling. By rotating the MAF-sensor itself so the air pick-up tube is on the outside of the curve on the bend around the fender, the velocity is higher and stays within the MAF-sensor's range.
You've got too much fuel in the areas where you're experiencing the stumbling. The K27 has more lag than stock and at certain operating zones, it will actually have less flow than stock. Meanwhile your chips are notorious for being too rich in the mid-range, a double whammy! Easy troubleshooting step is to turn down the fuel-pressure, if you have adjustable FPR. Then you would know for sure if you're too rich or too lean when that happens.
Another troubleshooting step is to turn down the boost. Does this still happen? Then install your stock chips and see if the stumbling goes away. Most likely you've got too much fuel in the mid-range.
"What do you mean by twisting afm?"
I remember corresponding with Ian when he was installing his MAF. I'm assuming you have the stock AFM which isn't plagued by the low-flow/idle problems that Ian and big MAF users have. Apparently there's some stalling of the sensor where air-flow isn't sufficient; could be caused by some reversion or interference from the compressor blades. Sporadically, the MAF-sensor would output zero-voltage (no flow) and cause stumbling. By rotating the MAF-sensor itself so the air pick-up tube is on the outside of the curve on the bend around the fender, the velocity is higher and stays within the MAF-sensor's range.
