Fuel randomly cuts under WOT -- 2nd gear ~4K RPM
09-13-2009 | 06:04 PM
#1
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My 8 looks like a Smurf
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From: Ottawa, ON, Canada
Fuel randomly cuts under WOT -- 2nd gear ~4K RPM
Had an eventful day at autocross today.
My first two runs I ended up spinning out from going too hot into a corner so this may have something to do with it.
From runs 3 to 6, after about 20s of driving, I go down a straight in 2nd under WOT and when it hits about 4K RPM, fuel randomly cuts for 1s, then goes back on, then back off, then back on. I was able to reproduce this pretty consistently and by my 6th run, it did it about a dozen times during the run.
I tried putting TCS on, off and "fully off", no effect. No CEL. Checked the coils and wires, everything seems tight. MAF was clean. Intake was clear.
I had just under half a tank of gas when this happened. After my 6th run, I decide to go top up to see what happens. For my last 2 runs, all is fine. Although I'm not convinced it will stay that way. Wasn't able to reproduce it on the street.
Any thoughts?
My first two runs I ended up spinning out from going too hot into a corner so this may have something to do with it.
From runs 3 to 6, after about 20s of driving, I go down a straight in 2nd under WOT and when it hits about 4K RPM, fuel randomly cuts for 1s, then goes back on, then back off, then back on. I was able to reproduce this pretty consistently and by my 6th run, it did it about a dozen times during the run.
I tried putting TCS on, off and "fully off", no effect. No CEL. Checked the coils and wires, everything seems tight. MAF was clean. Intake was clear.
I had just under half a tank of gas when this happened. After my 6th run, I decide to go top up to see what happens. For my last 2 runs, all is fine. Although I'm not convinced it will stay that way. Wasn't able to reproduce it on the street.
Any thoughts?
09-13-2009 | 06:16 PM
#4
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Joined: Apr 2004
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From: USA
premixing isn't going to clog jack squat unless you're dumping in potting soil along with it.
if you have an accessport, data logging will help a lot. Otherwise we're randomly guessing.
I found with fuel pump issues, it degrades as it overheats, so at the start of your trip it will be OK, and it gets worse as you drive.
The last "fuel pump" issue I had ended up being a poor ground (MazdaManiac accurately diagnosed it). I had my doubts that it was fp related because the situation was not degrading as expected.
if you have an accessport, data logging will help a lot. Otherwise we're randomly guessing.
I found with fuel pump issues, it degrades as it overheats, so at the start of your trip it will be OK, and it gets worse as you drive.
The last "fuel pump" issue I had ended up being a poor ground (MazdaManiac accurately diagnosed it). I had my doubts that it was fp related because the situation was not degrading as expected.
09-14-2009 | 12:53 PM
#8
Thread Starter
My 8 looks like a Smurf
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Joined: Sep 2007
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From: Ottawa, ON, Canada
Some information for everyone else
I'm pretty sure it's fuel starvation.
In my previous RX-8, I used to get this on lapping days with just below an indicated 1/2 tank. In a turn, the car was always fine, but getting back on it after the straight it would get very eratic (switching back and forth between full accel and nothing at all) at full throttle and be ok at about half throttle or less. This would continue for several seconds, basically until the fuel pump was able to fill the fuel line back up. Typical problem with RX-8s.
Another factor is that "indicated" fuel level. RX-8 fuel gauge is also sensitive to G-loading, since the fuel tank is really two tanks connected by a "bridge" over the driveshaft and when the fuel level is not equal in both, the gauge gets confused. You may have had much less than half a tank when you had this issue.
In my previous RX-8, I used to get this on lapping days with just below an indicated 1/2 tank. In a turn, the car was always fine, but getting back on it after the straight it would get very eratic (switching back and forth between full accel and nothing at all) at full throttle and be ok at about half throttle or less. This would continue for several seconds, basically until the fuel pump was able to fill the fuel line back up. Typical problem with RX-8s.
Another factor is that "indicated" fuel level. RX-8 fuel gauge is also sensitive to G-loading, since the fuel tank is really two tanks connected by a "bridge" over the driveshaft and when the fuel level is not equal in both, the gauge gets confused. You may have had much less than half a tank when you had this issue.
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