Motor surges at partial boost
04-10-2003, 08:29 PM
#16
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[QUOTE]Originally posted by Danno:
[QB]I think the most likely culprit is fuel. Put the stock 2.5-bar FPR back in and the problem will go away. You have 9% more fuel with the 3-bar FPR. Combined with the already excessive mid-range fuel-mapping on the APE chips and you're well into the bucking & stumbling range./QUOTE]
Danno, I hadn't thought of the 3-bar FPR. Here's why: the bucking/surging problem only became truly bad after the new fuel injectors were installed on Monday (I replaced the fuel pump recently and installed the 3-bar FPR in February, which didn't seem to affect the motor negatively at all).
So, would new (Bosch, stock) fuel injectors richen the mixture sufficiently to cause the motor to stumble and buck severely at partial boost?
I've also noticed another strange symptom: if I lift off the throttle while building boost over 3500rpm, the entire drivetrain shakes and bucks violently. Off-boost, or at low boost situations, all is well.
Is this a fuel-related problem too? Could this in any way be related to the Reliaboost-1 that I recently installed? (just a WAG).
Sorry to beat this issue to death, guys. Your advice is truly appreciated (meanwhile, the hunt for my stock 2.5 bar FPR is underway).
Thanks
[QB]I think the most likely culprit is fuel. Put the stock 2.5-bar FPR back in and the problem will go away. You have 9% more fuel with the 3-bar FPR. Combined with the already excessive mid-range fuel-mapping on the APE chips and you're well into the bucking & stumbling range./QUOTE]
Danno, I hadn't thought of the 3-bar FPR. Here's why: the bucking/surging problem only became truly bad after the new fuel injectors were installed on Monday (I replaced the fuel pump recently and installed the 3-bar FPR in February, which didn't seem to affect the motor negatively at all).
So, would new (Bosch, stock) fuel injectors richen the mixture sufficiently to cause the motor to stumble and buck severely at partial boost?
I've also noticed another strange symptom: if I lift off the throttle while building boost over 3500rpm, the entire drivetrain shakes and bucks violently. Off-boost, or at low boost situations, all is well.
Is this a fuel-related problem too? Could this in any way be related to the Reliaboost-1 that I recently installed? (just a WAG).
Sorry to beat this issue to death, guys. Your advice is truly appreciated (meanwhile, the hunt for my stock 2.5 bar FPR is underway).
Thanks
04-10-2003, 08:52 PM
#17
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Hmm...
I would expect that new injectors would flow slightly more fuel than old, dirty injectors. So this would imply that Danno and the others are correct because the problem got worse when you installed new injectors, this giving you slightly more fuel.
I could be wrong, of course.
I would expect that new injectors would flow slightly more fuel than old, dirty injectors. So this would imply that Danno and the others are correct because the problem got worse when you installed new injectors, this giving you slightly more fuel.
I could be wrong, of course.
04-23-2003, 02:43 PM
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It's cured. My mechanic adjusted the stock airflow meter and the boost now comes on smoothly, this despite retaining the Bosch 3-bar FPR.
Within the last month, I've had a host of other ills that have been fixed. The car no longer backfires. I no longer choke on gas fumes when the windows are down. My windshield no longer leaks. The car now starts easily and idle is stable at 950 RPM. CO at idle has been reduced to 1.7% (previously between 7 and 8%!)and hydocarbons have gone from 250 at idle to 35 (which I think would get me through emissions in most places, but feel free to correct me if I'm wrong). The gearbox no longer grinds when I shift into second. This of course was only made possible by hemorrhaging significant amounts of cash from my bank account.
After the M030 sways go on early next month, I'll decide what (if any) additional performance mods are necessary. Until then, I plan to enjoy what I've got, since all is well. Even without a MAF or MAP kit, this car is still a kick to drive.
Within the last month, I've had a host of other ills that have been fixed. The car no longer backfires. I no longer choke on gas fumes when the windows are down. My windshield no longer leaks. The car now starts easily and idle is stable at 950 RPM. CO at idle has been reduced to 1.7% (previously between 7 and 8%!)and hydocarbons have gone from 250 at idle to 35 (which I think would get me through emissions in most places, but feel free to correct me if I'm wrong). The gearbox no longer grinds when I shift into second. This of course was only made possible by hemorrhaging significant amounts of cash from my bank account.
After the M030 sways go on early next month, I'll decide what (if any) additional performance mods are necessary. Until then, I plan to enjoy what I've got, since all is well. Even without a MAF or MAP kit, this car is still a kick to drive.
04-24-2003, 03:31 AM
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</font><blockquote><font size="1" face="Verdana,Tahoma,Helvetica">quote:</font><hr /><font size="2" face="Verdana,Tahoma,Helvetica">Originally posted by RJP 951:
<strong>Gatorbait, do you know what adjusting the AFM entailed? Glad you got that solved.
Ron</strong></font><hr /></blockquote><font size="2" face="Verdana,Tahoma,Helvetica">Ron, sorry I don't, but I'll find out and will report back. The shop that I went to for all of my recent work was Broadfoot Racing, an indy Porsche shop in Jax, FL. Here's a link, fyi: <a href="http://broadfoot-racing.com/" target="_blank">http://broadfoot-racing.com/</a>
Albert Broadfoot, the owner, has twenty or so years of P-car experience, the vast majority of it with 924/944/968's. He builds engines and races the cars as well (I believe he builds/sells a 3.0 liter, 500HP motor for our cars). In any event, he seems to know how to get a lot out of the stock 951 airflow meter, which came as a surprise to me based on all that I've read about the barn door's deficiencies.
Hats off to Danno as well, for pointing us in the direction of the TPS switch. Mine was toast and was completely responsible for the backfire problems I suffered until it was replaced.
Andy
<strong>Gatorbait, do you know what adjusting the AFM entailed? Glad you got that solved.
Ron</strong></font><hr /></blockquote><font size="2" face="Verdana,Tahoma,Helvetica">Ron, sorry I don't, but I'll find out and will report back. The shop that I went to for all of my recent work was Broadfoot Racing, an indy Porsche shop in Jax, FL. Here's a link, fyi: <a href="http://broadfoot-racing.com/" target="_blank">http://broadfoot-racing.com/</a>
Albert Broadfoot, the owner, has twenty or so years of P-car experience, the vast majority of it with 924/944/968's. He builds engines and races the cars as well (I believe he builds/sells a 3.0 liter, 500HP motor for our cars). In any event, he seems to know how to get a lot out of the stock 951 airflow meter, which came as a surprise to me based on all that I've read about the barn door's deficiencies.
Hats off to Danno as well, for pointing us in the direction of the TPS switch. Mine was toast and was completely responsible for the backfire problems I suffered until it was replaced.
Andy
