Hot weather, severe hesitation/stutter on accel
Thread Starter
Newbie
Joined: Jul 2012
Posts: 8
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From: Illinois
Hot weather, severe hesitation/stutter on accel
I'm having a problem with hesitation/stuttering after the car sits in hot weather. Dealer was unable to fix it, and I've tried a bunch of stuff that didn't help. This forum has been awesome in troubleshooting stuff like this, and I'm hoping I can tap into some of the expertise of the forum members. Any help/suggestions would be greatly appreciated. Here are the details:
THE CAR:
08 Evo X GSR. AMS cold air intake and intercooler, downpipe, hi-flow cat, and catback exhaust. Grimmspeed EBCS. AMS tune (about 5 yrs ago). All else stock. 345 WHP. 72k miles.
THE PROBLEM:
In cool weather, car runs perfect, for at least 30 mins (my commute). After sitting in the sun for a few hours, car has slightly rough idle, but hesitates so badly, I often can barely get it out of the parking lot. Bogs on any attempt at acceleration. I've gotten stuck in intersections several times because of this. After a few minutes, I can usually get it moving by very gently reving up the motor to 3k rpm or so and easing out the clutch. Cannot accelerate at any normal rate. Once at speed (on the highway) it runs ok at constant rpm, but again will not accelerate well. Problem does not go away in the 30 min commute home.
WHAT I'VE DONE TO ADDRESS THE PROBLEM:
Changed fuel pump relay (green to yellow) and MFI relay (to gray). Took it to the dealer, who drained the tank, replaced the fuel, and replaced the fuel pump. No help from any of those changes.
ADDITIONAL NOTES:
* MFA was giving codes before the problem began (in winter). I changed the MFA but still got the 'out of range' code a couple times right afterwards, but it has stopped giving codes after that.
* I generally don't get any codes (nor could the dealer) during or after the hesitation events. I once got a 'multiple cylinder misfire' and once got a 'O2 sensor response time' code, but those have not repeated after clearing and a month of driving.
* On two occasions, filling a quarter-full tank with fresh (cold) gas has significantly reduced the problem. Not sure if that is repeatable though.
* Does not seem to be running especially rich or lean during problem episodes.
* I'm attaching 3 logs of 0-60 acceleration: One from when the car is running normally, and two from when it is not.
Running out of ideas, and would greatly appreciate any ideas people might have.
Thanks in advance!
THE CAR:
08 Evo X GSR. AMS cold air intake and intercooler, downpipe, hi-flow cat, and catback exhaust. Grimmspeed EBCS. AMS tune (about 5 yrs ago). All else stock. 345 WHP. 72k miles.
THE PROBLEM:
In cool weather, car runs perfect, for at least 30 mins (my commute). After sitting in the sun for a few hours, car has slightly rough idle, but hesitates so badly, I often can barely get it out of the parking lot. Bogs on any attempt at acceleration. I've gotten stuck in intersections several times because of this. After a few minutes, I can usually get it moving by very gently reving up the motor to 3k rpm or so and easing out the clutch. Cannot accelerate at any normal rate. Once at speed (on the highway) it runs ok at constant rpm, but again will not accelerate well. Problem does not go away in the 30 min commute home.
WHAT I'VE DONE TO ADDRESS THE PROBLEM:
Changed fuel pump relay (green to yellow) and MFI relay (to gray). Took it to the dealer, who drained the tank, replaced the fuel, and replaced the fuel pump. No help from any of those changes.
ADDITIONAL NOTES:
* MFA was giving codes before the problem began (in winter). I changed the MFA but still got the 'out of range' code a couple times right afterwards, but it has stopped giving codes after that.
* I generally don't get any codes (nor could the dealer) during or after the hesitation events. I once got a 'multiple cylinder misfire' and once got a 'O2 sensor response time' code, but those have not repeated after clearing and a month of driving.
* On two occasions, filling a quarter-full tank with fresh (cold) gas has significantly reduced the problem. Not sure if that is repeatable though.
* Does not seem to be running especially rich or lean during problem episodes.
* I'm attaching 3 logs of 0-60 acceleration: One from when the car is running normally, and two from when it is not.
Running out of ideas, and would greatly appreciate any ideas people might have.
Thanks in advance!
I know our cars can hesitate if they're hot with an open element filter, but thats usually only for a few seconds after starting until the fans kick on. Do your fans work?
From your logs it looks like the only difference is that the air temp is much much hotter in the bogging scenario. You can also try raising your idle RPM a bit (1k?)
From your logs it looks like the only difference is that the air temp is much much hotter in the bogging scenario. You can also try raising your idle RPM a bit (1k?)
Thread Starter
Newbie
Joined: Jul 2012
Posts: 8
Likes: 0
From: Illinois
I appreciate the feedback. Fans seem to work ok.
UPDATE:
Sent my logs by email to AMS, and they diagnosed it as a MAF sensor issue (even though there were no codes). Replaced the sensor, and have been driving 2 days in very hot weather without any hint of a problem.
I'm a huge fan of AMS. They've always been very helpful!
UPDATE:
Sent my logs by email to AMS, and they diagnosed it as a MAF sensor issue (even though there were no codes). Replaced the sensor, and have been driving 2 days in very hot weather without any hint of a problem.
I'm a huge fan of AMS. They've always been very helpful!
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