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View Full Version : ECU going into "limp" mode?



vtluu
07-04-2005, 12:18 AM
Good times yesterday and today at Buttonwillow, but as I'd been warned, it was HOT; well into the 100's yesterday and high 90s this afternoon. The new wheels and tires worked very well but I did encounter a problem yesterday afternoon and most of today. I noticed yesterday afternoon after around my 3rd sessions that the the engine seemed to "stumble" while idling every once in a while. Seemed to be gone early this morning, but after my 2nd session I noticed the car felt fairly weak power-wise, and then I noticed that I was only making 10 psi of boost (my boost normally peaks at a bit over 20 psi). After I pulled into the paddock the idle was extremely stumbly, RPM dipping as low as 500 on and off.

Someone suggested it was a boost line problem so I took off the airbox, checked the boost lines (all good), intercooler piping (good as well)... Lacking any other ideas, I disconnected the battery for a while and reset the ECU. I went out for a few laps and sure enough, I was making 20 psi again. Went out on another full session and maybe a lap in, I was riding top of 3rd gear at full boost when I abrubtly felt the ECU kick things back to "weak" mode again. I didn't feel like resetting it again and I figured it would be safer not to, so I ran the rest of the day with a ~200hp Evo :(, still had a good time but really could have used the power pulling into the straights.

Reset the ECU again before driving home and it seems to be boosting and running normally. I'm wondering what happened, was it just the heat and/or might there be something mechanically wrong with my car that caused the ECU to freak out like this? :?

MarkSAE
07-04-2005, 01:10 AM
Hmmm... it sounds like you were detonating enough during your runs to cause the ECU to go into limp mode. This is actually a GOOD thing as your ECU is saving your engine. Did you ever get your ECU retuned since you put an 05 boost line in?

Had you bypassed the stock boost control system with a MBC or EBC, you may have probably damaged your motor.

vtluu
07-04-2005, 07:16 AM
Hmmm... it sounds like you were detonating enough during your runs to cause the ECU to go into limp mode. This is actually a GOOD thing as your ECU is saving your engine. Did you ever get your ECU retuned since you put an 05 boost line in?
I'm still running on the original P1 reflash; I'll probably put the '03 boost line back in for now. I did try to up my octane to 93 by mixing in 100 octane but I don't know how well it mixed, and also I'm told the heat (did I mention it was HOT? 8)) will increase the incidence of knock.

earlyapex
07-04-2005, 10:04 AM
You weren't running 100 octane?

:?

Cheap insurance.

Eclipse
07-04-2005, 10:44 AM
+1

I usually mix 91 & 100 in spring and fall. When it's over 90 then(could be spring and fall as well at BW). I run straight 100.

vtluu
07-04-2005, 11:04 AM
You weren't running 100 octane?
I've never needed to run straight 100 before but I've never run at BW or under such hot conditions either. Guess I'll be running 100 next week at Willow Springs... I'd never call 100-octane "cheap" but it's less expensive than an engine rebuild I'll admit.

earlyapex
07-04-2005, 11:12 AM
I'd never call 100-octane "cheap" but it's less expensive than an engine rebuilt I'll admit.

Which is what I meant by cheap insurance. :D

You going to be doing a write up from buttonwillow?