ktm Posted September 13, 2009 Share Posted September 13, 2009 Last weekend I finalized the installation of my rebuilt motor and fired the car up for the first time. It fired up immediately, even better than when I first bought the engine. The car idled beautifully. After checking timing, leaks, etc., I took the car for a quick little spin around the block to check for road worthiness. The car almost left me stranded at the bottom of the hill 1/2 mile from my house. It was sputtering and jerking badly, the AFR gauge was reading 16 to 18+ AFRs. Any time it was loaded up, even slightly, it would lean out badly and buck like a pissed off bull. Ah, fuel issue. I pull the fuel filter and it was FULL, I mean FULL, of crap. I clean the filter and try again. I pull out of my neighborhood and everything seems fine. I head for the gas station and it starts to do it again. I fill up and try to get home. I have to nurse the clutch, get the car moving while I can and coast until I get home. Ok, fuel issue again. I pull the filter suspecting it fouled up again but it was clean. I am now puzzled. I am suspecting the FPR after idling in the garage when I got home and giving it gas. It would immediately sputter and the FPR would not respond to MAP as I would expect. I head in to eat dinner and glance at my lap top (which, during all these runs, was connected to the car) that had Wolf up and was showing the last state of the car before I powered off. The first thing that catches my eye is that the overrun cut is on. However, check the attached image. It should NOT have been on. I have it setup to activate over 1500 rpms and turn off at 1450 rpms. My rpms as shown in the attachment are 1360. You can see that my AFRs are 21.5 indicative that overrun is engaged. However, my load was only 27%. I tested this theory just now and disabled overrun fuel cut. Sure enough, the car idles beautifully and revs freely. No sputtering what so ever. Any thoughts? 1 Quote Link to comment Share on other sites More sharing options...
TrumpetRhapsody Posted September 14, 2009 Share Posted September 14, 2009 This is Megasquirt knowledge, so take it with a grain of salt I'm pretty sure overrun is only intended to be used above 2500-3000rpm or so, as you're decelerating. Having it set as low as you did would probably cause it to kick in during cruise, likely causing on oscillation condition of kicking on and off, hence the bucking. Try setting it to a higher RPM and see if it still does it. I've disabled overrun completely. I never could get it to transition smoothly in and out, and it just generally made me nervous. Quote Link to comment Share on other sites More sharing options...
ktm Posted September 14, 2009 Author Share Posted September 14, 2009 I hear you and have made the changes already for the reasons you cited, but the fact remains that overrun should not even be on under 1450 rpms. For it to be on is rather strange. Quote Link to comment Share on other sites More sharing options...
TrumpetRhapsody Posted September 14, 2009 Share Posted September 14, 2009 It's possible that either your overrun has a taper to it, or that it's a simple matter of lags. Lags as in the ecu was a little behind in turning it off after reacting to the rpm trigger... either in reality, or just in the logs. I've noticed Megasquirt acting like this on occasion. Maybe a Wolf guy can add more about what goes behind the scenes. Quote Link to comment Share on other sites More sharing options...
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