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ECU spiking AFR at 2000rpm and up?


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I recently rebuilt my 1983 L28E NA with stock EFI and have just broken it in. At idle, it's fine. At WOT, also fine. But, at low to mid throttle, I'm finding intermittent hesitation between 2000 rpm and 4000 rpm. The hesitation is accompanied by spikes on my AFR gage, apparently going full lean for some reason?

I did an rpm sweep in the garage to track the behavior. Please check out this video:  


At 2000 rpm, it starts acting like there is a rev limiter, but there isn't one. The power seems to be cut in short pulses, which are repeated very consistently, leading me to beleive the ECU is doing this intentionally. The AFR gage shows spikes going full lean, as though the fuel is being cut momentarily and then restored.

Does anyone recognize this?

I'm going to start checking out the TPS, AFM, ECU, O2, and all the associated wiring, but I was hoping maybe someone had seen this before, or had any clues for me?


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Likely the MAF carbon track is worn and making bad intermittent connection where it gets the most use. I couldn't find the zx you-tube for this but the Beemer one is close enough at least to see what's wrong and what's needed to move the arm to an unused portion. Not saying it is this.... just very likely.


The in rushing air pushes past a swinging door on a light spring. The more air the farther the swing. This moves a contact across a carbon trace producing a variable output from the variable resistance. This track can become worn and make poor or intermittent contact. I'm guessing the intermittent contact briefly forces the ECU into a fail safe over rich 'limp home' mode which is safer than extremely lean in this worn area..



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