1.8 VVT - MS3 - intermittent lean
 

NA '92 with 1.8VVT swap, Reverent build MS3, base map with minor adjustments on rolling road, spark map backed off above 6k to keep HP below allowed target. Car is a trackcar running local Youngtimer class.

The car has been run for 18 months without issues. Lately we have seen an increasingly annoying intermittent lean condition. It suddenly goes from like 13 AFR to 18-19 ARF, bogs down and runs like crap. Shutting off and restarting clears the problem for a while, but it comes back and the car is currently unable to race a stint.

As the car is not road legal it has been difficult to catch the problem on a log, but we managed to get a short log today.

Please see attached log from 515 sec's onwards. Tune is attached as well.

Not being a MS wizard, I dont see any obvious coarse for the lean condition. Fuel pressure problem maybe?

Any suggestions and feedback is highly appreciated, thanks

Hans

I see some manifold air temp action in that time frame but nothing that would make it idle from 13 to 18. It doesn't help that you start revving it as the conditions need to be somewhat steady for a useful comparison.

Thanks for the prompt reply Rev.

I noticed that correlation as well and the increase in MAT directly correlates with CLT as well. The intake is placed just in front of the radiator in the "mouth", I believe it's a touch of heat soak we see.

I will consider changing the fuel pump and the fuel filter.