Engine stumble at 2800--3500 RPM

[Freeman2005]

I've been fighting this problem for months. At part throttle accelerating or steady at 3000rpm in 4th gear the engine is stumbling intermittently, especially under load climbing hills. Replaced valve springs last year, new plugs and plug wires. Running EDIS 8 ignition with Explorer coil packs, GT40P heads, Explorer intake. Vacuum leak, TPS, MAF??? Any ideas?

 

[a91what]

Do you have a timestamp in the logs where this is happening?

looking at the MAP signal vs the MAF load I see where the engine is under heavy loads [above 80kpa] and the AFR is targeted in the 15.5 range...

Your AFR map is targeting a very lean value when the engine is under load, this is likely the issue under hard acceleration you want to be near the low 13 or high 12s

 

[Freeman2005]

Thanks for the help--duh, I should have seen that. I revised the AFR table and it's doing much better. I wish I could get a little more MPG out of it, but that may not be possible. The first log is with the problem at 447, 2177, and 2715 times. The second is after adjustments with time stamps at 450 and 1071. Love the looks of your new engine!

 

[a91what]

Thank you! you can likely eek a bit more milage out of it if you lean it out more in the low load areas [you can add more timing to facilitate the leaner burn cycle without fear of damaging anything] but overall I dont think you are going to get much more without changing hard parts