O2 sensor problem?

[Jay Lee]

I kind of found some reasons for my part throttle hesitation with my Hondata. I was getting a hesitation between 3000-4000 rpm, just before boost, and I thought it was fueling being a problem. It turns out it was only part of the problem. My idle for some reason is very lean and the ECU would register 0% long term fuel trim after an hour commute in mixed traffic, but according to the datalog, it began a slow ramping up of the long term fuel trim driving the last couple of miles to work off the freeway, stop lights galore. It finally leveled off at +20%!!!. Then looking at the low speed ignition table, I noticed the hesitation would occur when the trace was going through a rat's nest of curves in the region of 750 mBar absolute. Also, the injector coefficient was wrong at 0.454 for 240cc to 440cc swaps, and when I reset it to 0.545, the idle stabilized at around 14.2-15.0 a/f, vs the estimated (narrow band) 15.5-16.9. The hesitation was greatly reduced at these settings.

[B18C]

but I've been using the same tune for over a year now and I've only started having the problem lately.

[Jay Lee]

I can't say definitively but I think most fuel pump problems are either when they are completely shot or when the cannot keep up with the power demands. I've never heard of one where it causes idle problems because they either pump or they don't. How about the fuel pressure regulator? Incorrect fuel pressure from a defective regulator could cause some of the problems you described. Can you datalog when it's running badly? It would help in diagnosing the problem and in helping to show whether it's ignition or fuel related.

[B18C]

I datalogged it. I don't have anywhere to post it though. If you give me your e-mail I can give it to you that way.

Thanks

[Jay Lee]

Send it to me at [email protected]. Also, if you remember when in the timeline the problem was occurring, it would help so I won't have to view the entire log.

[Jay Lee]

I didn't get to look at it yet -- my grandmother's funeral was last weekend... I'll look at it tonight...

[Jay Lee]

I noticed the variations in the graphs after 2 min of driving as you mentioned (about the 4:30 mark) but I'm more concerned about the O2A Long Term behavior. That's the point at which the O2A Long Term begins to ramp up. It's showing over +15% at the end of the graph, which means you're running quite lean overall. I can't say what would be causing the lean running if it was fine for over a year but the lean running does seem to be contributing to the hesitation problem. You might want to check out the electrical connections throughout the car, especially the oxygen sensor connections in the harness.

[B18C]

This is embarassing but I found the problem. 2 of the injector clips were slightly loose. I just fully seated them again and everything is good again.

Thanks for all your help.