can anyone give any suggestions of what would cause this?

freshly rebuilt engine. i haven't done a comp test, but i'm sure i've got enough miles on it to do one, i'm just waiting until i have some time off work.

anyway, Jay @ BoostedTuning.com is trying to get my fuel trims set. idle doesn't seem to be much of a problem, but after doing my cruise it will be -5% one time, he'll make a tiny adjustment, then it's 5% the next. it just seems to be changing randomly.

i've done a boost leak test up to 20psi with no issues. i sprayed every vacuum line i could find with carb cleaner with no change. i haven't felt under the IM yet, but i will be doing that tomorrow along with the comp test.

i'm holding 14in of vacuum, which is exactly what i did before the build (mild 264 cam). car drives fine but idles rough at the proper a/f. no hunting idle, it's nice and steady.

plugs were new OEM plugs put in about 10mos ago, but car has been sitting the past 7mos until this build was finished. there is now about 65mi on the fresh build.

pistons are BR drop ins, so i'm told stock C/R.

i checked all manifolds to be sure they are all tight. i did have to extend my primary O2 sensor wires to reach my POS O2 housing. i crimped them instead of soldering and pulled on them to verify none were loose.

BISS is at 0.

i think that covers it. anyone have an idea or dealt with this before?

we've never had a problem setting trims before.

 

Wrong section for it but it can be multiple causes. The O2 sensor itself can be damaged, common with turbo swaps and anytime it comes out of the O2 housing, bad grounds, a batter relocate to the trunk with insufficient grounds, etc. The O2 sensor getting oil or moisture on it at any point while it sat or if the engine had failed.

 

crap. is the wrong section. the screen moves before i click sometimes (slow loading at work).

can someone please move it for me?

since everything was good before and the only thing i changed was extending the o2 sensor, i'm thinking that may be the culprit, though my wideband shows everything is running okay. i'm gonna start by swapping O2 sensors first.

 

Yeah, wrong forum. +/- 5% is perhaps a bit high, but not by alot. Has there been substantial weather changes, or have you been varying the driving conditions (stop'n'go vs cruising)?

 

actually, i found the issue. when i put the engine together, i tossed the plugs in to keep stuff out but never tightened them down beyond hand-tight.

oops.

 

That'll do it lol. Lucky you didn't push one or all of them out and ruin the head..

 

You know it. Good isn't usually my kinda luck. LOL

On the bright side, I have a new O2 sensor and set of plugs. Ha ha.
And spare, used ones just in case.