Hey guys I just wanted to ask if any of you have had this prob before. I recently changed out the sparkplugs (last sunday). Yesterday i did some logs to make sure everything was running good and i found out my car is running a bit leaner than what it used to. The car is running a BP turbo and was tuned with the original plugs on it so i wanted to add fresh ones(ngk irridium, same heat range). I read that adding cooler ones help with detonation but arent necesary, plus i figured since the car has ran a few months with these no prob, whats the harm. Anyways i did a few pulls at the track and found that it takes longer for afr to fall to 11s and stay there. I checked the tune but the targets are the same as before it seems that for whatever reason the computer isnt giving me the amount of fuel that it needs. Aside from that i got a random cylmisfire code, but no CEL(i check it every now n then). Lastly it did get pretty cold over the last couple of days, and the idle has gotten consistently worse(wont go under 1k eventhough i have it set at 900). Do you guys think i need to adjust the tune? or could this be a mechanical issue?

Any imput would help
thnx

 

could be unburnt fuel, unburnt fuel makes the gauge show leaner because the sensor cant read it. idle could be not enough energy in the spark and might need gapped down some. big thing no one ever does with iridium/plat plugs is check the gap since they think you cant gap them, there can be a pretty big difference in gaps.

 

What boost and what AFR? If it's safe it doesn't matter (11's on pump gas in boost is just fine). Cooler weather is going to provide more mass air.

 

The gaps on the new plugs were around .037-.039 when installed however the plugs according to ngk's website are .044. Could it make that much of a difference? i checked the gap on them with an orrellys coin looking thing. The old plugs were at .044-.046 when i took them out so i figured the difference was because they were worn.

@RCDash im running round 6psi on 91 octane. the weather when i first got it tuned was about 80-90 and afrs would drop to around 11-4 to 11-1 very quickly. Now it has a hard time going under 12 and when it does it ocillates too close to it 11-7 to 11-9. It does drop quickly though but not far enough. Ill post some pics so you can see what im on about.

thnx guys

 

This was around 80-90F weather. as you can see when i step on it the afrs drop quickly and stay there no prob.

Yellow=load
Red/White=bank1/2
green=rpm



This was at around 50-60F and while it does drop quickly it doesn't go low enough.

Ill change the plugs later see if it makes a difference but Im kinda worried its gonna be something else.

 

could be but either way those gaps are pretty big. smaller gaps ensure firing in a rich environment vs bigger gaps(if the ignition system can support it) have a greater chance of igniting the charge due to more area the spark is traveling through.

could also be something going on with long term fuel trim adjusting it leaner.

 

I changed the plugs and it got a little better but not great. Clearing the learned fuel settings would help? assuming the fuel adjust has something to do with it. Idle did get better though

 

I cleared the fuel settings and did a few pulls i got an average 11-7 to 11-8. Could the cold weather cause a lean shift? has anyone else experienced this?

 

The strange part is your load graph isn't even going as high during the leaner areas as it did originally. To me it looks like your not making the same power, e.g. less boost, MAF isn't reading correctly, boost leak, or other mechanical issues. I reaaaally doubt the plugs have anything to do with it. In my experience with Uprev tuned boosted VQ's, colder weather causes higher load and a lower a/f.

 

Its defenetly not a boost leak, if anything boost hits sooner. The car doesnt smoke or sound funny at all. Im starting to think it might be the maf or fuel pump going bad maybe? I did some pulls with some drag radials at the track so there is no slip, and the afrs ocillate at 11-8/9 constantly. I dont have a boost controller.

 

Heres a pic of last nights TNT run. AFR is in the 11s but varely.
I did notice that when i first got this tuned injector duty cycles were at 85% max. Now same gear, same boost, aside from the weather same everything. Duty cyles are at 73-76% max. while load seems to be the same.