dhirocz

02 z06. 65k, stock fuel pump, new Delco filter, Hot wire kit, H/C/I/E, 42 lb injectors, Bosch 13111 front ‘post cat’ 02’s.

Trying to finish tightening up the tune using HP Tuners. Ive got it driving pretty good, tuned it pretty decent midrange and top end with my AEM wideband, pulled in my 02’s, and have been doing idle and off idle tuning with the NB 02’s to get fuel and VE on point.

It really starting to fight me. I notice after running for about 30 minutes or so the data I’ve gotten on the scanner ALWAYS starts going lean. It will slowly lean out to the point that this manifests itself into degraded engine performance. I’ve seen this with the WB, also with the narrowbands. It’s just a slow, uncommanded leanout, and it’s making it difficult to finish dialing it in. This isn’t a WOT leanout, it happens while cruising and creates a big hole in the middle of my data.

i have to assume this is either a weak pump loosing pressure or high fuel temperature…last night when it did this is was 39 deg. I was under 1/4 tank, to be honest.

The other day I got stuck in holiday traffic on 95 and it heat soaked and started running AWFUL. Uncommanded leanout.

Im going to go back out with a fuel pressure gauge and see if I can replicate this. I can’t see anything with the tune that would cause this, all within the same session.

anybody had any issues with this phenomenon in their car? I do eventually plan on going FI, so I should probably figure this out sooner rather than later.

aaronc7

Maf on the car? If not what sensor for IAT and where is it mounted? Only thing that comes to mind is the IAT heat soaking and indicating higher IAT than actual, resulting in pulling fuel. Good idea to look at fuel pressure too.

Any logs to compare it running well and the 30 minutes later running lean?

dhirocz

IAT is moved into the cold side of the air box and the tune has been changed to 50/50 ECT/IAT bias. It’s not nearly as sensitive to under hood heat as before.

when I get home I’ll post logs. Can’t do it from my phone.

dhirocz

Sorry for the delay, getting ready for christmas. I'm hoping to go out today with a mechanical FP gauge on it and drive it long enough where it starts to lean out and monitor the pressure at that time. My guess is it's dropping fuel pressure slowly as the fuel/pump warms and the PCM doesn't see the change so it's leaning out and the fuel trims are compensating. Again, just a guess until I see whats going on.

I dont see what else it could be but it does make sense. Considering the pump is now running at 14.5 volts because of the hotwire kit, it makes sense.

I do plan on going FI with it sometime next year so this might be a good opportunity to upgrade the pump to at least a Walbro 255. I'm kind of nervous about putting in more pump than I need at the moment, and running the pump too hot; but whatever this thing is. I need to solve it before I strap a supercharger on it.

Tune is still a work in progress. Found out recently that bad injector data was causing a surging issue at idle and throwing my 02's out of whack so I'm in the middle of tightening it up. I was hoping that good injector data and low end tuning of MAF and VE with the NB's combined with double checking my PE and the top end of the VE table with the WB would have cleaned it all up. While it does run better...it's not quite there yet.

aaronc7

I quickly skimmed thru the logs and tune. I really think the IAT bias might be messing with you here. EFILive software states that the equation is Dynamic air temp = IAT + (ECT- IAT)*bias. In other words, if bias = 0, then dynamic IAT = IAT. If bias = 1, dynamic IAT = ECT. In EFI, you can datalog this final/dynamic air temp, don't think you can in HPT to verify this 100%... but either way, if you're running the stock MAF/IAT I can never this change helping you out and probably just make you chase your tail forever.

Could be other things going on too (fuel pressure), but I don't think this change is going to help at all. I have a H/C car and I've never had to mess with this or never had consistency issues with fueling

Did the car already have a tune on it and you're picking up where they left off or did you start the tune from scratch?

dhirocz

Already had a tune. An awful one. Ran super lean at idle, surged, whole nine yards. I don’t think the original builder was much of a tuner to be honest. Vacuum leaks, holes drilled in the TB, etc… I ended up taking it half apart, fixing issues along the way.

It does have the stock MAF, but the IAT is relocated further away with a breakout harness. It was easily reaching 60+ degrees over ambient. Now with it moved it is much less sensitive and closely reflects ambient temp.

it was explained to me that the original setup biased IAT. It has now been set to 50/50 ECT/IAT. It stabilized a lot of the IAT based fueling issues I have here in the south, sitting in traffic, heat soaking. Moving the IAT further away near the filter also seemed to lessen it absorbing under hood heat while stopped to a decent extent. Now it struggles to reach 20 over ambient, sitting for half an hour running. Now the issue seems to only creep up after a certain amount of runtime and not necessarily at idle…and doesn’t go away regardless of IAT temp, but it does go away after it’s had time to cool off.

dhirocz

Found it. Fuel check valve. The sound of gurgling fuel during fuel pump prime led me to it. It always seemed to happen at or below 1/4 tank for some reason. It would start leaking, lowering fuel pressure and causing the engine to go lean. Parts on order.

fatbillybob

good find!