Running Lean, Especially at Cruising Speed

[tec_41]

I've run into an issue after my rebuild here...Current setup:

Eagle Rods
8.8:1 JE Pistons
Crower Stage 2 NA Cams, springs, and ti retainers
UDP
New everything else

The issue I'm having is that the car runs lean under normal cruising speeds (2000-3500rpm). My LC-1 Reads 15-18afr while cruising, and is a little rich usually at idle, maybe 13-14. I'm still putting on some break in miles, but it also seems lean under WOT, maybe around 13...but that's not for sure yet.

I've got an Aeromotive 13109 FPR paired with a Vortech 12:1 FMU. I did a boost leak test and found a small leak in the FMU and fixed it. Everything else holds about 15psi just fine, my current wastegate spring is 7psi.

I had a set of 250cc Accel fuel injectors lying around and tossed those in there. They didn't make much of a difference with the AFR, maybe made the idle a little richer.

I read on here that if you're using an AFPR with an FMU you should disconnect the vacuum line to the AFPR, so my Aeromotive is set at about 50psi base fuel pressure with vacuum line going to it.

I'm running out of ideas, I'm going to check the CEL codes now, there should be quite a few with no cat, EGR, and whatever else. If you guys have any ideas for what I could try though I'd appreciate it!

EDIT:
The only CEL I currently have is 32, for the EGR. The battery has just recently been reconnected, though.

 

[technodsm]

Yes you should set up your base fuel pressire at idle with the vacuum line removed and the line plugged to eliminate the vacuum leal caused by disconnection of the vacuum line.
My opinion is 250cc injectors sound a bit small for your set up.

 

[tec_41]

Yes you should set up your base fuel pressire at idle with the vacuum line removed and the line plugged to eliminate the vacuum leal caused by disconnection of the vacuum line.
My opinion is 250cc injectors sound a bit small for your set up.

Thanks for the confirmation. 250cc is small, yes, but I have to retain the stock ECU for now. But if anything I thought I'd run pig rich with bigger injectors and the stock ECU

I'm going to recalibrate my LC-1, I figured it'd be a good idea to do that after a rebuild.


Update:
Okay, I've calibrated the LC-1 and no change. However, it will frequently flash to full lean then blink as if it were warming up. The only way to correct this is to shut off the car for a few seconds and restart. This just happened twice on my little 15 minute test drive.

I've also messed with the fuel pressure. No matter what it seems to run the same. I tried all the way from 40-70psi with no different results.

 

[VelocitàPaola]

Maybe there's an issue with the LC-1's wiring. I'd check where it's grounded first, then where it's powered. Make sure nothing is loose or frayed.

 

[tec_41]

I'll go over the LC-1 Wiring tomorrow. It looks okay after a quick visual inspection, and it shares a ground with all of my other gauges which are working well.

Should I maybe be looking at something else? Like map sensor, or IAT, or what have you? I switched back to stock injectors today, pretty much runs exactly the same. Anything above 2k rpm in any gear and it gets lean, 17-18afr.

I've messed with the fuel pressure as much as I can. I even went all the way up to 90psi just to see what would happen, but results were the same. I also popped off one of the intercooler pipes and drove up the road with no turbo, no change.

This issue is similar to what caused my engine to melt a piston initially. It had a nasty lean spike at WOT before the rebuild, but I don't remember it being this lean while cruising.

 

[Slo2gen]

Are you using an FCD or ML? As far as injectors go I would go with some 270's. They are big enough to make a difference but will still allow the stock ecu to control them. Maybe also check your IAT and CLT sensors to make sure they are within spec.

 

[tec_41]

I have the 95 fuel system, so there is no ML or FCD.

I can do a search, but do any of you guys know what voltage I should get from the IAT/CLT sensors?

Thanks for the help so far! I'll keep troubleshooting until it snows

 

[VelocitàPaola]

No voltage, just resistance... They should be around 2k ohms to 10k ohms at room temperature.

 

[Slo2gen]

You can go bigger to an extent, IIRC 270 is about the max a stock ecu will run. As far as your 14/15:1 while cruising, thats actually about where it should be. Your lean spike when going WOT could be a number of things. Do you have a fuel pressure gauge, what happens to it when you stomp on the gas? Have you disabled the factory fpr?

 

[T is for TURBO]

Exaust leak? My wideband shoed lean when I had a leak at the down pipe flange pre wideband. It wasn't a big leak, just a slightly misaligned gasket. But it was enough show 18:1 (AEM max).

 

[tec_41]

Exaust leak? My wideband shoed lean when I had a leak at the down pipe flange pre wideband. It wasn't a big leak, just a slightly misaligned gasket. But it was enough show 18:1 (AEM max).

Hmmm I do have a small exhaust leak at the turbo flange...one of the bolts stripped (its on my to do list). Guess ill make that a priority!

Is it possible the leak could be causing the o2 sensor to read incorrectly, thus causing the Ecu to tell the car to run lean?

 

[T is for TURBO]

Yes. An exhaust leak isn't so much exhaust leaking out, but rather fresh air being leaked in. When the exhaust flows past a leak, it creates a vacuum, sucking air in. More air in the exhaust flow, the leaner the a/f will be. This is, of course, only if the leak is upstream of the wideband senor, which in your case, it is.

 

[tec_41]

Coolbeans. I'll probably fix the stripped bolt and slather some exhaust sealant on there until I can find a better DP.

 

[T is for TURBO]

Hmmm I do have a small exhaust leak at the turbo flange...one of the bolts stripped (its on my to do list). Guess ill make that a priority!

Is it possible the leak could be causing the o2 sensor to read incorrectly, thus causing the Ecu to tell the car to run lean?

I may have mislead you here. I reread what you wrote. Do you still have a narrow band o2? Also, if you do, where is it in the exhuast stream? Sorry, I'm not familar with N/A or N/A with turbo setups. I'd imagine that if the narrow band sees a lean condition, it would add more fuel causeing rich at idle. But I'm nt sure as I'm not knowledgeable with your platform.

But is won't hurt to fix that leak. That would be my first step regardless of what car it was on. If the Wideband goes back to stoich, I would say your problem is solved...

How are you determining that it is lean? Are you strictly going off of what the wideband says? Or are you also checking plugs?


-Shawn

 

[VelocitàPaola]

Is it possible the leak could be causing the o2 sensor to read incorrectly, thus causing the Ecu to tell the car to run lean?

Like T is for TURBO said, an exhaust leak is more likely to make the car run a little rich; that's true for all cars -- 4G63 or 420A. Your wideband is probably reading really lean, even though the AFR is closer to stoich.