Dave 90TT

iTrader: (4)

Ok, suddenly, my G35 with JWT TT kit is running lean. What would cause this? (lean condition is only below 3k rpms; in boost it is just fine and has not changed)

more information:

Tuning is done by Haltech above 3k rpm and in boost, via a MAP (manifold air pressure)

below 3k rpm, an Osiris reflash controls things, and uses the stock MAF (mass air flow)

About 2 months ago, my G started running lean, in the below 3k rpm area. Obviously, something was up with the Osiris or MAF, or something.

Lean code was being thrown P1273. lean condition bank 1.
Wideband AFR gauge(atermarket) was reading 16 (max lean) at idle, as well as most of the time, when below 3k rpm. Above 3k rpm, Haltech took over, and everything was fine with that.

Another important point: also about 2 months ago, I removed and replaced the front bumper, hood, radiator support, and radiator, due to a very minor front end collision. The intake piping was not damaged, nor were the intercoolers, or any thing else along those lines. The G still holds boost just fine, and there are no vacuum/boost leaks anywhere. I';ve inspected all the clamps and connections and pipes, and all is well.

Oh, and despite the lean condition, it has a nice steady idle with no misfires. There are no hesitation or any drivability problems.

I've replaced the sensor for the aftermarket AFR to make sure it wasn't giving me false readings.

I've replaced the fuel pump.

I've checked to make sure that everything is plugged in correctly and such.

Air intake temperature still reads correctly when checked through the OBD2 connection; the weather has gotten markedly colder during the last 2 months (down into the 20/30's) Colder air means denser air means leaner conditions if the ECU doesn't compensate for it; is there some sort of sensor for this that I missed?

I've changed the tuning in the Osiris tuner (increased the K value) which has caused the AFR to read better when under power, but it still is idling at 16.0 (lean) Still a steady idle, though, no issues.

Any ideas why my tune would suddenly change?

Thanks for any ideas to look at and/or things to check.

westpak

iTrader: (19)

If the car runs the same and no operating issues it could be an exhaust leak causing the lean reading condition, but not really running lean

rcdash

iTrader: (18)

Check the manifold heat shield bolts. I've had the center one back itself out on both sides requiring replacement - and it causes a lean condition...

Dave 90TT

iTrader: (4)

I'll check and look for both of those.

djamps

iTrader: (1)

Exhaust leak and/or bad OEM sensors.

Dave 90TT

iTrader: (4)

Got under the car today, and removed and replaced the gaskets from the cat-back exhaust to the cats. Used some high temp exhausts gasket sealant on them as well, letting them cure overnight before I drive it.

Also changed the tune back to what it was before all this started happening, as it appears that if it was indeed an exhaust gas leak that caused this, then the tune should stay the same, despite the artificially lean readings on the AFR.

See how it goes when I drive it tomorrow.

djamps

iTrader: (1)

Your tune cannot change on it's own... tuning around another issue is the last thing you wanna do :P good luck

Dave 90TT

iTrader: (4)

Yeah, you're right.

Unfortunately, driving today, nothing has changed. I thought I had found an exhaust leak on the gaskets. Maybe there was, maybe there wasn't. But that didn't fix the problem. The exhaust leak has to be further upstream, then. Maybe at the turbo to the cats or the exhaust manifold to the turbos, both of which are a PITA to get to.

westpak

iTrader: (19)

the leak would be near the sensors.

Some times with use the turbos will loosen up the bolts to the down pipes or exhaust manifolds due to their weight, specially if you did not use the support at the bottom of the tranny to bolt the exhaust to

Also look for a lose 02 sensor

Dave 90TT

iTrader: (4)

O2 sensors are good. They are about six months old, and I just checked them, they are tight. I will check the bolts on the turbos and cats this weekend.

Thanks everyone for the tips, I appreciate it.

westpak

iTrader: (19)

No problem, good luck.

I had a similar issue but in my case since I had AF feedback to the Fcon it did screw up my tune.

It ended up being bolts lose/missing where the down pipe connected to the turbo as well as a lose 02 sensor, the one up top in the down pipe.

Dave 90TT

iTrader: (4)

Only found one loose bolt, bolting the cat to the turbo downpipe. The O2 sensors are all on tight, as well. Tightened up the loose bolt, as well as applied some extra torque to the other bolts. Some of those bolts on the cat to turbo connections are a PITA to reach.

Still shows running lean when not on boost.

Bah.

westpak

iTrader: (19)

hmmm I guess back to basics.

I assume your aftermarket AF gauge is on the same side your stock AF is showing lean condition, bank 1, and if exhaust leaks are ruled out, you would seem to have a fuel or vacuum issue.

either an injector(s) is having issues or you have a vacuum leak affecting that side.

vacuum leaks affecting a specific side or piston would be around the gasket between lower plenum and collector or collector to head, or around the injector if a seal ring is bad.

and of course if an injector is not working properly could also cause lean issues.

if it were me I would swap injectors, all three from one side with the three on the other side and check the gaskets and torque of those bolts. Ohm check them while they are out

then if the issue follows the injector swap you have a possible solution and then swap again one at a time.

Another test could be done using Cipher, by shutting down one cylinder at a time and see if there is one that doesn't affect idle as much as the rest

Dave 90TT

iTrader: (4)

Put in new inectors, did not solve the problem. Confirmed it was not due to Osiris reflash or haltech by flashing back to stcock, and removing the haltech, problem still happened. Also put new spark plugs in when I had the manifold off to replace the injectors. As I said, replaced the fuel pump as well.

Bit more description of some details: while sitting at idle, the AFR is pegged at 16.0 but occasionally, it will go back to a solid 14.7 for 30-60 seconds, and then back to 16.0. When it goes to 14.7, the idle jumps up a bit, but is nice and steady, just like it is/was when it was at 16.0.

Also, all the spark plugs looked fine, none of them were any different than the others.

I thought I got all the exhaust leaks (if any), maybe I missed some? I swear, I hate having to get under then and contort my hands and arms up to where the turbos are and try and tighten bolts.

Any other ideas?

rcdash

iTrader: (18)

All 3 bolts on the heat shield on both sides for each JWT log manifold is intact?

Dave 90TT

iTrader: (4)

I think so, but I will get under there this weekend and check again

josenq06

If the car gets tuned in the shop with regular temperature weather and it's under 20s outside? Would that throw my AFR off? Cause I'm running lean on idle, but it goes from 13 to 16 at a rough idle

rcdash

iTrader: (18)

It's a silly design - the bolts go all the way into the manifold. So if the heat shield bolts back out, hot gases get sprayed onto the coolant pipe (at least on the driver's side).

Dave 90TT

iTrader: (4)

Thats crazy! Anyways, I had some minor outpatient surgery on my back this week, so no working on the car for a bit. So I have not been able to check just yet.

kacz07

iTrader: (15)

Failed cam sprocket assy. or sensor?