Jameasun

Hello all,
Well I have done my best to diagnosis my truck but I need some ideas. I have exhausted my experience.

2000 Chevy Sivlerado LS
Issue ruff idle and lean fuel trims bank1 & bank2 (continuious LTFT of 25 on both banks with a variable STFT of 3-25)

Codes PO171 and P0174 were observed but cleared; codes have reappeared since replacement of intake gasket set.
Diagnosed the following and has been unable to find the root cause of the lean trims.
-MAF sensor Tested OK: KOEO 39.8 inHg; running at idle 10.8 inHg observed
-Fuel Pressure Tested OK: KOEO 56psi (new fuel filter has been installed as of 9-8-15 by owner) Fuel pressure maintaned 52psi with engine running at idle and 3000rpms.
- New fuel filter installed within the last month
-New intake gasket installed by owner (9-3-15)
-Split in vac. hose at intake for the fuel pressure regulator (repaired by owner) tested ok.
-Vac hose from intake to PVC valve tested ok, as well did the PCV valve. When intake port was plugged no change was observed in fuel trims.
-Air inlet tubing from MAF sensor to throttle body tested ok.
-Trottle body gaskets are not leaking.
-EGR valve, piping and gaskets are not leaking or bypassing.
-Hose from intake to break booster tested ok and when pluged no change was observed.
-Battery was disconnected for 48hrs to reset the computer, no changes noted.
-Smoked intake, no leaks noted.
-Noid tested injector connections, all ok
-Ohm'ed injectors, all tested 12.5-12.6

kenziekay21

Idk if it will help but ive done the Catalyst Cleaner by Mr. Gasket in my truck and it helped my rough idle a little. Have you pulled the o2 sensors and cleaned/replaced them?

tech2

you posted fuel trim readings but are missing an important diagnostic piece of information.....at what rpm does the lean condition occur




report the fuel trim at idle and at 2500rpm.

Jameasun

idle
Calc load 1.6
Stft B1 17.2
Ltft B1 25
Stft B2 15.6
Ltft B2 25
Map (inHg) 10.9
Rpm 614

Jameasun

Calc load 5.1
Stft B1 12.5
Ltft B1 25
Stft B2 12.5
Ltft B2 25
Map 7.7
Rpm 2100


I will get FF data but the code was issued at higher RPMs.

Jameasun

Freeze frame Data P0171 P0174

Fuel Cl
Calc Load 12.5
ECT (deg F) 194
Stft B1 9.4
Ltft B1 24.2
Stft B2 8.6
Ltft B2 24.2
Map 21.3
Rpm 1712
Speed 20mph
Maf 4.1
Tps% 22.7

tech2

is the engine is warmed up and in closed loop for the data you posted


the numbers are not clear cut so there may be multiple problems. the fact that the ft is at its adaptive max at idle and less so at higher rpm is indication of a vacuum leak.


I would run the engine at idle and listen for a vacuum leak with a mechanic stethoscope or have the induction side from the intake to the air snorkel smoke tested.


did you remove the injectors from the manifold when you did the intake gaskets.

Jameasun

Thanks for your reply,

Yes, the posted data was during CL operation. I did not smoke the snorkel, however I did test it with propane and carb cleaner.

I removed the injectors yesterday and cleaned them on the bench. All were firing and appeared to be flowing well. I am purchasing a pulse generator to do a balance test.

I suspect that I have a one or more bad injectors even though they ohm'd out to spec and are clean. My stft on both banks went up and stayed up after removal and cleaning.

tech2

I was thinking the injectors were not seated properly and creating a vacuum leak into the manifold.




imo if it was a fuel delivery problem it would be maxed out during a hard accel...but that it not the case. its leaner at idle. gm injectors rarely go bad. I doubt they would be bad on both banks the same amount.


does it have the stock air cleaner box and filter. cai with a crappy oil soaked cone filter destroy maf sensors.

Jameasun

Ok well my problem persist. I went ahead and ordered and installed a new intake. I opted for the dorman replacement intake. While I had the intake removed I replaced the injector o-rings.
Currently i am using the K&N stock replacment filter.