Stumped... can't find reason for lean condition. No vacuum leaks to be found. Any one good at analyzing a livelink datalog and possibly give some opinions?

 

did you test the egr valve yet? if not, get a vacuum pump to connect to the egr valve. have the engine running, pump your vacuum and see if the engine changes tone/running.
on a good egr valve, the engine will misfire as the egr valve is opened with your vacuum pump. vacuum leaks are difficult to find, keep looking.
good luck

 

thank . I'll try to get a pump and check out the egr. It's been a nightmare trying to figure it out.

 

What are your short term fuel trims while parked and at operating temp (180+)?

 

short term fluctuates from plus to minus 3

 

That sounds right (per my understanding) and does not coincide with a vacuum leak.

 

but long term stays around positive 15 to 20 and occasionally higher. Which indicates a lean mixture

 

Overall runs good but lean and fuel mileage has dropped about 2.5 or 3 mpg.

 

Check the exhaust system for leak points upstream of the O2 sensors. Look for broken or missing exhaust manifold bolts, cracked manifold, etc. Believe it or not, an exhaust leak in this area sucks air in in between pulses. That air brings with it oxygen. The sensors see the extra oxygen (lean) and push the fuel trims to richer (+ve LTFT)

Other sources/causes of lean condition are:
- dirty MAF sensor
- intake leak anywhere between the MAF and the intake manifold. Check all hoses and their fittings, thoroughly.
- aftermarket air intakes that miss or modify a vaccuum line.
- cracked intake manifold
- IAC valve sticking

So, a few ideas there for you to check through one by one.

 

thanks. I've checked my vacuum lines before. Just started checking them all again last night . Also cleaned the maf again last night. I've even used the starting fluid already method and got no response from that. Haven't checked the iac at all. It seems to idle fine. Occasionally hard start but never not start. Gonna finish checking vacuum lines tonight and I will check the iac too. Any other symptoms of an iac?