DCAWD.com

So I have been getting a really rough running engine every once in a while; running stoopid rich, balking, hesitating, and generally sounding like my cams are in backwards.
Then things are fair. Having a 12:1 idle AFR, only reaching 9 psi, but running.

I have cleaned the MAF, changed the O2 sensor, plugs, coil packs, checked for leaks in the intake. I even try running straight E85 and the AFRs still drop down to 12:1. This shit is supposed to be 9 or 10:1 and the ecu is pulling max long term fuel trim of -25?

I have done all that I am capable of doing and need to call in the professionals..

I limp it on over to Carlos at Bilbo Automotive since he knows the fuel system pretty well after replacing 80% of it last time.
Leave it there a day and get a call back "yep, your car runs like ass(*sic*). Problem is, there is no problem."(said in a Spanish accent)
Fuel pressure within limits, MAF voltage readings within limits.
I pick it back up feeling slightly better. At least I didn't miss an obvious diagnostic step.


So here is the kicker, it is really running rough, just barely burbling and I remove the intake elbow. The whole thing with the filter AND the MAF housing.
Car smooths right out and idles fine. I can pull the throttle cable and get the revs to come up nice and smooth, let off and hits solid idle.
I could see one or two injector sticking open, but not all 4

Oh, and just in case you missed it, this was WITH NO MAF METERING OF AIR!

Tell me that is not counter intuitive.

Since things are better without the MAF... I'm guessing it's related to the MAF. Any chance that the STI and WRX one are the same? If so, you can borrow mine to test my theory. Since the MAF provides both temperature and flow, I'm guessing one of those is really screwed up and giving the ECU bad readings. The MAF voltage is only giving you flow, but not temp.

MAF works fine. Can see the cfm and IAT through the OBD-II. That is not saying that the signal is getting processed right, but it is being sent.

I just done get any of this. If you pull the MAF the car should just shut down. I remember trying to start my car w/o the intake and MAF in place after an install and the engine would NOT start. Period. CEL flash and no ignition. I just can't imagine how it would start, let alone idle and run WELL.
Have you been able to follow the MAF voltage through the entire rev band?
Is it steady or does it bounce around? Is it possible there is some sort of interference/iconsistancy in the voltage across the wireing?
Is there a leak/blockage in the intake piping somewhere, including the IC piping?
Is your filter completely clogged with crap as to be restricting airflow?

I left the MAF in the housing and did not disconnect it, just removed the whole filter/elbow piece, kept it wired in, and put it to the side.
Have not looked at MAF voltage in dynamic use, but Carlos said that he performed the MAF diagnostic test and said it was within "normal" numbers. I have not logged the MAF voltage directly, but just looke at the chassis data from the OBD-II for the IAT and CFM numbers.

Filter has about 6 mo of crap on it, but even if it were blocked, why would it run fine one time, and then like crap another?

Next step is to read MAF numbers while engine is running fine, but without the MAF in-line. That would be the real kicker if I see numbers running when it is supposed to be sitting to the side.
Little phantom MAF readings being generated from some evil MAF imposter.
I can imagine it now, I have an unknown enemy that is following me around with a wireless controller spoofing MAF signals and laughing his ass off each time I go under the hood.

zaxrex wrote:I can imagine it now, I have an unknown enemy that is following me around with a wireless controller spoofing MAF signals and laughing his ass off each time I go under the hood.

Sabre wrote:

I said unknown.
You, I know about.