Experienced Help Please

[black96aurora]

1996 Aurora 126,000 mi. Runs excellent but emissions issues. Codes for lean bank 1 and 2 killing me! Replaced fuel filter, checked fuel pressure, replaced post cat o2, replaced MAF. Cannot find any vacuum leaks. Tested vac w/old style mech vac gauge. Readings to spec and steady.
Any further ideas would be appreciated.

There seem to be alot of experienced DIY's in this group and you all have helped sooo much with damn good tips! I hope someone can give me a little miracle!

Any good Ideas why my mass airflow readings would be 3.8gms/sec while book calls for 5-6 ? New MAF reads the same as the old one!!

Thanx

[frs64]

There is a backfire valve on the end of the intake manifold. It looks like a spring loaded gate. I read that they leak air sometimes and cause problems.

[zimaad]

First off, did you test this at idle or at a prescribed RPM? Your value doesn't seem too far off for idle, but it should increase as you increase RPM. Can you get a reading of a few point and see if it goes up at you increase RPM. 3.8 really doesn't sound too far off for idle.

An obvious thing to check the inlet ducts to the throttle body and make sure there are no obstructions. This also includes the screen at the entrance to the throttle body. If that was bent up, it could slow down flow a lot. Make sure all the cables to the throttle body are connected and actuating the butterfly valve correctly.

I was having a problem with a hot/lean situation. Don't know if you ever noticed, but the passenger side of the intake manifold has a spring actuated blow out valve. It is in the center of the side of the manifold just next to and lower than the power steering resevoir. I'm not positive, but I assume it's there in case of a backfire, so the plastic manifold doesn't get blown apart. The spring isn't all "that" strong and the seal can get worn out. It's any easy place for air to possibly get in and cause a lean/hot situation.

Could it possibly be a fuel related issue? Is fuel pressure regulator working correctly? Are all the injectors leaking or dirty?

This is a far reach, but there is a TSB regarding the use of to much oil in aftermarker air filters..... oiling a K&N too much can cause issues w/ the MAF. Eventually, MAF problems leads to probs with the transmission.

Hope you figure it out - Drew

[black96aurora]

zmaad is there any replacement for the valve in the intake or do you have to replace the manifold? I thought I heard a leak from that area but wasn't sure. I attatched a mechanical vac gauge to fpr and the reading was to spec with no fluctuation. Do you know what the ignition timing is supposed to be? My scanner tells me that I am running -22deg!!!

[black96aurora]

frs-thanks for the heads-up. Do you have any info on repairing this condition?

[black96aurora]

You guys were correct that it was the pressure relief valve. I tested that area with propane and trims went rich. Waiting for part#3546341 . The gasket had seperated from the valve. What kind of combined mileage do you guys get? I'm hoping that after the fix and my 26% trims drop I'll get better than 14 mpg.
Thanks again! As usual, the members of this site provide a wealth of info.

[zimaad]

Hey there....

First off, glad you were able to figure out the problem. Also, sorry I didn't get back. I went on vacation and just got back today. I ended up putting a light amout of silicon on the outside of mine instead of buying a new piece, although buying a new one is probably the best idea. I do a mix of round town and highway and get around 20-21 mpg. I think my highway mileage was a little better a few years ago, but it's still decent.

Something else, you may want to check your spark plugs. The lean mix will cause your plugs to run hot, become damaged, and not spark correctly. That too will hurt your gas mileage.

good luck

[black96aurora]

zimaad, Hope you had a good time on vacation. The part only cost me $20 and a two day wait (special order). It lists for $27. The new intake gaskets were only $10. For a total of $32.50 (including tax). It was such a quick and easy repair that I think everyone with a bad valve should just replace with new.
Thanks again for your help!!

[frs64]

Sorry for the late reply. Glad I could help .I read about this problem at a forum , most likely this forum. My 4.0 is apart for a rebuild and my valve will have to be fixed or replaced because the gasket has separated.