Possible MAF issue w/IATS Reading High

[logray]

One more......since this appears to be a preexisting condition -could the DME code be a suspect ?If the default maps work and it shows up in processing real data that might be a clue .

Yes I absolutely am wondering myself if the default DME map (program) requires some tuning/modification to deal with the increased displacement.

Or perhaps the DME is bad.

As for any check engine lights or diagnostics codes, there are none.

The last code this car popped was a faulty variocam solenoid (but was actually a bad DME). I have another DME in the car now, running a stock map.

I'll PM bypro and see what he's running as far as injectors. Thx.

Interestingly, I added 10 more miles to the car with the evap purge intake blocked and the brake booster port blocked.

The results are odd. The long term FRA have moved back to 1.03/1.02 from where they were before in the 1.06/1.08 range. And the TRA continues to go south, to -0.10. While the car was peforming poorly before with -0.10, it seems to be doing better now especially at idle. Perhaps the brake booster or evap purge are the source of a vacuum leak.

Let me tell you it's a good thing we have power brakes. Don't block or remove your brake booster and drive the car unless you have a deserted road to drive on.

[logray]

Also injection time at 680 warm idle was spot on at 3 ms which is the factory setpoint. Maybe up or down 0.1 from that.

Perhaps that is also part of the problem, if it only thinks it needs to be open for 3ms, and it's a smaller injector so it's not opening long enough.

Of course, I would think the O2 sensors would pick up on that and adjust the injection time accordingly (which it's not while idling, unfortunately don't have data or info on what it's supposed to be above idle).

[logray]

Continued driving and the TRA continues to go further negative. FRA probably pulled back a little towards 1.02/1.03 because I wasn't as hard on the pedal.

This is with SAI, fuel evap, and brake booster blocked.

During rebuild I replaced AOS, epoxied intake manifold, new intake seals, sealed AOS tubes, new AOS tube orings, new throttle body seals, new SAI tubes, dismantled and cleaned IACV, new IACV gasket, ugh.

If there were an intake leak it wouldn't run so well during a fresh DME reset with new fuel adaption values.

Tested vacuum, appx 16 psi @ 680 rpm idle. :( :( :( :( :( :( :(

Ordered a set of 3.6L white injectors @ about $93 each incl. shipping. Fingers crossed. Don't know what else it could be at this point. Even though my old injectors were cleaned maybe they were tired and had enough, which would explain the pre-existing condition. That and if the flow rate calculations by the professional cleaner are correct, they are only putting out 60% of their original capacity ... and I'm expecting them to work harder than they did before with larger displacement. I really hope this is right because this could be the final straw.

[wvicary]

Continued driving and the TRA continues to go further negative. FRA probably pulled back a little towards 1.02/1.03 because I wasn't as hard on the pedal.

This is with SAI, fuel evap, and brake booster blocked.

During rebuild I replaced AOS, epoxied intake manifold, new intake seals, sealed AOS tubes, new AOS tube orings, new throttle body seals, new SAI tubes, dismantled and cleaned IACV, new IACV gasket, ugh.

If there were an intake leak it wouldn't run so well during a fresh DME reset with new fuel adaption values.

Tested vacuum, appx 16 psi @ 680 rpm idle. :( :( :( :( :( :( :(

You mean 16 inches of vacuum right? Why is it so low? I'd be happier to see 18+ inches. Have you checked for a vacuum leak or a exhaust restriction?

[logray]

16 inches yes. :(

Vacuum leak and exhaust restriction just does not make sense to me, if you can reason this please provide an explanation.

Upon DME resetting the fuel adoptions, the engine runs great until about 40 miles, then fuel trim starts to go bad even after all of the work I've done. The idle is soooo soooo smooth at TRA 0.02 or 0.00 after DME reset, then it gets bad at -0.10.

Released propane into engine bay over various intake locations, no change in idle. I don't own a smoke machine.

I think I'm losing it. They say the definition of insanity is repeating the same thing over and over and expecting different results.

Same results even after doing the following several times over now.

RE Vacuum leak.

• Plugged SAI holes in the cross over boots
  
• Clamped brake booster line
  
• Clamped EVAP purge intake line
  
• Did not plug fuel pressure regulator hose
  
• New AOS, AOS bellows, & clamps (4th time I've put a brand new AOS on the car)
  
• Flange sealant around base of AOS bellows ferrule in 1-3 head
  
• Flange sealant around AOS port into case
  
• Flange sealant and new oring around AOS breather on 4-6 head.
  
• Epoxy around entire perimeter edges of intake plenum parting lines
  
• New AOS tube orings with recommended lube
  
• Epoxied and tested for leaks on AOS tubes to T-plenum behind T/B as well as the 4-6 head.
  
• New intake plenum orings/gaskets (3rd time)
  
• New intake plenum bolts (3rd time)
  
• New intake riser gasket (3rd time)
  
• New intake riser bolts (3rd time)
  
• New brake booster and alternate side intake plenum brake booster cap orings.
  
• New throttle body oring (4th time)
  
• Dismantled and cleaned IACV (5,000th time), new IACV gasket (twice)
  
• Cleaned throttle body (8,000th time)
  
• New fuel injector orings with recommended lube
  

Exhaust restriction:

• Cleaned and inspected headers inside and out (4th time).
  
• New gaskets for exhaust manifold (5th time)
  
• Fabspeed stainless steel headers resurfaced (cost a mint to do stainless)
  
• New header bolts
  
• Heli coiled bad threads in heads
  
• Purchased and installed used 3.6L stock mufflers (same prob existed with aftermarket mufflers)
  
• Bolted on old cats (pulled off at 45k miles and then reinstalled at 65k miles).
  
• Cleaned and inspected cat tubes with boroscope
  
• Cleaned exhaust tips, lots of fuel soot after only 20 miles of driving. Doesn't look like oil soot this time around with the new rings, pistons, and cylinders. However with new rings, pistons, and cylinders appx 300 miles on them, perhaps rings haven't fully seated allowing excess blow by. Or perhaps the lean condition resulting in excess fuel inserted by the DME due to inadequate injectors caused poor conditions for good ring seating (fuel wash), snowballing from there, causing below normal intake vacuum readings.
  

[logray]

Spent the better part of several hours with the smoke machine on the intake system.

I will spend more time and smoke out the EVAP, SAI, and brake booster systems.

There were two intake leaks located. I pulled the alternator to get a really good look underneath.

A miniscule leak in the throttle body where the screw holds the bracket that attaches the throttle body to the power steering pump bracket

Another miniscule leak from the IACV, actually from the electrical connector in the IACV, which once was plugged in the leak vanished.

I'm really hoping my old injectors are tired and clear this problem up, because I doubt those two leaks would be enough to account for a 1 inch drop in intake vacuum mercury or the fuel trim issues.

The only other thought that came to mind was a flat cam lobe or timing issue. I am running with 3 degrees advanced cam timing though, which I would think should theoretically increase intake vacuum. I'm wondering how flat a lobe would need to be to explain the 1 inch of mercury below normal intake vacuum.

Or I'm beginning to think 15-17 inches of mercury is normal intake vacuum on the 1999 996 (16 is what I measured). It would be totally awesome if someone else out there had this car, or a 1999-2001 car and measured their intake vacuum. It's really very simple to do if you patch off the brake booster or evap purge line.

Edited February 19, 2012 by logray

[logray]

I really believe 16 in HG at 680RPM hot engine idle is totally normal for an early 996. Any early 996 owners out there with a vacuum gauge and 15 minutes of time to spare? Easy to reach around to the fuel pressure regulator and pull off the small hose to connect straight into your gauge.

I found a diagnostics link for lean running and DTCs P1127 and P1129 (neither of which have been reached yet) about reading intake vacuum with porsche special tool 9103/2. The manual states the reading should be between .4 and .6 bar, which works out to 11.8 in HG to 17.7 in HG.

Here is the link:

http://www.google.co...tSnXE-Q&cad=rja

Since I'm measuring at 2000 feet, it might account for slightly lower numbers. I might take a drive to sea level and re-measure.

Edited February 19, 2012 by logray

[wvicary]

I forgot to take in account sea level with regard to your vacuum readings so I'll assume that your 16" is fine.

[logray]

Yep, when I went to about 90ft above sea level the readings were between 17 and 18 in HG. Thanks.

Anyhow, the new injectors are due to arrive and we'll see if that clears it up.

I'm starting to run out of things that could cause the fuel trim issues.

[911fiddler]

Hi logray. Am staggered to have found someone chasing the same issue that I have been for the last 3 years, on my 1998 996.

I have done very similar tests hwever you've done a more than me. It would be great to know whether you have fixed the issue now?

Some things I have done which may be useful to you....

-measured crankcase vacuum as water-inches to check AOS, did you do this?

-lapped the mounting face of the idle control valve as I discovered 1mm off flatness with the 0.5mmm gasket.

-checked the inlet manifold resonance flap bearing for vacuum leaks.

Some things I have spotted which I need explanations for...

-at idle the ignition advance is unstable between 3 and 9 degrees.

-if I tamper with the airflow meter wiring, just move it around slightly, thereafter, for a while the engine idles more smoothly, runs better.

Same as you though, a DME reset from power disconnect also makes the engine run nicely for a short while.

Pete.

Peter.shephard@o2.co.uk