split71

********Solved********
See page 2 for details
*********************

After a long exhausted couple of weeks trying to chase down this issue, I thought I'd come to the resident experts here on RL. I've done my due dilligence and have searched until my heart's content on the internet for this. I'm very mechanically minded as well as a programmer, so I feel like I have a very good grasp on these issues (B5 S4's anybody )

Issue

Car drives amazing below 4k partial OR full throttle. But the car has hesitation/falls on its face/breaks up in acceleration/ whatever you want to describe it as from about 4000 RPM to 5000/5200 RPM. Then it pulls just fine to redline, no hiccups. Only CEL's in the past were from boost leaks, and these crop up after driving the car for a bit then I'll be idling and it'll just pop on in traffic.. P0171, P0174. Never any other codes besides the ones for a bad MAF last year when I replaced it (including the ABS/PSM lights).

What's been replaced

MAF - (1 year ago, new Bosch unit)
Plugs, updated 997 coilpacks, fuel filter (15k miles ago, 2.5 years ago)
Fuel pump (last week)

What's done to the car?

EPL 91 Tune
72 lb Injectors
Billet K16s
EVOMS Intake
EVOMS Diverter Valves & Silicon F Hose
Speedtech 3" Xcellerator Catless Exhaust

What I've tried

Took the car down to a local Porsche Indy, had them take it for a spin. They tightened up a drivers side intercooler hose after a boost leak test, and still saw the same problem @ 4k. Put a fuel pressure guage on it and saw it going all over the place when the car reached 4k, so we put a fuel pump in it, no dice, still same issue of hestitation @ 4k-5k RPM

I did some logging today to dig into this a bit further and have attached it to this post. I did a 3rd gear pull from 2k RPMS to ~6.5-7k RPMS. Parameters measured can be seen in the attached spreadsheet.

I noticed my MAF is being pegged @ 5v (max possible voltage it can read) right when it's hitting 4k rpm, but the MAF is continuing to measure increase in Air (based on column F, rows 28-44). Is this normal? Does it need to be replaced again?

Also, IDC's look good, AFR seems to be stupid rich in high load/high rpms/high boost (based on Column K, rows 28-44) based on the Oxygen sensing bank 1 Lambda Value.

Timing seems to be all over the place in 4k-5k rpm range also. I'm running out of ideas and I don't want to start replacing parts just to replace them

Thanks in advanced guys...

John D II

Classic bad/worn plugs symptoms. Put in fresh spark plugs and see what happens...

split71

While I would lean towards agreeing with you, don't you think I would have seen a misfire code by now? I haven't seen one...

John D II

I have had the exact same situation with no codes and it was simply plugs. Nothing else. You're due for them anyhow. Your mileage since the plugs were installed says plugs, too...so, if I were you, I would do plugs next

"02996ttx50

^ true..also hard to determine from your "list" whether that was 15k miles ago on plugs n coils? or if that was simply the fuel filter. but tuned cars and issues, well.. you know..

plug n coils..plugs n coils. etc ad infinitum. cheap insurance and fix and tuned cars eat plugs. thats just the way it is, as you know. i also would bet on that just shooting in the dark, if a coil isn't in fact even possibly cracked?

i also wouldn't let the absence of any misfire codes stop me from 6 x 8 bucks. i'd go in with plugs and not be surprised to find even, a cracked coil.

TheDeckMan

Also check for broken clips on the coil packs. And broken clips for the Varioram sensors.

Macster

Based on this: Only CEL's in the past were from boost leaks, and these crop up after driving the car for a bit then I'll be idling and it'll just pop on in traffic.. P0171, P0174.

I could read the above and believe there are still error codes appearing. Just so it is clear any suspected boost/intake leaks must be addressed first. You can replace plugs until you are blue in the face but no plug can make up for boost/intake leaks.

If there are no error codes I'd still make darn sure the intake system is leak free. Just tightening a suspected loose hose is not good enough.

A gotcha with these cars is an intake hose when being slipped onto the connector has a loose flap of rubber that gets bent back. The hose is tightened up but this flap can and does represent a boost (or possibly a vacuum) leak. It is imperative that when the hoses are being installed this condition is avoided.

Last but not least stock Turbos are hard on plugs, coils, the MAF and O2 sensors. These engines flow a lot of air. Even though they are just 3.6L they make more power than for instance my 2006 GTO with its 6.0l engine which made just 400hp compared to the Turbo's 420hp. This increase in air flow taxes the MAF and of course the increased air flow means more fuel is being burned and this is heat and this heat takes its toll on the plugs, and sensors and even coils. They are exposed to the elements and the heat from the exhaust/turbos.

Modified Turbos are harder still on these components.

split71

Good to know. Thanks John

I know the plugs/coils were replaced ~ 15k ago. But as you said, tuned cars...

Plugs were not high on my list due to zero misfire codes, but thinking they may be worn out. Any recommendations on plugs for this setup?

Saw those threads for the broken bracket(s) in between plugs/coils. Will definitely check if I do plugs.

Correct, I've never seen any other codes on this car since I've taken ownership. I have a durametric and as you can see, very handy and understanding of this. I had the shop firstly tighten up all boost leaks if there were any. It was the same hose that had been tightened up in the past, so I know it's just 'problematic' or maybe your suggestion is what's happening on it?

I will have to go take a look at the FPR vaccum setup near the throttle body, I have a feeling those lines that are 'T' off there may be finicky.

Nobody has answered any of my technical questions regarding max airflow reading. How does the ECU correct,or better yet...doesn't correct past a 5v reading??

Macster

It is not clear to me the ECU isn't correcting even though the MAF V reading is 5v. In the column: Mass air flow; I see increasing values even though the MAF voltage is pegged at 5v.

The sensor measures the difference of the temperature of the film -- which is a just a thin film temperature sensor -- between the leading and trailing edges. The difference in temperature corresponds to the mass of air flowing past. To signal the amount of air the MAF emits a square wave and observing this -- its smooth progression up and down the RPM and load scales and its uniformity at constant load and RPMS -- can tell you if the MAF is bad or not.

Oh, plugs. 15K miles on a tuned engine is a lot of miles. Plugs are funny. They can be bad, due to be replaced, but not trigger misfires. And often by the time they do deteriorate to the point they cause misfires, they should have been changed long before they reached their current state. At 15K miles on the plugs I would have no problem were I in your shoes changing the plugs. And I'd cast a critical eye over the coils too. Any signs of deterioration and I'd replace them as well.

For plug recommendation my advice is to rely upon what the tuner who produced your setup advises. He is in the best position to know what plug is suitable.

wross996tt

Any chance you still have the original intake? You might try swapping out the EVOMS intake. It could be making the air turbulent entering the MAF...

split71

Excellent feedback Macster, thank you. I will probably start the removing the necessary components to do plugs soon.

Regarding this..

To signal the amount of air the MAF emits a square wave and observing this -- its smooth progression up and down the RPM and load scales and its uniformity at constant load and RPMS -- can tell you if the MAF is bad or not.

Can you expand on how to dive into the maf signal to air flow relation more?

split71

I do not, these issues have just started happening and the intake has been on for a couple years.

"02996ttx50

feel like i may be cross posting, too much time on my hands coupled with an obsessive willingness to type/share lol

http://www.pelicanparts.com/catalog/..._pg1.htm#item2
Spark Plug - Bosch FR-6-LDC , Beru 14 FR-6 LDU, (7410)
Part #: 999-170-195-90-M47

i wouldn't mess with "success" good enough for gt2, now the recommended oem replacement for 996 when they originally used "5" heat range. this for tuned car. cant go wrong. pre gapped out of the box.. but you can dbl check. i go with .027.

split71

Just to keep this thread consistent with one over @ 6SpeedOnline..

Tony@EPL called me back today regarding this. Advised plugs as well, these specifically.. Ordered them via Amazon (for a bit cheaper ). Also free next day shipping...Prime can be lovely.


Thanks for the help 02996ttx50

"02996ttx50