Out of Options, Hesitation at 4-5k, Occasional Surge, Need some more input

[Kenneth Behrman]

Afternoon guys/gals,

 

First off, these forums have been great to learn and utilize for DIYs.  So, big thank you to all that contribute.

 

I have had my 911 for 3 years,  its is a 1999 Porsche 911 Carrera C2.  I bought it as a roller (Old engine spun rod bearing) and sourced parts for almost a year before I finished it in 2017.  Long story short, I have one remaining issues I have spent 2 years chasing.  I have a friend who is a Porsche tech that is going to take a look at it when I can get it to him in a few months.  Before that, I thought I would give the community an opportunity to weigh in since there is a lot of knowledge here.  I have read every post I can find on every relevant forum,  I did not post the error codes in the title for a reason, I have ruled out the MAF which is where these codes always point to.  Here is a summary I provided him:

 

The car has great driveability.  There are no issues with day to day.  Unless I am driving hard, the only thing I may notice would be a slightly hunting idle, maybe +-100 max.  Torque and Power feels close to what I would expect from a 300 hp car.  I keep up with a chipped 135i so its not lacking a lot performance, but maybe some.  No strange noises, knocking, or pinging.  No detected misfires.  No smoke has been noticed.  

 

Issues:

• P1123 CEL
• P1125 CEL
• Only activates after long idle periods, not dependent on mileage after reset
• Slight Hesitation 4k - 5k, Occasional Buck, TorquePro Shows Lean Condition, LTFTs averaging +10 - +15% (may be inaccurate, its torque..)
• Intermittent Hesitation on/off WOT at High RPM
• Intermittent Hunting Idle at Stops, Independent of Engine Temp
• Stalling after WOT or Sustained Throttle - Resolved with Removal of KN filter system that came with the roller

Car Modifications:

• Custom Muffler Bypass

Parts Replaced / Repair Attempts:

*All Porsche or Factory Supplied Brands Used (Bosch mainly)

• AOS Replaced 8k ago
• IMS Replaced 8k ago
• RMS Replaced 8k ago
• 3 Different MAFs, Cleaned before each installation with MAF cleaner, factory Bosch
• IACV Replaced
• TPS Replaced
• Thottle Body Cleaned / Butterfly Cleaned
• Upper Intake Boots Replaced, New Metal Straps
• Sparkplug Boots Replaced
• AOS Bellows Checked/Replaced
• Fuel System showing proper pressures checked at idle and off, according to RennTech
• Engine Vacuum Levels from MAP sensor appear normal
• Spark Plugs replaced twice, all 6 look perfect color, no signs of excessive fuel or lean condition, FGR-6-KQE
• Homemade smoke test, leaks all secured
• Fuel Pump Removed, Checked for Operation and Leaks
• Change Over Valve checked according to Porsche Spec with Vacuum Pump
• 6 Oil changes, all clear of debris
• Fuel Filter Replaced
• Always running 92-93 Octane

Maintenance to Take Place soon:

• All new Coil Packs
• Fuel Cap Replaced

 

I can't rule out that some has a modified ECU program or something like that, but I will find out in a few months.  Until then, any suggestions would be great!  Some candid conversation may spark something I didn't think of.

 

Thanks,

 

Kenneth

 

 

 

[DBJoe996]

The P1123/P1125 seem to always point to the MAF sensor.  See here

 

[Kenneth Behrman]

1 hour ago, DBJoe996 said:

The P1123/P1125 seem to always point to the MAF sensor.  See here

 

Hi Joe,

 

I am familiar with this post.  I started all the trouble shooting with the MAF and I have been through 3 at this point to no avail.  The one that came with the car, 1 new one, and 1 removed from a problem free 986.  The new one and one removed from another vehicle yielded the same result.  I think the original was dirty. I am currently running the new one with 3k on it.

[Ahsai]

Have you verified the fuel rail flow rate? Did you send out the injectors for cleaning when you rebuilt the engine? Have you tried using techron/seafoam fuel additives?

 

The coils will be good to replace if they are original anyway.

[Kenneth Behrman]

3 hours ago, Ahsai said:

Have you verified the fuel rail flow rate? Did you send out the injectors for cleaning when you rebuilt the engine? Have you tried using techron/seafoam fuel additives?

 

The coils will be good to replace if they are original anyway.

I did check fuel flow with a bucket when I did the fuel filter.  I don't remember the exact numbers but I could check again when I have it up in the air to do the coils and oil change in a week.  Does anyone have the numbers handy I should be looking for? GPH? I am sure it is in the service manual somewhere as well.

 

I did not send the I injectors out, and I still regret that.. I was considering a leaking fuel injector as a cause of the stuck rich condition, but with how many times I've checked the plugs I think I would have noticed something by now? Maybe not.

 

I ran injector cleaner after the rebuild and then again after last winter storage.  I could try some techron on a fresh tank when it's off the lift and the road salt has washed away a bit.

 

Thanks for the suggestions!

Edited March 20, 2019 by Kenneth Behrman

[Ahsai]

Your LTFT is +10~15% so your engine tends to run lean. Toruq pro is accurate (OBDII) and  LTFT should be equivalent to  FRA from Durametric, which is the fuel trim under load. So either too much air (MAF under-reading the actual air flow) or not enough fuel (low pressure and/or delivery).

 

Since the lean condition is during load (as opposed to idle), MAF and fuel delivery are two major suspects.

 

Try this. Log the intake air temp, MAF (g/s), and rpm using the Torque pro app. A 3.4L engine should get ~213g/s at 6-7k rpm.

 

Any internal mods to the engine such as increased displacement?

 

The fuel flow spec is here 

 

https://www.renntech.org/topic/51800-911-996-cut-out-now-wont-start/?do=findComment&comment=293051

[Ahsai]

BTW, it will give us much more clues if you can read the FRA (fuel trim under load) and TRA (fuel trim at idle) of both banks using Durametric.

The 1123 and 1125 codes are complaining the engine tends to run RICH during idle. You can check the fuel pressure at idle and off idle (per the link I mentioned above).

[Kenneth Behrman]

 

7 hours ago, Ahsai said:

Your LTFT is +10~15% so your engine tends to run lean. Toruq pro is accurate (OBDII) and  LTFT should be equivalent to  FRA from Durametric, which is the fuel trim under load. So either too much air ( MAF under-reading the actual air flow) or not enough fuel (low pressure and/or delivery).

 

Since the lean condition is during load (as opposed to idle), MAF and fuel delivery are two major suspects.

 

Try this. Log the intake air temp, MAF (g/s), and rpm using the Torque pro app. A 3.4L engine should get ~213g/s at 6-7k rpm.

 

Any internal mods to the engine such as increased displacement?

 

The fuel flow spec is here 

 

https://www.renntech.org/topic/51800-911-996-cut-out-now-wont-start/?do=findComment&comment=293051

Thanks Ahsai.  You have provided some good information!

 

I will run a log and check the fuel flow and check back in.

 

There are no internal mods.

 

7 hours ago, Ahsai said:

BTW, it will give us much more clues if you can read the FRA (fuel trim under load) and TRA (fuel trim at idle) of both banks using Durametric.

The 1123 and 1125 codes are complaining the engine tends to run RICH during idle. You can check the fuel pressure at idle and off idle (per the link I mentioned above).

 

Unfortunately I do not have a Durametric, so I will have to wait till my Porsche Tech friend could pull numbers such as these.

 

Fuel pressure was checked and double checked at idle and the car off, both were dead on.  I am not quite sure what I should see when I apply throttle.  Should I see any fluctuation? How much?  I can easily test pressure again.

 

Side thought:

I have read through some articles about different MAFs and DME programming.  Is it true there is an update for the DME that may have been installed which would make the original supply part number MAF incorrect?  Or does this only apply to Egas models?  I do not know which MAF the DME is programmed to be used for, but I have been strictly using the 996.606.123.00 MAF.  I tossed the original so I cannot confirm.

[DBJoe996]

Looks like the correct MAF part number for a 99 C2.  Is it OE Porsche or Bosch OEM or aftermarket?  Our cars are really picky about the correct MAF sensor.

 

Edited March 20, 2019 by DBJoe996

[Kenneth Behrman]

8 minutes ago, DBJoe996 said:

Looks like the correct MAF part number.  Is it OE Porsche or Bosch or aftermarket?  Our cars are really picky about the correct MAF sensor.

 

 This is the MAF I have.  It is a Bosch.  Porsche Part number 996.606.123.00 Bosch Part Number 0280217007.  Some I have seen have additional numbers beyond it like M14 or MS19.  Are these part revisions?

[DBJoe996]

Your DME should be at ME5.2.2 and you can check it out at the time you hook up the Durametric.

[DBJoe996]

The original Porsche MAF sensor is 996-606-123-00-OEM

The Bosch OEM MAF sensor is 996-606-123-00-M14.  I don't know the difference between the M14 and MS19 and I don't think they are revisions.

These are for cars without E-Gas.

[Ahsai]

I believe the M14, or M something is something Pelican parts added so you can ignore those.

 

Good call checking for the correct MAF.

 

Also check the MAF signal should be ~1.1v with key ON engine OFF and about ~1.3v at warm idle.

[DBJoe996]

You mentioned two other things in your first post.  The K&N air filter removal.  Did you get a stock air filter box?

What type of custom muffler bypass?  Fister or Gundo, or something else entirely.

[Kenneth Behrman]

1 hour ago, DBJoe996 said:

Your DME should be at ME5.2.2 and you can check it out at the time you hook up the Durametric.

Will do.

 

1 hour ago, Ahsai said:

I believe the M14, or M something is something Pelican parts added so you can ignore those.

 

Good call checking for the correct MAF.

 

Also check the MAF signal should be ~1.1v with key ON engine OFF and about ~1.3v at warm idle.

I have checked voltage and the MAF signal.  All appears normal.  If I recall my G/s on the Maf at idle was within spec as well.

 

51 minutes ago, DBJoe996 said:

You mentioned two other things in your first post.  The K&N air filter removal.  Did you get a stock air filter box?

What type of custom muffler bypass?  Fister or Gundo, or something else entirely.

 

I did install a factory air filter box.  This made any stalling issues I had go away completely.  With the K&N installed, I did not have any additional codes, but after going WOT, or sustained highway driving (cruising around 3-4K) for 15+ mins, if I put the clutch in the car would stall.  I could keep it alive with a couple blips of the throttle, but sometimes even this would be difficult.  Like an idle was non existent.  It also didn't always start right back up great.  It would take time for it to settle back out, assisting with some throttle.  That problem seems to be resolved. This is where the IACV, TPS, throttle body cleaning, thorough vaccuum leak searches came in.  All seemed to help, but not resolve the issue completely until the K&N was removed.

 

I did the Fister Mod.

 

Thanks guys!

Edited March 20, 2019 by Kenneth Behrman

[Kenneth Behrman]

Hey Guys,

 

Just giving a quick update.

 

My Porsche tech friend took the car for a week and really found nothing out of the ordinary except the rich condition at idle and lean condition at WOT.  He didn't have much time to dig deeply but we had quite a few conversations about it.  My timing was normal and I was not recording any misfires.  I am however, truly running rich at idle and lean at WOT based on trims and O2 feedback.  These conditions explain the issues I am experiencing.

 

Here is what I have found based on some previous post recommendations to check.

 

Coils have been replaced.  No change, maybe a little smoother acceleration, but nothing major.  Gas Cap and Oil Cap also replaced for good measure.

 

My MAF readings at idle when hot = 5.7 g/s with very little variance.  (My friend is checking on the factory spec)

 

I logged my MAF readings up to 7k when hot, and found that the MAX reading I got from the MAF was about 185 g/s.  This seems low.  Someone stated I should be seeing 213 g/s or so.

 

I am currently trying to figure out how to create a sensor in Torque Pro to read MAF voltage, but I am not quite there yet.  If anyone knows the correct configuration for the OBD2 PID editor to read MAF voltage, that would be great.  I used some number from a different car I found on a forum to no avail.

 

Looking at the data, the car is acting like it has a vacuum leak under WOT, and is maybe ingesting extra fuel at idle.  Could a potential cause be a failing EVAP system?  Is it possible that a check valve has failed and the car is sucking extra fuel from the EVAP system at idle, and then acting like a vacuum leak at WOT, hence the low MAF reading.  If I remove and cap the inlet from the purge valve into the throttle body could this prove the theory?

 

Any thoughts are welcome.

 

 

[Ahsai]

MAF voltage is not available to OBDII. At idle (~700rpm) fully warmed up with a/c off, your MAF should read about 4g/s. If it's reading 5.7g/s under this condition, definitely something wrong with your MAF. Are you sure the MAF and airbox are from a 3.4L engine?

[Kenneth Behrman]

1 hour ago, Ahsai said:

MAF voltage is not available to OBDII. At idle (~700rpm) fully warmed up with a/c off, your MAF should read about 4g/s. If it's reading 5.7g/s under this condition, definitely something wrong with your MAF. Are you sure the MAF and airbox are from a 3.4L engine?

I am positive the airbox is from a 3.4L and I confirmed the MAF part number, same as previously written in posts above.  My idle is steady at 700rpms.

 

I will run the other MAF I have tomorrow and confirm that I pull the same numbers.

 

Side note: I disconnected the purge valve and plugged the intake port, but not change in MAF numbers or performance so that theory can be ignored.

[Ahsai]

You really need Durametric to further diagnose your issues.

[Kenneth Behrman]

Unfortunately, I agree.  I may have to wait until I can bring it back to the dealership and we have additional time on a Saturday or something to truly dig into the issues.

 

I am still concerned there is some sort of tune or modification to the MAF calibration that is interpreting the signal differently then it should be.

 

When I purchased the roller, the previous owner supplied a MAF that was not a factory part and called it a "performance MAF".  Again there were alot of running issues I worked through in the beginning,  most of which have been solved, but that comment he made sticks in my mind.  I threw out that MAF, which I feel was a mistake now.  IIRC, the rich condition at idle went away with that MAF (No CEL at least) but the car was significantly down on power and had serious stalling issues.  So I tossed it...

Edited May 7, 2019 by Kenneth Behrman

[dwtaylorpdx]

Been a while, but you might bench test the throttle position sensor, they wear and can get weak spots that the DME doesnt like.

 

 

[Kenneth Behrman]

Hey I figured I would give an update since it always bothers me to see a long thread with no solution.

 

I completed the coils and new plugs, checked again for vaccuum leaks.  Then went out and took some logs.

 

The MAF was reading 5.7 g/s at idle, at 7k it maxed out about 180 g/s.  I ran logs a couple times and found the same result over and over again.   Fuel trims showing rich at idle, lean at high rpms.  I found the specs on the MAF readings and at idle it should be near 4 g/s and WOT at 7k Should be near 215 g/s.  Knowing that these are the nominal values, if the car is pulling proper airflow and reading the numbers I posted above it perfectly explains both the rich and lean conditions.

 

So.  I called my friend at the Porsche dealership again, asked him to find me a known good MAF so I could try it.  He gave me two, both pulled from running 986/996 matching my required part numbers.  The first one dropped the idle reading to 5.2 g/s and maxed out at 195 g/s, car pulled well, but it did trigger a CEL after a couple days.  Switched to the other one and BINGO!  4.1 g/s at warm idle, 213 g/s at 7k WOT.  NO CEL with 1000+ miles.

 

Frankly  I am beside my self.  That is 2 DOA MAFs and just seeing the variation between two known good MAFs is crazy.  Although there is a large amount of information trying to prove that K&Ns do not damage MAFs, I have a feeling that may have caused my 2 new MAFs to operate incorrectly since day one.

 

Anyway.

 

Check your MAFs.  and then check again.  Torque app helped out big time to see the changes.

[dwtaylorpdx]

They really really don't like being dropped,, had a similar experience with Mustang MAF sensors,, 4 to get a good one..

I noticed the counter guys would throw anything that a customer didn't buy into a shopping cart from about 20 feet away.. Hmmmm.

Changes stores and no more issues..