How to diagnose and resolve engine issues using Durametric.
 

I recently had an AOS failure and proceeded to replace the AOS.
After the replacement the engine idles poorly and has hesitation at various throttle settings it seems.
I cleaned the TB and got the new MAF installed and it seems a lot better and it has not thrown any codes yet but it has this odd hesitation.

I would be cruising at 4000 rpm and 50 mph with steady pressure on the throttle pedal and I can suddenly feel a hesitation and small loss of power for a second and then it carries on again with regular power for about 5 seconds(random interval actually) and then has this hesitation again.

Also when punching throttle it revs right up and at over 5k revs it hesitates momentarily.
It does idle fine, and I have reset the computer and done the DME adaptation thing with the ignition on for 1 minute and then off etc.

I did get a few P0507 codes the Idle Air control Valve but since the new MAF install have not gotten that or any other codes.

Seem now like the issue is with higher rev range.
I do have some suction at the oil cap but its not at all strong and the cap come off easy so I don't think its an AOS issue anymore.
I have tried but can not detect any vacuum leaks using TB cleaner spray around hoses.
The gas cap rubber ring does look like its a little cracked so I plan to change that as well since anything vacuum related is the only thing I can think of at this point.
It throws no codes since the new MAF is in place but I suspect a vacuum leak or something else perhaps, although I have not found it yet.

I decided i just dont want to blindly start replacing things and needed to determine how to figure out the problem and fix the actual cause of the problem.

After a bit of online sleuthing I found a series of excellent videos that explains how to use your Diagnostic tools like an ODBII reader or Durametic and determine the nature of your problem without replacing or testing unnecessary components.

I have a Durametric and now know how to use it to figure out what is going on.

Watch these videos and you will be able to save yourself a lot of time and cost and be able to verify repairs done by yourself or the shop.

The first 2 are about learning how the Fuel Trims work and what you can diagnose with them. Fuel Trims Part 1 Fuel Trims Part 2

The 3rd video takes a scenario from start to finish describing the technique to diagnose and verify resolution of an engine problem. Practical engine problem solving Part1 PEPS Part 2

I will do likewise this weekend with my own issues and document how I determined what the problem actually is and verify its resolution.

Wish me luck.

hah! i like this guy.

"if we have these conditions, and you put an oxygen sensor in the car to fix it - you're an idiot."

I hope you can find the problem. I've had the same problem for over a year and can't figure it out.

I am experiencing a similar problem but it is intermittent....and random at hwy cruising speeds...no cel.

Soooo it feels almost like bad fuel.....so I will be changing the fuel filter. Not sure if the injector rail pressures are avail via OBD....could log them. Would one see anything
meaningful there ?

Let us know what you find

Thanks for the link. Really interesting videos! This guy does a great job of explaining a very technical diagnostic tool.:)

Check the MAF ground. I have a similar problem and last time we find out ground signal was spiking. Sometime signal is good, engine running strait. Sometime signal spike and engine have a thought idle or it hesitate. We have to check three things ( we know MAF is good)
1- MAF plug look in pour shape, might have bad contact
2- ground wire, make sure no short circuit
3-ECU might be going bad

You may want to look at that.

Good luck
Chris

This problem started happening after replacing the AOS? I would double check all the hose connections to the throttle body and the three hoses to the AOS. Those hose connections take some effort to properly seat/lock-in.

This may sound crazy but how's the flow out of your exhaust? Many years ago I had a clogged CAT on a car and it would build too much back pressure. Otherwise you may need to have in indie shop connect their computer to self test various components.

Chris

Found some free online Porsche workshop manuals
http://workshop-manuals.com/porsche/

I'll be compiling my results and putting together an explanation, but in short for now I found that the RKAT fuel trim was elevated, indicating that the computer is adding extra fuel to compensate for a lean condition, which could be caused by:

- Intake air leak
- low fuel pressure
- exhaust manifold air leak

since the car was running fine prior to my AOS issue it was most likely to be the intake air leak so I loosened and retightened all the intake tube clamps and removed and reattached the upper AOS to intake tube.

the value of RKAT is reduced slightly but the car seems to be running fine, so i'll drive it this week and see if anything further develops.

in the mean time I ordered new fuel cap, spark plugs and fuel filter as these items are due at 70k miles and can only improve the current situation.

more to follow as things progress this week.

Got a new Fuel filter, Gas cap, Oil cap rubber seal and spark plugs to install.

I still feel its a vacuum leak so I'll probably recheck the new AOS install for leaks.

I have this feeling that when I removed the part of the AOS that sticks into the engine block the rubber seal from the old one did not come out on the spigot so when I installed the new one perhaps it did not seal properly.

I will pull the new one and get the inspection camera in there so I can see if that is the issue, as I'm not sure what the old one had on the spigot for a seal, but its reasonable to assume something like the new one has, which was missing when I pulled the old one.

After Replacing AOS, and a new MAF there is still a random hesitation on acceleration.

Here are some graphs of
1) FRA RKAT fuel trims, 2) RPM, 3) MAF
Seems to show a need for a bit extra fuel (lean) but nothing drastic and nothing that would indicate a serious vacuum leak. Blue line does spike every now and then, wonder if thats normal.
https://lh5.googleusercontent.com/-5...1200/test1.jpg

After replacing plugs and fuel filter, some improvement but not cured.
Showing a need to reduce fuel trim (rich) a bit, perhaps the replaced fuel filter is allowing the extra fuel now.
https://lh3.googleusercontent.com/-Z...1200/test2.jpg

Another trace after cleaning the throttle body actuator (E-gas) Seems to work same as before. Seems even more balanced than before. Not Likely a vacuum leak
as it would cause the line to be much higher on the + side above +10 (+ indicates Lean condition being compensated for -5 +5 is very normal from what I have read)
https://lh5.googleusercontent.com/-4...1200/test3.JPG

After checking fuel pressure, flow rate and smoke test to check for vacuum leaks. No Leaks, pressure and flow to specs.
https://lh4.googleusercontent.com/-t...0/raytest4.jpg

The hesitation does not necessarily occur where the blue yellow lines spike. Not sure what those are.

I think the next place to look may be fuel pressure.
I'm thinking that the pressure regulator may not be responding properly and causing a hesitation.

Perhaps the thin vacuum line controlling the pressure regulator is leaking.

Go man go!!!
 

Just a few words of encouragement to keep going and thanks for the continued postings. I've got a durametric but know very little about how to use it. Learning more and more thanks to posts like yours. Thank You!

If you are not throwing any codes, and the drive ability problems are at the upper rev range, I would look at the fuel delivery system. Check the fuel pressure and volume delivery of the pump.

Thanks for the words of encouragement XCELLR8.

Its nice having the tools (Durametric) but if you dont know how to interpret the data your not getting maximum bang out of it.

I bought a couple cigars last evening for my DIY smoke machine for vacuum leak detection. That should be amusing and of course a video will follow with the results.

I'll be getting a Fuel pressure gauge this evening and have read how to measure flow rate....so many liters per minute although I forget the exact number but will document it here when I do the test. (No codes yet)

update- I discoved that Autozone Loans equipment, no charge, so I brought home a nice expensive fuel pressure test gauge for my weekend pressure test...nice surprise.

The car is at 74K miles so replacing a few parts was due anyway so it wasn't unexpected. However the failed AOS precipitated this issue which I find rather odd, so I am expecting to see some vacuum leaks in that area and would make a lot of sense.

Not really expecting a fuel pressure issue but since its easy to check I might as well do it.

I did read something about the Fuel injector rail port where the pressure guage would connect to and wondered if a new washer was necessary when replacing the cap? I read that its a Schroeder valve ?

It is a metric Schrader valve, and the cap with washer is supposed to be replaced each time, but you can usually get away with taking it off once or twice before it starts to leak. Caps are cheap.

Fuel pressure is good at idle 45 psi vs spec 47 psi
Beyond idle 57 psi vs 55 psi spec

I measured fuel flow at 3 locations.

just before fuel filter 1650 ml per 30 second s.
at fuel rail schreader valve 350 ml per 30 sec
At fuel return 825ml per 30 sec vs spec 850ml per 30

I also did the smoke testing and found no vacuum leaks except a very minor one at the intake variable length intake tuning flap bearing. Its in the second intake manifold crossover.

Smoke Tester config that worked: Old paint can with a scrap rag soaked in baby oil, crumpled up and lit on fire. Air compressor line into can at 3-5 psi and a line out near the top of the can.
Turn on air compressor, light the rag on fire and close the paint can lid. I also threw the cigar in there for good measure since the cigar only method did not work for me.
It then produce lots of smoke for a couple minutes before you have to relight it. I had to relight a couple times to be fully satisfied that the system was completely smoked through.
I put a plastic bag around the air filter and reinstalled it to effectively seal the intake system. I removed the MAF since you don't want to foul it with smoke residue and I used the MAF opening to introduce the smoke till it exited the oil cap, which I then closed and looked for smoke leaks.
Then I did the test again but this time with the smoke being injected at the oil fill until exiting the MAF opening and then I sealed the MAF opening and checked for leaks.

So no Vacuum leaks is the verdict on that.

The test drive did not exhibit the hesitation this time but seems to run a bit milder with less aggressive more normal acceleration than previous test drives.

Perhaps the computer is relearning and fine tuning the curves?

I wonder what the odds are that the DME computer is having issues or gone bad?
Do those fail often?

The last Test drive and fiddling introduced new codes P1128, P1130,MAF code, fuel relay. Probably due to my fuel pressure tests as I pulled the fuel pump relay and cranked the engine over to release all residual fuel pressure before doing the fuel flow and pressure tests.

I'll reset all the codes by disconnecting the battery, redo the throttle adaptation and start with a clean slate to see what materializes now that it seems to be running somewhat better.

While I was under the car I did notice some burnt oil residue on the pre Cat O2 sensors on both sides. It looks like it was from the AOS failure as it was not there prior to the event.

My car did pass about 2 quarts of oil during the AOS failure so I'm thinking it could have fouled the O2 sensors and plugged catalytic converters but I am not seeing any codes to indicate that either have failed.

The Durametric trace that I got from the O2 sensors this weekend to see what was going on made little sense as the lines were wandering everywhere.

I was looking for a sine wave on the pre cat sensors and a nearly straight line on the post cat Sensors but got a little bit of everything all mixed together.

It made me think that perhaps I was not getting enough samples per second from the Durametric to see the proper wave form.

I think I need to pull the precat sensors next to inspect them and use my inspection scope to look inside the cats to see if I can see whats going on.

The front side of the exhaust manifold cats look good, no heavy deposits.
http://lh6.googleusercontent.com/-QA...245%280%29.jpg

Update.

I replaced the pre CAT O2 sensors and there is no improvement.

I looked inside the CATs with an inspection camera while replacing the O2 sensors and the CATs did not look fouled or damaged in any way.
I also looked at the pistons when replacing the spark plugs and could not make out clearly or understand what I was looking at but it sortof
looked like heavy deposits and the cratered surface of the moon.
Unfortunately the camera would not fit down the spark plug hole so I'm skeptical of what I thought I saw.
Anyone have a reference of what a ~70K mile piston would look like?

I have ruled out:
- Fuel Filter (Replaced)
- Fuel Pressure (Tested OK)
- Fuel Flow (Tested OK)
- Pre CAT O2 sensors (Replaced)
- Air Leaks (Smoke Tested)
- AOS (Replaced)
- Spark Plugs (Replaced)
- Oil cap seal (Replaced)
- Gas cap (Replaced)

I'm still getting the codes 1128, 1130 consistently and sometimes 0507

All the symptoms still point back to the MAF since when I disconnect it the car idles and seems to run normal, although I have not road tested it without MAF.

I returned my new MAF to Pelican and will try another one to see if somehow I got a bad one.

I pray its the MAF because I'm running out of ideas of what it could be.

I considered a bad or intermittent ground or dirty connection but the hesitation happens consistently so a loose connection would be more random I would think.

I had also considered removing the new AOS and reinstalling just in case the port to the engine block is somehow obstructed or to see if the bellows has a tear, although I would have thought that would show up with the smoke test.

Update

Got the replacement MAF sensor from Pelican but attempting to start the car revealed a dead battery showing 10.9 volts, not enough to start the car.

Once a lead acid battery has died there is usually little chance of it being reliable after that so I simply replaced it without trying to revive it.

With the new MAF in place the same issues are still present. However the P1128 and P1130 codes have not come back.

and the RKAT is up around 4.5 which makes me think perhaps there might be an air leak after all.

[Graph place holder]

Wandering Idle, and a random hesitation.
Only codes P0507, P1571 and P0102 now.

However with the car idling in the driveway for some time while I'm looking at various Durametric parameters being graphed
the idle suddenly goes back to normal and the car seems not to exhibit any symptoms anymore.

I take it for a test drive and everything is back to normal.

I shut down, then start up again and its still fine.

WTF ????

Perhaps a bad ground like Wawa suggested?

Maybe those little random FRA spikes are indicating a wiring problem.

I hate these kind of problems, a pain to debug, and if you don't find the issue you can never really trust it to be reliable.

I'll have to start wiggling wires to see if that might be the issue.

Maybe the DME hit it's learning time set and brought the car back to the original programing. Not sure of the time frames for each or all the adjustments. Have had problems that were corrected during an extended test drive as the computer learns and adjusts the cars program.

I'll try putting some miles on it and see what happens. My new Triple A card just arrived, it must be a sign from the Porsche Gods to just go for it! :D

Just a Thought
 

Hi Guys
I just came across this and thought,are these fly by wire gas pedals,ie: No throttle cable,if so maybe it's something to do with the operation of that,connection,wear etc as it is in a position that gets dirty and used all the time,and just thinking that there are mods available to plug into electronic gas pedals to increase response so maybe that's a possibility

Hi

I dont have my 986 anymore, sold it for a brand new 981. But related to the egaz, my mechanic had change the tb to check for faulty egaz, but no change. But your problem really look like mine. You have done about everything
Il had try. I really hope you'll find out whats wrong.

Later

Wawa

I did take apart the Throttle plate actuator and spray electronic contact cleaner on the wipers and there was no change.

I think I'll take the car for a spin tonight and go get some fresh fuel.

I can start driving it to work and see if the situation improves with the new battery and the computer relearning after resetting everything.

As I mentioned I was idling in the driveway looking at the Durametric data on the laptop when suddenly it started running consistent again. Perhaps the DME made a correction?

If it was the egas I would think that the problem would be consistent and not wandering idle and then suddently steady again.

However, problems do love to hide right under your nose in the most unexpected places and often the last thing you think it could be is precisely what it is.

Update -

So since the last time the car shut down it was running perfectly.

I startup and everything runs perfect still, so I go to the gas station and fill the tank.

Upon restarting, it quickly stalls and then I try again and it starts but now its running horrible again with the wandering idle and hessitation when accelerating and just coasting along. No check engine lights and probably the same codes as before but I will check tonight.

I get a block from home at a light and it stalls.

My first attempt to restart and I get nothing when I turn the key, no clicks or starter turning...nothing.
Then I take a breath, wait a couple seconds and try again and it starts and runs perfectly again all the way home.

WTF is going on :confused: I'm in the pulling hair out realm now....damm F$%#@!*&^%$#%)%##

Any suggestions, I'm running out of ideas, or do I just give up and take it to an Indie at this point and hope they can figure it out?
Anyone know of an excellent shop that does Boxster work in my area?

Is my computer going bad? Is there a way to test it?

Trying to apply logic which never seems to work with car problems like this: :(

The Facts:
Car runs perfectly at times and then suddenly it runs like crap with wandering idle, hesitation on acceleration, stalling at idle.
It seems that after it stalls and restarts it could go either way running good or crap again.

No Engine light is triggered.
Codes thrown are; P0102 MAF Low Input (connections/supply?),
P0507 Idle Speed too high (Wandering idle?).
P1571 Immobilizer - Open Circuit / No Signal

Since its my second new MAF I think I can rule out a faulty MAF as the source of the problem,

A faulty ground on the MAF or electrical is still a possibility but a low probability based on common issues I read here. Also I drive over some pretty bumpy roads and the faults do NOT correspond with vibrations making/breaking electrical conductivity so I'll rule that out as well for now.

Replaced AOS which had died and perhaps precipitated these issues?

Replaced Pre CAT sensors but no change there.

New Spark plugs and Coils look good and would be causing missfires if damaged and I am not getting misfires so cross the ignition section off the list.

New Fuel Filter, Checked Fuel pressure in the shop but not while driving and experiencing the hessitation so Fuel Pump is still a possibility.
The Fuel Pump relay can also be added to the potentials list since it is related.
Fuel flow is also good in the garage so that eliminates obstructed fuel lines and filters.

New Air Filter, better check the duct work for any obstructions just in case.
I have heard that turbulence at the MAF can cause problems and is why EVO intake folks sometimes experience MAF problems.

The battery had died while in the garage so it might have been weak, but its replaced now.

The computer ECU seems to work fine in every respect and the car still starts so the Computer is not fried,
however cold solder joints in the computer or loose ground connections to sensors is still possible but a low probability.
I did jiggle all the connectors leading into it and no changes were evident.

Vacuum leaks and smoke testing did not reveal any obvious leaks but that does not mean there is not a crack that could open up under real driving conditions and pressure, however nothing blatant was revealed as it was smoked from the intake side and through the Oil filler side with no leaks showing up under a few psi of pressure.

The only high probability items I can think of is the Fuel Pump and Ignition switch as many folks have done it from what I have read.

Those items don't seem to be monitored by any fault codes either so perhaps those should be my next efforts.

I have read that ignition switches going bad can produce all manner of strange issues but have absolutely no evidence or history pointing to the switch as suspect.

I have found a diagram showing the MAF pin-outs so I think I'll check that before buying more parts just in case its a faulty sensor ground connection or an out of spec supply voltage.

http://986forum.com/forums/uploads01...1406146366.jpg

Looks like I'll have my 90,000 (Its only 72k on my odometer) mile service done by the time I replace all the wear and tear parts !
Should be good for another 10 years if the engine holds out.

I had change the fuel pump without any change. I had been told it usualy is not faulty, but I didnt want to take the chance.

You could try passing a second ground wire and run it for a time to see if it still happen?

Later

Wawa

Being that it is intermittent and seems to be all or nothing, working as normal or running bad, its hard to imagine a fuel pump failing in that way, unless there is an obstruction in the tank.

Perhaps its worth a look at least as I have heard of one fuel pump that broke free from its brackets and was hanging loosely in the tank by its hoses.

You never know if someone has shoved a plastic bag up the fuel noozle so the next person pumping gas gets it in his fuel tank.

The saga continues and I'm near the point of giving up and taking it to an indy and letting them try.

I read some stuff about testing the MAF for a bad ground so yesterday I was fiddling with the MAF and trying to get my
multimeter hooked up so I could test the ground in situ.

I used sewing pins in the top of the MAF harness to make the connections but something slipped and the
MAF ground pin touched (shorted) the Supply 12v pin.

I heard the throttle plate make a hard smack at the same time and feared I damaged something
with the momentary short.

I then started the car and the Egas throttle was unresponsive, although the car started and idled.

I checked all the fuses and they all seemed fine.

I reset the computer disconnecting the battery, no luck, still no gas pedal response.

I checked the codes and the Egas Potentiometer codes are now present with implausible reading,
as well as the throttle position sensor codes and the MAF code that was there before.

I hope I did not fry something.

I took the throttle body apart and looked at the potentiometer and it looks fine and does not smell burnt.

I'll need to find the Egas potentiometers next and see if they look OK.

I hope the ECU is ok, as the car runs and otherwise functions properly.
Just no gas pedal response.

I wonder if the ECU has its own fuses?

It still acts like the ground is bad for the MAF so I read that the C9 pin at the ECU is the MAF ground
so will check that as well.


I found these helpful but I need to add a DSO scope to my toolkit.
https://www.youtube.com/channel/UCrf6f8hn5oy4alB2WXJCIqA

Ordered a working Throttle body and Pedal module from a dismantler.

Hopefully that will fix my "Mistake/Accident" issue.

If not then I'll have to take a look at the ECU to see if it got damaged.

I also bought an ECU, Immobilizer, Ignition/key assembly matched set in case i need to try the ECU replacement, only $265 delivered for all 3 for my exact model year 2001 S.

I also discovered/read about another set of high amp (60A+) fuses hidden away in the car but I doubt these have anything to do with my problem.

I'll try the Throttle body first, then the pedal, ECU is a last resort.

Update -

I tried swaping out the Throttle Body and the E-gas pedal potentiometer/sensor and still no luck.

The car starts and idles ok but does not respond at all to the gas pedal.

It just seems like there must be a fuse somewhere thats blown but all the fuses look good except the drivers seat adjustment, which has an issue that I know about.

I also found some more relays and fuses in the trunk but the fuse there looks fine as well.

I also disconnected the ECU in the trunk and used contact cleaner on the pins.

I took the ECU apart and nothing looks burned or fried. Solder joints look good.
I was surprised the ECU is not even a sealed unit, and looks cheap. Any moisture in the trunk would be a bad thing for sure.

As a last resort I have a matched used ECU/DME/Ignition assembly for a 2001 S same as mine, so I'll give that swap a try and keep my fingers crossed.

If no luck then I need to find a very talented Indy with the right skills and tools to figure this out.

Still the same codes for the egas potentiometer, Throttle Body and MAF but those are symptoms, not the root cause, as my swaps have proven.

No Check engine light suprisingly.

Wow- just read the whole thread. It's been a while-- have you taken it to a pro???? If not keep up the good fight! Either way I appreciate that you've detailed your efforts...

This weekend I will replace the stock ECU, Immobilizer and ignition assembly with the matched set I got from a dismanteler.

Wish me luck!

If that option fails then I need to talk to a good indy with the diagnostic tools and experience to figure out what is going on, as I have replaced a lot of stuff already, all the typical suspect things.

Im having Boxster driving withdrawl symptoms too so I need this resolved soon.

Wow is right.

Try the new DME and if you don't get results it is probably time to take it in. Document your path so they know where you have been and why. Black Forest in SD might be the best for diagnosing phantom issues like this. Good luck Ray!

This thread is probably a pretty good account of all the things I've tried, and I have become intimate the car inside and out. I'm hoping its the DME system and that I'll have a bunch of spares afterwards.

I was also thinking that Black Forest might be able to sleuth this issue, if it comes to that, so thanks for your suggestion.

I figure that at 72k miles its just as well that a bunch of things get replaced anyway so its not a waste in any case.

Fortunately my mindset with the Boxster was a fun Project Sports car/racer, 2ndary transportation and expected a few bumps in the road on a lucky 13 year old car.

Like I always say, every broken part is an upgrade opportunity :D
, but you have to be able to determine which part is broken first :eek:

Finally some positive results.

Today I put in the ECU, Immobilizer and ignition module set that I got from the dismantler.

I swapped the matched set key RFID chip into my key as they all have to match to work, but the key is cut for my door and ignition, hence the swap of RFID chip and transmitter from the dismanteler key into my original unit.

So I got it all hooked up crossed my fingers, reconnected the battery and turned the key to ON and let it do the 1 minute adaptation process without touching the egas pedal. Then off for 10 seconds and START.

The engine started right up and settled into a nice idle. The gas pedal was responding and reving the engine....hurray!!!!
It was not acting funny at all, the idle was steady and normal.

Tomorrow I will test drive it to verify its all working normal again and check for thrown codes.

Now the only issue I am seeing is the airbag light and the doors will not lock.
I click the remote to lock and I can hear the doors lock, and then they click again and unlock.

I used the key to lock the driver side door which works but the passenger side will not lock, and then I found out that the passenger door does not have a key opening. Hmmmm never noticed that before.

Since the donor cars ECU, Immobilizer were from a car that was in an accident and the front air bags deployed I figured I may have to reset something to get rid of the airbag light.
I figure that the computer also makes sure the doors remain unlocked in an accident when the bags deploy so its probably related.

Well done......
A lot of us would have given up long ago and taken it to the OPC for evaluation and fix.
You now deserve a cold beer (or two)!!

Ooooh great post!

Congratulations..! Like the saying goes;

Persistence drops panties.. :-)

.

On to the Test drive.

It now runs better than ever, with all the new plugs, O2 sensors etc.

Test Drive was flawless.

I cleared the airbag error codes with the Durametric.
It had a voltage to unit error and a seat belt system error.
I'm assuming those were stored from the Donor Boxsters crash.
Looks like it hit a pole head on from the pictures.
No more Airbag light once those codes were cleared.

The only remaining issue is not being able to lock the doors.

I'll do some google searching and see what turns up on that issue.

May have to visit the dealer or indy with a piwis system to reset or enable something in the security system.

Every thing else works normal.

The one thing that bothers me is WHY my computer died?

Just a coincidence or did something short out in the process of replacing my AOS which was the beginning of all my trouble.