bldn10

I have a 997.1 3.8 X-51 (Power Kit) engine w/ Softronic tune in my Farnbacher Loles-built 987.1 w/ around 62000 miles on the engine. I have been tracking it for 5 years and drive it hard. I just got back from a D.E. last weekend and it ran perfectly. This morning on the highway I was thinking to myself how it purred like a kitten, then I slowed to make a turn and - what? - a miss. Several. I took it out and got on it and could not perceive a miss but there may have been one that was not evident at high rpm. It is missing at idle and most obvious at low speed but also cruising at 70. No CEL or codes. I hooked a code checker up and the idle varies from 750ish down to 650ish; I guess that's the miss - a 100 rpm drop. Do fuel trims tell me anything? All plugs and insulators and 1 coilpack were replaced around 26,000 miles ago due to persistent cyl. 1 misfire.

What is the most likely cause of this miss? Thanks,

DC911S

Bad gas? Fuel filter a bit clogged? Is your TB due for a cleaning? Lots of variables

bldn10

The gas is the rest of the tank that ran fine at Putnam. There is no serviceable fuel filter on the Cayman, a lifetime item.

Yesterday I removed and cleaned the entire intake from the filter to TB, the MAF, and TB. None looked overly dirty. Still missing and now I have a Cyl. 1 Misfire code.

ChicagoSpeed996

Look at what the computer is telling you. Cylinder one is having an issue. Multiple components to look at, coil and plugs (already changed, but the coil could have failed again), fuel injector on cylinder one, cylinder of cylinder 1, valve train issue with lifters, intake vacuum leak at cylinder one.

Check those first.

bldn10

Chapter 1 The shop replaced all the coils and plugs and the guy drove it around and declared it awesome. Except it was making an odd, never-before-heard sound from the intake.

Chapter 2 I opened it up and the 9-year old after-market venturi was cracked at the flange and I think the rubber filter was acting like a reed. Changed the flange. I then test drove it and got on it and had a big hesitation, it caught, and then started cutting out badly. I pulled to the side and let it idle a bit, revved it up, and it sounded OK. Got on it again a few times and it seemed OK.

Chapter 3 So, I took it to Bowling Green and it was fine the first 2 sessions. A few laps into the 3rd it started cutting out again. Parked it, unhooked the battery overnight, still cutting out. I have an OBD dongle and app it is was showing that the A/F was going way lean when it was cutting out. LT Fuel Trim 98%, ST 25%. My thought was that it was not getting enough fuel. No codes.

Chapter 4 Straight to the shop. He is saying it might be MAF. I don't know what, if any, tests he has done.

Can I have a bad MAF w/o any codes? FWIW I recently cleaned it. What tests should be done before I go and buy one?

bldn10

Chapter 5 I replaced the MAF sensor and it ran good at NOLA, Hallett, and a test day at Memphis. Out of the blue on 12/3 I get errors for lean in both banks. I cleared it and a few miles later they came back along w/ random and every cyl. but 1 misfires. Cleared them out again and drove about 50 miles in town over several days. Then came back again. I cleaned the air filter and MAF sensor and cleared the codes. Drove about 25 miles and then had random and cyl. 4-6 misfire and pending lean code. Idle is wandering - I can be driving down the street, put it N and coast, and it will drop to 1100 then move up to 1900 then wander between 1100 and 1900. Yesterday I cleared the codes and drove about 150 highway miles and no CEL although still have the wandering idle.
Some OBDII data:
Idle 790 rpm 2000 rpm
MAF .53 1.33
O21 no signal ? (not getting code for O2)
O22 .6 to .75 .06 to .75
Timing 6 to 11 42 to 45
A/F 14.6 to 14.7 14.5 to 14.7 (obviously, going lean is sporadic)
STFT1 -4.7 to .023 .8 to 10.2
STFT2 -.8 to -3.1 -2.3 to .8
LTFT1 99.2 99.2
LTFT2 99.2 99.2

Going to Sebring 2/1 so I'd like to get this figured out if it is a serious matter.

996AE

Fuel Injector on cyn 1.

Swap them for easy check.

bldn10

Why 1? I may not have been clear, I have gotten misfire codes for ALL cylinders at one time or another.

bhvrdr

You said you had a chronic cyl1 misfire and the mechanic put in plugs and packs.

Then you just had another episode of cyl1 misfires recently.

And then you have misfires in all cylinders except cyl 1.


This still all points to cyl1. I'm wondering if you have a cyl1 injector that was starting to fail open and it was cauising rich misfires on cyl1. Lets say it finally fails and turns into a stuck open injector on cyl 1 perhaps causing the o2 sensor to read rich and cut back fuel causing all the other cylinders now to run lean and misfire. Just a guess.

Mike

Bruce In Philly

You need a better tool to see what is going on in there. A Durametric tracking live values, ignitions and such, should help you spot it. One of your track friends should have one.

Peace
Bruce in Philly

alexb76

Hey, you have done everything but look at your tune?! What if the Softronic chip is not handling the track back to street setup, it looks like you have a good track day or session, then something goes off. I'd try to switch back to OEM ECU (if you can), and see if that improves anything.

I don't have any experience with chipping Porsches, but with my VW and Audi, done a ton of chip tuning and literally every single tune had one issue or another... they're never perfect.

bldn10

I'm taking it to my indy shop next week to get it checked on a Durametric.

The other day I went back in and really looked over the intake run and saw one junction that looked questionable. Hose was askew on metal elbow and I thought it might be leaking at the bottom where I could not see it. I loosened it and made sure it was on all the way around. It sat a few days and I just now went to start it up and, wow, WTF! It starts right up but goes like WOT and promptly dies. Tried 3 times w/ same result. Now what? I'm trying to warm it up w/ a space heater and will retry later.
Edited:Let it warm up a bit and then tried starting it again. Same thing but I tried to keep it going by feathering the throttle but then it started backfiring so I quit. I guess I'll have to flatbed it to the shop.

bldn10

The problem w/ the runaway throttle turned out to be a split in the line from the AOS to throttle body. Lots of unmetered air!

But after they fixed that I am now getting an ugly noise between 2800 and 3200 rpm when under load. Engine seems to be running fine except for the noise. If it is just in that rpm range it would not be internal, right? It seems to be coming from under the plenum in the location of the AOS. I'm wondering if it is the AOS although I'm not getting plumes of smoke. Here is a video w/ audio of the noise. You can hear it coming and going as I speed up and slow down.

DC911S

bldn10

That shop gave up on it and I took it to a race shop this morning. Unfortunately, what was just a bad noise turned into a flashing CEL, misfire codes, and very obvious misfires. I was lucky to get it to the shop. I'm afraid it may be more serious than I thought.