Progressively worsening misfiring
Three Wheelin'
Joined: Nov 2005
Posts: 1,250
Likes: 44
From: Bahrain = somewhere in the Middle East
FPR vacuum line can be checked faster than I can type this message.
If you have skinny hands (or kids).
Just pull it off at the bottom (the FPR end) and feel if it gets wet at the bottom of line. If so, the FPR is shot and should be replaced.
If not, just plug the line back on and move on to the next point to check.
AFM contacts perhaps or head temp and knock sensors could be acting up too.
If you have a diagnostic tool you should be able to read the sensor values and determine from that.
No expert, but done my chasing rough running issues a few times. Last time was oil in TB and all the way up to ISV and AFM... And I thought it was no issue with a minor overfill.
Good luck chasing.
If you have skinny hands (or kids).
Just pull it off at the bottom (the FPR end) and feel if it gets wet at the bottom of line. If so, the FPR is shot and should be replaced.
If not, just plug the line back on and move on to the next point to check.
AFM contacts perhaps or head temp and knock sensors could be acting up too.
If you have a diagnostic tool you should be able to read the sensor values and determine from that.
No expert, but done my chasing rough running issues a few times. Last time was oil in TB and all the way up to ISV and AFM... And I thought it was no issue with a minor overfill.
Good luck chasing.
Thread Starter
Advanced
Joined: Feb 2008
Posts: 54
Likes: 0
From: Tampa FL
Hiss at rear of engine sitting in front of the engine, at the back of the car so the front of the engine, see, gets me turned around every time!!! 
It's just somewhere around the intake area of course in the area can't see and can't get ear too close, especially while she's let'n out some pops and bangs every now and again (very minor at idle)!
Ends up temp gauge isn't working so another thing to add to the list although again, after reading about fuel regulator issues, that sounds like the next point of attack and have a new one on the way.
It's just somewhere around the intake area of course in the area can't see and can't get ear too close, especially while she's let'n out some pops and bangs every now and again (very minor at idle)!Ends up temp gauge isn't working so another thing to add to the list although again, after reading about fuel regulator issues, that sounds like the next point of attack and have a new one on the way.
Pro
Joined: Sep 2006
Posts: 717
Likes: 17
From: Toronto
did you figure out the misfire and backfire issues?
i had similar issue and was the distributor incorrectly indexed.
i had already replaced: coils, wires, plugs,
checked afm, isv cleaned, ecu in for check up
also had issues with improper timing - fixed that too...
finally got it purring like a kitten...
idle switch and wide open throttle switch a little delicate on mine though... sometimes surges in traffic...
i had similar issue and was the distributor incorrectly indexed.
i had already replaced: coils, wires, plugs,
checked afm, isv cleaned, ecu in for check up
also had issues with improper timing - fixed that too...
finally got it purring like a kitten...
idle switch and wide open throttle switch a little delicate on mine though... sometimes surges in traffic...
Thread Starter
Advanced
Joined: Feb 2008
Posts: 54
Likes: 0
From: Tampa FL
Can't say conclusively but sure seems spot on with what happens when the fuel regulator goes and actually glad it did in seeing the condition of the fuel return lines - lines from the rails to the regulator. The main fuel lines were in great condition making me think someone replaced them at some point. I pulled off basically the top of the motor in getting to the regulator and then while I was at it changed the plugs, found a broken stud and now she's getting prep'd for surgery (top end job). Since it was running perfectly before and this all happened very quickly, it does seem like a single failure although the symptoms were all over the place (seemed like could have been electrical, fuel, demons...). The most noteworthy symptom was raw fuel in the air housings and ended up being a lot of it which was a fire waiting to happen and did, just glad I was there and finally put my big blow hole to good use (literally just took a big blow to put it out).
Last edited by dleefsu; Jul 23, 2016 at 03:58 PM.
Instructor
Joined: Jul 2008
Posts: 158
Likes: 0
From: Hobart, Tasmania & Darwin, NT
The other thing is the oxygen sensor on the exhaust failing - my car has gone through 7 weeks with a porsche dealer to try and work it out and it was probably just a dodgy O2 sensor the whole time.
New porsche mechanics only know how to plug a car in rather than actually knowing how to work on our older cars :-(
New porsche mechanics only know how to plug a car in rather than actually knowing how to work on our older cars :-(
Thread Starter
Advanced
Joined: Feb 2008
Posts: 54
Likes: 0
From: Tampa FL
Glad they finally found it and hopefully not too huge a bill and too much of 'well that other part we replaced was also bad...'. Honestly, I simply can't imagine having a car like this and not being able to do a decent amount of the work/diagnostic and more honestly, I probably only gained this belief recently in discovering that the car is actually pretty easy to work on. I have had to really commit and have had challenges making time for it but don't know what's worse, carving out that time or having to listen to dealers/mechanics go through the process of elimination at $100/hr. My approach is usually examine and replace the little things starting with things that are on the maintenance list and at least narrow down what the issue is not first (rule out easy and cheap things). The biggest thing other than the time was to get over the intimidation that I would screw something up, I wouldn't remember how things go back together and there's been plenty of frustration but usually only when I don't have the right tool (you need a host of tools to approach nuts and bolts from various angles) or I try to take short cuts. Actually today I'm dropping the motor and very glad to do it because then I will clean everything to a T in the engine compartment and under the car... There's a lot of surface rust on the various metal around the motor but still appears to just need cleaning up and powder coating. It's funny because my state of mind, confidence level and experience with the car from the start of this thread to now has changed immensely.
Back to the mechanic issue, I would search long and hard for an independent shop as I can't see newer mechanics being versed in the air cooled motors.
Back to the mechanic issue, I would search long and hard for an independent shop as I can't see newer mechanics being versed in the air cooled motors.
Thread Starter
Advanced
Joined: Feb 2008
Posts: 54
Likes: 0
From: Tampa FL
To conclude my part of this post, and after having a complete top end job done with A LOT of 'while we're at it' tasks, about $15k worth, the car is running great. By the time the mechanic got it it was taken apart enough that there was no further analysis of the issue, just the strategy to do the top end. However, I feel very strongly that it was the fuel regulator which is in the very front of the motor, dead center which unless you know what you're feeling around for back there, you have to take all of the intake stuff off. I think the biggest reason feel it was the regulator was the fuel in the intake and other than replacing the regulator as part of the top end job, we didn't do anything else related to the issue except cleaned everything up but the same intake parts went back on, same O2 sensor which actually we did replace later (we ran it with the old one before)...
I will say to all those that go to mechanics that simply start replacing parts and going by the codes, RUN or at least be careful and participate in the plan for troubleshooting! We had an issue spring up after the mechanic had it running great, he was doing some tweaks and I was standing there and all the sudden started running rougher and rougher, all the sudden the check engine light came on... The code read hall sensor and of course that is where we started and fortunately the mechanic had a spare distributor around so he rebuilt it and put it in and that wasn't it. I actually did a lot of the research and somewhat determined the troubleshooting 'path' and pretty quickly we narrowed it down to a coil that went bad. Based on reading about that issue, A LOT of mechanics by the time they got to the coil could have had you replacing, well, the entire ignition and half the electronics (DME, relays, harnesses...).
I will say to all those that go to mechanics that simply start replacing parts and going by the codes, RUN or at least be careful and participate in the plan for troubleshooting! We had an issue spring up after the mechanic had it running great, he was doing some tweaks and I was standing there and all the sudden started running rougher and rougher, all the sudden the check engine light came on... The code read hall sensor and of course that is where we started and fortunately the mechanic had a spare distributor around so he rebuilt it and put it in and that wasn't it. I actually did a lot of the research and somewhat determined the troubleshooting 'path' and pretty quickly we narrowed it down to a coil that went bad. Based on reading about that issue, A LOT of mechanics by the time they got to the coil could have had you replacing, well, the entire ignition and half the electronics (DME, relays, harnesses...).
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Thread Starter
Advanced
Joined: Feb 2008
Posts: 54
Likes: 0
From: Tampa FL
Thanks Rob, I just find myself a bit let down with the posts when you read through them with no 'conclusion' and this was a tough issue. I wasn't led to the regulator very quickly or easily but then one post out there got me to it but not before most others had me headed in all different directions. I don't remember everything I wrote here but I gave into the top end job when I went to change out the plugs and found a broken head stud and at 90k miles figured it's about time... It's actually pretty amazing how much stronger she runs where I had heard people say that when discussing modifying the older engines to just go for a top end job or full rebuild and may be surprised. That most certainly is now my experience although I did do the cat bypass so perhaps experiencing some benefits of that as well.