jlturpin

Do you have a wideband O2 setup? what are the readings on cold start? An adjustment to your amf may solve this issue as it sounds like a cold fueling issue to me.

divil

Nope, no wideband. I hadn't really considered installing that before as the car is totally stock. However it might be handy to have for situations like this. Given the cost of parts like the ISV and TPS, it might be the cheapest way to figure the problem out

What kinds of adjustments can you do to the afm?

I will definitley check this again. There could easily be some noise that escaped me before.

divil

Tried measuring fuel pressure today. I'm not really sure what I found out though because I just realized the gauge doesn't make sense to me. This might be a stupid question, but why the hell is the 0-5 bar scale smaller than the others? How are you supposed to read that? This is the Arnnworx gauge, but I have a HF one lying around, same story with the gauge on that.

Here is what I had with the engine off, fuel pump jumped:



With the engine idling, the needle was jumping quite a lot - sometimes it would settle down, sometimes it got quite erratic, by as much as 1/2 a bar. When I revved the engine a little it would smooth out:



Here is a video of it at idle - this was not the most erratic behavior I saw, it got much worse but I didn't catch it on video (sorry if this video appears upside down, that should be fixed as soon as youtube is finished processing):



Does that seem right? I just remembered that is it actually a 3 bar regulator. It was on a spare fuel rail a friend gave me after mine got damaged. I left it on there to avoid the risk of damaging the rail...but the car has always run the same as it did with my old 2.5 bar.

travisgreen

What chips are you running? Are they set up for a 3 bar regulator?

divil

Stock chips

travisgreen

If you have stock chips you shouldn't be running a 3 bar fpr. Did you have this problem with the stock fpr?

divil

Yes I had the same behavior from the car with the stock FPR, so I thought nothing of it when I discoverd the new one was a 3 bar.

travisgreen

Ok. Well I would start by putting the factory on back in

RSlite

I had a similar stumbling / irregular running on my 951.

dont know if this helps, its a long shot, but I actually had a jubilee clip (the big J Boot one) go wrong. It failed in a strange manner, i.e. - at almost the point it was torqued up it jammed on the thread, and I thought the J Boot was tight. It was not and the leak which followed made the car run just like yours.

I was over familiar with the various intake pipe connections as I have been DIY maintaining one of these cars for 10+ years.

At tick-over, there is no boost pressure as you will be aware. If you fitted a boost guage it would read negative pressure. Therefore the arnnworx pressure test is irrelevant at tick over. Failing that, HT leads are a favourite, tick over, enrichment on the afm, good luck, you will sort it.

divil

Put the original FPR back in - no difference. Well, there is a big difference on the pressure tester - the needle no longer bounces around erractically, it's now very stable, but the car idles and drives exactly the same as ever.


Funny you should say that - last week, as I mentioned, I resealed the throttle body. It was leaking, and the reseal kit fixed the leak, but had no effect on how the car ran. A week later, I disovered that I had completely forgotten to tightnen up the AFM/J-boot hose clamp when I put the TB back on. It was loose, and I mean about an inch too big. The J-boot would undoubtedly have poppd off the AFM if there was enough room in the engine bay. I tightened it up, and of course, it made no difference. Weird though...the car ran for a week, the same as ever.

Still, if the behavior you saw was the same as mine, it does point back towards a vacuum leak. I need to make a new test cap and test again.

Not sure what pressure test that is...I was trying to pressurize the system from the J-boot in my test.

divil

I think I have begun to isolate at least 2 different issues here. I tried adding 6% more fuel via the FQS switch, and drove the car for a few days. It definitley seems to have improved the idle and general running of the car. Previously the car would always shudder when idling as if a train was driving past...with the extra fuel that problem went away. Acceleration was also smoother, and my exhaust did a lot less popping than usual.

However, it didn't have the slightest effect on the weird stumbling issues on cold startup.

I did check the TPS again very crefully...opening the cam as slowly as I possibly can I cannot get anything from the idle switch except 0 ohms or infinity. When I release it I do see a very brief flicker of some value but it's too fast to read. I don't think that's the issue.

I did find a few small vacuum leaks around the 2 small banjo fittings on the intake manifold. There are a few small vacuum lines and fittings there I never replaced so I'll get to that next.