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 Post subject: 944S running issues
PostPosted: Sun Nov 05, 2017 5:26 pm 
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I have had an intermittent running issue that has gradually got worse, the car is spluttering/hesitating when I accelerate hard and will lose all power and sometimes stall.

It would only do it on track when right up the rev range and probably only do it every two or three laps. I did the charity trackday at Goodwood where it again did this on track but this time when I was driving home it spluttered a couple of times when accelerating. Got home fine but since then I have found it does it even more. Its fine driving until you open up the taps then it splutters and can die almost like it is running out of fuel then it won't stop doing it when pushing on. Once left for a day it will fire up no problem. I have a video of it happening on track if that helps?

The fuel filter was changed last year so I have ruled that out but I have a list of other possible problems but it is quite a big list and I would like to get straight to the heart of the problem if possible. I did a compression check recently (before and after comparison after I rebuilt the engine) and I noticed all the spark plugs were blacker that I would have expected/wanted.

Possible culprits,
Fuel pump
Fuel pressure regulator
Vacuum leak (checked and ruled out)
Fuel filter (new)
AFM connection (checked and cleaned)
HT leads
Coil
Cam timing
Rotor arm
Dizzy cap
Knock sensors

Anything you would go straight for in the above or anything additional to add?


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 Post subject: Re: 944S running issues
PostPosted: Sun Nov 05, 2017 5:33 pm 
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From the symptoms you describe I'd suggest it was fuel related. So fuel pump, which can be checked for flow easily, pressure is more difficult. Also FPR but these tend to work or not work, not go intermittent. Also check fuel pump fuse is good & clean.

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 Post subject: Re: 944S running issues
PostPosted: Sun Nov 05, 2017 6:13 pm 
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This is where I will start testing then, I'll check the pump and fuse tomorrow and I have ordered a fuel pressure tester gauge so will check the FPR output once that arrives.

I just took it for a blast and it behaved perfectly but when I stopped at the shop for supplies it struggled to start again, I had to keep the revs up once it did start to make it back home but idled perfectly once I got back, feels like its flooding a little.


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 Post subject: Re: 944S running issues
PostPosted: Tue Nov 07, 2017 10:53 am 
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Crank sensor

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 Post subject: Re: 944S running issues
PostPosted: Tue Nov 07, 2017 1:18 pm 
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Good shout, is that coming from the idea of a hot start issue, although this was the first time this had happened?


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 Post subject: Re: 944S running issues
PostPosted: Tue Nov 07, 2017 5:18 pm 
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hot start issues can be caused by the pressure retaining valve in the fuel pump

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 Post subject: Re: 944S running issues
PostPosted: Wed Nov 15, 2017 12:44 am 
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I've managed to get the fuel pressure tester on the engine today, I'd had an issue with the test kit sealing but I used and extra O ring and loads of PTFE tape to seal the joints in the end.

Image

I tested with the guide of Clarks Garage and started off with fuel pressure from the pump by jumping the DME relay part on the fuse box to switch the pump on and engine off, this put good pressure to the tester. Recommended 3.8 bar and I was easily getting that +/- 0.2

Image

Image

The next test was the fuel pressure with the engine running which was also good. Recommended 3.3 bar and was getting 3.4 bar, again +/- 0.2

Image

The final test was a leakdown of the fuel pressure after 20 minutes, it actually lost no prssure at all.

So I am assuming the FPR and pump are both good, unless the pump pressure retaining valve you mention could still be causing this issue?

I will now move onto test the Crank Sensor and reading today that there has be be 0.8mm clearance and I just installed it back in unaware of this figure at the time, so it may be fine but equally may not?


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 Post subject: Re: 944S running issues
PostPosted: Wed Nov 15, 2017 9:18 am 
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You can use a 1p stuck to the tip of the crank sensor to get a mark for the gap

They do go intermittent and are not that expensive for a copy one for testing, seen some as low as £26, not the best quality but good enough for eliminating issues

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 Post subject: Re: 944S running issues
PostPosted: Wed Nov 15, 2017 2:52 pm 
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infrasilver wrote:
I've managed to get the fuel pressure tester on the engine today, I'd had an issue with the test kit sealing but I used and extra O ring and loads of PTFE tape to seal the joints in the end.

Image

I tested with the guide of Clarks Garage and started off with fuel pressure from the pump by jumping the DME relay part on the fuse box to switch the pump on and engine off, this put good pressure to the tester. Recommended 3.8 bar and I was easily getting that +/- 0.2

Image

Image

The next test was the fuel pressure with the engine running which was also good. Recommended 3.3 bar and was getting 3.4 bar, again +/- 0.2

Image

The final test was a leakdown of the fuel pressure after 20 minutes, it actually lost no prssure at all.

So I am assuming the FPR and pump are both good, unless the pump pressure retaining valve you mention could still be causing this issue?

I will now move onto test the Crank Sensor and reading today that there has be be 0.8mm clearance and I just installed it back in unaware of this figure at the time, so it may be fine but equally may not?

Pump valve looks ok mine, was loosing pessure immediately and dropped to zero after 10 mins.

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 Post subject: Re: 944S running issues
PostPosted: Wed Nov 15, 2017 5:25 pm 
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DME temp sensor? Although i'd expect that to be more of a constant issue when hot but maybe you can have an intermittent fault there - wiring perhaps?.


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 Post subject: Re: 944S running issues
PostPosted: Tue Nov 28, 2017 4:01 am 
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I think I may have stumbled across the issue whilst stripping everything down to get to the crank sensor. I removed the J pipe and found a crack in the rubber joint from the J pipe to the throttle body, at first I thought I had caused this when removing it but there was oil residue in the crack so I think it has gradually been getting worse over time.

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Called OPC to order a new pipe but it is on back order from Germany, fingers crossed this is the problem, although I will still check the crank sensor and fit new knock sensor plugs as the bare wire is showing through the sheathing, and I found these replacement plugs made by Durite.

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 Post subject: Re: 944S running issues
PostPosted: Mon Dec 04, 2017 12:01 am 
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I removed the inlet manifold today to repair the knock sensor wiring/connectors and to check the crank sensor but as I looked at the crank sensor and I traced the grey cable from it, I noticed the plug is not connected at all. When I put my engine together I assumed the reference sensor was the crank sensor, so now I'm confused why this is not connected but the reference sensor is. How is my engine running without this connected and where should it be connected as there is nowhere for it to plug into? This has never been connected to the car in my ownership.

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 Post subject: Re: 944S running issues
PostPosted: Mon Dec 04, 2017 10:12 am 
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Interesting thread, looking forward to updates :)


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 Post subject: Re: 944S running issues
PostPosted: Tue Dec 05, 2017 1:13 am 
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More strangeness today. I have measured both sensors in the clutch housing for clearance before I put everything back together and after that I had a nosy around the back of the engine and have found the other end of my speed sensor but it has a loop back plug where the sensor should be plugged into, this doesn't look particularly home made so were there any cars that where like this? The sensor is still in the clutch housing as you have seen, I would of thought both ref and speed sensors would need to talk with the camshaft sensor for the engine to run or will it run with only the speed sensor and cam sensor talking.

Anyone seen anything like this before, should I plug back together or leave it as it is, it was running fine and has been like this since I've had the car?

I have left both plug ends accessible so if I do need to put them together I can, I just need to get it running tomorrow to test how it now runs with the new J pipe rubber.

Image

Some better news, I replaced the knock sensor wiring and connectors and they look a whole lot better.

Image


Last edited by infrasilver on Thu Dec 07, 2017 3:20 am, edited 1 time in total.

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 Post subject: Re: 944S running issues
PostPosted: Tue Dec 05, 2017 9:21 am 
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I do believe that the knock sensor bolts should be replaced on changing the sensor and they need to be at the correct torque

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