Is my 944 S2 fuel pressure regulator working?

Is my 944 S2 fuel pressure regulator working?

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hartlandcarr

Original Poster:

21 posts

95 months

Sunday 10th July 2016
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I'm having problems with intermittent rough/weak/lumpy running, especially at low RPM, and idle speed fluctuating low. Generally when I start up from cold, after the initial surge as ignition kicks in, RPM drops to about 500rpm then bounces back up to about 900, where it stays. Generally whenever the engine comes down from high revs it does the same - dropping low then coming back to decent idle speed. When warm, it idles around 750rpm, fluctuating a little bit with regular shudders, such that it feels like too slow an idle speed and it could die at any moment.

My best theory is that this is a fuel pressure and/or vacuum issue. I don't have the kit to prove this definitively, so I'm going on circumstantial evidence and my flimsy (but improving) understanding of how engines work:
  • The spark plugs are very white, suggesting it's running lean.
  • If I pull the vacuum lines from the fuel pressure regulator (or the dampener), it makes absolutely no difference to the idling engine. But it really should, right?
  • Putting my finger over the end of the removed vacuum line I can feel the vacuum, but I have no idea how strong it should feel. It's such a tiny pipe it's never going to feel like much suction.
  • When the throttle is closed and engine is coming down from high RPM is theoretically when vacuum is highest, but I don't understand how that relates to the symptoms I'm seeing.
  • I wondered if it could be a speed/reference sensor issue, but I looked and my car, being a late model, has just the one sensor (though I initially panicked on seeing just one and an empty hole). I figure it the sensor was problematic then I'd probably have bigger problems and it wouldn't be dependent on temperature.
Thoughts?

This car is my daily driver, so I'm trying to avoid invasive/risky DIY efforts so far!

Monkeythree

511 posts

228 months

Monday 11th July 2016
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Has it gradually deteriorated to this point or was it not there one day and there the next?
I'm thinking it sounds like a worn track on the air flow meter. They wear out more in the low rev range and then the DME gets an erratic signal which causes the engine to hunt around as the DME is responding to the variable input. It's not an easy thing to check unless you can find a friendly owner with a known good AFM and swap it over and see how your engine runs.

Monkeythree

511 posts

228 months

Monday 11th July 2016
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Could also be the idle control valve. The clue is in the name! Easy enough to remove and clean out with petrol to make sure it's not sticking.

hartlandcarr

Original Poster:

21 posts

95 months

Monday 11th July 2016
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The car actually died on me a month or more back as I was at the head of a queue waiting for the lights to change. Lights went green, engine died. Every time I restarted, it hunted high and low at idle a few times then failed as it dropped to zero rpm. That was with it quite hot, but cooling down as I waited for the AA man didn't see to help especially. It ran really rough, even at speed, sometimes stuttering and lurching, or going *slower* if I hit the throttle with anything other than the gentlest touch.

Since then it has not failed outright on me, or exhibited that very poor high RPM behaviour. Now on most journeys it goes through phases of rough running. For instance this evening, at one point, even though it was idling at a decent 900rpm, it sounded like it was really chugging, with weird vibration through the car.

I've just had the front of the car apart to test the AFM with the 'bamboo cane through the air box' approach - as detailed at Clark's: http://www.clarks-garage.com/shop-manual/elect-22.... This showed no problems: the voltage smoothly ran from 0.250 up to 4.7V with no blips. The air temperature sensor was also reading resistance in the right range. I think the problem probably lies elsewhere, but maybe it was just playing nicely for me on this occasion.

hartlandcarr

Original Poster:

21 posts

95 months

Monday 11th July 2016
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I note that it often idles with a really tractor-like 'chugga chugga chugga' sound at the moment. Sounds really rough.

I did have the timing belt changed a short while ago, but haven't yet been back for the 1000km re-tensioning. Could that explain it? Perhaps the timing is out because the tension is out of whack? Clutching at straws a bit perhaps.

hartlandcarr

Original Poster:

21 posts

95 months

Tuesday 12th July 2016
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Looking at where the idle control valve is, I would question the statement "easy to remove". In fact, I wouldn't know where to begin, other than dismantling half the intake system. I assume the fuel rail and inlet manifold has to come off? And if I try that, I'm almost certain to break something or shear a bolt, not to mention I'll need a new inlet manifold gasket etc. :-/

I can't see how I could even disconnect the hoses on the ICV otherwise. Is there a guide for doing it anywhere? Best I found was http://motoriginal.blogspot.co.uk/2009/12/idle-con... though that's not an S2 in that example.

Hallsy01

350 posts

180 months

Thursday 14th July 2016
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I cleaned the ICV on my old 944 S, and it involved removing the inlet plenum to get to it - I'm not 100%, but I'm pretty sure you have to do the same on the S2?

Certainly before removing the plenum, I would at least check the fuel pressure regulator - this is easy to do if you can lay your hands on a pressure gauge and fitting. I have one that fits the S (which I'm pretty sure will fit your S2), welcome to borrow it if it will help you out?

If you follow this write up, you should be able to tell whether your FPR is operating correctly:

http://www.clarks-garage.com/shop-manual/fuel-01.h...

hartlandcarr

Original Poster:

21 posts

95 months

Friday 15th July 2016
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I've been trying and failing to find a cheap fuel pressure tester online. It looks like I probably need a 12mm (with 1.5mm thread) female connector to go onto the male connector that's built onto the side of the fuel rail. It may also need an angled adapter because it's close to the intake manifold. I'm just not sure! Most of the cheap test kits seem to have Shrader valves or male threaded adapters, which would be no good.

@Hallsy01 - I'm in St Albans and it looks like you're in Suffolk, so though I'd love to try your tester, it might not be possible to make that work.

Hallsy01

350 posts

180 months

Monday 18th July 2016
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I would happily post it to you...have done so before for another 944 owner smile

Hallsy01

350 posts

180 months

Monday 18th July 2016
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I would happily post it to you...have done so before for another 944 owner smile

hartlandcarr

Original Poster:

21 posts

95 months

Monday 18th July 2016
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That would be awesome. How can I best contact you to set this up outside of this forum?

Hallsy01

350 posts

180 months

Monday 18th July 2016
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Just drop me a mail via my profile.

I'll dig out of the garage for you.

nsa

1,682 posts

227 months

Monday 18th July 2016
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The symptoms you describe sound similar but worse to what I had on my 968. One HT lead had corroded where it joins the spark plug. Slightly lumpy idle and it kangarood on slight throttle. It would respond to full throttle through the gears if I kept the revs high enough. Then, at idle I could hear ticking coming from the offending lead.

Are you sure it's fuel related, not spark? Either at the lead or the distributor cap? Worth asking in the Technical section also.

When you get your timing belt tension checked, make sure they do it according to the Porsche service manual method, not with a metal bar to prise the tensioner back. I had a £2,300 head rebuild due to tensioner failure after re-tensioning.

ETA more detail.

Edited by nsa on Monday 18th July 21:41

hartlandcarr

Original Poster:

21 posts

95 months

Tuesday 19th July 2016
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I have been wondering about the leads/plugs/distributor. You've tipped me over the edge and I have just ordered new leads (cheapest I found was £105 from frazerpart) and plugs. Also a new fuel filter, though that looks like it will be irritatingly difficult for me to change (it was a 10 second job under the bonnet on an old Citroen ZX I once had).

I'm also wondering about the probable lean-running - the plugs that I inspected were very white. Maybe that's a whole other issue, related to fuel pressure or something else.

hartlandcarr

Original Poster:

21 posts

95 months

Saturday 23rd July 2016
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I've been busy testing things, but still haven't solved the problem.

- I acquired a vacuum gauge, which seems to show that everything is as it should be in the vacuum lines.
- I've replaced the spark plugs, plug leads inc. lead to the coil (which necessitated removing the headlight motor), distributor cap and rotor. That made precisely no difference, which is disappointing as I was really hopeful it was an ignition issue. Could it be the coil - the only bit I didn't replace?
- I note that the old spark plugs that came out actually don't look as white as I feared when viewed in more normal lighting, rather than the LED of my head torch in the dark of my driveway. So perhaps the engine isn't running lean.
- I've just tested fuel pressure using @Hallsy01's gauge (many thanks). Everything was bang on the numbers from http://www.clarks-garage.com/shop-manual/fuel-01.h... 3.8 bar jumpered, 3.3 bar idle, no loss of pressure at all after 20 mins off.
- Removing the vacuum from the fuel pressure regulator did cause pressure to change a bit, in the direction expected (higher), so it's probably working.

Remaining ideas:

- An air leak somewhere, but not one which is significantly affecting vacuum.
- Timing issues, due to something or other (still need to get timing belt re-tensioned after it was changed 1000km ago). I don't have a good understanding for how timing issues occur and if it might explain the symptoms.
- Fuel injectors not working properly somehow, but I wouldn't have thought that would only be crappy at idle / low RPM.
- Idle control valve not working properly.
- Some sensor somewhere not quite working properly.

Generally, the engine seems to be lacking power. It only really picks up at about 4000rpm, and below that is embarrassingly sluggish IMO, but I don't have much to compare to.

Thoughts? Especially for simple tests/replacements I can conduct to eliminate further possibilities. It's my daily driver and I'm a rank amateur so significant disassembly isn't really on the cards.



hartlandcarr

Original Poster:

21 posts

95 months

Sunday 24th July 2016
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Tonight's tests:

- Pulled out the ICV connector whilst idling - I felt/heard mechanical things happening inside it, and the engine died within about 2 seconds. Presumably the ICV is working therefore, though I didn't actually expect the engine to die as I assumed it would simply stay in its current position when the plug was pulled.
- Pulled out what I *think* was the O2 sensor connector (3 pin round plug at back of fuel rail) but it made absolutely no difference to idling.
- Pulled out the connector that's right next to that one (on the other side of same bracket) and engine died immediately. I don't know what that connector is and couldn't see where the wires go - would someone care to enlighten me? Clearly it's important!
- Tried pulling out a couple of spark plug leads one at a time. Frankly, it made only the most minor difference to the sound/speed of idle, which surprised me.

Overall the engine sounds very 'clicky' at idle, though it comes and goes a bit, and occasionally shudders. Maybe the problem is a more physical one underneath the cam cover?

NJH

3,021 posts

208 months

Monday 25th July 2016
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hartlandcarr said:
I
- Some sensor somewhere not quite working properly.
3 things I have replaced over time sensor related, two were a real pig to diagnose. Temp sensor on radiator (common to fail), O2 sensor going slow (very common on all cars), and crank angle sensor. In my case neither of the last two produced faults when plugged into Porsche diagnostic laptop. The 02 sensor one was interesting, I asked one of my Porsche garage friends if I could browse the diagnostic pages and we found one which allowed us to look at the raw data coming from the 02 sensor. It was taking several seconds to do a pass and of course massively over-fueling during that pass (should sweep really quickly). Strange that even on the 968 this doesn't result in a fault. My other one the crank angle sensor was dropping out when the car heat soaked on track, and was eventually diagnosed by the tacho needle not bouncing when trying to restart the engine (but fine again after cooling down).

Honestly though you are not giving any of us much to go on, it was the same in your last thread. Not to be offensive but I really don't think you know what you are doing and are just playing around with the car, you should be taking it to someone like EMC Motorsport, Hartech, Jon Mitchell garage, NineX and the one or two others whom have extensive experience with the front engined cars and can work through a fault finding routine properly.

hartlandcarr

Original Poster:

21 posts

95 months

Monday 25th July 2016
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You're absolutely right - I don't know what I'm doing.

But... I presume everyone had to go through this stage at some point, and I'm trying my best to learn fast. I'm spending hours every day reading on the internet and tinkering with the car. It's my daily driver that I commute in, and it runs well enough for now that I'm happy to keep slowly investigating it myself and gradually learning more and more about how it all works (and doesn't work). If I take it to a garage they will fix it, possibly at great expensive, and I won't learn much at all. But I'm strongly considering doing exactly that.

What I would really *love* to be able to do, is take it to a garage, but stay there and work through it with them so I can get that learning from someone who really knows what they're talking about and can diagnose the fault effectively, like you say. Or to find another local-ish 16V 944 owner who knows their stuff.

My usual Garage is JAZ in St Albans, who mostly deal with rear-engined machines, but who do seem to have lingering expertise in 944s. People come to them from all around the country and they have some incredible machines there, so I'm hopeful that they're a good place. If anyone has any opinions on them, or alternative local recommendations, I'd be very keen to hear them.

I do *really* appreciate the help of people in this forum, which has already been invaluable.

FWIW I do see tach bounce when starting, so I'm hopeful that the speed sensor is OK.

Hallsy01

350 posts

180 months

Wednesday 27th July 2016
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A garage with a Bosch Hammer may be able to shed some light.........this is the diagnostic tool needed for the 16v's - well, it was definitely what is used for the S, and I'm pretty sure the S2 has the same type of ECU.

From memory, there is an adaptation routine which should be run routinely (like when serviced) and will adjust idle and possibly CO.

I made a lead some time back to connect up to the 16v ecu. We tried plugging into a more modern Porsche diagnostic, a PIWIS, it made connection to the ECU OK but would not run the adaptation process.

Even then, it probably isn't an adaptation issue, but you may have some fault codes stored.

hartlandcarr

Original Poster:

21 posts

95 months

Wednesday 17th August 2016
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To follow-up...

The car has been with JAZ for the past few days and we're near to a resolution. They identified cylinder 3 as having a misfire, but a rather odd one that goes away on revving, but then comes back slowly after a certain amount of time. They suspected a broken valve spring (based on previous experience) but we agreed to check the fuel injectors to start with because it's a lot cheaper and they probably needed an overhaul regardless. So they were taken out and checked/cleaned in their special machine. Apparently they were fairly bad, so I'm glad I had that done and I hope it makes a noticeable difference to running and fuel economy. However it didn't fix the problem, so they've had the cam cover off and confirmed the broken spring on an exhaust valve, as per their hunch.

So that spring will be replaced and at the same time the cam chain (which was stretched) and tensioner will be replaced.

This is all going to add up to quite a big bill :-/

But hopefully the engine will be in much better shape all round. They also checked cylinder leakage, which was at 15% - apparently about right for mileage (5% for a new car, 30% is problematic I am told) and fuel pressure (same as I did) which was fine.

I'm looking forward to getting the car back, and hoping it purrs like a kitten!