Rough Running

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Discussion

ukflyboy

Original Poster:

235 posts

50 months

Tuesday 16th August 2016
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So I'm reaching fed-up territory with my S3, it just doesn't seem to want to come out to play this summer :-( After sorting a clutch problem that stopped it going into gear a few weeks ago, it started rough running, lurching at low revs and 'farting' when asking for moderate amounts of power. A few people on here suggested changing the fuel filter (now done after a few leak issues) and cleaning the sensor and tracks of the AFMs (completely cleaned 2 spares and replaced the ones that were on there); unfortunately it still isn't running well.

Symptoms are:
1) Engine struggles to catch on start, seems to require a lot of pumping of the pedal and generally only fires with a lot of throttle. There is a smell of fuel when it doesn't catch, but guess that is to be expected.
2) When I get it running, it still runs pretty rough, giving a farting sound most of the time when power is applied and often just idling to a stop.

I've tried using the Gunson Fault Code Reader but all I get is 11 - no fault found; given that my ISCV has been disconnected for the past few years (but still running perfectly), I don't have much faith in its accuracy if it can't even detect that!

Last bit of work I did before this started manifesting was bleeding the clutch, but everything seems to be fine in and around down there, so don't think I have knocked anything.

Anyone got any idea of where to go next? HT leads? Spark plugs? Failing any suggestions that lead to a quickish fix, does anyone know a Cologne V6 expert that I can give it to to sort this and the long term issue that has resulted in the ISCV being disconnected?

GreenV8S

26,105 posts

218 months

Tuesday 16th August 2016
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I don't know much about that engine management system but just in general I'd check the fuel pressure and ignition timing. Fuel pressure should vary with manifold pressure and you should try to find out how it is supposed to vary - it might be a constant offset, but it might not be. When checking the ignition timing I suggest you don't trust any timing marks you find on the front pulley but find TDC mechanically and verify the timing marks first. Also check the header temperatures after a run to see if there is any significant variation that might point to a problem on one cylinder. If you have any doubt about the mechanical state of the engine you can also do a compression test easily and cheaply.

PotlessPaul

307 posts

174 months

Wednesday 17th August 2016
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I had a similar sounding problem on the S tour a couple of years ago which turned out to be one of the pipes from the AFM had come off and it was sucking in too much air, could be an easy fix??

mentall

221 posts

64 months

Wednesday 17th August 2016
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Vacuum leaks, anywhere at all? On mine, the PCV valve (right-hand rocker cover) pops out every now and then.

greymrj

2,945 posts

138 months

Wednesday 17th August 2016
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More a 2.8 man that 2.9 myself but surely it shouldnt need any pumping at all at start? If the management is right it shouldnt. Must admit it does sound like a mixture problem which is defeating the ECU, vacuum leaks are an issue on these set ups.
I know it is very old fashioned but it does work. Get a length of hose say 1/2" bore, put it to your ear and run the other end along all the places where an air/vacuum leak could occur. Listen for anything unusual at all. Be sensible and careful as you have to have the engine running. Used carefully that method can pin down some electrical issues as well as you can often hear tiny arcing noises, or trace that elusive tapping noise. You can even listen to water flow in pipes. Takes a bit of time, care and practice.
Borrowed a medical stethoscope one...man those engines are noisy...nearly deafened myself.
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ukflyboy

Original Poster:

235 posts

50 months

Saturday 27th August 2016
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Still chasing this one unfortunately...

I've spent this afternoon blocking off all of the ancillary sources of air to the plenum and none of it has made a difference. It still requires full throttle to get it to start, runs very rough until revved high a few times and then still doesn't idle that nicely; if left to idle it will just conk out after a few minutes.

Unfortunately my mechanical abilities don't extend to the stuff V8S suggests above, so I'm kinda lost where to go now. Feels like my car has spent most of this years sunny days stuck in the garage!

steve j

3,222 posts

162 months

Saturday 27th August 2016
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I`ve heard of this before and it was an air leak, check all the pipes that go to the plenum, the brake servo pipe is a favourite, it perishes and lets in air to the plenum, hope this helps.

GreenV8S

26,105 posts

218 months

Saturday 27th August 2016
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If you suspect you're chasing an air leak then get yourself a can of cold start spray and spray it around the outside of the induction system while the engine is running. If you have an air leak causing lean running then it will pick up when the vapour is drawn in. If you can't find cold start then you can use spray oil but note that it'll mess up the outside of your engine and smoke if it gets on the exhaust - cold start spray is better.

ukflyboy

Original Poster:

235 posts

50 months

Monday 29th August 2016
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I've got 2 new TVR intake hoses ordered so hopefully they will reduce the likelihood of any leaks. In saying that, I have tried spraying a bit of carb cleaner around the likely areas, in addition to completely blocking off supplies of air to the plenum with no luck at all. I've also measure the voltages for the TPS, AFMs and temperature sensor and all are operating within the limits of the diagnostics article (below). The only disrepancy in the figures they give is that (if I'm measuring it correctly) my 0.25 v earth is actually 0.0025v.

I've done key on engine off and engine idle diagnostics tests but neither show up any faults however, the instructions that come with my Gunson fault code reader are so terrible that I have little faith in being able to do the dynamic test correctly. For example, it talks about being prompted to start the engine but doesn't say what this prompt is. It also talks about the LED on the left of the display, which it doesn't have, so not ideal! The fact the idle test doesn't show up any errors codes despite being disconnceted also doesn't fill me with confidence!

I can get the car to start every time but it requires me to hold full throttle until it catches. Sometimes it will then idle ok (but eventually cut out) sometimes it runs rough as a dog and will splutter out instantly. Sadly starting to think I might be out of my depth here, but have little faith in a modern mechanic knowing what to do with it either!


http://www.gbsportscar.com/TVR%20Body%20Off/wiring...

GreenV8S

26,105 posts

218 months

Monday 29th August 2016
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The symptoms suggest a tuning problem rather than a total failure. It could be fuel or ignition related. Finding out which would be a good first step.

If I were you I'd get a can of cold start spray and spray it into the intake while it was idling - if it picks up, it was running lean; if it starts running roughly, the fuel was about right. I'd also connect a passive strobe in series with #1 lead and see whether the spark frequency or strength was changing significantly when the problem occurred. Note that a cheap passive strobe is much batter than a more expensive active strobe for this sort of diagnosis. You can also get test lamps designed to fit in series with an HT lead (often attaching directly to the plug) specifically for this sort of test, although personally I prefer using a more conventional strobe lamp on leads because it's easier to position.

I'd also try to work out whether the rough running was affecting one cylinder or all cylinders. If you can keep it running for a minute or so with the misfire then you can check the exhaust header temperatures to see whether any are significantly colder than the rest. Ideally use an IR thermometer, but in a pinch you can just touch the exhaust with a bit of plastic to see how much it smokes.

None of the test equipment involved is expensive or difficult to use but you do need to have a basic understanding of how the fuel and ignition systems work and be prepared to get your hands dirty. An old school mechanic who knows how to diagnose engines manually rather than relying on the computer should be able to do this sort of thing in his sleep.

ukflyboy

Original Poster:

235 posts

50 months

Monday 29th August 2016
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Thanks Pete (I'm also Pete btw), having just removed the HT leads, tested them with the multimeter, replaced them with an old set which I also tested with a multimeter etc, I can pretty confidently rule out another part of the system.
I like your idea of spraying starter down the intake, I will try that this week. I've also got some new intake pipes on the way that should rule out any air leak around there (though carb cleaner test would suggest that there isn't a problem) so will try it then. I've also got a temperature probe on my multimeter so will sheck its range and give that a crack during the week if it is up to the task!

Thanks again for your help Pete. I did buy this in part to learn a bit about mechanics so can't complain too much, but this summer hasn't been the best and is really frustrating me now. On the plus side, I'm cleaning as I go, so it is looking progressively nicer under the bonnet!

ukflyboy

Original Poster:

235 posts

50 months

Sunday 16th October 2016
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Well I'm making slow progress on this one...

Squirting a bit of carb cleaner down the AFMs almost killed the engine and a spark plug check last weekend showed they are all pretty badly dry fouled so I've been leaning towards over-fuelling as being the cause. After cleaning up all the sparks plugs I tested them and am getting a good spark all around so I don't think it is anything ignition wise.

I purchased a cheap fuel pressure tester off eBay and it seems to be pretty close to the 2.5 bar (3 under vacuum) that the Ford Diagnostics article suggests, so I don't think incorrect fuel pressure is the cause. However, in chasing down a brand new electrical gremlin (more about that one later if I can't solve it!) I found that if one of the electrical connectors in the foot well was touched or wiggled then the fuel pump would prime with the KOEO. Clearly there was a dodgy connection there which I HOPE was causing the rough running (maybe fuel pump cutting out which wasn't enough to provide pressure under load?).

I need to go for a test drive to see how it is going now but need to get the gremlin in the electric mirrors sorted which has caused my volt me to drop to zero. One step forward, two back...

ukflyboy

Original Poster:

235 posts

50 months

Sunday 23rd October 2016
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Got the electrical gremlin sorted (put down to a short in the electric mirror joystick) so managed to get the car out on the road. Seemed fine for the first 15 mins but once fully up to temp it starts coughing and kangarooing again. The connector in the foot well seemed to be behaving itself fine and the fuel pump primes every time I turn the key, so don't think that is the issue.

It was running very rough by the time I got it home and couldn't even get it into the garage it was that bad. I tried a bunch of times to get it started but it would run rough and die as soon as I took my foot off the gas. Interestingly resetting the ECU by removing the power for 5 mins allowed me to start it and get it in the garage sounding like it was running ok.

I'm really running out of ideas with this one now. I think I'm going to have to be brave and take it for a drive with the fuel pressure gauge attached to see if the pressure is dropping out such that it is being starved of fuel under load. Now that it may be temp or ECU related, does anyone else have any ideas what could be causing my troubles? It is effectively unusable now and I'm not convinced it would even drive for long enough to get it to a garage that knows what they are doing, so I'm stuck! :-(

GreenV8S

26,105 posts

218 months

Monday 24th October 2016
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I'm not familiar with that ECU and really you do need somebody familiar with it. The symptoms seem to point to over-fueling although it could still be an ignition related issue causing a misfire and it might even be a fuel supply problem leading to *under* fueling.

If you can find anyone able to diagnose it via the ECU it should be pretty quick to resolve since that ECU has a lot of diagnostics built in. Otherwise I can only suggest looking at the basics - check the spark strength and timing when the problem happens, check the fuel pressure, check the injector duty cycle. Unless you're pretty comfortable with the test equipment needed to do this I think it's going to be quite challenging to DIY. Worst case you have to pull over to let it cool down every ten minutes when you drive it to your favorite specialist, or pay a hundred quid to get it recovered on a flatbed - are those options out of the question?

glenrobbo

11,713 posts

84 months

Monday 24th October 2016
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Have you tried using the proper Ford "Star Tester" diagnostic kit?
This has proved effective on a number of occasions for peeps on here with a persistant or intermittant fault.

There are two S Clubbers who each have one available for others to borrow and use, can be sent to you by post or courier.

Try contacting Phillpot or RayTVR by PM via their profile page.

Good luck OP.

Spathodus77

309 posts

143 months

Monday 24th October 2016
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My 2.9L had the 'run ok until warm then start being jerky' problem. Turned out to be corroded connectors on the wires going into the AFMs. Note that this issue does n't generate a fault code. In the end I ordered new connectors from Vehicle wiring products because the problem would reoccur every 6 months or so. The issue was spotted by Paul at the now closed Austec racing...if someone knew where he is now I'd recommend taking the car to him. He used to work at Tvr tuning their cars and maintained and enhanced that knowledge at Austec.

Ralph

Mr Clifford

804 posts

161 months

Monday 31st October 2016
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Had this same problem when i bought mine 10 years ago.
Turned out to be simply dirty/corroded fuel injectors.
First thing the garage looked at because they had seen it so many times before.
Took 30 mins to sort out.
Completely different car afterwards.
Main rough running got worse as car warmed up. kangaroo runner etc !

Mr Clifford

804 posts

161 months

Sunday 20th November 2016
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Still running rough ?

ukflyboy

Original Poster:

235 posts

50 months

Sunday 20th November 2016
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Yip, still running rough although I've had a couple of other projects on the go that have kept me from looking further into it. Still want to test the fuel pressure on the road (little bit nervous about that one and the risk of a fuel leak!) and to test the manifold temperatures to see if one is significantly colder than the others.

Thanks for checking up though, standby for update in the coming weeks!

Mr Clifford

804 posts

161 months

Monday 21st November 2016
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ukflyboy said:
Yip, still running rough although I've had a couple of other projects on the go that have kept me from looking further into it. Still want to test the fuel pressure on the road (little bit nervous about that one and the risk of a fuel leak!) and to test the manifold temperatures to see if one is significantly colder than the others.

Thanks for checking up though, standby for update in the coming weeks!
Am convinced its worth cleaning the fuel injectors ;-)