Jump to content

Recommended Posts

Posted

When running in traffic, say trickling along in 2nd gear my car feels as though it has a case of kangaroo petrol, or a wah-wah throttle pedal.

 

It will accelerate cleanly, though there is the ghost of this effect felt when cruising at much higher speed.

 

Any ideas?

 

Recent work: fuel injector service (ultrasonic clean, new seals, filters), distributor cap & rotor arm, HT leads, plugs, CHT sensor.

 

Some of this work was carried out follwoing my Le Mans trip last year, where the smooth French roads m,ade me notice something not quite right.

 

This is not abig problem, and won't stop me taking the car to France for a week starting this Friday, but clearly all is not well.

 

Ta.

Posted

Sounds like maybe a vacuum leak on the advance or a timing problem, hard to say on tinternet.

  • 1 month later...
Posted

Just back from spending an hour with Bob Watson.

 

So, Bob puts the car on his dyno, spends a few minutes with it, then shuts it down and comes out with 'so, what's the history on his car'?

 

Heart sinks at this point - what does he think the problem could be?

 

Anyway, to cut a boring story short - the car is (to Bob's ears) clearly pinking in the low part of the rev range. Stupidly, and this despite thinking of it before I went over, I forgot to take my original chip to swap with the SW one fitted. Bob thinks the chip is either leaning out the fuel too much in the low range, or is running with too much ignition advance.

 

So I have just put the OE chip back in - not much chance to drive it yet, but may join in with the PCGB Impact Day and Sunday. WIll give Bob a call on Monday to let him know what I think.

 

My 'confidence' (ahem, clearly misplaced) in my ability to recognise what a car is doing is now severley battered - how could I not recognise that it was pinking? Thought it was just valve gear noise.

Posted

He is the boy mate - go with whatever he says. Whatever about the disappointment, it's better that you know these things ;)

Posted

BW doesn't always say very much when he's working, but you should note every word. If he says it's pinking, I'd be listening very intently indeed.

 

I found this link quite informative on the topic of detonation and pre-ignition generally:

 

http://www.sacskyranch.com/deton.htm

 

(Most light aircraft have manually-adjusted mixtures to cope with the affects of altitude or to compensate between cruise or climb power modes - they also tend to have instruments to monitor CHT and/or EGT, though).

 

Detonation isn't the big bogeyman though - it's not instantly fatal (of course, you already know this! :D).

 

Small amounts of it under transient conditions will actually remove carbon deposits from the combustion chamber and don't cause any damage - if not too prolonged...

Posted

Have e-mailed Steve Wong for his thoughts.

 

Evidence does seem to point to the chip being the problem.

Posted (edited)
Have e-mailed Steve Wong for his thoughts.

 

Evidence does seem to point to the chip being the problem.

 

 

Hi Chris,

 

I don't believe I ever received your email. So based on the comments of your posts above, in what rpm range is this happening at? Pinging should not be an issue unless there was something else off that would put the car on the edge. A couple of things you can check. Make sure your fuel quality switch is in the full counterclockwise position, you are using the minimum recommended fuel octane for the chip you ordered, and try renewing your air flow meter as per the directions shown on this link: http://frwilk.com/944dme/afm.htm

 

AFM wear is a major cause of part throttle havoc because it causes the fuel to run excessively lean, and part throttle ignition timing to be all over the place because the engine is not receiving the correct load signal. Here is for example a picture of the wear on my AFM after just 65,000 miles:

 

AFMwear.jpg

 

If you still have problems, try resending me an email again and perhaps at stevekw@pacbell.net

Edited by steve@911chips
Posted

Hi Steve

 

Thanks for your thoughts - don't know why you didn't get my mail.

 

The car is currently showing 59k miles. I have had the fuel quality switch set as per instructions and 99.9% of the time use Shell petrol - 95 RON mostly with a sprinkling of fills of 'V-Power' for its detergent qualities.

 

Evidence does seem to point to the chip being the problem.

 

Apologies for that comment on this board, knee-jerk reaction I guess - I'll investigate the AFM as per your notes above. A quick look will show me whether the tracks are badly worn.

 

I have the OE chip back in and the engine definitely 'sounds' quieter. However, I remain appalled with myself for not being able to notice the pinking that Bob so clearly heard. He told me he had some special headphones but didn't need them in my case! The pinking was in the 'low' rpm range, probably extending to somewhere around 2300 rpm.

Posted

Let me know what you find about the AFM. This is Chris T. correct? If so, I have changed the part throttle fuel mapping on the 95 ron chips in the 1500-2500 rpm range to run a slight bit richer since around this time a year ago. A chip update may address it. You could try fuel quality switch position 1 first to see if that makes any difference and report back to me.

Posted
Chris how much does BW charge for this kind of diagnostic

One MILLION dollars :D

 

800px-Dr_Evil.jpg

Posted (edited)
Chris how much does BW charge for this kind of diagnostic

 

I actually just paid him a 'few quid' for his time - I won't say on here how much.

 

Removed the AFM last night and opened it up. I've got some pics which I will sort out soon.

 

Whilst there are tracks in the copper they don't look like a cause for concern - also they appear to be consistent right across the arc of the unit, i.e. wear looks consistent. I did push the wiper down on the shaft to move the contact points out on the copper track - it would only move a very slight amount, but enough I think to contact fresh copper.

 

Pic attached but not very good - I will take some better pics before I re-seal the lid.

 

Just need to find something to seal the lid with - any suggestions if my work buddies can't come up with any pukka stuff?

post-100-1186555820_thumb.jpg

Edited by Chris_911
Posted

OK - have some RS 'Non Corrosive Silicon Rubber' sealant sat on my desk. 24hr cure time - the alternative was a hot cure sealant but didn't fancy cooking the AFM at 150 deg C.

 

Have also arranged to be back with Bob W this Friday pm for him to give the car a look in its OE condition.

Posted

I had the same problem with my 3.2 carrera two years ago,

 

I removed the AFM, opened it up then inspected it for wear,

 

There didnt seem to be any wear visible to the eye,

 

I then gave it a good clean, mainly all the contacts, sealed it up then replaced it,

 

The problem of "kangarooing" had gone, :woohoo:

 

But after a few weeks the problem reappeared :eusa_boohoo:

 

So I removed it and cleaned it again, problem gone,

 

Then it reappeared again !!!!!

 

This went on for about 4 or 5 removal and replacements,

 

In the end I bought a second hand AFM from Porsch-apart for 50 quid.

 

No more problems so far. :signs118:

 

So if you clean it, replace it and your problem has gone it will more than likely be the AFM,but like mine it might reappear.

 

Hope this helps.

Posted

A couple of other points that I might mention, and I've already mentioned it to Chris is what John initially brought up is intake air leaks. Though you may not have this problem, it is a pretty common one, especially at the two bolt intake manifold gaskets that get sucked in causing runner leaks right before the intake ports. The leaks cause cylinder to cylinder imbalances, and air that bypasses the air flow meter door so it does not open properly, leading to a lean condition. To check for leaks, use engine starting fluid, and spray around any suspected connections and points around the intake system while the engine is idling. If the idle shoots up, you've located a leak. Disconnect the idle control valve plug to prevent it's influence from counteracting against your search.

 

And although this may not have anything to do with a lean mixture, clean dirt and grime away from the throttle plate inside the throttle body and in the flow meter. Temperature differences have a funny effect on low flow conditions that make for unpredictable behavior.

Posted (edited)

A bit more to flesh out this post - might help someone else, etc, etc.......

 

Really difficult to take a good picture of the wiper and copper track, but the two best ones are here, which show the tracks in the copper made over time by the contact points of the copper wiper. These photos show the wiper after I had loosene the central clamp bolt and pushed it down on the central shaft. It did not move very much at all - and there appears to be no further potential for movement. I think that the wiper points are contacting fresh coppoer, but it's a close-run point!

 

Longest part of the job was cleaning all of the old sealant from around the lid and the AFM to allow for a good seal with the new sealant. There is no mechanical fixing of the black plastic lid on the AFM - the sealant also acts as a securing adhesive. Only problem (so far) with the stuff I snaffled from work is that it is white.

 

Removal of the AFM from the car is very straightforward - I took it out with half of the airbox attached (there are four bolts that attach the airbox to the AFM which are easier to remove/replace with the whole assembly out together.

 

The AFM is currently sat on my desk allowing the sealant to cure and I shall re-fit this evening.

post-100-1186660284_thumb.jpg

post-100-1186660293_thumb.jpg

post-100-1186660300_thumb.jpg

post-100-1186660307_thumb.jpg

post-100-1186660313_thumb.jpg

Edited by Chris_911
Posted

Chris

 

Make sure when you re-fit the electrical connector to the AFM that the pins seat correctly. Read on PP when i took mine off that occasionally the pins push back into the connector and don't actual fit into the female bit properly

 

Shirish

Posted

Quick session with BW this afternoon.

 

Car definitely not pinking now with the OE chip fitted. Idle and running emissions are spot on according to Bob. However I'm not happy with the transition on/off throttle. Bob drove the car to see for himself. He doen't think there is anything wrong with the AFM.

 

SW is sending me his latest chip, which is slightly revised in the range I have the pinking problem. Plan with Bob is to fit that then he'll look at the car again.

 

I may change the idle air control valve as a matter of course. Whilst not a trivial sum of money it's not stupid expensive either. There is definitley a problem with the car smoothly dropping back to its idle speed.

  • 2 weeks later...
Guest DanRyan
Posted
Quick session with BW this afternoon.

 

Car definitely not pinking now with the OE chip fitted. Idle and running emissions are spot on according to Bob. However I'm not happy with the transition on/off throttle. Bob drove the car to see for himself. He doen't think there is anything wrong with the AFM.

 

SW is sending me his latest chip, which is slightly revised in the range I have the pinking problem. Plan with Bob is to fit that then he'll look at the car again.

 

I may change the idle air control valve as a matter of course. Whilst not a trivial sum of money it's not stupid expensive either. There is definitley a problem with the car smoothly dropping back to its idle speed.

 

 

Chris

 

What's the latest? very good thread.

Posted (edited)

Hi Dan

 

Not much to report - busy with work and soon to go on holiday (yippeeee).

 

Have bought & fitted a new idle control valve. Clearly this was not part of the running problems I was seeing but the existing valve, whilst working, didn't seem to be catching the engine idle as it should. Basically the revs would dip below idle before the valve did its job. The new valve has cured this - no matter how sharply the throttle is released the revs drop smoothly back to idle. I managed to locate a Bosch parts supplier that supplied the valve at a much lower price than I had seen elsewhere. (BTW I had removed and cleaned the valve several times before and gave a slight improvement here)

 

I also have the latest 95RON euro chip from Steve Wong (many thanks Steve!) but no chance yet to fit it. This also will not cure the running issue I feel I have - the main reason for this is that the SW chip I had was causing pinking in the sub-2500 rpm range.

 

The plan with Bob is for him to have another look at the car once the new SW chip is in. I'm unlikely to get back over to Bob's until the latter half of September though.

 

I have been researching new AFMs (more as an aside than anything) - found a place called ATP that will rebuild for £150+VAT but not spoken to them directly and hence don't know what this actually means (i.e. which parts are replaced, etc).

 

Basically the car is 'bucking' slightly when coming off/on the throttle.

 

More developments as they happen.

Edited by Chris_911
  • 1 month later...
Posted
Hi Dan

 

Not much to report - busy with work and soon to go on holiday (yippeeee).

 

Have bought & fitted a new idle control valve. Clearly this was not part of the running problems I was seeing but the existing valve, whilst working, didn't seem to be catching the engine idle as it should. Basically the revs would dip below idle before the valve did its job. The new valve has cured this - no matter how sharply the throttle is released the revs drop smoothly back to idle. I managed to locate a Bosch parts supplier that supplied the valve at a much lower price than I had seen elsewhere. (BTW I had removed and cleaned the valve several times before and gave a slight improvement here)

 

I also have the latest 95RON euro chip from Steve Wong (many thanks Steve!) but no chance yet to fit it. This also will not cure the running issue I feel I have - the main reason for this is that the SW chip I had was causing pinking in the sub-2500 rpm range.

 

The plan with Bob is for him to have another look at the car once the new SW chip is in. I'm unlikely to get back over to Bob's until the latter half of September though.

 

I have been researching new AFMs (more as an aside than anything) - found a place called ATP that will rebuild for £150+VAT but not spoken to them directly and hence don't know what this actually means (i.e. which parts are replaced, etc).

 

Basically the car is 'bucking' slightly when coming off/on the throttle.

 

More developments as they happen.

 

Chris, any update to this story...?

Posted
Chris, any update to this story...?

 

And also who was the bosche supplier for the idle control valve?

 

Cheers

 

Andre

Posted
And also who was the bosche supplier for the idle control valve?

 

Cheers

 

Andre

 

 

Hi Guys

 

Thanks for your interest!

 

New idle control valve has subjectively improved the car no end in terms of transition back to idle. Eeven with the valve just cleaned the idle transition was not right, but now it's absolutely steady.

 

I have a revised chip from SW - but only got around to fitting it a week or so ago. Next step is to get over to Bob Watson so I can draw on his well-tuned ears - Bob has suggested it might be worth getting the car on his dyno.

 

Subjectively I actually think the car is running well at the mo with the new chip.

 

Bosch supplier is Truckstop Mobile, Worcester 01905 758600 - about 5 mins off junction 6 of the M5. Speak to Stuart - very helpful and the prices are basically 'trade'.

 

In my search I also found this company for the AFM: ATP Electronic Development Ltd, 01543 427900. They currently have no cores to rebuild my unit, BUT will test it against their calibration curve for £27.50 + VAT (but including return postage).

Posted
Hi Guys

 

Thanks for your interest!

 

New idle control valve has subjectively improved the car no end in terms of transition back to idle. Eeven with the valve just cleaned the idle transition was not right, but now it's absolutely steady.

 

I have a revised chip from SW - but only got around to fitting it a week or so ago. Next step is to get over to Bob Watson so I can draw on his well-tuned ears - Bob has suggested it might be worth getting the car on his dyno.

 

Subjectively I actually think the car is running well at the mo with the new chip.

 

Bosch supplier is Truckstop Mobile, Worcester 01905 758600 - about 5 mins off junction 6 of the M5. Speak to Stuart - very helpful and the prices are basically 'trade'.

 

In my search I also found this company for the AFM: ATP Electronic Development Ltd, 01543 427900. They currently have no cores to rebuild my unit, BUT will test it against their calibration curve for £27.50 + VAT (but including return postage).

 

Nice one Chris - out of interest, how much was the Idle Control Valve?

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now
×
×
  • Create New...