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Not running very well


Ian Comerford

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I made the rig as shown.  The tubing is 4mm bore fuel hose from Amazon.   The tee piece is brass from Amazon, you have to buy five.   The unions are from an old pipe connecting the distributor to the WUR, removed some time ago.  The gauge was in an old box.    There is no shut off valve, you just clamp the tube to the WUR with a tube clamp (as used for brake hoses etc.) to see the system pressure.  I used crimped clips to secure the plastic tubing, but small jubilees will do OK.    This set up gave reliable and repeatable results.   You need to take a view about the residual pressure test as the plastic tube acts as a pressure store and may flatter the results.

There are kits on Ebay and Amazon that come with lots of adapters.  I had a job to work it all out and was never sure that the actual connectors would be there.  he official Bosch device costs about £1K.   

1095876583_IMG_20200902_1626467081.thumb.jpg.97a046c3812575c30273e8c67bda1aed.jpg

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I’ve looked at buying one of the ready made kits a few times, but the generic versions didn’t seem to have a pressure gauge capable of displaying the required range of values. Easy to source an alternative no doubt, but I lost interest...

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Got the WUR fitted yesterday, made a couple of adjustments to mixture and then tickover.  Aim was to get it very slightly rich/hunting.  Started and ran well, certainly a big improvement.  Pulls ok in high gear and low revs, all good.  I did notice a slight lack of pull from around 3.5k revs upwards and when I got back from a decent run and left it ticking over I noted it going from very slight hunting to smooth tickover to slight hunting in a cycle.  No idea!  I contacted Steve at KMI who is happy to help and he suggested first of all get a correct CO reading, recommending setting it between 3-3.5%.  It’s booked in tomorrow at the MoT place I use, so it will be interesting to see what it’s actually reading.  Any thoughts on the changes in tickover?

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Just a thought.   My car is very sensitive to ignition timing when idling.  Slight adjustment of timing has an impact on idle speed.   So if car is hunting and vacuum may be affected it could feed back and cause a cyclic effect.  Getting the idle mixture some where near right would seem to be important.   You could verify this effect by pulling the vacuum advance pipe from the distributor.

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If the line to the distributor is under vacuum, when you remove it the ignition will retard.   This probably causes a change of engine speed and hence air and fuel demand.  I may be grasping at straws but this could cause a cyclic change creating the conditions that you have described; a feed back loop.   Whether my suggestion is valid is dependent on how much vacuum exists in the line to the distributor.    The hunting at idle is another issue.

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^ No, not on a U.K. SC.  The vacuum only advances the ignition 5 degrees at cruise. It does not come into play at idle. 

Edit:  I guess hotfrog is saying that a periodic vacuum ‘appearing’ on the pipe might cause timing variation.  Can’t see how that could occur.  

 

Edited by Jonny Hart
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Ian, I think hunting at idle is highly likely to be mixture, adjustable at fuel distributor head. Test each adjustment by very slightly lifting then lowering the sensor plate whilst listening what happens to the idle (revs stumble then recover / revs increase then settle / stall etc.). There’s a very good description of the procedure in Jim’s CIS Basement Guide.

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On 01/09/2020 at 14:29, hagarep said:

Is there a recommended pressure gauge or kit for checking CIS?

Just got new seals, sleeves and gaskets so will refit later this week. Thought I ought to check the pressures as well.

Jason

Here is another version of the DIY fuel pressure testing rig. A lot cheaper than buying a purpose built unit !

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Ok we seem to have a fix.  I booked a short session at the garage that does our MoTs to plug the car into their CO meter.  The garage is about 9 miles away and so the car was nice and warm on arrival.  Sitting there ticking over it was going from smooth to very slight hunting to smooth.  I was relived it was still doing this as it meant things haven’t changed from the last drive.  The CO reading was 5.3%, which is some way over the 2-4% window for the car and also the recommended setting from Steve at KMI which was 3-3.5. I then spent a while trying to achieve that setting and found that the previous adjustments I was making were quite coarse in terms of the amount of movement I was making on the adjuster.  It took a while to get it just right at 3.35 with some very small movements and then waiting each time for the change to settle in to a steady reading.  It now seems to tickover steadily and also pull nicely through the gears.  The Golden Bullet is back, I am happy!

PS sincere thanks for all of your advice and thoughts.  Very useful and appreciated.

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Thank you all, it has reminded me that sometimes the trick is in identifying when you can’t fix it and need proper help.  If I had taken the WUR to KMI a couple of weeks again I would ave saved, well, a couple of weeks.  It also made me realise that turning the WUR into an adjustable one just hid the problem for a bit longer.  The WUR was blocked and needed a refurb

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18 hours ago, Ian Comerford said:

Thank you all, it has reminded me that sometimes the trick is in identifying when you can’t fix it and need proper help.  If I had taken the WUR to KMI a couple of weeks again I would ave saved, well, a couple of weeks.  It also made me realise that turning the WUR into an adjustable one just hid the problem for a bit longer.  The WUR was blocked and needed a refurb

Hmmmm, I'm not sure it was as simple as that

Having said that, before you started changing fuel pipes, it was not obvious that you had any pre-existing issue with the WUR, and maybe you didn't ?

In hindsight, it is likely that changing the fuel pipes dislodged sludge that (further ?) blocked the WUR, tipping the WUR over the edge.

Testing fuel pressures highlighted that there was a cold pressure issue that was likely WUR related as system pressure was spot on.

Changing the fuel pump eliminated the fuel pump as the source of the issue. Possibly the system pressure being spot on suggested that anyway, but it confirmed the WUR was more likely the issue

Making the WUR adjustable enabled you to establish that the WUR was not responding correctly to adjustment because we couldn't get reproducibility on cold pressure and the WUR was unstable -suggesting the WUR was not OK That is the point when KMI's expertise was necessary.

 

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