FOUL FOUL Plugs

[bat10man]

I have just got the 6 back on the road after a short layup and am now suffering with my plugs fouling up after a very short time and low mileage. I have used the car on my short commute to work which in the past has never been a problem.

During the lay up I replaced the metering unit with a recon unit from a reputable supplier along with the injectors and have also rebuilt the inlets. This is the only area I have affected change to that I believe may be the cause of the problem I am seeing. The plugs get so bad that the engine is only running on four cylinders. The worst culprits are 1,2 & of course no 6 which is particularly bad. Any views or advise as usual is most welcome. I am particularly puzzled as I have never had any issues in this area before.

regards

Andy

[jonlar]

The worst culprits are 1,2 & of course no 6 which is particularly bad.

1 and 2 are generally the leaner, has your ignition timing been altered.   Have you tried advancing timing?   Was the MU a correct, direct replacement, or could you have one that's for a different (hotter) camshaft, or vice-versa?

[Guest harry dent]

Bat10man,

I suggest you have the metering unit timed 180 degree,s out of phase.

Regards Harry TR5 nutter  

[Richard Crawley]

Andy,

From you post, I assume the motor is not oil fouling so it has to be something to do with the fuel system “improvements”. Check the distributor timing as Harry suggests; it’s easy to get it wrong, even when following the manual & you really need to remove No 6 outlet to check it’s correct (a real B**tard as the recon merchants never supply you with a new seal!). Failing that, I’ve very recently found an exchange “recon” unit not set up as accurately as one might expect! My problem was with the PRV but it could equally be the injectors or the metering unit itself causing the problem. If you can’t cure it, I would seriously consider going back to the supplier & ask him to set it up with his exchange units!

[bat10man]

Folks,

Thanks for the reply's. The timing is definately o.k. and not 180 degrees out. The injectors all give a fine cone spray as required so I think that the fault may lie with the metering unit and will have it checked out. I have just cleaned up the plugs and the car is running beautifully, so I will monitor the performance drop off more closely this time. Just a thought though do rebuilt/recon metering units require a 'running in' period ?

 

cheers

 

Andy

[Schnippel]

Hello Andy,

the engine runs too rich.  You must adjust the metering leaner  that is very simple.  Turn in addition the whole screwing block a half turn or more to the left .   CO tester in a garage helps. 3-5 % CO is OK.

Schnippel

[jonlar]

Just a thought though do rebuilt/recon metering units require a 'running in' period ?

No, but you can tell your better half that it does, so loads of fuel in a short time to keep it well lubricated!!!

[Bob Stubbs]

Just a thought, but I had my PI into an injection specialist just recently.  The car was running raesonably OK when it went in and in just inspecting the set up of the MU, we took off the diaphragm cover to reveal the 2 springs inside. On top of the diaphragm were tiny glass beads which had been left in there presumably from shot blasting when it was reconditioned.

 

We put the springs and cover back on, fired it up and it ran like a dog.  Rich, misfiring, yoy name it, it did it, just like your symptoms.  Off with the cover again, we completely cleaned out the glass beads, rechecked the seating of the diaphragm and springs, put it back together and away it went first time.

 

Moral for me was that these units are really sensitive to fine set up and you really have to be careful tinkering with the settings.

[Richard Crawley]

Moral for me was that these units are really sensitive to fine set up and you really have to be careful tinkering with the settings.

Yes they really are, even removing the top cover & putting it back can upset the unit calibration. Unless you have a good idea of what you are doing or it’s only returning 10 mpg & you have nothing to loose, don’t fiddle with it! I have adjusted them “in situ” in the past but without the right equipment or unless you are really lucky, I found  impossible to get the thing to run properly over the whole rev range.

[jemgee]

At last years International I put my 6 in for the mobile tune up. When the metering unit cover was taken off the comment was made that the unit had been previously adjusted from the factory settings as the yellow paint stripe on each 'ring' was not in line. I was advised that if it was running OK it was best not to disturb the settings, and on the analyser it appeared to be running only very slightly rich at higher revs. A test drive afterwards showed that the accurate timing check etc resulted in smoother tickover and much smoother at low speeds in top gear. All in all a very worthwhile £45's worth

[JohnC]

Before you run off & do anything drastic, I'd suggest you bleed the injectors thoroughly, even if you've already done it. I know you're seeing a cone spray, but I've been amazed in the past at how persistent those little air bubbles can be. Hold the valve open with a fingernail for several injections.

 

I think it's very unlikely the metering unit calibration is at fault, or all six cylinders would suffer. It's possible that the rebuilt unit has faulty seals, but coming from a reputable supplier that's unlikely. A wrongly set PRV would more likely cause too lean a charge, and it sounds like yours is too rich or not well mixed. Most likely is something not quite right in the installation.

 

Incidentally, I had the same problem in the last couple of thousand miles before I rebuilt my engine. Amazing how a rebore and new pistons, rings, valves & guides fixed the injection system! I assume you're not seeing any blue smoke?

 

With all due respect to those who have successfully tweaked their metering units in-situ, if you can do that then buy a lottery ticket! If the change required is very simple (e.g. too rich at full throttle only), then you may get away with it. If it's more complex, I'd keep well away. The only reliable way to set up a PI is using a fully equipped calibration bench. Oh, and I can imagine the reaction of your supplier if you go back & complain after "tweaking"  

 

John