Running Rich - MU Alignment?

[MJaggard]

Am having problems with the MPG and consumption.  The plugs are fouling black and on "booting it" I get a cloud of something coming out of the exhaust.

 

I have checked most things but thought I would summarise as this seems a fairly popular post.  Has anyone got any comments/ideas:

 

1) Cleaned out the tank, new fuel filter and flushed all lines for contamination

2) Check spray of the injectors into a jam jar

3) Balanced up the butterflies, set the gap of the choke cam and checked the return of the excess fuel lever

 

Now with the plugs still fouling I am left with the following options:

1) Check the pressure relief valve (PRV), firstly with an ammeter across the pump (>5 amps is bad), but then I'll have to take it to the local injection man to get the fuel pressure tested (106-110 psi)

2) Send injectors to Mike Bilney for a service as they could be dumping excess fuel?

 

I was going to check the alignment of the metering unit.  Has anyone got any ideas how to do this.  Is it possible without taking the whole MU off?  Presume you put no1 to TDC on the firing stroke, but then not sure where to go from there?

 

I think this problem is the bain of the lives for the PI owners - grrr it is getting me down already

 

Thanks Matt

[jonlar]

Matt, try disconnecting fuel pump (raise Inertia Switch if fitted) while the engine is running, if the engine keeps going for a couple of secs or more, you can be sure MU is U/S - engine should die immediately.    As regards Fuel Pump current, what make is the pump?

[Richard Crawley]

Matt.

You appear to have carried out most of the checks but others may throw up something I have missed. Clearance on the choke lever & excess fuel lever returning home are the most common culprits. You could check the vacuum tube (from the top of the air box to the top of the metering unit) is sealing properly & is not cracked. The metering unit rotor timing can be checked in situ but follow the advice/recommendations of the BL manual (free download – check previous posts). However, this will not significantly affect fuel consumption; it will just run like a pig. Forget any possible problems with the injectors dumping excess fuel (not heard of that one before!) again this will only make it misfire & run like a pig, usually at low revs; it will not give excess fuel consumption – if you’ve got a consistently good spray pattern you are doing better than most! You can check/adjust the metering unit datum track; some say this is all that is necessary but, personally, unless you are really intent on DIY, I think it’s an awful lot of messing about & a bit hit & miss if you are not experienced at it. Your engine could be knackered (only you will know!) & this will lead to poor manifold depression & excessive fuel consumption. Don’t know how old your metering unit is but my experience indicates these will only last around 20K miles before wear starts to significantly increase fuel consumption.

It sounds to me like your metering unit is either out of calibration or you’ve blown a diaphragm/seal. Any which way, I think the easiest option is for you is to phone Prestige Injection & get them to send you a recalibrated metering unit for £130 or so. Bolt it on, check the fuel line pressure (you can get your own gauge from RS Components & the necessary adaptors for around £30) & away you go!

[Andy Moltu]

If this is a new problem you need to check the most likely causes of the car running rich.

These are a leak in the pipe from the metering unit to the inlet manifolds or a leaking/split diaphragm.

Pull the vacuum pipe off at the manifold end & suck on it - it should hold the vacuum - if you can draw air through the diaphagm is split.

It's not a big job to change and is far cheaper than a recon metering unit.

Make sure that none of the screws holding the black covers on the side & top of the MU are missing - again they allow air to leak in.

Excess PRV settings don't tend to send the MU over rich.

Egil Kvalberg's PI pages are a useful pointer to how to check things out & access the diaphagm if it's split.

I would not advocate tinkering with the mixture control rings nor the max fuel lever unless they have obviously worked loose. Metering units don't tend to go out of calibration abruptly - rich mixtures are generally vacuum leaks or split diaphgragms (has the same effect). Occasionally the datum can jump off it's track (rare). Also check the vacuum pipe to the brake servo isn't leaking (& the servo too) along with the balance pipes between the inlets.

Black smoke may also reflect ignition timing that's way out or a clogged air filter.

[JohnC]

Could the "stuff" from the exhaust be *oil* smoke? If so, I'd be checking compression, and suspecting the rings. Of course shot rings would be accompanied by increased oil consumption, but it would certainly explain the plug fouling - you're describing the symptoms my car had just before its engine rebuild.

 

Worth also checking if you have a valve guide problem - does the "stuff" appear as a puff when you floor it after using engine braking? Or continuously when the pedal is floored?

 

John

[john.r.davies]

Matt,

From recent experience, check the choke cable.  In fact disconnect it from the meter unit and tie the choke lever back (to the rear) with a cable tie.   The cable should be piano wire, and modern versions are not, they are multistranded.  These are stronger and less likely to wear than wire, but cannot push and will kink.  The result is a choke lever that cannot close and an engine that runs rich all the time, with exactly your symptoms and signs.

John

[MJaggard]

Thanks for the help guys - good suggestions.

 

A few answers to the points:

1) Pump is a bosch conversion and about 3 years old with 10K on it

 

2) The engine is running like a pig at low revs - I have checked all vacuum seals hence I am guessing either injectors or MU is off alignment - I'll check this

 

3) Will check air filter

 

4) I think it is putting out oil smoke when "booting it".  It only happens through the revs and not once it has reached high revs.  I have checked compression and they are all fine. Oil consumption has been up a little lately.

 

5) Don't think the problem is excess lever or cable settings as I have checked/balanced all these.

 

I am guessing this might be a mixed picture with some engine problems and an MU off kilter.

 

Thanks for your help, would welcome any further suggestions

 

Thanks Matt

[jemgee]

Andy - that is a great tip about the vacuum pipe onto the manifold. I have been running slightly rich - the MU is holding the vacuum but I think the pipe is not tight enough onto the manifold so I am going to use a jubillee clip to be sure.