Mfi Runnin Rich High Idle (enough Said)

[denson]

My 1970 811 S has a chronically high idle at about 1200. My mechanic advised that there is an adjustment fork in the mfi pump (area) that lowers the idle. He say that he cannot get the fork to adjust and therefore cannot achieve a regular idle. We also believe that a fair amount of gas getting dumped into the oil. Is the gas going into the oil a concern?

Any thoughts and/or can anyone explain this if it makes sense.

A million thanks,

John

[caproader]

Do you have the hose connected that runs from the left side heater box to the MFI pump? Hopefully I have not insulted your expertice, but if the hose is not there (both lower and upper sections), the pump sees the engine as 'always cold" no matter how hot the engine really is. This results in the pump running extremely and continously rich with the further result that the excess gasoline washes down into the oil.

John
73 S with sporto and 69 912 in re-hab

[Jeff Higgins]

Second what John says; make sure the warm-up hoses are there and functional. Make sure the discs in the warm-up solenoid are clean and the plunger moves freely. This thing is pretty easily disassembled for cleaning; just use carb cleaner on the inside of the housing and the disc stack. Beware of the spring under the cover when you remove it, and don't let the discs fall off the shaft.

The idle speed on an MFI system is controled by the six air bypass screws at the base of each intake stack. The throttle arm on the pump, as well as every butterfly in each throttle body, should rest on their stops when at idle. If the various rods are incorrect in length there may be a preload in the system that precludes them from resting on their stops.

Even a little bit of gas in the oil is not good. Do not drive the car until you have that taken care of. There are two ways oil gets contaminated with gas on an MFI equiped car. One is cheap and easy to fix; the other is not. John already covered the cheap and easy. Too rich of a mixture will do it. That rich mixture is usually due to a non-functioning warm-up system. The other way is expensive; the pump is leaking internally and it's rebuild time. Hopefully it's not the latter...

[304065]

John,

I have written extensively on this issue and my efforts to resolve it over on Pelican. As complicated as it seems, if the engine is running too fast there are only two causes.

The first is that too much air is getting into the engine. One of four things is happening:

1) Air corrector screws too far open (not likely, they should be set five half-turns open as a basic adjustment per CMA);

2) Leaking gasket between head and throttle body;

3) Throttle stops set too far open; or

4) Air leaking around the edge of throttle plate due to worn-out throttle body.

These are listed in increasing order of difficulty to fix.

If it's the air correctors just dial them in for less airflow as part of CMA.

If it's the gaskets, replace them, they are available new. Budget three hours to remove the stacks, throttle bodies replace the gaskets and put everything back correctly. Having done it three or four times I can do it in about 90 minutes.

To fix my throttle stops, I devised a simple flow bench out of my shop vac and used an STE synchrometer to measure the airflow. You loosen the lock nut and turn the screw to dial the throttle plate as far closed as you can without it actually being closed. If you close it all the way it can stick or wear out the throttle body at rest, so make sure it's open, but BARELY open. On the STE I used a reading of 3Kg/Hr of airflow and that was STILL too much, so try to get it less than that.

On a high-lift, high reversion cam like an S, the throttle plate slaps against the throttle body every time the intake valve closes. This tends to wear a groove in the soft magnesium that will pass air. When you have the TB's off the engine, pour some B12 on top of the plate and see if it drains away. Hold them up to a light to check, although this is less reliable. If you can feel a groove with your fingernail it's probably wear. Bieker or Supertec or Eurometrix can bore the TBs and make new plates, it's very expensive.

So that's the airflow problem. It's NOT too much fuel, the idle mixture adjustment should be adjusted AFTER the part throttle to give 5-6% CO at idle speed. If it's too rich then this contributes to high speed if there's even slightly too much air getting past the throttle plates-- a stoch mixture will burn better than a 10:1 smoke show.

The OTHER reason for a high idle is incorrectly set ignition timing. Use a timing light and verify that the timing setting is exactly equal to the values for the "S" at idle. If you need tech specs for those let me know and I'll refer you to my work on the subject on Pelican. What happens is, when the idle speed is too high, the advance weights swing out and give more advance which speeds up the engine. To test it, retard the timing to TDC at idle. The fact that TDC may not give you the requisite 30 degrees at 6000 doesn't matter for this test.

That's it in a nutshell. Now, about your mechanic. There is no such fork and that explanation does not make sense. You should be able to get the idle down to 900 RPM.

[304065]

Forgot to talk about fuel dilution. It's because the pump is set too rich. Best way to fix is with an LM-1, doesn't have to be permanent, you can use the exhaust clamp. This is also the correct way to set the part load adjustment following the procedure in CMA. You set part load at 7-8% CO with the car moving up a slight incline and then go back and do the idle, not the other way around. If you do idle first it messes up part load.

The danger is not merely that you will scuff the cylinder walls because the fuel washes off the oil film. The danger is that the fuel displaces the oil in the oil tank, so as oil is consumed, the tank fills up with fuel-- until you run the car hard enough to evaporate the fuel from the oil tank and the engine seizes.

So, fix the mixture and the fuel dilution will be solved.

Here's my other link with the advice on advance. Good luck!

http://forums.pelicanparts.com/showt...=mfi+high+idle

[neilk]

John,

When you have the TB's off the engine, pour some B12 on top of the plate and see if it drains away. Hold them up to a light to check, although this is less reliable.

So if the valves are completely closed, no B12 should pass the valves, not even a trickle?

[304065]

Neil,

You have to back off the throttle plate screw to get it to shut all the way, and close the air bypass screw. B12 should hold there for a while, if it leaks, air leaks. It's the same idea as pouring liquid in the port to see if the head is leaking (with the head on the bench, of course).

[denson]

You guys are the best. When I get home, I will check all this out and shall post the findings soon.

I may need to let the mechanic take a peek. I am printing this information for he and I so we can both get an education.

Thanks a bunch,

John

[304065]

John,

The BIBLE for all things MFI is a factory publication called Check Measure Adjust. It was put out by the factory after cars started showing up at the dealer's service department and mechanics decided to change the injection pump. Of course this was not the solution, just that the system wasn't adjusted correctly, so CMA set forth a sequence of procedures designed to identify what the problem was BEFORE touching the MFI pump.

This procedure must be followed every time the car's not running right, and there are a few "extensions" (as Grady Clay calls them) that include things like fixing the thermostat that also affect the system.

Anyway, a link to CMA is provided on the Ultimate MFI Resources thread which is below. http://forums.pelicanparts.com/showt...t=ultimate+MFI

And this one too: http://forums.pelicanparts.com/showt...hreadid=270610

Finally, where in New York are you? Feel free to send me a PM and I can give you some suggestions as to who to contact locally for MFI assistance.