Strange MPS issue, Lew's car Options

[914itis]

I am helping Brian with Lew's car. As most of you may know, it is a 2056 with djet.
The car was running fine, he drive it to CT one day and when he came back he noticed that the MPS was hanging. The car starts to run on 3 cylinders with #4 not firing. We checked for spark and injectors they are all fine, but if you remove spark wire #4, it had no effect.

The strange thing is if you elevate the mps about 6 inches up, it's all fine, even that 4th cyl works. All the electrical wires on the unit are fine

(IMG:style_emoticons/default/confused24.gif) ?

Dies the 2056 uses 1.7 or 2.0 MPS?

He would like to make it to Hershey.

[914_teener]

When I read the post and suggestions......there are two that suggest checking the distributer first....

Maybe that's not what you read? (IMG:style_emoticons/default/beer3.gif)

[achman_73_2.0]

When I read the post and suggestions......there are two that suggest checking the distributer first....

Maybe that's not what you read? (IMG:style_emoticons/default/beer3.gif)

Not sure what you mean, as this had nothing to do with the dizzy

[914_teener]

When I read the post and suggestions......there are two that suggest checking the distributer first....

Maybe that's not what you read? (IMG:style_emoticons/default/beer3.gif)

Not sure what you mean, as this had nothing to do with the dizzy

I mean this:

You first suspected your MPS and then it turned out to be your wiring.

Now you have a high idle and you still suspect the MPS?


High idle and pinging could mean several issues. Don't forget the FI system is a System. Therefore you need a systematic approach. The FI system is also an electromechanical system.........so I am suggesting you check the mechanical stuff first to rule those out....otherwise you will be chasing your tail.

High idle could be a vacuum leak which could also cause the detonation due to an overly lean mixture and or timing.....the MPS can also cause the lean mixture as Dave has mentioned....or it could be comorbid.....meaning all the above.

Rule out one thing and then check the next component.

So you MAY want to check out the dizzy to make sure it is functioning correctly for arm movement, correct vacuum hose routing, and vacuum leaks at the advance and retard diaphrams............

That"s what I mean.

[achman_73_2.0]

When I read the post and suggestions......there are two that suggest checking the distributer first....

Maybe that's not what you read? (IMG:style_emoticons/default/beer3.gif)

Not sure what you mean, as this had nothing to do with the dizzy

I mean this:

You first suspected your MPS and then it turned out to be your wiring.

Now you have a high idle and you still suspect the MPS?


High idle and pinging could mean several issues. Don't forget the FI system is a System. Therefore you need a systematic approach. The FI system is also an electromechanical system.........so I am suggesting you check the mechanical stuff first to rule those out....otherwise you will be chasing your tail.

High idle could be a vacuum leak which could also cause the detonation due to an overly lean mixture and or timing.....the MPS can also cause the lean mixture as Dave has mentioned....or it could be comorbid.....meaning all the above.

Rule out one thing and then check the next component.

So you MAY want to check out the dizzy to make sure it is functioning correctly for arm movement, correct vacuum hose routing, and vacuum leaks at the advance and retard diaphrams............

That"s what I mean.

No offense meant.

I don't remember saying anywhere that I suspect the MPS for the high idle.

I said I would adjust valves and check timing, as I don't know when this was last done or if it was correct before I got the car.

There seems to be a debate as to whether the MPS can't affect the car running lean. Some say yes, some say no way. It seems that if the MPS is determining injector pulse length, and you have a larger displacement engine than stock, and the injector pulse length is not long enough at max load, then you will not get enough fuel into the cylinders, causing it to run lean, which could result in pinging.

Does this not seem logical?

Of course this is determined also by timing, injector size etc.

On a supercharged car I built, I went with slightly larger than stock injectors and then had a "band aid" controller which lengthened injector pulse under boost to add extra fuel. The injectors were near 100% flow, so the pulse was lengthened which added fuel and prevented leaning out and detonation. Sounds crappy, ran perfectly, and works for low boost just fine.

I will try to adjust the valves, then set the timing, and re-evaluate the idle. If it still runs high, I will know that the timing and valves are correct and that it the issue lies
somewhere else. I will then check the dizzy, vacuum lines, dizzy advance etc. and see what I come up with.