Problem after endind CMA with MFI
 

I've did all the points of the CMA guide..

After finishg, i found that some problems still presist in the car. The engine now sounds much better, not so loud at idle, it's almost quiet.

But still i have 2 problems.

The first one is that i've used the unisyn synchrometer, and i think, i am using it the bad way, because i can't get all the intakes to have the same air. I know i have to buy a STK synchrmeter, it's better and easier, but it's impossible to find it here in Argentina.

The second one and biggest. I am having a problem keeping the car idling... When the engine is cold, i can use the manual throttle (now i have it back :) ) until normal temperature reaches. But if i left the car some time at idle, it will low the RPM a little bit, then another bit until it dies.

I think 2 possible problems for this problem, let me know what you think.

1) somewhere the fuel circuit is a little bit cogged, and is restrincting some fuel to enter the MFI pump, or from the PUMP to each cylinder.

2) maybe an electrical problem with the cables or the coil, or maybe the CDS box i have isn't ok for the system requeriments. I prefer imported CDS boxes if you can recommend one from a modern car, or with the specifications. This one is 12V with negative to gorund and with platines.

Also i found that, when i have the air filter removed when measuring the air intake, i can hear some noise like every open and close of air, like "ts ts ts ts ts ts ts", it incrases if i open more the IDLE screw and decrease when i close it.

Also, i was reading 4.5% CO with rear wheels of the gorund with 2 jacks. And 6% CO at idle. Are those ok?

Thanks!!!

Ariel

Ariel,

Good for you. You are making progress.

First, I don’t think either of the two potential issues you list (fuel supply or ignition) are the cause of your immediate problems.

MFI shouldn’t idle when cold unless the hand throttle is in use. If it does, then the mixture is way too rich and probably diluting the oil with gasoline.

With your combination of 1971 911E MFI pump on a 2.4T, you will probably never get ideal results under all conditions. I would consider making the engine/MFI all one or the other. The GOOD news is it sounds as if you have excellent throttle bodies. Old, worn throttle bodies typically have difficulty coming down in idle.

Your description almost sounds like the mixture is too rich and the sparkplugs way too cold. Your measured mixture numbers are very acceptable. What are the sparkplugs? What do they look like? What color after idling? What is your oil consumption? Any blue smoke at idle? What color is your exhaust after a ‘sporting’ drive?



A good first step is to clean the fuel tank, the screen filter fitting, replace the fuel filter and measure both fuel flow and fuel pressure under all conditions.

Obviously the complete ignition system must be functioning perfectly. The high voltage components should be like new all the time.

With our nice old MFI systems there is much more than just the CMA to pay attention to. Porsche’s CMA assumes everything is new. Do a Pelican search on my name and CMA2.

Best,
Grady

Grady, thanks for the answer. For some of your recommendations i have an answer..

The fuel filter is almost new, i think 3 or 4 complete fuel tanks, and 800/1000 miles with it. The screen filter at the tank is new, i have just installed it 3 weeks ago. How can i measure the fuel flow and pressure safely?

When the car is stone cold, it will not idle alone, i have to keep the throttle a little up to keep it idling, the problem is when the car is hot (180-210) it wont idle now. Before i started all the CMA, and before the last mechanic touched the idle screw at the MFI pump the car can idle when hot, but had the problem of dying when coming from sport driving with the engine complete hot (and had to wait some minutes for the engine to cool before starting the car again).

This problem of dying as you said on other of my posts is because the car was too rich, and getting very hot at high speeds.

But now, it seems the probelm comes with the IDLE screw. I want to know if i can "reset" it to full close or something like that, so i can get it to the right position.

Or maybe, i though i can rerun all the CMA and at the end, again check the CO contents.

Also i will be posting my sparks, because maybe they are making some trouble if they are not recommended for this car, or not compatible with the CDS box i have.

By the way, can you recommend a good sparkplug (maybe 2 or 3 models, because i can't get all of the models here in argentina) for my car, and also the right voltage and specifications for the ignition coil? And also.. the CO content i have to get at part-load and idle, because maybe i can rent for some hours a dynamometer to do a fine adjustment of the MFI pump

Agian, thanks for al grady!!!

Ariel

Well, i've taken out the sparkplug.

It's a NGK BP6ES and it's black and smells like fuel. I think this indicate bad fuel/ratio proportion.

Thanks!

bump

Making some tests today, i found maybe the coil is also making problems.

The question is, which coil should i buy? I want to get a BOSCH coil, but doesn't have the right part number and also if the blue one will work. Does anyone have the original black coil part number so i can trace which one goes right into the car??

thanks!