MFI, 1972 warm-up issues (combined)

wahoofan · 07-16-2005, 12:04 PM

My 72T with MFI runs terrible when started cold for the first minute or so - sputtering, won't take gas to even back it(and the fumes) out of the garage. After about a minute, it smooths out and starts to rev enough that I can back off of the hand throttle, but the idle is around 500 or so. When it is warmed up it runs great and it starts right up when warm, but the idle is always 500 rpm. Are these two symptoms related, and if so is there any temporary fix I can do without taking it to an MFI specialist? Any thoughts would be welcomed!

svandamme · svandamme's Garage

does it start well when it's cold or does it take ages of cranking if it has been parked for more than a 1-2 weeks?

mine did that, and also ran like crap the first minutes
on hot starts , no issues, instant click and run

for mine , it was caused by bad compression
worn valves, a crack in 2 heads, worn valve seats
worn cylinders and piston rings... hell , everything was worn on mine...

when things warm up ... they expand, and compression improves...

wahoofan · 07-16-2005, 12:20 PM

It starts right up cold, very little cranking. I've had it about a month and it hasn't sat more than 2 days between starts for me. It is runs poorly at start-up even if it has just been sitting a few hours.

You're scaring the crap out of me with this compression talk........please say it's just an adjustment to the fuel system!!

svandamme · svandamme's Garage

only one way to find out the compression thing... leak down test on all cylinders....

did you have a PPI done when you bought the car?
do you know if there has been any engine work done recently? valve adjustment , anything?

cold cranking is a good thing , but mine did cold crank too if i ran it with no more than 2 days in between...
now , maybe somebody else can come up with some other things to try
but i'm just saying what mine did, and your description sound familiar to me... didn't mean to scare you , but it could be just that...but it is a 33 year old car.

2 hours is sort of a cold start
a hot start is withing 15 minutes after shutoff
in 2 hours time, it should be reasonably cold again
unless it's in the sun and it's a really hot day

Jeff Higgins · 07-16-2005, 05:10 PM

Is the warm up solenoid still in place and operational? Is the paper hose to the left heat exchanger still there and in good shape? It sounds like a problem with this system, but without a little more information, it is hard to tell what is happening. Some folks seem to like to remove this system entirely and use a screw that must be turned by hand to adjust the cold running mixture; that's why I ask if it is even still there. If you are unfamiliar with what these parts are, could you post a picture of your engine showing the MFI system?

pwd72s · 07-16-2005, 05:19 PM

Jeff's questions are spot on...

Grady Clay · 07-16-2005, 06:39 PM

Thanks Paul & Jeff.

Wahoofan,

You have very valid questions. Do a Pelican search on MFI and read everything. Study the CMA Porsche document. Post images. Most important, post very clear descriptions of the symptoms.

This will allow you to ask the right questions and provide the information necessary. There are many very experienced experts on this Forum. The goal is to get you to speak their language for a diagnosis and possibly the best solution.

I just spent the past few days in the hospital, forcing the docs down the same road on my bod. You have to ask the right questions to get informative answers. We have the advantage over the medical profession in that we have a repair manual and a spare part.

Best,
Grady

pwd72s · 07-16-2005, 09:42 PM

Grady? Cindy & I are both hopeful that the docs had some good answers...
Wahoofan? Jeff's questions of the cold start system are a beginning point. Even a crack in the paper tubes mentioned, which often happens where the tube hooks to the engine surround tin, can cause the stumbling you mention...but that's only one thing it could be.
Grady is darned knowledgable...if he writes more, take heed!

larry47us · 07-17-2005, 01:32 AM

Don't let svandamme scare you. My 73E has similar hard start problems. I still curse at it as I flood it time after time while trying to start it. I've put in new injectors (part of a panic resolution of a perceived problem), and it runs better, but the cold start is still a problem.

The MFI is a bear to adjust, and from what I understand it is a finicky demon. But what I have been told is that time spent, and following the CMA manual will get you there. I haven't taken the time yet. maybe next year (sound familiar?)

Grady - Hope that things are OK with you. While you're in the hospital, can you get them to do a withdrawal from your Porsche veins and send it my way? I could use an injection of knowledge, and you're the most knowledgeable one that I know of.

Get better

larry

wahoofan · 07-24-2005, 09:37 AM

Anyone know of a good mfi tech in NE Ohio area? I live in Canton.

Grady Clay · 07-24-2005, 12:10 PM

You don’t need a MFI mechanic – you become your own expert.

With the information and advice on this Forum you can do it all. Yes, you will need a few specialized tools and some equipment. You will pay for them the first time you use them.

It is fun and satisfying. This is pre-WWII technology, built by Porsche 25+ years ago. There isn’t much mystery. It was designed and built by human beings, mortals can work on it. Think of the satisfaction when asked “Who do you get to work on this?” and you reply “I do it all myself.”

Get together with likeminded MFI owners in the Canton-Akron-Cleveland-Warren area. There is comfort in numbers and many lend tools and assistance. Of course there is Stoddard in Willoughby.

OK, what is the problem?

Best,
Grady

wahoofan · 07-24-2005, 05:57 PM

Grady, thanks for your encouragement! I'm a 911 newbee and only moderately mechanically inclined so this system scares the crap out of me! I do know that my first step will be to tune this thing up properly, after which I should probably have the compression checked by the local Porsche mechanic, and I was hoping to find one that knew a lot about mfi and kill 2 birds with one stone. Am I correct in that there seems to be something missing from my system, and would that cause problems(ex. runs bad when cold and idles at <500)? Please go gentle with me and talk slowly

wahoofan · 07-24-2005, 06:15 PM

Thanks to all who replied! I've finally posted some pics of my engine/mfi that might be of haelp, but on a different thread "mfi mechanic needed" Perhaps we can continue this discussion there??

Zeke · 07-24-2005, 08:04 PM

As per your request, I will continue the discussion here. See that thing in front of the coil and next to the air intake with the long black hose going to it? That is most likely your problem by the description you have given of your symptoms. Take the hose off the thing and see if it's clean or packed with dirt. Take the whole thing off anyway. Four screws, don't touch anything else. Get it all clean inside and make sure everything is free to move. Don't sramble the little discs if you take it that far apart (you don't always have to). Reinstall it and try your car again from a cold start.

Get back to us.

LeeH · 07-24-2005, 08:54 PM

Quote:

Originally posted by wahoofan in his other thread
After about a minute, it smooths out and starts to rev enough that I can back off of the hand throttle, but the idle is around 500 or so.

I'm curious as to why you would "back off" the hand throttle after only one minute. This isn't a choke for starting. It's a hand throttle to keep the revs up until the car is warm. I need to leave mine up for about 10-15 minutes or it will stall at idle. After that I'm good.

As other's have mentioned, follow that black paper hose that's below and to the left of the air intake. It goes down to the engine tin. Make sure it's connected at the tin, and on the other side. Follow it and make sure it's attached to the heat exchanger.

Biff · 07-25-2005, 05:37 AM

Is your drivers side heat exchanger in good shape? Are the hoses coming off of the heat exchanger still there up to the mfi thermostat?

1972_911T · 07-25-2005, 06:09 AM

Hi

My car has sI'milar trouble I found that by increasing the mixture it solved the problem but then has the car heated up it was too rich and ran poo.

I have done alot of research into the cause of this problem and so far I'm at a loss I'm thinking along the line of it been the MFI pump that needs work doing on it.

As for the suggestions the he check his warm up hose and heat exchanger am I not right in thinking this would cause the opposite as the purpose of this hose is to supply warm air to the warm up reg so as the engine heats up it it lowers the mixture, therefor if these were broken the car would run fine cold and the problems would come as the engine warms up and the warm up reg fails to compensate by lowering the mixture resulting in the engine been too rich when warm! One bit of advice I got that you could try (didnt work on mine but good place to start) is to strip down the warm up reg and make sure its all clean and not jamming as if this dose not retract the pin that goes from the warm up reg into the MFI pump enough when the engine cools it will result in the engine been too lean on startup causing the problems you described! The procedure for doing this is explained in the MFi info section on pelican parts!

One bit of advice if doing this though is not to lose any of the expansion disks and DO NOT mix up the order that they are in else you will interfere with the warm up characteristics or the engine!

Hope This Helps

jpnovak · 07-25-2005, 06:15 AM

To me it sounds like the system is working fairly well. Many times the thermostat is not working and the MFI pump gets adjusted for easier cold starts instead of fixing the thermostat problem. Yours description sounds like it is tuned properly. I would check to see that the thermostat is clean and the proper hoses are connected.

Grady has said before that the mixture should be set warm and that the car may run lean (barely idle) upon cold startup. This type of tuning also prevents you from driving the engine hard until its warmed up and ready to go.

LeeH · 07-25-2005, 06:33 AM

Quote:

Originally posted by LeeH in your other thread
I'm curious as to why you would "back off" the hand throttle after only one minute. This isn't a choke for starting. It's a hand throttle to keep the revs up until the car is warm. I need to leave mine up for about 10-15 minutes or it will stall at idle. After that I'm good.

wahoofan · 07-25-2005, 07:30 AM

Lee,
Actually, that was probably a little misleading - my idle never goes above 500, no matter how long I drive. Also, now the hand throttle seems to have stopped working. It doesn't seem to have any effect on engine speed - last week I could bring the idle up to about 3000 by using it. Does that seem to be related to my other issues?