MFI cold start problems
 

Just bought a '69 E with a '73T/MFI motor. Very hard to start from cold. (easy once warmed up). Spoke with the mechanic, who seemed very knowledgeable, about the problem. The previous owner, experiencing the same problem, installed a button under the dash, that activates some sort of mechanism that injects fuel when the starter receives power. Doesn't seem very helpful. Any thoughts here? thanx steve

Can you post a pic of the motor/pump?

That would be the easiest way to look for the proper cold start thermostat and plumbing.

Couple thoughts ...

The button may be to trick the cold start fuel solenoid into squirting fuel for starting. You can check a few things to make sure it is working. Here's an old thread here on the forum talking about it and looks like it gives instructions how to test the cold start circuit.

http://forums.pelicanparts.com/porsche-911-technical-forum/220188-1973-cold-star-valve-mfi.html

One thing to check is that the warmup circuit is working. Without getting into too much detail, if it isn't and someone re-tuned the car to run without the warmup circuit, the car will be hard to start and run poorly when cold. The key thing is a small diameter hose that runs from your heat exchangers to the MFI pump on the engine. Make sure the hose is securely attached at both ends and not torn, obstructed, crimped, etc.

One thing to try while you get the above sorted out ... I have racecar that uses MFI with the cold start and warmup circuits eliminated. On advice I got from another racer, if I hold the gas pedal to the floor while cranking, it usually starts firing pretty quickly. Lift to low throttle position as soon as it starts firing of course.

Scott

thanx so much. hope to post a picture this weekend. much appreciated. s

Hold the button while cranking the engine. The button bypasses the thermal time switch which activates the cold start cylinoid. Should start right up when cold. Will flood the engine if used when engine is hot.

Or replace the thermal time switch in the triangle of death and connect the wire currently going to the button. The thermal time switch is not cheap but easy to replace.

Chris
73 E

thanx Chris, but it takes 3-5 tries even holding the button. However, this PM it was a bit better with the throttle all the way down. suggestions? and what of the hand throttle? thanx. s

I'm just a new guy here, and new to these antiquated air-cooled engines, but I have a '71 911E 2.2 MFI engine in a 914 I just bought. Recently it shut down while I was driving, and after going through the whole ignition system to pinpoint the lack of ignition spark, I had the CDI rebuilt.

My point in saying this is that, not only did it fix my spark problem, but it also made the cold starting procedure much more consistent. Mind you, I don't claim to be an electrical or fuel expert (not even vaguely close), but empirically, it made my cold start procedure much more consistent.

What I'm suggesting is that MAYBE you should have the CDI checked out.

yes, I thought of that and once i'm sure I have the best technique for starting the beast, that was my next thought. "90% of all carburetor (MFI here) problems, are ignition". thanx for the congent reminder. steve

I have been driving my 1973 MFI 2.7 for 20 years. When I first got it I had to hold down the throttle to start it cold.

I studied and searched for all the MFI information I could find and I ended up removing the cold start stack of bi-metallic circular disks and installed a switch to run the solenoid valve on top of the fuel filter manually. I have never looked back. I don't have to worry if the thermo time relay is working etc.....

Make sure you can hear the solenoid click when you push in the button. Also remove on the the little lines at the base of the one of the stacks to see that the fuel is squirting when you push the button.

The start technique is push the button a couple of times before cranking, and then crank and it the button for a second at a time until it catches. Then punch the button when the engine slows down from being too lean.

I second installing a better CDI. Best investment I made. I also put in a Pertronix points replacement.

SPARK is very important to these MFI systems for starting and running.

Remember the Bosch system is 50 years old.

Thanx again for all of the info. The car started on the first try this AM, so I think it's just finicky and requires the button to be held for a few seconds, throttle about 3/4 down and fingers X'd. More later should my check list of how to start the car fail. thanx again. s

Cold starts on my 73S work best with pedal to the floor. Warm starts work best with no pedal. It has been that way for 15 years.
Rob

Hand throttle all the way up. DO NOT remove the thermostat. Porsche designed it and that is a big component and helps with warm up.

Chris
73 E

My 73 is so much better without the thermostat. Why not take it out?

Actually I replaced it with an adjustment setup and I use my AFR instrument that is permanently installed to adjust for precise AFR that makes the MFI work wonderfully.

hope to driver her this weekend and will report back. thanx again....much appreciated. steve

My 2 cents.... Pull hand throttle up about 3/4's. Now, the amount you pull up depends on where it actually grabs the rod because you can adjust that. Once up, press pedal down once and let go. Then crank car over with foot at the ready so when you hear it start to catch, give her some gas. Once it starts, modulate it with hand throttle and foot. Once car is warm you can release hand throttle. this is usually a few minutes of driving for me. Done. Now, I don't have the push button. I also have the org cdi and points. Starts like a champ even after sitting for months on end.
Good luck and have fun. MFI is a black art.

Thanx for all of the ideas...I come away with the distinct belief that the plethora of ideas provided shows that these MFI cars have personalities all their own. What works great for one car might not be the best way for another. Dark magic as stated. thanx again. s

What kind of "adjustment setup" did you install?

MARK, You are and expert here. i just made an aluminum plate with a 6mm screw with a lever at the end to depress the lever normally hooked to the warm up regulator.

Reason I asked was because your post said that you can adjust the AFR for the precise setting. So with your aluminum plate & 6mm screw you can screw in or out the thermostat rocker lever in the pump (just behind your plate)
which in turn moves the pumps balance bar up or down which moves the main rack forward or backwards to obtain
your desired AFR. Before I go any further,
You must be running headers, not the stock heat exchangers right?

you got it, and I am running stock heat exchangers and Bursch exhaust system which is 2 small round "glasspacks" that "Y" into a larger "glasspack".