Electrical Help

[Jon E 85.5 944]

Today, my 85.5 944 (non-turbo) died while driving at about 35MPH. For the last week or so, my 944 has intermittently refused to run above 1800 RPM. Acting like a rev-limiter. Engine started well, even in extreme cold, idles well, and runs good, except for this problem. As long as I up-shifted to the next gear, and didn't get to the 1800 RPM level, engine did not miss. If I did hit the 1800 RPM, engine would die momentarily, I would up-shift, and engine would pull strong again up to 1800. I don't think its fuel starvation, because the engine cut-out is so abrupt and consistent at 1800 RPM.

Now it is not running at all. Turns over strong - but not firing. Any ideas? I would like to steer the shop in the right direction.

[Razorback1980]

Welcome to the forum. Takes four things to make an engine run...spark, fuel, timing, and compression. Probably not the last two so that narrows it down to two. Take a spark plug out and put the wire back on it and lay it on the intake and see if you can see a spark there. If you do, then look to fuel. Turn the engine over for a few seconds, then loosen (but don't remove) the nut on the end of the fuel rail. Fuel should spray out for a second. My first guess is it's in the distributor cap area....when was the last tune up?

[John_AZ]

Greetings Jon E,

It seems the 1985.5 944 has a recurring flaw and my offer of advice to pass along to your mechanic/shop would be for you to print out all of the possible suggestions from June of 2003:
Will Not stay running
Pay close attention to the Clarks-Garage links.

Since many shops/mechanics have no idea on how to fix a 23 year old 944, you can be prepared to pay for their education. I say this in the kindest manner because you may be able to save some money by doing a few tests yourself. Your post said it is freezing, a real hard time for trouble to happen.

Could you provide additional information on the car-improvements or recent work.

Welcome,

John_AZ

[onZedge]

Since you have only one post, I'm guessing you just bought this car. Try giving your car a tune-up first. Replace all the old vacuum lines. Then the fuel and air filter. Cap, rotor, plugs, wires. If you do all that routine stuff first, troubleshooting will be much easier because then we will know what the problem ISN'T and we can go from there.

[autoxr]

Excellent suggestions from the above-mentioned seasoned veterans. Razorback1980 should have added AIR to the formula, however. How many miles are on the car? When the fuel pump dies, you may get lights on the dash, electricity and even turn over from the starter, crank, engine and all that. However, no fuel pump and your dead in the water. The fuel and spark testing techniques are a great place to start. I have seen broken rotors (as in under-the-distributer-cap-rotor)...A vacuum leak will make the car run when accelerating, but would not run on idle. Good luck

[Jon E 85.5 944]

Thanks everyone for the advice. I'll start with the distributor cap and rotor, and move on from there. Checking for spark and fuel pressure makes sense and I'll do that at the same time.

I also received a suggestion from Kelly-Moss Motorsports in Madison, WI to check the DME relay, and the flywheel sensors on the back on the engine block-bell housing area. I realize these will be secondary to the basic checks for spark and fuel.

I've owned the car for just a few months, share it with one of my sons, and use it as our daily drive. Its been a great car, though being 23 years old, has some issues. I've only had to replace the clutch master and slave cylinders, and tires to date. The odometer in not operating, and I do have some minor electrical issues, temp gauge, heater fan comes and goes on lower speeds, etc. I'll keep the forum posted as to our progress.

[John_AZ]

Jon E...
Now I know why you said it was freezing. If you live near Madison, WI. I saw on the TV the 80 vehicle snow delay on the freeway a couple of days ago. When it thaws out, your car will run fine. The blower motor switch fails internally when the contacts arc or the fan resistors open. Its frustrating to get no fan when you need the defrost.

Clarks-Garage www.Clarks-Garage.com, has a detailed writeup on the DME:
http://clarks-garage.com/shop-manual/fuel-05.htm

Many members carry a spare along for insurance.

Update: here is a suggestion from a man in Milwaukee--cracked solder joint in computer.
http://forums.rennlist.com/rennforums/showthread.php?p=5108711#post5108711

Kelly-Moss looks like a nice shop. http://www.kellymoss.com/

2nd Update: another 85.5 poster says its the fuel pump. Jimbo7.1
http://forums.pelicanparts.com/porsche-924-944-968-technical-forum/392447-car-wont-start-post3771815.html#post3771815

John_AZ

[John_AZ]

Here is a thread new owners relate to after the first year:
http://forums.rennlist.com/rennforums/showthread.php?t=365136

John_AZ

[Jon E 85.5 944]

Thanks everyone for the posts.

After some research, and some reading on the "Clarks Garage" site (great site), I determined my problem might be the throttle position switch. I was having a hard time believing DME relay, because the problem seemed too much RPM related. I checked the relay anyway, took it apart, inspected for cracked solder joints, seemed fine.

Today, I removed the throttle body and throttle position switch, and found the switch full of moisture. After blowing it out, swabbing it out with about 20 Q-tips, and blowing a hair dryer into it for about 20 minutes, I did the Ohm-meter tests, re-installed on the throttle body, re-installed the throttle body, and wow, the car runs great. Its idling below 1000 RPM, acceleration is strong and smooth. Hope that was the problem.

As I mentioned, I live in central Wisconsin, and the 944 is my daily drive. It's parked outside in sub-zero weather often, and I'm guessing the moisture in the switch would freeze, and then as the switch would thaw, the moisture would cause internal shorting and send incorrect signals to the DME unit. We'll see how long this lasts - maybe I won't have to purchase that $80 switch after all!