Hard Cold and Warm Starting Issues - Need Help Troubleshooting

[uvachief]

Okay. I have a 1986 944 na. About 18 months ago, I noticed it starting to have a hard warm start issue. Every morning she would fire up no problem. However, if I drove to a gas station, stopped and fueled up, I would run into a hard warm re-start issue. Happened maybe once every 2 months. Then every month and then about every week. Now it has evolved into a hard cold start as well. I am getting the problem both on cold and hard starts. Here is what I have done so far trying to troubleshoot the problem:

1. Replaced both the cross reference/speed sensors (new parts)
2. Replaced both the fuel pressure regulator and damper (new parts)
3. Replaced the fuel filter (new parts)
4. Replaced the fuel pump check valve and fuel pump (new parts)
5. Replaced the fuel pump/dme relay (but that was in early 2010) (new parts)
6. Refurbished all fuel injectors (re-seal kit) and replaced one faulty leaking injector recently (new parts)
7. Replaced throttle position sensor in 2011 (new parts)

When I run into the problem, I have to pop the hood. Usually, if I jiggle the cross reference sensors up top near the fire wall, she will fire up. However, even that is getting hit or miss now. I am guessing I have a DME box on the fritz or something I haven't thought of yet. Any other suggestions? Is it possible to do a bench test on the DME box or some other way to narrow down the problem? This is driving me nuts.

[pfarah]

If possible, swap out the DME. I had a similar problem and a replacement did the trick.

[uvachief]

I have one on order. Anyone care to post step by step instructions on how to remove and replace?

[John_AZ]

uvachief,

Clarks has a basic text;
DME Control Unit Removal and Installation

Have a fully charged battery.

There is no easy way to "bench test" a DME
You can consult the WSM for ideas and testing or send it to a shop to test --$50 and up + sh

The Porsche 944 Motronic DME

J_AZ

[pfarah]

uvachief,

If you a bit familiar with electronics and the new DME cures the problem, try the following:

1. With the old DME removed, carefully inspect the connector for any damaged pins;
2. Remove the cover and look for any corrosion on the printed circuit boards as well as on any jumpers;
3. Carefully inspect all solder points for "cold solder" connections. You'll see a funky solder point as shown with attached pics.
4. I also would inspect each component (resistor, capacitor, diode, etc.) for burn marks; a clear sign of component failure; and
5. If you still have the patience, look at all the circuit traces for damage including breaks or burns (possibly due to a failed component.

Good luck with the project.

[pfarah]

Oops, I forgot the pics...

[GreenWater]

It might not be your problem but I would also check out the DME engine coolant temp sensor. When mine went bad it would have trouble starting when the engine was warm. It would have to cool off a bit before it would restart. It's an easy part to check. You never know, you might have more that one problem. I would probably put my money on the DME though.

I also had a DME go bad. Car just shut off while driving one day and never started again. I swapped the DME and the car came back to life.(after trying many other things) I looked over my bad DME a few times and never found a bad solder.(even with a multimeter) Maybe I will check it out again someday. Never know when it could come in handy.

Here is a clarks-garge write up on checking the DME temp sensor if you want to check yours.
DME temp sensor

[uvachief]

Okay. It is allegedly placed in the passenger footwell under the variety near the seat correct? Towards the firewall I see someone had installed and amp and nearly hid it under the carpet and covered it with a door and four screws. How do you post pictures in a reply message?

[uvachief]

Okay. It is allegedly placed in the passenger footwell under the carpet near the seat correct? Towards the firewall I see someone had installed and amp and nearly hid it under the carpet and covered it with a door and four screws. How do you post pictures in a reply message?

[pfarah]

Very easy, simply "Go Advanced" then "Click here to Upload a Photo", then :Choose file", Browse your computer for your picture file (jpeg) then hit "Open", then hit "Upload now". It gets much easier once you do it a few times..

[uvachief]

Okay. I bought a replacement DME/ECU unit from a Pelican Parts patron and swapped it out tonight. I had a heck of a time starting it just to move it into the garage. Swapped the old unit for the replacement unit and voila! Started right up. Cut it off and on about 5x with about 60 seconds or more between shut off and restart. Worked every time. Hoping that has solved my problem. I think I am going to ship my old unit off to Specialized ECU Repair in Florida, let them repair it and install a Rasant performance chip. It is $350 to complete repair and restore your DME/ECU unit back to factory specs and another $100 to add the Rasant performance chip. Supposed to increase horsepower by 15% and torque by 20%.

[GreenWater]

Awesome, it feels really good when you fix something like this. When you plug it in and the car starts up is really nice.

[uvachief]

Originally Posted by GreenWater

Awesome, it feels really good when you fix something like this. When you plug it in and the car starts up is really nice.

That good feeling just turned to POOP. Started this morning. Drove to gas station to get coffee. Came out and grrrrrrrrrrrr...rrrrrr......rrrrrr......grrrrr. Wouldn't catch. Popped the hood and installed a brand new DME/fuel relay just in case. Turned over after a few seconds. Drove to work. Sat for about 6 hours. Just went out to take some packages to Fedex and grrrr....rrrr....rrrr....grrrr. Wouldn't catch again. SO FLIPPEN FRUSTRATED.

Here is another little tidbit I have noticed. The MPG gauge on the tach has been getting stuck. This, like the hard starting issue, was intermittent and occurred only once in a blue moon about a year ago. It has slowly been getting stuck more often. Now it is stuck on almost every drive. Sometimes it is stuck until you warm it up and sit at idle as when you come to a stop light. Sometimes it doesn't come unstuck the entire 30-40 minute drive to work. Sometimes it works fine. Is there a connection between the two? What else can I do to trouble shoot this incredibly annoying issue!

[uvachief]

Bump...Switched out ecu/dme again and still no spark. Any suggestions?

[GreenWater]

The MPG gauge could have something to do with your problem, or be a separate problem. ha ha, I guess that wasn't very helpful. No one mentioned it yet, but it could be a bad ground. Your engine looks very clean, but there could be a problem with a ground somewhere. I don't remember where they all are, but it might be a good idea to check and clean the connections. A bad ground could cause both problems. Or there is just something wrong with the MPG gauge, but I would lean more towards a bad ground.

You said that it seems to help if you wiggle the sensor connections. There might be something wrong with the sensor plugs. They get brittle and crack/break very easy. Maybe the wires are broken close to the plug. It's fairly simple to check resistance of the wires from the DME plug to the sensor plugs. I hope that's not your problem, I believe the wires are shielded and hard to fix.(could be wrong)

A multimeter is a great tool to have and you can get a cheap one for about $10 I think. Harbor Freight tools for a cheap one.

This picture isn't the one I was thinking about, it's a little unclear. Maybe someone else can help out with the correct hole number to check on the DME plug.

[uvachief]

Picture of dme ecu box

[uvachief]

What is the second little disconnected plug suppose to be for or disconnected?

[Chad T]

I didn't see anywhere if you replaced the DME relay? That cured my warm start issue.....oops nevermind. Just saw you put a new one in.

[GreenWater]

Ha ha, I was just looking at that plug 2 days ago when I was trying to fix my own problem. My car has a plug that goes in the other end with a wire that loops back around into the plug. It just connects one wire to the other. It's used in other countries and is listed as a code plug. I'm guessing it's to read codes from the DME for other countries? It shouldn't matter if there is nothing connected or if the plug has a looped wire.

[uvachief]

Dme relay is item no. 5 and I switched it out with a new one again about 4 weeks ago.