I did the DME reset and no change in symptoms. However, I noticed that there was a strange clicking sound coming from around the CCU. Not in any rythmic fashion. Just every so often there would be a faint almost not audible "click". Sounded almost like those little beetle bugs that pop their backs to make themselves hop (if you haven't seen or heard one of those I certainly apologize for the technical description). Don't know how else to describe it.


I was not able to check out the ground issue that was brought up. Shooting for one night this week to get under there and make sure I've got good metal to metal contact. The CAT is very rusty so this idea may not be all that far off.

 

Well here's a new twist on the (I think) same problem. Went to try the car out today real quick. It has been particularly cold here. Mid 20's at night. I know that's not real cold for some of you. Anyhow, the car started REALLY HARD. Chugged and sputtered and had to be restarted 3 times to keep it running. The odd part is that it had the same symptoms as when I have the A/C running after warm-up. Couldn't touch the throttle or it would die. Finally it caught itself and idled pretty good. Took it for a spin and all ran great. Turned on the A/C while still a little cold and the car ran fine. Turned the switch for the fan and NOTHING. No fan at all. Rotated it back to 0 and back on to 4 and this time it worked. Ran the car with A/C on for a while at setting 4 and no problems through the normal area where it was a problem in the past. Then after running for maybe 15 minutes it started up again with it's chugging and sputtering. Got home and tried to tap one the CCU to see if that would help. Didn't seem to change anything. Again A/C runs very cold. No weird noises from engine compartment or condensor fan (which runs fine).

The only strange noise I heard was again that little clicking sound from behind the dash around the area of the CCU.

Now the cold start issue may be an entirely different subject at this point. But, I find it showed remarkably the same symptoms as the A/C on, no go, issue.

ANy enlightening thoughts?

How do you test the CCU? I am an electrician (but not an electronics genius) so some detailed info would be O.K.

Are there any specific readings I can take at the CCU that maybe will shed some light on whether that is my problem?

How do you get the CCU out?

Would/could the CCU have anything to do with the cold start problem that arose it's ugly head this morning? It was set BTW at about the middle temp setting (i.e. 12:00) with no fan on and no A/C button on.

Thanks again all. Looking forward to putting this behind me.

 

Hi Slant,

I don't know how to test the CCU internals (does anyone?), but I can lend you my spare unit if you'd like. The only thing it won't do is start your oil cooler fan . I can either mail it to you, or you can pick it up if you're coming to Orange County soon. Of course, please return when you're done testing.

The shop manual shows the special factory tool for removing the CCU. I understand it's inexpensive to purchase?? Otherwise, four tweaker screwdrivers placed in each hole worked well for me. Other people have used allen wrenches. Be sure to push the unit out from the back, so as not to crack the face or pull out buttons!

 

O.K. well things get more weird by the day. Last night I decided I was going to determine this fault. I couldn't get the damn thing to fail. I drove and/or idled in my driveway for an hour and at any temp setting, A/C on or not, any fan setting it wouldn't fail.

Clearly this is an "Intermittent" problem.

I'll try again today and see what happens.

Thanks Randall for the offer. I'm going to try and determine if that will even help me at this point. I'm going to get my CCU out and see if anything "looks" funky then go from there.

John

 

HELLO SLANT,

Try this:
Most electrical problems are very often reason of 'bad ' ground [- 31'.
When you have wierd things, please check first all ground negative [31] connections from the car, especially the one from the Dme and Engine!!!!!!!!!!!!
This is not only for Porsche, it is for all cars the same!!

Check your ground wires for corosion and green dubris [cupper does that].
Then check all the postive main wires of the Dme and other important things of they get enough power or to less of it.
Are you sure that you have checked them all, try aigain to start.

May be the a/c has bad ground, and takes it from somewhere else........
Then you get so many wierd faults, you don't want to know!!
May be your car was painted somewhere, and the groundwire on that place did not get enough negative connection, because paint is inbetween it.

Motronic is normaly very relaible in use, so most faults are coming from other directions:
Rpm sensors, Airflow meters, engine temp.sensors, to high voltage by altenator, ground problems.....

This is just a hint, I had many hours spent the last years on different cars on these type of faults.

CHECK YOUR BASE THINGS FIRST BEFORE YOU BUY EXPENSIVE PARTS!!!!!!!!

Hope you find it soon!!!!!!

Arjan Brinkcate
964 C2 1992

 

Arjan,

Where is the DME ground? Are you talking about the actual unit under the seat or is there a grounding point in the engine compartment. Where is the engine ground? I know there is a ground strap between tranmission/engine. Is that the item you are referring to? I am certainly going to look at these items. Just slightly more info please.

 

Slant, I have not checked my 964, but on my 930, I was getting REALLY wierd things happening. Ex: Put a bit of sideways pressure on the sunroof switch,, and other stuff turned on. Drove me crazy. I finally found a multi prong ground behind the instrument cluster that was so loose, you could spin it. Tightened, and all problems went away. In the 964 shop manual there is a page with schematic which has grid coordinates on a diagram of the car which shows all grounds in the car. Really useful. Might be worth your while to go through and check them.

 

slant:

One thing you may want to try if the car is working OK now is to do the following:

1. Warm up the car and put all the fan/AC settings where the car would normally fail.

2. Start going through the car and jiggle/move some of the cables associated with all this stuff around.

If the problem is wiring/ground related and it's intermittent (which it obviously is) you might be able to "hit" the offending cable/wire/ground and suddenly induce the problem. Once you do that, you may be able to move the offender around to make the problem come and go.

Just a suggestion,

Bill Wagner

 

Dear Slant,
Blaupunkt radio removal tools work the best with the control unit, if you have a set of course.
Now to your click click sound. This is a bit of a worry because there are no relays behind the dash. I doubt that an intermittant relay in the central electric would be heard. So what could it be. Well happened tome on the radio. There was this intermittant clicking sound. What it was, was a power lead chaffed through (cut) and shorting out on the radio rack. The clicking sound was the sparks flying.
I highly recommend you get to the control unit and check the wiring throughly. There are 2 connectors on the back. This could be the source of all your problems but you will never know until you look. Follow the wiring and look at clamps, brackets, screws etc for signs of blackness.
As for the DME earth. Tough to loose unless you have major connector corrosion. There are a number of supplied earths to the connector and the case of the DME is also hard earthed through the mounts. The seat rails and the mountings under the seats are by far the most solid of earths. A major failed earth circuit would affect other systems as well. Your problem is obviously related to the control unit somehow. The fan is controlled by the control unit, the aircon is activated by a switch in the control unit and the control unit sends data to to the DME.
Ciao,
Adrian
911C4

PS: The offer from Randall is a great one. I would sincerely consider it. With this temporary replacement you could eliminate a whole bunch of things plus have a good look. Nice one Randall.

 

Hello Slant,

I drive since December 2001 Porsche, but I did noticed that ground of the DME is some place else then under your left seat.
I know that under your right seat is a groud junction, under yout hood in front is a junction for groud on the left side near the cylinder for the hood.
I noticed that all the groudwires I saw have the colour BROWN. Easy to find them.
I checked some of them my self while I put in a Alarm, that's why I know these places.

In most cases has Motronic direct engine ground, because this is the best gound for motormanagement systems.
If you check voltage, you see that some parts could work with 5 volts, this is normal.

Look forward,
Arjan Brinkcate

 

Well my plan of action is to tear the dash apart in the way of the CCU and radio to check out the clicking noise and to see if any loose wires show up on the back of the CCU. After that I will go through the ground points and clean/reattach.

I appreciate the help. Unfortunately I will be out of town next week and will not get to this until the weekend after. I'll certainly let you all know what I find after that.

John

 

O.k. here we go. I didn't have time to pull the CCU or radio. I did however go through all the ground points I could find and cleaned and reattached. Still runs the same. I have for the time being disconnected the O2 sensor as the car runs great without it.

SHould I just try a different CAT? Someone on here was willing to lend me his to test. Do I just drive it like it is with no O2 sensor installed and not worry so much? Isn't this the same as having a test pipe? No CAT?
How the heck do you know if the CAT is bad or not short of having another one around to test it with?
Driving with the O2 sensor off gives off a smell of like unburnt fuel. Can't really describe it. It's the same smell my 2000 Yukon gives off for the first few minutes of warm-up. Like the CAT is not hot yet.
(Obviously, mine is disconnected)
Is there any major harm that could come from leaving the O2 sensor disconnected.

Could I just have the infamous LWF issues? I do have a LWF on my C4. Do I just try a modified chip to see if that will do it?

After all this I could end up with a new CAT I don't need, a modified chip that doesn't help, and a $1000 hole in my pocket for the trouble.

Thanks for any input.

John

 

Dear John,
Without the O2 sensor you are going to run rich all the time. This is going to cost you money. Plus if you have compulsory emissions tests you will fail them.
It may well be related to the LWF. I think we established in the early days of this thread that Porsche highly unrecommend ther use of a LWF in a C4 because of the sensitivity of the flywheel sensor.
It is obviously related to calculations carried out in the DME. Closed Loop calculations.
Ciao,
Adrian
911C4

 

Yes I think you are probably correct on the LWF. I wish I knew then what I know now about the LWF issues. I'm certain I wouldn't have gone that route. Sure sounded like a great idea at the time.

Do you recommend trying a chip to see if that fixes the problems? Supposedly that is the answer if it is LWF issues.

Thanks again.

John

 

Hey John,

FWIW, the car's performance improving when the O2 sensor is removed is an indicator that the cat. is plugged. Per the below link, "When a clogged converter is suspected, some mechanics temporarily remove the 02 sensor from the exhaust pipe ahead of the catalytic converter and look for a change in performance."

When you disconnect your O2 sensor, are you removing it altogether, or just disconnecting the wire?

<a href="http://www.howstuffworks.com/question482.htm" target="_blank">How to Tell if Cat. is Shot</a>

Perhaps it's a good time to pay for shipping Kevin's cat to Las Vegas and give it a try? Certainly cheaper than buying a new one (!), and I imagine you only need to pay to ship it back to Kevin if it doesn't fix your problem.

Best of luck!