slant911

I've found that my car runs pretty bad when cold and gets better and better as it gets warmed up until it runs nearly flawlessly at temperature. I found yesterday though that even at temperature if I turn on the A/C the car runs crappy again. Hesitates and things like that. A/C operates real good. Not a stuck compressor or anything like that. Battery is brand new. Any ideas???

Thanks.

Kevin

Have you replaced your cylinder head temp sensor?

slant911

No I have not. How can I test that item?

Bill Wagner

Sounds like a typical problem with a light weight flywheel. Didn't we sort of go over this about a week or two ago???

Your car has all the typical LWF problem symptoms...the REAL question is can you learn to live with them? I really think that's about what it amounts to....can you learn to adapt your driving habits to match the changes the light weight flywheel introduces to your system???


Good Luck,

Bill Wagner

964Cab

Kevin: Any surprises if I want to change my head # 3 engine temp sensor ? I have the 14mm tool. I have yet however found said temp sensor as the rear blower motor fouls my visual access. I assume I can get to it from the top side ? Or is under the engine ?

My cars starts fine in cold and warm weather but for some reason at cold temps the engine stops suddenly and doesn't settle down until I get it nice and warm.

Thanks,

Patrick

Kevin

Patrick;

The temp sensor it located on the #3 cylinder head. You have to access it from the underneith. It is angled toward the front of the car.

Randall G.

Hi Slant911,

As I recall, you have the shop manual, don't you? The test procedure for the engine temperature sensor is on page D24/28-12.

I don't believe a LWF will cause your engine to hesitate or run crappy (sorry Bill ... perhaps I'm missing details from a previous discussion?). It should only affect your idle and launch, maybe your shifting (engine RPMs fall off faster) and torque characteristics (less mass spinning). When I had the LWF in my car, it ran wonderful--when it wasn't stalling or idling erratically with the AC on.

Best of luck!

slant911

Yes I do have the manual. I tried to get the DME connector off to test the leads associated with the temp sensor and I can't for the life of me figure out how to get the one side off. I've gotten the side off closest to the actual wire harness via the silver lever, but, the other side will not release no matter what from the latch that holds it in. What is the trick? I've shoved little screwdrivers in there to push/pull and nothing happens. Does the seat have to come out in order to do it?

Bill,

I do have the lightweight flywheel. I wouldn't expect a lightweight flywheel to show problems whether the A/C is running or not.

BTW - I'm still trying to find out from my mechanic EXACTLY what was put in. Clutch/flywheel/etc...

964Cab

Hi,


I took my DMe brain out of a '90 C4, wish
I hadn't as now I can't get the reconnected brain to "take" new parameters and my dash looks like a XMAS tree !

Why not measure the engine temp sensor at the disconnected wire from the sensor itself rather than messing with the DMe brain connector ?


Anyway, if you must: There are four 10mm nuts holding the brain to the floor. I backed the seat all the way back and raised it as much as possible. Took those 4 10mm nuts off and also clipped those wire clamps that hold the wires free movement along the floor. Then I was able to get that hooked end to release out. Trying to get that connector off while the brain is bolted to the floor is a hassle and those wire tie clamps don't help matter either.

Patrick

Bill Wagner

I've been interested in light weight flywheels as potential solutions when (and if) my Freudenberg decides it's time to die.

Not all light weight flywheels are created equal...they are, after all, after market parts and manufactured by several different companies. I've read about several success stories with them, but I've also read about several that were problematic.

If a light weight flywheel is going to be troublesome, it will do so because the flywheel causes the engine to decelerate too rapidly. Since the DME is monitoring all this stuff (engine RPM at the flywheel) it attempts to compensate for what it sees as unusual conditions (rapid deceleration) by adjusting the fuel maps for what would be an "odd" or perhaps "out-of-spec" condition, since the engine is no longer decelerating at the rate it's intended to. The problem becomes worse when the engine is carrying an additional load (like the AC). Several aftermarket shops offer upgrades so the DME will handle these conditions better. I know of one person who went with a LWF after his Freudenberg failed, then added a chip, and then finally replaced the LWF/chip with the original DME setup and a LUK flywheel. This type of problem seems to show up more on C4s rather than C2s, for what that's worth.

There is currently a survey going on at SmartGroups, and I made a point of including LWF info so we could see what works and what doesn't. All input is welcome.

Cheers!

Bill Wagner

Adrian

Dear Randall,
A LWF will certainly cause all the problems reported by Slant911. There are many examples of this. This question has been gone over time and time again. Bill quite rightly says that the problem is much worse on a C4 than on a C2. Porsche have released documentation on this which has been posted to this forum and others "Many" times. The DME, flywheel sensor and timing ring are part of the problem but the sheer change of mass in the drivetrain causes major problems which vary from 964 to 964. A number of people reverted back to the dual mass and all their problems disappeared. I have data from around the world on this subject. Many of the more reputable shops in the world will tell you that you have a 1 in 4 chance of having major RPM problems and running problems with a C2 and a LWF and 2 or 3 in 4 with a C4 and a LWF. Most people and shops do not even know that the flywheel sensor setups are critical and different between a C2 and a C4.
Patrick. Was this DME the one originally installed. Did you remove it with the battery still connected. If you did then I recommend you disconnect the battery with the DME in place. Wait 20 minutes (yes there is a reason for this) then disconnect the DME. Remove the DME and check the pins and connectors for damage. It is not 100% clear from your post why you played with the DME. What other work have you carried out. Have you played with the ignition system. Have you tried to install a "Check Engine Light".
Ciao,
Adrian
911C4

Randall G.

Similar to my own story, except I never tried a software fix. Back in '95, when I replaced my LWF with the LUK, there was no talk of a software fix for the idle problems--at least none of my mechanics told me of such.

Anyway, I had no problem with how the car ran with the LWF--once it was moving. It was the stalling and embarrassing erratic idle (when running the AC) I could not tolerate.

Off to add my input to the SmartGroups survey ...

Randall G.

Hi Adrian,

Would it be possible for you to post (or provide a link to) Porsche's documentation on a LWF causing problems other than idle problems? I've been following this board for about a year, and this is the first time I've heard it suggested that a LWF can cause the engine to run crappy--other than idle problems. Which doesn't necessarily mean it's not true ... Anyway, I would like to understand the phenomenon by which the LWF is causing hesitation, running like crap, etc., and I'm guessing the Porsche documentation would at least give a thumbnail sketch.

I suppose a good piece of data is whether slant's problems just started recently, or have existed since he bought the car/the LWF was installed.

Don't get me wrong .... I don't mean to defend LWF's. I hated mine (because of the idle problems), and the day the LUK replaced the LWF was a beautiful day indeed.

Adrian

Dear Randall,
I am afraid I am not able to cut out sections of my book anymore. Complicated issue now. Part of the trademark and copyright approval process. I am sure it is or was printed at the www.alldata.com site. I know I posted it either to this board or to rennlist before I got into these book issues. Was some time ago though. However the explanations provided on this thread including the description by Bill is very accurate. It has everything to do with the Maps programmed into the DME. These Maps were recorded in a lab and on the test track using a DMF. The DME expects to see certain RPMs under certain conditions. The LWF provides different RPM measurements for the same conditions. This causes the DME to create the wrong calculations and ultimately provide the incorrect fuel and air mixture. Timing and Dwell Angle Maps are calculations are also wrong.
Ciao,
Adrian
911C4

PS: When the single mass flywheel and light weight clutch were installed into the 964 RS, Porsche reprogrammed the Map chip and installed a special motronic timing ring which is the key to the problem.

Adrian

Something I forgot to add. How bad the problems are, can be directly related to the part number DME installed. If you have a 1989 C4 and install a LWF you may have less problems than with a 1990 C4. Why?, because the 89 C4 has a single sensor and a single mass flywheel and the DME is mapped for a single MF. A lot less complicated than the DMF system. However if you have a later 1991 model DME on a C2 you will have a better adaptive circuit system than the earlier models. C4 problems remain. If you live in the USA, you have a better chance of having the later DME part number (964-XXX-XXX-03) being installed than if you have a ROW.
This is a complicated issue. There are no simple answers and no simple solutions. A typical grey Porsche subject. Not Black and White,
Ciao,
Adrian
911C4

PS: Unfortunately you cannot go back with DME part numbers. If you install a LWF in say a 1991 DMF C2 you cannot (should not)install a 1989 DME. Unless of course you want to be game and see what happens.