Yes - no problem at all - they are 100% pin compatible. The only thing that could happen is that your idle might be hunting. This is because the later DME has a higher idle setting in its code and requires adjustments to the idle on the throttle body. Just disregard it. If it fires up you have identified your DME as faulty.

You can also swap your questionable DME into your friend's car. Again, start and see if it fires up. If not then it is bad. Shops do these swaps all the time to decide if a DME is bad.

There are only a few very rare occasions where a faulty DME could cause damage to a good car or vise versa:

- A wrongly wired engine transplant in an early car can take out a good DME (not an issue with a stock car). I had to repair several that were damaged in that way.

- A shorted fuel output stage in a bad DME could potentially burn good injectors and flood the engine of a good car to the point where there is raw fuel dripping out of the tail pipe. This is only happening if the ignition is left on for a while. My advise is to turn the ignition to ON, crank and see if it fires up. If not switch the igniton off and draw your conclusion.

Ingo

took my DME out and put it into my friends '89. It would turn, but not fire....so, the problem looks to be with the DME itself and not the sensors...etc.

Is there a likely IC/part on the DME that I can replace OR is this better left to those with the proper expertise and test equipment?

J.

NOTE: I had a hardware engineering friend look for signs of cracks in the existing solder joints under a microscope as well as inspect for water damage...nothing was found at the time of inspection, but this would of only been surface mount problems. We do not have the respective test equipment to identify which circuit is at fault in the DME.

The fault can be anywhere from the signal processing stage of the flywheel sensors to the igntion output stage. You probably did the right thing in inspecting for obvuious damage such as cracked solder joints and corrosion. Beyond that I recommend proper test equipment to track down the issue.

I built a specific simulator to test the 3.2 DME on the bench. This device will simulate all inputs and measure outputs. See here for details: http://forums.pelicanparts.com/porsche-911-technical-forum/492967-3-2-dme-tester-my-newest-project.html Without this or something similar it is more like a random guessing game to find the problem.

Ingo

That's pretty cool, but not something I plan on attempting myself...0's & 1's can be confusing enough!

I'll search for a local DME shop...should be able to find something in the 300-400$ range, under the assumption that I have to send in the faulty unit.

Thanks to all whom replied!

Five years ago my 84 just died one day. Towed it to TRE and they spend 2 days going over it. It turned out to be an internally shorted fuel injector that sent a screwy signal back to the DME. They said they'd never seen that before. You might check your injectors.

Reference sensor

I replaced the reference sensors and the head temp sensor prior to biting the bullet and sending off the DME for a rebuild. I don't regret doing so because I have eliminated those as potential points of failure in the future.

It is pretty clear that it is your DME at this point. I guess it is just the cost of the rebuild which makes us dread that the problem would be the DME. I had mine rebuild in Florida and had a good experience with the shop even though I live in New Hampshire. The tech told me that it is not at all uncommon for them to fail.

They got my DME at 2:00 PM and they were on the phone with me by 4:00 PM to let me know it was fixed and on it's way. The repair process was that rote to them.

A word of caution. I had mine chipped for an extra hundred bucks. It ran great at speed but the idle was to low and it would stall without my foot on the gas. Back to the stock chip and it was back to normal.

It was probably just not the correct chip for my 87. Porsche remapped the DME in 87 so the chip may have been tuned for an older model.

Good luck with you endeavor and if you still have issues, return to the sensors as the most likely starting cause.

For those interested, the inspection of the DME "found that the flywheel decoder IC was non-functional. This caused the DME to not see any flywheel activity and thus to not produce spark or fuel signals at all."

I should have it back next week and hopefully be on the road again soon!