Replacing DME... Chip Problem
 

My engine has a fast (2000+-rpm) idle and occasional starting problems. Trial and error parts replacement has isolated the DME as the culpert (with a new "test" DME car works fine).

A used DME will arive tomorrow AM with a stock chip. Old DME has a Steve Wong chip which it ran for over a year with no issues.

The question: is there any reason not to put the SW chip in the new DME or could the chip have caused the old DME to fail?

I can't think of any way a chip could cause a DME to fail after a year. What do you think?

Thanks.

The chip can't hurt the DME.
-Chris

Are you sure the SW chip isn't the culprit? You might wanna try the stock chip in your "broke" DME before you put a suspect SW chip in your "new" one.

Thanks Chris. What might have caused the old DME to fail... no electrical surges etc, nothing done to the car, just the sudden idle problem? Should I look for some other cause for the DME failure and if so what should I look for?

Thanks again.

ZOANAS... thanks, I'll do that.

corrosion will do that....especially in a Targa....a 17 year old Targa...

I've heard of a the idle stabilizer circuit (inside the DME) failing. (Happened to someone on the list.)
-Chris

fiminod... will look for corrosion, thanks.

Chris, not certain I can identify the idle stabilizer circuit or that I could do anything about it if I found it. I'll look in Bentley.

Thanks.

I've also heard of cold solder joints inside the DME. Usually on the connections that feed the circuit cards from the giant connector on the front. The DME is very robust, and is almost never the cause of problems. Don't get rid of it. You can send it in to have it "refurbished" for significantly less than buying a new one.

A chip can't affect a DME, but if you have a fast idle, I'd check the idle microswitch on the throttle body first. A high idle is a symptom of a switch that is not activating when the throttle is closed. A stock chip will hide a failing idle microswitch better than the SW chip would. Occasional starting problems can be the symptom of a failing DME relay (cracked solder joints), and results of swapping the DME may have just been a coincidence as a result of moving/jolting the DME relay while pulling out the DME. I wouldn't rule the DME as being a culprit yet.

Steve, Thanks!

Will definitely check both things this AM.

I wouldn't say that a "chip can't affect a DME". The chip is simply a very small electrical circuit that operates on a pretty small current. It can, if shorted inside, affect surrounding circuits. Most surrounding circuitry in a TTL circuit is much more robust than the chip itself, but damage can still occur.

Here's an idea: if your DME needs rebuilding, send it to Loren with the SW chip in it. That should keep us entertained for several weeks.

Hey Wavey, that's a GREAT idea. Maybe we could arrange to have a videographer on scene when he opens up the DME and finds the SW chip!

Better than a Master Card ad!

Installed a used DME with an original stock chip today and everything now works fine. The car is not as responsive in the 3-5K range as it was with Steve's chip.

Didn't put the SW chip in because the replacement DME did not appear to have been opened and I need the car this weekend at Summitt Point(why bother trouble if it doesn't bother you). Next week the sorting out of the other items will be done, to include verifying the status of the original DME.

Again thanks to all for the help.

Happend to me twice, after swap out the chip / relay still does not resolve the problem.

I refresh all solder joints on DME box, work fine for a while then quite again

Check the big connector that plug into the DME, saw some pins got platten, that could cause matting contact issue, fix it. problem gone

I think just a coincidence when you plug & unplug the box back, that make the pin has good contacts, and you car work fine, so I do not think chip cause the problem.

Check the big connector and put the SW chip back, hope you can solve the problem

Hey, TJ_sc, Thanks.

I'll follow your advice.

After extensive testing (new/old DMEs with stock & SW chip), the car runs fine in all combinations/permutations except those which include the SW chip.

So... currently running with original DME and stock chip. Will ask SW to please check the SW chip.

Checked the old DME with SW chip and new throttle idle switch and this made some improvement but did not solve the problem. Currently using the original throttle idle switch.

BTW, had an incidence of difficult starting with the "new" DME and stock chip similar to what I experienced in the past. Occurred in early AM after car sat out in the cool damp air prior to driving to Summit Point. Ran/runs fine otherwise.

Thoughts/suggestions?

"I wouldn't say that a "chip can't affect a DME". " - ZOANAS -

The only one that got it right!
Check out here www.systemsc.com/tests.htm .