DME swap question

c5pilot · 08-22-2010, 05:02 PM

I posted in the past about my poor running and new to me '83. Turns out the DME is bad so I am planning on buying a rebuilt one. Since mine has never run good enough to find out if I have the classic stumble issue that most had, my question is this. Should I purchase a late model DME and matching AFS vs my early one to eliminate the stumble issue ? Also , I understand this would allow the DME to be chipped although I understand the gains are not huge. I plan on tracking and autocrossing the car so this type of stumble could really be annoying. Some say the FR Wilk chip is certainly worth it.

Thanks

fmartenies · 08-22-2010, 05:40 PM

How do you know your DME is bad?

c5pilot · 08-22-2010, 06:31 PM

In short, the original shop that serviced the car before I bought it said that the DME was bad. I tested everything and thought the same. Bought a used DME and it ran just as bad as my original. I thought , what are the chances of two bad the exact same way ? I gave in and took it to another shop, and they swapped a good DME in and she ran perfect.

HondaDustR · 08-22-2010, 07:45 PM

I would pull the old one apart and look for bad solder joints. It might be an easy fix, as the solder joints for the fuel injector drive transistors are known to crack with age and heat cycling. They were not originally heatsinked IIRC, but later were, due to this. Just get a small 30W or so pencil iron from radio shack and remelt all the solder joints and try it again. What have you got to lose if it's dead already. Otherwise, I would go with the late DME if it's not too hard to aquire one. You will then be able to chip it, and there are a couple good chips out there that really breath some life into the low and mid range part throttle maps. They will quicken the throttle response a bit and gives the motor more grunt (at least the 944MAX chip does)...nice for autocross I would assume.

c5pilot · 08-23-2010, 05:39 PM

Hey HondaDuster.

I looked at all the solder joints and they looked good to me. I guess I could touch them up , as long as I don't overdo it and mess it up so I could not exchange it as a core if need be.

HondaDustR · 08:09 PM

Check this out.
DME Repaired w/pics - Rennlist Discussion Forums
In the picture kind of behind and to the left of the big transistor in the foreground are two TO-220 package transistors bolted to the board. I believe those are the fuel injector drivers and are heatsinked in the later models. Check their connections as well as the large transistor in the article. There's a link to another thread with pictures, but the pictures can only be accessed by members. Sounds like the guy just re-melted every joint on the power board and that fixed his. Look for any large joints connected by large traces to spot the higher power circuits that are more likely to have solder joint problems. Look very closely, wiggling the component if you can. Cracked joints can be very difficult to spot. That's why some people just hit all of the joints with the iron just to be sure. Be careful not to heat it any longer than is needed to completely melt the joint. A 30W pencil iron should be hot enough to melt all but the largest joints on the board nearly instantly. If any of the joints don't already have enough solder to make a nice cone shape, feed a little bit of 60/40 rosin core solder to the melted joint to fill it up. You don't need much at all, so use thin guage solder. Iron tip on one side of the pin, solder fed on the other side. Make sure the joint does the melting of the new solder, not the iron.

Good Luck.