Motronic DME picture - how bad is this?

[julahti]

I have a badly running 944 1986 that seems to have one cylinder (one closest to firewall) not running well. Checked this and that, no effect.

Thought I could also check how my DME looks like. Opened the box, and this is what I got. Seems like someone has touched the solder joints at some point, but to me the brown areas and "bubbles" seem quite bad.

Is this common that they look like this, or is this especially bad looking? If I buy a used replacement, what are my chances to get one that functions well?

Anyone selling one with # 944.168.121.03 ?

[vdubr928]

Looks like old flux. Normal. From the pic everything looks fine bit that's like asking a dentist if you have any cavities over a faxed picture where you had your mouth closed. Lol. Either way, the brown is flux and it's used to help flow soulder. It should have been cleaned better from the factory so I suspect someone worked on this. It will not affect function.

[s14kev]

Not sure that is flux. Production solder joints are completely clean of flux. If someone has tried to 'refresh' cold or cracked solder joint then there will be brown residue from the rosin flux.

Looks maybe like water damage to me.

[MrTibbs]

I've not opened up a new one, but that looks quite similar to a dead one I opened up from my parts car. That one had been leaked on for quite a while I reckon (a lot of water dripped out when I took it out).

If I ever get more pressing jobs done I was going to try to re-flow the solder on mine to see if it could be brought back from the dead.

The dead DME I had meant the car wouldn't run at all though (wouldn't spark). I've not heard of a DME causing bad running on one cylinder (but I'm not that experienced in these cars - someone with more experience could chime in here). Don't know if that suggests it might not be the DME but hopefully someone can confirm or deny; would be a pain to buy a DME if you don't need one.

Buying second hand from anywhere other than a company that gives you a guarantee is always going to be a bit of a risk. might be worth your while to buy one from somewhere local and insist you plug it into a car before buying (then at least if your problem turns out to be something else you have a known good DME).

[julahti]

Thanks for replies so far. I think I should try to find another to test the car first, as suggested.

I put a close-up of the bubbles that don't seem normal to me.

[vdubr928]

Water damage is usually white. It would only look like rosin if rosin flux was used. It looks like an organic flux that wasn't cleaned. Im not saying its good and these other guys are wrong. Just telling what experience I gained from years of manufacturing. Either way, the bubles are not the problem. The copper underneath looks fine. They may be a symptom but not the problem.

[mikepellegrini]

Your DME looks a lot like one I got out of an 88 NA that my son and I resuscitated. This isn't the greatest picture, but you can see similar damage:



The car had sat outside in the rain for seven years (in Washington state) and had a thumb-sized hole in the battery tray - which drained directly down onto the DME.

I was horrified and sure it was a goner, but as it turned out, the damage was superficial and the car runs just fine.

Is your passenger side floor ever wet? Have you checked your battery tray for holes?

Mine was actually still wet when I took it out of the car (last February). I let it dry for a few days, then cleaned it with circuit board cleaner, using a fluffy brush and compressed air.

If your car runs well, except for one cylinder, how about:

• Plug wires
• Spark plugs
• Distributor cap
• Injector
• Check compression (to see if that cylinder is different)

With just one cylinder running badly, I wouldn't think the DME was the culprit. My understanding of how DME's work is that either they work or not - no halfway stuff.

[vdubr928]

See the white lines surrounding the damage? That is what you look for with water damage. Surprised that one didn't catch fire.

[Dan Himan]

Are you sure you didn't bust a valve spring on the non performing cylinder?

[Guest765]

Originally Posted by vdubr928

See the white lines surrounding the damage? That is what you look for with water damage. Surprised that one didn't catch fire.

Oh hell from what is visible in the pictures that isn't even that bad. I would wager an experience person with time a soldering iron and some 99% rubbing alcohol could clean that up and replace anything that shorted enough to break

[vdubr928]

Anything can be repaired. Love it I resemble that remark. And was being a little fesicious about the fire. Really my point was the first pic is probably not water damage.

[Along4ride]

The flux residue is completely normal for all BOSCH Motronic v3.1 DMEs. The factory used a wave solder process where the entire bottom side of the assembled board is pass over a pool (wave shaped) of molten solder. The rosin flux is a "no-clean" type so they just leave the residue because a cleaning step would cost more and be purely cosmetic. When the rosin was fresh it was basically clear; it only turned brown once it fully oxidized and dried out.

All the fuel injectors are connected together and fired simultaneously. If only one cylinder is having issues the DME is not at fault.

[carlege]

Originally Posted by Dan Himan

Are you sure you didn't bust a valve spring on the non performing cylinder?

OHC with hydraulic lifters...... no springs.

[nota]

Originally Posted by carlege

OHC with hydraulic lifters...... no springs.

?????????????????

[Jrboulder]

Originally Posted by carlege

OHC with hydraulic lifters...... no springs.

Pelican Parts - Product Information: 928-105-905-09-M260

Jackson

[Rasta Monsta]

Originally Posted by carlege

no springs.

[carlege]

Originally Posted by Rasta Monsta

Yep i was wrong. But i've never heard of the springs failing

[Rasta Monsta]

They can break in extreme circumstances (high rev, high lift, too many miles) but are more likely to lose tension/seat pressure. . .this will give you float and charming little marks on your piston tops.

[John_AZ]

Picture on Post 36 recent thread..(also Picture of johnkoawood in engine bay post 35).

Head scratcher...

John