Replacing DME?

[Jay87]

Hey guys,

Having an issue where my car will occasionally die briefly at highway speed, with the tack dropping to zero, and pick right back up and continue. Thinking it is either the main relay or the DME. Any way to tell which?

Thanks!
Jay

[StereoInstaller1]

Bypass the main relay and drive.

[u3b3rg33k]

If it's not the main relay, try the crank position sensor.


Do you get a CEL? Stomp codes?

[jlevie]

Also check the fusible link in the DME power cable (in the smaller wire from the battery) and the DME ground on the right strut tower.

[nando]

unless power to the rest of the car is cutting off, it's most likely the CPS. People forget to put the clips/cover for the CPS wires as they pass over the timing cover behind the waterpump pully, the CPS wires rub on the pulley and eventually shortout, causing synch loss. The car will cut out and the tach will die, sometimes the check light will flash momentarily.

[Jay87]

I will look at the wiring to the CPS, but what do you mean by power to the rest of the car? Speedo stays good, as to temp and fuel gages. Stereo stays on, etc. Just notice power cut and dying tach.

I will check for stomp codes.... currently the car is 300 miles away (will see this weekend) because a TRE340 failed on me.... trying to get some satisfaction out of those guys now.

Anything else I should check?

[nando]

if the main relay died then more than just the engine would shut off

[Jay87]

Ok guys, updates. I checked the CPS and the resistance seems to be in spec. Cant find any visual issues with its wiring either.

Checked for stomp codes and got 1261, fuel pump relay. Is this indicative of a main relay issue? Replaced main and fuel relays tonight. Could this also be because I deleted my in-line fuel pump and taped the leads off so that they dont make contact?

Anything else I ought to be looking at?

Thanks!

[Jay87]

Well, the problem persists. Doesn't happen predictably, just every once in awhile. Sometimes it is bad enough that I can barely maintain speed between bouts of heistation.

Tomorrow evening I hope to look at the fusible link. Ground on the strut tower looks just fine, no noticeable corrosion.

Does anybody know what the internals of the DME look like? What could be going bad to cause this?

[u3b3rg33k]

You say you deleted your in line fuel pump. To what end? How old are your plug wires?

[Jay87]

Deleted inline pump for a hi flow pump in the tank, instead of the combo transfer pump and in-line pump that came stock on the '87. My transfer pump in the tank was dead and causing the main pump to whine like crazy.

Plug wires are fine - resistance checks out.

[Jay87]

Checked the fusible link... looked slightly green like it may be corroding, but this doesnt seem severe. Upon closer inspection, I found a small fray in the crank position sensor wiring. Ordered a new sensor tonight. Hopefully this will work. I hate diagnosing intermittent issues. I'll let you guys know!

[Jay87]

Replaced the crank position sensor, whose wiring was worse than I thought. This didn't fix the problem... Drove 300 miles home and for about 50 miles it stumbled like the original problem almost constantly, and then behaved.

I cleaned the DME ground and power supply lines from the junction block and drove back today, and did not see the issue. These electrical connections were dirty, but I've seen worse too... not sure what to think.

If the DME was intermittently losing power/ground, would the check engine light be flashing when the engine was cutting out?

[jlevie]

I fought this sort of problem for two years in a Spec E30. During that time every part of the engine management system was replaced at least once, the engine was replaced, and after being wrecked the car was replaced (using a rebuilt engine and the engine management system from the wrecked car). The ultimate fix turned out to a third engine harness. Apparently the original harness and the one that replaced it both had problems.

[Jay87]

Well, I've been driving the car without issue for awhile, but last night it happened again!

It wasn't nearly as bad as it has been before (only happened once rather than multiple times in quick succession), but it was still there.

I will clean the contacts again and protect them with copper paste, but I'm starting to wonder if the DME may be going bad. Would the tests in the Bentley manual illuminate an issue like this?

Jim, thanks for the reply. When you say engine harness, did you also replace the DME power cable? Also, does anyone know exactly where the DME grounds? Is it the right strut tower?