DME relay or other...

[gerry100]

'86 3.2 125k miles

3 months/< 1000 miles ago, the engine stumbled and quits twice in 10 miles.

Replaced the DME relay with one of the German made spares in the glove box.

Same stumbling/quitting issue yesterday. Restarted after a few minutes.

Before I put another DME relay in, I'd like to see if there is another cause.

inputs appreciated

[Dpmulvan]

https://forums.pelicanparts.com/porsche-911-technical-forum/1121248-4000-rpm-stumble-2.html

[gerry100]

Just tried starting in garage.

- fired right up, typical rough idle and then shut down
- 2nd time - fired a little then died
- now just cranks well but wont fire

?

[GH85Carrera]

I would GUESS that is is your two crank sensors. Replace them, and the head temp sensor unless they are new. If they have never been replaced, they are long overdue.

[grb008]

Do a search for the BMW part numbers much cheaper. I also posted an amazon link in a previous post with a nice little cheap tool to remove and replace the temp sensor. Its a socket with a cut out but its less than $10 and fits into a craftsman's type screwdriver socket handle.

[john walker's workshop]

Old style one contact head temp sensors do that. Ohm the ref sensors at their plug. two lower terminals should ohm 950ish.

[RobFrost]

Testing the sensors seconded. I can't understand the mentality of replacing things without testing what's not working, when there are so many possible causes.

If the sensors are within spec, move on to bypassing the ICV. There is a document called DME test plan, which gives you the order to work through things.

I had a similar problem to yours on my 88 and it was a jammed fuel pump. Bypassing the dme relay a few times made it spin up and now working fine again.

Sent from my SM-G988B using Tapatalk

[gerry100]

Thanks for the inputs, wont have much time to get into this for at least a few weeks.

In the meantime I will switch out the DME relay for laughs.

I'll be back

[Quicksilver]

Parts cannon bad.

Test test test good.

[gerry100]

Originally Posted by Quicksilver

Parts cannon bad.

Test test test good.

True, I've been a parts hoser myself,

Not to good at testing electrics, so I'll be back for help on tools/techniques

[gerry100]

Went out and it started right up and settled into a 900 rpm idle for five minutes,(same DME relay)

Repeated with same effect.

Engine seemed to rev freely < 3k rpms, no load.

Seems like some kind of intermittent issue?

[Quicksilver]

Ewww. Now that sucks. Nothing worse than a car that "might work".

Putting a temporary fuel pressure gauge on the injector rail can help rule that out.
A really cheap oscilloscope can test the reference sensors to be sure that they are giving a consistent 2.5V signal.
Go through all the electrical connectors in the engine compartment to be sure they are firmly connected.
But for a weird intermittent issue I'd think about pulling out the DME, opening it, and inspecting the solder joints on the circuit boards looking for any joints that aren't still smooth and shiny.

Other than that: You are going to have wait until it REALLY breaks.

[gerry100]

Originally Posted by gerry100

Went out and it started right up and settled into a 900 rpm idle for five minutes,(same DME relay)

Repeated with same effect.

Engine seemed to rev freely < 3k rpms, no load.

Seems like some kind of intermittent issue?

Just repeated the drill with same results.

I suspect a current drain based on battery issues, dont know if this is at all related.

[gerry100]

Just did the idle drill and it idles fine.

Anybody have a video of pic of disconnecting the speed sensor, dont want to pull to hard on a 37 year old part part.

[gerry100]

Tested the speed and ref sensors at 1k ohm, the temp sensor tested about 250, which I think is good.

Of Course there is a problem-

Does anybody know the trick with the connectors, The while fooling around I connected the speed senssor before I slid the lock plate back on. Now I cant get it open.

Dont like to strong arm a 37 year old connector. I noticed the other ones click on forever If you align it exactly right.?

Any tricks to know before I get back to it in the morning?

[MStier]

Check your battery voltage. I had an intermittent start problem several years ago. Replaced DME relays a few times, seemed to fix it, then I'd have the same problem. One day, after going through many tests myself and three mechanics, I tested the battery, it was low when it shouldn't have been, took it to the place I bought it, they said it was bad and replaced it, and I haven't had a failed start since, it's been seven years with the new battery, so I'm probably due to replace it.

[gerry100]

Battery cranks well and is 6 months old.

Car started and idled fine (twice)

Still trying to disconnect the speed sensor so I can get it back in the loom

[gerry100]

Did some AM garage yoga and got the connector disconnected.

Back where I started, sensors tested out OK.

Gonna get my DME relay change tools and take a ride later.

Anything else to check first?

[gerry100]

Decided to switch out the DME relay

When I pulled out the old one one of the six pins (marked 85B) stuck in the female part of the connector. Looks like it snapped off inside the housing.

I'd send a pic if knew how.

This is Bull****, how can a pin fail in a no load situation. Especailly when it's the higher priced "German" build.

On the bright side, the car runs/pulls great and I'm confident I've solved my issue.

Time to order the traditional "glove box" relay.

Does anybody have an alternative/suggestion to the POS I purchased before?

Thanks

[gerry100]

Our hosts have stepped up and sent me a replacement under warranty

Will put it in the glove box with a 10mm open end wrench.