2nd day on the road and my '86 Carrera left me stranded.

PabloX · 07-02-2011, 04:58 PM

I went to my dad's for a bit this afternoon. I got about a mile from his house and the engine quit right in front of a Catholic church and I was able to coast into the parking lot. Certainly some sort of sign and surprisingly, I wasn't inspired to let loose with a litany profanities.

I'm 99% sure it's the fuel pump. I used my dad's AAA to get it towed to my house and it's already up on jack stands.

rick-l · 05:07 PM

Do you have a spare DME relay?

Do you want to McGuyver it and try jumpers?

DME Relay - from "The 944 Motronic DME" by FR Wilk

PabloX · 07-02-2011, 05:38 PM

Quote:

Originally Posted by rick-l

Do you have a spare DME relay?

Do you want to McGuyver it and try jumpers?

DME Relay - from "The 944 Motronic DME" by FR Wilk

Hmm, I don't have a spare one, though I should probably order a couple (are the Kaehler ones ok?). I can certainly do a bit of diagnostic with a multi meter.

If it is the DME relay, it's totally dead which seems to be somewhat unusual based on what I've read. The engine chugged a bit and then died while I was on the road. I coasted in and the engine caught twice and ran for a second or two each time, then that was it.

I'll probably order the relay, fuel pump, check valve and a new fuel filter and just replace them until the car fires. It'd be good to have the spare parts on hand anyway.

rick-l · 06:52 PM

If you don't have a spare relay you should go to the standard troubleshooting steps.

Spark
Fuel -- does it run for a sec on starting fluid.

If you suspect the fuel pump you can jumper the fuse in front and hear fuel squirting through the regulator in back

Edit: did I mention spark is an important thing to verify?

Edit: Edit: As in if you get a regular spark all the DME sensots are working.

DRACO A5OG · DRACO A5OG's Garage

When the DME relay dies, it dies. Try tapping on it while trying to crank it over. The solder joints maybe cracked.

But +1 you need a spare relay regardless & check above as indidcated^^^

scottb · 07-02-2011, 11:26 PM

Two thoughts --

Is your battery dead? If so, then it's likely your alternator. My 84 behaved exactly the same way as you described when my alternator went bad.

If your battery is still good, then the first thing I'd check is the DME relay.

dhagood · dhagood's Garage

is your charging light illuminated when the ignition is on and the car's not running? if so, your alternator is most likely not charging.

ischmitz · ischmitz's Garage

If it turns over the battery and alterantor are good. Next, check with a new DME relay. If that is bad the fuel pump shuts down. Once a new DME relay doesn't fix it you need to check whether fuel, spark or both are missing when cranking. This will help differentiate between DME, coil, sensors, etc.

ingo

nesslar · 07-03-2011, 09:56 AM

"(are the Kaehler ones ok?)" Kaehler DMEs are rated at 30 amps, I believe, as opposed to 15 amps for the originals. Should make them tougher, no? I mean, the connections/solder joints are "beefier" I imagine.

DRACO A5OG · DRACO A5OG's Garage

As I recall from previous threads, higher amp relay may cause connected component/s i.e. wiring or worse the DME to over load/ burn out. Relay is much cheaper to replace then the DME or for that matter the wiring loom/harness $1300

Liken to putting 30amp fuse on a a 25 amp fuse that keeps blowing. Defeating the designed purpose of the fuse.

my 2 cents,

Jim

brads911sc · brads911sc's Garage

Agree.

By the correct relay at the correct amperage. I would not use one rated double the amperage. You are just asking for trouble if you have other issues...

Quote:

Originally Posted by DRACO A5OG

As I recall from previous threads, higher amp relay may cause connected component/s i.e. wiring or worse the DME to over load/ burn out. Relay is much cheaper to replace then the DME or for that matter the wiring loom/harness $1300

Liken to putting 30amp fuse on a a 25 amp fuse that keeps blowing. Defeating the designed purpose of the fuse.

my 2 cents,

Jim

nesslar · 07-03-2011, 11:06 AM

Yep, I hear ya, but it's only "a rating", doesn't draw any more juice than the OEM relay, and should (must) still of course be protected by the "stock" (proper) fuse. It's just a "sturdier" relay, I'm sure, assuming the rating is accurate, and would probably last much longer (in theory).
It's like a 200 amp house/commercial electrical panel vs. a 225 amp panel; stronger/heavier bussing in the 225, i.e., thicker copper or aluminum "bars" to connect various circuits to. If each panel is loaded to say 150 amps, same items/circuits, with everthing connected "turned on", no diff. in performance. Many more dollars for the 225....

PabloX · 07-03-2011, 11:17 AM

I realize this is a German car we're talking about, but if the system was really designed to have the relay double as a fuse, that's pretty horrifying from an electrical engineering standpoint.

Canada Kev · 07-03-2011, 12:10 PM

You mean like all the unfused circuits in these cars...?

+1 on all the stuff listed, and get yourself a couple DME relays, even if it turns out not to be the problem. Good luck.

rick-l · 07-03-2011, 12:50 PM

You guys are writing way too much into this relay thing.

dshepp806 · dshepp806's Garage

Quote:

Originally Posted by PabloX

I realize this is a German car we're talking about, but if the system was really designed to have the relay double as a fuse, that's pretty horrifying from an electrical engineering standpoint.

What relay "doubles as a fuse"?

Higher "ratings" mean (only) beefier material(s).....little to do with "current draw"...

Best!

Doyle

PabloX · 07-03-2011, 06:37 PM

Quote:

Originally Posted by dshepp806

What relay "doubles as a fuse"?

Higher "ratings" mean (only) beefier material(s).....little to do with "current draw"...

Best!

Doyle

I was referring to the person who stated that a relay that handles higher current could allow something downstream to get damaged, like the lower amp relay is acting to protect the DME.

Maybe I missed the point of what he was saying but I'm not worried about a higher rated relay in any event.

DRACO A5OG · DRACO A5OG's Garage

Actually, if I may, the DME relay does not blow like a fuse. it usually fails due to fractures of the solder joints inside.

If heavier component would include hefty does of solder then maybe, I say maybe it might be OK but I still default to not putting a higher amp relay.

My 2 cents.

PabloX · 07-03-2011, 06:51 PM

I just placed an order for two DME relays and a fuel pump.

The DME relay that's in the car says "made in West Germany" so it's probably the original and that'll be my first try. I'm thinking of replacing the fuel pump even if the relay does fix it, just because.

DRACO A5OG · DRACO A5OG's Garage

Best wishes on the relay, Brother!

How many miles do you have on your Fuel Pump? They are supposed to be good fro about 100K miles. I believe I am on my second and I have 230K miles so I may be due soon.

Hey I think we just Hi-jacked your thread