88 carrera no spark issue

[porsche badger]

Hi, this is my first post so hello to everyone

I have a 1988 3.2 that I've owned for 5 years with no issues to date and 82K on the clock. I use it frequently and it's a good reliable car....until yesterday!!!

The car started fine and after driving about 1/4 mile it just cut out and wouldn't restart. The breakdown company came out and diagnosed no spark at the distributor and towed me to friends garage. A couple of hours later I tried it again and it started and ran for about 10 seconds, then cut out again and wouldn't start. This procedure was repeated later in the day with the same result. Today I tried again, it started, ran for about 30 seconds, then cut out again and wouldn't start anymore.

I have checked the DME relay and the first relay inside fires with the ignition switch being turned on and the second fires when the engine starts to crank over. I have tried starting it with the fuel pump relay by-passed so that the fuel pump runs continuosly and this didn't work. I have measured 12 volts on either side of the coil and I have measured about 1K ohms across the speed and reference sensors.

When I used a spark plug connected to the end of the HT lead from the coil it gave a spark when the ignition was turned on, but nothing when cranking the engine over.

Any help or guidance would be gratefully received as I have no idea. I have checked the forums but most seem to be complete non starters where as this one starts after being left for a while then dies again.

Gary

[Tippy]

Hmmm, no spark in the "START" position.

Sure it sparks in the "ON" position? If so, it should jump start and run if so.

[porsche badger]

Yes, when you turn the ignition to the "on" position it sparks once, but when you turn the key to the "start" position the engine turns over, but there is no spark present

[Tippy]

The ignition switch should keep power to the DME/ignition (through supplying power to DME/fuel pump main relay) in the "START" position so the engine will start.

I think a DME expert will have to chime in since you confirmed power to the coil, reference sensor has resistance, and DME/fuel pump main relay is acting normal.

[Chuck.H]

Search the forum for DME solder joints, when I had this condition I had to reflow several solder points around the coil transistors... these parts stand off the circuit board so they put a lot of stress on the solder. If you take the DME apart you can use a magnifying glass to look for telltale rings around the solder to see the broken ones.

Hope this helps,
Chuck.H
'89 TurboLookTarga, 332k miles

[Joe Bob]

DME Relay - carry the spare.

LOCATE the DME under the seat. Put your hand on it and turn on the ignition if you feel it click, it's likely OK. If it doesn't, replace it.

Also above is a recent thread on DME relays....a guy designed a jumper relay for emergencies.

[Tippy]

Originally Posted by Joe Bob

LOCATE the DME under the seat. Put your hand on it and turn on the ignition if you feel it click, it's likely OK. If it doesn't, replace it.

He already stated he did that, must be something else.

[Joe Bob]

Not how I read it....but carry on.....

[krshome]

This might help if it is the DME. 911Chips.com - DME Relay

[porsche badger]

Thanks for the suggestions. I have removed the DME relay and the main Motronic DME unit and will take them into work tomorrow to inspect the solder joints under a microscope. The thing I don't understand though is why it will start, run for 30 seconds or so and then just cut out, it doesn't splutter or mis-fire, it just stops. Then it won't start again for several hours, but will repeat the same sequence of events the next day?

[Tippy]

Wonder if a component inside the DME is overheating and resetting?

[dshepp806]

A failing DME component could give this type of intermittent nature (well, possibly). Some components DO breakdown "thermally",..I used to use a can of freeze spray on other circuits to help me along with thermal failure/diagnosis.

I'm not quite sure I'd rest my laurels on listening for clicks...although this may very well tell you that the coil(s) are doing they're thing, it doesn't tell you of contact integrity..I'd just ensure a fresh swap-out, as to the relay.

I have, however, repaired a friend's DME coil driver circuit, as this particular component had failed (hard fail)...some other successes were solder reflows of suspect areas (both visually AND circuit assignment-wise)....

Based on your description, couldn't it possibly be the dist cap/rotor button? (You mention the end of the coil wire, but no mention of the spark plug wire side of the distributor).

This is a good time to have a spare coil, as well. How "healthy" is that coil output spark?

BEST!

Doyle