Daggone No Spark issue on my 1988 3.2 Carrera

[djk_wff]

Hello Pelican forum good people...

Last Thursday, while driving home, the engine just all of a sudden stopped running. Power was still there, radio still played, just the engine cut off. It occurred 3 times during my 30 minute ride, each time after pulling over, the engine started again (thankfully!).
Now on this Monday morning, I was about 1/4 mile from my destination, and it quit again... This time it did not restart .

Since then here is what I have done,
I verified that it is getting fuel (at least smells like it's getting fuel)(with new DME),
but NO spark to the plugs.
replaced the distributor & rotor,
replaced the coil,
inspected the 3 sensor connectors (CHT, speed, reference) as per a previous thread,
shorted across the CHT sensor,
still no spark ...

the spark plug wires are relatively new, so i think they are ok.

One other recent crazy feature electrically in the last week, the elec windows stopped functioning. The fuse is okay, or at least the single one that I believe controls them. Other than that, no other issues, at least electrically.

Any additional suggestions?

***************
1988 Porsche Carrera 3.2
Triple Black

[db_cooper]

DME relay?

[djk_wff]

Tried my spare Mr. Cooper...

so that appears to not be the issue.

I know of 2 other sensors feeding the computer, the reference and speed sensors. Have not figured out how to check their status.

[Joe Bob]

Turn key to on position and feel or listen to the relay clicking. If you get a click, crank engine and feel if it clicks continously. Could be a 12v power issue.

Do a search on speed sensors, lot's of information on testing.

[Chuck.H]

Do a search for DME cracked/cold/bad solder joints; this is a common failure that is easy to fix, and exactly the symptoms you describe. When the joint makes contact the car runs great... warm it up and the joint moves, loses contact and car stops like a light switch.


Chuck.H
'89 TurboLookTarga, 339k miles

[O'Grady]

Had similar issues with my '87 checked and replaced reference sensors still a no go, ordered a rebuilt motronic, paid next day air and good to go. Many here,a deep knowledge pool, have repaired their own, I do not have the eyes nor the stomach to ruin my own. There is an excellent article on this by our host.

[john walker's workshop]

check the flywheel sensors at their plug. 3 terminals per plug. should get roughly 950 ohms across the two lower terminals in each plug (as they are mounted in the bracket). open circuit or a few milli-ohms are not good.

[Joe Bob]

Contact Ingo, 3.6@cox.net if the Motronic is suspect.

[Socbum]

See if you can borrow someone's DME to test in your car.

[steely]

I saw your other thread about the connectors.
You should be able to do as John Walker suggested above.
This will tell you if you speed & reference sensors are ok.
If they are not, the DME will not allow you to start.

You mentioned in your other thread that you have a new DME. Did you mean DME relay, or do you have a new ECU?
Let us know and stick with this thread.

[LJ851]

A factory alarm unit can cause your symptoms as well.

[djk_wff]

Good tips .... thanks.

There is a new DME relay (so the spare and new are both ok, it appears). have not dug into the computer yet. Trying to verify proper sensor readings before that computer hornet nest.

The CHT appears to be good, as I shorted across it and still no spark.
Need to check the "950 ohms across the two lower terminals in each plug " as the sage John Walker stated.

we will get to the bottom of this!!!

[djk_wff]

The factory alarm unit comment by LJ is very interesting...

what is the technique to check that interrupt?
is it as simple as turning the key inside the driver's door?

many thanks...

[Chuck.H]

I think you will find the computer very simple and easy to examine - just make sure you keep yourself grounded by touching something metal before you start. It's just two circuit boards connected with stiff ribbon cables. The most problematic parts are the power transistors that stand up from the board, I could imagine these vibrate more than the other parts. You will have to remove the lower circuit board from the bottom cover to examine these solder joints.

Chuck.H
'89 TurboLookTarga, 339k miles

[Joe Bob]

Just because the relay is new doesn't mean it works or has power to it.

Search on URO DME fails.

[djk_wff]

Update 9/22/2012 on my no spark malady...

The 3 sensors feeding the dme checked out good (CHK - shorted at conn., speed - reads 1k ohm, reference - reads 1k ohm).

I have used 3 different dme relays ; the one in the car when the problem started, my spare in the glove cmpt, and a new behr relay from pelican.

It appears that I need to take out the computer and check for cold solder joints. Perhaps reflow the solder joints after a good inspection. Does that seem like a reasonable next step?

thanks for all the pelican help...

[Quicksilver]

Originally Posted by Socbum

See if you can borrow someone's DME to test in your car.

Not the best way to test. Some failures such as a short can fry a DME. If you have someone willing with an 80s Carrera try plugging in the suspect DME into the known good car. If the car stops working you know it is the DME.

Originally Posted by djk_wff

Update 9/22/2012 on my no spark malady...

The 3 sensors feeding the dme checked out good (CHK - shorted at conn., speed - reads 1k ohm, reference - reads 1k ohm).

I have used 3 different dme relays ; the one in the car when the problem started, my spare in the glove cmpt, and a new behr relay from pelican.

It appears that I need to take out the computer and check for cold solder joints. Perhaps reflow the solder joints after a good inspection. Does that seem like a reasonable next step?

thanks for all the pelican help...

Not a bad step. If you see an issue then you know that you have something to fix. When my DME decided to go south I spent 3 evenings with a 12x loupe splitting my attention between the idiot box and examining every solder joint on the 2 boards. I never found a visible joint issue... But a friend with an 87 let me plug my DME into his car and it was stone dead. A resolder and an update to the 28 pin chip and it was better then ever.

---
Big thing about these problems that makes me shake my head is when people start replacing parts till the problem goes away. All of these parts can be tested. You can even buy an oscilloscope off of Craigslist for a lot less then the cost of the flywheel sensors and then you can test that and lots of other stuff.
The DME relay can be temporarily replaced by a 3 connector jumper with crimp-on bullet connectors and I guarantee that will connect the current to where it needs to go for an investment of a couple dollars.
The cool bonus that you get from going down the "test everything" route is you will learn a whole bunch about your car and it is well worth it.

Being a parts replacer and a mechanic isn't the same thing. If everything tests out ok then you might start replacing parts because there are a few things that can test good and still be bad (like the stinking new coils...).

[djk_wff]

Thankso wayne, now you have me thinking about the stinkin' coil that I replaced new......

[djk_wff]

Hmmmm, inspected every solder on the 2 dme boards. they looked good and only some extra flux was questioned. So now, check the cables..

let's see...
- intermittent no spark and engine shutoff until the hard failure
- sensors and computer appear okay
- check another new coil? is there a nominal resistance?
- 3 bad dme relays?
- check the grounds? is there list of em?

approaching officially stumped...

[kidrock]

Well, I suppose you could thoroughly clean the 2 main grounding points in the 3.2 which are located at both intake runner #1 and behind the fuel filter. That might be a good place to start.

I have to ask....have you actually checked your fuel flow, or are you just assuming you have sufficient fuel because you smell it? Also, you state that you "shorted" the CHT sensor....what process did you use when you did this?

Quiksilver is absolutely correct. We should probably start from the top, and do a thorough analysis for fuel and spark. So many people have posted similar issues as you, only to find out they had a clogged fuel filter or something of the sort. Make it easier on yourself and your wallet.

EDIT: Be sure to inspect and clean the grounding point where your battery ground cable attaches to the body, as well.