going down the no start highway well walkway

[kljfamily]

***update it runs see the latest post!

Hello,

New here..not new to auto repair but new to Porsche.

I have a 1987 924s, automatic...it had been sitting since 2004 in the NM desert. Overall though it has a good body and only had 87K on odometer.

Going thru the no start check list here is what I have done.

fuel spark air right..
1. Cleaned out gas tank completely added new fuel pump. cleaned out air box ensure no obstructions
2. replaced dme relay
3. completely removed POS $80 aftermarket alarm system that started going off as soon as I added a battery.
4. took off fuel rail and cleaned up injecters...spark plugs/wires looked good cap was iffy so replaced that.
5. Tested coil with omhs meter across and met spec
6. tested speed sensor and ref sensor at sensor ohms was ok...at the ecu plug coundt get voltage to show so iffy and tach wasnt jumping on start..replaced both sensors..tach now jumps

so now i'm still getting no spark...my spark tester inst lighting but its not led so may be an issue. i'm getting 12v at both termin of the coil when key in on position.

so Im thinking the DME ECU itself may be an issue. im sure sitting in the NM sun for a almost a decade wasn't too nice on any parts.

questions:
1. is the a way to test the DME ECU itself? its an expensive part to have rebuild or buy a new/rebuilt one and I dont want to buy a who-knows-if-its good one off ebay.

If I can be sure its a bad ecu than I can stomach the spend.

Any other ideas?

Thanks

Kris

[944 Ecology]

The easiest way to ensure that a DME ECU is working is to temporarily install it into another working car. In your case, your ECU is shared with series 2 944 cars, and, to some degree, the 944 Turbos, and, of course,the 924S cars.

It will not work in the series 1 944 cars, built between 1982 and 1985/1.

Also, it will not cause any damage to a car it is installed to.

[kljfamily]

that's a good idea,

Ill post locally on Craig's and facebook to see if someone will help me out with a test car.

Kris

[walfreyydo]

You mentioned you replaced the distributor cap, but did you also replace the rotor?
You also may have done this already, but did you put in new plugs and gap them correctly?

And just to be sure its actually bad, or the one you installed is actually good, you tried jumping the DME relay right? (http://www.clarks-garage.com/shop-manual/fuel-05.htm)
Another spark tester wouldn't hurt either. The aftermarket alarm system is a bit iffy too (its good you removed it), but wondering if any wires were inadvertently snipped or spliced in between the aftermarket immobilizer that need to be reconnected...

[kljfamily]

Originally Posted by walfreyydo

You mentioned you replaced the distributor cap, but did you also replace the rotor?
You also may have done this already, but did you put in new plugs and gap them correctly?

And just to be sure its actually bad, or the one you installed is actually good, you tried jumping the DME relay right? (DME Relay Information and Testing)
Another spark tester wouldn't hurt either. The aftermarket alarm system is a bit iffy too (its good you removed it), but wondering if any wires were inadvertently snipped or spliced in between the aftermarket immobilizer that need to be reconnected...

...yes, new rotor. plugs were cleaned and re-gapped but not replaced..(I have a spark plug sand blaster).. tried a spark plug tester but no light showing... I also did jump the DME with the spade and wire setup using example on clarks but that didnt make a difference either. Lastly the alarm though junk was installed prfessionally allowing simple removal. they used clip in's with spade connectors so nothing was actually spliced or cut just tapped so removal was simple.

[ERAU944]

It would be well worth scrutinizing the wiring to make sure the tapping didn't sever a critical wire somewhere.

[kljfamily]

thanks for the reply's and the pointers..know this is a long rode when something sits for that long...but I have plenty of time, patience and 3-4 other projects to focus on when things like this stall progress...i'll update when I figure it out, but im pretty sure ive tested all that can be tested (though I'll run the old ohms meter thru the wiring)...hopefully I can find someone local who can test out the ecu for free or eventually bite the bullet and send it in to ecu doctors.

kj

[ERAU944]

I'd be happy to put the ECU into my car (I'm running a late DME/AFM in my car but can switch to early AFM to help diagnosis) to verify if you can't find someone local.

[kljfamily]

I may hit you up on that offer!

Like I said plenty of time so I wouldn't mind shipping it off for awhile.

Thanks

Ill reach out to you if I don't get any offers here in Albuquerque.

[Jfrahm]

A simple spark checker is really handy and cheap. You can check at the coil also to see if you have a distributor problem.

Do you have tach bounce?

Have you tried a DME relay jumper instead of the relay?

I suppose you have shot some starting fluid, gas, carb cleaner, etc. in to see if it catches on that?

-Joel.

[Chalt]

I am not sure if the 87 924S has the same factory alarm system as a Late 944 NA?

If it does, you can disable it with a jumper to rule it out. When you said you took out the aftermarket alarm I wasn't sure if you bypassed the Porsche one too.

If it has the same alarm as the 944 you may want bypass it while diagnosing the no start.

[kljfamily]

Originally Posted by Jfrahm

A simple spark checker is really handy and cheap. You can check at the coil also to see if you have a distributor problem.

Do you have tach bounce?

Have you tried a DME relay jumper instead of the relay?

I suppose you have shot some starting fluid, gas, carb cleaner, etc. in to see if it catches on that?

-Joel.

Joel,

I replaced both speed and reference sensor and tach is bouncing nicely. I tried a spark tester no spark though there is 12v to the coil and the coil checks out ok on ohms test. I also replaced the DME and tried the 3 wire jumper trick with dme socket.

Kris

[kljfamily]

Originally Posted by Chalt

I am not sure if the 87 924S has the same factory alarm system as a Late 944 NA?

If it does, you can disable it with a jumper to rule it out. When you said you took out the aftermarket alarm I wasn't sure if you bypassed the Porsche one too.

If it has the same alarm as the 944 you may want bypass it while diagnosing the no start.

Hmmm, where would this factory alarm be located in a 924s? I dont see anything under the driver dash near the cpu that looks like that.

Kris

[Chalt]

I don't know for a 924S, but since it has the same motor and DME etc I would think it likely it has the same alarm box? If it isn't near the DME in the passenger footwell, maybe check behind the radio. On the Early 944, that is where they put the alarm box. Late 944 had the alarm box behind the DME in passenger footwell.

I had a 1979 924 many many years ago but that was a completely different animal.

Hopefully someone with more knowledge of the 924S can comment.

[kljfamily]

Originally Posted by Chalt

I don't know for a 924S, but since it has the same motor and DME etc I would think it likely it has the same alarm box? If it isn't near the DME in the passenger footwell, maybe check behind the radio. On the Early 944, that is where they put the alarm box. Late 944 had the alarm box behind the DME in passenger footwell.

I had a 1979 924 many many years ago but that was a completely different animal.

Hopefully someone with more knowledge of the 924S can comment.

On mine the dme relay, all the other relays and cpu are all on the driver side ride under the pedals. there is nothing under the carpet on the passenger side.

[Johnny O]

My issue with not starting was my battery cable with green death. My negative cable especially, after changing them I've been running ever since... Good luck 🤘

[kljfamily]

Originally Posted by Johnny O

My issue with not starting was my battery cable with green death. My negative cable especially, after changing them I've been running ever since... Good luck 🤘

I’ll look t the negative cable this weekend thanks

[kljfamily]

Originally Posted by Johnny O

My issue with not starting was my battery cable with green death. My negative cable especially, after changing them I've been running ever since... Good luck 🤘

Well,

Time for an update.

I replaced negative cable and cleaned ground but no change.

So I did some tests.

1. But back in old dme relay...no tach bounce and no fuel pressure....pit back new dme relay and I had fuel shooting 10ft and tach bouncing

2. Got new fancy led test light that checked grounds and 12v. I get 12v on both sides on oil when in on position

3. Bought new fancy online spark plug tester and get no light at spark tester when cranking(waited till night to test to make sure I wasn’t missing it)

4. Coil tested with ohms meter as within tolerances according to Clark’s specs

So am I down to the cpu then?.
I found these items upon tearing the dash down one is above the cpu one is behind the glove box and the last is some connections that are not connected?

[kljfamily]

Ok, I sent the last post off my phone so sorry for the bad text and spelling.

On the pics the first two are of a mystery box that is above the cpu in the drivers side.

Then another mystery box that is behind the glove box On passenger side

The last is two molex plugs that are disconnected under the dash on drivers side

Anyone know what these are?

[Jfrahm]

I would get the pinout for the DME and look for the negative pulse to the coil and injectors.
You can also probably find the pins related to the alarm/disabler at the DME and verify they are correct for starting. I think if you see tach bounce the DME is powering up and that should mean the factory alarm is not a factor, but an aftermarket one might have spliced into the coil ground signal between the DME and the coil

Google "how-to-wire-the-ecu-ignition-on-a-944-race-car.html" and there is a good pinout and thread on another forum, but I am not sure all the pins are the same on your ECU.

If you have a coil ground signal at the DME but none at the coil then ohm out that wire in the harness.