85(early) 944 starting issues...

[shiftdrift944]

as i have posted on another thread 944 only runs on 2 cylinders!! help!!
after replacing the crankshaft sensors(both) i wasn't receiving fuel to the rail so i first jumped the relay and it got fuel to the rail... then i tried to started and it started several times... then since i knew it was either the sensor not gap right or the relay. so insert the old relay i had on it and gave a try and it turn on normally.

till i go back the next day and try to start it and nothin? this is with the old relay... so i tried with the (new) relay i bought a few months ago... and nothing... and for also when im turning the key and as soon i release it would start and everything but it runs for like 30 sec. and dies? could this first be either the fuel pressure regulator? or the computer itself?

[Outback Porsche]

If there is truly nothing wrong with your dme relay, a new dme relay will give you the same fault symptoms. The fact that you have different symptoms when you use the new dme relay is a worry. It's highly likely that the 'new' relay is a dud, and that the old relay could be faulty.

Try using the wire jumper (as per clarks garage) in place of the relay. If you still have the same fault (starts then dies), check your sensor gap again, check your start switch then try another dme (or send it away to be checked - the dme could have bad solder joints within it).

Cheers,

[mattdavis11]

Have you tried the ignition switch? It's probably old and brittle, just making contact every now and then. $12. Just curious, when you put the key in the ignition, does the radio work? It should.

[shiftdrift944]

outback porsche: so here is how i check if the dme relay was, i did the jumper first as clarks garage procedure and got fuel to the rail and then added pressure. Then it started up fine and i shut it and restared several time to check it just the dme relay. it started up thos time i start it up but then a few mins (5-10min) i put the old dme relay and it fire right up! all this is in room temp. inside a shop and it happen yesterday....
when i went today to started up with the old fuel pump relay it wouldnt start...
so i remove and check the cranckshaft sensors and they looked clean and not hitting anythin like the original ones... pic are up on 944 only runs on 2 cylinders!! help!!

so if im ever so off on the gap could this cause it to not run and run sometimes?

[shiftdrift944]

mattdavis11: yea well i dont have a radio install on it right now but it does have one... and i just switch the ignition switch like last week i have pic posted on this thread 944 only runs on 2 cylinders!! help!! so i have either a bad computer or the gap is of the sensor is off...?

[jamesjedi]

Clarks-garage.com has a 'step by step' to follow. It helped me.

[Outback Porsche]

Originally Posted by shiftdrift944

so if im ever so off on the gap could this cause it to not run and run sometimes?

Anything is possible. Having said that, I doubt it. The signal is weak anyway but from a new install I'd expect it to work or not. Not be intermittent. It would take some time for crud to build up on the sensor to block the signal if the gap was too large.

Here's how the DME relay works (there's two relays inside the package);
When you turn your key to ON, the first relay is energised. I stays energised in the START position. This relay provides 12V to the DME. When the key is in the START position, 12V is also provided to the DME on Pin4. Through circuitry in the DME, this 12V causes a GND out on Pin20 that energises the second relay and turns on the fuel pump. After the car has started, the speed sensor sends its signal to the DME and again through the DME circuitry also produces the GND signal from Pin20 (Pin4 no longer has 12V because the ignition switch is now in the ON position). This keeps the fuel pump running.

Thus, if you lose the speed sensor signal in any way, the fuel pump turns off and the car stops.

Hardwire jumpering of the DME relay hides any intermittent faults within the DME. It is not a conclusive test that the DME relay is faulty. What it will do is confirm that your sensors are okay or not.

So, you have two choices. The relay is intermittent or the DME is intermittent.

Cheers,

[shiftdrift944]

ok ill see thanks outback porsche for clearing things up , well the DME it self should be fine since it stared up fine when i got the car, and then i replace the fuel pump and relay and i had to start it with starting fluid everytime... then after that i replace the head and new sensors.

so ill see if i can pull out the DME and check if 12 volt are going to the dme and on pin4 and with gnd pin 20 or on the car from the plug to the DME.

what the Pin # the first relay provide the 12 volt to the DME?

well i could lose signal from the sensor since; last time i tried to start it, it will start once i had the key back on the on position and then it dies 5 sec. later. i could also check the wiring from the connector of the sensor to the DME plug, and ill see if the resistance are correct.

[Outback Porsche]

Originally Posted by shiftdrift944

what the Pin # the first relay provide the 12 volt to the DME?

Pins 18 & 35 on the DME for 12V.

Good idea to check the wiring.

The relay panel can get brittle. Working it as you have by replacing the relay a few times could cause wires to push back. It's worth checking for issues in there too.

Originally Posted by shiftdrift944

it will start once i had the key back on the on position and then it dies 5 sec. later.

This does sound like you lose the 12V to the fuel pump when the ignition switch is in the ON position.

Cheers,

[shiftdrift944]

ok thanks ill check the wiring to the DME and the wiring from the sensor to the dme.

[hanzgeier]

Outback Porsche: -- Totally OT and I am probably next to no use for helping resolve your problem - but a 944 in the Alice? Nice!

I thought Wagga Wagga NSW meant parts were hard to come by....

Congratulations on your dedication

[Outback Porsche]

G'day Hanzgeier,

I'm having a ball out here in this thing. Your right though, parts are a bugger to get. Enjoy the forums, there's lots of info here and great help by all participants.

Cheers,

[HondaDustR]

Originally Posted by shiftdrift944

ok ill see thanks outback porsche for clearing things up , well the DME it self should be fine since it stared up fine when i got the car, and then i replace the fuel pump and relay and i had to start it with starting fluid everytime...
well i could lose signal from the sensor since; last time i tried to start it, it will start once i had the key back on the on position and then it dies 5 sec. later. i could also check the wiring from the connector of the sensor to the DME plug, and ill see if the resistance are correct.

You might be right about the sensor signal, since Outback explained the fuel pump section of the DME relay will only stay energized when going from START to RUN if the DME is getting a signal from the speed sensor and the wiring and connections between the DME and the relay are good. 5 seconds is about how long it would run with a correctly operating fuel pump suddenly stopped, seemingly caused by the DME relay losing the energizing voltage supplied when the key is in START when the key is released and not replaced by the voltage delivered when the DME gets the speed signal.

It's definitely a good idea to test the applicable DME wiring. Test the sensor resistance at the sensor connector, then at the DME connector. They should be pretty close, otherwise you have some sort of wiring or connector problem. Test voltage at the assorted inputs and outputs at the DME and relay to see if voltage is getting to/coming from where it sould be when it should. Work from the battery outward to the ignition switch, DME/relay voltage inputs, DME/relay voltage outputs, fuel pump. Somewhere it's not getting through when it's supposed to.


Just like the DME relay which also has solder joints prone to cracking, the DME could just as easily work fine one day and not the next, so it is a possibility if everything else checks out and the voltage is stopping there for no other apparent reason. Others have successfully fixed theirs by re-heating all the solder joints inside.

(just in case you don't have these.)

DME Connector 35-pin

Pelican Parts: Porsche 924/944 Electrical Diagrams

[shiftdrift944]

damn... ok well i checked the volts from the dme plug and they are above 2 volt and for the other its over 2.5... but i did happen to get a reading of less than 2 volt.... i forgot which sensor it was.(used clarkgarage procedure) ill check them again since i forgot to check the resistance...

well i opened the dme i didnt get to take pics of it but it looked i had a coating to protect it form water damage but i wasn't cover all...also the solder looked good no burned or bad solder joins. So idk if previous owner has some else open it and fix it... but i did notice that it had the top two crew different to the bottom, this is inside what holds the chip down. This is the same on the other side... so idk if is how it should be?

either way i found online a harness and dme from a 85.5 car mine is the early 85... and im wondering if i can just swap everything? or just the dme itself?

and ill go futher with checking wiring like honda said

Test voltage at the assorted inputs and outputs at the DME and relay to see if voltage is getting to/coming from where it sould be when it should. Work from the battery outward to the ignition switch, DME/relay voltage inputs, DME/relay voltage outputs, fuel pump. Somewhere it's not getting through when it's supposed to.

oh and outback the connection to the dme relay where okay.

well i check all the wiring to the dme, the 12 volts from 18 and 35, the ignition switch, and resistance from the sensors, and the dme relay wires tomorrow,
thanks hand and outback for the great info.

[HondaDustR]

Yep, especially if you lose that fuel pump relay energizing voltage from the DME once the key is released from START. Don't know which wire exactly...I got the concept pretty well from outback's explaination (never quite knew how that worked...thanks!), but good and lost on the details...

[shiftdrift944]

ok i finally check the wiring from the sensor and the resistance is the same from the sensor to the dme plug.
and the only way i can get 12v. to the pump is if i jump it i tried with the relay and no volt going thru to the 1st coil so either both of my dme relay are bad? or the dme itself is bad??

[Outback Porsche]

944online will test the DME for free.

Cheers,

[shiftdrift944]

really? what do i have to do?

[shiftdrift944]

well couldnt i just re heat the solder joints? if i could do it, but does anyone have any hits or tip so i dont end up messing the dme?

[shiftdrift944]

ok well on of my friend has 86 944 so hes gonna lend me his dme computer to see if it for sure the dme