no spark cylinder #2 and #3

[speedingmofa]

Hello you all,
i'm having a major head ache with my 1983 Porsche 944.

After a normal night of driving, I parked it ouside and went home. The next day to work, it would start, but i noticed it idling very much out of the ordinary. RPM was at 200!! Something I had NEVER experienced before.

Done a lot since, its been over a month and I've been to other forums, with no remedy so far.

What i've tried:
- another ignition coil
- new distributor cap and rotor
- cleaned out MAF sensor
- replaced air filter and all spark plugs
- check all water and vacuum hoses
- check most wires

I am running out of options here, I want to fix this myself since I've always done everything on the car myself, so I'm really trying to get to it, but I'm starting to loose patience now... Its just so rediculous, from one day to the other, it just got "sick"

What else can I try?
I've been scouring the internet, where there isnt much to find about a Porsche 944 doing that.

Some things I have come across that could point out the problem...
- faulty DME
- faulty ECU
- faulty speed sensor
- damaged wire
- damaged spark plug wires

Help is much appreciated. Thanks.

Jay

From the Netherlands

edit: a few more things, i can smell gasoline when its running. so I doubt the fuel pump has anything to do with this. i've put an old spar plug in the spark cable and it did not spark. pulling the spark cable out of plug when the car is running makes no difference. so its basically not getting any spark....

[vdubr928]

Bad plug or wire.

It sounds like you have done some thins bit when you say "I tried another ......." does that mean you popped one off of a friends car or you replaced yours with new? Reason I ask is some problems have multiple triggers. I would be putting new parts on that way you KNOW you have been down that road.

Im not thinking of much in the dme that would cause a parrtial failure but im hoping to get so.e chime In from someone who knows here. I could see intermittant or complete failure but always missing the same pair? Not sure. Help here please.

Here is what I would try that you said you hadn't.
Your test plug (just to verify your issue)
Wires (to test these move he wire from #1 to the #2 spot on distributor. Now try it with your test plug. Spark yes? Bad wire.
Do you have a dwell meter? You can't adjust dwell bit you can see what it is. This might help verify what is coming from the dme.

[speedingmofa]

Thx for ur reply vdubr928, I could do what u mentioned today after work. If it won't rain... :S

The coil i used is from a guy that is very certain it works well. It looked relatively new, but no, i don't think it was new.
I measured the Ohm on my coil, the secundary was fine and the primary coil was a bit off, it was 1.2 Ohm instead of 0.4-0.6 ohm from the factory. But i have never had any problems untill now...

[vdubr928]

Originally Posted by speedingmofa

Thx for ur reply vdubr928, I could do what u mentioned today after work. If it won't rain... :S

The coil i used is from a guy that is very certain it works well. It looked relatively new, but no, i don't think it was new.
I measured the Ohm on my coil, the secundary was fine and the primary coil was a bit off, it was 1.2 Ohm instead of 0.4-0.6 ohm from the factory. But i have never had any problems untill now...

Coils almost never go badand these symptoms point away from the coil. Wires plugs cap rotor or computer. Not much else if your troubleshooting is acurate.

Let me clarify. If you are always missing the same two its not the coil. The coil could give an intermittant issue but not with the timing of a death metal drummer. Lol

[Outback Porsche]

Originally Posted by vdubr928

with the timing of a death metal drummer

Thats funny, but correct.

This would mean your DME is okay too (same reasoning).

Sounds like plug wires to me.

Cheers,

[944 Ecology]

Originally Posted by Outback Porsche

Thats funny, but correct.

This would mean your DME is okay too (same reasoning).

Sounds like plug wires to me.

Cheers,

Don't forget that plugs wear out, too. The platinum plugs have a nasty habit of failing without any symptom that can be determined by just looking at them.

[Outback Porsche]

Originally Posted by 944 Ecology

Don't forget that plugs wear out, too. The platinum plugs have a nasty habit of failing without any symptom that can be determined by just looking at them.

Hey George,

would a classic symptom be something like poor operation until they got hot?

Cheers,

[944 Ecology]

Originally Posted by Outback Porsche

Hey George,

would a classic symptom be something like poor operation until they got hot?

Cheers,

Yep, could be...

[speedingmofa]

Hi guys, today i got the chance to do some measurements on the car.

Remember, I got brand new plugs fit with basically 0 km on them.

TOday i tested the spark plug caps/cables on impedance. according to the manual, 3k Ohm is good.
cyl1: 3.2k Ohm
cyl2: 2.98k
cyl3: 2.90k
cyl4: 3.1k

So ok, its not the DME cause otherwise it wouldn't start at all. What else regulates which cylinder to fire? The computer? Can it really cause 2 and 3 to misfire?? Could the cambelt have sprung a few teeth or something?

ANd i could not start the car cause my batt is dead... SO i couldnt try for instance cyl 2 with cyl 1 cable... of course, connected to the correct pin on the distributor cap.


Its unbelievable i'm the only one this is happening to... SO frustrating! Can't find much about it on the internet either!

[944 Ecology]

Sorry, missed the fact that you have already replaced the plugs with new.

If it's not the wires, then it might be the ECU.

Any chance that you have #2 wire in the #3 spot in the distributor and vice versa?

[Outback Porsche]

Doubt it's the DME.

The coil signal is common an the injector signal for No.2 is shared with No.1, and No.3 is shared with No.4.

If plug wires are okay, it could be injectors or injector wires (ie not enough fuel being delivered).

PS. sorry to hijack you in my previous post, I may have a plug issue myself (intermittent missing when cold).

[speedingmofa]

My injectors are firing as far as I know, cause i get this strong smell of gasoline when its running. I specifically tested the plugs by shoving a plug in the cap, hold it against a metal part and starting. No spark....
The wires could not be wrong.... Cause I never touched them before. And when I put the new cap, i put them on one by one...

[HondaDustR]

The only other thing I can think of to question is the crank sensors. Are there any teeth missing on the ring gear and are the little reference screws around the edge of the flywheel still there? The injectors are all coupled together and all fire at once on the 8 valve motors. http://www.the944.com/Inject2.htm

Are 2 and 3 stone dead for as long as the car is running or do they ever get any action? Do you have a timing light to clip to the wires or something to show even a very intermittent spark? Seems really weird how those can drop out given the way the DME works. Even if the crank sensors were bad or getting a weak signal, there's virtually no way for the DME to perfectly divide the timing to always miss 2 and 3, and the sensors usually either completely work or completely not work, since the DME needs both signals to be present and correct. Have a look in the dark for any arcing from the wires or distributor that could be seriously grounding out those two wires. I know it sounds stupid but check that the wires are snapped down onto the plugs completely, although even if they are not, the spark will usually jump the gap and fire the plug anyway.

Try a different DME if you can.

[Outback Porsche]

Originally Posted by speedingmofa

i've put an old spar plug in the spark cable and it did not spark. pulling the spark cable out of plug when the car is running makes no difference. so its basically not getting any spark....

Is the old spark plug you used to test okay? Did the old spark plug work in pos 1 or 4?

[speedingmofa]

Yes, this one came out of cyl 1.

I've installed a new clutch about 6 months ago. There weren't any teeth missing on the ring gear. Although i did not check the speed sensor/crank sensor.

As far as I know, cyl 2 and 3 didnt give any spark. Unfortunately I don't have the tool to be 100% sure on that one. But I could not see any spark when holding it against a metal part while running.

I have watersprayed all the caps before, but couldn't find any electric arcs.

At the moment I don't have another DME or ECU I'll try and find some volunteers at the dutch forum. Thanks again guys.

[speedingmofa]

Help? Anyone?

[vdubr928]

Here is what I know. The coil breaks up the spark and the distributor sends it to each plug. The coil is not a likely suspect here. The cap and rotor is the most likely place. The wires would be next. The crank sensor is also not likely as it triggers so much including the fuel pump. If it was bad not likely to start at all.

Im not sure what triggers the coil on your car. (Something has to perform the function of the points. Breaking upthe coil voltage. ) it will probably feed off of the cps through the dme. This would mean it could be a dme issue. Some of the 928 were green wire fed like an old mercedes. Im not sure about these. What year?

[Guest765]

Originally Posted by vdubr928

Here is what I know. The coil breaks up the spark and the distributor sends it to each plug. The coil is not a likely suspect here. The cap and rotor is the most likely place. The wires would be next. The crank sensor is also not likely as it triggers so much including the fuel pump. If it was bad not likely to start at all.

Im not sure what triggers the coil on your car. (Something has to perform the function of the points. Breaking upthe coil voltage. ) it will probably feed off of the cps through the dme. This would mean it could be a dme issue. Some of the 928 were green wire fed like an old mercedes. Im not sure about these. What year?

theres no need to "break the coil voltage". the distributor and rotor assembly performs this function, mechanically setting up the connection. the dme controls spark timing, which is why the rotor contact is so large, to facilitate adjusted spark timing.

[vdubr928]

Originally Posted by fwayfarer

theres no need to "break the coil voltage". the distributor and rotor assembly performs this function, mechanically setting up the connection. the dme controls spark timing, which is why the rotor contact is so large, to facilitate adjusted spark timing.

You're actually contradicting yourself. The break up of the coil voltage is how the computer controls timing. The coil receives 12v+ constant but the ground is broken up at the correct time. That's how a distributed system works. Used to be the points would break up the ground and you would set your dwell angle to correctly time your ground then you would set your timing. I washoping somebody would clarify the circut. Is it cps fed or is there a green wire. What year is the car?

[jpk]

Originally Posted by vdubr928

Im not sure what triggers the coil on your car. (Something has to perform the function of the points. Breaking upthe coil voltage. ) it will probably feed off of the cps through the dme. This would mean it could be a dme issue.

You've hit the nail on the head. The coil is driven by a pair of power transistors in the output side of the DME; they take the coil to ground at the appropriate time to fire the spark. There are two transistors, one handles cylinders 1 and 4 and the other, you guessed it, 2 and 3.
These are big, discrete TO3 case transistors mounted on heat sinks inside the DME.
Two modes of failure; one is a cold solder joint on the cathode/anode, the other is over load and burn out (shorted output). Anyone that understands this stuff and is handy with a soldering iron ought to be able to fix things up; otherwise, look for a ne DME.

This should be last course though - make sure the plugs/wires/cap/rotor are all good before biting the bullet on a DME.