[Harvey]

I just completed a T-belt/balance belt/waterpump/seals change and cam inspection but after putting it back together it won't start. Laying a sparkplug on manifold, I see no spark. I checked the checking timing marks, replaced DME, checked fuses and other relays, checked coil wire, pulled and checked the distributor and rotor, checked wiring to MAF, etc. Can't see anything wrong. Am I overlooking something obvious? I pushed in clutch (it's on stands with hood and deck lid open). The only thing that occurs to me is that a small piece of the plastic rim on the rotor assemby broke off and the distributor contacts are quite corroded. I cleaned them, still no spark. It ran fine before I tore into it. Any ideas on how to troubleshoot this? I didn't hear the fuel pump humming and thought that might be the problem but checked the spark first. I was sure hoping it would crank first try. Any suggestions on where to go next would be appreciated. Thank you.



Harvey

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[rustech]

I would disconnect the coil wire from the distributor and hold it a couple millimeters (with the insulation rolled back) while someone cranks it over (don't shock yourself). If you see a spark, then my guess would be that your rotor was installed in the wrong position (nothing to burn).

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[Harvey]

I just got through double checking the rotor orientation (it's fine..I had marked it before)...then I checked the coil. It's dead...no spark...nada. I'm wondering if I bumped a wire or sensor or something that's causing the coil to not get spark? If the coil died...it was abrupt. Is there an easy way to check to see if juice is getting to the coil? Or if the coil is bad? Or?



Thanks, I really appreciate this since I want to get the 968 running again.



Harvey

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[Greimann]

Be very careful testing and troubleshooting the ignition system at the coil. There is a significant possibility that you can fry the DME (the computer, not the relay) (as well as getting a hell of a jolt)



Refer to page 24/28-3 in the service manual. There is a whole page of cautions!

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[rustech]

Yes, there is an easy way to check to see if the coil is getting power. There is a plastic cover on the top of the coil that is removable with two wires underneath (power feed). Get under there with a voltgauge and see if you get a reading. If it checks out, then it's the coil, if not, then we have to consider something upstream.

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[Harvey]

I checked the coil as per Clark's Garage directions and, if I did it right...the directions were a little confusing as to grounding wires) then the coil must be dead. I checked it with and without the coil wire. Sooo...I guess my next stop is to buy a new coil and coil wire and hope I don't have to work further backwards than that. I also jumpered the DME to see if the fuel pump works (it does) and tried yet another DME (I have 3), as well as double check all wires and connections that I might have touched in working on the car. All looks good. I'm hoping that none of the sensors are bad that might affect spark.



Harvey





[quote name='rustech' date='May 24 2005, 08:55 PM']Yes, there is an easy way to check to see if the coil is getting power.  There is a plastic cover on the top of the coil that is removable with two wires underneath (power feed).  Get under there with a voltgauge and see if you get a reading.  If it checks out, then it's the coil, if not, then we have to consider something upstream.

[right][post="5040"]<{POST_SNAPBACK}>[/post][/right][/quote]

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[Harvey]

BTW, I am getting 12 volts to the coil black wire with the switch on....also shows 12V on the green wire.



Harvey

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[Harvey]

The coil checks out fine. I must have misunderstood Clark's directions since I took the coil to an electrial specialist here and he checked it and said the coil was fine in every way. Sooo..it must have something to do with the triggering device(s) before it gets to the coil. Now, I'm getting in over my head. Not sure what to do next. I'll go check the wires once more. I did put the flywheel lock on too but I can't think of anything under there that I could have accidently unplugged or messed up. I'll do more web searching for info. Not sure what to do next.



Harvey

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[Greimann]

Can you get any blink codes out of the computer?

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[Harvey]

Greimann,



I'll have to study up on how to get blink codes out of the computer. That's new to me. However, more data...



I've spent all day futzing trying to figure this no-start puzzle out. No spark coming out of coil, 12V to Coil, Coil is OK, DME is OK, fuel pump works if you jumper it without the DME BUT it does not come on when you turn the key on and crank. However, there is adequate voltage at the plug on top of the gas tank that you get to from inside of the deck lid. I find it puzzling that there's voltage but the fuel pump only works when directly jumpered. I suspect it's not getting the trigger pulse from the DME? I read the following in an earlier post:



"If you don't have both fuel and spark signals, it's either the alarm disabling the DME-relay or the speed and reference sensors are off. To distinguish which one, check for power on the fuel pump when cranking." (Note: I have power but the pump does not actuate when cranking) "If it was the spark and reference sensors being off, you'll still get power to the fuel pump on cranking, but the DME won't even know that the engine's spinning, so no spark & fuel signals."



How might the alarm disable the DME? I'm guessing the speed sensor is on top of the flywheel housing. It's as it was before I started the belt change. Where would the reference sensor be? I've checked all plugs for corrosion, slipped pins, broken wires and all looks well. What do you make of this puzzle? Am I getting closer to the culprit?

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[Harvey]

My CHECK ENGINE dash light never comes on like the book indicates so I can't figure out the Engine Fault Codes based on blinking lights. Something else to get to I guess. I hate going behind the dash.



Harvey

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[Greimann]

I think if you can get the check engine light to illuminate so the DME can talk to you and tell you if it feels bad, you'll be miles ahead on this diagnosis. The attached document has trouble codes and troubleshooting tables. The Method of getting the blink codes is on page 24/28-31.

968_DME_Diagnosis_tables.pdf Size: 312.45 KB  Downloads: 40

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[Harvey]

Thanks, Greimann,



That fault code info is great...although it will be a while before I pull my dash to fix the lights for the Check Engine. It's not quite a chicken and egg thing but I'm concerned that I might inadvertantly introduce a new problem. I'm now trying to figure out how to figure out how to trace wires in the system to see if I can find the bad one.



What's for sure is that the spark is not sparking (elec to the coil from battery...but apparently not from some sensor). Also, on turning the engine over, the fuel pump is not activated...so no spark NOR gas is getting through...and 3 different DMEs don't make a difference. I have new coil, wire, dist. cap and rotor on order allthough I'm sure that's not the problem. I'll need new ones anyway and use the old for spares.



Thanks for the great fault code resource. As soon as I fix the dash lights this will be a great resource to have.



Harvey

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[Cloud9...68]

Now it's my turn to ask for one of these - does anybody happen to have a copy of the 968 DME Diagnosis Tables Dave Greimann refers to in post #12 above? Is this in the manual? I'm not at my home computer, so I don't have access to the manual at the moment. If someone has a copy of this pdf file (unlikely, as this post is nearly 8 years old), please send me an IM. Thanks.



After jumpering the DME relay connectors, the fuel pump is turning on, but the engine won't fire. So I removed one of the plugs, and I'm not getting any spark. Any advice on how to troubleshoot this problem in the most efficient manner possible would be appreciated. I'll check the connectors at the flywheel reference sensor (I was careful to gap it correctly), do a blink test, and check for spark at the coil wire.

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[flash]

yes, it's in the manual



did you check the DME fuse?

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[Cloud9...68]

[quote name='flash' timestamp='1357744160' post='137217']

yes, it's in the manual



did you check the DME fuse?

[/quote]

Thanks for confirming it's in the manual. And yes, I did check the DME fuse, and it's good.

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[flash]

if you have a durametric, you should be able to check the ECU through that.

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[Cloud9...68]

I don't have one, but I know someone near me who does. I'll check a few basic things, and if I don't discover something obvious, like a wire I forgot to connect, I'll give him a buzz. I discovered the no-spark issue late last night, so I haven't even done a blink test, confirmed that I have power going to the coil, etc. Hopefully it's something simple, as I didn't have this problem before I took the engine out and took it apart, so most likely it's something related to something I touched along the way.



Edit: I do have one question. The DME relay actually has two coils, one to complete the fuel pump's circuit (terminal 87b to terminal 30), and one to enable power to go to the DME (term. 87 to 30). To attempt to start my engine when I discovered that my fuel pump wasn't turning on, I made a 3-wire jumper to energize both the fuel pumps and the DME's coils in the DME relay. But when I'm troubleshooting the DME (determining if it has power going to it, etc.), I'd rather not energize the fuel pump and run down the battery. Does anybody know if it would be OK to just jumper terminals 87 and 30, leaving the fuel pump without power? Here's a link to a schematic of the DME relay:



http://www.clarks-garage.com/



After clicking on this link, you have to select "Site Search" on the left, and then enter "DME relay" to bring up the document describing the DME relay. For some reason, I can't link this document directly.



Thanks.

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[jfrahm]

Making and trying the DME relay jumper wire is a good early step. Naturally you also want to see if your tach is bouncing, if not your reference sensor might be disconnected, broken, not installed properly, etc. or the DME itself is not playing along.



You can get the blink codes without the tool, this is super easy and it'll tell you if your DME is booted up at least:



http://www.durametric.com/porsche968faultcodes.aspx



I do not recall if the 968 uses the same alarm module as the late 944 but it can be bypassed also to eliminate a failure point.

http://www.clarks-garage.com/shop-manual/elect-23.htm



I should probably print this up and keep the relevant jumpers in the car in case I get stuck somewhere with a brain-dead alarm.



A damaged ignition rotor is not uncommon in the 968 also, in some cases due to corrosion of the cover the cap attaches to. This can cause the rotor to break when it hits the cap and then you will get no spark. You might see the (negative) tach signal at the coil but you won't get a spark unless you bypass the coil and jump the coil wire spark to ground.



-Joel.

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[Cloud9...68]

Thanks, Joel. So what should the tach needle do exactly when trying to start the engine (been so long since the car ran that I don't remember, and I wasn't paying much attention to it when trying to turn it on last night) if the reference sensor is healthy and connected correctly?



And as far as the blink test, it's been a long time since I did one, and even then, it confused me a little. So, as a "blink test for dummies" test, is this how it works?:



1. Go through steps 1-3 in the link in Joel's post

2. The check engine sign (the "!") will illuminate for several seconds

3. The CEL then turns off for several seconds

4. The CEL then should flash briefly once (apparently to confirm that the DME is communicating)

5. The CEL then turns off for several seconds

6. The CEL next either flashes briefly once, signifying a constant problem, or twice, indicating an intermittent problem. I assume if it doesn't flash either once or twice, there is no problem, and this flash is skipped(?)

7. If there is a problem, indicated by the second flash, it then goes through its sequence of flashes and pauses (x number of flashes with brief pauses, followed by a longer pause, and then another set of y flashes and brief pauses). The number of "x" flashes and the number of "y" flashes gives you the code.



So, since I know my DME relays are bad, I assume I have to do the blink test with the DME relay terminals jumpered. Also, what if there are multiple issues? And what happens at the end of the test? Does the CEL stop blinking, or does it cyle through again?

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