1990 C2 does not start after valve adjustment, distributor cap, rotor, and plug

[lae2]

I just completed a valve adjustment on a 1990 911 (964) C2 air cooled. I replaced distributor caps and rotors. This was my first 911 valve adjustment. I own a 912 and routinely do the valve adjustment plus I have done my share of solid lifter muscle car valve adjustments.

The valve adjustment went perfectly to my knowledge. No left over parts and no ill feelings about anything. Nevertheless, the car will not start. When I first attempted to start it, it ran above idle for about 5 secs with mild throttle applied. During this time the engine sounded healthy. At no throttle, it quickly died.

Thereafter, it will not start. If you let the starter continue to crank the engine, the engine will reliably fire every every few revolutions but it will not hit on all six. The throttle has no effect. The sound of the engine when it fires is appropriate. There is no backfiring. Now that I write this letter it appears to me that perhaps it is only running on 2 or 3 cylinders.

I had an assistant (the owner of the car) who helped me on some of the work (I did all of the valve adjustment). She plugged in the plug connecters on CYL 1-3. I forgot to check her work. Is it possible for the connectors to miss the plug heads? The connectors look like they are correctly seated in the valve covers. I am about to remove the blower motor and exhaust system and backtrack but I have a nagging feeling that there is a simple solution.

Any suggestions? Is it likely that the engine starting failure is coincidental to the valve adjustment and the fuel pump relay failed?

Please help - Loren

[85Gold]

I would check all electrical connections in the engine compartment. If it ran before you worked on it and does not now always look at what you might have disturbed when you did the work. Not an expert on 964's but on my 993 it is tight working on dist and changing plugs so it would be easy to disconnect an electrical connection.

Good Luck
Peter

[Peter C2]

You might also want to post this same question on the 964 forum at rennlist.com. Both forums can offer different solutions and perspectives that may be helpful to you.

http://forums.rennlist.com/rennforums/forumdisplay.php?s=&forumid=59

[lae2]

I managed to get the engine to run with gentle coaxing from the throttle, but it will not even idle.

I removed the heater fan and checked the electrical connection in the area. The oxygen sensor was not fully seated. Additionally, there is a 6 pin connector, about 1" dia that clamps to a brace. The lead out heads over to what I assume is the fuel distributor or some such device. The clamp was open and the connector part way disconnected. reseated the connector and clamped it in place. I suspect that the connection was compromised by removing or installing the heater blower. Further, I doubt that I did it. I would like to credit it to a previous mechanical. Reconnecting the connector did not fix the starting or idle problem.

I checked the upper spark plug connectors on cyl 1-3. Indeed, one of them had missed the target. I practiced putting the connector, under visual guidance, on an old plug and sharpened up on the sound and feel of a correctly seated connector. I discovered another incorrectly seated connector. Thus, two of 5 on the top were not seated correctly. I am unable to test the upper connector on Cyl 6 due to the power steering pump.

The upper connector on cylinder 5 does not feel right. I can feel the boot go over the plug but rather than a distiinct click when the electrical connector seats there is a kind of weak double click sound. This same connector when connected to a removed plug makes the characteristic single click. I suppose I will have to remove the plug and see if the cap came off. But then, I would hate for the cap to fall into the cylinder. Maybe I willl have to remove the valve cover to take a look.

I guess I have no choice but to remove the entire exhaust system and heat guards and double check all of the spark plug connectors. However, I find it hard to believe that, with two plugs per cylinder, I would have botched enough connectors for the engine to not run. I suppose if one of the coils is not firing this could happen. All 12 of the old plugs look equal in appearance and indicated a healthy engine. Thus, I doubt that a coil is bad.

I checked the secondary distributor belt and inspected the new rotors and caps. There was no evidence of rotors crashing into the caps. The weights and shaft in the secondary distributor are rusted but the shaft still moves freely against the the springs.

Anyway, after discovering two improperly seated connectors and a disconnected oxygen sensor, the engine will start. It will not idle, but with a gentle pumping of the throttle, I can keep it running for several seconds.

I can smell gas coming from the exhaust. I imagine this lets the DME relay and the fuel filter off the hook. This is a step in the right direction.

Any further suggestions before I remove the exhaust system? I suppose no matter what, I have to do it. I won't be able to sleep at night if I don't recheck all of the spark plug connectors.

[lae2]

I have to say that what I stumbled upon during this evenings round of fiddling with this 964 is like nothing I have ever seen in nearly 40 years of shade tree mechanics.

I am resigned to the fact that I have to remove the exhaust system and sheet metal so that I can double check all spark plug connectors for proper seating. I have been thinking -- might as well replace the spark plug wires while I am at it.

So, before ordering replacement wires I decided to test the high tension circuitry to verify that there are no problems other than possibly an incorrectly seated spark plug connector.

I started out by removing the coil wire from the secondary distributor. I connected the high voltage coil wire to an old spark plug, grounded the plug casing with an aligator clip and attempted to start the engine. The engine idled long enough that I could see a strong spark generated by the coil. In fact, the engine behaved as always -- difficult start and can't find idle. The fact that the engine would fire with only the primary distributor having a high voltage source told me that the primary coil was good.

Nevertheless, for completeness, I removed the coil wire from the primary distributor and connected it to the old spark plug and once again grounded the plug with an aligator clip. I reconnected the high voltage wire to the secondary distributor. I fully expected the primary coil to test good because the engine fired when only the primary distributor was connected to the high voltage source.

So now the situation is that the primary distributor has the coil wire removed and this wire is connected to an old spark plug for testing. The secondary distributor is normally connected.

A flip of the ignition key and what happens? The engine starts right up and purrs like a kitten. Never sounded better. I am delighted to hear the engine ticking them off. At least I know that I might not have to call a flat bed to haul the darn thing off to the dealer.

So what is the bottom line here? The engine starts right up and runs great if the primary distributor does not have high voltage available to distribute. All right, I must have made a mistake on the firing order. I have digital pictures of the original connections. Plus, each wire was labeled. The connections are correct. Still, the engine will not run if high voltage is fed to the primary distributor.

Once again, I removed the high voltage wire from the primary distributor and connected it to the old spark plug for a load. As before, the engine started right up and purred like a kitten. I decided to remove the rotor from the primary distributor and reconnect the high voltage wire to the primary distributor. Without a rotor there could not be voltage going to the wrong places. What happened? The engine would not run despite that I removed the rotor. So once again I removed the high voltage wire from the primary distributor and connected it to the external spark plug load. Once again, the engine started right up and idled perfectly.

So here is the upshot. It appears that the primary coil has to be loaded by an external spark plug in order to let the secondary distributor run the engine. That is, the engine runs fine on the secondary distributor as long the the primary coil is loaded by a spark plug.

All right, so this 964 is not exaclty my 912. It certainly is not that 1965 Dodge Dart that taught me about ignition systems. Am I to believe that the primary distributor is not providing an adequate load for the primary coil because I misconnected a spark plug connecter? And further, that a non-loaded high tension wire generates enough radiated EMR to kill the engine? This is outrageous!

[Britwrench]

Yes, that is exactly what hapens on 964s. Connecting the spark plug wires incorrectly can indeed cause non-start or poor running (usually with all the warning lights on the dash coming on). You should also double check that the distributor drive belt has not broken.
It simply comes back to this: if the engine ran correctly before you worked on it, then the overwhelming probability is that something you did stopped it running after the repair. Go back and check all the wire connections. I doubt whether you need spark plug wires as the 964 items tend to be long lasting. Also make sure that you torqued the spark plugs to the correct specification.

On the twin distributor it doesn't matter ( for testing purposes) to which cap the primary lead is attached, the engine will run regardless. The wires are different lengths so naturally fall to the correct position.

[lae2]

Thank you for verifying my observation. The belt can't be broken or the car would not run on the secondary distributor. Nevertheless, I verified this on visual inspection and the observation that both rotors move in synchrony. I will check to verify that both indicate TDC cylinder one at the same time in case the belt slipped. The plugs were torqued to 17+ ft lbs. I used the Nm equivalent. Thanks again

[lae2]

Solved for the most part. There was a misconnected spark plug on cyl 2 and on cyl 5. Lower plugs (primary distributor) in both cases. Now the car starts on a dime.

I would consider it fixed except that now I know how smooth it runs on just the secondary distributor. With both distributors in play it goes on little hunting trips at idle. It never comes close to dieing but it changes tone. You could put a cup of coffee in the intake manifold and not spill it.
It runs fine on the road and has plenty of acceleration. It bucks ever so slightly at a constant speed in a lower gear at about 3k rpm. I will drive it awhile and see if the computer relearns some things. The owner will take it off my hands in a week.

I suspect that getting it to be totally smooth might require distributor work or new spark plug wires. Maybe a new distributor belt is in order. Then again, doesn't the DME time the spark for both distributors? I don't understand how the two outputs could ever be totally synchronized. One has counterweights to somehow track the other.

The primary lesson for me to have learned is that EMI interference can stop a 964. I never thought that, even though all cylinders have a functioning plug, a single misconnected spark plug can render the engine useless. This is the case. All upper plugs were firing. The engine would not run until every last one of the lower plugs were firing. One unterminated plug wire and the engine would not run. Makes me think of Magnacore wires in my future. What a lesson!

[ischmitz]

Hm,

Interesting lessons you learned there. In my case I can disconnect one HT wire from the coil to the distributors and the engine still runs fine.

On the topic of spark timing between the primary and secondary distributor think about it this way: Many (me included) believed that the exact time when the spark is fired is determined by the rotor position on the cap contact. Wrong. The rotor has several degrees of contact area. It's the points opening (in older cars) that trigger the spark or the optical sensor on newer cars running off the dizzy shaft. In the Motronic case it is an electric pulse send by the DME to the ignitors (black boxes on heatsink at the coils. The timing is determined by the flywheel sensor. If that pulse is sent to both ignitors at the exact same time they fire the spark at the same time. If one of the rotors in the dizzy is 3 degrees advanced with reference to the other it does not matter at all as long as the rotor end makes contact to the spark plug contact in the cap. The spark plugs fire at the exact same time (given that the cables are of equal lengh of course)

Ingo

[lae2]

Thank you for the explanation of the dual spark timing. Do you know the function of the advance weights in the secondary distributor? Do they simply keep the rotor in the "ball park?"

Do you know of design differences between 1990 and 2001 that would account for you being able to remove a HV wire and still have the engine run? This 1990 C2 will not run without terminating the removed coil wire with a old plug.

[ischmitz]

Loren,

The weights in the dizzy do exactly what you say in a 964. They keep the rotor in the ball park.

My engine in the 74 is a 91 964. I did the installation myself. Maybe I got more lucky with grounding. 964 engines are known to be very sensitive to electical noise from the ignition. If the shielding anywhere is borderline that'll cause a lot of issues. On stock 964 cars with one bad plug wire the noise genereated there is sometimes enough to cause what you have experienced. So I can see that one disconnected plug wire causes the engine to run like $hit.

BTW: The 2001 does not have a distributor any longer. It has individual coils for each plug.

Cheers,
Ingo

[lae2]

Thanks again, I think I will give this machine a clean bill of health. I took it out about 2AM for a one hour and a half drive through the local mountains. I was dodging deer and rabbits the entire time. The car shakes your teeth out (17" Ruf and Bridgestone) but it responds faster to my reflexes than does my brain.

It is kind of interesting. I use to routinely drive my 912 for 30 hr straight trips. For most of the time I would have 2-3 fingers on the steering wheel and just listen to the engine for hours on end. I would arrive refreashed.

You have to drive this C2. Every little road bump holds a surprise. Nevertheless, with both hands on the wheel, it is a driving machine. My poor little o'l 912 is a totally different animal. They both have their place.

It accelerates from 3k to 6.5K in 2nd and 3rd about as fast as my reflexes can handle it. The initial bucking at 3K is totally absent. That appears to have been a one-time observation. I only wish that I owned the car. I have to give it up on Sunday. Thanks to everyone for their help.

[ischmitz]

Loren,

I am with you on this. My 74 with the 3.6 in it a real hand full, too. Once you step on it all hell breaks loose. The only mods it has are some hotter cams and a chip. But since the entire car weights only 2500 lbs you can imagine what that in combination with a short 7:31 ring and pinion gear box does. I just recently upgraded the front suspension to Carrera with Carrera brakes. Still, on it 205 tires you get really busy keeping all the torque on the road in a semi-straight line.

Have fun,
Ingo