Hi all,

New to this forum, but not new to fixing old cars. I was told you might be able to help, I am helping a young friend who has a 1976 Porsche 912E with the FI system that I think is the same as the 914. It has not been running for some 5 years except for the rare occasional start and short run.

Somehow the battery was installed backwards during one time when it was removed for recharging . I came over to help get the car started after it had not been running for about 8 months, the owner installed a new battery (swore he put in it in the same way it came out ) and he was cranking and cranking it when I arrived. I found no spark and no fuel, and noticed the dash lights did not come on with the key in the "run" position. I inspected the battery and discovered the leads were connected to the wrong terminals. We corrected that and now the dash lights came on, but of course the car still would not start. Appears to have no spark since it would not even sputter when I sprayed starter fluid into the air cleaner (as a test).

So my question is, what most likely has to be replaced? I was surprised to find that this model still had the points and condenser distributor (rather than electronic ignition) even though it has the bosh electronic fuel injection system. It seems the ignition system should have not been harmed but it appears I am getting no spark. Also, how much damage would have been done to the fuel injection system? Anything else we should check or be concerned with?

Thanks

It cranked with the battery backwards? Sorry, I know that wasn't helpful, I'm just surprised to learn that.

Wait, did you say you checked spark with starter fluid? Maybe try pulling a plug wire, putting a plug in it, ground to case and watch for spark while someone cranks it backwards.

IIRC, this looks exactly like an old thread from several years ago - same car, same issue, except the battery was installed by Walmart or some other store.

My son used to say "warmart." At the same age he said he was "burping in his pants"

He'll do it again too ... when he gets older

A battery installed backwards can do damage to the alternator. That should not keep the car from starting. The points may be bad. As stated in an earlier thread, try putting a plug in one of the plug wires and grounding the plug. Crank and see if the plug has spark. If not, there is something wrong in the ignition system. Once you have spark and it doesn't start, then check for fuel pressure.
Tom

That was not me, I have never been on this forum before. The last Porsche I owned was a 1962 356B, and that was before there was an internet.

Someone took a Porsche to Wal mart for service? Almost as bad as allowing this 20 year old kid mess with a classic 912E. It was a High School graduation "gift", not running because it was sitting so long, and now he created some real problems.

I suspect it was cranking backwards, but yes it was cranking. I do not recommend trying it.

Yes, I tried that too, but that was before I realized the battery was connected backwards. I pulled the distributor cap and looked at the points, did some adjustment to get a reasonable dwell time, and put it back. Sometimes when an engine sits around here moisture gets in everywhere and makes a strong spark difficult to achieve. Putting some starter fluid in it (just a short puff), will allow the weak spark to start the car. After it starts and everything warms up, the moisture is driven out of everything and it will start easy. It is also a quick test to determine if there is no spark or no fuel, it it starts and dies, it is getting no fuel, it was running only on the starter fluid.

Actually, that's a poor test if you are trying to verify spark. Whether it's a Porsche or a Pacer, the proper way to test for spark is to ground the lead from the coil. If you have spark there then you move on to one plug wires which would verify that the distributer and cap are working. While your process "may" work, it is not a true test for spark.

A simple tool that I use is an old spark plug with a wire soldered to plug and an aligator clip on the other end. Clip it to ground and plug a wire on it and watch for the spark to jump while cranking.

You've come to the right place for help... just stay open to the suggestions you get.

You can also try measuring the voltage on the hot side of the coil just to make sure that the coil has power.

Even though you don't have a 914,

Was the starter turning backwards or the engine was cranking backwards? Is the latter even possible? I thought that with most starters the bendix (not sure if that is the right term) would not even allow such an occurence?

I'm willing to bet the electronic fuel injection is fried. Dont know if that would affect your spark. Are you certain you have points and no one replaced them with an electronic unit? Look under your cap. Check all the fuses, sometimes one will blow before the diodes let go.

If I'm feeling lazy and just want to get the motor to barump sputter over a few turns to know that I have spark, I dribble a little bit of gas in the carb. But, the spark plug grounding is the surest method to check for spark. I wouldn't let the kid do that, if he messed up the battery there's a good chance he'd mess up the spark plug threads trying to put the spark plug back in. It's a pity he didn't get some auto shop class time in before obtaining this vehicle.

I'm with the comments on here. I just went thru reinstalling the engine on mine and the folks on here were outstanding with helping me to systematically trace through to make sure wires were good and went where they were supposed to. Check the fuses and the points...and the wiring. make sure the wires are going where they are supposed to. Verify things before the endless cranking. Teach the kid that there is more to owning a car than just cranking it up and driving. The privelage of owning that car should include the responsibility of knowing how to keep it running. I hope I can teach my kids that some day.

If you want to teach your kid proper troubleshooting I suggest you don't include the "dribbling of gas" anywhere. And, you don't need to remove a spark plug to check for spark... maybe you misunderstood my post.

Speaking of dribbling gas, when I was a young man I set my mother-in-laws car on fire by trying to verify that the fuel pump was working and not having the coil properly grounded. I learned a lesson that day. It's also likely one of the reasons that she is now my ex-mother-in-law!

Condenser could have shorted. Electrolytic caps don't like reverse voltages.

Use an extra spark plug to check for spark. I like the suggestion of a test plug with a ground lead soldered to it--but you can also just ground the threads or outer electrode. You probably don't want to have air moving in and out of the combustion chamber (with fuel in it, if the injection is working!) while creating sparks nearby.

After you verify that you have spark, check for fuel. Does the tailpipe smell like gas? Or pull an injector or two and stick it in a jar. Look for gas when someone cranks the starter. A clear jar will let you look at the spray pattern as well.

Oh--the L-jetronic injection that is used on the 912E is not only very similar to that used on the 1.8 liter 914, but also to that used on later VW Buses. So the FI resources at http://www.type2.org can come in handy as well. The exact parts are different, of course, but they work the same way.

--DD

If you reverse the voltage on a DC brushed commutating motor, you reverse the current in both the stator and rotor. This will cause the motor to turn the same direction as before. If it was a permanent magnet DC motor, the motor turns the other direction.

The solenoid pulls in regardless of which way the current flows.

I imagine that reversing the +12V to the FI electronics could fry it though.

Stu

One thing at a time. First get a test light or volt meter and check to see if you have 12V power to the coil. The problem could be a fried coil. Then check to see if the power continues through the coil to the power connection on the points. Easy to check 12V with a test light or volt meter. Then check to see if you can get the volt meter to read by touching both sides of the open set of points. Then your ready to move onto the plug wires themselves. Start at the beginning and assume nothing and you will locate the issue.

Never trust a Shart!

thanks for all the suggestions. I have all the tools I need, I have been at this kind of thing a long time. In 40 years of working on old cars I never had to to deal with this kind of issue, it seems a very easily avoided problem. I do not even see how someone can get the wrong terminal on the battery, they are different sizes, one has to be smashed down to a smaller dia, the other has to be bent open. I think it takes real effort to do something that stupid, and easy to avoid. I am just not sure where to start on it, but checking each system one at a time is what I have to do. I was hoping there is a short cut, no such luck.

First thing I did was pull a spark plug wire and hold it near a good ground, nothing. Next I took the dist cap off to inspect inside, and found it had points in it, and they appeared out of adjustment. the cam barley opened them (wear on the rubbing block causes that, why points systems always need adjustment and timing reset). I "eyeballed" the gap, which is usually enough to get it started. Could not smell fuel in the intake, which you always will with that much cranking with this kind of system. That is when we need to jump the new battery with another car, and when I noticed the terminals did not look right, bent out of shape like they were on the wrong way.

Now that I think about you are correct, the bendix drive should not allow it turn backwards. But it cranked the engine with the battery installed both ways. I did not think DC motors would work that way, but it did.

I have owned and worked on a number of EFI cars, and I have owned and worked on a number of German made cars: porsche, VW, Mercedies, and have worked on BMWs and Audis. I am just not familiar with the system used on the 912E.

This is what I have learned from others that had had this happen: the diodes in the alternator get damaged (but that will not stop it from running), and the ECU gets damaged. Odly sometimes the ground wires get overheated. Most of the other stuff in a car this old does not care which way the power flows through it. That would not be true in most modern cars that use micro processors to control everything from the radio, the heater and the brakes (which is why I will NEVER own a modern car, this is just too much unreliable junk that a car does not need).

thanks for your ideas.

When power was applied to ground, the condensor and coil were fried.

Fuel in the intake is a hopeful sign--it is likely that the ECU is OK, or at least somewhat.

So you have no spark, that's a good known point. Time to start checking the distributor. Do you have +12V to the coil? Does the other terminal get shorted to ground and then disconnected as the points open and close? Do you get a spark if you manually connect and disconnect a ground at that terminal?

Unplug the tach signal wire (black with purple stripe, the purple fades and can be hard to see; it is thinner than the coil power wire) and see if you get spark after that. If the tach wire shorts out, or if the tach itself shorts out, the coil will never "see" the signal from the points.

Keep checking, one step at a time. Isolate and test. Sounds like you're already on the way to finding the problem. (Hopefully it's just one problem.)

--DD