Mysterious Electrical Apocalypse

[Zarbuck]

So I just bought a 944, a black 1987 with tan interior, wanted one for years. I knew when I bought the car that it needed a new alternator but the car was running very good albeit just off the battery. So as soon as I got the car it went straight to the mechanic with a new alternator. They installed the new alternator and took the car for a test drive and it died about 3 blocks away from the shop. They pushed it back and found that the ignition switch had been fried. There was no power going to anything at this point and the car would not start. So I got a new ignition switch and had it installed. Now the car was starting and seemed to be running good again but if you turned on the head lights or the a/c the car would die.

The mechanic came back and told me that he checked a solution database the shop had and came up with 10 instances of the same situation that was fixed by replacement of the dme/fuel pump relay and the dme temp sensor. So I got the parts and had them installed and tried to start the car, nothing. The engine turns over but dose not start. Apparently there is no spark coming from the coil and no fuel pressure coming from the fuel pump. I have been told this is a bad anti-theft control unit part number 911 637 104 02. I have tried the bypass from pin 1 to 4 and 7 to 8 but the car will still not start.

So I'm left to assume that the anti-theft control unit is not the problem since the bypass didn't work. I really don't care to replace something that doesn’t seem to be broke and that doesn’t hold much promise of actually fixing the car. But I am still left at the same place with a coil that's not giving off any spark and a fuel pump that has no pressure. At this point the only thing the car will do is when the key is turned in the ignition the starter will turn the engine over. Nothing electrical works head light, tail lights, indicators, windows, door locks. The only sign of any electricity even being in the car at all is the red warning light on the dash lights up.

There seems to be something very wrong here as every time I replace one electrical component another burns out. I was very suspect of the new alternator or the voltage regulator but it seems that the little the car was running it was producing the proper voltage. I'm not a mechanic and don't have any idea what would be causing all of this. My mechanic is getting frustrated with the car and can only think of very time consuming things to check from here. He has suggested that it might be a bad ground connection and he has check a few but can't get to all of them with out a lot of time. His only other idea is that there might possible be some wires behind the dash that are shorting out but it would take a ton of work to remove the entire dash, check every wire, and replace it all.

I'm afraid if I can't figure out whats wrong with this car soon then I'm going to have to end up selling it as a parts car and take a pretty bad loss. I also don't live in a large city so taking it to a dealership to have someone that actually knows what they are doing to look at it really isn't an option. Even if I wanted to have it hauled to a dealership the closest one is 250 miles away. This forum seems to be my last stop before my dream dies.

Please, has anyone ever seen a problem like this before or have any idea what it could be?

[vdubr928]

Sounds like more than one problem. Where do you live.

[Zarbuck]

Amarillo, TX

[vdubr928]

Too far for me but hopefully you can find some help. Its way over your mechanics head obviously. I would not have changed dme anything if the car was running. Put the pieces back and see if you can get it to start. Otherwise you need me (or equivalent ) with a good meter and a diagram and about a week. Start looking for some local Porsche friends.

[Zarbuck]

I have tried changing the relay back to the old one with no effect. I'll change the temp sensor back also and see if there are any better results.

[John_AZ]

Zarbuck,

You need to do more reading and understand the 944 better.
Clark's Garage Home Page

Buying a 944 that has electical problems and paying a mechanic it do the work is not a good idea. You have to do the work to understand why the part failed. If not, you car will be in the shop or parked and you will spend a lot of money foolishly.

The "brain" or Motronic DME is the computer that has to be treated carefully or it will burn out and you will spend another $350 to $500 for a new one and pay a mechanic to have it insatlled.

Dead batteries, bad alternators, battery cables with corrosion and bad ground will kill a DME.
Never jump a 944 or use a battery boost pack to start!



Take car of the DME:



Is the new alternator charging the battery?
What is the battery voltage?
Did you clean all the engine and cabin grounds?

Do you have a volt-amp-ohm meter?

Read Clarks for the info?

GL & welcome
John

[Guest765]

John I still maintain that stuff about jumping our cars or not is h.o.g.w.a.s.h. I jumped mine more than a few times before I replaced the battery this is only a concern if you hook up the jumper wrong and that will damage ANY car.

[John_AZ]

Aw come on,
Would it sound better if Jamie said it?



"just" should be "JUMP"

From GermanAutoForums.com


John

[Guest765]

Ok. I still maintain its right up there with the belt nonsense until I see it with my own two eyes an verify it wasn't something else.

[Zarbuck]

Well I know the guy I bought it from was charging the battery so the car could be driven but the car ran just fine for several days after that. I guess it could have caused some serious damage but it seems odd that it took a few days to show up.

I tried putting the old temp sensor back in the car to no effect.

When the car was running the alternator was working just fine and charging the battery.

I don't know what the voltage of the battery is right now.

I don't own a meter.

Before I bought the car the only thing that I had read was about the 944 was the maintenance schedule and a list of problems to look for when buying a 944. Every thing mechanic seemed fine on the car other than the alternator being out.

I spend a good chuck of time reading Clarks this weekend and have gone through the trouble shooting for the ignition system (IGN-04) and most of the page on the fuel supply (FUEL-16) and pretty much came to the DME on both. I tried the tapping trick with no luck, so I pulled the DME and opened it. There are two pins on the back side of the upper board that look black and the board has small signs of heat damage around them. There is also some rust in one of the corners of the case and a couple of small yellow/brown spots on the back side of the top board. The water damage looks to be old, not sure this is what killed the DME but I'm sure it didn't help its life span very much.

The DME unit in my car has the parts number 944.618.121.04 made by Bosh but the replacement units I have seen for the car have part numbers of 944.618.121.DX made by Porsche. Is this correct and normal? Has my DME already been replaced in the past?

Any other suggestions or ideas?

I'm trying to decide if I should replace the DME just to discover what other electrical problems might exist or if I should just cut my losses and sell the car before I put even more money into it. I really want to fix this car but I'm just scared that its going to be one thing after another untill I have spent so much that I could have just bought a second one that actually runs.

Thank you all for all the information you have already given me and thank you again in advance for any additional information you might have.

[djnolan]

Could be the rectifier in the alternator is shot. These could cause the battery drain, too. About $80 to get the alternator rebuilt. Get it tested at autozone first.

On second thought buy a meter and use these troubleshooting guide on Clarkes and figure out what is wrong first. Not that difficult.

Excessive Battery Discharge Rate

Troubleshooting - Electrical (including Instruments)

[John_AZ]

Zarbuck,

Let me try to help you.
You can always sell the car as a "roller" and maybe get $700 to $1200 if the interior is good and some of the major repairs have been done like a new clutch, head gasket and waterpump.

Here is what you need to do.
Go to Harbor Freight in Amarillo.
Harbor Freight Tools Amarillo, TX

Get a cheap volt/amp/ohm meter. for $7 or less. Coupons in many papers. I have at least 5 "free" meters gotten with coupons.

Charge your car battery out of the car.

Put the battery in the car fully charged.

Clean all the battery wires on both ends. If a battery cable has acid corrosion it should be replaced with a HD cable----not a cheap thin guage cable found at Omallys, PEP Boys or Walmart. Go to NAPA and get some HD cable--4guage minimum, 2 guage or less is better.

Get a new DME/FUEL pump relay or learn how to make a jumper on Clarks and use it.
DME Relay Information and Testing
Put the new relay in or the jumper.

Try to start the car.

Stare at the tach--do you see the needle jump 1/16 of an inch ---It has to jump a little

If it does not jump, Check the refence sensors with you new VOA meter
Clean the connections. Check the resistance per Clarks.
Speed and Reference Sensors - Checking, Replacement, and Adjustment

Check the distributer rotor. Pull the cap and make sure the rotor is tight.
Does the cap feel sloppy when installed? It should be real tight.
See Clarks.

You can do a lot of these tests and more found in Clarks No Start Trouble shooting page.
Troubleshooting - Engine

You can send the DME to have it tested for free.
If it is bad a new/used rebuilt DME will cost from $350 to $600.

Member George at 944 Ecology has mentioned he will test your DME (and sell you one if needed)

There are other electronic shops that provide the service as well.

The car is a DIY car and hands on. You must learn and get the tools to keep it running.

GL
John

[Zarbuck]

I have a new alternator.

I'll pick up a meter.

The battery should be fully charged, it was charged about two weeks ago and still turns the starter just fine. I can take a look at it and see if it is running low from trying to start the car and charge it if it needs it.

I have a new DME / Fuel Pump Relay.

I'll have to look at the tach a little closer but I believe it is coming up enough to create the running signal.

The distributor looks good.

Already been over TS-01... That's how I got to ING-04 and FUEL-16.

Testing the DME before throwing away a few hundred on something that's not even needed would be great! I didn't even know that would be an option to try. I was also going to look into getting the unit repair/rebuilt but I'm worried it might have to much damage?

I'm by no means a mechanic but I know my way around a car just fine. I just don't know anything when it comes to Porsche’s apparently.

[alfadoc]

Originally Posted by Zarbuck

At this point the only thing the car will do is when the key is turned in the ignition the starter will turn the engine over. Nothing electrical works head light, tail lights, indicators, windows, door locks. The only sign of any electricity even being in the car at all is the red warning light on the dash lights up.

Here is the big clue. A major circuit that is controlled by the ignition switch is not getting energized. Your mechanic has a wiring diagram for the car, right? Otherwise, it's like throwing darts at a board blindfolded (darts=expensive Porsche parts).

Start with a circuit diagram for the ignition switch. Make sure that the wires that are supposed to be energized when the switch is on are indeed being energized. Start at the back of the ignition switch and move forward, component by component, following the wiring diagram. Eventually you'll find the place where power is going in, but not coming out. That's how you perform electrical diagnosis.

[Guest765]

Alfa is 100% right and I have no idea how we all got this far without saying that and gettingninto Dme and jumping myths/gremlins. The Dme doesn't control any of that stuff that isn't turning on, to my knowledge.

[John_AZ]

Originally Posted by alfadoc

Here is the big clue. A major circuit that is controlled by the ignition switch is not getting energized. Your mechanic has a wiring diagram for the car, right? Otherwise, it's like throwing darts at a board blindfolded (darts=expensive Porsche parts).

Start with a circuit diagram for the ignition switch. Make sure that the wires that are supposed to be energized when the switch is on are indeed being energized. Start at the back of the ignition switch and move forward, component by component, following the wiring diagram. Eventually you'll find the place where power is going in, but not coming out. That's how you perform electrical diagnosis.

Good stuff alfadoc.

Zarbuck,
You might want to buy a NOID light to test the signal to the injectors.

WILMAR BOSCH PFI FUEL INJECTION NOID TEST LIGHT W85102 | eBay

To add to alfadoc, here is a simplified sequence of events to start a car.



Remember also that when cranking, the tach needle has to jump 1/16th inch to send a signal to the DME.

GL
John

[TibetanT]

Zarbuck:

First and foremost, "welcome" to Pelican! You have come to the right place for answers and for help from some of the finest people in the Porsche community!

Second, if you need to find out if your DME/ECU (computer brain) works, there are two (2) options. 1) Send it to IAN at 944online in Florida, he will test it for you for free. 2) On this forum is a member named ischmitz, his name is Ingo and he fixes ECU/DME Porsche units. This will save you some time and money.

Third, and most important: As stated by members above, before you start spending a bunch of money on this "non-starting" 944, please make sure you have covered the basics. These are as follows:
a) does the car have spark
b) does the fuel injectors get 12V (use noid light to test)
c) does the fuel pump run

As John has mentioned, the Clarks-Garage has many write-ups on how to troubleshoot and narrow this down.

Now, I have always said, "it's always something fundamental" and it usually is. Such as, if the battery is charged, or rather was charged at one time, is it still showing a charge of at least 12.5V when idle? If not, there may not be enough voltage getting to the fuel injectors or the other electrical circuitry to start the car.

The reference and speed sensors play a vital role in ensuring that your car starts and continues to run.

One test not mentioned earlier is this, try spraying some starter fluid into the AFM and see if your car will run. If the car starts and runs for a short time, then your problem is electrical and the most likely cause is the reference sensors not being hooked-up completely or they are faulty.

The DME relay by-pass wiring shown in Clarks-Garage will ensure that your fuel pump is running, so your car will start if it is getting the correct voltage. Also, ensure that all of your grounds are clean. There are several places on the car's body that these grounds exist. There are ground connections near the front of the car near lights on the frame, on the back of the engine bell housing right near the sensors, and most importantly under the dash on the driver's side.

Hope this helps and good luck.

[John_AZ]

Right on. (60s style). Something simple or failed to check will cause hours of anguish.

I am going to bookmark this post on my "no start checklist" and just give out the link.

Pelican member Nick - many944s - Owns a shop that specializes in 944s.

Here is his "No Start" page:

Bennington Motorsports

John