Speedtoys

Thanks!

Mrmerlin

Dr Bob thats a great post, thanks for taking the time to put it together,
its members like you who really make a difference for everyone.
I learn from your wisdom.

dr bob

Very kind words, especially from others who share their knowledge so freely. And you know who you are...
Thanks!

Prof Requiem

Dr. Bob thanks for the reply that makes lots of sense. I only have a digital multimeter not an analog so won't be able to do the test you suggest at the bottom. I will try once more reinstalling the relay to see if it will run with it, if not it sounds like I might be in need of a professionals help as I am not sure if I will be able to diagnose a fix with my limited experience and tools. Bummer. Thanks for the detailed reply I will update once I tinker with it a bit more. It also might be an issue to find a competent electrical guy around here, I live in rural north Ga in the mtns and there's not a lot of options. I have asked around but apparently electrical mechanics are a disappearing breed.

Prof Requiem

Dr. Bob, when you say the ignition box needs replacing which part are you referring to specifically? Are you referring to the CID electronic ignition box? How difficult is that to swap out? Thanks again for the help.

Prof Requiem

Ok, one more question and then I'm off to work.

I am wondering if the ignition coil might also be in need of replacement. My question is how many coils are there and are they relatively easy to get to and replace? I haven't been able to find much in the way of online tutorials which likely means it's a pretty simple operation, but figured I'd ask on here. The ignition coil might explain the poor idle and stall issue as well as be a part of the relay problem. From what I've been reading failing coils can burn out the ignition box, so it might be that both need replacing.

Thanks again for all the help! I really love this car and want to get it back into good running shape.

outbackgeorgia

There are a few of us Rennlisters in the Atlanta area who make runs up to "rural north GA" from Alpharetta frequently. In my case, to western NC. Send me a PM. I do have an analog meter and know how to use it. (have a full 928 shop manual set with wiring diagrams for your car.)An oscilloscope would be better, but I sold mine years ago. Always happy to help. Dr. Bobs post is spot on.
Dave

dr bob

The potential for stupid stuff is always high, especially when you don't have knowledge of what has been done to the car in the past. Stupid stuff includes things like CE panel relay socket connections that have been loosened by someone jamming a meter probe into them. The 31b connection is small/narrow to start with, and it's way too common to find damage where some well-meaning person has tried to fit a relatively large round meter probe into a connector designed for a small thin flat relay terminal. Sometimes visual inspection is enough to determine if it's been damaged. The terminals can usually be extracted out the back using a small thin blade to push back the locking tab on the connection. But, the terminals use a particular crimping tool that you won't find at the local parts place, and a replacement terminal may not be handy either. The terminal is used in Volkswagen cars so a trip to a VW dealer parts counter with the old one will usually get you what you need. They can sometimes be 'reformed' to work again too. Anyway, not saying that's your problem, just using it as an example.

I think the two biggest challenges to the electrical systems in these cars are corrosion and stupid, in no particular order. Corrosion and neglect can be dealt with, using proper techniques and materials/tools. Stupid opens up a huge array of possibilities, with no apparent limits. Jumpers such as the one you found are pretty easy and obvious, so long as no wires are melted. Car phone installations, stereo hacks, lighting and cooling fans added on, bigger fuses in smaller circuits, the list is long and extinguished (hopefully).

dr bob

We are looking to make sure that the ignition box is generating a tach signal, the one needed by the fuel pump relay. A missing tach signal won't prevent the car from running if there's another way to get the fuel pump to run. The analog meter test is easy, and oscilloscope is better, a fast digital DC voltmeter will show a rapidly-changing voltage that moves between maybe half and close to full battery voltage as the car comes off of cranking speed to idle speed. I wasn't suggesting previously that a digital meter won't work at all, just that the reading is difficult to predict since it's so depndent on meter sampling and response time. If you see no voltage, or possibly a constant pull-up voltage closer to battery volts and it never changes as you crank and run, look at the ignition box. The testing goes into wiring if your tach works but no pulses to the relay.



The coil...
In my deep dark teenage past, I sold auto parts in a retail store after school and Saturdays. Folks would buy an ignition coil when they just couldn't get their car to run. I'd warn them that the coil wasn't their problem and that electrical items can't be returned. When their car still wouldn't start, they'd return the new coil... defective. So I built a little coil test fixture, with an old distributor, a spark plug and a small battery. Just put this fat wire in your mouth and I'll spin the distributor with the 'defective' coil. Nobody would do it. Then make a spark with their new and their original coils.

So coils do fail sometimes. Mechanical abuse will do it, either thermal or impact damage. Electrical failures happen when something else in the system isn't right. Caps, rotors, wires, plugs, open up and cause firing voltages to rise too high, and there's internal arcing as the coil's charge finds an easier internal path to ground. Otherwise, coils are amazingly robust and will last forever if not abused. Usually, if a car starts at all, the coil is OK. That's not an absolute, but I'd be checking all those other things before I'd be replacing a coil. And only after determining that I was chasing an ignition issue.

James Bailey

VW had a bad bunch of coil on plug units used on the 1.8 liter turbos in early 2000s so bad they did a full recall and replacement with improved parts at no charge.....But like was pointed out the coils on our cars rarely fail. The 81 has a single coil on the left inner fender...

Prof Requiem

Thanks for the further posts, and yes this car has some significant stupid in its past history. The car came with a shop manual set from the PO but it was for the '84 year... not the '81. One of the various doofus things I discovered was that the '84 fuse and relay chart had been followed, consequently the fuses were jumbled up and also pretty heavily corroded. I replaced those and have been gradually working on getting all the relays replaced. The only two that have given me trouble are the horn and the fuel pump. The horn is very weird, when I hooked it up it would randomly engage when I would turn the wheel. Haven't hooked it up again to see what the issue with that is I have been working on more pressing issues.

I found the ignition coil and am going to give it a good cleaning as the contacts seem pretty crusty. Will have to check on the ignition box per doc's instructions to see if it is misbehaving.

As I have only limited electrical know-how I am hoping that I can convince my uncle to come down for a visit maybe over the summer as he is an old-school mechanic and specialized in electrical systems. He is a Ford guy but would still be able to get me going with working on the electrical system as this car has a lot of gremlins in it. To name a few:

Speedometer works intermittently (and sometimes comes on in the middle of driving...)
Headlights usually work... but sometimes they will come up but only the fog lights will turn on, and then not go down until the car is turned off and back on.
A/C has been disabled, but the fresh air blower also works only intermittently and even when it works the heater doesn't appear to function
Passenger window works sometimes
Sunroof doesn't open or even make an attempt to do so

Thankfully I also have an '86 944 that is in better running condition and is what I usually drive, but it has been in my garage for the past month or so as I have been slowly (very) working on repainting it. As soon as I get the paintjob done I will be pulling the 928 back in and will start back to work on it.

Any other ideas or pieces of advice are greatly appreciated.

Wisconsin Joe

Your horn randomly honking is because of the contact for the steering wheel. It's on the multi-switch (turn signals, wipers, ect). Taking the wheel off is easy, you will then see the little strip that is the contact.

Passenger window and sunroof are most likely the switches. They are known to get dirty and stop working. Check the fuses first, but the intermittent nature of the passenger window is almost certainly the switch (I'll bet it works if you push hard, or if you put some "sideways" in when you push).

Speedo is probably corrosion on the rivets on the plastic circuit board. There's a good writeup on it on the "Dwayne's Garage" site. You can find a link to it in the "New Visitor" sticky.

dr bob

^^^ What he said about the horn contacts. My limited experience on this is from replacing the ignition switch, a project that requires removing the steering wheel, loosening the multi-switch on the column, and lifting pod up and towards the rear of the car ever so slightly. When reassembing everything, getting the position of the multi switch "just right" on the column was made easier with the voltmeter. The horn relay is always fed with voltage on one side of the coil. The other side is grounded in the column by the horn button on the wheel when you want the relay to close.. There's a ring, and a mating contact shoe that need to just barely touch. There's the wire from the contact up into the wheel where it plugs to the horn pad. So start with the switch a little forward (towards the front of the car) on the column. Pull the horn pad off carefully Hard sharp pull towards your chest, NOT your chin...) and disconnect the wire. Now connect your voltmeter to the wire, other side to actual chassis ground, reading DC volts. As you slowly move the multi-switch towards the steering wheel, at some point your meter will indicate voltage. Turn the whel lock to lock and verify that the voltage is showing through the whole range. You want the switch as far foorward as possible while maintaing the voltage through the whole range. Tighten the switch again on the column. Test the horn by touching the wire to ground; it should sound. Turn the wheel lock to lock, and there should be no horn. Plug the wire into the pad and snap the pad back on again. Test at a few spots in the wheel rotation to verify horn function.

I suppose you could warn your family and neighbors, and do the same adjustment just holding the horn down as you slowly move the switch towards the wheel. When the horn sounds, you have contact. Tighten the switch, verify function through the wheel's turn range, and call it good. My voltmeter way was easy and fun, since I already had everything out for the ignition switch change. Turns out changing the ignition switch did nothing to affect a particular gremlin I was chasing, but I could still claim the small success that came with the horn still working after all was done.

Alan

Dr Bob is correct - this a 15/87 jumper and is always bad news - the 15 connection is sized to feed the relay coil - not the fuel pump - it is vastly overloaded here.

Since you see fuel pump relays not working - I'd suspect the 31b connection - make sure you have no jumper plugged into Z4 which connects to 31b on the relay.

Alan

Landseer

First thing you should do is remove the fusepanel and inspect it thoroughly, esp the backside for wiring melts and fixes. These situations are common when wrong charts cause wrong amperage fuses to be installed. Look for very subtle melting of one wire into another. I'd not turn the key again until I did that first.

Then thoroughly clean the contacts. Stan has used deoxit; I generally use a dremel wire brush on these, they are solid, not plated contacts.

Your fusepanel currently might have the proper amperage fuses now installed assuming you found the right diagram, but you've utilized the wrong brand. Those look like BUSS, they are generally about 3/4 of a millimeter too long and don't seat well at all, causing the top springy contact on the fusepanel to be angled too far upwards They have what appear to be aluminum conductors. It is not possible to twist-seat them without damage. 928 Intl or 928sRUs should have the right ones, ask for 'ceramic' fuses for the early cars.

Am curious about your set of manuals. Perhaps they were cobbled up. The six volume set should cover all model years from 78 through 84. Its pretty much impossible to operate on these cars without the proper diagrams.

Regarding parts source, abandon your concept that local parts import store is good enough else continue to deal with wrong-brand relays and wrong length fuses. One of the suppliers also stocks a CD containing not just the workshop manuals and wiring diagrams for all years, but a treasure trove of original technician documentation that augments the shop manuals.

Actually, upon further review, you have a significantly bigger issue with which to deal. The fusebox pictured in post#1, 928-610-105-07 is for a 1984 USA / Japan car. The 1981 car used 928-610-105-04. The -07 fusebox is not backward compatible to the 1981 car. (This is from Porsche documentation on the CD's I mentioned.) I wonder what else they swapped along with the panel? Could they have swapped-in the whole harness??? I have somewhere recorded the wire colors for all the bottom row plugs for 84 USA, so if you need that cross reference let me know.

A proper panel is likely available from 928 Intl used. Local NAPA or Advance Auto or Carolina's-based Bap Geon will struggle with sourcing that.

Stay positive on all this, the good news is that you've heard it run, right?