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'79 CA FI bus ran fine then suddenly won't start
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Happyfolk
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PostPosted: Sat Sep 09, 2017 9:49 pm    Post subject: '79 CA FI bus ran fine then suddenly won't start Reply with quote

Our bus has been starting great since we got it 3 years ago. We went on a trip a couple of weeks ago that was 2.5 hrs each way. It ran great there and back. Pulled into the garage, unloaded, sat for a week, then went to start and it turns over, fires, sounds like it will start, but then dies. Won't start.
It fires on the first half dozen tries then quits and just turns over without firing. If I wait a half hour it fires again for a half dozen tries. I've gone through the vacuum hoses, checked the fuel pressure, changed the fuel filter, checked all of the ground connections, tested the cold start valve, TSII, etc... I put a NOS Hall effect dizzy on it 2 years ago which helped resolve some timing issues.
I've been using the Bosch AFC manual and have been systematically going through everything. Seems like it will be something simple but just can't find it.
It runs as long as I keep the starter going but dies when the key returns to the RUN position. I unplugged the AFM and no difference. I was thinking maybe bad ignition switch but still getting 13+ volts on the coil when in the RUN position.
Any ideas?
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Last edited by Happyfolk on Sat Sep 09, 2017 10:37 pm; edited 1 time in total
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busdaddy
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PostPosted: Sat Sep 09, 2017 10:02 pm    Post subject: Re: '79 CA FI bus ran fine then suddenly won't start Reply with quote

Quote:
It runs as long as I keep the starter going but dies when the key returns to the RUN position.

Black wire to fuse holder on left of engine off coil #15?
Large vacuum leak preventing AFM flap from lifting off the stop?
Severely worn tracks in the AFM board?
Bad pump switch contacts in the AFM?
Double relay issues?

A fuel pressure test would likely be my next move.
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Happyfolk
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PostPosted: Sat Sep 09, 2017 10:09 pm    Post subject: Re: '79 CA FI bus ran fine then suddenly won't start Reply with quote

Thanks busdaddy for the input!
Black fuse holder wire from 15 connected.
Double relay 2 years old.
Fuel pump running when starter engaged.
I did a fuel pressure test. 35 psi with the hose off of the regulator. 29 with the hose on. These numbers are while trying to start.
Pressure holds very well afterwards. I applied voltage to the cold start valve and pressure dropped as required.
Colin was at my place last year and tweaked my AFM a little. No overly worn tracks.
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BayCreamPuff
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PostPosted: Sat Sep 09, 2017 10:39 pm    Post subject: Re: '79 CA FI bus ran fine then suddenly won't start Reply with quote

Check that 86c on the double relay is making good contact. Pull the connector off to see if it's been pushed back.

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Happyfolk
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PostPosted: Sat Sep 09, 2017 10:51 pm    Post subject: Re: '79 CA FI bus ran fine then suddenly won't start Reply with quote

BayCreamPuff wrote:
Check that 86c on the double relay is making good contact. Pull the connectors off to see if it's been pushed back.[/img]

Thanks! I did pull the double-relay connectors off to see if any of the blade connectors were pushed back or not connected. Everything looked good.
I've read how finicky these engines can be with vacuum leaks, but I've pulled hoses off on mine before with absolutely no effect. I've gone through them now to check for leaks, but I don't think vacuum leaks are the issue.
Maybe ECU or Hall Control Unit malfunction?
I realize that my EFI setup is California only and just '79-'82 so maybe not much experience out there to chime in but hopefully this correspondence will help someone in the future.
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PostPosted: Sun Sep 10, 2017 12:12 am    Post subject: Re: '79 CA FI bus ran fine then suddenly won't start Reply with quote

To test the AFM fuel pump contacts.
Turn the key to the 1st run position
Remove the air filter
Push the flap open in the AFM (air flow meter) with a chopstick.
Fuel pressure should shoot up to 35-38 psi
Image may have been reduced in size. Click image to view fullscreen.


The above test simulates the Engine running.
Double Relay Explained. . . In Color!
No joy test for power on all the red dots on the double relay.
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PostPosted: Sun Sep 10, 2017 8:51 am    Post subject: Re: '79 CA FI bus ran fine then suddenly won't start Reply with quote

you need to turn back to when you got home. Was it running fine when you pulled in the garage? Did you leave the key on when you got home - say listening to music while you unloaded? Did you buy a tank of gas around the block from where you live when you got home? Did it backfire or do anything strange when you turned it off last time?
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PostPosted: Sun Sep 10, 2017 9:15 am    Post subject: Re: '79 CA FI bus ran fine then suddenly won't start Reply with quote

You might be getting voltage at the coil but are you getting spark at the plugs? I have had both the hall sensor and the control unit fail on a water cooled Rabbit which had a very similar setup to the 79 CA unit I currently have on my bus.

If you can get the Mk2 golf/jetta Bentley manual, check the ignition section. The ignition troubleshooting section is much better that the Bus Bentley one.
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PostPosted: Sun Sep 10, 2017 5:18 pm    Post subject: Re: '79 CA FI bus ran fine then suddenly won't start Reply with quote

86c on the double relay is firmly seated and I'm getting 13v on 88a, 88b, 88e, & 88f when the ignition is turned on.
The dual relay tests out good and is fairly new.
The fuel pump runs when starting and I get 35 psi on the pressure test port.
I seem to be getting spark because it fires and runs as long as I keep the starter engaged but dies as soon as I let the key return to the RUN position.
The ignition switch must not be the issue because it is only involved in the relay coil circuit, which seems to be working fine.

I filled the gas tank before the 2.5 hour drive each way on our trip two weeks ago. The tank was fairly low when we got back. I put a gallon of gas in it after it wouldn't start to see if that was the issue but that didn't work. I've turned it over with it firing but not starting at least 50 times since.

When we got back from the trip I parked in the drive to unload, then started it and pulled into the garage to put it away. No radio left on. Battery seems fine. I go to start it two weeks later and it won't start.

The fuel pump contacts in the AFM weren't right and made contact all the time, so the pump always ran as soon as the key was turned to RUN. In the process of trying to get it to start I adjusted the AFM pump contacts so they're 1mm apart when OFF and now only make contact when the starter is running, drawing air through the AFM. So the bus wouldn't stay running before even when the fuel pump was constantly on, so I don't think the AFM is causing this problem.

I also replaced the fuel filter after it wouldn't start just to rule that out. It wasn't very old and I cut it open to inspect the contents. There were a few pieces of crud in there but not much; not nearly enough to clog it or cause problems.

Also I just now checked the resistance between dual relay wire harness plugs 86b & 85 and it was about 5.6M Ohms, which is what those contacts on the relay measure directly so I must be getting good contact there. This is across the coil on that side of the relay. I was thinking that bad contact at 86b would cause the fuel pump to shut off when the ignition switch returned to ON from START, but that doesn't seem to be the issue.
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PostPosted: Sun Sep 10, 2017 6:31 pm    Post subject: Re: '79 CA FI bus ran fine then suddenly won't start Reply with quote

Quote:
I seem to be getting spark because it fires and runs as long as I keep the starter engaged but dies as soon as I let the key return to the RUN position.


One of two problems

(1) bad ignition switch. The engine runs off a different set of contacts inside the switch when in the start positon. The test is to temp jump the + on the battery to 15 on the ignition coil and try starting it. Remove the jumper and see if it dies. Don't leave the jumper on for more than a minute or to or it can damage the ignition points and coil.

(2) Bad double relay. Start position sends power directly from the starter solenoid to the fuel pump. Have to get the volt meter out to trouble shoot this one.
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PostPosted: Sun Sep 10, 2017 7:04 pm    Post subject: Re: '79 CA FI bus ran fine then suddenly won't start Reply with quote

I just tried jumping from the battery + to contact 15 on the coil. I used one side of a set of jumper cables. No change. It still won't start.

I spent most of the day checking the double relay, connections, voltages, resistances, etc...

I'm getting voltage on 86c and subsequently 88a, 88b, 88e, & 88f. I also made sure 36 from the AFM is making contact at 86b.

I also made sure that applying voltage on 86a caused contact between 88y and 88c & 88d.

The relay seems to be working properly. Think

I spent some time checking the operation of the relay to make sure that the contact numbers are the same as the 11-pin Fed version. The 13-pin California version contact numbering is the same it turns out, with the addition of the 88e & 88f contacts that are fed by 88z like 88a & 88b are. The #85 contact is also moved to the opposite half of the relay compared to the Fed version. I couldn't find a 13-pin diagram and didn't want to assume that all of the pins are identical to the Fed, but it turns out they are besides the two additional contacts.
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PostPosted: Sun Sep 10, 2017 7:38 pm    Post subject: Re: '79 CA FI bus ran fine then suddenly won't start Reply with quote

Please just perform all the ignition system checks located in Section 5, pg 78 (20.1, 20.2) of the Bentley manual. And make sure that you have 12V at terminal 15 of the coil when the ignition key is in the run position.

In addition the Bentley says you can not check the Hall unit but that check is located on pg 33 of the AFC manual.
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PostPosted: Sun Sep 10, 2017 7:50 pm    Post subject: Re: '79 CA FI bus ran fine then suddenly won't start Reply with quote

pittwagen wrote:
Please just perform all the ignition system checks located in Section 5, pg 78 (20.1, 20.2) of the Bentley manual. And make sure that you have 12V at terminal 15 of the coil when the ignition key is in the run position.

In addition the Bentley says you can not check the Hall unit but that check is located on pg 33 of the AFC manual.


Thanks for the input! I plan to go through everything. I worked all weekend on it and probably will every night this week, and next weekend. Hope to figure it out by then but know I may not.

Every other time I've not been able to start the engine it turned out to be a bad ground connection or bad TSII connection. The other times with the bad grounds, connections, etc... it didn't fire at all but just turned over. Now it is firing but just won't quite start.

I've never had a cough or backfire from this engine.

The fact that it was running fine, parked in the driveway, and restarted to put away in the garage a week before keeps me thinking it is something simple.

But it possibly could be a bad electronic component, most of which are NLA or at least difficult to come by, especially the California versions of each.
I've been checking out all of the basic stuff and moving on to the more complex.

I removed the transmission ground strap today and brushed the connections, mounting locations, nuts, bolts, and washers. Did the same with my battery - strap and went over all of the FI ground connections. I keep thinking in the end it will be something simple.

We hope to do some Fall camping!
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PostPosted: Sun Sep 10, 2017 9:51 pm    Post subject: Re: '79 CA FI bus ran fine then suddenly won't start Reply with quote

Keep at it. Pretty much everything is available for that system or can be rebuilt by pros.

Don't forget many of the components were used on water cooled vw's into the 90's.

Good grounds and making sure the various connectors are tight and making good contact are an absolute must. It is a never ending battle.
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PostPosted: Sun Sep 10, 2017 10:13 pm    Post subject: Re: '79 CA FI bus ran fine then suddenly won't start Reply with quote

Cranks Won't Start Test

electronic ignition spark tester
https://www.google.com/search?q=electronic+ignitio...ptYe__G8E4
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PostPosted: Mon Sep 11, 2017 6:45 am    Post subject: Re: '79 CA FI bus ran fine then suddenly won't start Reply with quote

Get the VOM out

see if you have 12V at the pump when you turn the starter key to start it, and if it goes away when you let go of the key.

Next check to see if you have 12V on pin 15 of the coil when you turn the key, and see if it goes away when you let go of the key
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PostPosted: Mon Sep 11, 2017 9:23 am    Post subject: Re: '79 CA FI bus ran fine then suddenly won't start Reply with quote

Oh believe me, the VOM has been out and will continue to get plenty of work!
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PostPosted: Mon Sep 11, 2017 9:35 am    Post subject: Re: '79 CA FI bus ran fine then suddenly won't start Reply with quote

Happyfolk wrote:
I also made sure that applying voltage on 86a caused contact between 88y and 88c & 88d.


Assuming you supplied voltage to 86a at the relay itself. Can you try from the coil side of the black wire that connects to 86a. Or just check the resistance between both sides of that wire. Want to confirm there isn't a break in there somewhere.
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PostPosted: Mon Sep 11, 2017 7:02 pm    Post subject: Re: '79 CA FI bus ran fine then suddenly won't start Reply with quote

SGKent wrote:
Get the VOM out

see if you have 12V at the pump when you turn the starter key to start it, and if it goes away when you let go of the key.

Next check to see if you have 12V on pin 15 of the coil when you turn the key, and see if it goes away when you let go of the key


I get 13v at the pump when I turn the starter and for a short time after I let go of the key (a second?)

I have 13v on pin 15 before I start but it drops to 9 or 10v while turning the engine.

Colin said to remove the center wire on the distributor and hold it 1/4" away from the distributor while starting. He said the sparks should be purplish whitish. The sparks I'm getting are more orangish. **Maybe I've got a weak coil?** The sparks were big and easy to produce at varying distances from the center of the distributor. I've got a new coil ordered. If that isn't what's keeping it from starting I'll need a new one eventually anyway. I have an old black one.
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PostPosted: Mon Sep 11, 2017 7:08 pm    Post subject: Re: '79 CA FI bus ran fine then suddenly won't start Reply with quote

BayCreamPuff wrote:
Happyfolk wrote:
I also made sure that applying voltage on 86a caused contact between 88y and 88c & 88d.


Assuming you supplied voltage to 86a at the relay itself. Can you try from the coil side of the black wire that connects to 86a. Or just check the resistance between both sides of that wire. Want to confirm there isn't a break in there somewhere.


I had the relay out and put a jumper wire between the battery (+) and 86a and another between battery (-) and 85. That closed the connection between 88y and 88c & 88d like it should have.

I checked the connection between coil contact #15 to 86a and got 4 ohms resistance.
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