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Running again: A Repair Ramble...
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Daverham
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PostPosted: Tue Jun 15, 2021 3:40 pm    Post subject: Running again: A Repair Ramble... Reply with quote

Back in at the end of March, my dear sweet bus left me stranded a few miles from home. Unfortunately, I live UPHILL from that location and I don't have a tow-bar. So I had her brought home on a flatbed. Then I got REALLY busy with work and didn't have a single moment to work on her, so she's been sitting for like 10 weeks. That's the first time in like ten years that she wasn't running. And the weather is getting nice. So it has been a real bummer. I really want to go eat tacos in the bus by the beach, ya know?

Eventually, I swallowed my pride and called a local shop. I haven't had anyone else work on my bus - as a matter of personal policy - in a long, long time. I hated doing that. But I have just been too busy. But it didn't matter. BOTH of the local German shops are short a tech and nobody could take it. So work finally let up a little and I rolled up my sleeves…

So she had been sitting since December. I know, I know. I'm supposed to start her up a few times. Time was going by really fast.

So, I dusted her off in March and it seemed like everything was just fine. But a mile or so down the road she started running really rough. Would idle OK, but puke on acceleration. Then it got worse, started idling really rough. Then wouldn't idle at all. I couldn't get home.

So I checked all the FI and ignition wires, connections and ground. I dumped some fuel injector cleaner in there. looked for disconnected vacuum lines. Nothing helped. I changed the fuel filter. No dice. I looked inside the old fuel filter and the tank - both pristine. So I started diagnosing a little more scientifically. I got a $30 fuel pressure gauge on Amazon. Fuel pressure was good. I put a new cap and rotor on. No dice. Ignition is electronic, so there are no points. Then I removed the double relay and noticed that the left-side connector was not pushed all the way down on the terminals. This is literally the very first thing I had checked! But it was the forward part of the connector that was up a little, the back (where you can see) actually looked snug. Anyway, I had a surge of hope. I snugged it up. Tried the key, she started right up and ran like a champ! So I put my air cleaner back together and put away all my tools and then fired her up one more time. Running really rough again. So I figured I had narrowed it down to a bad relay. I ordered a new one. Installed it. No improvement.

So I decided to just go over everything again. This time I pulled all the vacuum lines off and then put them back on. A couple of them came off really easy. Too easy. I snugged those down a little better, wiggled all the wires again and boom - she's running perfectly. Now that I finally got her idling I adjusted the timing (which was pretty good) and did two different tests for vacuum leaks (smoke and starting fluid). Couldn't find any. The first 5 minutes or so of just idling there I noticed white/blue smoke coming out of the tail pipe more than normal. Not sure if that’s a clue. That cleared up eventually. Maybe just because she was sitting for a while.

I drove her all over town and everything seems just fine. Idles and accelerates like a dream. I GUESS I fixed it. Or something. I pulled one of those little vacuum hoses off to see if I could duplicate the problem and it did start idling rough. Not exactly like before, but similar. Maybe that was it. Maybe it was a different hose. Do you suppose a vacuum line can LOOK like it’s connected well but just be fitting loosely? And that’s enough to make it hardly run at all? I’m going to replace all the rubber vacuum lines and do a total tune up asap. Hopefully that’s the end of it.

I was sitting there, hovering over the engine while it idled just looking and listening - and she’s running great now - but I did notice a little bit of a hissing sound. Subtle. Like maybe coming from inside the intake air distributor. Is that normal? I can’t say that I’ve ever noticed that before. But maybe I’m just forgetting it.

Getting a ride home back in March:
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back on the road, today!
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Daverham
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PostPosted: Tue Jun 15, 2021 5:27 pm    Post subject: Re: Running again: A Repair Ramble... Reply with quote

Well, here's a "fun" little update. The spark plug wires that I ordered arrived today, so I popped them on. One at a time. Nice and snug. I went to fire her up and... back to that same stumbling, stuttering idle and no acceleration like before. I UN-fixed it! What did I do?

I kind of thought this might happen since there was no smoking gun in the first place. I must have bumped something when I was putting the plug wires on. I just got some 4mm vacuum hose and replaced ALL the little T connections (which were pretty dry & cracked). But no improvement.

I'm starting to think there's an intermittent loose/broken wire in the FI harness or something ridiculous like that. Any other ideas?
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busdaddy
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PostPosted: Tue Jun 15, 2021 5:35 pm    Post subject: Re: Running again: A Repair Ramble... Reply with quote

The "hissing" isn't uncommon, it's air passing through the throttle plate, but if you can hear it more than usual there may be a rip in the S boot you can't see from behind.

Sadly fuel and ignition issues are very similar with the outward symptoms, installing a different used condenser often fixes most of them, your plug wire swap may have also exposed a resistor problem in the rotor, or a plug issue. I don't often condone shooting the parts cannon at things, but if you have spares, or previous used items sitting around it's worth trying them one at a time.

Another thing to look at is the temp sensor in the head beside #3 intake runner, clean threads and tight?, good connection where it plugs into the harness?, got a spare to try just in case?
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PostPosted: Tue Jun 15, 2021 6:00 pm    Post subject: Re: Running again: A Repair Ramble... Reply with quote

The quality of your new plug wires could be sketchy. Best thing would be to use an ohmmeter and make sure they have continuity from one end to the other. Sometimes the spark plug end might not be engaging the wire core
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PostPosted: Tue Jun 15, 2021 7:38 pm    Post subject: Re: Running again: A Repair Ramble... Reply with quote

First, let me tell you how much I appreciate y'all taking the time to read all that and think about it and comment.

To answer your questions, I just replaced TS2 (parts-cannon style) yesterday. That was in my very first round of suspicions: TS2, double relay connections and bad grounds. I don't mind buying one because I don't mind tossing the old one in my spare parts bin.

But here's the update: I was just out there measuring the resistance of the pins on the AFM, per Bentley. All checked out. Then I looked at the plug. Three of the terminals (for pins 8, 7 and 27, I think) looked like they were significantly deeper in the plastic socket than the others. Deep enough that I wondered if they were contacting the pins on the AFM. So I pushed the wires up in there a little better, from the back, through the rubber boot. They came forward easily. Then I plugged the whole socket back onto the AFM, double snugged those three wires in there real deep and gave her a try... purrs like a kitten. Great low idle. Great acceleration. I took a little cruise through the neighborhood. Perfection. Back in Business for now. I very well may have found my smoking gun. It really seemed to me like something was getting bumped, like a wire. I had pushed that plug on tight a hundred times, but I hadn't yet really looked closely at the terminals inside the plug. I should have taken a picture of it BEFORE, but I'd say the metal connectors of those three were about 3 mm deeper (farther from the AFM pins) in that socket that the others.

Has anyone else ever had that problem? Is this a thing? For all I know the pins on the AFM are more than long enough to contact even the deepest connectors. I don't know. But for now the results seem to speak for themselves... I'll report back if anything changes.

Also, I was just re-reading my original post and I have two updates about that:

1. I just saw that it all went south again after I re-assembled the air filter box. Seems like a great time to bump that AFM plug. I bet that's what happened.

2. To answer my own question, YES the 4mm vacuum line connectors can indeed LOOK good but be very old, loose and cracked on the inside. After I pulled those off and inspected them I can safely say that they were more than overdue to be replaced.
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PostPosted: Tue Jun 15, 2021 8:19 pm    Post subject: Re: Running again: A Repair Ramble... Reply with quote

Daverham wrote:
Has anyone else ever had that problem? Is this a thing? For all I know the pins on the AFM are more than long enough to contact even the deepest connectors. I don't know. But for now the results seem to speak for themselves... I'll report back if anything changes.

Yes, not often, but it has happened, good job finding that, lets hope it's the final answer.
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PostPosted: Tue Jun 15, 2021 8:44 pm    Post subject: Re: Running again: A Repair Ramble... Reply with quote

we have had a hard to trace bad running issue on one 79 fuel injection.
swapped out every part but the harness.
then noticed that the ECM plug had some recessed pin sockets.
popped the rubber boot, massaged them into line like the others
et voila..

we have also had the HALL wires inside the Distributor chaff touch and short intermittently on hard turns in one direction. (if yours is so equipped).
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PostPosted: Wed Jun 16, 2021 3:09 am    Post subject: Re: Running again: A Repair Ramble... Reply with quote

Sounds like a good fix, but if the stumble comes back, dont discount the double relay connector pins. Ive had two that the pin lock detents inside the white nylon blocks have worn, allowing a pin to push back when the plug was inserted.

Hard to imagine why this happens as these two blocks rarely get messed with. I can only assume that over the years people have pulled these connectors off by grabbing the wire bundle and pulling down on it instead of grabbing the block itself.

On one of them I pulled the wires out of the block and just plugged them directly to the relay sans the block. Would be nice if these blocks were available as a replacement piece.
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PostPosted: Wed Jun 16, 2021 4:13 am    Post subject: Re: Running again: A Repair Ramble... Reply with quote

Buy or make a release tool for the terminals in the plug so that you can remove the questionable ones. Once you have them out bend up the little retaining tabs a bit more and then push them back into place.
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PostPosted: Wed Jun 16, 2021 9:10 am    Post subject: Re: Running again: A Repair Ramble... Reply with quote

Jetfxr69 wrote:
Would be nice if these blocks were available as a replacement piece.


They are out there. Try Newark, DigiKey or your favorite electronics store. Or just by a new harness from Kyle - http://kyleautomotivespecialties.com/76-79-bus/
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PostPosted: Wed Jun 16, 2021 12:27 pm    Post subject: Re: Running again: A Repair Ramble... Reply with quote

Recessed pins in black box (rack) connectors causes a lot of problems in big airplanes too. You change the black box 2-3 times and then find a bad pin. Happens all the time

https://aviation.stackexchange.com/questions/46240...tronic-bay
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PostPosted: Wed Jun 16, 2021 12:52 pm    Post subject: Re: Running again: A Repair Ramble... Reply with quote

danfromsyr wrote:
we have also had the HALL wires inside the Distributor chaff touch and short intermittently on hard turns in one direction. (if yours is so equipped).


I did notice, while looking closely at everything, that the red wire of my Pertronix electronic ignition module is showing significant wear in the insulation. I think maybe the bottom of the rotor is touching it. It's not worn all the way through yet, but it's pretty deep. I'll have to keep an eye on that.
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PostPosted: Wed Jun 16, 2021 1:07 pm    Post subject: Re: Running again: A Repair Ramble... Reply with quote

Jetfxr69 wrote:
Hard to imagine why this happens as these two blocks rarely get messed with. I can only assume that over the years people have pulled these connectors off by grabbing the wire bundle and pulling down on it instead of grabbing the block itself.

It's generally caused by forcing the connector back onto the relay without making sure all of the pins are started onto a relay terminal. Mostly an issue with the small 0.110" pins. The terminal doesn't hit the pin square, and the pin gets pushed out of the block. The little retaining tab isn't very big, and bends easily.
Quote:
Would be nice if these blocks were available as a replacement piece.

I think German Supply has them. The pins (with retaining tabs) are available from DigiKey:

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PostPosted: Wed Jun 16, 2021 1:07 pm    Post subject: Re: Running again: A Repair Ramble... Reply with quote

Oh and - by the way- this is what all my 4mm vacuum line connectors looked like after I pulled them off.

At first glance, they all looked pretty decent. The cloth wrap was hiding the fact that they were all dry and cracked underneath, and fit very loosely. I'm glad to have replaced these again. Last time I replaced them all was about ten years ago. My how time flies Smile

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PostPosted: Wed Jun 16, 2021 3:04 pm    Post subject: Re: Running again: A Repair Ramble... Reply with quote

the ozone factor varies around the US, I just consider changing woven hose when ever my wheel cylinders get funky. Or anytime the intake system on a dual-carb bus needs attention. Constant Vigilance. VW bus owners need it.
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PostPosted: Wed Jun 16, 2021 3:23 pm    Post subject: Re: Running again: A Repair Ramble... Reply with quote

Nice find. Lots of people replace an ECU/DR and make the car run better, blaming the ECU/DR, when the pins were really the culprit, and the issue comes back hours or months later.

A well-tuned FI bus will drive and idle fairly well with cracked 4mm vacuum hoses; it's the larger ones that destroy drivability.

You can even pull the 4mm hose off the decel valve and do a finger on/finger off idle mixture test. Finger off and speed goes:

Up - mixture is too rich
Down - mixture is too lean
Stumble but recovers - just right

See you on the road,
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PostPosted: Thu Jun 17, 2021 9:54 am    Post subject: Re: Running again: A Repair Ramble... Reply with quote

Two days and two short pleasure cruises later, she's still running like a champ. I'm going to change the oil and put new plugs in there (both are a bit overdue) - and see if I can avoid messing it up again in the process.

I might just pull those three wires off the AFM again and see if I can repeat the problem, just so I know for sure that was it. But I already feel pretty good about it.

Thanks again for the thoughts and suggestions. Keep on bussin'
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PostPosted: Mon Jul 26, 2021 10:21 am    Post subject: Re: Running again: A Repair Ramble... Reply with quote

Over a month later and she's still running like a top. It was definitely those loose wires inside the AFM plug.
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