The Guac's bucking re-re-re-re-re-re-visited

[DurocShark]

It came back a couple weeks ago. I thought I had fixed it for the umpteenth time.

I think I found it this time.

I was checking grounds (again) and noticed the thermotime switch was loose. The screw wouldn't go in any further (wouldn't come out either) so I shoved a piece of wood in there to wedge it in place. Bucking went away!

We did the trip to the Continental Divide on Saturday, then on Sunday I helped a friend move. On the way home from the friend's house the bucking had returned. I checked the engine compartment and my wedge came loose. Replaced wedge and the bucking went away.

I wouldn't think the TT switch would be in the circuit for something to ground on besides itself or the CSV, but it seems to be the issue. I just bought an impact driver today so I'm gonna get that screw out and get the TT switch mounted properly.

[vwlover77]

That is just bizzarre!!!!

[Amskeptic]

Replaced wedge and the bucking went away.
I wouldn't think the TT switch would be in the circuit for something to ground on besides itself or the CSV, but it seems to be the issue.

You're right. It is a stand-alone circuit completely independent of the injection. Look at the effects of wiring movement for frayed wire inside of harness that gets "cured" by the wedge. Also, grounds are very near the TTS.
Colin

[DurocShark]

Ya know, thats how I found that grounding the TTS housing made a difference.

I could wiggle the harness and stall the bus. When I wedged the TTS I could wiggle, twist, tug, and talk dirty to the harness and get nothing.

I'm wondering if there's a ground somewhere that's weak and somehow the TTS is filling in. When I pull the engine to do the clutch someday I'll pull the FI apart and see...

[campinpoptop]

IF YOUR ISSUE RE-APPEARS........Here is a PM I just sent to Colin that is a conclusion to PM's sent between Colin and I after his recent visit that I think might help. After our day working together I noticed a little hiccup thing in third at high rpm's under load that was occuring on my drive home form the in-laws where our work was carried out. The drive home takes me over a pass that has notorious head winds.

My opinion is that you buy the pressure gauge, and the Bosch L-Jetronic manual to troubleshoot your issue. I did everything you did and more, until a friend brought over his pressure gauge and L-jet manual. I know what it is like to have this issue keeping you up at night like the illustration in the Muir book with the guy laying a wake dreaming of all the parts to his VW.

Have you tried taking the gas cap off and seeing if the problem at least degrades a little? Mine got more and more consistent over time so I could tell a big difference between the cap off, and on. My line was also so clogged that after letting fuel flow out of the line with gravity the flow actually came to a stop after about a gallon poured out.

Colin,

I am 99% sure the issue was found and repaired. When I originally cleaned my tank, I did not clean the little metal tube that carries fuel from the tank to the filter & fuel pump. About a year ago I had a symptom that was similar, but on a larger scale. Bogging down at high RPM's. I went through the process of checking for vacuum leaks, and then went through the ignition system. I discovered using the Bosch L-Jet manual that the problem was less harsh when I had the gas cap off. The book states that you then must have a clogged inlet filter, which of course we do not have. However this helped me determine that it was a fuel issue, and it had something to do with the tank. it also helped be rule out the pump, and pressure regulator. I just couldn't believe that it was the tank, since I was thorough in following the directions of the Por 15 cleaning process. It got so bad that it became almost un-drivable. Eventually pulled the hose between the metal tube, and fuel filter. Let about a gallon of fuel poor out and flow came to a stop. Pushed air through the line using compressor. Huge pop and a bunch of crap leaked out. I hoped that all the crap either leaked out, or became diluted enough in the tank to not cause another problem. After our e-mails and me trouble shooting the ignition, I started to remember the whole scenario and the fact that I never cleaned the little tube. Pulled the tube, cleaned it with Carb Cleaner & wire. Alot of corusion was found inside the tube. Got steel wool stuck in there for a bit. Got it out. Shot some degreaser in there. Used the pressure washer to blast it out. Blew it out with compressor. Re-assembled....test drive....floored it up hill in third for long period of time and had no hesitations at all. I am keeping my fingers crossed. I don't recall the bus ever running this well. Perhaps there had been intermittent fuel starvation this whole time, but it was only noticeable when things got really clogged up. Thanks for your help. Steve

[Amskeptic]

I just couldn't believe that it was the tank, since I was thorough
in following the directions of the Por 15 cleaning process.

Perhaps there had been intermittent fuel starvation this whole time,

This symptom is insidious for its effects on the exhaust valves/seats. Intermittant lean-outs are like a blow-torch. Of course when the car is sitting still while you pore over the engine, everything looks and acts hygienic. Then you go onthe road and once again the exhaust valves slowly stretch like taffy and the heads soften up imperceptably and allow the seats to slowly disappear into the aluminum.

Any loss of power on the road must be investigated thoroughly, and as Steve notes, your recent first class repair/restoration work should still be inspected yet again as a potential cause or trigger.
Colin