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ARCHIVE- Guac`s Bucking Issue

NOTE: This issue has NOT been resolved. What appeared to work in this article didn`t... The intermittent symptoms just became intermittent again...

The Guac`s Distributor Failure

Resolved 12/29/2006



Shortly after buying the Guacamole Bus last April, these symptoms appeared. At high (over 4k) rpms, and immediately after upshifting into 3rd only, the bus would buck like there was either no fuel, or the ignition just shut off. This was intermittent, and didn`t seem to affect highway driving at all. In fact I drove to CA in May with no problems until I got there. But once there it was even worse.

Troubleshooting and further misery

As mentioned, once in CA, the problems were worse. Happening nearly every time I drove. This was bad because I didn`t want to try driving back to CO with this problem. In fact, I stayed in CA an extra day to try to resolve it.

I went to VeeDub Parts in Huntington Beach ( and bought new points, condensor, cap and rotor. I talked to the counter guy there about a coil, and he insisted that a bad coil would be an all-or-nothing problem. Nothing intermittent like I described. The guys there tend to be more knowledgeable than most counter monkeys I`ve run into, so I took his word for it. (This will haunt me later.)

So new points and condensor, same problem. Sigh.

I got back to my in-law`s house (where we were staying during our visit to CA) and started going through the fuel injection system testing everything and looking for vacuum leaks. Everything tested good. I couldn`t test fuel pressure because I couldn`t find a fuel injection pressure gauge without all the bizarre fittings that every other car seemed to have. But the double relay tested fine, the injectors tested fine, etc.

I was going batty. I posted on both The Samba ( and the Type 2 List ( and everybody suggested what I`d tried. I also went ahead and bought a coil at Autozone which had no effect. (See my writeup about that piece of crap here: Until someone suggested fuel pressure. Since I had no way to test it, I was told try just replacing the fuel filter. I happened to have a spare with me so swapped it out, replacing some of the rubber lines in the process since they were pretty deteriorated.

The problem went away! YAY!

Drove home and had no more problems.... For a while. It would appear every so often, and a quick fuel filter swap would always resolve it.

Next trip to CA, in late July, it started happening again in earnest. Fuel filter swaps were lasting shorter and shorter periods of time. But there was an additional issue mixed in. I noticed vacuum leak symptoms as well... Misfires, gentle bucking when maintaining speed, etc. "Ah ha!" I think. It MUST be vacuum related!

After much fiddling I found the elbow to the aux air regulator was cracked. The PO had repaired the elbow with silicone. I knew about this, since he did it while I was present, but had forgotten. It lasted pretty well IMHO. A new elbow was available at Vee Dub for a few bucks so I bought it. I still had a vacuum leak, and the main bucking problem was also still present.

I went ahead and bought a Bosch Blue coil at Vee Dub during this period, with no difference in any effects.

Just before I was scheduled to head back to CO, I swung by my in-law`s (I`d been staying with my mom this trip) and started looking for the vacuum leak with my father-in-law. Finally found it. The fuel pressure regulator uses vacuum to help reduce the rail pressure during decel and at idle. The diaphragm was leaking in the FPR. I pulled the vacuum line off and plugged it. No more vacuum leak! Yay! Still have that @#$^ bucking though...

A little while after getting back to CO (with zero bucking on the way home, thankfully) I started looking for the problem again. I posted over on the IAC board ( about the problem, got the same kinds of answers I`d been getting. Note: I stopped posting over at The Samba because of some personal issues with other members.

I cut open a fuel filter to see just what was blocking it. If it was rust I`d need to pull the fuel tank. Here`s the results:

As you can see, NOTHING was blocking the filter!!! Aside from a slight darkening in the bottom half of the filter element (where the filter is constantly soaked in fuel) there was nothing at all in there.

I started considering the possibility of something in the tank blocking the outlet. This is bad on a fuel injected bus because the outlets don`t unscrew like on a carb`d bus. That means a definite tank pull, with an engine drop. Crap.

While all this is happening, I`m exploring any other possibility to avoid the tank pull. Also, during this time the fuel pump died. The death of the fuel pump was a perfect fit with the theory that something was blocking fuel delivery since the pump requires a constant flow of fuel to keep from overheating. I bought a rebuilt pump from Bus Boys ( - a great deal at $120 for a rebuilt pump done by Fuel Injection Corp. Pics here if you`re curious:

Through all this I`m still trying to understand why replacing the fuel filter is resolving, even temporarily, the bucking problem. Vapor lock and tank not venting were both eliminated when I tried popping the gas cap, popping a vent line, and just pulling a fuel line at the filter and putting it back on. None made any difference.

I also checked the Air Flow Meter (AFM). Took it out and popped the cover. Everything looked perfect, or nearly so. Some odd burn marks that look like they were designed in. Nobody could tell me much about those, but it tests out ok so I left it. Pics here if you`re curious:

Burn marks

Guts 1

Guts 2

The bucking after upshift wasn`t much of an issue until just recently. Since I`ve pretty much decided swapping fuel filters was a waste of money, I started trying to drive through the bucking. The high RPM bucking would go away, but the upshift bucking would happen EVERY shift now. But if I let the RPMs drop to 1k between shifts, the bus wouldn`t buck at all.

AH HA!!!

These two issues point firmly at the distributor. But I had replaced all the stuff on the distributor, and even checked the internal ground strap, which is well attached and not rusted through.

But the symptoms say distributor. So I grabbed the one out of a 79 engine I have in my garage. The condition of the points and condensor are unknown, but I gave it a shot.


Here`s what happened:

(I`ll get better pics of the cap up when I get a new cap to replace it.)

The cap has a scorch mark right above where the ground strap is. Somehow the ignition spark from the rotor was grounding to the strap or nearby instead of going to the cap terminals. Note that the same cap and rotor are being used on the 79 distributor and working flawlessly.

In the second pic you can see the dust from the cap that got burned off / blown off by the spark being misdirected. It`s a nasty muddy mess.

I want to thank everybody at IAC, the Type 2 List, and The Samba that suffered with me through finding the cause of the Guac`s bucking. I suspect I would have given up and taken it to a shop if it hadn`t been for everybody`s support.