Itinerant Air-Cooled

Hello, my bus is randomly shuddering while driving, like the fuel is cut off for a very short period of time. Starts at first key, never happens at idle, usually takes 15-20 minutes of driving from cold for the problem to appear. I've been able to replicate it in 2nd, 3rd and 4th gear driving both hard or gently. Less frequent on the highway, actually it seems to correct itself at high speed. Opened the AFM and it was unmolested (factory silicone under cap) and used contact cleaner spray to no avail. Engine was done and converted from carb to fuel injection 400 miles ago so it has a new fuel filter and pump but all the other FI parts are old. The tank is clean inside except from a few tiny rust spots. I would really appreciate some help in diagnosing. Thank you

ohiowesty wrote:Hello, my bus is randomly shuddering while driving, like the fuel is cut off for a very short period of time. Starts at first key, never happens at idle, usually takes 15-20 minutes of driving from cold for the problem to appear. I've been able to replicate it in 2nd, 3rd and 4th gear driving both hard or gently. Less frequent on the highway, actually it seems to correct itself at high speed. Opened the AFM and it was unmolested (factory silicone under cap) and used contact cleaner spray to no avail. Engine was done and converted from carb to fuel injection 400 miles ago so it has a new fuel filter and pump but all the other FI parts are old. The tank is clean inside except from a few tiny rust spots. I would really appreciate some help in diagnosing. Thank you

Grounds. All of them. From the battery post to the body, from the body to the transaxle, all fuel injection grounds, like #5, #16, #17, make sure make sure make sure that they all seat firmly onto spades that are cleanly secure to the case. If you see a brown wire from the double relay, follow it to its ground. The cylinder head temp sensor is a ground, it needs to be clean and seated securely as does the connector into which it plugs.

Check all wires that relate, for abrasions or busted strands at the terminals. That includes fuel pump wires under their boots.

Air intake security. All of it. I just found that I did not secure the clamp on the s-boot last week. It was FINE when cold because the temp sensor was dialiing in extra fuel. As soon as the engine needed its usual warm mixture, stumbles upon acceleration. Sometimes the movement of the engine would make it "go away".
Report back.
Colin

ohiowesty wrote:Engine was done and converted from carb to fuel injection 400 miles ago so it has a new fuel filter and pump but all the other FI parts are old.

If one of those old FI parts is the AAR elbow, be sure to check that one for splits. Under a good light. Replace with factory part or one from Airhead Parts. Most aftermarket ones are garbage, but Airhead seems to be a cut above.
Edit: I have no personal experience with Airhead's AAR elbow, so I can't attest that it is any better than the other aftermarket offerings. I'm just going by the fact that Airhead has gone to the bother of remanufacturing some rubber hose parts in Viton, so I'm making the possibly flawed logical leap to thinking that maybe they actually care.

For a truly final solution to the AAR elbow problem, however, I highly recommend a 1/2" silicone elbow.

This is after you check all the grounds as per Colin's instructions.

Thank you guys for your advice. I checked all the grounds, tightened the brown ground from the double relay, checked all connections, S boot, collars. I still have the shuddering but I noticed something: as I swerved left in an intersection, the problem went away on the section of road until the next intersection, Then I swerved left again and the shuddering reappeared. Can it be some debris in the tank or fuel filter that causes blockage and if I agitate it it unclogs momentarily? I can't see inside the fuel filter as it is a white plastic block, not a see through glass one. I might take out the filter and cut it open to inspect. Any other advice?

Change the filter but no glass ones for us FI guys. Cut open the old one and look in there.

Did you clean and tighten the Temp Sensor II? It needs a good snug fit into the head and a nice shiny clean electrical connection into the engine wiring harness.

Colin said-in his ground message:

from the body to the transaxle

Did you get to cleaning this particular ground-the small woven metal strand one underneath the bus. When I removed mine, and cleaned all of the contact surfaces, I noticed an immediate improvement. The brown ground at the double relay was also a bad connection. I like the exercise of going through the grounds, and imagining the electricity singing its way through all of the bus circuits after, with no shortness of breath at connection points.

The tranny to chassis ground was replaced three months ago when I noticed that the clutch cable was acting as ground (I was having problems starting, but the bus would start with ease with the clutch engaged). I just checked the new ground and it is clean and secured solid.

ohiowesty wrote:The tranny to chassis ground was replaced three months ago when I noticed that the clutch cable was acting as ground (I was having problems starting, but the bus would start with ease with the clutch engaged). I just checked the new ground and it is clean and secured solid.

Help us narrow it down. Check off each suggestion here with a response of what you found. I once found that a "I checked the battery terminals and they were good" was actually a loose negative terminal that had been tapped down on the post. I have visited many people whose vacuum leak sign-offs missed the SlowLane-mentioned AAR elbow, "I didn't see that crack."

And I missed for years that locoqueso's TSII was internally intermittent.
Colin

I had almost the exact same problem. Our 76 westy would stall suddenly and we would either coast to a stop or sometimes I could press in the clutch and restart as we coasted along. Usually would start right up, after the key was turned off, but never without doing that first. I went and cleaned and retightened all of the grounds I could find and also pulled all the wires off of the distributor and cleaned and squeezed each connector tighter. It has been two weeks now with no stalls. I had been sure it was something in the gas tank before reading this thread.

Hubster43 wrote: ↑

Sat Jul 08, 2017 8:17 am

I had almost the exact same problem. Our 76 westy would stall suddenly and we would either coast to a stop or sometimes I could press in the clutch and restart as we coasted along. Usually would start right up, after the key was turned off, but never without doing that first. I went and cleaned and retightened all of the grounds I could find and also pulled all the wires off of the distributor and cleaned and squeezed each connector tighter. It has been two weeks now with no stalls. I had been sure it was something in the gas tank before reading this thread.

It is an excellent idea for us to rinse our minds of assumptions before we tackle the mysteries . . . I love to get stuck on my own ideas and it just slows the progression to the real problem.
Colin