76 FI bus - no max power/max speed cannot be obtained

V. Powers 21 years ago

Just curious if anyone else has run across this problem before..

My son's bus was recently overhauled and it ran great for the past six months but now whenever you step on the throttle it doesn't respond at higher rpms.

It idles fine and responds to quick throttle inputs while sitting in the driveway but when you take it on the road it bogs down and takes forever to go through the gears.

At first I thought it was a vacuum leak, repaired cracked hose from oil breather to air intake plenum -no help. I have gone through the rest of the hoses and they appear to be in good shape.

I replaced the cap-rotor-points-plugs, adjusted points to .016 and plugs to .026 thousands. Timing to 7.5 BTDC. Also adjusted the valves.

Could the points be floating? Vacuum advance on the dizzy not working? Engine Control Unit (ECU) failure? Fuel pressure regulator?

Any thoughts would be greatly appreciated.

Vince

1976 Transporter - 2000cc FI

Vote

Speedy Jim 21 years ago

Check that the advance is *actually* working with a strobe timing light.

ECU? Not likely. Point float? Nah. Fuel pressure/delivery? Ah. Maybe. Put a pressure gauge on the test port (left side). Check at idle and also as revving. Cyl head temp sensor? Hmmmmmm worth checking.

Speedy Jim

formatting link

Vote

Busahaulic 21 years ago

First thing to check - When the pedal is all the way down, how far open is the throttle valve? It is very common for the throttle cable to be attache not quite tight enough or even for the conduit from the firewall forward to the end of the steel tubing to have been 'hung-up' during initial adjustment and slipped into place eventually, causing a loosening of the cable by about a half inch (considerable.)

Not a vacuum leak. Not the head temp sensor (it would be blubbering and blowing black smoke.) Could be something screwed up in the airflow meter or air cleaner. If the fuel filter is clogged it would act like this and if the lines are kinked on the suction side. If the vent lines to the fuel tank got blocked off it might have a problem. My money's on the throttle cable until I get some better clues.

Oh - '76's had a throttle position switch on the throttle body. They tend to come loose. Let us know what you find and if there are any more clues. -BaH

Vote

Join the Discussion

Have something to add? Share your thoughts — no account required.

Didn't find your answer?

Ask the community — no account required