Hey, I have an old 1993 uhaul with a 366 in it. Not well versed in gas motors. I've managed to get the engine running pretty well after some work (new fuel pump, took apart TBI and cleaned/changed injector seals and fuel regulator, checked resistance on all wires, cleaned all spark plugs). However, I'm running into some funniness with the butterfly valve. Sometimes it doesn't rotate with the throttle shaft. I can open the butterfly valves by pushing down on them with a screwdriver. Usually that loosens things up where the throttle linkage will turn the valves again. Eventually they'll stick again. Is there some set screw between the throttle linkage and the throttle shaft that could have become loose... or are they supposed to be able to do that?? Another question I have is regarding vacuum. I have a gauge hooked up and it reads 0 vacuum at idle. When I rev it goes up. Should it be like this? There doesn't look to be any vacuum reservoir on the truck. Here's a video I took showing both behaviors: https://youtube.com/shorts/OV3dVn6JXxY Thanks for any advice. John
I think I fixed the throttle sticking issue. I think I might have put one of the butterfly plates on backwards when I took it apart before. Took it apart again, cleaned up the edges with fine sandpaper, and they seem to be good again
Any advice on assessing vacuum leaks would be appreciated. Where to hook up the gauge, etc. I swapped the gauge over to the tap that feeds to the pcv and it started reading about 10inHG at idle and would climb to about 14 with revs. Pcv appears to be working (took it out and it holds vacuum one way and doesn’t the other). Tested pcv hose and that holds vacuum. Unfortunately haven’t been able to find a service manual for this thing.
10 seems low to me. I’d expect it to be closer to 20. One trick to find them is while running squirt ether around the various gaskets, vacuum lines etc and if the engine idles up you found one. Spray around intake gaskets, throttle body to intake, vacuum lines etc. Depending on transmission you may have a vacuum line to it, I’d assume the brakes are hydraulic booster and not vacuum. Generally if the vacuum leak is bad enough it doesn’t run right you’ll hear it. Should have highest vacuum at idle or no load and drop as you apply throttle under a load.
Ok so I guess I was taking the vacuum readings in the wrong spot? I was teeing off a nipple at the throttle body. I found the vacuum diagram for this truck on the air filter cover, which pointed out a manifold vacuum port. There are two things hooked up there, one to the fuel evap canister, another larger line to something on the transmission (in picture attached, wonder what that does?). The line to the Evap canister was disconnected. I fixed that and teed the vac gauge into the intake manifold nipple. Now im getting about 15 at idle. I plugged the ecm control wire back in (to enable ecm controlled advance) and it’s running great now. Time will tell how she pans out. I got the truck on trade for some lumber, not really running. Had been sitting in my neighbors yard forever. I’ve had it for 2-3 years and have been using it as a tool shed. Might be a mobile tool shed now! another random question, how does the egr work on this? I’m used to seeing a tube come off the exhaust and head towards the intake, with a solenoid valve controlling flow into the intake. This engine has some kinda vacuum actuated valve atop the intake…. But no obvious passage to the exhaust??
The line to the trans is for the vacuum modulator which affects shift timing and to an extent how hard it shifts. As far as the emissions stuff my brain is foggy on them, I don’t think the two old trucks I have are equipped with any emissions stuff. You are correct, there has to be a passage exhaust to engine if it’s got some sort of EGR on it. Maybe it’s just an air pump setup and doesn’t tie into exhaust? I don’t recall. 15 is closer to normal I’d say.