Square Body Crane Truck

[special-K]

I'd suspect something in the TBI area. Something like mass air flow or temp sensor type of thing

[MARKDTN]

The TBI engines are pretty bulletproof in stock form. I think a "tuneup" as you suggested is a good place to start. Fuel filter is also a great idea. Not exactly sure where it is on that one, but I think inside the frame on the passengers side. What is the rear ratio? A truck like that may have a pretty low ratio. Is the SES light on the dash on? If it is, I would pull codes and see what it says and go from there. But I have seen many TBI 350s go over 200K and never have a SES light come on.

[v30crewcab]

check for vacuum leaks around the base gasket. I remember something about them having vacuum leaks sometimes.

[79vette]

I finally got some time to do a tune up on the truck today. Its been a long time since I touched anything that wasn't a diesel though, and I have some more questions.

I installed new plugs, wires, cap/rotor, air filter, and valve stem seals. I also got an O2 sensor, but I want to try driving it with the new ignition parts before introducing new variables
It seems to pretty much run how it did before, but I need to get a good highway drive in to check the MPG.

It still surges at idle, and it now also makes a high pitched rattling/clicking from the distributor or possibly the throttle body area. I don't remember this noise from before, but its possible I just didn't notice it... Video below.
0:00-0:16 clicking noise. Any idea what this could be? It doesn't sound loud or deep enough to be valves to me, but I guess its possible I set all the valves to loose after changing the seals? Or maybe thats just how fuel injectors sound, I'm not sure.
0:26-0:36 surging at idle. I am resting my hand near the throttle linkage, but not touching it.
https://photos.app.goo.gl/TEZSbMb6Bd3o98167

Originally Posted by special-K

I'd suspect something in the TBI area. Something like mass air flow or temp sensor type of thing

Would bad sensors cause a service engine light? Can they be tested, or should they just be replaced outright?

Originally Posted by MARKDTN

What is the rear ratio? A truck like that may have a pretty low ratio. Is the SES light on the dash on? If it is, I would pull codes and see what it says and go from there.

SES light comes on when you turn the key, and goes out when the engine is started. Is this normal operation?
It has RPO GT5, which I think would be 4.10 gears. That sounds about right, but I haven't pulled the cover to check.

[MARKDTN]

Yes on SES light. Comes on with key and goes out once it starts is "normal" operation.

Yes, bad coolant temp sensor, oxygen sensor, or MAP sensor etc. can all cause issues. But since the light is not on, they would not be my first guess. Might check fuel pressure and make sure it is in spec just to rule that out.

The noise on the video is odd. Could be the distributor? Is anything loose inside it? lots of play if you try to move the rotor? Hard to tell exactly what is going on there.

[79vette]

Well the truck still makes the strange ignition/distributor noise, still gets 8-9mpg (TBI 350, sm465, CC 14 bolt with probably 4.10 gears). No obvious vacuum leaks, though it does seem to be losing coolant with no external leaks. Could be intake or head gasket problems? Honestly as long as keeps running down the road well, I'm probably just going to run it.

Did about 250 miles on the highway yesterday to go put a heavy duty roof on a shed and everything went well. I made a 5' extension for the crane boom last week which came in really handy for that job. See pictures below.