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Discussion Starter #1
New member here from Western Oregon. I have a 1995 Super Duty (15,000 GVW) that is probably sort of an F450 that is a service truck equipped with a gas drive air compressor, gas drive welder/generator, and a 5,000 lb. hydraulic Autocrane. The truck has a 7.5L engine and ZF 5-speed manual transmission. I use it to work on equipment and repair things on our timberland. We have two parcels that are about 15 miles apart, and I often tow equipment between the parcels. The trailer can weigh up to 21,000 lbs. when loaded.

I have had the truck for over ten years. I have put less than 5,000 miles on it in that time, so I don't drive it much, but I would be lost without it.

I recently had a problem, and currently have it torn down to repair a leaking head gasket. I'll be posting about that in the tech section.

I've been looking through the forums and really appreciate the information shared there by the members!
 

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I made a few modifications, none of which are very serious. The biggest performance mod was to replace the exhaust system after the Y-pipe with a Walker BTM resonator that feeds into a 2000 F250 7.3L Powerstroke muffler and exhaust pipe. I had to tweak the pipe to clear everything, but it gives me 3.5 inch pipe all the way out.

I cut the silencer "horns" out of the air inlet after I discovered the blown head gasket, and have only driven it once since I got it back together. I seems to have more power than it did, but that can be because of several things I fixed while it was apart:

1) Blown gasket from cylinder to water passage at #4 cylinder
2) #8 spark plug had been screwed into a piece that I identified as an adapter for a compression tester. This kept the plug from firing in the combustion chamber itself, and judging from the color of the insulator, firing the charge fully.
3) Slightly leaking exhaust port/manifold joints on several cylinders spread across both banks.
4) New oxygen sensor replacing one that was obviously not working.
5) Replacing the leaking EGR transfer tube and making sure the valve was working properly.
6) While I had the heads off, I removed small ridges in the #6 and #7 combustion chambers, just in case they might cause "hot spots" and pinging in marginal conditions.
7) I found that the inlet ports in the heads matched the intake manifold, except that the manifold had a cutout for the injector to discharge into that was not continued into the head. I relieved that area in the heads so the injector wasn't discharging into a "brick wall" perpendicular to it's axis. I don't know if this helps at all, and perhaps the engineers had good reason to do it that way. It doesn't seem to have hurt anything. I posted photos of this in the thread I started in the Engine Tech section here: Blown Head Gasket

It didn't run smoothly before, and seemed to lack power. It also overheated, and replacing the radiator and hoses didn't help. Now I am sure the overheating was due to the head gasket, but also to a partially collapsed hose between the oil cooler and the water pump. It would trigger the check engine light as soon as I opened the throttle.

The test run after the repairs was to climb a short, steep hill for a half mile, then three miles of up and down hills. I then reversed course and climbed a steep hill for a mile, followed by two miles of up and down, and then back down the short, steep hill. This is a regular route I have driven it on, and it seemed to climb the hills much better (holding RPM's 2-300 higher than before), and running much smoother at all speeds. It used to be uneven at idle, and that has smoothed out a lot. When I stopped at the stop sign at the top of the short hill, I thought the engine had died, but it was still running! It was so smooth and quiet, I couldn't hear or feel it running.

My next step is the check the ignition timing and advance it following the suggestions I have been given on this forum. I think that may be the last improvement I make, since it had "adequate" performance before I did the repair work.

As I said in the first post, I don't use this truck much, and don't expect much from it. I'm very pleased with how it performs now, but I haven't pulled the loaded trailer with it yet. I expect it will do just fine when I get around to it, but I have several other projects to work on first.
 
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