Diagnosing rough running 460?
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Mountain Pass
Joined: Dec 2006
Posts: 225
Likes: 44
From: OR
Diagnosing rough running 460?
I just picked up an '89 F250 with a 460 that runs terrible. It will start but if you put too much load on the engine (even just revving it up) it dies and won't restart. It sounds aweful from an exhaust leak at the exhaust manifold to head and also smells bad. I figure an exhaust leak before the cat wouldn't make it run this poorly. It should still be able to move out of its own way. It starts ok cold but idles fairly low by the sounds of it(no tach). I pulled the codes and got codes 21 and 24. I read it has something to do with outside temps below 50...it was in the 30's. Checked fuel pressure and I am getting low 30's idling and 40 when I pull the vacuum hose off the FPR. I swapped MAP sensors with a spare and no change in performance.
I'm not sure where to go from this point? I was thinking maybe clogged cat but have never personally encountered this issue. Any help or suggestions would be much appreciated. Thanks!
I'm not sure where to go from this point? I was thinking maybe clogged cat but have never personally encountered this issue. Any help or suggestions would be much appreciated. Thanks!
Cargo Master
Joined: Nov 2013
Posts: 2,168
Likes: 4
From: South Central,MO
Codes 21 and 24 were probably because the engine wasn't completely warmed up, but checking the codes is always the first place to look. Check all the vacuum lines real close for leaks, that can really screw with things. After that, look at the usual tune-up stuff. Condition of the plugs and wires, check the timing, air cleaner, stuff like that.
Thread Starter
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Mountain Pass
Joined: Dec 2006
Posts: 225
Likes: 44
From: OR
Codes 21 and 24 were probably because the engine wasn't completely warmed up, but checking the codes is always the first place to look. Check all the vacuum lines real close for leaks, that can really screw with things. After that, look at the usual tune-up stuff. Condition of the plugs and wires, check the timing, air cleaner, stuff like that.
Thread Starter
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Mountain Pass
Joined: Dec 2006
Posts: 225
Likes: 44
From: OR
Found a couple vacuum leaks but it didnt fix the rough running. Decided to check fuel pressure again and it took a long time to build fuel pressure when the gauge was hooked up. Probably close to 10 seconds to build 40psi. I swapped to the rear tank and the pressure built up instantly. Then switched back to the front and the pressure built up instantly. I've never encountered that before but decided to leave it on the rear tank. I tried to check timing but noticed the timing mark was about 90 degrees off with the spout pulled and running. It was far btdc. I turned the distributor clockwise and it ran a whole lot better. Put the spout back in and it ran worse but marginally better than before I started. I still couldn't see the timing mark.
Any ideas where to go from this point? I put on a vacuum gauge and it was a pretty steady 21in.
Any ideas where to go from this point? I put on a vacuum gauge and it was a pretty steady 21in.
Thread Starter
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Mountain Pass
Joined: Dec 2006
Posts: 225
Likes: 44
From: OR
Made a mistake and had the timing light on the wrong spark plug wire. Got it on the #1 spark plug and timed it. Had the fuel pressure gauge on and the truck died. No fuel pressure. I tried restarting and it wouldn't restart. I cant hear either in tank pump now. I jumped the pumps and got under the truck and can only hear the frame mounted pump run. I'll do some more research and see what I find
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