1989 F-250 5.0L 4X4 159,000
Put new plugs, dist cap, rotor, and timed it. Runs great idles smooth but now when it get up to 55 mph thats like top end. Pedel all the way to the floor. Never had a problem with getting 70 and 80+ before I changed out plugs and stuff. Any ideas?

 

Your catylitic converter(s) may be clogged. That could be causing your lack of power. At 159,000 miles, if you are running the original cats then they could very easily be clogged.

 

maybe you put the plug wires back on the wrong place.

 

The truck would be running rough or missing if he put the plug wires back wrong.

 

How exactly did you set the timing? Did you have to make a substantial adjustment? Did you remove the spout plug before setting the timing, and replace it afterwords?

 

conanski hit it on the head you probably advanced the timing too far you need to either get a light and unplug the spout connector and re time or if you remember which way you turned the distributer loosen the holdown clamp and put it back in that position!Next time or when you get it right take and paint or scribe a line on the distributer and engine to use as a benchmark

 

yeah we did set the timing correctly with the spout connector removed and set to 10 degree btc, it might had been off 1 degree or so before we set it. I now think it's the catylitic converters. It just puzzling that it runs so good up to the 55mph. Thanks

 

Once you start getting up to higher speeds, you need to run at higher rpms. At higher RPMs, your engine is sucking in and pushing out air in large quantities. If your converters are clogged, your engine cant push the exhaust out therefore you cant run at the higher RPMs.

 

I highly doubt the converters are clogged. Unless it's been running extremely rough for a long while, I don't see it being possible. The majority of converters will fall apart internally before clogging. I pulled mine with about 210,000 miles on it, and it wasn't plugged up the least bit.

What really turns me away from the converter is the fact that he had no problems until he changed the plugs out.

ryanstoy- What plugs did you put in? If you installed Bosch, go ahead and smack yourself for me. Go get a set of Motorcraft ASF-42c's or Autolite (24's?.) I can't remember if the 302 runs the same plug as a 351. Also make sure they are gapped correctly, which I believe is 42-46 thousandths.

 

what handyman said and recheck the plug wires, maybe one is not on all the way or it hit the exhaust or they are in the wrong order.

 

What leads me to believe that it IS the converters is that the truck runs fine until higher speeds. If it was bad plugs or wires put on wrong wouldnt it show symptoms other than just at above 55mph? My experience with bad plugs or wires on these trucks is that you feel the symptoms at lower rpms when the engine is already struggling to make power, not up higher cruising along. By all means correct me if Im wrong and tell me why, Ill be more than happy to learn from what you guys have to say.

 

LOL - handyman43358 we did install motorcraft asf42c and we even set the gap correct

 

whats you fuel pressure doing when you try to reach those speeds?

 

mrl390- A clogged cat would be a problem at high rpm's, not high speeds (55 and over.) Not only that, but he said it ran fine until he changed the plugs. The cat wouldn't just all of a sudden plug up.

jonah- Fuel pressure is a possible problem, but just like with the cat, wouldn't just all of a sudden be a problem, unless Ryan's luck is that bad.

I could go on for days about possible causes to the problem he's having, but I don't have to. Why? Because after he changed out the plugs/wires, rotor, and distributor cap, and then timed it, is when he started having problems. So right there tells me its a problem in that general area.

Ryan- what I need from you is more info. Are you having problems in the higher RPM range at low speeds? If not, then rule out the cat and fuel pressure problems. When you're at 55 MPH with the pedal to the floor, is the truck revving high, or staying pretty low?

The other thing I'm thinking of, which I HOPE isn't the problem, is I'm beginning to wonder if your parking brake is still set...?

 

Handyman- I do understand where you are coming from. I said in an earlier post that it would be a problem at higher RPMs. I did mention higher speeds but I didnt mean that bogging down at 55mph showed the problem, I meant that bogging down at the rpms you would be running at at 55mpg showed the problem. To clear things up, ryan, what rpms are you running at at 55mph when you top out? Im willing to bet its at least above 2000. He said he set the timing right, put the plug wires on right and set the right gaps on the right plugs! You keep telling him that those are the problems but he did it correct so how can that be? You even said yourself that running at higher rpms and bogging down would mean clogged cats. When he is topping out, he is probably running at steady higher rpms. At lower speeds, unless you punch it, his rpms are probably not staying up high long enough to notice any bogging. Yeah it would be a good idea to check to see if he messed something up by accident, but he seems like a somewhat knowledgable guy who would know what he is doing. I dont really think his problem is in that department. Im sorry I enjoy a good friendly arguement now and then. lol.