I hope someone can give me some ideas,my truck is a 97 4.6 with 95k mi. It is developing a miss above 3krpm while under slight load, on level road or down a slight grade doesn"t seem to do it.I replaced the plugs with motorcraft dbl. plat. and the wires with MSD 8.8 superconductors about 10k mi.ago.The truck idles very smooth at 500rpm,and doesnt seem to miss till about 3k rpm going up grade at WOT.

 

I forgot to say the engine trouble code light is NOT on.

 

I don't know if you did a search. If you didn't it might help as there have been several threads lately on this issue.

Have you checked the fuel filter?

 

I have a 97 4.6. I changed the plugs and wires last year. Two weeks ago, my truck started to miss and had no CEL. I pulled one wire at a time off of the spark plugs. I found the number four cylinder plug and wire was all corroded. I replaced the plug and cleaned the boot and it runs great. The number four cylinder is the one that the condensation gets into from the AC. Hope that helps. Like I said, I never had the CEL come on.

 

Have you checked your fuel filter?

I had a boat that we used in a tournament. Inboard 5.7L gas engines. We could usually hang with the fastest boats at the start, hitting about 50 knots. We would usually firewall the throttles at the start and we'd be flying by the time we crossed the start line.

Well, this one time, one engine bucked and missed when firewalled. We could accelerate slowly and barely get the boat on plane. We couldn't get the engine to turn over more than about 3,000 rpm as I remember it. Above that, it would miss and stumble all over the place. Mechanic team member thought it was plugs so we pulled the plugs and they were fouled. Cleaned them and still had the problem. Plugs got fouled again.

Mechanic started saying it's probably rings.

All day long I kept thinking about the problem. I didn't think there was a problem with the rings because all the plugs were fouled and the engine had less than 500 hours on it. Of course, there was no way I could say anything to contradict the mechanic. Kept thinking about either fuel or ignition system. When we got in, the rest of the crew went off to the hotel while I farted around with the engine.

Did the easy stuff first and decided to change the filter. When I pulled the filter, it was black. Changed both filters and the next day we were hitting our usual 50 knots again. I never said anything about the filters and all the mechanic friend could do was scratch his head and say that sometimes things seem to fix themselves.

Ever since then, if I have an engine that doesn't run right under load or at higher rpms, I check the fuel and air filters.

I also demanded that all subsequent boats have vacuum fuel guages to watch the vacuum pressure of the fuel line between the filters and the engine. It's easy to know when to change the filter just by watching the vacuum guage.

 

Changed the filter,cleaned the MAF with no help.Ime thinking,maybe coilpack.They are still original.

 

Bad coil is also another one that can cause loss of power at higher rpms. I think you're on the right track if the filter change didn't fix it.

 

mine developed a miss, changed wires, plugs...ran a lot better but still had a miss over 3000 rpms. #1 plug looked worse than the others, changed that coil pack, and the fixed the problem. i went with the borg warner coil, it has a lifetime warranty and about $50.

 

I had the same problem couple of weeks ago. I went through a huge rain storm big puddles and two weeks later the truck started to miss so I removed the wires and put die-electric grease on both ends of the wires problem solved. no miss under light load. Vince

 

I s there a way to check the coilpacks,I hate to use the trial and error method ,but without the cel light on what can I do?

 

The heater hose above #4 spark plug is notorious for leaking down onto the plug boot and causing the spark to short to the head. That would probably explain the corrosion also.