I have a 97 with the 4.6. It has begun to miss under load after the engine warms up and will backfire intermittently. I have replaced both coil packs, all plug wires, all plug. I am thinking it may be a sticky intake or exhaust valve. Any help, please.

 

I take it you have no codes? The best thing to do when you have a problem like this and you remove the sparkplugs is to inspect each plug. The cyl or cyl's that are missing usually will have a sparkplug that is gas soaked or heavily carboned up and fouled. Then focus on that cyl and determine what the root cause of the problem is. In other words narrow the issue down to a specific cyl. Any specific noises related to the problem? Has the fuel filter been changed lately or ever? Does it appear to be missing on one bank or both? How many miles on your truck?

 

No codes, and running it HARD when it misses won't make it throw codes. It is hard to tell what bank it misses on because it doesn't do it all the time. All the plugs looked alright when they were pulled out last month. Changed the fuel filter a week or two ago, no specific noises, which makes me doubt the stuck valve. Truck has 127,000 miles.

 

Oil from your K&N can contaminate the MAF sensor and cause problems. Try cleaning the MAF and see if it helps. If you have to use the K&N then make sure it is oiled very lightly.

 

I have cleaned the K&N and the MAF sensor, nothing changed.

 

Did you change the plugs, wires, and coils before this problem started or after?

 

Here is the entire story just so you're completely filled in.:
It began to run bad out of nowhere, we took it to the shop 3-4 times, all of those times they worked on EGR. It was still running bad, took it back, they replaced a spark plug, spark plug wire, and coil. It ran perfect for about 2 weeks and then began to run bad again and throw EGR valve - insufficient flow codes. Took it back and they cleaned the EGR, again. We brought it home replaced the other coil, found that did nothing, then replaced all plugs and wires.

 

Remove the throttle body and clean it. Make sure you clean out the EGR passages in it.

 

I will do that tomorrow, any idea on how long that will take to do?

 

If you had it in 3-4 times and they worked on the EGR everytime I can't imagine what they are doing. The EGR is not some complex creature that takes days to repair or clean. Something had to point them in the direction of that one cyl they changed the plug on and when they did change the plug the engine ran perfect for some time afterward. Thats what I would focus on. Anytime you change a component and the engine either runs better or runs worse then that component is suspect good or bad. Maybe cleaning the throttle body will help but after 3-4 times at the shop I would think they would have at least done that already. If that doesn't work go back to the original cyl that the plug and wire were changed on and it ran good afterward. Find out why they suspected that one only and then determine if the same thing is happening again with that cyl. Good luck.

 

Tried it all, even put the stock air intake on it, nothing changed, it actually got worse when I put the old intake on.

 

The last time that it threw the egr insufficient code and you took it back in to have them clean the egr again, they must have reset the pcm, did the code come back?

 

no, the code hasn't come back, no matter how much I try to get it to throw a code, nothing throws codes.

 

I would still suspect the one cyl they changed the plug on and then it ran great for two weeks. Did you remove that plug again and take a look at it? Possibly take it in and have them scan for a code maybe the dash light is not working.

 

I just went and pulled out all the paperwork. After they replaced the #2 plug, it did not change how it ran. 2-3 weeks later, we took the truck back and they replaced the coil pack and #8 spark plug wire and it ran great for 2 weeks. It then began to run bad again and throw EGR insufficient flow, code - P0401. The shop then replaced the EGR Valve solenoid, and I replaced all wires and plugs, even the ones they changed. Still ran bad. Nothing looked out of the ordinary when we changed plugs/wires 3-4 weeks ago. I will check them again but I do not think it has anything to do with plugs/wires.