I have a 97 w/4.6 that has been missing under light loads - small hills, low rpm's, etc. Though it is starting to miss more now when I am accelerating quickly (on-ramps, etc.) It doesn't have the COP system like a lot of you guys have trouble with. I have replaced the plugs, installed motorcraft racing wires, etc. It is getting to the point that at times it is missing badly and it will not give me any codes. It also has an issue with idling rough, but usually only after having driven on the freeway then coming to a stop at the first stoplight??? After that the idle smooths out and is fine. I have cleaned the MAF sensor though I should probably do it again - it's been a year or so. Any ideas guys??
Thanks

 

No you don't have COPs but you do have coil paks that do the same thing.

 

EGR could be stuck open

 

Would a coil pack problem be intermittent like this??

 

usually they just get weak. my stockers had a 130K on them never caused a miss they just got weak in the upper RPM's

 

EGR problem wouldn't cause missing would it?

 

the EGR usually will dump primarly into one or two cylnders on the passenger side of the motor causing a miss. pull it off spray it with penetrating oil or wd40 make sure its not stuck open. but u can hook a timing light up to it see if u do indeed have a coil pack not firing

 

I would do a complete intake cleaning

MAF
EGR valve and ports
Throttle body
elbow ports cleaning
PCV
IAC
check hoses

My truck was not missing, but it was "wimpy" after I did that, it really was much better, very smooth idle.

 

Yeah, I guess I'll tear into it and go through everything. Does this sound like a stuck/dirt Idle Air Control Valve (the rough idle portion) I read a couple threads that indicated this as the culprit some of the time for the idling issues. The misfire is my main problem though - really getting irritating.

 

Rough idle could definetly be caused by gunk and grime in the IAC and the IAC ports. Make sure to blast away at the IAC ports with high pressure brake cleaner or carb/choke cleaner. And blast the IAC as well (wear safety glasses) and after you clean it with brake cleaner, lube up well with WD-40, soak it really good.

 

Nice truck - Identical to mine - color and all. I still have the stock grille though. I cleaned the MAF and the IAC tonight. I also found an injector connector that was really loose and I thought maybe I got lucky. I drove it a bit and it seemed to be much better but alas - once it warmed up it started missing again. I used brake cleaner to clean out the IAC - hit it several times but I didn't put WD40 in it before I put it back on. Is that something that needs to be done? I'll have to get into it deeper when I have a bit more time I guess. Still very odd that it won't give any codes with the scanner???

 

Yes. I switched from MSD's to Accell's and had the problem you describe under acceleration, but not at idle. I switched back to the MSD's, and the problem was cured.

 

hey nyford guy and arctic blue , my 97 is that blue color also. thay only did that color for a few years huh?? dont see many around.

 

It could be anything that's been mentioned above - especially the EGR valve.

In normal operation the EGR system should be undetected by the owner. If the system fails with the EGR valve closed there will be no driveability concern. No MIL light means that the owner will remain unaware of it. Since emission testing is at idle (when the EGR does not operate) the vehicle will not fail the MOT.

However, if the system is not gas-tight then air can be drawn into the inlet system instead of inert gas. This weakens the mixture sufficiently to cause misfiring, and manifests itself as a noticeable misfire/hesitation at speed and light throttle, not present when accelerating. If the leak is serious enough it may manifest itself as a hunting/rolling idle, caused by an unmetered leak of air into the inlet.

Thought I would mention that since faster already covered what happens when they stick open. Also, giving your mileage might help as well.

Good Luck

 

I had the same problem while towing my camper, as soon as I would pull off and stop at aight it would start idling rough and almost quit. I changed both forward oxygen sensors 2 years ago and haven't had the problem since. Good luck.