I have a 98 F150 super cab 4x4 with the 4.6. It sat for 7 weeks while the city tore up my storm sewer. It's always run fine. Now when I start it it seems to run smoth and idle ok(about 500-600 rpm warm). Problem is when I get on it there seems to be a miss and the exhaust sounds different, after you drive it a while it runs ok. But everytime you shut it off it does the same thing all over again. It was full when I parked it and I've run a tank of gas through it and put in some injector cleaner.

It had 64,000 on it when I bought it a year ago last March. Now it has 68,000 on it . I don't drive it every day, That's the tempo's job. I've changed the fuel filter. and air cleaner the last oil change. It almost feels like a bad plug, but am looking for ideas about where to start to track it down. I've been reading all the posts on the 4.6 . Would the egr do this. I cleaned the MAF with electrical cleaner. No change . Where should I start?

Rick

 

How does it sound above idle in park? can you here it miss then or only while driving? It sounds like a coil issue, sitting outside night after night without being drivin moisture builds and a little to much of that will compromise a coil and that is sometimes hard to figure out Primary and secondary test can pass when tested , but the coil could still be bad under a load. You might have to wait for an engine light in order to pinpoint. Myself, I had a simular problem and ended up relacing all to fix the probem. This is just a guess and I'm sure others will chime in with there opinion. Does your 98 have COPS or do you have plug wires?

 

When I step on it and rev it up it misses . then after a few times it quits. I talked to my neighbor tonight who is a mechanic at a GM dealership . He's goning to grab me a can of some super injector cleaner that they use. He also suggested putting a quart of ATF in my gas tank. He says it sounded like an injector is sticking and to quit using the ethanol grade of fuel. He says they see the same thing happen alot at work. I will see about the coil too though
thanks Rick

 

Don't know what COPS is, but I've traced all the plug wires.
When it sits, it's in the garage. A clean truck is a happy truck.

 

My 98 has Coil Over Plugs and no wires, I believe they done away with wires period in late 98 - never heard of ATF in the gas tank?????? That freakin sounds scary to me...... I also havent heard of injectors sticking on anyone in this forum. You sure he said to put atf in the gas tank??? My suggestion is do not do this. If you have dirty injectors and want to clean them there's a very simple method that will do that and infact it will clean the insides of your intake and throttle body as well. Get a can Seafoam (look it up within this site) infact get two cans, put one in the tank and use the other to flush your injectors - To do that, pull the brake booster vac line and suck up at least 6 ounces of seafoam from the can, actually let it draw from the can until you here your motor studder and fluctuate a bit then shut the motor off and let it set for 10 minutes - a half hour. Start it back up and it should smoke for bit , the smoke will be whitish or darker , the darker the dirtier the insides were and the seafoam is working - its burning off existing deposites inside your mnifold and thottle body , thus cleaning it along with your injectors. I really mean it about the ATF - don't do that, it may lead to other problems like gumming things up, it's not a GM it's much better bigtime!! Like I said , do a search on seafoam for what you want to do..