I have a 94 f150 with the 302, i just replaced head gaskets, vavle guide seals, intake seals, exhausts seals, sensor seals, etc... and cleaned eevrything up all nice and paint and what not .. in the process i removed the a/c. no need. my thermactor air pump did not work before and was not even on the belt so i ripped the hose junk and and i plugged the heads witha big bolt. i lwft the sensor in so i would have codes. everything else pretty much was plain jane back together... so i fire it up after 2 weeks of working on it in spare time and it starts on the first roll this is open exhaust manifolds and it purrs at a idle(to loud at this time to really hear anything wrong) next day i put the y pipe and cat, muffler on... let it idle a bit its sounding good. so i give it some gas and it sputters a lil nothing i figured it wouldnt being cleaned now... go to take it for a ride and when it gets the load of the truck on it about half throttle it misfires like a son of a B. if i put it to the floor its not that bad but it seems to have no power whatsover...(10x better before) =[... anyways i figure its been sitting ..bad gas.. premium gas and stabile **** later ...no affect.. so i borrow a snap on scanne and get 111 codes passed for KOEO ..then i get 311 i thik for thermactoer air junk that was a given and a 411 code for unstable rpm or somethging...then i gots to thinking about that one and one chamber in the trottle ...one plate only has one screw so at idle its reving 200 rpm too high due to a extra...(bigish hole). So then as for the misfire part goes i have no clue what i did!
Sorry for the story.
Any help i mean any would be great.
Thanks, Ryan

 

This is just a wild shot in the dark and i'm probably wrong but ...

The computerized fuel injection system for our trucks relies heavily on the readings it gets from the oxygen sensor to keep the motor running right.

If something about the sensor isn't right it can cause a lot of headaches.

As nearly as i can figure the air pump system dumps air in to one of three places depending on what the computer tells it to do.

1: Upstream of the O2 sensor into the exhaust manifold.

2: Downstream of the O2 sensor into the cat.

3: Directly into the atmosphere.

I would imagine that it could throw off the readings that the O2 sensor was getting if the computer was calling for air to be pumped in upstream but none was being introduced.

Probably result in a really rich fuel mix, poor engine performance, and lousy gas milage ?

 

Check the firing order

 

The air pump was on the truck prior to rebuildibg it but it never worked it seized up i just got a smaller belt and never ran it... All the hoses were still there thpugh that arent now..one ran from the exhaust .air pump and the back of the heads i believe. It also had lil.hoses running to the sensors i left the little hoses and sensor plugged in.
I will check the order again but i believe it is correct..
I did not remove the entire distributor assembly bit could it of been bumped could that throw it off enough to cause misfire over 2000 rpm... Anyrhing under that it runs pretty smooth

 

Ok .... I don't know as i really understand. It sounds like there are bits & pieces of the old thermactor system left ?

The reason i brought it up before was because you can get a misfire up through the throttle body if one of the check valves is bad. ( Don't ask me why ... it's just something i read.)

That's just one thing of many that could cause a problem. More likely it's firing order but if that doesn't pan out make sure that the inlet ports on the manifold & the cat are capped off real good.

Rule that out as a possible cause.

I know with my truck i'm going to try and restore the thermactor system so that i can clear the code and get the CEL of my dashboard. (It's gotta be done for the yearly state inspection.)

No reason somebody else should go to all that trouble if they don't have to.

 

 

This is where I set mine....I'm sure Sean will correct if I am off! Make sure you remove the spout before setting.....