I have an 85 ford f150 with a 300 6 that has very little power. It starts and idles good but hesitates and feels like something is holding it back when driving. I rebuilt the carb and put on a new fuel pump, changed the plugs, and when i put on new plug wires, distributor cap, and rotor cap it got a lot worse. any help would be greatly appreciated.

 

Hi Jason,

Have you checked your engine over for vacuum leaks? If you put a vacuum gauge on direct intake manifold vacuum, what reading do you get? This can tell you a LOT about the state of your engine. If you have leaks elsewhere in your engine, no new parts is going to fix anything.

Did you check to see if you have a slipped harmonic balancer? If your balancer has slipped, your timing will be off because the pointer on the balancer won't be pointing at 0 where it should be. You can quickly test this by bringing the #1 piston to TDC and then checking to see if the pointer on the balancer is pointing at 0. If not, you need a new balancer.


Next idea is that your '85 is what's commonly known as the feedback carb, or "Dreaded" feedback carb as many call it. It's a computer controlled setup that was Ford's last ditch effort to keep it carb'd before switching to full fuel injection.

When it's in 100% working order, it works excellent. But, as soon as parts start to fizzle, the computer goes into LIMP mode, richens the fuel mixture, and doesn't let the timing advance, giving very poor performance and bad gas mileage.

Have you ever changed the oxygen sensor? Is any of the emissions equipment missing?

Another alternative is what most people do and revert the ignition and carb back to a pre-feedback setup, or the DuraSpark II. These were on the 300s from around 75 to '83. It's an easy to do swap and can really clean up LOTS of issues from a poorly working feedback setup.

 

the emissions equipment are gone, where is the oxygen sensor? what you said about the carb sounds exactly like whats going on. thank you for the good information.

 

In that case that's most likely your issue. The computer controls the timing and since there's no emissions equipment to get its signals from, it's not letting your timing advance, which is going to make it gutless.

The oxygen sensor should just be down on the exhaust pipe near or in the manifold.

 

So i will need to get a dsII distributor and a non feed back carb to get power out of it?

 

"So i will need to get a dsII distributor and a non feed back carb to get power out of it?"
The only other option is to restore all the emissions equipment and sensors. As AB said the DFC is computer controlled and it is not a bad system...BUT, everything has to be operating properly...just like on EFI vehicles.

One of the horrendous mythologies that seems to be floated around is all one has to do is plug/remove/unplug, etc., emissions equipment and everything will be lovely. It just don't work because it is only half-arsed re-engineering.