300 i6 bad idle and lacking power.
 

i recently got a good deal on an 85 f150 4x4 with the 300 engine and 4 speed man trans. the truck runs and is drivable, but seems to be lacking power, like top highway speed of around 60 mph. it also has a weird idle problem. when idling it starts to cut out and sounds like its going to die then it revs back to normal idle and continues this cycle without ever actually dieing. the po said it has ran like this since he bought it and he has been driving it this way for 7 years.

i think these problems are due to a faulty emissions system. the air pump has no belt, and seems to be locked up, also the long tube from the air pump to the cat is broke off at the cat. it is also missing a hose or tube from the air cleaner assembly to the exhaust manifold.

do you guys think the lack of power and the idle problem are due to the nonfunctional emissions system?

what are my options to get this thing running good? I live in area where i do not have to worry about any kind of smog emission tests.

i am looking for a low cost fix for this, and would like to keep the original carb and Distributor for now if possible.

Thanks for any help.

I don't think the idle problem is directly related to the emissions system. It sounds like the idle mix is too lean. There's an idle mix screw on the base of the carb - try turning it out about 1/4 turn and see if that helps.

As for top speed, 60 is too slow unless you have really low gears. One of two things is likely there - a worn out engine with no compression, or a problem with engine timing. Late timing will contribute to the idle problem and also keep the engine from producing much power. You need to find out where the timing is set as opposed to the spec, which is probably 6 degrees BTDC.

I think it has a feedback carb and with the disconnected emissions stuff the computer is throwing a fit.

If it has the feedback carb then you are right. It needs a full DS-II swap. Look in the stickies for how-to's. But, I don't think you need to replace the carb itself as its default mode w/o the computer will be pretty close to what is required.

These were never high revving engines, with a low rear end ratio, 15" wheels and no overdrive I could see it not being able to get out of it's own way much past 60.
I wonder about exhaust restriction too...

yes it has feedback carb. i was hoping there was some way i could remove the emissions stuff and trick the computer without doing the DS-II swap. but it looks like my best option is to do the swap.

i will go to my local salvage yard tomorrow and hopefully find the DS-II parts i need.
if i am able to find a non feedback carb, is there any additional parts i need to grab from the donor truck to make it work properly? also when i have installed the DS-II and non feedback carb, will i be able to remove the rats nest of emissions junk that is non functional?

for now i am just looking for a cost effective fix to make this truck run better. in the future i plan on going with an aftermarket intake, carb, and exhaust system.

Thanks for all the help and Happy Memorial Day.

And I'm proud to be an American,
where at least I know I'm free.
And I won't forget the men who died,
who gave that right to me. -Lee Greenwood

I don't know of additional parts beyond the DS-II distributor, blue-grommeted ignition module, and wiring harness. But I've not converted a 6, just 8's.

And, in the early years, like up to 82 at least, the computer's wiring was completely separate from the rest. So it could be removed after/during the conversion. And, all of the inputs/outputs like the TAB & TAD relays.

You need the coil and bracket too.

I have the same engine. I have 0 emissions equipment. I had similar issues, my problem was a bad ecu and some bad wiring. I would def test it koeo and koer. It will tell you alot. I run pretty good when warmed up, I have a code 41 (lean) that i traced to the fbc solenoid but runs well. Vacuum leaks, tps, timing (unplug spout), map should be tested. I got my engine running good with no emmisions (rotted lol). I feel blaming emisions is incorrect I get no codes and have plugged everything nicely to prevent leaks. i will be switching to ds2 for 4bbl reasons and will miss the fbc dependability and gas milage though.

The local salvage yard only stocks 99 and newer vehicles:-arrgh i might just order a replacement air pump and weld the pipe back to the exhaust.

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