I just purchased a 1985 F150 for my 15 year old son. The truck has great bones but I believe someone has changed the motor from EFI to Carb. Things I do know.... It still has an EFI distributor, C6 transmission, Carter YF carb, newer starter but switch was bypassed and it uses the switch on the firewall, someone put a GM 1 wire alternator on it. We have put a new battery, cables and wires, cleaned up a bad ground. We put new cap, rotor, wires, coil, fuel pump, thermostat, flushed coolant, new hoses and serviced the transmission filter, fluid & gasket. The 2 problems I currently have are this. The biggest issue is the truck runs decent in park & neutral. When put in gear it shakes real bad. My guess is that the engine is running retarded because it doesn't have vacuum advance. (thoughts on that and is there a way to keep the EFI distributor or do i need to go to a vacuum dist.) Also there is a drain on the battery i can't find. with the battery cable off, i tested with a volt-meter and have a 3-4 amp draw. I pulled all the fuses and nothing changed. (Could something be wrong with the alternator when the truck isn't running? The battery drains while the truck is off and i believe it does charge when it is running.

 

Hello and welcome to the forums!

Nice looking truck you have there.


The 300 didn't get EFI until 1987. In 85, it was a computer controlled "feedback" carburetor setup, so it's either partially, or fully still original. If you post up some pictures of the carburetor and the distributor, that'll help us know for sure.
These systems were only used from 84 - 86, so there's not a lot of support for them. Most people will pull it all out and convert it to the pre-84 setup, which is known as the DuraSpark II. It's very reliable and is all plug-and-play.
If you want more info on that, let us know.

Have you timed it with a timing light? It still should run and drive, even if the distributor isn't being advanced by the computer. It'll still have mechanical advance, which is done with weights inside the distributor. You'll just get less gas mileage on the open road.
Shuddering when putting it into gear may be a different issue.


On the battery drain, that's definitely a tough one to diagnose online, as that mostly takes going through it with a voltmeter and trying to track down the drain. Some people might have some tips and tricks that may help. However, unless there's some sort of short in the wiring, I don't see how an alternator would drain the battery when the engine isn't running.

Good luck!

 

Not that I know of?

 

No? If so, I may be mistaken. But I thought the feedback distributor was still advanced mechanically. It was just the "vacuum advance" that was replaced by the computer.
Is all of the timing advance on the feedback setup done by the computer? Otherwise it just stays at base timing?

 

The last 1983 distributor I took apart only had the trigger wheel and sensor.
AFAIK all advance was controlled by the computer.

 

Yep thst distributor. Is locked at what ever you set base timing to.
Also remember when checking timing on feed back system you need to pull the sprot wire to stop the computer from trying to adjust it.
Do you need to do a smog test?

You can get a lot more help over in the 80 to 86 truck area for both problems as we deal with it all the time, feed back that is.

Even the battery drain is pretty easy to track down but this is the motor area.
When you do make it over there start 1 post on the running issues and 1 on the power drain. It's easier to help when done that way.
Dave ----

 

I appreciate the help. Here are some photos of the carb and inside the engine. there seems to be a lot of blocked off vacuum lines. the truck still has what appears to be a map sensor as well. If it has a computer, i have no idea where it is.

 

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Ah, learn something new every day. I thought those were still mechanically controlled timing on the feedback setups.
Yeah, if it's locked at completely base timing, that would definitely hinder performance quite a bit.

pmuller, that's the DuraSpark II ignition module, so he wouldn't have one of those on his '85 as it looks like his feedback system is complete.
The computer is inside the cab, up underneath the dash. It's roughly inline with and up above the gas pedal.

I've never diagnosed and fixed a feedback setup, as I usually pull it all out and convert to a DuraSpark II (or equivalent), so I don't know where to tell you to start.
But it does look like you're missing a vacuum cap on the carburetor (driver's side, first picture). Hard to tell since the picture is kinda small.

Also, your passenger side motor mount is missing the upper bolt. Adding that and tightening it down might help with the engine shudder.

 

The carb is not a feed back carb as it dose not have wires going to it other than the idle kicker.

Because of that and who knows what else the computer is in limp mode and timing locked.

Let's step back to the ruff running motor have you done a compression test on it yet.
If you have a weak or dead hole it will run ruff.
I would do that before putting any money into the truck.

I also see a GM ALT installed
Dave ----

 

Overall, what you've got there is what we call a "mess". Not that it isn't solvable. That isn't the *correct* carburetor for 1985, although it might be a perfectly servicable one that just needs to be tuned.

Your larger issue is really going to be addressing whether the ignition is timed and/or advancing correctly. It's completely common to see the "Hybrid" EEC setups, where a prior owner has made a dogs breakfast of them, due to ignorance, laziness, or just not being able to find proper diagnostic procedures (And I'll be honest, while it worked, this wasn't the greatest setup in the history of automobiles, and I'd probably remove it, if I had one).

One of the easiest things to check? Pop the distributor cap off, grab the rotor, and can you move the rotor at all? If you can't move it, that means there's no mechanical advance mechanism in the distributor. If there isn't, *I* would personally recommend switching to the earlier Duraspark II, or even an aftermarket setup, like you can get from DUI.

Basically, your carburetor and other stuff is probably fine, but the ignition setup isn't working, because I'm going to bet good money if the ECM is still there, there's been some hackery done to the wiring harness, in conjunction with removing the original carburetor.

 

Because the carb has been swapped out the computer is in limp mode and timing is locked at what ever it is at.
If 1 sensor stops working the computer goes into limp mode and timing is locked where ti is.

I would do a compression test before doing any thing more.
If you have a dead hole no matter what you do be it tuning of carb or a different dist. so the timing advances the motor will still run ruff.
Once you know the compression is good in all holes then I would replace the dist.

You can get all factory parts from a junk yard or get a new dist & IGN box.
The hardest part is the wiring. This can be from a junk yard from any car or truck 6 or v8 with a DSII system and it is plug & play.
Painless wiring also sells a wire but it is $$$.

What a lot do is buy a HEI that fits the 300 Ford motor off Ebay.
It only takes 1 wire, power with key in start & run, and you are set.
Some wire in a relay so it gets full 12 volts and others find a wire on the fender well made to wire in the DSII system to power up the HEI dist.

Once you have it running with the carb you have now and hope it is good, a dist. that advances we can then dial in everything to run its best.
Then we can start to remove the old computer & wiring starting with the computer inside and work your way out to the engine bay.
It is best to go slow as 2 or 3 wires that the truck still uses is in the feed back harness.

Same goes for the vacuum lines. You only need a few: power brakes, vacuum advance timing, HVAC, PCV, Evap system.
In the end what you will end up with is what is on my 81 F100 with a 300 six, I am running the factory DSII system.
Dave ----