hey guys, i’ve got a 86 f150 with the 300 in it, i replaced the valve cover gasket and now i’ve run into a idle issue. the truck will barely hold its idle and misfire like crazy, then pick up to around 900-1k, then bog down again. throttle response is still the same, but the idle is absolutely atrocious. being at a red light is a nightmare as i have to keep the revs up or else it’s really close to dying. i’ve checked for vacuum leaks around the valve cover, but can’t find any. Any insight?

 

I would check the PCV valve and the hose going from it to the carb. Since you disturbed that, the hose may have cracked or something else may have happened with it.

 

Being a feed back system I think there are a lot of plastic vacuum lines across the valve cover to solenoids at the rear of the cover.
The plastic line crack with age so check them really good.

I would also pull the vacuum hose off the EGR and plug it and see if that changes anything.

Grab the top of the carb, air filter off, and try and move it look the for it being loose. They like to loosen between the carb body and base.
Cant remember but dose the carb have a TPS? Could that be a cause?

I would also check the bolts holding the manifolds to the head if loose.

Last check for codes.
Dave -----

 

Many of the lines have been disconnected and cut, but regardless, it still ran fine with them disconnected prior to the VC change.

 

This may a sign. Change the distributor and the carb and rid yourself of that system. When it throws a fit idling, go out under the hood and look at the motor that is hooked to the carb that adjusts your idle speed. If it's running in and out causing the problem, you can blame your computer friend under the dash for that. You can get rid of him and all those wires for good if you change the distributor and the carb.

P.S. I may be treating the computer unfairly, if you have some other problem it may be trying to compensate for it, but not doing a very good job of it.

 

checked PCV, and all seems in order. And i don’t exactly have the greenbacks to change the carb/dizzy right now, and i kinda need the truck now as it’s my daily. should i recheck the VC gasket to make sure there’s a full seal? i was also spraying carb cleaner to see where it would even out the idle, and i found a spot in the rear of the carb by the idle screws where if i spray carb cleaner, the idle will stay high and steady. any ideas?

 

Pursue this some more. There is obviously a leak in that area somewhere.

 

Update: ended up ripping out the mess of wires, along with the carb. there isn’t anything i need from that whole mess of wires, correct? currently waiting on parts to come in so i can swap out the dizzy as well.

 

One thought comes to mind:



One has to be careful of making too many changes all at once. When a new problem crops up, one has no way of knowing exactly what caused it. You then have to revisit all changes made since the last time it ran well.

The truck had been running fine. After some minor work (new valve cover gasket), the engine suddenly runs poorly. i don't believe the gasket itself was the issue, more likely something else disturbed in the process. You even located a vacuum leak. Not trying to bust your butt, but you've opened a real can of worms (they taste awful, by the way) by proceeding with some major mods without having cleared up the original issue. I dread hearing the conversion induced a second new issue on top of the first. That would be a troubleshooting nightmare.

Fingers crossed it all goes well, but I STRONGLY suggest resisting the temptation to "fix" everything at once. Whenever possible, take a big project in small bites, and test after each step.

 

My thought process is that with the conversion done, if i happen to still run into some issues, i will have already removed many variables (sensors, vacuum lines) that i would have had with the old system.
besides, i think my truck was overdue for the conversion. it never ran as it should, but ran okay enough to drive and daily. i always ran into high idle issues among other things. hopefully this conversion allows pinpointing an issue a whole lot easier.

 

I hope you went with pre 83 carb & dist. that dont use a computer.

If you found spraying cleaner around the back of the carb it could be the carb is loose, grab the top and try and move it.
Or the gaskets are bad. carb to EGR plate, EGR plate to manifold.
I dont think there is any vacuum line back there from what I remember.

Now down under the rear of the manifold there is a vacuum tree that has vacuum hoses and caps.
Wonder if the spray was getting to it?
Over time the dry out, crack and fall off causing a vacuum leak.
check that tree over really good as some of the nipples are hard to see.
Dave ----

 

im going with the HEI distributor, along with a pre smog carb. should be fine, right? is there anything else i should know to make this conversion?

 

Nope you should be good with them parts.
From what others have posted you will not believe how good the motor runs after the parts swap.
Dave ----

 

If you want to complete the conversion, the first thing to do is find the original ignition coil small wires. One of them should be white/blue. Cut this wire close to the coil connector and tape it and save it. It should go back to some connectors on the driver's side inner fender. Keep it plugged into these connectors, this wire will power your new HEI. It gets hooked to the BAT terminal on the HEI.

There are some other wires you might want to save. They come from the connectors on the driver's side also. One will be a red/white and the other will be a white/red. These are for your temp gauge and oil pressure sensor.

Check you alternator wiring. You might have a white/black going to the old carb. You will hook this to your new carb choke if it has that connection.

You can also look inside behind the dash over the tranny hump. There should be a box under there, it is the old engine computer. Unplug the large plug. Take the computer out, and then bend the large plug around and work it through the firewall. Anything hooked to this plug can leave, it was all computer stuff that you do not need. Once everything is free it will come out and really clean up the engine bay.

 

are these the wires that i need for the HEI power and temp gauges?

and is this the big plug im undoing?