Hey y’all..another issue cropped up with my 84 f150. It ran great for the last two weeks..but then last night, after I installed a proper oil pressure gauge, I went to take it out and it started stumbling at idle..like it was close to stalling. So I turned around and parked it over night. Now it starts quickly, but won’t idle even once warm. Once it dies it’ll again fire right up pretty quickly. It’ll run just fine as long as I keep my foot on the gas. No smoke no odd noises. Any ideas?

Just for reference this is what I have: 84 f150 302, it has an edlebrock carb, I have a fuel pressure gauge hooked up post fuel filter and I’m getting 3 to 3.5 psi. I’ve recently replace the alternator, spark plug wire and plugs, new battery, new air cleaner, entirely new duraspark system including rotor and distributor. Oil pressure seems good too..at least 10psi per 1000rpm. Kind of hard for me to pinpoint it exactly since I can’t keep it at idle.

Thanks!

 

How long ago did you install the duraspark system? A bad coil will spit and sputter once it warms up. It doesn't necessarily mean the engine needs to be warmed up, just the coil. Where is the coil mounted? What brand coil did you buy? Some coils require a transistor to be installed with them. So you should check to see if yours needs one. Just trying to rule out the coil

 

Was the oil psi gauge the only thing you did / install and then this happened or did you do other things also?
I ask because if it was the only thing it "should" not be to hard to follow your steps and path to see if you knocked off a vacuum line or cap.
When cold the choke is on so it should idle faster and run richer till warm and the choke comes off and then runs poorly.

BTW I hope you did not use that white plastic hose that most gauges come with.
Throw it out and get copper, the plastic will dry out and crack or melt and hot oil will spray out and could cause a fire!
Dave ----

 

The duraspark is maybe two months old, with less then a 1000 miles. The coil has an internal transistor and if I recall I got the coil from Napa. It’s mounted in the factory location.

 

Yeah the oil gauge is the only thing I did before this happened. Prior it ran fine..even took it on a 30mi round trip ride to help a friend move. Also, I forgot to mention the choke is not hooked up yet. It’s pretty hot here in Atlanta at the moment so I’ve just been using my foot..it’s been working fine so far, though I have a choke ready to be installed. I’ll keep it at a reasonable rpm and feather it out.

Dang! I did you use that little white tubing. I’ll pick up some copper tubing like you suggested. Thanks for that..i don’t think I would’ve thought of it.

 

Update. So I got a chance to mess around with the old gal this morning before work. After doing a little reading, I saw that some people have started the vehicle and revved it high and then flipped the choke plate to choke it out to almost stalling and the opening it again..I guess it has the effect of blowing whatever maybe clogging the idling circuit out.

So so I did that. And it helped..a little. I did that method a few times, and as soon as I’d open the choke plate back up for a few seconds it would seem really good. Very nice idle. But after that few seconds it would slowly begin to fade. On a plus note I turned the truck off as opposed to it stalling..but it was awfully close.

So im assuming something is going on in the carb?

 

You said that the choke is not hooked up... is it opened fully?

Go back and check for vacuum leaks as suggested by FuzzFace2, since this symptom began after the seemingly unrelated mechanical work.

 

I think I would back the idle mixture screws out a little bit.

 

Yes the choke is opening fully. As far as vacuum lines..I have one going to the distributor, one to pcv, one to the brake booster, one to the window wipers, and one to the transmission. I’m pretty sure that’s it correct?

 

So when I got home from work this evening I tried starting her up again. Same deal..runs well as long as my foot is on the gas. So I hooked up my remote starter and did that carb trick again. That makes it at least idle, although very very low..on the verge of stalling. I sprayed some carb cleaner on all the vacuum lines and heard the rpms slightly smooth out when I got to the line connected to the trans. Went to the auto parts store before they closed and got some tubing. Replaced that line and clamped it down and still the same issue. I guess tomorrow before work I’ll just go ahead and replace all the vacuum lines just to be certain.

If I get the same non starting results, think it’s the carb idle circuit? Maybe something lodged in there?

 

When you sprayed back by the trany lone what other vacuum line or ports are close by?
There may be a cap fell off and the spray just was close enough to find it.
Is the carb also close?
Maybe it is loose and gasket not sealing?
What ever it is you partly found the area you need to look over for a vacuum leak.
Dave - - - -

 

Don't feel bad. I changed the water pump on my Dodge Dakota, accidentally forgot to plug a hose back in. I could here it sucking air for a few months and couldn't find it. Finally someone pointed it out right at the front of the throttle body. My eyes just didn't see it..

 

So..got up this morning to replace the vacuum lines. I replaced them and gave an extra snugging to the carb mounting bolts. Still the same thing. However whenever I’d do that carb trick it would at least stay running. So I turned my idle screw in (the screw connected to the throttle linkage) and it stayed running to a smooth idle. I hooked up my timing light, timing is spot on, and I set my idle rpm (according to my timing light) so that I hovered between 780 and 800 rpm. I set it there because that’s what the sticker says inside the truck.

So should I consider this fixed? Or did I just put a band aid on it? Also, how that rpm sound to you?

 

I think you fixed it. That is what both of those adjustment screws are for. When the weather turns cold it might need another tweaking. Don't be afraid to turn them, just remember how many turns in or out you have gone.

If you think there is crud in that idle circuit, you can take each screw and turn it all the way in while counting the number of turns, turn it lightly till it stops. Then turn them back out to where they were. If there is any crud in behind the needle closing it all the way sometimes pokes through the crud and dislodges it.

 

Best to set fuel mixture with a vacuum gauge. Cheap and easy.