I have a 78 F-150 Ranger XLT with a gremlin. The truck runs great for a while then seems to starve for fuel and sometimes backfires. Sometimes it fixes itself, sometimes i toggle the tank selector switch and that fixes it. Sometimes I put it in neutral and rev it - sounds great then when I go back into gear - sometimes it's working again - sometimes not. Happens usually after about an hour & 1/2 of driving but has happened sooner and sometimes doesn't happen at all. I have changed the fuel pump & filter twice, taken the EGR plate out from between the carb & manifold, blown out the fuel lines, bypassed the fuel tank valve to run on one tank all to no avail. Sometimes I get the fuel guage telling me that the tank is suddenly totally full or empty - then it goes back to normal. Sometimes the heater blower goes off then I wiggle the key and it comes back on but the truck stalls. These may or may not be related. The motor sounds and runs great usually but then bogs down - then fixes itself. I know that there is a leak from a bad donut ring on the exhaust manifold and a hole in the muffler from backfiring.. also a mechanic told me he thought that the motor was running lean but not to adjust it, and then removed most of my vaccuum hoses (I kept them in case I need to put them back on).

It has no problems starting, (even when it's running rough) and has always fixed itself so I haven't been stranded - but I'm worried it's a sign of a bigger problem developing as I'm about 1/3 of the way though a 1,600 mile trip and will have to travel the last 800 miles with virtually no services, parts stores or cell phone service.

Thought at first fuel supply, now wondering about electrical system, maybe float level..

Any help - especially stuff I can test before replacing would be extremely appreciated.

 

Welcome Larivee,,,, I would check all your electrical and grounds, check the wires where they come through the firewall, sounds like maybe a short or something,,,

 

Have you changed the ignition module.
A bad module can sometimes act as if you cut the key off and back on with a loud backfire but it would not effect your gauges and heater,those are ground issues. The modules are famous for acting up.

 

... having fun in the snow today with my ford... been doing things for the last few days and the truck seems happier. Here's a strange one though. It's reasonably cold here today. (-10 C - about 16 F). Went out to start the truck to move it into the shop for some more work. When the key is in the start position - the truck runs nice.. let it go back to the on position - the truck shuts off.. also the radio and heater too!! Wiggle the key and the radio and heater come back on. Repeatedly... Turned the key upside down - truck still shuts off when I let it go back to the on position but the radio and heater stay on this time.. Kept trying to start it.. even gave it gas in the "start" position and it runs great - until i let the key back to on position.. After several attempts and keeping my foot on the throttle - it seemed to warm up enough to continue running..

I'm seriously considering changing the ignition module but they are quite expensive and I don't want to waste any more cash on stuff that is working properly. Wondering if my problems all along are more likely to be a bad ignition barrel or even key...??? grrr!!!

Today's jobs will be to tighten the intake manifold bolts, new gasket between the carb and intake manifold (noticed it was leaking a little gas) and new valve cover gaskets. Yesterday I changed out the spark plugs and the motor sounds awesome (when it's running)..

Any idea's (and is there a way yo test my ignition module???)

Thank you - much appreciated.. freezing in Edmonton, AB...

 

.. also (sorry to ramble).. could the bad donut ring on my passenger side exhaust manifold be creating some kind of backpressure that is effecting compression/power? The muffler has a big hole and I'm going to change the whole thing - but would rather wait until I get home to Whitehorse (Whitehorse is 1,400 mile from here), and do it in the warmth of my own shop - instead of my friend's driveway here...

Thanks again.

 

well - I would really hate to jinx it - but the old ford is a very happy truck now... here's what I did.

New fuel pump, new fuel filter, took the EGR plate out from between the carb and intake manifold, got rid of all the vaccuum crap except for the essential stuff, new Bosch 4008 spark plugs (and gapped them to spec - .42 - .46), new gasket below the carb (that was a great idea) new bolts to fasten the carb on, tightened all the intake manifold bolts (that's what the problem was I think - fingers crossed). Now to go through the other stuff that I have to go back and change....

Being the ******* that I am - when I took out the EGR plate - I broke the little metal exhaust line from the intake manifold to the choke - so right now I have to pull the air filter and manually drop the choke once the truck is at normal operating temperature. Also when I thought that the problem was the fuel selector valve - I bypassed it with a piece of fuel line - so I need to clean out the old lines (in case some dirt got in there while they were disconnected) and put them back on so I can use both my tanks again. Also after blowing the back off the muffler - I'll need to replace that so she purrs like a kitten istead of belching like a stockcar!!!

I'm still pretty sure my timing is slightly out - but my buddy Jim has the Golden Touch with the disributor so I'll wait and get him to do that..

Being pretty much a Chev guy for most of my life - I have to say this old 400 in this old truck sounds fantastic, and just smokes down the hiway now - thanks Henry for starting such a great company, I think I'm the newest convert to the family...

Cheers and safe travels to all..