engine sputter dies within a mile

[Pipehitter]

Per a previous post, I removed my thermostatic vacuum valve that had the EGR plumbed to it and one line from stock motorcraft carb. I then installed a BC Bronco heat shut off valve. I connected the EGR vacuum line and the carb line, started fine, idled fine, after about a mile it started to sputter and died. Very hard starting then. Left it sit for 10 minutes, started up and went another mile and died.

I then installed a "T" into existing vacuum lines off of another port, same result. I then capped both lines, very same result. Pulled fuel line off of carb, removed coil wire to check fuel, seems to work fine. This is a stock 302 with a stock rebuilt motorcraft carb. The thing is, I drove it over 150 miles the day before the change and it never skipped a beat. Any ideas other than going back to the thermostatic vacuum valve?

It almost feels like a fuel issue, but it has to be from the changes I just made. Any ideas are appreciated.

 

[6t6bronco]

Maybe water in our great E10 corn syrup they call fuel.

 

[Pipehitter]

I would believe that, except I am still running on the same tank of fuel when it ran great before the change. I have new fuel in both tanks, both tanks removed and cleaned prior to filling up, so has to be something different. Seems like a fuel problem, as when it stalls I have to pump the crap out of the pedal to get it to even fire while turning over.

 

[Pipehitter]

Bump.... anyone got some ideas or ran into something similar??

 

[brownb4]

vapor lock?

 

[Pipehitter]

Kind of thought about that, but the metal fuel line to the carb was cool to the touch when the symptoms occurred. I think what I am looking for is the operation of the EGR under load, seems like that is my culprit. Idles fine, under load it stalls out quick and very hard restart. Timing set to 10 deg BTDC

 

[Rustytruck]

to test unplug the vacuum from the egr valve and plug the vacuum line. this will keep the valve from opening. The engine should run fine. What I suspect is by removing the thermostatic valve the eger is opening when the motor is too cold or is opening at idle. eithor secenerio will cause the issue you are having. If your motor also has the dual port vacuum advance these changes could also effect that system from working properly depending on how the vacuum system is plumbed. All the years of Bronco's and wether they were 49 or 50 state truck are slightly plummed differently so you have to look at the system as a whole.

 

[Pipehitter]

Thanks - will give it a try. I am almost thinking of removing the two nuts and completely take off the EGR and put a plate over this opening and try it. I would then just cap the vacuum line that connect to the front drivers side lower part of the stock Motorcraft carb. Sure acts like a huge vacuum leak with the EGR issue, and probably why its so difficult to start when warm.

 

[Pipehitter]

well for anyone that may be following this, here is where I am at. Removed the EGR valve which was completely carboned up and closed. Blocked it off with a plate. Warmed up the engine, rechecked the timing and let it idle up to operating temp. Idle was fine. Ran it up and down the driveway only to run into the same symptoms. The minute it died, I check the acceleration pump, only one squirt of fuel on several pumps. Removed the fuel line to the carb, turned over several times before any fuel came out. Got it started and home, traced the fuel line from the fuel pump, only to find that the PO had a steel fuel line rubbing directly against a header pipe. My only conclusion is that the bronco is vapor locking from this condition. I did wrap the headers behind the location of the fuel line, which may be causing more heat in this area. To the auto store tomorrow to purchase fuel line and completely reroute the line and try it again. It ran fine before I wrapped the headers, which was the same time I made the other changes. Process of elimination I guess

 

[Pipehitter]

Well tonight I ran brand new fuel lines from my electric selector valve to the fuel pump. Ran the line outside the frame rail to keep it away from heat. Got it all clamped in place, started right up and idled fine. Left it idle for about 8 minutes, took it down the driveway and after about 300 yard it started to miss and it quit. Immediately pulled the fuel line to the pump and no fuel till after 3 seperate cranks of the engine. Sure seems like a fuel pump. From looking at another new selector valve, it should allow fuel from one tank or another, even if its now switching ok. I have fresh fuel in both tanks and a new filter. Not sure if a mechanical fuel pump can puke under load?? Maybe a bad diaphram in the pump?? Accelerates fine in nuetral when parked, but dies under load. Removed the gas caps and no sound of air coming in our out upon removal, and it has the stock fuel caps on the bronco and the vapor canister on the truck, all replumbed. Any one else got ideas??

 

[Pipehitter]

bumping up - thoughts

 

[dave67fd]

It maybe benificial for you to get a cheap in-line fuel pressure gauge or you could buy one of those inexpensive glass fuel filters or both. The pump could be at fault. If truck runs fine in-gear (idle) and dies with any amount of load i would suspect fuel delivery or even the carb. Double check carbs fuel float level as well as blockage at inlet
Could just be coincidence that the carb is at fault.
What carb are you running?

 

[Pipehitter]

I am running the stock 2 barrel Motorcraft carb. I just rebuilt it and it ran fine for around 100 miles or so, then this problem started to act up. Not sure how much fuel is used at idle for 5 minutes or so, maybe I am just using up what is in the bowl and once I start to drive I am starving it for fuel. Either pump or carb I guess. Due to the fact no fuel comes from the line attached to the pump when it dies for several cranks of the engine, leads me to believe the pump is bad. I guess a $15 mechanical pump is a cheap test. Issue starting to wear on my patience - but comes with the territory I guess.

 

[dave67fd]

You can purchase a cheap inline electric pump as well. Just make sure it's designed for stock 3-5psi pressures or you will need a regulator.

 

[asinor]

Sounds like a fuel filter or fuel pump issue.

 

[Ranchtruck]

Have you changed out the fuel filler caps? After it sputters out and stalls, hop out and open the fuel fillers. If you hear a hiss of air getting sucked in, you're pulling a partial vacuum on the tank and the fuel pump can't suck gas up to the engine.

 

[Pipehitter]

The rear cap is stock, and the front cap is a new cap from JBG. I removed both caps and ran it and it still stalled out within a few minutes Its amost starting to stall quicker as time goes on, supporting my theory that the diaphram in the fuel pump is shot. New fuel pump is going on the Bronco tonight. Will report back on any progress after the change.

 

[Pipehitter]

Well, time to put this post to bed. Finally got it fixed. After removing the thermostatic vacuum valve it started to miss and die. Seemed to run out of fuel. I removed the EGR completely due to the removal of the TVV, in hopes that was causing the issue. No luck. Changed out the fuel filters, tanks were all flushed at the end of the restoration, no luck. Found that the PO had a hard fuel line rubbing on the header pipe, thought I may have had vapor lockm so I ran all new fuel lines. No luck. Still lacked fuel. I changed the fuel pump in hopes that was it, no luck. Since I had a new coil on the work bench I changed that and the coil wire, no luck. So I removed the carb to see what was going on. After another thorough cleaning, keep in mind I just rebuilt the carb 50 miles ago, I found that the inlet screen to the main fuel inlet was completely clogged with crap. When I removed that jet and screen, the entire intake portion of the carb was clogged with crap. Not sure how this stuff made it by two fuel filters and clogged the carb, but it runs llike a million bucks. Well at least as good as a 302 can with 100k on the clock. Maiden voyage to work today, 70 miles round trip. Thanks for all the suggestions in the thread.

 

[NDFess]

Great job tracking it down! Cheers!