400 ignition issues
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Senior User
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From: Elk Creek Virginia
400 ignition issues
My 77 highboy dually is just about road ready. I was doing some carb tuning and had her running for about 5 minutes got it just about right so I took it up the road just for the hell of it. I was pulling in the driveway and it was like I cut it off. Got it to start back by holding it to the floor but as soon as I got pulled in it died again. This has happened every time I take it out. I've had the ignition module checked about 4 months ago, rebuilt the carb and put a new fuel pump on. New coil, cap and button, and fuel filter. The engine is a 400 built with flat tops and 2v heads, 524 lift 290 duration cam topped off with a 600 holley. The truck is an early 77 f250. I dont think the engine even has 20 miles on it. Oh and its the np435 4 speed. Any help would be great.
MSEE
Joined: Apr 2004
Posts: 10,386
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From: Austin, TX
Can you please describe in more detail what specifically you're doing to get it started again? It's misleading to immediately call it an ignition issue, especially since the pedal appears to be at play.
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From: Elk Creek Virginia
I've got to let it sit a minute then I pump it a couple of times crank it then floor it and she comes to life. But when it dies I can be on the pedal or not its like you cut it off and pulled the key out. Thats why I'm assuming its in the ignition. Last time I was holding it at about 2500rpm and she died with no warning. I don't know if flooring it helps or if its where I'm used to working with junk but I guess its instinct?
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From: Elk Creek Virginia
Is there anything else it could be? Is there anything in the wiring harness that could be the cause? I'm at a loss. I really want to get her on the road before I go to Panama for work. It will drive me crazy if I don't.
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From: Elk Creek Virginia
Doesn't seem too. Just tried it I let it run for about 10 mins in the drive way and she died. Pumped it but did not touch the gas. Still cranked for about 4 seconds and started but died about 10 seconds after.
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MSEE
Joined: Apr 2004
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From: Austin, TX
I'm not trying to sling you out, but we're 8 posts in and I still don't understand what you're saying. What are you pumping if you're not touching the gas pedal?
I'm going to move forward assuming that the position of the gas pedal has nothing to do with ease of starting. For future reference, you'll get better help if you don't add details until you've verified they're actually related. Otherwise folks get hung up on details that are ultimately just a red herring.
The next time it's stalled, check for spark. Report your results.
Also for future reference, 8 PSI is probably a little on the high side, but that's not likely the cause here.
I'm going to move forward assuming that the position of the gas pedal has nothing to do with ease of starting. For future reference, you'll get better help if you don't add details until you've verified they're actually related. Otherwise folks get hung up on details that are ultimately just a red herring.
The next time it's stalled, check for spark. Report your results.
Also for future reference, 8 PSI is probably a little on the high side, but that's not likely the cause here.
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From: Elk Creek Virginia
Pumped the gas twice then I took my foot off the pedal. Cranked it till it started. Let it Run without touching the gas. It died so I pulled a plug out laid it on the intake and had a friend crank it. Its getting spark and its getting fuel.
Postmaster
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On the fuel pressure.. is it 8 psi when running OK or 8 psi when it dies? If you are measuring continuously and can watch it as it dies holding 8 psi that's one thing. If it was 8 psi when running right but not measured when it dies that's another.
Reason I ask is it sounds a lot like a problem I had. Drive a little bit and it stalls. Will re-start after a few minutes and stalls again. In my case it was old collapsing rubber fuel lines. They got soft and sucked shut when wet. A few feet of rubber hose, some hose clamps, an hour or two and it was fixed.
Reason I ask is it sounds a lot like a problem I had. Drive a little bit and it stalls. Will re-start after a few minutes and stalls again. In my case it was old collapsing rubber fuel lines. They got soft and sucked shut when wet. A few feet of rubber hose, some hose clamps, an hour or two and it was fixed.
MSEE
Joined: Apr 2004
Posts: 10,386
Likes: 35
From: Austin, TX
It's strange that it would have spark, yet cuts out like the key was cut. How is the float level in the carb? Does this one have a sight plug? I'm assuming you're starting cold; is the choke closing properly?
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From: Elk Creek Virginia
Manual choke, I set the floats properly. Once when died I pulled the sight screws and rocked the truck a little. Gas came out the sights on both bowls. Did that after I put the new fuel pump on. I've been working on it all day so no it was not cold I didn't pull the choke to start it.
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From: Elk Creek Virginia
Idling it stays at 8psi. When it dies it starts to bleed off pressure but keeps it till the last rotation. Its all new metal line from the tank to the pump. A short piece of new rubber line to another metal line that goes by the block and head behind the PS pump then rubber,filter,rubber, carb
MSEE
Joined: Apr 2004
Posts: 10,386
Likes: 35
From: Austin, TX
Sounds like you're on top of things. Do you consistently have spark every time it fails? Maybe the time you saw spark, it would have started anyway. You want to catch it when it's dead as a doornail for a little while.
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From: Elk Creek Virginia
OK today I went to start the truck to load her on a trailer to get exhaust. she was real hard about starting. Cranked longer then normal and when it did start it was cutting out and would not idile at all and seemed like it was not getting good fire. But when it died I checked it and I'm still getting spark. In the back of my mind I keep think its either the ignition module going bad or its something in the distributor. How far am I off? What should I check next? I've got a couple of day before I can pick it up. Any help would be great? Thanks for the help and suggestions so far.