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Discussion Starter #1
Hi everyone!

I have a 1985 F250 with a stock 460 carbureted V8 engine and C6 transmission. I went to start my truck today and had issues getting it to start and stay running. When it does start, it runs very rough at idle and when pressing the gas pedal (while the transmission is in park) it backfires and stalls. I let the engine fully warm and the choke gradually opened, but engine still ran poorly, no improvement. I've never had any issues with it running thus far, I drive it every day and never had issues.

It has a newer carburetor, a Holley 4160 600 cfm on a 1 inch phenolic spacer and an Edelbrock performer intake manifold which I installed about 2 years ago. My truck has 2 electric in tank fuel pumps which were also replaced 2 years ago.

Some steps I've done so far in diagnosing: I first thought maybe the carburetor has an issue. I have a good Holley 4160 carb from another vehicle I swapped over and the problem did not go away, still ran poorly and backfired and stalled. I changed the fuel filter with a clear plastic WIX filter but it did not help any. However, I noticed that while it runs, the fuel filter is only about half way full of fuel while the engine is running. Is this normal? When the engine is running, shouldn't the filter be full of fuel?

I also checked for compression and have 120 psi on all 8 cylinders. I measured the vacuum at idle and the gauge reads about 14 HG. When the engine was running well before, the vacuum reading was 20.

So far I'm stuck. It seems like the engine is starved of fuel. Not sure if this is a fuel pump problem. If I switch from the front tank to the rear, it runs the same.
 

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Sounds more like an ignition issue.

Check wires and plugs at night to see voltage leakage.

Distributor pick up or advance mechanism frozen.




SJ
 

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Sounds more like an ignition issue.

Check wires and plugs at night to see voltage leakage.

Distributor pick up or advance mechanism frozen.

Failing ignition coil




SJ
 

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Like above, most likely problem is ignition. I had same issues last summer on my Lincoln. Turned out it were fried ignition points. Probably different ignition system but same symptoms.
 

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Hi everyone!

I have a 1985 F250 with a stock 460 carbureted V8 engine and C6 transmission. I went to start my truck today and had issues getting it to start and stay running. When it does start, it runs very rough at idle and when pressing the gas pedal (while the transmission is in park) it backfires and stalls. I let the engine fully warm and the choke gradually opened, but engine still ran poorly, no improvement. I've never had any issues with it running thus far, I drive it every day and never had issues.

It has a newer carburetor, a Holley 4160 600 cfm on a 1 inch phenolic spacer and an Edelbrock performer intake manifold which I installed about 2 years ago. My truck has 2 electric in tank fuel pumps which were also replaced 2 years ago.

Some steps I've done so far in diagnosing: I first thought maybe the carburetor has an issue. I have a good Holley 4160 carb from another vehicle I swapped over and the problem did not go away, still ran poorly and backfired and stalled. I changed the fuel filter with a clear plastic WIX filter but it did not help any. However, I noticed that while it runs, the fuel filter is only about half way full of fuel while the engine is running. Is this normal? When the engine is running, shouldn't the filter be full of fuel?

I also checked for compression and have 120 psi on all 8 cylinders. I measured the vacuum at idle and the gauge reads about 14 HG. When the engine was running well before, the vacuum reading was 20.

So far I'm stuck. It seems like the engine is starved of fuel. Not sure if this is a fuel pump problem. If I switch from the front tank to the rear, it runs the same.
I couldn't tell from your description if the "backfire" meant popping through the exhaust or through the carburetor. Though the mechanism is different, it still makes me think about an ignition shortfall.

Intuitively it seems like the fuel filter should be full; however I have seen engines run well when the filter wasn't full. You could check the PSI & flow rate of the fuel pumps, but it is unlikely that both would fail simultaneously.

I'd probably start by looking closely at the ignition system. And don't forget the infamous control module. Usually they prevent starting completely, but I wouldn't discount anything at this point.

Everything should be considered a suspect until proper component performance is confirmed.
 

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Discussion Starter #8
Either roll pin on distributor gear or timing chain.Try advancing timing and see what happens.
Bingo, it was the roll pin. I was poking around again trying to figure out the problem this weekend. I measured fuel pressure at the inlet of the carb was 4 psi. I was able to start the truck with it running poorly and advanced the timing and it ran much better. Then I opened the throttle, it backfired again and stalled and I was unable to get the truck to start again. Then I took off the distributor cap to check the timing, and after rotating the crankshaft I noticed the distributor rotor wasn't spinning when spinning the engine. Sometimes it would spin and sometimes it would not. I removed the distributor and saw that the roll pin was broken in two, so while the oil pump shaft was spinning sometimes the two broken pieces of the roll pin would touch and spin the rotor, sometimes not. I replaced the roll pin, rotated the engine to TDC compression and the timing mark was aligned correctly. I reinstalled the distributor and the engine started up and ran fine with no more backfiring.

I haven't test driven it yet due to the cold weather here in Michigan, but will check it again to see if its fixed but so far so good though. I am not sure why this happened. The distributor was replaced some time ago with a Spectra brand from O'Reilly's so maybe the quality isn't as good as OEM, I am not sure.

Thank you all for your replies and kindness in helping me out. I really appreciate your time in responding to my post.
 

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Do you have the OEM distributor or an aftermarket replacement???



SJ
 

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Discussion Starter #10
Do you have the OEM distributor or an aftermarket replacement???


SJ
It is a replacement distributor from O'Reilly auto, a Spectra Premium. I guess like the saying goes, they don't make them like they used to. The quality of the roll pin must not be very high.
 

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It is a replacement distributor from O'Reilly auto, a Spectra Premium. I guess like the saying goes, they don't make them like they used to. The quality of the roll pin must not be very high.
It is a spindly 3mm roll pin.

We upgrade all of our distributors to a hardened 1/8" spiral roll pin when we recurve them be they remans or our new ones.

The gear is supposed to be a press fit. In some cases the fit is loose and this happens. In that case we just double pin them.


SJ
 

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It is a spindly 3mm roll pin.

We upgrade all of our distributors to a hardened 1/8" spiral roll pin when we recurve them be they remans or our new ones.

The gear is supposed to be a press fit. In some cases the fit is loose and this happens. In that case we just double pin them.


SJ
^^^^^^^^^^^^^^^^^^^
Another solid reason why it is advantageous to deal with the vendors on this site as they know and practice procedures that the layman is not aware of until there is a failure, and the pocket pays more in the long run, not to mention the frustration and down time by trying to go it alone. You can not beat a man at his own game.;)
 

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Totally agree with replacing the roll pin with a spiral wound 1/8" spring pin. In my 40+ years of building all displacements of Ford engines, I've seen numerous sheared stock roll pins, especially with a performance build and a high pressure and/or high volume oil pump installed.

I suspect that the cold Michigan winter has thickened your oil to the point that the pin simply gave up. The aftermarket distributor may not have had an OEM quality pin as well.

When you said it happened overnight, I was pretty sure it was an ignition timing related issue. You're lucky the timing chain hadn't jumped a tooth!
 

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I have a similar problem. 85 F250 460 that backfires through the carb when I accelerate too fast. If I ease into the gas it's fine but it backfires when I step on it. Any ideas?
 
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