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Cyclical misfire out of nowhere

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Old 07-27-2018, 07:41 AM
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I was going on that same assumption. And me capping everything but the PVC was me double checking that. If it fixed itself it would track down a leak.
Old 07-27-2018, 08:28 AM
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Prob wouldn't hurt to check that your PCV valve still closes during idle and opens towards WOT. Just unplug the rubber hose at the valve and plug the valve with your finger to feel the lack of air flow at idle and vice versa.

PCV valve stuck closed can be associated with oil leaks. I need to check mine...

Mods...I joke. I swear I have an increase in throttle after putting a summit racing sticker one time. May have peeled off.

Old 07-27-2018, 08:30 AM
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New PCV valve as of yesterday.
Old 07-27-2018, 10:34 AM
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The forward opening in an 22-RE series valve cover connects to a nipple on the air cleaner box. You have unmetered air entering the intake system thru the PCV lines. Also keep in mind leaks along the gasket surfaces for the top and bottom covers, IE leaking gasket flows unmetered air thru the pcv valve.

This isnt necessarily your primary issue, but it's an issue.

Fouling of the cap, rotor, sparkplug, or just a badly placed (loose, or leaking) high-tension cable. These will cause it to burble.
Old 07-27-2018, 10:52 AM
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Originally Posted by Co_94_PU
The forward opening in an 22-RE series valve cover connects to a nipple on the air cleaner box. You have unmetered air entering the intake system thru the PCV lines.
Pretty sure it connects to a nipple on the intake manifold. In the pictures he shared, he has that intake port blocked.
Old 07-27-2018, 10:57 AM
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Make sure all the ports on the ac/power steering idle up valve are blocked. If you’re not using it at all, you can remove the whole thing with a 10mm wrench/socket and plug the port.
Old 07-27-2018, 10:59 AM
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Originally Posted by RASALIBRE


Pretty sure it connects to a nipple on the intake manifold. In the pictures he shared, he has that intake port blocked.
Early 22re does not have a port on the intake tube
Old 07-27-2018, 11:13 AM
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Originally Posted by tgell001
Early 22re does not have a port on the intake tube
Never said it did.
That front pcv port connects directly to the intake manifold.
Old 07-27-2018, 11:17 AM
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Originally Posted by RASALIBRE

Never said it did.
That front pcv port connects directly to the intake manifold.
Yes, I just made that change trying to reduce the odds of vaccum leak thru the things that I just manipulated i e the valve cover. The problem was bad before that I did that as a fix. Or fact finding more so. What is on the other side of that hose on the manifold is it direct vacuum?.
Old 07-27-2018, 11:21 AM
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Originally Posted by tgell001
Early 22re does not have a port on the intake tube
Sorry, quoted the wrong person
Old 07-27-2018, 12:21 PM
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I have a development. So with the diagnostic port jumpered itll idle indefinitely. Still can't rev it much over 2k without the stumble. But it'll idle forever. As soon as I remove the jumper it'll stumble and die.

I put my vacuum gauge on it and it's pulling 20 lbs.

While I had a steady idle, I put a welding glove on and pulled the spark plugs 1 by 1 and all evenly made the engine almost cut off. So I have to believe they're all getting spark and fuel evenly... Or MOSTLY

More information, not closer to fixing the problem.
Old 07-27-2018, 07:57 PM
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Originally Posted by tgell001
I have a development. So with the diagnostic port jumpered itll idle indefinitely. Still can't rev it much over 2k without the stumble. But it'll idle forever. As soon as I remove the jumper it'll stumble and die.

I put my vacuum gauge on it and it's pulling 20 lbs.

While I had a steady idle, I put a welding glove on and pulled the spark plugs 1 by 1 and all evenly made the engine almost cut off. So I have to believe they're all getting spark and fuel evenly... Or MOSTLY

More information, not closer to fixing the problem.
hmmm, not sure what that would imply;
timing advanced too far, so with jumper in/timing retarded it idles better?
Have you checked timing?

Maybe you are having a random issue with your fuel set up and it is running lean, so with the timing jumpered/retarded it runs better.
Do you have a fuel pressure gauge?
Maybe you’ve fixed enough vacuum leaks that it’s now running rich?
Pull the efi fuse and disconnect the battery for a few minutes.

Or timing and fueling is fine and and there is still a vacuum leak evading you somewhere.
Have you checked the bottom most port on the ac/power steering idle up valve. There’s a 90* one underneath the bottom of it. This port circled in red is at the very bottom of the valve
I’m just spitballing simple quick cheap things to check out.
Old 07-28-2018, 04:51 AM
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No i really appreciate it, the reason i post in forums isnt because im looking for someone to tell me what to do but its like an idea factory.

​​​​​​Thats capped, I caught that a few days ago.
Fuel pressure holds 40 measured at the CSI.
I set base timing at 5* just to rule that out

I just have this feeling you're right about it being lean, that's what my feeling has been since the beginning but I can't figure out why. I'm leaning towards a computer in put is causing the lean condition but that just leads me down a terrible rabbit hole I wish I wasn't so familiar with.
Old 07-28-2018, 05:47 AM
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What year is the truck?
Old 07-28-2018, 05:49 AM
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Originally Posted by rasalibre
what year is the truck?
1986... Great year, truck and I were born the same year. I'm doing better at the moment
Old 07-28-2018, 05:51 AM
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Here’s voltage and resistance checks at the ecu from the 1986 fsm.
I use this for my 87. Should work for 85-87.
Old 07-28-2018, 05:53 AM
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what's the measuring plate? The AFM? Thanks btw

Last edited by tgell001; 07-28-2018 at 05:56 AM.
Old 07-28-2018, 06:02 AM
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It’s probably worth checking the resistance of the coolant temp switch and cold start timing switch too.
Heres the cold start time switch:
http://www.lcengineering.com/LCNewsl...tart_Tech.html
Here’s the ecu (thw) coolant temp sensor.

Old 07-28-2018, 06:03 AM
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Measuring plate is referring to the door in the afm.
Old 07-28-2018, 06:29 AM
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Also, the ac/power steering idle up screw, mine was leaking past that screw, so I just removed it and plugged it. Looks cleaner that way regardless. I found my plug on a truck with no ac/power steering from factory. The threads might be weird British pipe threads or Japanese imperial pipe threads or some such nonsense. Take the valve to the hardware store and check the brass fittings section.



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