Missing on #5 cylinder
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Missing on #5 cylinder
I have a 1994 f-150 with 5.0 bored .040 over. small cam, diablo sport chip,
headers, I have around 6500 miles on the engine, i just changed tranny and torque converter (4r70w) its been running fine and all of a sudden it dropped
#5 cylinder. (not firing on it) so i have spark, i checked compression and it only
had 35lbs. then i waited a while and checked it again and have 125lbs.
i changed plug on #5 but still misses on #5, changed plug wire, no help,
changed injector, no help, pulled diablo chip off my computer still misses on #5
pulled codes and there is none, check engine lite does not come on. i have tryed everything i can think of. oh i pulled valve cover off checked pushrods and lifters ok, turned it over and watched the valves open and close, I am getting pissed and cant figure out what is the cause of this missing. cap,rotor, good msd.
anyone could help me out i would be thankfull, Im thinking the computer died but who knows.
thanks dave
headers, I have around 6500 miles on the engine, i just changed tranny and torque converter (4r70w) its been running fine and all of a sudden it dropped
#5 cylinder. (not firing on it) so i have spark, i checked compression and it only
had 35lbs. then i waited a while and checked it again and have 125lbs.
i changed plug on #5 but still misses on #5, changed plug wire, no help,
changed injector, no help, pulled diablo chip off my computer still misses on #5
pulled codes and there is none, check engine lite does not come on. i have tryed everything i can think of. oh i pulled valve cover off checked pushrods and lifters ok, turned it over and watched the valves open and close, I am getting pissed and cant figure out what is the cause of this missing. cap,rotor, good msd.
anyone could help me out i would be thankfull, Im thinking the computer died but who knows.
thanks dave
Elder User
Joined: Feb 2007
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From: Mulege south Baja ca. Mx.
do a leak down test. and check the other cylinders also. it must be the problam if you are getting 35 one time and only 125 the second. you should be seeing more like 160.
Last edited by Bruce R Leech; Apr 9, 2007 at 02:37 PM.
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i checked all 8 cyls they are all at 125-130 lbs thats all they have ever carried. i also did a leak down test on #5 let it sit for 45min still held 125 i havent got a noid tester to see if injector is getting a pulse or not.
Post Fiend
Joined: Mar 2002
Posts: 19,402
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From: Bonita Springs FL
125? Who built your engine? Is it forced induction?
An engine that has 35 lbs and then goes to 125 lbs the next test has serious internal issues, I think.
Edit: Oh yeah, it's not the computer.
An engine that has 35 lbs and then goes to 125 lbs the next test has serious internal issues, I think.
Edit: Oh yeah, it's not the computer.
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Joined: Feb 2007
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From: Mulege south Baja ca. Mx.
that would be my guess. but if I did that I would not post it here so it could be real. but the only thing I can think of that would allow that to happen would be some thing stuck in a valve the first time and freeing up the second. and that is not very likely
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no its not operator error it was hot when it only had 35lbs and when it cooled it went back to 125 what i want to know is why wont it fire on that cylinder? i think for some reason a lifter pumped up and held a valve open so no compression till it bleed down
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From: Mulege south Baja ca. Mx.
Originally Posted by dv_shane
no its not operator error it was hot when it only had 35lbs and when it cooled it went back to 125 what i want to know is why wont it fire on that cylinder? i think for some reason a lifter pumped up and held a valve open so no compression till it bleed down
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i did pull the valve cover and nothing wrong there i did loosen up the rockers for that cyl. but it still misses only on that one you can put your hand on the header tube for that cyl and its not even warm where the rest as you would think is hot how else can i tell if the injector is working and being pulsed or not it acts like there is no fuel into that cyl. but i tryed changing the injector did not help so i wonder if its being pulsed or not? i dont have a noid tester
Post Fiend
Joined: Nov 2001
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From: Topsfield, MA
125-135 is what I get on my worn out 190k mile 351....
You should have way more compression than that.
A broken/damaged ring could cause an intermittent compression figure like that.
Did you do a wet test? If not, check the compression dry, then put some oil in the cylinder and re-check it. If it improves, it indicates towards the direction of rings.
you said you did a leakdown test and it held 125 psi for 45 minutes...?
That doesn't make sense to me.
A leakdown test will give you %'s....and a cylinder will not hold compression for 45 minutes...5 seconds maybe. The gases seep right past the rings (they cannot hold compression over time).
It sounds to me like you need to talk to your engine builder. If your engine really has 125-135psi for compression on each cylinder...that is really bad for a new engine. Put it this way, a good used engine should have about 150.
Either your rings didn't break in right and mate to the cylinders, or your valves aren't sealing properly, or something of that nature. And if #5 is getting 35 psi at times, something is either wrong with the valvetrain or there is an internal problem.
You should have way more compression than that.
A broken/damaged ring could cause an intermittent compression figure like that.
Did you do a wet test? If not, check the compression dry, then put some oil in the cylinder and re-check it. If it improves, it indicates towards the direction of rings.
you said you did a leakdown test and it held 125 psi for 45 minutes...?
That doesn't make sense to me.
A leakdown test will give you %'s....and a cylinder will not hold compression for 45 minutes...5 seconds maybe. The gases seep right past the rings (they cannot hold compression over time).
It sounds to me like you need to talk to your engine builder. If your engine really has 125-135psi for compression on each cylinder...that is really bad for a new engine. Put it this way, a good used engine should have about 150.
Either your rings didn't break in right and mate to the cylinders, or your valves aren't sealing properly, or something of that nature. And if #5 is getting 35 psi at times, something is either wrong with the valvetrain or there is an internal problem.
Last edited by MustangGT221; Apr 10, 2007 at 12:18 PM.
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thats all the compression it has ever had it was setup to have a turbo added to it later on. i thought it was kinda low but thats what i was told it was a shop in portland ore. that built the engine.then it had a cracked head and i put e7te heads on it and they had all new valves but they had a bigger chamber so i lost a little there does this help to know thats why i only have 125 per cyl
i still think it had a lifter pump up or washed out the cylinder rings with gas and thats why i lost compression for a short time. and i still think the computer is not pulseing #5 i took a known good injector and installed it on #5 and still misses.
i still think it had a lifter pump up or washed out the cylinder rings with gas and thats why i lost compression for a short time. and i still think the computer is not pulseing #5 i took a known good injector and installed it on #5 and still misses.