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could worn timing chain cause a misfire under load ?

R72K5

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anyone think or know if a timing chain can cause a complete total misfire under low forward acceleration ? total misfire where the rig actually bucks once ?

starting to wonder about this one out here.. i dont know what else could cause that to occur with a TBI engine, does it now and then, not every time though.



thanks for anything
 

velocitiii

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I agree. The higher the pressure the weaker the spark will be.
More throttle means more pressure.
Could be ignition.
 

jakeslim

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check all your distributor stuff...cap, wires, springs(distributor-may be a technical name but its not coming to me right now)
 

R72K5

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wires are two days old, cap also, no change in how often or how bad it bucks once now and then

thanks
 

djsblaze

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I feel your pain. Having a similar, if not the same problem. Fortunately, its now my mechanics problem. My guy thinks it is the "fluctuator" or something within the distributor that wont stay adjusted. I dunno, but it sure gets my attention when it cuts out on an on ramp. Good Luck. /forums/images/graemlins/dunno.gif
 

R72K5

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plug wires brand new, fuel filter is next ot change,

i noticed a bit ago that if you hold a piece of paper at the tailpipe just right it will suck it in real quick real fast and back out real fast again consistent with engine rpm and everytime you hear a pfft sound in the exhaust pipe it wont suck in the paper right then which messes up this consistent pattern of the paper being sucked in and out of the pipe

what you think ?
 

87GMC

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Mine has done the same thing since I bought it. I replaced the cap, rotor, wires, fuel filter, coil, plugs, and wires. Still does it. I gave up and put a lift and tires on it /forums/images/graemlins/thumb.gif
 

POWERMAD

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[ QUOTE ]
noticed a bit ago that if you hold a piece of paper at the tailpipe just right it will suck it in real quick real fast and back out real fast again consistent with engine rpm

[/ QUOTE ]
That's a pretty good indiacator of a burned or bent valve.
The only way to know for sure is to do cylinder pressure test.
A few outfits have the swanky gage set but I made my own.
I modified a compression tester hose and fitting, attached it to a regulator with a ball valve and pressuregage.
Roll the slug untill it is on BDC and both valves are closed.
Hook it up to shop air and open the regulator and start to build pressure. Usualy by 30 psi if that hole has a bad valve you will hear the air leaking out of the intake or exhaust.
A bad intake valve will backfire out of the carb.
Generaly valve train component problems don't come and go.
Usualy it starts out as "what the hell is that noise" and gets to the better not run it anymore real fast.
I would do more diagnosis on the ignition and emmission stuff first.
I would still do a cylinder test to rule that out. And it will let you know the condition of each hole
 

R72K5

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no it doesnt come back and go away, i meant it does it constantly but every few seconds or less it will be no pfft sound in the pipoe and it wont suck the paper up the pipe, i dont know how to explain it any better,

the engine is now starting to cough back up in the air cleaner, you can hear it poof/pop in there, when it does this the truck dives down in front/coughs/misses opnce real quick, it seems to be getting worse,
and the white cloud smoke isnt getting worse or better, same big cloud of white smoke at startup warm about 60 or 70% of the time

otherwise it runs fine and has power and all that

i think its time to sell the rig before it gets worse, he has already put 500 into the stupid thing within the last year that he has had it and he gave 1300 for it with rust and 170k on the clock, it didnt do all this when he got it but started developing these issues in the last few months.


going to do cylinder pressure test later today or in the AM, lookign for 150PSI and no more than 20% differnce form highest reading to lowest, correct ? im pretty sure thats right


thanks for anything further
 

avgas

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Actuall a streched timing chain CAN cause the exact symptoms he is desrcibing, especially with the number of miles he has. If a timing chain has been stretched it will operate ok at constant speeds but as soon as the engine speed changes their is a lag between the speed of the crank and that of the cam. Check all the other stuff everyone else is mentioning first, since most of them are more common problems.
 

POWERMAD

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With over 170K on it I would have to say that the chain is beyond service. Does it rap on the cover? sorta sounds like a rod knock.
With the cap off turn the crank untill the rotor starts to turn, then turn the crank in the opposite direction and watch how much the crank rotates before the rotor starts to turn. A few degrees is ok but more than that and you have a stretched chain. With that many miles on it and prolly being a nylon gear that may well be the source of the trouble.
A compression test and a pressure test are two different procedures.
A pressure test will tell you if it has a bad valve and if it doesn't then you build pressure to about 100psi and shut the ball valve and see how fast the pressure drops. Rapid drop in pressure with no bad valve is bad rings. Which after a few revolutions will prolly still build to 130psi or so with a compression test.
With either test be sure to remove all the plugs.
If there is a blown head gasget it will give faulty readings if the plugs are installed.
 

R72K5

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timing chain barely has any play/slop in it at all, looks like someone already has replaced it

hmmm

thanks
 

R72K5

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welp i found out the filter thats under the thing is about 6 months old, i put a new one on the other day and its been a perfect angle ever since, but still has the white clouds of smoke issue, but thats it, it must really have a tank or line issue with the filter having been clogged up already hmmm..


any comments or anything?

thanks
 
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