1995 wrangler backfiring at High RPM

[1995yjguy]

I have a 1995 yj with a 4.0 liter. It has some upgrades like the 62mm throttle body, banks cat back exhaust, cold air intake. It drives fine at normal speeds, but feels like a little hesitation is there, kinda like missing some power. NOW the real issue I have is that at High RPM shen I get on it, just about when it peaks out it will almost like missfire and backfire, then it will stumble for about 10 seconds popping and gurgling and then come right out of it! I did new fuel filter and no change, timing right on.

HELP, what is it

 

[HiHood]

Cam/valves

 

[1995yjguy]

what makes you say Cams or valves and what is the fix....New cam, or valve adjust? thanks

 

[SteelHeadz]

X2 on the cam or valves and or valve springs. Worn valve springs will make your valves float on high rpm's. Worn lobes on the cam shaft will cause the valve's to loose timing on the intake and exaust valve's opening and closing at high rpm's.

 

[HiHood]

X2 on the cam or valves and or valve springs. Worn valve springs will make your valves float on high rpm's. Worn lobes on the cam shaft will cause the valve's to loose timing on the intake and exaust valve's opening and closing at high rpm's.

:yeah-that:

 

[1995yjguy]

OK, In 10/2005 there was a brand new Cam kit, connecting rods, pushrods, a lifters put in the rebuilt motor. So there is less than 10000 miles on this. Would there be an issue with those items failing this quick, if so where should I start and what is the proper was to diagnosis the issue and start ruling out things. thanks

 

[HiHood]

I had a nonJeep vehicle that did that. Finally it lost power and I nursed and babied it home at top speed 30-40 MPH. When we pulled the heads and valves. The valves looked like rose buds just before they bloom. That's why I think it may be your valve train. And yes, my truck had less than 8 thou on a comp cam. We put in oversized valves, intake/exhaust switched to crane, and SUPERCHARGED the MOFO.

 

[1995yjguy]

great! So I should pull the head off and check all of that huh! Will I have to replace the cam or just the valves, lifters and springs? Thanks again

 

[SteelHeadz]

great! So I should pull the head off and check all of that huh! Will I have to replace the cam or just the valves, lifters and springs? Thanks again

Remove the valve covers then check the valve lash to the rockers first and see if that falls within specs. if any of them are border line max. then i would check the rest of the cam lobes on the compression stroke and see if the flat spots are evident. A bore scope would be most useful to see the conditions of the valves without removing the cylinder head.

 

[1995yjguy]

could it be the timing chain or tensioner. I have the valve cover off right now and am a little confused at what I'm seeing. Its supposed to have comp cam kit in it but the lifters and springs look stock. Also the lifters are tight and cant wiggle them at all. There are maybe 2-3 that I can wiggle a very little. all the push rods are tight and cant be spun . is this normal?

 

[SteelHeadz]

Yes it's normal to be able to spin the push rod so as long as its not on the compression stroke of the cam. Out of curiosity, have you checked the fuel pressure to see if its within specs?.

 

[1995yjguy]

I have not however, I do have a furl pressure gauge in it that seems to be working but I guess you never know. Should I check it from the fuel rail? Tank

 

[SteelHeadz]

Check it at the fuel rail.

 

[1995yjguy]

I took the timing chain cover off and put cylinder #1 at top of cylinder head. The chain marks on the small and big gear do not line up! Also how much slack should be in the chain. Is there a tensioner on my rig. Could this be my issue? Thanks again you've been a great help

 

[roadking951]

if your not over reving the engine then i would think it is a lean burn fuel problem, you did say only when you really hit it hard

 

[1995yjguy]

yes, it has hesitation under acceleration. It comes out of it sometimes ith all its power, then goes back into hesitation. I can put the pedal to the floor board and it doesnt go, then shift or let of the gas pedal and power will come back. If i hit high RPM it will cut out and back fire! WTF

 

[SteelHeadz]

I took the timing chain cover off and put cylinder #1 at top of cylinder head. The chain marks on the small and big gear do not line up! Also how much slack should be in the chain. Is there a tensioner on my rig. Could this be my issue? Thanks again you've been a great help

There is no tensioner for the timing chain on a 4.0.

Also check the ignition wires on both ends for corrosion. I've seen this cause misfires on high RPM's but not at idle.

 

[1995yjguy]

has new accel plugs .035 gapped, wires, cap, rotor, fuel filter, timing chain, no rust at all or corrosion, new temp sensor. 62 mm hesco throttle body off and cleaned, LOST, LOST, LOST and frustrated! No Codes right now. there was map sensor and TPS codes but that was becuase the map sensor vaccum was unplugged!