Engine will idle but backfires thru the exhaust and air box

Just rebuilt the 4.0 put it in and started it up. let it idle to fill the rad. and when i tried to bring up RPM's it would bust out like intake AND exhaust valves were open. good compression on all cylinders replaced almost everything except flywheel and computer.......heeeeelp

3 more comments
Anonymous Feb 09, 2009

the timing order is correct but the #1 is the 2nd one from lower screw acording to my book. cap& rotor are good. it runs fine at idle just backfires at acceleration ,
Anonymous Feb 09, 2009

it idles fine just starts busting out at 1200+ RPM firing order is OK #1 is 2nd from lower screw according to my book(clockwise) cap&rotor are good
Anonymous Feb 09, 2009

thanx, T-god will try that.............pc302001 , you cant adjust the timing it is set by the PCM
Anonymous Feb 10, 2009

1st.... thanx to every1 for the help, put scanner on jeep and it said the sync was off, turned distributor cam gear one tooth clockwise and solved the problem.....thanx again
Barry N Melissa Spring May 11, 2010

Correct timing order? Correct timing order?

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Barry N Melissa Spring

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Posted on Feb 09, 2009

Barry N Melissa Spring

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How about adjusting the timing.

Barry N Melissa Spring Feb 09, 2009

Was dealing with my problem when I came across yours. Wasn't thinking fully about PCMs. Hope "GURU" solved it for ya. Please post if that helped. I'd like to know. Good Luck!
Barry N Melissa Spring Feb 11, 2009

Outstanding! Outstanding!

Anonymous

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Posted on Feb 09, 2009

Anonymous

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Are you certain that you have the ignition wires hooked up to the correct cylinders(153624 from front of engine back, #1 on cap 1st post past the lower cap screw, clockwise) That's the only thing I can think of that will give you misfire in both intake & exhaust. Cap & rotor are new?

Anonymous Feb 09, 2009

OOPS... That's what happens when I attempt thinking before 1st cup of coffee!!! Second tower cw from screw on right side.Lets boil it down... If valves were open at wrong time, cam would need to be out or phase.(possible) If valves were open because they were not closing, lifters would need to be "pumped up" too much and acting like solids. Or, too much material had been milled from head. Since they are hydraulic, that is so unlikely as to be a non issue. Unless oil pressure is something like 100!! Either way, a valve sealing problem would give you a rough idle and if checked with vacuum gauge, a rapidly fluctuating reading.It's nearly impossible to put the injector harness on wrong (you'd really have to work at that) You can't do anything to the crank or pistons to cause this.
The distributor (and cap/wires etc) are only going to do what the cam is telling them to do. if the cam is incorrectly installed, spark will happen in relation to that position. OK, I've mentioned cam position twice. I have seen an incorrectly installed cam give fairly normal idle, incredible low end torque and major misfire on acceleration. ( a long time ago... If I remember correctly it was in one tooth retarded) I'm not sure you can accurately check this without real teardown. Possibly with dial indicator on rockers and piston (carefully through plug hole) you may be able to check it.But backside of lobe ramps is pretty wide and may cause innacuracy unless centerline is established. Therefore, if after a careful check of everything outside, you come up empty, remove the timing cover and check that cam is in correctly.

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Fans not turning on and replaced the coolant temp sensor? Coolant in reserve but not in radiator?

why do you have ? on facts? odd that.
my guess replaced ECT ! not ?
my guess, doing so , now engine is full of air, and not fails.
as all do.
front RAD cooling FANS, right? (not heater blower )
it don't work like you think, ? huh?
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means you trust the silly side tank and not look in rad? fail you will.
when doing cooling service, learn read a book first.
read how to fill and burp your engine, Just like feeding a baby it is.
is engine overheating?
did it , has it, or ? , what started this saga, tell a full story?
and WIN !
Facts: on this system.
the fans are controlled by the computer brain, under a complex set rules now. it's not some mindless switch like days of old.
sorry!
ill now answer for USA 03, how ours work,
ONLY!
ours has one fan., (not fans)
ours has a 3 speed fan (at rad back side.)
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DO NOT!
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do tell?

temp gauge lies its buns off... use a real tool called a thermometer to see real temps. we use a IR pyro gun to see it and not GET burnt.

gauges is telling truth, so......................

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Green on the ground,? for passengers feet.
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Motor pinging and loss of power. (do not allow pinging, it will wreck the engine)
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Does it only over heat while moving ? ( a bad pump, or Rad)
Overheats, only on hills? (bad RAD)
Only overheats pulling heavy loads ? (inside, full of bricks, or pulling a 1000 trailer ? ONLY?
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RTM read the manual the FSM>
there is more im sure, cant think of them all now.

That pyro gun allows me to test any RAD easy , ask.
ok , i check all rad tube top and bottom and bingo find any tube clogged fast. if all are equally clogged.(partial) i cant find that.
that is caused by zero service, so...and there are signs for that too.

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Terrific question!
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