swapped engine now backfires/sputters above 1500rpm
#1
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Year: 2004
Model: Grand Cherokee
Engine: 4.0
swapped engine now backfires/sputters above 1500rpm
Here is the story; I bought a 1997 xj with a "blown head gasket", well it turned out to have cracks in the head and one of the pistons had a fragment leave itself in the cylinder wall. So I went to craigslist and found a 91 HO 4.0 that "ran good". I install it and hook everything back up and it starts up; idles a little rough then I go to give it gas and it pops and backfires out the intake. it will not rev past 1200 rpm or so.
I have checked; distributor position is correct; I rotated the engine clockwise until compression was felt and stopped then found TDC then used that as indexing the #1 cylinder. I then confirmed with a timing light that my timing is about 10 degrees BTDC. it jumps around a bit but it is ball park.
Fuel pressure is good and stable at 49 psi or so.
The catalytic converter is not clogged; I hooked up a pressure gauge to where the O2 sensor was and it never got above 1 psi as much as I could rev it.
I even swapped out the entire throttle body assembly with another xj's and it did the same thing!
weird observation; just now in the dark I noticed that the exhaust manifold was starting to glow when I let it idle!
I am thinking that it is either; 1) the timing has jumped or 2) crank position sensor?
Help!
I have checked; distributor position is correct; I rotated the engine clockwise until compression was felt and stopped then found TDC then used that as indexing the #1 cylinder. I then confirmed with a timing light that my timing is about 10 degrees BTDC. it jumps around a bit but it is ball park.
Fuel pressure is good and stable at 49 psi or so.
The catalytic converter is not clogged; I hooked up a pressure gauge to where the O2 sensor was and it never got above 1 psi as much as I could rev it.
I even swapped out the entire throttle body assembly with another xj's and it did the same thing!
weird observation; just now in the dark I noticed that the exhaust manifold was starting to glow when I let it idle!
I am thinking that it is either; 1) the timing has jumped or 2) crank position sensor?
Help!
#2
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Year: 1999
Model: Cherokee(XJ)
Engine: 4.0
Personally I swapped in an engine and had the same running issues. Even though your gut says the timing is right I would still try a tooth forward and a tooth back and see if it helps at all.
#3
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Year: 2004
Model: Grand Cherokee
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So I pulled the valve cover off to check the valve timing and everything looked good; the exhaust valve opens near BDC and the intake valve opens just past TDC. After some jeep meditation I am thinking that since I reused the distributor that maybe it was damaged in the overheating and that timing wheel has moved? I think this is my problem.
#4
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Year: 2004
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ok, so I am mature enough to admit when I made a mistake. I installed the distributor incorrectly. Once I installed the pin to hold down the rotor plate and re-installed it, it runs great. A few teeth go a long way on the distributor!
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Year: 1999
Model: Cherokee(XJ)
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Originally Posted by mobile-command-unit
ok, so I am mature enough to admit when I made a mistake. I installed the distributor incorrectly. Once I installed the pin to hold down the rotor plate and re-installed it, it runs great. A few teeth go a long way on the distributor!
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