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Old June 12th, 2013, 07:44 PM   #1
burnsie
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Default 99 Cherokee new motor backfiring HELP!

So here's the deal.

I bought a Titan 4.0 short block and put on a reman head with new lifters, push rods and rockers. I reused the distributor, tins, intake, exhaust manifold etc.

I put the motor in and after screwing around and making some adjustments and setting the timing correctly (I had it wrong and it would only crank doh!) I got it to start and run. I noticed that when I drove it that when I went to accelerate past 1/4 throttle it would backfire through the exhaust. Since initial start up I have replaced the CPS, starter, battery, tps and 02 sensor and no change, still backfiring past 1/4 throttle. I have also swapped out for comparison the cam position sensor, coil and PCM/ECU with spares I have on the shelf with no change.

I'm stumped! It starts and idles fine and even drives ok to 1/4 throttle but when you push down further it sounds like its reving but its not and its not going any faster then it starts popping back through the exhaust until you back off .

I'm at a total loss. HELP!!
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Old June 12th, 2013, 07:53 PM   #2
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Timing is obviously off. Pull it apart and try again.
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Old June 12th, 2013, 08:02 PM   #3
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Damn it! I had it at TDC on #1 when I set the distributor and thought for sure I had it right. Just wish I knew where I missed it... Any suggestions on setting the timing?

Thanks,
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Old June 12th, 2013, 08:36 PM   #4
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Try retarding the timing
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Old June 12th, 2013, 09:13 PM   #5
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It sounds like the dist is off, which fires the injectors, it does not affect ignition timing that is set by the crank sensor and doesnt move.
unhook the battery.
Put it at tdc on #1.
Drop the dist in so that the rotor points exactly 3 centimeters clockwise from the edge of the hole where the rubber grommet is and the ears stradle the bolt.
It should be about 5 oclock looking at it from the pass side I believe.
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Old June 12th, 2013, 09:15 PM   #6
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^^^^ this is asuming you used a stock cam and broke it in properly.
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