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Old 09-01-2009, 08:47 AM   #1
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Default cold engine misfire- 4.0

I recently put a 99 XJ 4.0 motor in my 96 XJ, and it now has a cold engine misfire from about 2500-3000rpms. If i let it idle til its up to operating temp, or run it easy til its warm then its not noticable.

I am going to start by replacing the spark plugs first to see if one of them may be fouled, but I am wondering it it has something to do with the ECM and how it adjusts fueling for engine temperature conditions.
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Old 09-01-2009, 08:52 AM   #2
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Need more info.

What sensors did you use? Which PCM?
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Old 09-01-2009, 10:04 AM   #3
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everything is from the 96, basically just swapped the long block over.

i initially thought it might be the CPS acting up, but when I had that happen before the tach would drop out from no signal. now when it stutters going up the road is seems like maybe 1-2 cylinders not firing, and just losing power. you can also smell the raw fuel when it misfires.
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Old 09-02-2009, 08:15 PM   #4
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ok went to autozone, got the computer scanned.

codes came back for-
random cylinder misfire
cylinder misfire #1
cylinder misfire #3

so i bought spark plugs...installed them today, the old ones looked like crap, toasted, put the new ones in. went for a drive still misfiring. now when it misfires its popping, sputtering etc. its very random, i can drive 10 miles and it never does it, or i can go 10ft before it starts acting up. also its not just when its cold, it does it all the time. also it was missing real bad on the highway last night, the CEL starting flashing, and you could smell the raw fuel. i read that the flashing CEL means its missing, causing a rich condition and can damage the CAT. so im gonna ssume the injectors are good, and its something causing the ignition to not fire.

my guess is it has to be a sensor somewhere throwing something off.
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Old 09-02-2009, 08:19 PM   #5
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The other things it could be are the ckp,or dist and rotor. The cps can still be the cause. Do you have the tools to test these things like a dvom.
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Old 09-02-2009, 08:22 PM   #6
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Did you check cap and rotor? Or maybe a plug wire is shorted out?
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Old 09-02-2009, 08:28 PM   #7
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cap and rotor is new, wires dont look that old and seem to be in good shape (i bought it used 2 years ago)

this is starting to get annoying, its been a year since i was able to drive this thing daily without it breaking down.
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Old 09-02-2009, 08:44 PM   #8
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also what bugs me is that before the motor swap the only problem i had was the worn out distributor gear throwing the timing off, and it would not idle.

all i did was replace the long block, all wiring, sensors etc are the same, and i now have this misfire problem.

if it was the cps wouldnt it cut out completely and the tach drop to zero rather than just misfire on random cylinders?
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Old 09-02-2009, 08:46 PM   #9
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Ive heard that it doesnt cut out completely, but it will run like crap.. Iit might be worth a check. Theres a write up on how to check it around here somewhere... Or you could take it to a shop and have them check it for you..
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Old 09-02-2009, 09:06 PM   #10
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Quote:
Originally Posted by getblown5.9 View Post
also what bugs me is that before the motor swap the only problem i had was the worn out distributor gear throwing the timing off, and it would not idle.

all i did was replace the long block, all wiring, sensors etc are the same, and i now have this misfire problem.

if it was the cps wouldnt it cut out completely and the tach drop to zero rather than just misfire on random cylinders?
They can go out all at once or they can cause this kind of problem,if you have dvom,or multi meter you can check the resistance across terminals b and c,it should read low resistance or no resistance,open,but yours also has a cam position sensor that can cause the same issues.
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Old 09-03-2009, 06:51 AM   #11
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swapped the cam position sensor last night with an extra i had, no change.

i guess ill check the crank sensor tonight
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Old 09-03-2009, 07:39 AM   #12
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Before you start replacing more stuff......

Did you try indexing the distributor?
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Old 09-03-2009, 07:56 AM   #13
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link to procedure? i thought on these motors there was no adjustment on the distributor.

also this problem is not constant...its intermittent. going to work today, it misfired bad for about 2-3 minutes, then seemed to clear up.
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Old 09-03-2009, 07:57 AM   #14
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Also check the injectors with noid lights. You could have a bad connection at the injector.
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Old 09-03-2009, 08:06 AM   #15
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They are not adjustable, but if installed improperly the engine will run but very poorly.

Remove the #1 Spark Plug
Remove the Dist.Cap
Remove the distributor.
Bring the #1 piston up to Top Dead Center on the Compression Stroke. Stuff your finger in the spark plug hole while someone bumps the starter. When yo feel air blowing by your finger STOP.
Use a 19mm socket and turn the harmonic balancer bolt clockwise (only) while keeping an eye on the timing marks on the timing chain cover.
Once the #1 piston is at TDC, re-install the distributor so that the rotor is pointing at the 5 O'clock position when the distributor is fully seated.

A word of caution.
Make sure that you rotate the oilpump shaft with a long screwdiver so that it lines up properly with the distributor. Failure to do so will prevent the distributor from fully seating.

Reinstall the cap
Reinstall the sparkplug
Double check the plugwires to make sure you have the correct sequence.
Fire it up.
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