another timing or missmatch problem jeep tj

Joshua Faas

New member
helping a friend with what should have been a straight forward motor swap.....ya right.

so here I what we got....
A 2000 jeep tj sport with an automatic trans ....motor threw a rod out the side.
bought a 2004 grand Cherokee motor with low miles.
striped and swaped the pullys and alternator...
had to wap a few sensors on the throttle body...

the result is backfiring through the intake...
swapped the cam senor got us no better...

any hints on things missed?
was told to swap intake and exaust but I don't know what difference that would make if any.
 

Hey Joshua ! My first thought is to double check the oil pump drive for correct installation since it is crucial for the cam position sensor to signal the PCM the correct timing . After you've seen this for yourself , you no doubt know how important this is . If you have any questions regarding proper installation , there is good reference on line . Basically , your just looking for a similar alignment as you would a distributor but instead of a rotor that must align , it is the tab on the shaft that must be centered through the open window . There actually is an aligning tool for this which resembles a cam position sensor to hold the tab and shaft in the correct position for installation but not totally necessary since you already know what your looking for and will be able to see the difference between one tooth off either direction . The actual position of the sensor and what direction it faces is only of importance as far as wiring harness install but the tab and shaft must be in correct alignment or timing is affected. I believe this may be the issue. You already know there is no "dwell " adjustment as you know from the 4.0 liter distributor as we would expect from a conventional distributor . As long as the engine is set on top dead center , theoretically , there shouldn't be an issue of stabbing the oil pump drive and finding the correct pump shaft tab alignment for the cam position sensor. I did say theoretically . Your already well versed with the reality of that . But I believe this could be the issue and a good place to start. Sorry for a late reply and hope this is the fix and all to be well.
I know the feeling of helping a friend. I just recently completed an engine install into a ford windstar . Although we successfully planted the transverse engine/trans/subframe through the bottom and went well , I'll take a normal through the top motor swap over a bottom install any day ! Besides , I'm supposed to be working on jeeps , not mini vans !
 
helping a friend with what should have been a straight forward motor swap.....ya right.

so here I what we got....
A 2000 jeep tj sport with an automatic trans ....motor threw a rod out the side.
bought a 2004 grand Cherokee motor with low miles.
striped and swaped the pullys and alternator...
had to wap a few sensors on the throttle body...

the result is backfiring through the intake...
swapped the cam senor got us no better...

any hints on things missed?
was told to swap intake and exaust but I don't know what difference that would make if any.

As an after thought , make certain no vacuum lines were missed and wondering if you feel that there is any slight change in rpm if the TPS is moved in any direction . They do have a little tolerance . Voltage slightly varies and could matter to the PCM but that shouldn't produce the back fire your experiencing . Couldn't hurt to double check firing order too but mixing up ignition wires on an in line engine with the coils close to the plugs makes it easy . Just some thoughts from my own experience since these things do happen when there's a lot going on at the same time.
 
I would have kept all accessories, sensors and PCM from the donor vehicle. 99-00 is different from 01-03 and 04-06 and WJ to TJ
The 04 does have a nicer intake and exhaust manifold than the 00


I'd guess your ODPA was shifted while pulling or installing the engine.

Also check your plugs and gapping.
 
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The 2000 tj has coil packs so crossed plug wires can't happen. I however suspect things were swapped be for he got the jeep because it has 3 o2 senses and only 1 plug to plug them in. All plugs are new and gaped corectlly ...

I have seen a few people claim the tj OPDA won't work in the wj block however I see no visible difference. ....also was told the flex plate won't work and same thing there....they look exactly the same....I get the same part number if I look them up so not sure.

Also as an afterthought...tthe original cam sensor was left in place and untouched. The motor never actually fired up yet.....just want to be clear on that part. Feels like it wants to then pops out the intake
 
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Agreed , secondary ignition pretty much fool proof. The coil arrangement makes it easy. Yes , something IS wrong if the wiring harness only has ONE harness plug for an O2 sensor . A 2000 is an OBD 2 model year and will have at least TWO O2 sensors I believe the distributor disappeared in model year 2000 and on so WJ's running from '99-'04 would have seen a production change but if the shaft in fact engages with the oil pump and gear engages with cam and drive body sits in block right , why would there be a problem . Agreed. I couldn't answer the question of any difference with the flex plate if crank sensor could be having issues but it's a good thing you've got parts numbers to research . Although this sounds like an ignition timing issue , you'll want to be sure valve timing is correct is correct just to rule that out in the diagnostics. Yes , the engine has low milage and a bad timing chain is unlikely but I realize you've got to start somewhere . From your personal experience , I know your aware a flywheel can only line up and mount one way which is of course the case for a flex plate since the crank hub can accept auto or manual trans so since the flex plate should be correct , it may have to be confirmed that the cam AND crank sensors are in time . This usually is done with an occiloscope but thats with a running engine so this is tougher. I can only think that a computer safe test light probed to the signal wire of each ( cam and crank ) sensor when engine reaches TDC #1 be applied to show if ignition timing is on. While your at it , it would be a good time to confirm that the valves are closed at TDC #1 also to rule out valve timing issues. The O2 sensor issue has me curious so I must first ask before any further diagnosing that the jeep has the correct PCM and no swapped engine wiring harness ? I sincerely doubt an OBD 1 PCM is installed but I believe up to '95 they all had ONE O2 sensor. My'92 does. Dosen't sound right . Does the PCM have three harness connectors ? Something's not right . Sounding like your first feelings of mismatched parts are right.
 
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I have re-indexed the sensor several times with the same result....I still cant help but wonder about the wiring harness missing plugs to plug in the 2 o2 sensors in the exhaust manifolds. the tj has 2 upstream and one downstream....however there is no catalectic converter between them....so that has me confused as well....this leads me to believe there was some swaping that happened before he bought it. unless im missing something....going to swap the flexplate just to eliminate that as a possibility
 
The 2000 should have a three cat system.
53461__ra_p-1.jpg
Again without the 02's plugged in it should still start. All 4.0L have a casting number casted into them on the drivers side near the motor mount bracket. XJ engine blocks also have a build date number identifying when the bare block was built into an engine.
Block Casting Numbers
Year............Casting No
1987-90......53005535 (8933002665)
1991-95......53008405
1996-98......53020569
1999-04......53010449
Stamped on the block about halfway up above the starter should be the vin # of the Jeep the engine came from.

As for the PCM. It needs to be programmed for the engine and transmission you are using. And if you have the security SKIM options.

CKP new?
TPS clean and plugged in?
Dirty injector dumping fuel in?
 
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well that's not whats under there. has 1 o2 sensor just before the flange and that's it....

just pulled motor back out and the part numbers are the same on the flexplates so that's not it....didn't think it was but now I know...

killed a starter from it trying to kick backwards while turning over.....it actually started for a moment this time before it backfired and quit. its almost as if its firing way advanced on 1 or more cylinders....and the others seem fine....however with a coil pack I cant just pull 1 plug wire at a time to find the culprit
 

Since this is sounding to be a toss up between ignition timing and possible valve timing , so more checks toward process of elimination may be needed. Realizing the engine is of low milage but not starting and backfiring , I suggest a compression test to verify that all cylinders are good compression and close in average and that a valve isn't hanging up either. JPNinPA has posted in previous diagnostics on other threads ( his last post on this thread too ) to check for stuck injectors that would load the cylinder(s) up with raw fuel and cause this back fire condition. That would be a good check as well by looking for a wet plug more so than any others . Since the engine haven't started yet , they all could experience this condition but an obvious flooded cylinder will be more apparent . Still pondering a jumped timing chain as a precaution which valve timing may need to be checked to eliminate a possibility . Sorry for the extra work to verify the correct flex plate but glad it isn't an issue. Hoping the cam and crank sensors aren't an issue as well or PCM which are probably not likely since the engine almost starts and runs. The fact that a back fire stalls it seems key and seems to remain the focus. It seems to be a toss up between ignition timing and valve timing. I see your point on isolating spark cables . It still remains to verify if any coils may be bad. Had that happen on a Buick 3800 V6 that caused a no start . Agree with JPNinPA to wait on the exhaust for time being and O2 sensors . Engine should start but run poor if no other issues exist. It didn't run before so there is an issue before the exhaust was installed . If cam sensor is in time and crank sensor is good and PCM as well , the focus is why the back firing . Vacuum leaks should not be overlooked whether be a line or intake .
 
In light of you guys just braving through the trans drop for the flex plate inspection , not wishing to make any more work for you. I don't know if you can count on trying to find TDC with just a zero mark if the harmonic balancer may have walked due to worn rubber between balancer and hub and valve rockers . That is only close but no cigar . You would need to know of the actual timing marks on the cam and crank sprockets on the timing chain are on mark. If you've exhausted all else , this would be one confirmation. Curious about compression and possible valve not closing .
 
I was also worried about exhaust not opening so i pulled valve cover and cranked over by hand. All valves seem to open and close however 3 and 4 exhaust valves seem to move less than the rest. Will check the vacume leak option next just to be sure
 

I was also worried about exhaust not opening so i pulled valve cover and cranked over by hand. All valves seem to open and close however 3 and 4 exhaust valves seem to move less than the rest. Will check the vacume leak option next just to be sure
Quick test that may tell you if you have a stuck injector. While cranking the engine hold the gas to the floor (WOT) and see if it doesn't start after a 5-10 sec crank. It work great on another vehicle of mine with a stuck injector. The WOT condition at the TPS caused the PCM to shut off the fuel pump allowing the gas to clear the cylinder and eventually start the vehicle.

You need to do the compression test.
 
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X2 on JPNinPA's post . Hoping you don't have seized valve guides or collapsed lifters . If so , you'll be pulling the cylinder head :redface: .
 
Changed iac for known good one and swaped all injectors for good measure. Still a no go....same thing. Do a compression tomorrow. Witch sensor would cause an early spark....crank or cam?
 

It would be more likely a cam sensor improperly aligned could cause a condition your speaking of since its job is to tell the PCM when the engine is on TDC #1 post on. The crank sensor will provide position for each cylinder vis the flex plate or flywheel position to provide the sequential fuel injection firing and the ignition timing firing order as well. Although you feel that spark is occurring early and both sensors alignment are essential it is still equally important to know that the valve timing is correct . Realizing that your trying to avoid excess disassembly but it may become necessary to confirm timing gears and chain still in alignment. The other thing on my mind is to confirm if the is no issue with the harmonic balancer that it still displays the correct position . If the rubber dampening material has slipped and allowed the outer ring to spin out its true position and fool us to believe that the zero TDC mark is still true of it isn't and the crankshaft is off some degrees that will create havoc with valve timing , cam and crank sensor alignment too. I know it wouldn't seem likely for a low milage engine to have trouble with its timing chain or harmonic balancer but we still haven't found the cause of the no start and the back firing and I feel that these are items that must be confirmed if in good working order and correct alignment. Before we can suspect a sensor , we should be sure that the engine is sound mechanically . It is also the reason I suggested the compression test . I say we take our cue from that test which will show all is well or not . Yes , back fire is likely caused by ignition timing but since there is no distributor it falls on valve timing and cam and crank sensor timing so yes , I follow your questioning. I do agree that cut to chase may bring luck but it's just my personal way to be certain by eliminating posibilities by checking components . I'm sure you know that if a chain , cam and crank sprocket are in correct valve time and a harmonic balancer is pointing to TDC then a cam sensor can be installed correct as well as a crank sensor reading the flex plate in correct position should get an engine started provided all components such as ignition coils for example are good as well. It still has me thinking about your observation of the #3 & 4 exhaust valves not fulling opening. The compression test will reveal more . Don't want to give scenarios like collapsed lifters , worn cam lobes as those are extreme and still not proven in this case. Just giving direction to test for . No,start and back fire , that is the focus. It ran shortly , back fired and stalled . Almost sounds like bad coil(s) but I still like to be thorough and check mechanically as I did once on a Buick 3800 V6 of all the items I posted here. We swapped the coils and module on to,another car and it ran but not on the car with the problem. Yes , these things throw us but is still like to be through . It's helpful. Sorry I'm such a stickler.
 
I realize a jeep and a Buick are two different animals but the no start condition is , to me , identical . The Buick had an ignition module that worked directly with the coils . Your ignition module would be the PCM. One thing we suspected on this Buick was the engine wiring harness that linked the ignition module , crank and cam sensors and fed back to the PCM . Since this jeep is a work in progress , is there any reason to suspect any issues with its engine wiring harness ? It was for us. We swapped out the harness and got sensor signal but no start and we swapped coils and got it to start. Not saying you need coils but just a thought . So much to check , I know .
 
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The coil pack is new as of 2 months ago. Thoe im not sure what else could have gone wrong when the old motor gave up....we didnt swap the harness but thats something to check ....do that while doing compression check and timing light today....just confuses me that only 1 or 2 cylinders seem to fire when they shouldnt
 

The coils do fire on a waste spark system but that means the opposite pole will fire lower voltage on a cylinder that is on its exhaust stroke while the other pole will fire full voltage on the compression stroke. I think what is confusing is the possibility of the exhaust valves you spoke of not fully opening and the spent mixture not leaving the cylinders combustion chamber which may be the source of the back fire. Your compression test will tell much of the engines condition . This diagnostic step will lead you in the right direction on what to proceed on next. If you have a valve spring compression tool that can be attached with the rockers off to manually press the valve springs down to test travel , that may be helpful . It's still possible the lifters are not at at fault but forced to bleed down since the rockers may not be able to push the valve springs down if this is happening. But I agree the compression test be performed first.
 
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