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timing issue after motor swap

billyjp2

billyjp2

NAXJA Forum User
Location
Indian Orchard MA
I recently swapped a 98 4.0L into a 2000 XJ. After doing some reading and researching I know I have the cam sensor installed properly in place of the distributor. When I went to start the engine it will crank but not start. It only backfires out of the intake. I know this points to clocking the cam sensor wrong but I've aligned it multiple times with the same result, even trying 180 degrees off to make sure I wasn't crazy. I also popped in a new cam sensor off a different jeep.

What else could my problem be? Any chance I'm missing a ground somewhere? I've checked fuel pressure and it's within spec.
 
Sounds like you have the distributor 180 out. Try again. Backfire is caused by timing, or a burnt valve, but since it hasn't started and the valve hasn't gotten hot, I still say it is timing.

Are you sure you didn't get the wrong year flexplate?
 
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I've brought the engine to TDC on compression stroke and aligned the cam sensor no less than 30 times over the past 2 weeks. I've also tried 180 degrees off just to make sure.

The flex plate is original to the 2000 Jeep and was swapped over to the new motor.
 
billyjp2 said:
I've brought the engine to TDC on compression stroke and aligned the cam sensor no less than 30 times over the past 2 weeks. I've also tried 180 degrees off just to make sure.

The flex plate is original to the 2000 Jeep and was swapped over to the new motor.
Click to expand...

After establishing compression stroke, did you align the timing slot on the crank damper with the zero (0) timing mark on the timing chain cover - then proceed with install and timing of the cam sensor? See pic.

DSCF2764.jpg
 
I've followed that to a T and it won't run. I can't even worry about step 10 yet.

I've been following almost those exact same guidelines from Mitchell ProDemand.
 
Long shot but verify #1 and #2 fuel injector connectors aren't mix up.

#1 driver wire is White/Dark Blue tracer and #2 driver wire is Tan.

~~~~~

How did you mount the coil rail to that '98 head - just curious.
 
Update here, I'm sure Billy can add more details if I miss any.

Compression test was performed, and Cylinder 6 had no compression. Thinking it was either an effed up valve or worse, a hole in the piston, we pulled the valve cover. No obvious issues, looked clean as hell. Digging deeper we pulled the head (I have a spare clearwater head that would fit the intake/exhaust direct anyway) and there's no obvious issues on the head, and there's no obvious issues in Cylinder 6. No scoring on the walls, no obvious piston failure at all.

Given the backfiring, and the compression result in Cyl 6, is there anything we're missing here in checking? We haven't put the new head on yet, but it certainly seems like we pulled it for no good reason to begin with. It's possibly still that we don't know what we're looking for in the head for problems.

Fuel injector connectors were fine, fwiw
 
Bumping this, because it still won't start. we've now replaced the head with the clearwater head that ran fine previously. Same backfiring out the intake. Haven't been able to check compression again but will.

Only piece of advice otherwise not followed up on is to replace the crank position sensor, but we ran into that being an issue because one of the bolts was broken on that. Bear in mind however that the jeep ran fine prior to the swap (outside the knocking of course)
 
Won't start, no engine codes? Did the engine you swapped in run before that you know of? I'm assuming it did but might as well ask I guess right =P
 
markjrs3 said:
Only piece of advice otherwise not followed up on is to replace the crank position sensor, but we ran into that being an issue because one of the bolts was broken on that. Bear in mind however that the jeep ran fine prior to the swap (outside the knocking of course)
Click to expand...

If you have spark, the crank sensor is generating signal. Maybe not the correct (accurate) signal but it is working
 
ehall said:
If you have spark, the crank sensor is generating signal. Maybe not the correct (accurate) signal but it is working
Click to expand...

Alright, thanks for that. It's our assumption it wasn't the issue because the jeep ran prior, but we're running out of things to check.
 
xCWolf said:
Won't start, no engine codes? Did the engine you swapped in run before that you know of? I'm assuming it did but might as well ask I guess right =P
Click to expand...

no codes, won't start. it supposedly ran fine, and we see no reason why that wouldn't be the case, especially after stripping the head and swapping that.
 
You said you brought it to TDC as you showed on the pix, but what stroke was it on? How did you determine the stroke?

I hate to keep harping on this, but it REALLY sounds like you are 180 out. I know you said you tested 180 out, but how did you do that? Did you pull the distributor and then stab it with the rotor rotated a half turn?
 
Put a socket on the harmonic balancer and spun the engine over with #1 spark plug pulled. When I felt air start blowing out I aligned the timing mark as specified. For my own sanity I've done it numerous times.
 
An engine needs spark, fuel, air

Do you have spark? Is it a nice bluish white spark or yellowish dirty spark? Do you have spark on all the cylinders? I've seen failures on new plug wires before...

Do you have fuel? Are you getting decent pressure at the test port? Are the injectors firing? You can pull the rail and lay it on newspaper or cardboard or something and watch the spray pattern. You can try spraying starter fluid into the throttle body too

Everybody overlooks air but its just as important. Try holding the gas pedal to the floor to eliminate the IAC. Try a vacuum test while cranking to see if you are getting reasonable levels in the manifold.

Could also check the CTS, IAC, MAP, and O2 sensors... if those are wrong the computer will get the AFR wrong
 
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billyjp2 said:
Put a socket on the harmonic balancer and spun the engine over with #1 spark plug pulled. When I felt air start blowing out I aligned the timing mark as specified. For my own sanity I've done it numerous times.
Click to expand...

Sounds like you did it right. Not everybody understands that there are two full crank rotations compared to a single rotation of the distributor.
 
i had something of the same issue after i drove my built 4.0 around. it had popping and backfiring and excessive cranking then no starting. what i did was spark plugs. not it. then i went to the cms. loosened the bolt but didnt take it out. i slowly moved the cms around until it had a spot there it ran then found its "happy home" but continuing twisting until it went into" limp mode" where it ran on 2 . then i twisted it back a few deg. locked it down and only had to adjust it once. let us know what this does for ya.
 
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