4.0 died while wheeling? ideas? weird compression readings...

[TEK4x4]

ok so this is what i have. Was wheeling today engine was running awesome. hit some high revs and it died. no pop no bang just shut down. have spark have fuel did a compression test and got weird readings. did test on cylinder 4 and 5 and four times each. readings were weird 60, 60,40,75. did a cylinder leak down test and everyting is holding. thought timing might be off checked it crank says its fine. I think the cam sliped a tooth or something weird like that. Anyone ever herd of this? or had this problem? another thing, i rebuilt this 4.0 about 6 months ago when i did the swap been running fine like i said it just quit. any help would be awesome be for i pull the motor again.

 

[RonD]

What were the other cylinder's compression?
Compression test needs to be done with all spark plugs removed so starter motor can spin crank at highest speed.

If timing chain "slips" a few teeth then all cylinders are effected, but engine should still run just not very well.


CKP(crank position) sensor tells the computer the engine is turning so to start spark and injectors, if it fails(or it's wires to PCM come loose) then a dead engine is the result.

If engine starts but runs rough then it is not the CKP sensor.

Whats the fuel pressure read on rail?
inertia switch can be tripped when 4 wheeling, which cuts power to fuel pump(s).
When key is first turned on can you hear fuel pump(s) come on for 2 seconds?


How did you check the crank/valve timing?
You can pull a valve cover and check valve timing.

 

[SenorNoob]

I'll be the idiot to ask the stupid question. Is the intake blocked somehow? (I'm thinking at or before the filter.)

 

[TEK4x4]

i didnt write the results all down for all cylinders definatly after the first two i tested were erratic, and yes i took all the plugs out. the fuel pressure is 40psi. If the cam sensor was bad wouldnt i not have spark or injector trigger? and i checked timing with a timing light and marked the crank on the 10 degree mark like specs say to. i realize that there is no adjusting the timing sense there is no distributor. If the inersha switch was tripped i wouldnt have fuel pressure and the pump wouldnt be running. i have yet to pull the valve cover. didnt have time today to get it in the garage. also the intake isnt blocked

 

[RonD]

There was no Cam sensor on most 4.0l, just the crank sensor, so outside of the PCM being bad the spark timing and crank position would be in sync no matter what position the cam is in.

yes, if crank position sensor was bad there would be no spark, but fuel pressure would still be high since that is primed each time key is turned on.
40psi seems high, when you did the compression test was the end of the tester wet with fuel?
i.e. are the injectors opening
Did you check pressure after or during cranking, it should go down as fuel is injected into the intake?
If you pull out a spark plug now is it wet?
Have you tried starting fluid?

 

[TEK4x4]

It was a timing issue. crank timing gear pin broke allowing the crank to spin but not to move the crank gear. in-turn not spinning the cam and not opening and closing the valves hens no run. good thing its a non-interference engine.