Hello, recently pulled and switched out a 4.0 v6 sohc on my B4000. Previous owner rolled the crank bearing. Regardless switched out with used warranty 4.0.

issues ensued, runs fine then intermittently bogs down to 1500rpm, runs rough for 12 seconds then carries on as normal.P0172 bank 1 rich

P0174 bank 2 lean

P0300 multiple misfire

P0301,02,03 cylinder misfires


ran some tests, pulled codes above listed and in addition changed a few sensors diagnosing - TPS, o2 upstream, thermostat and sensors, fuel filter, plugs, cables and coil pack.

improved running but still does this intermittent issue. Bank 1 lean and misfiring on 1,2&3 bank 2 rich(1 code, once only)

ran fuel pressure test 68psi continuous at the rail until the issue happens, then the pressure is up and down like a yoyo. Cleaned the Maf, ran a vacuum check.

vacuum off the brake booster at 16psi drops on load but settles on 16 psi and when load released climbs to 25-28psi and settles on 16psi when idling

checked resistance on injectors, now im not an electrical genius so bare with me: ohm meter set on 2 ohms and all injectors read 0.225ish ohms resistance. Some minor corrosion on injectors but cleaned and greased. Source voltage 12.5 and voltage on harness on those 3 injectors 12.4v so good i think...?

so question 1 what other test if any can i run
2: what am i missing
3: what is the issue here? Timing chains gone?

Any time there is a misfire code the first thing I suggest is to check the coil pack firing order
3 4
2 6
1 5
Front

The 5 6 4 side always gets me, either on the coil pack or at the cylinder
And if coil pack was mounted backwards
1 5
2 6
3 4
front

Second thing is compression test, yes its hard to do BUT.............its really a BIG waste of time and money to try to fix a compression issue, with bolt on parts, lol



Vacuum is low, 18-21" is expected unless you live in Denver
Red Deer is at 2,805ft though so 17-19" maybe
So could be compression issue

Thanks for the reply, checked the coil pack and i did do it right, the order is unusual.

compression test next then i guess, it is a mother to do on the passenger bank....

Go thru the wheel well, its a pain but not as hard on the back, lol

4.0l SOHC runs 9.7:1 compression ratio, so high
Expected pressure is 170psi
Thats with all spark plugs removed so you get good crank speed, compression is a temporary state with metal on metal seals, so not expected to be 'air tight', its the speed of the piston going up that builds compression, so slower speed shows less than higher speed
You can test just 1 with 5 spark plugs in, but test each one the same way, so put spark plug back in to test next one
Unplug coil pack of course, lol.

Ok got #1 done with five plugs in comes at 100psi and holds.

And holds?

100psi is way to low

Yeah holds and 110psi and holds on #2
working on #3 as a mouse couldn't fart in that space, going through the wheel well. Ill do all of them and post.

plugs in test and the throttle is closed fyi

I don't know what you mean by "it holds"
Compression is temporary, a compression gauge has a one-way valve so when you crank engine it records the highest compression of the 5 "hits", should do minimum 5 "hits" of compression strokes to get a good reading

Running compression is about 50% of static(what you are testing now), so 100, 110 are very low

You should test other side now to see if timing gear slipped on passenger side

Sorry i meant the gauge held the pressure. Anyway the other bank all hit 170psi

so.... ill drop some oil in number 1 and see if its rings?

Put oil down #1 and ran the test again no change in psi readings.

thoughts?

Valves are out of time on passenger side, bummer

If I remember there are no key,ways on these, you line up marks and tighten gears, so just a press fit holds cams in time

so you recon that if I do the timing chains it’ll be a win?

What year is this new/used 4.0l SOHC?

And did it have a warranty?

It won't have damaged valves or pistons being out of time like it is now, so yes of you re-time it that may be all it needs
When you get valve covers off you will see more

2004 with 162k km on it. Yes it had a warranty and LKQ refunded the money based on the testing ive done. Now to pull it lol

Well, pulled it all apart and found the #1 bank rear timing chain tensioner busted. So parts on order from Rockauto and timing tools from my buddy. Thanks for the help and support.

Sorry for the trouble but good work on getting to the bottom of it

Thanks for the updates