P0106 with low manifold vacuum

I have a 2005 ford mustang with 4.0l v6. It has a dtc p0106 map sensor out of range. It has no power and upon diagnosing ive ran across the followong, pid for map was showing 10.44 hgs vacuum at idle followed with a gauge with the same result. Snap the the throttle it drops to 0 and bounces to 21 22 hgs then back down to 10. Holding it at 2500 rpm the vacuum raises to 15 hgs. Compression check is around 105 to 115 on all cylinders, leak down test tested good so I'm leaning towards late valve timing causing this. Idk what to do next, timing advance at idle bounces from 3.5 up to 34 degrees and all around. Any incite into how to diagnose this problem the right way would be greatly appreciated. Also I watch a lot of your videos and habe learned so much thanks in advance...

If you had a scope you could check cam to crank relationship. So you ruled out a restricted exhaus? Sounds like it with the vacuum gauge test.

Yes ive done a back pressure test and was getting about 1psi at 2500 rpms also dropped the h pipe to be sure and the vacuum condition is the same with or with out the exhaust hooked up. I have a maxysis ts906 but I haven't bought the scope yet it is one thing I plan to get next once its paid off... The only pid I see for timing is timing advance and it jumps around feom 3.5 degrees to 36 degrees at idle but at 3000 rpm steady its 46 degrees, ive looked thru alldata wverywhere amd can not find any way of checking the timing or a spec for it. I am really leaning towards late valve timing but dont know how to prove it, ive learned so much from the youtube channel here but im lost as in what to do or what I can do to proove or disprove my theory...

From what I understand normal compression on the 4.0l is normally 160 to 175 with a high compression motor.. Leak down test it good leading me to believe the valves are opening late and its unable to build full compression . this is just a theory but I need to know how to proove or disprove this...

Hi,

You can also check O2 upstream sensor activity, so you can rule out a fuel delivery issue.

At wot, 02 voltage should be rich all the time.

Edit: On the road

By the way,

The final pressure in a compression test, depends on baro pressure (or altitude).

I dont see how a fuel issue could cause low manifold vacuum and compression, but everything looks good, even long-term and short term trims are plus or minus 3.5 both banks short and 0 long.

without a scope your probably looking at removing timing cover to verify timing.

I really hope you don't have to deal with timing chains on that one.

Fuel delivery issue is related to lack of power. I rather when diagnosing, rule out another hypothesis.

To discard valve timing issue, you can unplug valve actuators.

You can also perform again compression test with valve actuators unppluged.

105 to 115 psi seems to me a low pressure, but if you live like me at 3200 m/(8000 feet), that could be normal. What is suspicious is the difference between cylinders, but again leak down test contradics a mechanical issue.

I'm supposing fuel trims you mentioned, are under load? At wot?

That would be great to know the ones (fuel trims) which match with the lack of power.

Denisf wrote: I really hope you don't have to deal with timing chains on that one.

You're not kidding!

Yes I will, confirmed broken rear cassette.

Confirmed, pulled motor and rear cassette is broke clean off, I don't know how it wasnt making any noise. That's for the help tho

I pulled the valve covers and my theory has been confirmed. Broken rear chain guide

What I learned from this was the idle timing jumping around. I doubted myself for some reason, knowing that the idle timing timing should be steady.

When you get it back together... please post the idle timing.