Need some help, I don't post much but I read a lot and I cant seem to find anything on this. Working on 2004 996tt just rebuilt the engine due to # 6 rod failure. I can't get it to make boost. Car is modded with k24 turbos, AP y-pipe,5 bar fuel press regulator, Ap air box and fabspeed exhaust, AP diverter valves, Pauter rods. I am a 20yr Porsche tech and have built many engines. All that said this is where I'm at.
No codes at idle, Turbos spin freely waste gates are closed, Passes both smoke and pressure test @20psi. Since it is known that tuned cars eat maf I have swapped with a known good unit = boost sometimes if ease into throttle. Also would make boost high rpm but not clean kinda broken up. Threw p1508 in limp mode until clear code. Swap MAP = no change, Check diverter valves closed like they are suppose to be , even block off = no boost. Swap n75 = no boost. Replace spark plugs coil packs look good = no boost.
Im thinking this maybe of some issue camshaft deviation b2 is -6 while b1 is 2ish. Actual angle is 0 at idle and both climb to 30deg when reved. All seems to be fine. I just remember that on 7.8dme that the threshold is 5deg on NA cars not sure if it applies to turbo cars. My problem is that its b2 that is -6 and misfires are on b1. I have yet to have a Cam retard code. I know it is probably something simple Im just running out of ideas and about to pull engine and go over every detail.

 

Just a shot in the dark. A VarioCam Plus solenoid bracket can fracture and this can affect the intake valve timing.

While you have a 5 bar FPR installed are you sure it is set to deliver 5 bar fuel pressure? Are you sure the fuel system is in good condition and able to supply enough fuel and at the proper pressure under heavy load/demand?

 

Wait, I simply overlooked the error codes in the title of your post...

P0238 - Pressure Sensor -- Above limit.
P1136 - Pressure Comparison Charge Pressure -- Ambient. Possible fault cause: Charge pressure sensor.

IIRC the Charge Pressure Sensor is in the intake on the pressure side. The Ambient Pressure Sensor I believe is located in/under the dash behind the console?

Have you a Durametric you can look at/log the values from these sensors?

In short it reads like one or both sensors are bad, or possibly disconnected?

 

Macster, Thanks for the help, Both the p0238 and p1136 have cleared I think they were set because n75 valve was disconnected. Since I plugged it in those codes have not returned. I think your right on lift solenoid. I tested lift with scan tool and the idle does not change. I will look more into it tomorrow.
Fuel system should be fine. I haven't measured pressure but I haven't changed anything. The fuel mods were done prior to repair. I can check it and see where its at.

 

Quick update, no codes & no boost. Changed valve lift solenoids and tested the ones I pulled out all worked fine and brackets were not broken. This morning I had misfires on b1 but not enough to set CEL. Still no change in idle when I activate the valve lift solenoid. I'm going to swap out the DME and Alarm control unit tomorrow and see if a driver is dead in the dme. After that I'm pulling the engine and re timing b2 to see if I can get the deviation #'s below 5deg. Anybody else have a good suggestion.

 

Here are my cam deviation #'s

cold
Dev B1 -4.13
Dev B2 -6.42
B1 Actual 0
B2 Actual 0

5 min after start idle
Dev B1 -4.03
Dev B2 -6.40
B1 Actual 0
B2 Actual 0

Post drive cycle
Dev B1 -3.47
Dev B2 -5.88
B1 Actual 0
B2 Actual 0

 

You said "anybody else" but I have some more to offer I think may be useful.

There can be some variation in cam timing at idle. This arises from the slop in the cam chain drive. Also, there is some question as to whether the readings at idle are real.

What do you see when RPMs increase? The timing should change as RPMs climb. I don't know at what RPMs the intake timing changes, but it should reach 30 or possibly 40 degrees of advance.

If the two banks have different timing the mechanism of one bank that controls the valve timng can have failed.

If you have a Durametric you should be able to use I think the term is drive link to activate low lift/high lift on a per bank basis and then advance and retard timing on a per bank basis too.

I do not recall what they are called -- the factory manual refers to them as "actuating element for inlet camshaft" -- but these can fail and even though the solenoid is being activated and oil is routed to this device it can't hold the oil and timing doesn't advance. If timing doesn't advance the engine won't make boost.

The most (only?) failure mode involves the failure (disappearance actually) of the center ring of the 3 rings. With this ring gone the oil fed to this device doesn't advance the cam timing.

 

Macster, I did not mean to say anybody else, I meant anymore suggestions, I welcome your input. I have exhausted almost all my ideas. I don't have Durametric, I have a piwis, piwis2 and autel. You maybe on to something. I tested the solenoids manually in my hand with jumper wires, and looked at brackets. What your saying makes sense.
I have timing advance both banks evenly to 30 deg. The only way I can test lift, I believe is at idle. I should have a change when activated with scanner but it does not. From what I understand The lift system is separate from the advance system. looking at the passages in cam carrier the lift solenoid supplies oil to the top side of intake tappets to lock them. I can test b1 and b2 separately with advance solenoid but can only test lift on both banks, I maybe wrong. I'll double check that. Keep the ideas coming we are going to figure this out. I also have a test vehicle that runs fine and makes boost.

 

Interesting, no actual#s showed??

Mine:

Cold start-
Dev B1- 0.0
Dev B2- 0.0
Actual B1- 28.82
Actual B2- 26.68

5 mins idle-
Dev B1- -1.31
Dev B2- -2.55
Actual B1- -0.0313
Actual B2- 0.1094

After Drive-
Dev B1- 0.13
Dev B2- -2.23
Actual B1- 0.1406
Actual B2- -0.0938

When idling, my deviation holds fairly solid, it may change slightly every couple of seconds... When revving/under load, my deviation holds solid and actual angle goes up and tops out around 30.00. Actual angle constantly fluctuates...