[bluedoggiant]

2006 4.2 v8. I’m dealing with a strange set of symptoms I am trying to diagnose and curious if you all think they’re related.

I don’t have a starter or battery issue, but i am increasingly unable to start the vehicle on first try. I then have to turn the key to the left and try again with a manual crank, though I don’t need to crank long.

I’ve narrowed it down to the crankshaft position sensor or one of the fuel pumps, based on my readings here. I feel like it’s the CPS since it seems to only happen when the engine is warm. I hear the fuel pump when opening the driver door, and the vehicle doesn’t stall when driving, so I’m leaning less toward that.

If the secondary fuel pump (or filter, or regulator) is failing, is the main pump able to start the car still? Hence why I need to crank more?

Other symptoms that seem to have started at precisely the same time: the engine seems to rev higher/hold gears longer and despite so, power seems a bit down. This makes me wonder if it could be fuel pump.

Transmission seems to bang gears/shift more harshly on occasion, like a bad valve body. But could it be behaving this way because of a bad signal from the CPS? Totally realize it could be two sets of issues, though the transmission issue flared up suddenly with the hard start issue and trying to see if it could possibly be related. Holding the gears long and revving higher than usual doesn’t sound like a valve body issue to me

VCDS scan is clear.

 

[SaVAGeSoot]

If only there was some kind of tool that would read measuring blocks...... that would be neat!

 

[bluedoggiant]

If only there was some kind of tool that would read measuring blocks...... that would be neat!

I recall poking around but didn’t find anything that stood out. What locations should I measure and what should I look for? Seems engine RPM is being read correctly to my eye/ear on the tachometer and VCDS

 

[SaVAGeSoot]

Well, if you "think" that it's the crank position sensor, why not log its signal instead of using your eye\year\tach? (obviously, during the NO START condition, not when it works... so HOT engine, or whatever scenario you've associated with the fault)
The same goes for fuel pump, or whatever other suspicion you might have.

 

[MidnightTouaregV8]

My Egg never had hard start issues. But hard shifts and elevated rpm were caused by wonky secondary FP and temperamental G70 MAF.
Also, check every possible connection B+ and B- to ensure good contact.
Hook up the pressure gauge to the fuel rail and see how the system primes, KOER pressure and bleed down pressure KOEO.

CKP performance can only be confirmed with a scan tool that supports graphing if there is no dtc related to its fault.

 

[bluedoggiant]

My Egg never had hard start issues. But hard shifts and elevated rpm were caused by wonky secondary FP and temperamental G70 MAF.
Also, check every possible connection B+ and B- to ensure good contact.
Hook up the pressure gauge to the fuel rail and see how the system primes, KOER pressure and bleed down pressure KOEO.

CKP performance can only be confirmed with a scan tool that supports graphing if there is no dtc related to its fault.

I’m not sure where to even start to test the MAF sensor. As for the secondary FP, I’ll have the shop test the fuel system with a pressure gauge. I haven’t checked the carpet perforations but I suspect this vehicle is probable due for both fuel pumps/filter/regulator to be replaced.

Any suggestions for specific locations to check B+/B-? The vehicle has very intermittent battery drain and I’ve checked so many things but nothing has stood out.

What should I look for when logging CPS? There’s a bunch of measuring blocks for engine rpm, assuming they’re all the same, what would a bad CPS graph look like?

 

[SaVAGeSoot]

What?
Do you understand what RPM is?
Do you understand what CPS is?
If CPS reads RPM, you record\log the values when cranking in a NO START condition.... if you see ZERO but hear the engine cranking, does that tell you that the CPS is reading?
If you see X value, ZERO, Y value, ZERO, etc..... does that tell you the CPS is working or it's flaky?

A CPS graph on a non working CPS would look like a flatline
A CPS graph on a working CPS would go from ZERO to whatever cranking RPM you have until you release the key and stop cranking.
If it's just flaky, you'll see the values bouncing all over the place, or dropping to zero and then spiking......

 

[MidnightTouaregV8]

Check this out

Cheers...

 

[bluedoggiant]

What?
Do you understand what RPM is?
Do you understand what CPS is?
If CPS reads RPM, you record\log the values when cranking in a NO START condition.... if you see ZERO but hear the engine cranking, does that tell you that the CPS is reading?
If you see X value, ZERO, Y value, ZERO, etc..... does that tell you the CPS is working or it's flaky?

A CPS graph on a non working CPS would look like a flatline
A CPS graph on a working CPS would go from ZERO to whatever cranking RPM you have until you release the key and stop cranking.
If it's just flaky, you'll see the values bouncing all over the place, or dropping to zero and then spiking......

There are tons of RPM values to track in VCDS. I selected a bunch of them and they all correlated somewhat. However the VCDS refresh rate is like 2 seconds, so I really couldn't glean anything from the data. It looks about right. Cranked, idles high for a sec, settles down to idle. Values increase with acceleration.

Check this out

Cheers...

Thanks for sharing, very cool.

 

[SaVAGeSoot]

Sample rate degrades the more data points you select. I told you to log while in a no start condition which is not what you did.

 

[bluedoggiant]

Sample rate degrades the more data points you select. I told you to log while in a no start condition which is not what you did.

I’ll pick one of them next time then. And I attempted to, but the issue was not reproduced.

 

[SaVAGeSoot]

There are tons of RPM values to track in VCDS

Imagine if there was some sort of label that would give you a clue..... you know... something like....

IDE00021 Engine RPM 785 /min

 

[bluedoggiant]

Imagine if there was some sort of label that would give you a clue..... you know... something like....

There are several that show RPM live data.

 

[SaVAGeSoot]

How many of them say ENGINE RPM?

 

[bluedoggiant]

How many of them say ENGINE RPM?

I don’t have it in front of me but several did, and show the exact same values as one another. Would there be additional RPM metrics within the engine module?