FraserW

FraserW

Member
4.2 v8 sc

PCV. Slowly bringing this old girl back to life, currently dealing with lean codes bank 1 and 2. I’m pretty sure it’s a vacuum leak ltft gets better when i rev. Smoke tested today but couldn’t find a single leak. I took the PCV off and I can blow through it in both directions. Can someone please tell me if this is correct? Thoughts are the Pcv will give me a lean but won’t give me a leak test.

This is my last code to conquer so any help will be appreciated 😀
 
Lean is not enough fuel
Via diagnostics you can get fuel pressure
Around 50psi to start up, then its controlled by a module,
Cruising it seems to vary from 38 to 55psi Wide open throttle it gets as high as 70psi

I think i can blow through my pcv both ways il check tomorrow and its got the vacum hiss noise that is normal with the 4.2 sc

Check the boot at the end of the intake snout to throttle body

Sorry i can't be more help iv not had to deal with anything wrong that way on mine
 
stustrong said:
Lean is not enough fuel
Via diagnostics you can get fuel pressure
Around 50psi to start up, then its controlled by a module,
Cruising it seems to vary from 38 to 55psi Wide open throttle it gets as high as 70psi

I think i can blow through my pcv both ways il check tomorrow and its got the vacum hiss noise that is normal with the 4.2 sc

Check the boot at the end of the intake snout to throttle body

Sorry i can't be more help iv not had to deal with anything wrong that way on mine
Click to expand...

How many fuel pumps are there on the 4.2? They've not done something odd like the diesel, have they?

Simple stuff: I assume the fuel fter is new and it has fresh fuel?
 
Think can safely say I have no vacuum leaks. I tape a glove over the intake and then tape the smoker hose into it. Blowing the glove up (wanted to test again in a shed at work just incase I couldn’t see the smoke for the wind/breeze.

I’m assuming it’s vacuum because it’s lean and gets better under load going by the ltft's
 

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Grrrrrr said:
How many fuel pumps are there on the 4.2? They've not done something odd like the diesel, have they?

Simple stuff: I assume the fuel fter is new and it has fresh fuel?
Click to expand...
Just one in tank pump, bowl filter as part of the assembly
 
Get a computer on
Read fuel pressure and maf readings,
Id be inclined to say the mafs reading low and its trying to add fuel but the o2 sensors are contradicting it and hit its limits,
or fuel pressure is down and it its done all it can by opening the injectors for longer but it cant actually supply the fuel to compensate
 
stustrong said:
Get a computer on
Read fuel pressure and maf readings,
Id be inclined to say the mafs reading low and its trying to add fuel but the o2 sensors are contradicting it and hit its limits,
or fuel pressure is down and it its done all it can by opening the injectors for longer but it cant actually supply the fuel to compensate
Click to expand...

I’ve had my computer on it hence knowing what the fuel trims are doing. It’s lean and gets better under load. MAF sensors or fuel starvation wouldn’t get better under load fuel trims would get worse. it would become leaner?. MAF is reading around 5/6gs on idle which is where I’m lean. Fuel pressures are around 35psi on idle give or take. Unless it’s nothing to do with the sensing wire and the MAF is just throwing random numbers in but data streaming shows a very even and predictable reading. So looking at the above that’s how I came to my inclination of it being a vacuum leak but I’m showing no leaks…the only thing I’ve done recently is run some cleaner through the petrol.
 
Hi all sorry to jump on this thread but I've a feeling my s.c has a vacuum leak from the pcv I've noticed a slight misfire at idle and the engine pulling ignition timing.

had a smoke machine in the intake but it comes straight out the pcv valve.
 
T898Dan said:
Hi all sorry to jump on this thread but I've a feeling my s.c has a vacuum leak from the pcv I've noticed a slight misfire at idle and the engine pulling ignition timing.

had a smoke machine in the intake but it comes straight out the pcv valve.
Click to expand...
can you explain the engine timing to me please? That’s something I’ve not got into yet so would be good to learn more
 
FraserW said:
can you explain the engine timing to me please? That’s something I’ve not got into yet so would be good to learn more
Click to expand...

I don't expect theirs a lot you can do about the timing as its all controlled by sensors that decide when to fire the plug and is due to so many different parameters these days.

If its a keeper then invest in some diagnostics it would help alot rather than chasing your tail.

Good luck.

J
 
marjon said:
I don't expect theirs a lot you can do about the timing as its all controlled by sensors that decide when to fire the plug and is due to so many different parameters these days.

If its a keeper then invest in some diagnostics it would help alot rather than chasing your tail.

Good luck.

J
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I have diagnostics! it was more to do with how to read them and to understand what it’s doing not adjusting it
 
FraserW said:
I have diagnostics! it was more to do with how to read them and to understand what it’s doing not adjusting it
Click to expand...

What sort?

Any faults showing?

Can you run/record live data as that is often a better way of getting a better picture.

J
 
FraserW said:
can you explain the engine timing to me please? That’s something I’ve not got into yet so would be good to learn more
Click to expand...
Hi again

What I mean by timing is the target ignition angle.

See my photo I'm unsure why it's target angle is nearly 40 degrees. Since I wrote my first comment I've given the maf a quick spritz with contact cleaner which has helped the short term fuel trims greatly.
 

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As I say I don't know the SC other than, if I remember it has a really high fuel injection pressure as its direct injection?

You have 2 red numbers, maybe its retarding the ignition, (i dont know if that retard or advance but educated guess) cos it hasn't got enough fuel??

J
 
marjon said:
As I say I don't know the SC other than, if I remember it has a really high fuel injection pressure as its direct injection?

You have 2 red numbers, maybe its retarding the ignition, (i dont know if that retard or advance but educated guess) cos it hasn't got enough fuel??

J
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it sure as doesn't have direct injection, rail pressure at 1500 rpm is 45 psi which is well within specifications. I must do some more tests and ill let you know.
 
T898Dan said:
it sure as doesn't have direct injection, rail pressure at 1500 rpm is 45 psi which is well within specifications. I must do some more tests and ill let you know.
Click to expand...

Ok it must be the 5.0sc that has that then.

But at the end off the day you have 2 red "out of range" to check.

T898Dan said:
rail pressure at 1500 rpm is 45 psi which is well within specifications
Click to expand...

Not the way I look at your last dia pic it dont??? Although I have no ref to what the numbers mean.

How are you measuring this? and how are your diagnostics measuring it?

J
 
marjon said:
What sort?

Any faults showing?

Can you run/record live data as that is often a better way of getting a better picture.

J
Click to expand...
Please see the thread. I think you’ve read one comment and jumped to conclusions 😜. It’s all there
 
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