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V8esprit-TT

Crankcase ventilation question

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I am having an issue with a high idle, slight off idle hesitation, and surging idle.  All my previous experience tells me I have a vacuum leak, but I have hunted long and hard with no result.  The one part that doesn't make sense to me is the line that runs off the RH valve cover, through a one way valve, and into the EGR plate.  Lines 19/20 on the attached diagram.  This basically provides a open air bypass of the throttle plates.  If the engine was sealed, I would understand this provides a crankcase vacuum, however the lines of the fronts of the valve covers to the airboxes have no one way valves in them, so there is always airflow through the valve covers and into the plenum.  If I clamp off the line off the valve cover to the EGR, the idle stabilizes better.

I have replace the idle air controller, checked all injectors for leaks, resealed plenum, checked the evap system for leak.  The EGR has been removed and blocked off.  

Car has always done this since I bought it.  Sometimes it will idle fine, sometimes it will rev to 1500, sometimes it will hover around 2000.  I've done the idle reset procedure alot.  Sometimes it will idle fine after for about 100 miles, sometimes it will always idle high.  During the idle reset procedure when I leave the car to just idle, it will randomly rev up with nobody in the car!  Sounds like someone is blipping the throttle.

So what am I missing?  I know this car should be able to idle!

V8hoseRouting.JPG.69fb9303d3b404e301a77af76d447f90.JPG

Edited by V8esprit-TT

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Hello Jon @V8esprit-TT sorry, only just read this.

To illuminate your first question about items 19/L/20, this is from the service manual:

EMM.2 - W CRANKCASE BREATHER SYSTEM
Crankcase fumes are managed as follows:
Each cam cover is lined with a steel oil spray shield, the space above which is connected via a duct and
hose to the crankcase breather cover in the centre of the ‘v’. This breather space is ventilated by a hose connecting a spigot on the front face of each cam cover to the
adjacent ‘clean side’ air filter cover. A small bore hose connects a spigot on the rear face of the RH cam cover, via a one way control valve,
to the intake plenum common chamber. Under light load running conditions, the small bore hose maintains a small negative pressure in the
crankcase. Under boost conditions, intake plenum pressure becomes positive and the one way valve seals off
this hose. Airflow through the intake ducting is then sufficient to induce a negative pressure in the hoses connected to the front of the cam covers.

There isn't really much to go wrong with this apart from hoses being blocked/split/leaking, the one way valve being stuck closed or open or perhaps it has been refitted the wrong way round? It is worth checking those first I think.

Assuming that is all well then the floating idle speed is probably IAC related. Do you get a MIL light or error codes on OBD at all?

EMM.3 - P IDLE AIR CONTROL (IAC) VALVE
A ‘Tech 1’ scanner tool will display the ‘duty cycle’ of the idle air control (IAC) valve, representing the
proportion of time for which the valve is energised by a square wave signal, and consequently the degree to
which the valve is open. A 35% duty cycle indicates that the ECM is commanding the IAC to be fully closed,
which is not a normal condition, and indicates an attempt to minimise airflow by-passing the throttle plates in
order to lower idle speed. This condition is usually caused by an intake system air leak. The higher the duty
cycle (up to lOO%), the greater the valve opening and the greater the airflow by-passing the throttle plates.
If the IAC valve is unable to control the idle speed within calibrated limits, the ECM will cause a Code
PO506/PO507 to set.
The procedures detailed in section EMM.4 should be used to diagnose IAC system
problems. Refer to ‘Rough, Unstable, or Incorrect Idle, Stalling’ in the Symptoms Section EMM.6 for other
possibilities for the cause of idle problems.

image.png.18373265def467205c55794b4eb4ca94.png

If not then I think it is diagnostics time.

EMM.2 - P ‘IDLE AIR CONTROL (IAC) VALVE
The purpose of the idle air control (IAC) valve assembly is to control engine idle speed under differing
engine temperatures and loads. The valve assembly consists of a motor and a rotary shutter valve which
controls the airflow by-passing the throttle plates. The IAC valve is mounted on the underside of the intake plenum, and is connected by hose between the
RH compressor duct and the EGR manifold which is sandwiched between the throttle body and plenum. The
rotary shutter valve is sprung towards the closed position, and is opened by an electric motor under the control
of the ECM. The valve motor is operated by a square wave signal from the ECM, with the ‘on’ time, or ‘duty
cycle’ controlling the effective voltage to the motor and the degree of valve opening. A duty cycle of 35%
represents a fully closed valve, and lOO%, fully open. In this way, the ECM is able to regulate throttle by-pass
airflow in order to provide the desired idle under various operating conditions, amongst which are; raised idle
speed with low coolant temperature and maintenance of idle speed with engine load from operation of air
conditioning or power steering.
The rotary shutter valve is sprung to a preset partially open position to allow
engine idle in the event of a valve motor failure. The ‘Tech 1’ tool is able to display the IAC duty cycle.
When the ignition is switched on, the ECM calculates the IAC duty cycle required to provide the necessary
idle speed for the coolant temperature and other conditions pertaining at that time. During idle, the engine
speed is monitored, together with coolant temperature, engine load and other relevent factors, and the duty
cycle adjusted as necessary. The ECM ‘learns’ the normal duty cycle of the IAC valve and retains this information
in its memory. See Sub-Section EMM.l ‘- I; ‘ECM Learning Ability’.

You have probably already got Peter England's excellent OBD tool, but if not it is at:

https://www.thelotusforums.com/forums/topic/23500-free-v8-obdii-scan-tool/

You can monitor the values of these two fields when the car is playing up:

image.png.f7f2f107ef72e395d4c2ff94980c7b1b.png

...which should give you a clue as to which side of the equation is causing the problem, demand or supply.

Also worth checking is the battery voltage at the same time which can be a curved ball with your problem:

Battery Voltage Correction Mode
When battery voltage is low, the ECM makes the following compensations:
- The injector pulse width is increased to compensate for the slower injector solenoid operation.
- The idle rpm is increased to aid battery charging.
- The ignition dwell time is increased to maintain spark quality.

That's this field:

image.png.df8c1d63b805829dc208fd12de6bce63.png

Hope that helps, let me know how you get on.

Cheers

Alan

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Hi Alan,

Thank you for the very detailed reply.  Many of your suggestions I have already hunted through.  My idle demand is correct, and the idle duty cycle is about 48.  I was able to get the car to idle mostly correct by closing the throttle plates from a TPS voltage of .35 to .29.  Backed all the way down, the plates go to a TPS of .27 so I turned them back open just a touch to prevent any binding.  According to the book the TPS voltage should be .65 so my plates are closed more than desired from original. 

I blocked off the intake ports to the throttle bodies and pressure tested the system to 15 psi and the entire system held pressure with no leaks.  So I have no air leaks.

In all of this testing though, I did a compression check, and I have 135 - 140psi across all cylinders on bank 2 LH side and 150-155 across all cylinders on bank 1 RH side.  So it looks like my cam timing is off, and probably causing my hunting idle and hesitation.  I read of another person having the same problem.  I have a leaking valve cover anyway, so looks like I get to pull my cam sprockets and reset the timing with the setting pins.  

As a side note, my timing is "correct" by the book using the locating pins.  They all go in, all the way, with a few being a little tight.  I will take pictures of the hole locations when I pull it back apart, but I am guessing the LH bank with lower compression has the cams a few degrees off, still "located" but not correctly set.  I have speculated this for a bit, but the compression numbers really tell a tale.  This engine has been out and rebuilt with low compression pistons, so apparently it went back together slightly off from where it should have been.

I will report back my findings.  I sure hope this finally fixes this persistent problem!

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Hi All,

I have my plenum sitting on a bench (almost) ready to go back on the car, however before I do I would like to test the IAC to make sure it is working properly. Is there a test I can perform? I see from the above that a square wave signal is used to manage the valve:

The valve motor is operated by a square wave signal from the ECM, with the ‘on’ time, or ‘duty cycle’ controlling the effective voltage to the motor and the degree of valve opening.  A duty cycle of 35% represents a fully closed valve, and 1OO%, fully open.

What is the voltage operating range (what voltage would equate to 35% and 100%?) and likely current draw?

I assume a duty cycle of 100% would look like a DC voltage, right? Can I just a DC voltage equal to that of 100% duty to open the valve? 

One observation is that I can blow into hose no# 7 and hear air at the EGR manifold (end of hose #6 ) which suggests the valve is open. Should it be open or closed when power is disconnected?

Is the IAC expensive? Should I replace it as a matter of course? What about the knock sensor too?

Before the car was taken off the road (a few years ago now, embarrassingly) for belts and other work I had a very slight stumble when going from coasting to light throttle and I don't think I have ever resolved it, so this is a potential area to explore.

Thanks

-Chris

image.png.045f2db3006a5a69b17e923797ce06fb.png

 

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Ok, now I know I don't want to replace the IAC unless I have to... 😳

Table Number: 42_04a
Position: 01
Part Number: A918E6011F
Description: idle Air Control Valve (lAC)
Notes:  
Qty on Car: 1
Price (each): £284.30
Condition: New
Stock: Factory Order

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Hello Chris @cweeden, don't panic, there is a cross ref for the IAC, think it is Volvo 240 and they are about £20 new. Will look it up for you tonight. 

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After looking at the circuit diagrams to work out the ground and the signal input (as best I can tell), I tested it as carefully as possible (and with the belief I was only messing with a £20 part 🙂 ) with low volts increasing until something moved. 3v nothing, 5v nothing, 7.5v it moved. Not very scientific but I will declare that good enough to bolt back on and let the ECU figure out if it has a problem or not. 🙂

cheers

-Chris

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On 31/01/2018 at 16:41, V8esprit-TT said:

Hi Alan,

Thank you for the very detailed reply.  Many of your suggestions I have already hunted through.  My idle demand is correct, and the idle duty cycle is about 48.  I was able to get the car to idle mostly correct by closing the throttle plates from a TPS voltage of .35 to .29.  Backed all the way down, the plates go to a TPS of .27 so I turned them back open just a touch to prevent any binding.  According to the book the TPS voltage should be .65 so my plates are closed more than desired from original. 

I blocked off the intake ports to the throttle bodies and pressure tested the system to 15 psi and the entire system held pressure with no leaks.  So I have no air leaks.

In all of this testing though, I did a compression check, and I have 135 - 140psi across all cylinders on bank 2 LH side and 150-155 across all cylinders on bank 1 RH side.  So it looks like my cam timing is off, and probably causing my hunting idle and hesitation.  I read of another person having the same problem.  I have a leaking valve cover anyway, so looks like I get to pull my cam sprockets and reset the timing with the setting pins.  

As a side note, my timing is "correct" by the book using the locating pins.  They all go in, all the way, with a few being a little tight.  I will take pictures of the hole locations when I pull it back apart, but I am guessing the LH bank with lower compression has the cams a few degrees off, still "located" but not correctly set.  I have speculated this for a bit, but the compression numbers really tell a tale.  This engine has been out and rebuilt with low compression pistons, so apparently it went back together slightly off from where it should have been.

I will report back my findings.  I sure hope this finally fixes this persistent problem!

@V8esprit-TT Jon, did you ever resolve this?

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