The V8 Owners Forum -

Good Afternoon,
I have a 4.6 Rover V8 with Holley Sniper EFI fitted into a Dax Rush kit car. For a while now I have been plagued by an intermittent high idle rpm issue. This can be 1200 to 2500 rpm while at idle or when changing gear. The sniper idle is set via an Idle Air Control (IAC) screw while ensuring the TPS is at zero. Clearly any uncontrolled manifold air leak is going to affect this so my attention has turned to the PCV valve.

I fitted this valve some time ago when I ran a Edelbrock carb and not even sure it is the correct valve for this engine.(pic attached)

When looking for a replacement PCV valve there are so many that look the same but will have different characteristics. Could anyone please tell me which one i need for a Rover 4.6 V8 and even where I can buy one?

Is there perhaps an alternative Crank case ventilation system involving a crank case ventilation pump or would that just be overkill?

I look forward to hearing from you
Allan
[attachment=0]IMG_7254.JPG[/attachment]

That item has nothing to do with a 4.6 as the 4.6 does not have a PCV as such.

I know nothing of your modified system but I do know a little of the 4.6 crankcase ventilation system. Air intake for the 4.6 crankshaft is taken from just in front of the throttle body where it sucks clean filtered air from the air intake side of the throttle body - this is piped direct to the passenger side rocker cover - the short pipe on top of the rocker cover.

The air goes through the crankcase and comes out the short pipe on top of the drivers side rocker cover and is pipes into the drivers side front plenum (thor).

To stop oil misting a small plastic catch sits in the small pipe - see bottom pic. The top pis is where fumes from the crankcase are sucked into the induction system.

Thank you for the information regarding your Thor system, very interesting. I would assume that although your fresh air comes from the inlet of the filter is all part of the metered air and therefore not an issue with regards to the air fuel ratio.

Unfortunately I have what I would term as a universal setup very common in kit cars and the like. From the attached pic, air is drawn in through the passenger rocker filter, circulated through the crank and sucked out of the driver side rocker cover. This outlet contains the PCV valve which get its vacuum via a manifold pipe at the bottom of the Sniper EFI unit. Hence additional unquantified levels of unmetered air are sucked in solely governed by the PCV Valve.

There are a number of potential faults that could cause my sporadic high idle rpm but I would like to rule this out first.

So ideally I'm still looking for advice on which specific version of my PCV valve I should purchase and from where. I have now written to RPI, Rimmer Bros and V8 Developments who hopefully might shed some light on this.

Many Thanks
Allan
[attachment=0]IMG_7258 2.JPG[/attachment]

So the general layout is basically the same as a Thor 4.6 - why not buy the little plastic oil fume removing device that I indicated above, put it in the steel outlet pipe of the drivers side rocker cover and then just run the pipe to the same place as you do now - a thor did not need an extra pcv valve as the plastic insert does the same job - dont make it harder than it needs to be.

Thank you for the suggestion and I'm still churning this over in my mind. I'm not a mechanic so just using my own logic here. I believe my system needs a PCV valve because the air entering the crank has not been metered by the Sniper EFI unit (other than resulting AFR via the O2 exhaust sensor). In fact it has completely by-passed the unit. My understanding is the the PCV operates as follows.
1. Engine off or blow back the PCV is closed.
2. At Idle/high vacuum the PCV is fully raised and only a very small amount of air/fumes can pass. Providing this is only very small the IAC adjustment should be able to accommodate it. This is why I require the correct valve with characteristics for the engine.
3. Mid vacuum the PCV drops slightly allowing more air/crank fumes to pass.

If I were to just introduce what I think is basically an oil separator the IAC control would be completely overridden by too much air/fumes.

I could be wrong here but I believe your Thor system crankcase air intake might be after something like a Mass Air Flow (MAF) sensor therefore has already taken this air flow into consideration.

I'm sure there are others more knowledgable than myself; however, I'm always happy to be corrected.

Once again thank you for taking the time to reply with your thoughts and suggestions.
Allan

Don’t know if this helps but on the Hotwire system on my car the pipe from the crank case vent has an orifice built in to it, I think the is a similar thing in the air intake to the rocker cover so, although the air is un metered, I guess it must be a specific amount for a given manifold vacuum and accounted for in the ECUs program. Perhaps you could try something similar?

Nice looking engine bay by the way, I imagine that car is “quite lively” with that engine and so little weight?

Allan Robinson wrote: ↑Sat Sep 24, 2022 12:01 pm Thank you for the information regarding your Thor system, very interesting. I would assume that although your fresh air comes from the inlet of the filter is all part of the metered air and therefore not an issue with regards to the air fuel ratio.

Unfortunately I have what I would term as a universal setup very common in kit cars and the like. From the attached pic, air is drawn in through the passenger rocker filter, circulated through the crank and sucked out of the driver side rocker cover. This outlet contains the PCV valve which get its vacuum via a manifold pipe at the bottom of the Sniper EFI unit. Hence additional unquantified levels of unmetered air are sucked in solely governed by the PCV Valve.

There are a number of potential faults that could cause my sporadic high idle rpm but I would like to rule this out first.

So ideally I'm still looking for advice on which specific version of my PCV valve I should purchase and from where. I have now written to RPI, Rimmer Bros and V8 Developments who hopefully might shed some light on this.

Many Thanks
Allan
IMG_7258 2.JPG

Out of curiosity, what is the double can thing behind the intake and in front of the brake fluid reservoir? Your engine bay makes my Fury look positively roomy

scudderfish wrote: ↑Mon Sep 26, 2022 6:02 am
Out of curiosity, what is the double can thing behind the intake and in front of the brake fluid reservoir?

Looks like a double servo, master cylinder either end. I thought it was the heater system at first!

Hi Scudderfish. Sorry for the very very long delay in answering. Yes you are correct, it is one unit but is basically 2 servos back to back. I"m no expert in this area but having a balance bar peddle box was the only way I could achieve seperate front and rear servo brake control.

Allan

You could just vent the crankcase to atmosphere temporarily to prove that it's definitely a PCV issue.

Chris./

In the time that has passed I have explored many possible reasons for high idle and irratic running. Finaly came down to the Holley Sniper secondary valve slightly sticking open and also a Sniper injector electrical connector issue.

I have recently covered this under the heading. "Holley Sniper Issue". (I might have wrongly placed the post under Engine area.

Thank you for your input and very much appreciated.

Allan