What's this plunger for? (OHG X450)

[Maj]

Hi guys. I'm looking for a little technical help please.

Trouble shooting my '84 Grand Marquis 302ci.

What is the purpose of the vacuum plunger pictured here?



I've just renovated my propane system and have an issue that I think is related to the pcv vacuum pressure and that plunger which are on the same circuit. .

System: VFF30 + OHG X1 + OHG X450

The symptom is: Engine starts easily and runs smoothly for about 20 seconds then that plunger clicks and the motor shuts off.

I've tried holding the plunger closed and the engine keeps running fine.

Could someone please help me understand what's going on here? I concluded that the pcv system must be creating too much vacuum and popping the plunger which in turn somehow shuts off fuel flow. Not sure I've understood the process properly though.

Also fyi, the pcv system has been renovated too with all new parts.

Any help would be great!

Thanks in advance

[storm]

Power valve plunger. It open when vacuum drops and allows more LPG to flow into the mixer.

[Maj]

Power valve plunger. It open when vacuum drops and allows more LPG to flow into the mixer.

OK thanks for the info Storm.

So if I'm understanding correctly(?), the theory is when you put your foot on the gas (opening the butterflies) the manifold vacuum pressure drops pulling the valve open dumping extra fuel into the intake.

Does it sound right that it would stall the engine if the power valve opens at idle speed?

I think it has something to do with the pcv valve moving from its resting position when the engine is off to the restrictive position at idle after the engine has been idling for a few seconds thus activating the power valve and killing the engine. The power valve is T'd into the pcv vacuum line.

Can I just separate the two vacuum circuits? Plug the power valve into a below butterfly vacuum port and blank the T in the pcv circuit? Or is there a reason the power valve is connected into the pcv circuit?

Any input appreciated, thanks

[storm]

The power valve should open when vacuum is lower than 5". If it is opening at values higher than 5" (i.e. 6"-20") the power valve spring has either lost its tension or it has been cut to change its operating settings (which to me is a bit of a no-no).
The original springs were 16mm (or 5/8" in imperial) long so my suggestion would be to check it and even just get a new one.
My understanding is the correct hose to connect it to is the PCV hose via a T fitting so I would leave that as it is.

BTW all this is just what I have learned on this site and from Franz's excellent book.

[gottago]

I've run with power valve plunger vacuum hooked up both ways, dedicated vacuum line and t to pcv. Differences were subtle but t to pcv is recommended and seems best. I came across one where someone had installed a type of pcv that placed the valve off one side of the vacuum hole in valve cover and a nipple off the other side. The power valve was teed in to that nipple. It did not work properly at all. The pcv and power valve need to be on the same dedicated line, power valve teed in downstream from the pcv valve. No other vacuum connections on this one works best. Changing to proper pcv on that one made a big difference. The big vacuum trees multiple nipples feeding everything from power brakes to vacuum advance are not the place to tie into.

[Maj]

Super stuff guys, thanks for the info, I'd never have found any of that without your help!

I'll check the spring length next, it's probably the issue as I've eliminated most everything else. Plus that spring is now thirty years young!

I saw a write up recently explaining how to make a simple water manometer for testing vacuum. So I'll make one so I can confirm the valve is operating at the correct pressure.

Thanks!

[franz]

Thanks for the plug, Storm. The piston serves two purposes, the one you mentioned, where it allows extra fuel, plus it closes the vent to the top cover, allowing the air valve to raise, decreasing air restriction. By the air valve lifting, the metering pins also raise, allowing additional fuel, somewhat proportional to the amount of airflow. At low airflow speeds, the mixer uses the air valve to increase air velocity across the metered openings in the body. When the air valve raises, the mixer behaves more like a venturi. Its complicated and very efficient. Just make sure the metering pins move freely and the air valve moves without binding. You can loosen the three screws and gently move the top cover around until the valve doesnt bind.

Franz

[Maj]

Hi Franz, thanks for the description.
I've been trying to wrap my brain around the concept!

Would I be right in thinking it's more about a 'balance' of vacuum pressures? Rather than an on/off situation which is how I've been thinking about It.


Also, how does one go about getting ahold of a copy your book?

[gottago]

Indeed seems there is more to the simple little plunger than first meets the eye. From another thread below- Allen Athol talks about the function of the power valve..

Just in case you're not aware of it, the X-450 will not run properly unless the power valve is Teed into the vacuum line between the PCV valve and manifold vacuum. The PCV acts as a regulator to prevent the valve from fluttering as it will if connected directly to manifold vacuum. The bottom of the power valve also delivers LPG down the vacuum line when the valve closes, so if it flutters the mixture varies wildly until the engine stalls.

[storm]

Or you could PM or email Franz directly and purchase the book.

EDIT: I dare say using that site could amount to a copyright infringement.

[Frank]

I would like to see Franz put up the information from his old site back up on his new site. He's been too busy to spend much time on it now that he's retired.

I would contact him directly, either through a PM from here or through his contact page. His book was very reasonably priced and the revenue goes to support a scholarship fund and the National Hemophilia Foundation (his grandson has Hemophilia).

[franz]

That site doesnt have my permission to show that book and is indeed in violation of my copyright. I will be contacting them. For what its worth, I dont know that publisher nor did I give them permission to show my book.

I may put the book up for sale on my site, thanks for suggesting Frank. I've been extremely busy lately and have had precious little time to devote to it.

Franz

[gottago]

Apologies for posting the link to the online book. I assumed it was legit and that revenues were being properly distributed. I'll remove the post..

[franz]

You may leave it intact, I am in the process of filing a formal Violation of Copyright against the site in question. Everyone who has obtained this book via legal means is clear, that includes anyone who received my book by me personally or through one European contact who has my permission to distribute.

Thanks for bringing it to my attention.

Franz Hofmann

[Maj]

Indeed seems there is more to the simple little plunger than first meets the eye. From another thread below- Allen Athol talks about the function of the power valve..

Just in case you're not aware of it, the X-450 will not run properly unless the power valve is Teed into the vacuum line between the PCV valve and manifold vacuum. The PCV acts as a regulator to prevent the valve from fluttering as it will if connected directly to manifold vacuum. The bottom of the power valve also delivers LPG down the vacuum line when the valve closes, so if it flutters the mixture varies wildly until the engine stalls.

Awesomeness 'twas the now replaced plunger spring causing my stall issue. She runs like a top now! I haven't checked the vacuum values (no manometer) but I can see the plunger only operating when the engine is revved right up. So I'll get to fine tuning it down the road.

Franz's book has been a great help. I've learnt a lot about the hidden details of propane systems over the last few days.

Still don't know which is best for pipe joints tho, tape or paste