It was the coil.

Apparently you need some extra juice for the propane, or maybe the increased compression, too. I was using a Pertronix Powerblaster, but it was a couple of years old.

The new Accel Coil has me running better than ever.

Thanks for all of your help, Frank.

Joe




It's been since September, and I've been working slowly. The headlights and everything are not on my truck yet, but I needed to see how it would perform.

So, got everything back together and went out for a little drive today. It idles really nicely at 1000 RPM, and above 2000, it scoots right along. When I'm in idle and I shift into drive, though, it gets really rough and generally stalls out. A very unpleasant situation.

Any ideas?

Timing is at 10 degrees btdc, the O2 sensor hooked up to the propane controlling computer is where it ought to be bouncing around between 4 and 7 volts, new Erson RV cam, Dutra duals, stock 727 transmission w/ stock torque converter.

Thanks,

Joe

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Joe Hoppe

71 D100 225 Super Six 727 AT on 2008 Crown Vic CopCar frame

64 Valiant Wagon 225 904 AT 3:23 8.75"

Normally, propane systems can idle smoothly at very low RPMs so it's a bit surprising that it doesn't idle well. Can you provide a bit more information?

• What mixer and converter do you have on your truck?
• Did it run well previously? If so, what has changed?
• Does it only run rough when you shift into drive?
• An idle RPM of 1000 seems a bit high. What is its normal idle speed?
• Have you checked for any vacuum leaks?
• Is the ignition system in good condition?
• Have you adjusted the idle mixture previously to have a smooth idle?

Frank

Franks, Thanks!!

I appreciate your expertise--I've looked at your website and you look like you really know what your'd doing.

Mixer is an Impco 200
Converter is a Century Model H (rated at 130 HP) Is this too small?
Regulator(sorry about my terminology--forgetting the right words) is an Impco VFF30

It didn't ever reall run well. What has changed is the Erson cam, the head has been shaver .1", and the manifold has one of those fancy Australian gaskets. Seems to run a lot better at idle and while moving.

The rough running is when it initially has a load on. If I can get it rolling, it does fine after that.

I turned up the idle speed hoping that it would make it less likely to stall.

I've checked for vacuum leaks using the good old 10w4o method and have not found any.

Ignition system is good. Everything gets spark. HOWEVER, at idle, there is less of an effect when the #6 cylinder spark plug is pulled. The plug is fine and it is getting spark, though. Fuel distribution problem??

Valves have all been adjusted to .015" as per Erson

This really is the first time I've had the idle this smooth. It does sound really good w/o load.


ANother question--what is that adjustment under the fuel inlet for?


Thanks again,

Joe

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Joe Hoppe

71 D100 225 Super Six 727 AT on 2008 Crown Vic CopCar frame

64 Valiant Wagon 225 904 AT 3:23 8.75"

Some points:

• The Impco Model 200 is rated for 172 hp so the Century Model H is probably a bit undersized for it. Normally an Impco Model E or L (325 hp vaporization capability) is recommended. However, if it runs fine at full throttle, don't change it.
• A converter is another name for a propane regulator. It vaporizes the fuel and regulates the output pressure to -1.5" WC (sometimes -0.5"WC).
• The VFF30 is the fuel lock off. It is a safety device that shuts off the fuel when the engine is not running because it opens with vacuum. Mixer vacuum is recommended.
• If you didn't change anything with the propane system after the overhaul, the engine modifications seem to have made a slight improvement to your idle.
• Propane fuel mixtures have excellent (perfect?) distribution in non-EFI manifolds because there is no liquid fuel to fall out of the air stream.

When you ask about the adjustment under the fuel inlet, it sounds like the carburetor (mixer + throttle body = carburetor) may not have been properly adjusted. However, if you have the feedback gas valve in your mixer, the feedback controller should be controlling the fuel mixture at all times. Do you have the feedback gas valve in your mixer?

Impco's on-line information is limited to product information. Woodward (actually now NGVI NA) makes copies of Impco products and have some very good technical information in their carburetion product catalog (see pdf page 71). However, their old catalog had much better information in it and I've saved the LPG Carburetor Adjustment page, which shows the adjustments and is applicable to Impco carburetors as well. I also recommend that you get yourself a copy of Franz Hofmann's Diagnostic Guide.

About your observation with regard to #6 spark plug, this reminds me of a similar observation made by Tom Jennings on his closed-loop controller page. Where is the vacuum line from your VFF30 getting its vacuum?

Frank--

The vacuum is coming from the mixer, and is hooked up to a computer that adjusts air intake relative to an O2 sensor. I've been corresponding w/ Franz, and in fact got all my equipment from him.

I've got a kind of cobbled together set up that includes the mixer, and adapter from the mixer, and an adapter to the adapter that hooks up to the base plate from a Carter BBD. I went through and replaced gaskets, tightened things up, and now the engine runs smoother, but still stalls out under load.

I'm fairly certain that I'm dealing w/ a vacuum leak.

I was able to get a mixture change by spraying WD40 around the TOP of the mixer (didn't even think of trying that before). The diaphragm is a little ragged around the edges. I used some orange form-a-gasket stuff and am going to wait to see how it dries overnight before firing things up again.

This has been driving me crazy. Do you think a new diaphragm would be appropriate? The one I have now is not the black but the light tan--silicone?

Thanks again for all the help,

Joe

Anybody else out there running w/ sweet lady propane?

_________________
Joe Hoppe

71 D100 225 Super Six 727 AT on 2008 Crown Vic CopCar frame

64 Valiant Wagon 225 904 AT 3:23 8.75"

Normally, the diapragm inside the mixer lasts a long time before needing service. If you bought brand-new mixer and never experienced a backfire, your diaphragm (tan color indicates the better quality silicone) should still be good. You can check the condition of the diaphragm by removing the 5 screws in the cover. There is a spring between the cover and gas valve so be careful not to lose it.

If there are no holes or tears in the diaphragm, it is still good. If it's damaged, you can replace it with PN D1-16-2. Franz should be able to get a replacement if necessary.

Other than the top cover, there shouldn't be any places to leak vacuum on the mixer. Are all the cover screws tight? Are there any missing screws from the mixer body?

When you say it stalls out under load, is this just at very low (idling) speeds? Your earlier post seems to indicate that it runs well at higher RPMs.

A feedback system uses a gas valve that supplies a rich fuel mixture at all times. The feedback controller leans out this rich mixture to stoichiometric by applying a slight vacuum from the mixer body to the converter. The controller should have compensated for the WD40 if it was working properly. Is the controller in the right voltage range at idle?

Please check the following manual to make sure you've got it hooked up properly.
http://www.dualcurve.com/5952-frm23749.pdf

Hey Frank--

Feels like I'm banging my head against a wall. The gasket material around the diaphragm enabled the engine to run rich for a while, but then it went back to not very steady.

After working all afternoon, it currently will run between 3 and 8 volts w/o the computer connected. After connecting the computer, I can't get it to richen up enough to run right at all.

You're right about it running rough only when the initial load is put on. When I get it in gear, I can watch the voltage from the sensor go down as it stalls out.

It did run all right when I was able to get it rolling--over a week ago now. Now I can't even get it rolling.

I couldn't find any obvious problems with the diaphragm, but it is ragged around the edges.

Vacuum does from from the port on the mixer body below the diaphragm and above the throttle plates.

Are there any pieces on the regulator or converter that would be giving me a vaccum problem?

This really is bugging me in a big way.

Thanks,
Joe

_________________
Joe Hoppe

71 D100 225 Super Six 727 AT on 2008 Crown Vic CopCar frame

64 Valiant Wagon 225 904 AT 3:23 8.75"

The beauty of a propane system is that it is extremely simple in operation. The air-gas valve (gas valve for short) meters fuel in direct proportion to the air flow. Although there is no way to enrich the fuel mixture based on load with this type of carburetor, there is also no need for an accelerator pump circuit. The converter's only role is to provide propane vapor at a constant pressure. As long as the converter has sufficient water flow, it will work fine for many years.

The fuel mixture is primarily controlled by the shape of the gas valve. Vacuum inside the mixer created by airflow cause it to lift in direct proportion to the flow. When it reaches the top of its travel (the rated flow of the mixer), the fuel mixture will simply gradually become leaner with greater airflows. You can only change the overall fuel mixture by changing the gas valve.

These mixers have only two adjustments: power and idle (see LPG Carburetor Adjustment page). The power fuel mixture screw places a flow restriction in the propane supply to the mixer and has its maximum effect at full throttle. From what you have told me, the power mixture screw is adjusted close enough to give you good control with the feedback controller while cruising.

The idle mixture adjustment is really an Idle Air Bypass Adjustment. The total volume of air and fuel passing the closed throttle at idle is constant. The idle adjustment bypasses a portion of incoming air around the air-gas valve opening. As the idle adjustment is opened, the air-gas valve partially closes, thereby closing the gas metering valve and leaning the idle air-fuel mixture. To enrich the idle mixture, you must therefore turn this screw in.

The feedback controller can only make the fuel mixture leaner. If your idle mixture is very lean , it sounds like you need to make this fuel mixture richer. Can you turn in the idle mixture screw and tell us what happens?

Sorry if I didn't make myself clear, but I have been using the mixture adjustment screw to try to clear things up all along.

After running it for a while and getting to the point where it wouldn't run at all, I noticed a lot of condensation/freeze up on the connection between the converter and the shut-off valve. The gasket where the connector attaches to the body of the converter is cracked and torn up. I used a temporary solution of silicone sealant and it worked much better while the sealant held. I even got a ride around the block out of the deal.

So, it was a vacuum leak. Now I need to find a replacement gasket or an affordable new(ish) converter.

Any suggestions?

Thanks,
Joe

_________________
Joe Hoppe

71 D100 225 Super Six 727 AT on 2008 Crown Vic CopCar frame

64 Valiant Wagon 225 904 AT 3:23 8.75"

I'm not clear about how you have this hooked up. The converter should either be hard-piped to the mixer or connected with a vapor hose. The VFF30 fuel lock (or fuelock or lock-off) should either be close-coupled to the converter with a brass connector or connected with a short length of propane liquid hose.

There should not be any frost or condensation on any of the components. Inadequate water flow to the converter will cause the converter to frost up. Frost or condensation on the VFF30 (along with a rough-running engine) usually indicates a leaking diaphragm.

You say that you are getting frosting/condensation on the line between the converter and the VFF30. This seems to indicate that there is a fuel leak in this line and I don't understand why there is a gasket here but I'm not familiar with the Century converter either.

Can you take some photos of your fuel system, preferably with the frosting?

Anyway, it sounds as if some new parts are in order. You can use either a Model E or Model L converter but most people prefer the Model E. The Model L is a simpler design and is slightly lower in price. Franz should be able to fix you up with what you need. Try to keep the connection between the converter and mixer as short as possible for better cold-starting.

Frank--

Converter and the mixer are connected w/ about 2.5' of red heater hose.

Lock-off is connected to the converter with a short brass coupling. There is a plate the that coupling hooks up to on the Century unit. There is a rubber/neoprene gasket behind that. The section of the Century that I'm talking about has a small valve actuator inside. It pulls out of the converter's main body.

When you say leaking diaphragm, do you mean the one in the mixer or inside the VFF?

I hope the gasket explanation cleared things up.

Can I post photos to the board or do you have an address I should email to?

as ever,

Joe

_________________
Joe Hoppe

71 D100 225 Super Six 727 AT on 2008 Crown Vic CopCar frame

64 Valiant Wagon 225 904 AT 3:23 8.75"

When I first got my slant it had the same problem you are decribing, and after rebuilding my carb and alot of other things it ended up being the vavles to tight, after I ajusted the valves all was good. Maybe reajust themand see what happens

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All in a days work

There are diaphragms in the lockoff, converter, and mixer. The diaphragm I referred to earlier is in the VFF30 lockoff but I do not think this is your problem.

Are you referring to the VFF30 when you mention the shut-off valve? If you are noticing frosting/condensation on the converter where at the converter's fuel inlet, this could be a sign that the fuel is vaporizing with insufficient water flow to the converter.

When you replaced gaskets, did you rebuild the Century converter? If so, did you ensure that the water passages in the converter were clear?

There is a water supply and water return hose at the converter. Is the water return hose hot when idling? It should be as hot as the supply hose because very little heat is required to vaporize the very low amount of fuel required for idling.

The vapor side of the converter (where the fuel is supplied to the mixer) should be at a very slight vacuum under all conditions. If there is leak in the gasket in this area, it is possible for the idle mixture to be too lean. Did you try spraying WD40 in this area?

(I'm on vacation right now so I can only check the forum if our motel has an internet connection. You can try emailing your photos to me when I get back home next week. However, if you have your own web site, you can upload photos to a directory in your web space and provide a URL to it with the image button in the message editor. Click on the BBCode hyperlink under "Options" for more information.)

Just a follow up Joe's update on the first post in this topic.

Franz visited Joe last month and checked over his truck. Although there were a few minor issues with the fuel system, the cause of the poor low RPM performance was ignition related. Interestingly, Franz did not observe any frosting or condensation on the fuelock or converter.

Usually, when there is a drivability problem with a propane vehicle, the cause is almost always ignition related. Because propane is harder to ionize in the combustion chamber, this fuel places much higher demands on the ignition system.

Now that the fuel system is operating properly, there is no need for further fine-tuning of the mixer. Propane systems automatically compensate for altitute changes and plugged air filters . If you notice any misfires or rough running in the future, service the ignition system first and always use premium parts. Use platinum or iridium plugs (no need for fancy electrodes), mag-wire ignition wires (Aurora Electronics is an excellent choice), brass-contact cap & rotor, etc.

Is there any chance you can move the converter closer to the carburetor? This would certainly improve cold starting.