Mucked with propane system

[Rattlenbang]

G'day all, I'm hoping to find some help figuring out a dog's breakfast of a mucked with propane system I have on a 1995 dodge E350 with 4.9 litre 6 cylinder. The van was equipped with Ford's infamous dual fuel propane system, but sometime in the past a PO removed the gas system including tank, added a second propane tank, disconnected the electronics and modules for the OEM system and basically turned it into a manual system. I doubt any of the OBDII system is even functioning. There are a ton of disconnected wires and hoses with this, and my original problem was starting on propane. Basically I had to dump some raw gas into the intake to get it fired and then it would carry on with the propane and run quite well. If it sat for a day again, it wouldn't start. Im sure it doesn't help that there are so many things disconnected. I once did a conversion myself on an older dodge and the vapourizer and mixer were very simple, with no extra hoses or plumbing, but this thing has extra fittings on the mixer and vapourizer that I don't understand and might be contributing to starting problems.

First of all there is a small 3/8 line from the vapourizer to the top of the mixer - at the fuel inlet fitting on the top of the 300A mixer where there's usually an access plug to the idle adjust, there's instead a small 90 elbow installed with a hose that goes to a 90 degree fitting fitting on the vapourizer. No idea what thats for.

Also there's an electric solenoid on the vapourizer with 3 vacuum connections, one that goes to the vapourizer housing right above the fuel outlet to the mixer, and the other 2 ends have been disconnected. No idea where this goes. Perhaps a cold start? There's no power to the solenoid.
When I press the primer button, I can smell propane leaking somewere. Maybe from that fitting above the fuel vapour outlet.

The propane inlet to the vapourizer is on a solenoid shutoff.


There are two vacuum ports below the mixer that are disconnected - no idea where they go or what they were connected to. I tried connecting one to that possibly cold start solenoid, but the instant I do the propane to the mixer shuts off.

I don't think it helps that the run between the mixer and the engine is like 3 feet, and another 3 feet between the mixer and vapourizer. That's a long way to have to pull propane in while cranking.

Honestly, I'd like to get rid of the extra plumbing and simplify if I could. My dodge ran fine without all this extra stuff.

To make things more complicated, I pulled apart the mixer to make sure there were no problems with the diaphragm and clean it. Now I think I have a new vacuum leak because now it won't idle and runs rougher.

Final question: I believe I know how this system works, in principle. Vacuum pulls up the mixer diaphragm that opens the air inlet passages and opens the propane inlet valve. But for the life of me I can't see where or how vacuum is ported up there?

Engine has had a tune up otherwise, ignition is good.

I know it's a lot but I hope someone can help me with this. I've attached a drawing to help show the system I have to make it easier to understand.

[C3H8]

OOOOOHHHHH Boy! This may take a few back and forth posts to figure out. First, a 4.9 inline 6 in a Dodge E350 with a Ford propane system????
I'm going to assume you meant a Ford E350 as the dodges are B350. A 4.9L inline 6 is a Ford engine normally. Your description of the 300 distance from the TB would indicate it is the 4.9 with a dual TB intake. I am going to assume you have an IMPCO model E or L.
Any electronics attached to the propane system?
Electric or vacuum fuel lock off?

Since you say you would like to return to basics I am going to suggest this.

Remove all the hoses from the mixer except the 1 inch vapour hose. Plug any openings. Recheck your mixer and see if any of the through screws that hold the body together came loose when you installed the air cleaner nuts. Remove that three port solenoid and hoses and plug any openings left. Leave the vent opening on the vapourizer open to atmosphere. If it has a vacuum VFF30 lock off attach the vacuum line for the lock off to ported or manifold vacuum. Doesn't really matter in the short term. See if you can get it to run this way.

The extra hoses almost sound like an anti backfire system 90 Fords were notorious for back firing on startup. Many companies tried to stop this with some wild innovations. I find it hard to believe this thing even ran with a hose connecting the vapourizer vent to the vapour inlet fitting.

So lets get some communication started, some pictures if possible and any additional information on any electronics involved so we can get it figured out.

Since this was an injected engine your going to have to set the idle speed manually as I have to assume the idle air control motor no longer works. Correct me if I'm wrong.

[Rattlenbang]

Youre right, Ford E350. Dual fuel TB intake. IMPCO model 300A I believe (I'll double check today). The only "electronics" still connected is 12v to the propane shutoff valve, that I had to wire. No power to the other solenoid that isn't connected.

So to start, disconnect everything and plug? Good, I like the sound of that.

I'm totally unfamiliar with Ford's system. There is what appears to be a motor on the throttle body but I don't know what it's for.

In addition to the 6 feet of hose, there's also 2 feet of the stock Ford intake. That's a crazy distance to have to pull vapour.

[Rattlenbang]

So I went through everything, double checked all my connections, hoses, disconnected all the smaller hoses and plugged them. I dismantled the mixer again and doubled checked everything. Not much going on there. Tightened everything up. Primed. The good news is I was able to start the van on propane this time. The bad news is it won't idle and if it stalls it takes a huge amount of cranking to get it to start again. Eventually I killed my battery. It seems to run fine but absolutely no idle. Very frustrating as it was idling before I took the mixer apart and cleaned everything. I'm absolutely certain that there's nothing wrong with the mixer, or least nothing new that I've done. I've checked all vapour supply hoses for vacuum leaks and nothing.
The restart problem is very strange as there's tons of fuel. Even if you prime heavily or use ether, it takes forever to restart, even when warm. How sensitive is the system to low fuel levels? It roars well enough when you floor it. I've got like 25 litres of fuel in it.

[Rattlenbang]

Another couple of things. It's a model E vapourizer. What I discovered was that if I hold the primer button down and manually lift open the mixer, I can get the van to idle quite nicely. As soon as I let go of either the mixer or the primer it will stall. Revving the engine still works if I don't touch anything, but will stall at idle. I connected a home-made manometer to the vapourizer outlet side and it didn't move at all while cranking with the throttle wide open.

I also discovered that if I hold the primer down and hold the mixer open it will start right away after stalling. If I don't, it won't start. It seems like there's just not enough vacuum to pull fuel through or something.

I don't know if this is related but while cranking the engine I can clearly hear a Pfft Pfft Pfft coming from somewhere near the rear of the engine. It almost sounds like a loose spark plug, but I double checked those (just replaced them) and it's not coming from there. I can't tell if its a cyclical vacuum or pressure. There's a whole whack of vacuum plumbing to a bunch of solenoids and such but I tried disconnecting everything but the noise continued. Don't know if I'm getting sidetracked.

[C3H8]

OK. At this point I have to ask. Do you know how to adjust the mixtures on a 300. They are all the same no matter the model of 300. There are two adjustments. The external one on the side of the vapour inlet. Set it to the middle mark. You will need assistance with the next part. The gas valve adjustment is under the hex cap on top of the vapour inlet. Adjustment is done using a flat bladed screw driver. Have a friend keep the engine running while you adjust the mixer. Have him/her hold the throttle wide down just enough to keep the engine running. It sounds like you need to open the gas adjustment more from your description. Without pressing down on the screw driver open the adjustment until the engine smooth's out. Have the assistor release the throttle e little until the engine seems like it is going to stall. Adjust the screw a little more to smooth the engine. keep repeating the process until the engine will continue to run a idle. Once idling adjust the screw to the best idle. Make small adjustments as this is a very sensitive system. Also don't put any weight on the screw driver as it will change the setting since your adjusting the actual gas valve. After that look for the pufft at the rear of the engine. Could very well be an exhaust leak or similar.

[Rattlenbang]

We did try adjusting it, but it was my buddy on the screwdriver while i was keeping it running and he's a bit ham-fisted so I'll try it again. But here's the thing: It idled fine until I removed the mixer and replaced plugs, rotor and distributor cap. The mixer is such a simple device, with just 3 hoses and a diaphragm, and yet after I removed it, cleaned it, and put it back together it wouldn't idle. What could I have possibly done that would make it not idle? I've made damn sure there are no vacuum leaks from any of the hoses to and from the mixer.

[C3H8]

Do you have a schematic of the breakdown to be sure it has been assembled properly. I can send you one through a PM.
If your buddy is a little heavy handed you may want to try again. The trick is to set the screwdriver in place and turn it fingers from the side, not pressing down. When you turn it one of two things should happen.. The engine will pick up a little or slow down. You want it to be picking up all the time. There are differences in these mixers sometimes. Also rebuilding them and cleaning them will frequently cause idle and part throttle operation as getting the gas valve back in the identical position is almost impossible. As stated earlier even a minor adjustment has a big impact on 300's . Being 1/2 turn out will make it a non starter or no idle unit.

[C3H8]

Where are you by the way? Your responses are pretty quick.

[Rattlenbang]

Bingo. That was it. Amazing how precise it is; the screw can turn like 20 times top to bottom, and yet the engine will only idle on a single 1/4 turn section! I'm amazed I even found it. It runs incredibly sweet now, especially for an engine with 360,000 km on it. Those Ford 6s deserve their reputation. The only thing that's a little off is if you rev it, it drops back down to idle very slowly, taking like a good 10 or 15 secs. Another adjustment?

Thanks for your help BTW, I hugely appreciate it. I was really starting to chase my tail with this one. We live in Victoria, BC Canada.

[C3H8]

Figured you must have been up here or in the states. Glad to see it is resolved. Returning to a base idle is fairly normal on vehicles that were originally gasoline fuel injected. By the way it is highly unlikely the vehicle was manufactured as a propane unit. It was more likely converted at either a Ford dealer, an ICG Propane sponsored dealer or a Superior Propane sponsored dealer. I can't be 100% sure but I don't believe Ford was making factory propane units in E350's in the 90's.

Your right, the Ford 6 is a very hardy engine. Now to your return to idle delay.

The newer 1984 and up Fords have what is called an IAC (Idle air control) motor. This motor changes the idle speed by allowing air and fuel to bypass the throttle plates based on several inputs. Examples of this would be the AC, Power steering pressure when the wheel is turned, electrical loads such as headlights. When these are turned on a little extra fuel is sent around the throttle plates to compensate for the load. The IAC also opens to a pre-set position at any RPM over about 1200 RPM. When the throttle is released the motor keeps the engine at a higher RPM during vehicle deceleration to make sure engine vacuum does not go too high stressing intakes seals and to make sure the engine does not stall like carbureted vehicles were sometimes prone to do. The motor slowly slows the engine down to a computer controlled RPM as the vehicle slows or the throttle is released if the RPM is increased in park or neutral. It is an important function. There is a procedure to set what's called a "minimum idle speed" on this set up. The IAC is a stepper motor design on many vehicles or in Fords case a similar idea (shuttle valve in their case I believe). The IAC is supposed to be for trimming only. On all vehicles the throttle plates are supposed to be set at what is called a minimum or base idle(approximately 50 to 100 RPM below the computer controlled idle speed) in case the stepper motor fails. You could check a Ford manual for the exact procedure for setting minimum idle but they probably require a scanner to do it. Your throttle plates may be set open more then normal if the vehicle was experiencing idle issues by a previous owner.

I can offer a simple method to check this. Let your idle stabilize completely. Turn off all electrical loads including the AC/heater system. Check your idle speed on the tach and note it which is likely around 650 to 750 RPM.
Locate the manual speed adjustment screw on the throttle body linkage. It may be covered with a steel cap. If it is then it has not been played with since the engine left the factory. Turn the screw in and the IAC will compensate by closing to slow the RPM down. When the motor is closed as far as it can go the RPM will begin to increase. At this point turn the screw back out until the engine settles at its factory rated RPM. Place a mark on the screw and turn it out an additional turn so the IAC has full control. If you unplug the IAC electrical connection at this point the RPM will drop 50 to 100 RPM under the normal idle speed but the engine will or should not stall.

[Rattlenbang]

My bad - it's an E250. And it has the electrical control module for the propane, not just a basic analogue system, which is why I figured it was a Ford conversion.

Wow, that's a crazy complicated idle system. The thing with this beast is that I don't think the ECU is even operational. The propane electronic fuel system is completely disconnected and I suspect the electronics that run the injection system is disconnected. No check engine light at all. I haven't looked closely but I suspect they have hard wired the ignition module to run without any inputs aside from the distributor. Like rolling back the clock technology wise about 20 years. But maybe I'm wrong since the rpms at idle are so slow to decrease, as if that motor is still functioning. I should unplug it and see if it changes.
A lot of vehicles simply can't run without the ECU, but this propane system seems to allow it in this case. No engine sensors or injectors required.

[C3H8]

If it was a Ford product it would say so on the module. Unlikely as Ford would just place the module in the same location as they put all their ECU's which would be behind the right hand kick panel inside the vehicle right by the passengers feet. That ECU is probably still there and receiving enough information to operate the IAC, possibly the EGR if it is still operational and also the ignition timing although that could have been downgraded to an older system. Just out of curiosity are there any identifiers on the module at all. Manufacturers name, model number or part number?

As for the check engine light, does it even work? The light should be visible as soon as the key is cycled on and also momentarily during cranking. It's possible the bulb is burnt out or a previous owner may have disconnected it.

[Rattlenbang]

No check engine light. Of course the bulb could be toast.
Haven't had a chance to look at the module yet -no rest for the wicked. But I did have a less than stellar experience driving the van almost 500 km today. Just under 10 mpg (imp), with an empty van. Under gas, it's rated at at least 18mpg hwy, and giving it a 20% drop for propane, I should get around 14-15, so to burn that much fuel seems crazy (76 litres over 255km). Engine runs very well. There were some very steep mountainous sections that had the pedal to the floor and only making 80-90km and perhaps those sections hammered the fuel economy. Only a few kilometres of that but I know it has an impact.

[C3H8]

That's why I'm curious about the module. The picture you drew hinted that the module might be a feedback module. If that is the case a special gas valve will have been installed that is quite rich in the cruise section to accommodate the fuel control module. Without the module connected to control it the mixtures would be very rich. This could be corrected by installing the non feedback gas valve or we can work through reconnecting the module if it is still functioning, but to determine this I need any names or numbers on it. The second part is to determine if the timing is working perfectly. The 300 CI Fords can take a pretty aggressive curve with their long stroke. The long stroke is also detrimental to economy. The 4.9 has a checkered history mileage wise on both gas and propane. Claims have been made of anywhere from 14 to 22 MPG on gasoline in various models of pick ups and vans. 18 is not way out there for an E150 but on average these E250 and E350 ran more in the 14 to 16 neighborhood.

Get me the module info and we'll work through it from there.