Dies out when in traffic

Propane, Butane, LPG, GPL, C3H8, C4H10
Usamestizo13
Posts: 8
Joined: Fri Jun 17, 2022 4:38 pm

Dies out when in traffic

Post by Usamestizo13 »

Greetings, I just aquired a 1970 Chevy C30 (1 ton pick up ) that runs on propane.It was ordered from the factory that way in 1970. The engine is a 350.The system consists of all Impco components i.e. model E converter, vff 30 lock-off, 225 carburator.The truck starts,idles, accelerates, perfect until i have to sit in traffic for extended periods of time like a light or a drive thru. This happens at full running temperature and only in traffic. Will run perfect all day on open highway.It starts with very slight misses, and gets progressively worse till its dies.If I immediately try to re start after it dies, it just cranks without even a cough.i confirmed there was spark.The crazy part of it is that if i sit there for at least a minute after it dies, it starts right up and idles perfect, until i get into traffic again does same thing but starts right back up everytime if i wait for at least a minute to pass.The higher running temps in traffic is affecting either the lockoff or converter that is restricting fuel flow. I put new rebuild kits in all three components.The lockoff was real dirty at the filter and the converter was pretty funcky too. Looked like none had ever been serviced. Truck odometer reads 49 k and honestly it runs like a low milage truck when not sitting in traffic. Also changed ignition to hei but did not solve problem . Any ideas ? Thanks
Attachments
A379E6DE-7E21-4FDC-A6E4-DD7F8D8A1135.jpeg
07BED076-24A4-4D70-A831-A54E0EFC2804.jpeg
4A424EB6-3346-42EF-8685-E1014A2AA708.jpeg
628A383E-E532-445A-AB9F-10E2BF8A829E.jpeg
255D0CA1-1630-4113-95BA-5F87BED695FC.jpeg

Tom68
Posts: 64
Joined: Mon Jun 18, 2018 2:46 am
Location: Australia

Re: Dies out when in traffic

Post by Tom68 »

Does it actually run hot in traffic ?
Or do you think it's just heat soak into a component with less airflow ?

You've checked for spark when it won't start, have you pressed the convertor button to see if gas is flowing at least to the convertor ?

Usamestizo13
Posts: 8
Joined: Fri Jun 17, 2022 4:38 pm

Re: Dies out when in traffic

Post by Usamestizo13 »

The temperature in traffic is still well within the normal operating range although warmer than when moving.yes i did try try electric and manual enrichers,both verifiably functional, no go. Yes thats my thinking that the added heat from sitting in traffic is causing the malfunction.Trying to figure out where the malfunction is.Thinking has to be either the vff lock off or the converter.i don’t think the carburetor has a valve that stops fuel flow. Leaning towards the lock-off. Was hoping someone here would have had a similar experience and found a solution.

Tom68
Posts: 64
Joined: Mon Jun 18, 2018 2:46 am
Location: Australia

Re: Dies out when in traffic

Post by Tom68 »

Usamestizo13 wrote:
Fri Jun 17, 2022 10:03 pm
The temperature in traffic is still well within the normal operating range although warmer than when moving.yes i did try try electric and manual enrichers,both verifiably functional, no go. Yes thats my thinking that the added heat from sitting in traffic is causing the malfunction.Trying to figure out where the malfunction is.Thinking has to be either the vff lock off or the converter.i don’t think the carburetor has a valve that stops fuel flow. Leaning towards the lock-off. Was hoping someone here would have had a similar experience and found a solution.
I wonder if the engine vac is high enough to keep things functioning when the problem occurs, a higher idle speed could help the diagnosis.

Usamestizo13
Posts: 8
Joined: Fri Jun 17, 2022 4:38 pm

Re: Dies out when in traffic

Post by Usamestizo13 »

Funny younsay that because when i bought it ,the previous owner had it idling at 1100 rpm. I brought it down to 700rpm.

C3H8
Posts: 1103
Joined: Fri Sep 09, 2005 11:23 pm
Location: Winnipeg, Canada

Re: Dies out when in traffic

Post by C3H8 »

These old 350's were bulletproof. Although the problem you describe appears to be fuel I don't think it is. The GM Hei has an ignition module in the distributor. They were notorious for causing stalling and poor starting when hot. The module is cheap and easy to replace. When it gets hot it may still be firing the plugs but at the wrong time or intermittently. The country farm boy GM owners back then all carried a spare ignition module with them as they could fail at any time. The best way to find out if this is the issue is to just change it. Even if I am wrong you can keep the old one in the glove box as a spare.

If it doesn't solve the problem you need to do a systematic diagnosis which unfortunately will have to happen quickly and at the time the problem occurs. As fast as you can you will have to visually look for any frosting along the fuel lines. Then crack the line where it enters the VFF30. Is there liquid there? If not the problem is upstream towards the tank. Secondly, I was going to say remove the vapour hose but I see your hard piped in. So instead, take off the air cleaner and the adaptor on top of the mixer. Place a flat blade screwdriver in the mixer air inlet and gently lift the gas valve. At the same time push the model E primer and some gas should immediately flow into the mixer. If there is no flow, you likely have a primary seat problem in the model E. It's not a vacuum problem at the VFF30 as it only takes inches of water column to open the lockoff. The main issue here is you have a very limited time to check out the issue because you say it starts after a minute or two of sitting.

Bottom line. I really don't think you have a fuel problem. I would lean strongly toward an ignition problem. Heat is much more likely to affect the ignition components then the vapourizer or lock off.

Tom68
Posts: 64
Joined: Mon Jun 18, 2018 2:46 am
Location: Australia

Re: Dies out when in traffic

Post by Tom68 »

C3H8 wrote:
Sat Jun 18, 2022 12:03 am
These old 350's were bulletproof. Although the problem you describe appears to be fuel I don't think it is. The GM Hei has an ignition module in the distributor. They were notorious for causing stalling and poor starting when hot. The module is cheap and easy to replace. When it gets hot it may still be firing the plugs but at the wrong time or intermittently. The country farm boy GM owners back then all carried a spare ignition module with them as they could fail at any time. The best way to find out if this is the issue is to just change it. Even if I am wrong you can keep the old one in the glove box as a spare.

If it doesn't solve the problem you need to do a systematic diagnosis which unfortunately will have to happen quickly and at the time the problem occurs. As fast as you can you will have to visually look for any frosting along the fuel lines. Then crack the line where it enters the VFF30. Is there liquid there? If not the problem is upstream towards the tank. Secondly, I was going to say remove the vapour hose but I see your hard piped in. So instead, take off the air cleaner and the adaptor on top of the mixer. Place a flat blade screwdriver in the mixer air inlet and gently lift the gas valve. At the same time push the model E primer and some gas should immediately flow into the mixer. If there is no flow, you likely have a primary seat problem in the model E. It's not a vacuum problem at the VFF30 as it only takes inches of water column to open the lockoff. The main issue here is you have a very limited time to check out the issue because you say it starts after a minute or two of sitting.

Bottom line. I really don't think you have a fuel problem. I would lean strongly toward an ignition problem. Heat is much more likely to affect the ignition components then the vapourizer or lock off.
He changed to HEI. Problem stayed. Inline resistor ?

Usamestizo13
Posts: 8
Joined: Fri Jun 17, 2022 4:38 pm

Re: Dies out when in traffic

Post by Usamestizo13 »

I initially thought it was ignition also being it had the old inline resistor system. When i went with the hei ,it woke the engine up considerably especially at the higher rpms. I agree that it is going to be tricky to trouble shoot right as it stalls. I am going to try to get it to stall in my driveway. Thanks for the help men

C3H8
Posts: 1103
Joined: Fri Sep 09, 2005 11:23 pm
Location: Winnipeg, Canada

Re: Dies out when in traffic

Post by C3H8 »

Yes, he went HEI, but new or used. Most just go to the scrapyard and get one. They use the old module and don't think about it. If the unit is new OK. If used changing the module is cheap and ensures there is no problem with it. Resistor. Yep, maybe. A new 12 volt line has to be run or the resistor bypassed. Sounds like that has been considered and done already.

Usamestizo13
Posts: 8
Joined: Fri Jun 17, 2022 4:38 pm

Re: Dies out when in traffic

Post by Usamestizo13 »

Had the original converted to hei. All new electronic components. I think if it were ignition related it would not restart like clockwork after no more than a minute. Its like a diaphragm that gets stuck momentarily and slowly releases with engine off. Also thinking it could be propane is not staying in liquid form before it enters the converter. Somewhere between the tank and the converter it is absorbing enough heat to change from liquid to vapor.Just a theory but also one that might explain why it restarts after the wait time. When the engine dies, the liquid now has enough time to cool the components that are causing the premature vaporization. Once cooled, stays liquid all the way to converter as it should.This could be the metal 1/4 “ pipe that connects the converter to the lockoff,the metal housing of the lockoff itself or less likely,the hose hose from the tank to the lockoff where it enters the engine compartment. Cant come up with any other ideas at the moment. All comments on my theory's welcome!

Tom68
Posts: 64
Joined: Mon Jun 18, 2018 2:46 am
Location: Australia

Re: Dies out when in traffic

Post by Tom68 »

Usamestizo13 wrote:
Sat Jun 25, 2022 8:00 pm
Had the original converted to hei. All new electronic components. I think if it were ignition related it would not restart like clockwork after no more than a minute. Its like a diaphragm that gets stuck momentarily and slowly releases with engine off. Also thinking it could be propane is not staying in liquid form before it enters the converter. Somewhere between the tank and the converter it is absorbing enough heat to change from liquid to vapor.Just a theory but also one that might explain why it restarts after the wait time. When the engine dies, the liquid now has enough time to cool the components that are causing the premature vaporization. Once cooled, stays liquid all the way to converter as it should.This could be the metal 1/4 “ pipe that connects the converter to the lockoff,the metal housing of the lockoff itself or less likely,the hose hose from the tank to the lockoff where it enters the engine compartment. Cant come up with any other ideas at the moment. All comments on my theory's welcome!
Electronic faults do cool down and then work, lost a carbon bush in a HEI, it would overheat and quit, cool down, go again, took a few stops to get home.

But yer, I think you have a Gas or engine related problem.

C3H8
Posts: 1103
Joined: Fri Sep 09, 2005 11:23 pm
Location: Winnipeg, Canada

Re: Dies out when in traffic

Post by C3H8 »

I understand your rational on the propane but it is easy to see if you have a liquid to vapour issue prior to the regulator. Propane is like a refrigerant. If it vapourizes in the line or lock off before it gets into the vapourizer there will be frost all over the area. That is the point of the problem if it exists. Secondly it will take at least several minutes for the frost to melt and allow the propane to flow again. In addition this type of problem would manifest itself by a slow loss of power until the vehicle stalls or will not have enough power to keep the vehicle moving. Easy to tell because immediately after the vehicle loses power or stalls quickly inspect the fuel lock off, fuel lines and the outlet valve of the tank for a heavy frost build up. If you find frost anywhere that is the source of a blockage causing the liquid to vapourize before it reaches the vapourizer.

Even a vaporizer can freeze but that causes the engine to flood and become hard to start. A frosty vapourizer also usually means a low coolant level or poor coolant flow through the vapourizer. By the way the fitting connecting the model E and the VFF30 lock off is more then large enough.
    At the tank outlet valve it would indicate a faulty valve or a weak excess flow valve.
      Along the line it could indicate a collapsed line internally
        At the lock off it could indicate a faulty seat although it could also indicate a plugged filter. In this case the complete lock off usually frosts over.
        • Lastly, as soon as the engine stalls jump out and push the primer button on the vapourizer. If there is a blockage somewhere the button will easily depress right to the surface of the vapourizer indicating a lack of fuel. If fuel is still available the button will push back against your finger and become hard to press.
        Repair kits for the lock off and vapourizer are fairly cheap and considering you may not know the history it would be wise to rebuild them. You may just have a primary seat problem in the model E. If the seat has separated it could be causing this type of problem.

        I still lean towards some kind of electrical problem but you appear to have addressed the major areas. You might try looking for problems between the ignition switch and the distributor. One of the failures of diagnosing propane issues is just assuming propane is the problem. On gasoline mechanics seldom look at the carburetor because they can see if gas is entering the carburetor just by looking down the throat. You can't see propane so it is automatically thought tp be the issue.

        Usamestizo13
        Posts: 8
        Joined: Fri Jun 17, 2022 4:38 pm

        Re: Dies out when in traffic

        Post by Usamestizo13 »

        All true words sir! Have a extra distributor. Will put points back on it and give it a try. Will report back with results. Really like this truck. I like to brag about being able to drive a cool old truck with a V8 and only pay 3.50 a gallon for fuel!😆

        Usamestizo13
        Posts: 8
        Joined: Fri Jun 17, 2022 4:38 pm

        Re: Dies out when in traffic

        Post by Usamestizo13 »

        SUCESS SUCESS SUCESS! C3H8 you were 100% on the money! Thank you so much to you and others that tried to help. it was the newly converted electronic ignition.Faulty from the get go. I replaced it with another electronic iggy. I took it for a good 20 min drive and got her up to temperature then let her idle for 30 minutes. Did not skip a beat.When I shut her down, she fired right back up several times within 1/2 a revolution. This truck is now a joy to drive, idles great , accelerates great, and most importantly, feels dependable. Thanks again men!

        Tom68
        Posts: 64
        Joined: Mon Jun 18, 2018 2:46 am
        Location: Australia

        Re: Dies out when in traffic

        Post by Tom68 »

        Usamestizo13 wrote:
        Fri Jul 01, 2022 12:10 am
        SUCESS SUCESS SUCESS! C3H8 you were 100% on the money! Thank you so much to you and others that tried to help. it was the newly converted electronic ignition.Faulty from the get go. I replaced it with another electronic iggy. I took it for a good 20 min drive and got her up to temperature then let her idle for 30 minutes. Did not skip a beat.When I shut her down, she fired right back up several times within 1/2 a revolution. This truck is now a joy to drive, idles great , accelerates great, and most importantly, feels dependable. Thanks again men!
        Great result, C3H8 knows his stuff and read the situation perfectly.

        Loving my LP Gas car mid year 2022 Oztraylia, 89.9 c per liter, ULP up around $2.10 currently.

        Post Reply