I bought a 1988 F150 extended cab 4X4 running a 302 with EFI with Automatic OD about a month ago. It has dual propane and gas and has been run mostly on propane I am told. I believe it because when I switch to gas it pings under the slightest load so I believe the timing has been dramatically advanced for propane.

After driving on gas for about half an hour it quits and won't restart with gas for a couple of days. Then it will run again on gas and ping until the same thing happens.

Someone cut the wires from what I believe is the O2 sensor in the exhaust on the passenger side although the sensor on the driver side is still wired in.

The air induction tubes at the rear of the engine were not hooked up because the valve at the back had a hole burned right through it (looks like it melted from resting against something).

Reconnected the system using a T because that valve is expensive ($132 from Ford).

Still have the same problem. Any suggestions?

Also, should I reset the timing to the original spec to run better on gas or use a timing controller like the MSD variable controller to adjust it whenever I switch fuel?

Any help would be appreciated.

 

Welcome to FTE!

Knowing absolutely nothing about propane, the only thing I can think of is to have a custom Diablo chip burnt. You can have 2 or three different programs on the one chip selectable by a switch.

One program for the propane, one for gas and the other for stock calibrations. What this will do is give you different ignition advance rates for a given program from what I understand.

I would call them and talk to them to find out because this is definitely a custom setup.

Here is Motorohaven's (This site's sponsor) contact us page, they can set you up with the chip you need. Check this page during business hours to find out the number, otherwise you will only be given the email option which I don't recommend in your case. You can see the link for the info on the chips at the left side on that page.

Good luck.

 

I will look into that. I think part of the issue is that the propane fuel delivery system is not affected by the truck's computer...

I wonder if something in the computer is affecting the fuel supply in the EFI when I am running gas, but that doesn't happen on propane because it is a different fuel delivery system and not subject to control by the computer...

Is that the primary purpose of the computer, to affect fuel mixture and delivery?

 

The computer adjusts both fuel delivery and timing from inputs of various sensors.

The sensor in the exhaust is the O2 sensor, which will only effect the A/F. If it isn't hooked up it will richen the A/F. This isn't the cause of your problem.

The fuel delivery itself is controlled by the fuel pump and pressure is maintained by the FPR on the fuel rail. The A/F ratio is controlled by the computer by adjusting the pulse width.

The next time you run it on gas check the fuel pressure at the rail.

What is your base timing set at? It should be 10* BTDC for gas.
Also what color are your injectors?

 

Thanks for the info. If only having one 02 sensor hooked up doesn't affect this what does it do - simply mean the fuel mixture will be richer when running gas?

I'm from the old carburetor days so where do I look to see what color the injectors are and (sorry to embarass myself here but..) what is the fuel rail and where will I find it?

I was going to check the timing with a standard timing light and the vacuum disconnected at the distributor - is there anything else I need to be aware of because of the computer when I do this?

Thanks for your help. I can rebuild a carburetor but the newer engine controls are foreign to me.

 

you might have an autotronics dual fuel computer, my dad has a 93 F350 w/ dual fuel and it has the autotronics computer, what it does, is allow the computer, while on propane, to think that it is still running the injectors, while in actual fact, the prop. computer, shuts off the injectors but still allows the engine to manage the rest of the controls like normal, if in fact that you do, and most likley you do, is to check all the wiring that goes over to the prop. computer, make sure that there is nothing frayed or rubbing, or broken.

 

This is how the injectors are mounted. The body is colored.

This is the rail. This mounts on top of the injectors on the lower manifold. The shrader valve on the drivers side of the rail is where you check fuel pressure with a gauge made specifically for this.

No reason to be embarassed, we've ALL been there! Especially us carb guys. I've still got a LOT to learn!

You may have a harder time learning because of your dual fuel system. Just don't give up! (The only experience I have with propane is on forklifts, but they have carbs!)

Use this link to help. It's just an online repair manual.

 

Thank you for all the useful info. I will check the fuel pressure now that I know where the rail is and find the injector color and re-post once I have done that,

The problem is getting more serious because I am now getting a 'check engine' light sometimes while driving and the truck does something else I find unusual. It idles fine but when I shift from forward to reverse it automatically stalls, even if I shift into neutral first and then into reverse. It start right away again and goes into reverse ok after that.

Honestly, I think sometimes that if I could find a carburetor and manifold and disconnect all the electronics, the loss in fuel economy would be made up for by the simplicity of keeping the thing tuned

 

Since you light came on, check the codes to see why.

 

Sorry it took me awhile to get around to taking everything apart. I needed to clean up the top half of the engine anyway so I have taken off the upper intake plenum, the fuel rail and the intake manifold to replace all the gaskets (just did the valve covers).

Checked the injectors (they are yellow by the way) and it looks like the hard plastic shell around the spray nozzle end has swollen on three of them, probably something to do with the heat from running propane? One of the plastic shells has small hairline cracks in it. Despite this they all look unclogged and clean. Its just that where the plastic appears enlarged I can't tell if it might be reducing the amount of spray the nozzle could release.

After finding out the jobber wants $202 per injector if I were to replace them ($1600 for an entire set???) I'm thinking I will reinstall everything with the new gaskets, hope that fixes my problem, and then...

I will find a 302 to rebuild from the ground up, of an older vintage (say '86) with a carburetor! A nice Edelbrock manifold and a Holley 670 CFM will only cost me $850 and at least I know how to work with them

If I go that route I am anticipating I will have to change the fuel pump in the gas tank (right now there is a low pressure pump in the tank and a high pressure pump assist inline) - and change the fuel lines as well.

I can use an older electronic ignition distributor or switch to an aftermarket product but I have no idea where to start with that. I don't want to rewire the entire truck but I suspect putting a carbureted engine into the vehicle won't allow me to continue with the existing electronic ignition. Anyone out there ever done this?

 

It would be easier to find a stock computer at a junkyard and remove the propane setup, to do the carb swap you will have to replace the fuel tanks or the pumps to low pressure ones. The EFI uses 35 pounds of pressure where the carb only uses 6-7.

 

See my reply to this post.

However I do agree it would be easier to stay injected in your case.

 

I think your big problem is timing. propane has more octane, and most people advance the timing a good deal to get better performance. put a light on it, and you'll probably find your problem. if the timing is to far advanced, it'll ping. and it'll probably overheat / vapor lock as well.

 

I have put it all back together and of course, the one thing that is missing is the EEC label for the engine. There is a label on one of the valve covers that says +10. Does that mean the timing is 10 BTC for this thing? Does anyone know what the stock timing setup was for an 88 302 with EFI the the distributor that has the 2 lead SPOUT?

 

Yes 10 deg BTDC.