Hi folks,

I've got questions about my 87 F150 4.9 litre dual fuel, running on propane. First of all I'm having some problems with my RPM. Every now and then when I depress the clutch, while going down hill my RPM drops down to about 300 and then jumps back up to 700. I have had the engine analyzed and there was nothing found. But before that was done I replaced the spark plugs, wires, rotor,cap and 02 sensor. It improved the rough idle but didn't alleviate the RPM problem completely.

So here we go with the questions. First, could it be the (old) Vialle propane system thats causing the problem and if so why is it intermittent. A propane certified mechanic previously informed me that the old system on my truck doesn't usually malfunction,so I am thinking since it's intermittent that it's and electrical problem which didn't show up on the analyzer. This leads to my second question. I took a look under the dash on the drivers side and I found the kill switch on the fire wall and another switch just to the rear of the clutch arm. What is the second switch for and should the kill switch and this clutch switch have springs in them so they have some resistance when you push on them? BTW the kill switch doesn't kill the engine on propane so I don't know if thats normal or not. Could it also be that the fuel pump in my tank doesn't work so I have been running propane for the past year and a half? And finally........has anyone else experienced this type of RPM drop either on gas or propane before and if so how did you fix it.

Sorry for being long winded but this is driving me nuts.

Thanks in advance
F.O.G.

 

My 89 with a 302 5-speed runningon gas has a similiar problem. When I put the a/c on, and step on the clutch, the motor just about stalls. I asked around and no one seemed to be able to help me with this problem, all I did was turn the a/c off when Im switching gears lots.

 

Isn't there some type of sensor that idles up the engine when the AC turns on?

 

the iac does that job.

 

The IAC can be good, but the pasage in the intake gets clogged. Check it when you check the IAC.

 

I guess changing the IAC couldnt hurt either way.

 

Thanks for the info guys but I don't have air condtioning and according to the Autozone component locator I don't have an IAC valve or an Idle speed actuator. So I guess I'm back to square one. I'll take the truck into the propane guys and see if the problem is in propane mixer. $$$$$$$$$ if it is.

Still I'd like to know what the switch behind the clutch is and would appreciate any other ideas anyone out there may have.

Thanks
F.O.G.

 

I could be wrong but that switch is probably a clutch safety switch. IT wont allow the the starter to engage unless the clutch is pushed in.

 

Yea, that is the clutch saftey switch.

It could be causeing a short, or some sorta electrical problem when the clutch is pressed.

There should be 2 leads that you can easily pull off when you are back there.
I think.. wait thats chevy.

Anyways, If you can disable it while you are running and press the clutch to see what happens. Then let us know results.

 

Thanks guys Ill take a look and let you know what gives. BTW I got some good news, I found a place that has parts for the Vialle mixer so if thats the problem it shouldn't be to expensive to fix it. But the propane guy suggested cleaning the throttle body first. It seems that even with propane they get gummed up.

Thanks
F.O.G.