Strong gas odor

[Steve Doc]

I purchased a 1986 C10 Silverado in May. Since then the choke light has stayed on while engine runs and runs great. Has a 305 0.300 over and mild cam. Quadrajet carb with an electric choke and engine is very clean. Oil pressure is at 60. For the last week or so I've noticed a strong gas odor even walking up to to it within 10 feet. Inside cab as well. Is this odor choke related or possibly an oil pressure switch? Or maybe another issue I'm not aware of? Any help is very appreciated. Thanks.

 

[DanMcG]

Does it still have the fuel vapor canister connected, maybe a cracked or broken line somewhere leaking gas vapor.

 

[bucket]

Could also be a rusted fuel line or tank.

 

[77 K20]

Could be the seal failed for the sending unit. This can be seen/smelt between the cab and the bed.

 

[Handy Andy]

no fuel on the ground? I've actually had both of my tanks fail in the last year.... replaced the drivers side when it started pouring gas on the ground, and now 10 months later the passenger side is dumping fuel out. gotta find time to get it swapped out now.

 

[Steve Doc]

No visible fuel leaks. Vapor can and all other emissions disconnected by previous owner. Crawled under truck searching for worn or cracked lines, tanks, and leaks. All good. Seal for sending unit is going to be looked at asap, good tip, thanks. But still very frustrated with choke light constantly on.

 

[Charlie]

 

[Steve Doc]

Thanks for the welcome Charlie.

 

[PrairieDrifter]

No visible fuel leaks. Vapor can and all other emissions disconnected by previous owner. Crawled under truck searching for worn or cracked lines, tanks, and leaks. All good. Seal for sending unit is going to be looked at asap, good tip, thanks. But still very frustrated with choke light constantly on.

That’s your problem. You need that canister for it to not be smelly, I just ran my vapor line straight to the air cleaner instead of having a can, and it works decent. Look for a hard line in the engine bay, it comes up by the power steering lines from the frame, that should be the vapor line if it’s still there.

 

[Steve Doc]

Will do as soon as I get home from work. Worked on steering column yesterday and found that the odor is definitely engine bay related. Thanks.

 

[Rusty Nail]

Doesn't the choke light have some connection to oil pressure @ 60 psi ?!

I'd axe @chengny .

 

[Steve Doc]

I believe it does, but the choke light stays on at any psi. Would an electric choke with a bad ground cause this?

 

[chengny]

I believe it does, but the choke light stays on at any psi. Would an electric choke with a bad ground cause this?

Yes, a poor/non-existent ground at the choke heater coil will prevent the CHOKE warning lamp from being extinguished:

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On most vehicles, an electric assist choke is incorporated onto the carburetor to aid in reducing the emissions of hydrocarbons (HC) and carbon monoxide (CO) during starting and warm-up (choke-on) period. The electric assist choke is designed to give a more rapid choke opening at temperatures of approximately 60-65°F., or greater and a slower choke opening at temperatures of approximately 60-65°F., or below. The electric assist choke system does not change any carburetor service procedures and cannot be adjusted. If the system is out of calibration, the heater control switch and/or choke unit must be replaced.
The main components of the electric assist choke system, Fig. 39, consist of a thermostatic coil, ceramic resistor, cover, bi-metal snap disc and contact spring. The electric actuated ceramic resistor heats the thermostatic coil, gradually relaxing coil tension and allowing the choke valve to open.

At air temperatures below 50°F., electric current applied to the small section of the ceramic resistor, allows slow opening of the choke valve for good engine warm-up. As the small section of the ceramic resistor continues to heat, a bi-metal disc causes the spring loaded contact to close and apply electric current to the large section of the ceramic resistor which increases the heat flow to the thermostatic coil for more rapid opening of the choke valve.

At air temperatures between 50-70°F., electric current applied to the small section, or both the small and large sections of the ceramic resistor, will produce the amount of heat required to control the choke valve position for good engine operation in these temperature ranges.

At air temperatures above 70°F., electric current applied to the small section of the ceramic resistor and through the spring contact to the large section of the ceramic resistor, provides rapid heating of the thermostatic coil for quicker choke valve opening when leaner air-fuel mixtures are required at warmer temperatures.

Diagnosis & Testing
Possible conditions for the electric choke not operating properly are listed as follows (use a voltmeter to check oil pressure and choke coil circuits):

1. Low or no engine oil pressure.
2. Faulty oil pressure switch.
3. No current to oil pressure switch due to:

• 1. Burned out fuse.
  2. Broken wire to oil pressure switch.

1. No current between choke and oil pressure switch due to:

• 1. Broken lead wire.
  2. Wire terminal not properly secured on coil terminal.
  3. Faulty ground circuit between choke assembly and housing grounding plate.

1. Faulty choke coil assembly.

If it is determined that the choke coil assembly is inoperative, the following test must be made:

1. Remove choke coil from carburetor. After removal of choke coil, allow coil to cool to room temperature.
2. Connect a ``jumper'' wire between positive battery terminal and choke coil terminal assembly. Connect a second ``jumper'' wire between negative battery terminal and choke coil assembly grounding plate.
3. The tang on the choke coil should rotate 45°in 54-90 seconds.
4. If choke coil does not rotate or exceeds the 54-90 second time limit, replace choke coil.
5. If coil is within specification, check steps 1 thru 5 for possible cause.

How the choke heater controls the CHOKE warning light on the dash:

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[Steve Doc]

Thank you chengny for that detailed info. This is without a doubt my weakest area (schematics and carburetor). I tried to read book explaining the workings of holley carbs and it sent my head spinning. Your the first person to give me a direct proper answer to my problem. This I will learn.

 

[chengny]

Thank you chengny for that detailed info. This is without a doubt my weakest area (schematics and carburetor). I tried to read book explaining the workings of holley carbs and it sent my head spinning. Your the first person to give me a direct proper answer to my problem. This I will learn.

I wouldn't waste too much time trying to completely understand the circuit. Maybe consider just checking the oil pressure switch first - the one that has the two pin connector. Since your oil pressure gauge is working fine, don't bother looking at the pressure sender - one pin connector:

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The switch connector is kind of deceiving. The three leads (PNK/WHT, DK BLU & LT BLU as discussed above) enter the casing but there are only two sockets. The DK BLU & LT BLU are spliced and encased inside the connector:

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Anyway - sorry I got sidetracked - pull the switch's connector and insert a little jumper across the two sockets and note whether the CHOKE warning light goes away. If so, the switch is shot and - depending on whether you feel more comfortable with a illuminated warning for low oil pressure or if you constantly monitor your pressure gauge - you can replace it or just leave the jumper in. Also, if the jumper is left in, you will retain choke heater operation. Without it, the choke will still open - it will just take a while longer.