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Old 08-17-2019, 05:13 PM
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1966 Chevelle : gas smell and poor running

I’m running a66 chevelle w/ 383 stroker with a MSD atomic EFI. Starts great. Runs like a champ... until on the road for around an hour. Last two times, noticed a slight odor of raw gas right around the 50 mile mark. Temp around 190 & when I try to stab the throttle, I instantly loose power. Have to “feather” to maintain RPM’s. Each time I try to get on it, it sputters and doesn’t respond. It appears to only happen under load. (Works fine in neutral and park) After shutting er off and letting her rest for about an hour, temp drops below 150, problem is resolved. Any ideas?

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Old 08-17-2019, 05:29 PM
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I'm guessing here, but . . .

Sounds like a classic case of fuel percolation, where fuel is "boiling" before it reaches the jets in the carb. Can you see any areas of your fuel delivery system that might be exposed to high heat?
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Old 08-17-2019, 08:46 PM
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Quote:
Originally Posted by Grod117 View Post
I’m running a66 chevelle w/ 383 stroker with a MSD atomic EFI. Starts great. Runs like a champ... until on the road for around an hour. Last two times, noticed a slight odor of raw gas right around the 50 mile mark. Temp around 190 & when I try to stab the throttle, I instantly loose power. Have to “feather” to maintain RPM’s. Each time I try to get on it, it sputters and doesn’t respond. It appears to only happen under load. (Works fine in neutral and park) After shutting er off and letting her rest for about an hour, temp drops below 150, problem is resolved. Any ideas?

On the surface this sounds like a sensor or the brain chip is having a temp related problem. The easiest at home check would be to run it with low temp thermostat or none at all to keep the coolant temp under 150 to see if things remain steady. This might indicate the temp sensor is at fault but doesn't rule out the chip. Next would be just replace the temp sensor to see if there is a change. If not you're back to considering the chip is having problems.


You also cannot rule out electrical problems, check the wiring and connections carefully this applies to power in and grounds out.


Bogie
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Old 08-18-2019, 05:30 AM
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I've seen numerous post on Pontiac & Chevy Forums about Gas Boiling in the Summer "even on bone stock vehicles". Many also speak of the Raw Fuel Smell, a few say after an hour of driving they put fresh cool gas in to prevent it from occurring (thats a dam pita ). LOL

Many say when they release the gas cap there's a lot of pressure in the tank and a new gas cap fixed it. Others say Winter Blend Fuel has additives that will allow fuel to boil at lower temps. I know we have Ethanol in our fuel pretty much all yr round here in LI NY

As Bill said first thing to check is make sure none of the fuel lines are to close to a high heat source. Other things that could overheat fuel are to much unused fuel returning to the tank, (many people oversize fuel pumps & lines), or the pump itself is getting hot. I had an Aeromotive Eliminator Fuel Pump in a High HP car and it would go into Thermal Overload on a hot day (or after driving it a while).

A weak or low voltage situation would slow down the pump and create the issues of it not taking the pedal under load (happen to me last week in my ZL1, I had a weak battery). but I would expect that at any temp or time limit and you shouldn't get the raw smell. I think you can eliminate an electrical issue at this point unless your running a Hi / Low Pump set up and one of the pumps isn't ramping up or you have a bad relay.
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Old 08-18-2019, 05:43 AM
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Setting the system up for a return style or returnless fuel system is pretty important.

Did you set the system up with the hand controller?

Did you go through the instructions and set all the parameters?

When selecting camshaft type I have found that most builds run best on the street stock or mild. Your cam setting may be to agressive.

Timing control, should start at 12-14 degrees base and about 36 all in around 3000rpm.

Be sure to verify the timing at Idle and 3000 RPM after setting to insure it is correct.Use a dial back light and a tack,or tack provided in hand controller

I set the Target AFR at like 13.8 -14. for WOT and around 14.2-14.5 for cruise and let the learn system sort out the few extra points on its own.

The Target AFR may be the one setting you have really wrong , giving you fits.

Post the settings you are running at the moment so we can get an Idea wher it is all at. Thank you
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Old 08-18-2019, 12:38 PM
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Is your fuel system vented sufficiently.
I just worked on an old Chev truck that had about the same symptom, the fuel tank had no vent at all.
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Old 08-18-2019, 04:42 PM
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Did it ever work or is this new? Where is/are the fuel pump(s)? Percolating/boiling of fuel would be very rare with the higher fuel pressure with EFI unless a fuel line is dangerously close to exhaust. And I don't know of an exit for fuel odor, unless it's coming from the exhaust, which would point to a problem with the EFI or course.



If it does it at home, let it cool and check the plugs to see if it went way too rich.


And like LATECH said about a fuel return system, if it's not, and the fuel IS boiling, I suppose fuel pressure could build to much higher pressures screwing with the fuel delivery. Although if it takes an hour of cooling down (hood open I guess), I'd be looking at the electronics not the plumbing.
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Old 08-18-2019, 06:29 PM
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The raw fuel smell is why I was leaning toward incorrect tune.

The fuel system controller is pulse modulated and needs to be set for a return, or non return system. Pretty much one of the first things in the setup of the tune.

https://www.jegs.com/InstallationIns...1/121-2900.pdf
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