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  • July 23, 2019, 05:15:14 AM

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Author Topic: Erratic Idle/fuel mileage/Timing  (Read 437 times)

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Offline trucker79005

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Erratic Idle/fuel mileage/Timing
« on: January 18, 2019, 06:05:40 PM »
Hi all! Looking for any thoughts on this. So I adjusted my timing a while back and wasn't real sure I had it at the right spot (Didn't mark the proper marks ahead of time). It drove fine but was still only getting 15 mpg here at about 3000 feet elevation. I took it to front range Colorado and western Nebraska (4-5000 ft) and got 18-19 mpg. Came back home and went back down to 15. Maybe it could have to do with lack of wind or different fuel but think it had to do with timing.

I reset the timing a few days ago closer to the 6* that is stock and my idle sucked and i got about 12.5 mpg.

I reset it today to about 10* and haven't had a chance to test it out other than to make sure it ran. The idle still spikes randomly and it seemed like there were times that the timing would retard when I was setting it. It wasn't wavering all the time though. If there's a way to post a video I will.

Car has 180000 miles on it so my mind goes to timing chain but also wondering if it could be my computer messing up. I also feel it "drag" sometimes when i'm at highway speeds with steady throttle.
Laura (Shorty)
1978 AMC Concord 2DR Hatchback w/ Ralley package
1983 AMC Eagle Wagon Limited w/ 5 speed
1971 Ford F250:)

Offline AMC1

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Re: Erratic Idle/fuel mileage/Timing
« Reply #1 on: January 21, 2019, 12:06:42 PM »
Have you considered the thought that the EPA etc. actually changes the composition of the gasoline during the winter months. Here in the Chicago area I expect my mileage to decrease by 2-3 mpg during that time plus the fact that it's running a bit richer until warm-up.
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Offline trucker79005

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Re: Erratic Idle/fuel mileage/Timing
« Reply #2 on: January 21, 2019, 11:37:25 PM »
Sure hadn't thought about that. Maybe that could explain some of the recent drop but it wouldn't explain the drop from one day to the next like when I came home from Colorado. Hopefully I'll figure it out soon! I'm pretty tired of 12.9...
Laura (Shorty)
1978 AMC Concord 2DR Hatchback w/ Ralley package
1983 AMC Eagle Wagon Limited w/ 5 speed
1971 Ford F250:)

Offline eaglefreek

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Re: Erratic Idle/fuel mileage/Timing
« Reply #3 on: January 23, 2019, 09:47:15 PM »
I never used the timing mark on the balancer. They are known to slip. I time by ear and feel. Keep advancing until it pings under load and then back off a hair.
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Offline mudkicker715

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Re: Erratic Idle/fuel mileage/Timing
« Reply #4 on: January 23, 2019, 11:11:25 PM »
If you think the damper is going to pot. Replace it, plain and simple. It can cause serious wear to main bearings, and timing driven components including oil pump. Dont try to live with a bad damper, if thats the case. Otherwise i agree set timing by light than adjust to ping under load and back off till it stops.

Usuaully if a damper is bad the motor vibrates bad in my experience. There could be other symptoms?



Manitowoc WI

Offline mo.eagles

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Re: Erratic Idle/fuel mileage/Timing
« Reply #5 on: January 29, 2019, 05:36:35 PM »
Also, if your still running a cat make sure it's not plugged. You'll have symptoms like "drag at hyway speeds" .
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Offline trucker79005

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Re: Erratic Idle/fuel mileage/Timing
« Reply #6 on: February 05, 2019, 10:30:16 AM »
Thanks all! Don't think I've ever had an engine "ping" so hope I would recognize the sound. I don't think the engine vibrates bad so not sure if the balancer would be the issue but I do still have a cat. How would you tell if it was plugged?
Laura (Shorty)
1978 AMC Concord 2DR Hatchback w/ Ralley package
1983 AMC Eagle Wagon Limited w/ 5 speed
1971 Ford F250:)

 

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