Mpg, Dieseling, Pinging - The 1947 - Present Chevrolet & GMC Truck Message Board Network

79blazer · 09-04-2006, 03:19 PM

Hello when I got my blazer 1.5 years ago, it ran ok on 87 octane gas, then it started to diesel, which it try to run after its shut off, and light pinging sometimes. Worse if its hotter. So I put 89 octane gas in it, because I know pinging is very bad. I didn't know how to adjust the carb, so I switched the thermostat to 165 and 87 gas and it was fine. Later it started to ping/ diesel again, so I ran 89. Then about a month ago I forgot and put 87 in it and it dieseled. I started 91 gas now with that 165 tstat in there and I thought I heard it diesel just a little twice in the last week. It doesnt seem that powerfull. It sometimes hesitates when lightly getting on the gas. Also if it sits for 12 hours or more it won't even try to start until about 5 seconds. As if I have to wait for fuel to be pumped? MPG was 10-12 city for awhile backseat in 235 75 15 bald tires. Now its a consistant 11.4-11.6 mpg no back seat, some loads and 31x11.5 tires. I gave it the STP FI cleaner a year ago. I don't know what carb is on it but I think its original 2 bbl. Plugs and wires are a year old. What name/model of carb is it? How do I tune it? Can you buy better jets to better mix the fuel? thanks david

rcbildr · 09-05-2006, 04:09 AM

Try changing the t-stat. I've always ran a 180* thermostat and I remember a friend of mine saying his car ran better (and got better mpg too) with the right thermostat installed....the PO installed a cooler one in his car. Also, check your timing...maybe the distributor slipped a little. Hope this helps.

79blazer · 09-05-2006, 01:41 PM

http://www.misterfixit.com/deton.htm I think a hotter would make it worse. I put the coolest t stat for a cheep fix. 165* And I am starting to get preignition back again. So I know I should check for Lean mixture (vac leak, egr, carb) Hot temperature (air intake, coolant) Octane (engine should run fine on 87, but I think it is trying to predetonate on 91) Carbon (valve guides do leak) Cooler plugs may help too, but want to know what kind of carburator this is and I have tryed looking. Does anyone know? thanks

S_Lahnen · 09-05-2006, 10:23 PM

i dont know any model numbers or the cfm of it but its a rochester carb.

09-04-2006, 03:19 PM	#1
79blazer Registered User Join Date: Aug 2006 Location: Mesa, Arizona Posts: 136	Mpg, Dieseling, Pinging Hello when I got my blazer 1.5 years ago, it ran ok on 87 octane gas, then it started to diesel, which it try to run after its shut off, and light pinging sometimes. Worse if its hotter. So I put 89 octane gas in it, because I know pinging is very bad. I didn't know how to adjust the carb, so I switched the thermostat to 165 and 87 gas and it was fine. Later it started to ping/ diesel again, so I ran 89. Then about a month ago I forgot and put 87 in it and it dieseled. I started 91 gas now with that 165 tstat in there and I thought I heard it diesel just a little twice in the last week. It doesnt seem that powerfull. It sometimes hesitates when lightly getting on the gas. Also if it sits for 12 hours or more it won't even try to start until about 5 seconds. As if I have to wait for fuel to be pumped? MPG was 10-12 city for awhile backseat in 235 75 15 bald tires. Now its a consistant 11.4-11.6 mpg no back seat, some loads and 31x11.5 tires. I gave it the STP FI cleaner a year ago. I don't know what carb is on it but I think its original 2 bbl. Plugs and wires are a year old. What name/model of carb is it? How do I tune it? Can you buy better jets to better mix the fuel? thanks david Attached Images __________________ 79 Blazer Cheyenne, 2wd 305 3.42 stock 85 Caprice, TBI converted, new 350 crate motor, Monte Carlo SS Wheels, Bilstein shocks,

09-05-2006, 04:09 AM	#2
rcbildr Registered User Join Date: Sep 2000 Location: Gold Bar, WA Posts: 1,216	Re: Mpg, Dieseling, Pinging Try changing the t-stat. I've always ran a 180* thermostat and I remember a friend of mine saying his car ran better (and got better mpg too) with the right thermostat installed....the PO installed a cooler one in his car. Also, check your timing...maybe the distributor slipped a little. Hope this helps. __________________ My Projects: 1960 GMC 1/2ton with 305 V6 (daily driver) 1963 Chevy 1/2ton 2wd...converting to 4x4 1967 Suburban 1/2ton 2wd My Girlfriends Projects 1985 Chevy Suburban 3/4ton 4x4 with 6.2L diesel, 4" lift, converted to TH-400, Warn Premium manual hubs, & Wildcat 315/75/R16 tires. (daily driver) 1978 Camaro Type LT with a Marine 350 & vortec heads, Rochester Carb, & roller cam 1978 Camaro Z28

09-05-2006, 01:41 PM	#3
79blazer Registered User Join Date: Aug 2006 Location: Mesa, Arizona Posts: 136	Re: Mpg, Dieseling, Pinging http://www.misterfixit.com/deton.htm I think a hotter would make it worse. I put the coolest t stat for a cheep fix. 165* And I am starting to get preignition back again. So I know I should check for Lean mixture (vac leak, egr, carb) Hot temperature (air intake, coolant) Octane (engine should run fine on 87, but I think it is trying to predetonate on 91) Carbon (valve guides do leak) Cooler plugs may help too, but want to know what kind of carburator this is and I have tryed looking. Does anyone know? thanks Attached Images __________________ 79 Blazer Cheyenne, 2wd 305 3.42 stock 85 Caprice, TBI converted, new 350 crate motor, Monte Carlo SS Wheels, Bilstein shocks,

09-05-2006, 10:23 PM	#4
S_Lahnen Registered User Join Date: May 2006 Location: brocton, n.y. Posts: 20	Re: Mpg, Dieseling, Pinging i dont know any model numbers or the cfm of it but its a rochester carb. __________________ LAHNEN RACINGDEMO DERBY team GET BENT 1988 chevy k3500 1972 chevy c 10 1980 chevy 3500 dump truck

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