10 mpg runs fine

10 mpg runs fine

Postby Taffy25 [OP] » December 6th 2009, 8:43pm

Im currently getting about 10 mpg, no missing, no black smoke, seems fine to drive, its got all new leads, plugs, cap, rotor, air filter, fuel filter, i had to gap the plugs at 60 thou to get it to stop missing even though the fan cowl said .35 and i cant find any fuel leaks at all, engine vacuum is just over 18 in park.

Im guessing the o2 sensor and coolant temp sensor could be the problem but is there anything else i have over looked?

Thanks in advance Taff
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Re: 10 mpg runs fine

Postby astro355 » December 7th 2009, 6:56am

Hello,

why are you guessing its the temp or oxygen sensor? You have the wrong gap. What kind of plugs are you using? Having the wrong gap will make you lose power and eat a lot of gas. By using the wrong gap, you maybe covering up the real problem.
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Re: 10 mpg runs fine

Postby Taffy25 [OP] » December 7th 2009, 11:54am

Champions ( i know you can facestab me later) i bought them when i did the head gaskets before i found this site, they were recomended by usa automotives......

You cant drive it with 35 thou gap you get random missfires across all cylinders (you take a lead off any plug and it makes not alot of diffrence)

I have swapped out all the old ignition components i changed to check i havent bought something bad ( i always do a full service on every car i buy, but i keep the old components if they were working for spares)

o2 and coolant temp sensor both affect the amont of fuel put into the motor as i said its a guess.

This morning it started missing like hell as i pulled away from the house, as soon as i took my foot off the gas and put it back on it was fine hasnt done it since, but its never did that before.

Thanks for the reply astro

Forgot to mention the old plugs were gapped at .60 to.
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Re: 10 mpg runs fine

Postby moneymaker » December 7th 2009, 3:10pm

I've seen others on this forum saying there gap has to run 60 gap. According to an old chiltons book 85-90 vin e 4cyl ran .060 gap. 85-88 vinz tbi ran .040 gap. 89 and up vin z ran .035 gap. Looks like vin b? High output 4.3? Ran .035 gap. I would correct the gap, and check resistance in the wires and ig coil.
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Re: 10 mpg runs fine

Postby kevreif » December 8th 2009, 12:59am

i had my van start getting really bad fuel mpg. i pulled a trailor for 200 miles and got 7 mpg! i know something was bad! i had gotten like 13mpg and thought it was just my foot causing bad milage. 92 chevy highout multiport FI. my mechanic found a broken return line in the aluminum intake, basally every bit of fuel the fuel pump could pump was going into the motor. it would started a little hard, and had a small hesitation when gassing it suddenly. other then that it seemed to run ok. i had just bought the van and didn't know much better. ran like a champ after it was fixed. not sure if that could be your problem but it seems like it would have to be major to drop mpg to 10. mine went from about 13 to 17-20. hope this was some help
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Re: 10 mpg runs fine

Postby rev_les » December 8th 2009, 6:01am

Check your distributor gear, when they're worn it causes a random misfire, and it's a common problem on some of these engines. If you're having to gap at .060 to stop a misfire,there's another issue somewhere that you need to locate.
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Re: 10 mpg runs fine

Postby Taffy25 [OP] » December 8th 2009, 10:23am

Thanks for the replys, guess ill have to check the coil, i cant find any vacuum leaks anywhere, used a piece of hose to listen and sprayed crap loads of ez start all over anywhere that could leak, lol my gallons are bigger than yours by about a litre if i remember right so its thirsty, its the absense of black smoke thats getting me.
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Re: 10 mpg runs fine

Postby Leeann_93 » December 8th 2009, 11:13pm

1.2 US gallon = 1.0 Imperial gallon = 4.546 litres

Definitely check the distributor. Your gap is way to big...
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Re: 10 mpg runs fine

Postby Taffy25 [OP] » December 10th 2009, 10:26am

Distributer has plenty of play in it, its probally the one it rolled from the factory with, looks like the problem was there before i bought it though with the plugs already being gapped that way.
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Re: 10 mpg runs fine

Postby astro355 » December 11th 2009, 10:29am

Taffy25 wrote:Thanks for the replys, guess ill have to check the coil, i cant find any vacuum leaks anywhere, used a piece of hose to listen and sprayed crap loads of ez start all over anywhere that could leak, lol my gallons are bigger than yours by about a litre if i remember right so its thirsty, its the absense of black smoke thats getting me.


Its only produces black smoke if the engine is running rich. It can run way lean and also give you bad fuel mileage. Point being is that you will not be able to find the problem with the plugs gapped wrong.
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Re: 10 mpg runs fine

Postby Taffy25 [OP] » December 13th 2009, 1:09pm

Got code 42 today, ses came on so i pulled over and checked it, ses didnt light back up on the way home but the missing is getting alot worse when its cold.

Still waiting on my ohm/multimeter to arrive so i cant really check anything at the moment.
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