73-87chevytrucks.com
73-87 Chevy _ GMC Trucks => Engine/Drivetrain => Topic started by: ssgoodman on March 12, 2008, 12:18:05 pm
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I just bought a 90 GMC Jimmy, 350 TBI, 700R4, NP208 and its getting horrible mileage, 9 MPG going from Minneapolis to Fargo. after it sits for awhile i can smell the unburnt off gas, any suggestions on how to pull some better mileage with the Jimmy, 9mpg seems low. also it does seem to idle rough and it died a few times on me, seems to be all related to a fuel issue but not sure where to start with it.
Sutton
i will post some pictures of it after i get some good ones was too busy yesterday.
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Tune it up & set the timing.
Give it a good thorough going through, make sure no vacuum leaks etc. From there you'll need someone with a scan tool to make sure all of your sensors are correct. The first thing I would check is fuel integrator and block learn. This will tell you if the ECM is adding more fuel...then check to make sure you aren't getting any false inputs...
9 mpg is pretty bad. You aren't in low range are ya? :D
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man that was fast vile. would the vacuum leak effect the gas mileage?
i wish it was in low that could have explained the crap MPG.
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Absolutely. A vacuum leak creates a lean a/f signal and the ECM adds more fuel to compensate. A cooler thermostat or faulty ECT signal will cause it to add more fuel. High fuel pressure will cause it to use more fuel. A faulty or lazy O2 sensor signal will cause it to use more fuel. A faulty MAp Signal or leak in the MAP vacuum hose....etc...catch my drift? That's why the 1st thing I would do is check fuel integrator and Block learn after you do your prelimanries to verify if in fact it is adding more fuel.
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I only average 9 mpg in my carbed 350 blazer around town. I have never taken it on the highway though.
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A TBI Blazer should get about 15 in the city. You should be albe to get more out of a carb'd than 9mph if it is 2WD. My built 454 got 12mpg
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not sure why I cant pull more than 9 mpg out of this thing. it runs mint, 700r4 and 3.08 gears so you would think I could get better mileage out of it.
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You'll actually get better mileage with 3.55 or 3.73 gears. The
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The other thing(s) is/are, your jimmy is probably a few inches higher than a 2WD pickup or jimmy. That alone probably affects mpg a little. Just the fact that it is 4x4 means probably 1-2mpg less than a 2wd equivalent (Can you guess that my truck is 2wd?)
Although 9 is low even for a 4x4 jimmy.
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I have a 350 TBI 700r i get about the same but i no i've got a problem somewere also but i do not smell any gas and have no gas leaks but i got good tip's today.
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i found a hole in my gas tank today which might explain alittle bit of the bad mileage but its not a terrible leak so probably doesnt effect it much.
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you'd be suprised. Think of it like this... 3 drops of oil from a leaky engine every 100 feet = 3 quarts of oil lost in a thousand miles. Gasoline has nowhere near the viscosity oil has... I'm sure you'll see a significant increase in mileage without fuel simply pouring out of your tank.
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i got the steel guard off from the tank and the straps are non existent, is the steel plate the only thing that holds the tank in or are there straps that either got removed or rusted off? the leak is alittle bit less now that the plate isnt against it but i am going to have to remove the receiver hitch to get at the back bolts holding the sheet on.
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would the gas tank for a 1990 suburban fit into my 1990 jimmy? i can only find suburban tanks at the junkyards here.
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You try autozone?
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I agree, just get a nice new tank and straps.
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because i dont know if i want to keep it with all the little things i have been finding on it and if i end up selling it i would rather put a decent 30 dollar savage yard tank in it then a 150 dollar brand new tank in it. would a suburban tank fit into the jimmy?
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It appears so. What size suburban tanks did you find?
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its a 31 gallon like the jimmy i found it through their online parts search i didnt get to look at it. would the suburban tank be on the side of the vehicle or in the back under the rear floor?
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It's in the back under the flr just like the blazer/jimmy.
Are you sure it's out of a 90 suburban?
i think a 31 gallon tank out of a 87-89 suburban should fit. i don't think 90 suburbans had 31gallon tanks--only 40 gals. (i'm not 100% sure on this, so maybe the salvage yard is right)
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The 28 and 31 gallon tanks are the same, but a 40 gallon tank won't fit under a Blazer.
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yeah the tank was for a 90 burban which according to everything i could find wouldnt fit. i'm still trying to get the metal skid plate off the truck, i think i might have to take the bumper off in order to get to the bolts that are holding the plate on in the back of jimmy. i cant get my wrenchs into the small hole to get them off. anyone ever work with the skid plates on a 90 jimmy? i had to remove the receiver hitch already from it but didnt help. as far as gas tanks go i think i will just buy a new one as much as i dont want to.
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Just use the torch to get it down :P You may need to loosen or remove the bumper if you can't get a swivel socket on there.
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Loosen the bumper and let it sag down you should be able to get to the bolts. I sell gas tanks and can tell you the 25 and 31 gallon tanks are the same for a Suburban or a Blazer. The 40 Gallon is Suburban only.
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do you sell the tanks through your site captn? i am going to try to get the tank out and see how bad the rust is and if its as bad as i thought i will buy a new tank from you.
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Yes, I sell gas tanks. The freakin 25 gallon one is on backorder though (for a Month)
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i cant find the gas tanks on the website captn where are they?
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you gotta call to get them. I haven't put them on the site. If you know what size you want I can add it today as I have 3 thing I need to add...
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gonna try to fix the hole and cover it with rust bullet and see how well that works, maybe when i get it down i will change my mind and just buy a new one, but i am hoping to keep this Jimmy on the cheap.
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Ok, so we got that resolved---sort of.
If i could hijack the thread; i used to work at a salvage yard that dealt only with light trucks. i didn't do much dismantling, i mostly did parts delivery. Anyways, this thread got me thinking about fuel tank interchangability among 73-91 gm trucks and sparked some memories.
i was originally going to suggest that any suburban fuel tank would fit a blazer, but then i realized that a)i may have gotten the crew cab confused with the suburban (easy to do as i will explain in a sec) and b) even if the crewcab/suburban were interchangeable after looking at a picture of a blazer, there is no way a side, saddle tank would fit under the short wheelbase. Which is one of the reasons why blazer don't have side tanks, only rear mounted.
So,:
1)Are the crewcab and suburban frames actually the same design with only length differences? i never paid attention at the salvage yard because i ASSumed they were the same. From a logical standpoint, it is understandable-----the only visual difference between the two is wagon vs. open box.
1a) Are all 73-91 frames identical with only length differences?
2) i noticed some 3/4 pickups had rear mounted tanks? If so,why?
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whats the price on the tank capt? i dont know if i want to mess with trying to fix it or just buy a new one, i think i will need a new sending unit and i know for sure i need new straps. i would give you a call but i keep wierd hours.
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Which one. I can tell you the 25gallon is on back order. It is $147.95 + shipping The 31gal is in stock and it is the same price. the straps are 39.95 and 49.95 and the sending unit is 115.95 for the 25g and $125.95 for the 31g. Both sending units are on backorder (4 week turn around generally)
If you work weird hours as long as you call before say 8pm Central I will answer.... I'll just be at home.