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post #1 of (permalink) Old 03-09-2001, 10:26 PM
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Gass Milage for 2.8L

I drive a 85 or 86 GMC Jimmy the 2.8l engine was rebuilt about 10,000 miles ago some how it had a bent crank. After getting it rebuilt the guy painted over the timing marks on the fly wheel(is that what its called?) so after me and my dad put it back in the car he just guessed at the timing and never really set it and at the time i didnt care becuase i didnt have my licence but now that im paying for the gas im a little anoyed that it gets 12 to 13 mpg. that is during the winter time in WI. My mom says that its just so bad because its winter but shouldn't it be higher than that? I wouldn't mind it if i at least had some power. It also doesnt have much power i can hardly stay in over drive above 50 mph if theres any head wind at all it keeps down shifting to speed back up then when it up shifts it just slows down again so most of the time i use drive.


also if i step on the gas hard or fast when its cold out (even some times when the engine is warm but worse when its cold) it will just start to die, if i let off the gas it will some times come back to life. If im driving down the high way with the engine warmed up good (this is all in winter in WI) and just floor it, it will hesitate/try to die but then it will take off with what little power it has.


thanx for any help you can give me


Justin Behr

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post #2 of (permalink) Old 03-09-2001, 11:39 PM
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Re: Gass Milage for 2.8L

Either buy or get a timing gun fron a friend, thatsdefinatally your timing.. you should be able to see your timing mark on the flywheel(a littlr indented line) just mark it with some chalk... then tiime it to what it says on the emmissions sticker...


Tim

88 blazer
Like A Rock
post #3 of (permalink) Old 03-10-2001, 08:56 AM
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Re: Gass Milage for 2.8L

its sounds to me your truck is running too rich. you can use white-out on the mark (on the harmonic balancer) to see it with a timing light. if you dont have access to a timing light you can try to re-adjust it by ear. you want a happy medium between running rich and running lean. start your engine and loosen the distributor adjusting bolt. turn the distributor either way and listen to the way the engine runs. if it bogs down then its running too rich. if it increses idle then its getting leaner. you are looking for the point where where the idle goes from boggy to running smooth. tighten the bolt and check your throttle response, if it is hesitant, adjust the distributor some more. dont go too lean because it could burn holes in your pistons. this is only a temp fix you neeed to get a timing light ensure that vacuum presure will be correct.

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post #4 of (permalink) Old 03-10-2001, 10:27 AM
 
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Re: Gass Milage for 2.8L

<font face="Comic Sans MS">My 2.8L has been getting 16mpg lately (with me averaging 65-70 with a mix of city and highway driving in the cold michigan winter)... First of all, check your timing. I'm not sure about the figures for yours, however I would think it's around 8° BTDC. I have mine over advanced a little bit. In the cold I wouldn't recommend it. Set it to factory specs for when it's cold. Adjust the timing according to the sticker under the hood, with the engine running at the right RPM's and such.

Items I'm recommending you buy:[*]Inductive timing light ~ $35[*]Vacuum guage ~$20[*]Adjustment tool for the Rochester carb idle mix (it's a little rectangular screw type thing in the front. Look to see if you can see this screw, it's on the front of the base of your carb. If you cannot see it, then it's plugged, tell me and I'll get you the information on how to get the plug out of the way so you can adjust your idle.

The vacuum guage will help you set the idle fuel mix. Adjust it until you get the highest vacuum reading, then enrich the mixture 1/4 turn or so. If you need more in-depth explanations, let me know.

The 2.8L is a good little engine and if adjusted properly makes a decent amount of power (unless it's got an automatic behind it)... [img]/wwwthreads_images/icons/crazy.gif[/img]

You can not hammer the throttle when the engine is cold, it does not work correctly when it's cold if you do that. Have you checked the operation of your choke? Could be sticking shut. Spray some carb cleaner on the linkage. Have you checked all the vacuum lines? If they seem deteriorated, cracked, or if rubber comes off of them on your finger tips when you touch a vacuum line, replace it.

The combination of these things should help you to get up to around 16-17mpg in the winter... Perhaps a bit better in the summer. Good luck and let us know what you find out.

One last thought... Have you been running it in 4x4 a lot? Not sure if you mentioned it's a 4x or not but if it is that'll help kill your gas mileage also.</font>

Tim "Sandman"

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post #5 of (permalink) Old 03-11-2001, 07:21 AM
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Re: Gass Milage for 2.8L

Thanx for all the help my dad will be barrowing a timing gun today if not i will go get it from his friend. it is a 4X4 but it vibrates really bad when you go over 25 mph so i dont hardly ever us it. since its my dads and he wont ever fix it i hope to get a little more money and buy a jimmy or blazzer 4x4 with a 4.3L to go play in the mud this summer. im poor since i just bought a snowmobile this winter.



Justin Behr

post #6 of (permalink) Old 03-11-2001, 10:41 AM
 
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Re: Gass Milage for 2.8L

<font face="Comic Sans MS">About the vibrations in 4x4 make sure the driveshaft is "in phase" and check the u-joint to make sure there's no play in it. Definitely doesn't sound much like a problem in the t-case or front differential. If it was a problem in either of those the vibration should show up in most of the speed ranges from just barely moving to fast... </font>

Tim "Sandman"

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post #7 of (permalink) Old 03-12-2001, 12:21 PM
 
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Re: Gass Milage for 2.8L

<blockquote><font size=1>In reply to:</font><hr>

Adjustment tool for the Rochester carb idle mix (it's a little rectangular screw type thing in the front. Look to see if you can see this screw, it's on the front of the base of your carb. If you cannot see it, then it's plugged, tell me and I'll get you the information on how to get the plug out of the way so you can adjust your idle

<hr></blockquote>

Could you send me that info Tim?

--Drew
83 S10 4x2
I AM <font color=red>CA</font color=red><font color=white>NADI</font color=white><font color=red>AN</font color=red>!
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post #8 of (permalink) Old 03-12-2001, 12:49 PM
 
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Re: Gass Milage for 2.8L

<font face="Comic Sans MS">It's in the Haynes manual, otherwise I'll try to get it posted today. [img]/wwwthreads_images/icons/cool.gif[/img]

I think it's idiotic how they plug that stupid adjustment.</font>

Tim "Sandman"

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