ClassySoob Posted April 23, 2017 Share Posted April 23, 2017 I just finished rebuilding the engine on my 85 GL, and noticed that the mpg is less then it was before the rebuild. Is this normal for newly rebuilt engines or is there a problem? Link to comment Share on other sites More sharing options...
Dee2 Posted April 23, 2017 Share Posted April 23, 2017 How much less? Variations could be from driving / location / route changes How long have you monitored ? Variations could be from fuel itself Rebuilds in general should make things better Run a vacuum test on your engine and see if there are any issues to be considered. Link to comment Share on other sites More sharing options...
GeneralDisorder Posted April 23, 2017 Share Posted April 23, 2017 Depends on how tight the pistons are and how coarse the rebore/rehone was. Also valve seating, etc. Generally we see a reduction in fuel economy for a few thousand miles when we knurl the pistons on the EJ's. Were the pistons knurled? What was the ring gap and how were the cylinders setup? Have you compression tested it? GD Link to comment Share on other sites More sharing options...
wagons Posted April 24, 2017 Share Posted April 24, 2017 Are you wearing heavier boots? On a serious note, how did you do your rebuild? New or reused pistons? Valve job? Perfect bore and hone? Deck the block and mill the heads? Worse milage after a rebuild is not right. Check ignition timing, run higher octane fuel, check plug gap, pcv valve. If you haven't already, install new plugs, wires, cap & rotor, fuel filter, amd air filter. Give it a good oil change after 500 mile break in. Link to comment Share on other sites More sharing options...
idosubaru Posted April 24, 2017 Share Posted April 24, 2017 1. you are comparing last summer (before you took car off road for rebuild) with summer blend gases to winter blend gas you've been running since the rebuild this winter. for the eagle eye hyper milers, it should go up any day now as stations start switching. 2 maybe it's not actually getting worse mileage - you love that new go pedal feel and can't get your foot out of it...or the old engine was such a basket case you were driving cautiously. what all did you do to the engine? post previous and current gas mileage - is this a 0.5mpg difference or 10 mpg? how many miles have you put on it? have you driven enough to get an accurate measure - consistent highway miles or inconsistent urban/mountain driving? Link to comment Share on other sites More sharing options...
ClassySoob Posted April 24, 2017 Author Share Posted April 24, 2017 How much less? Variations could be from driving / location / route changes How long have you monitored ? Variations could be from fuel itself Rebuilds in general should make things better Run a vacuum test on your engine and see if there are any issues to be considered. It's like a 5-10 mpg difference Link to comment Share on other sites More sharing options...
ClassySoob Posted April 24, 2017 Author Share Posted April 24, 2017 I kept the old pistons, because they were like new (.002" worn), still had hatching. Link to comment Share on other sites More sharing options...
ClassySoob Posted April 24, 2017 Author Share Posted April 24, 2017 The pistons we're pretty tight when they went back in. Link to comment Share on other sites More sharing options...
Dee2 Posted April 24, 2017 Share Posted April 24, 2017 We need some data to help you. Vacuum test is the easiest to do and can reveal a problem in a number of possible areas, or point to best subsequent testing. Link to comment Share on other sites More sharing options...
GeneralDisorder Posted April 24, 2017 Share Posted April 24, 2017 5-10 MPG probably indicates problems with rich mixture or timing. It should not be that much different. GD Link to comment Share on other sites More sharing options...
ClassySoob Posted April 28, 2017 Author Share Posted April 28, 2017 We need some data to help you. Vacuum test is the easiest to do and can reveal a problem in a number of possible areas, or point to best subsequent testing. Ok ill do a vacuum test next time I'm in the shop, see what it shows. Link to comment Share on other sites More sharing options...
ClassySoob Posted April 28, 2017 Author Share Posted April 28, 2017 5-10 MPG probably indicates problems with rich mixture or timing. It should not be that much different. GD What would be the proper adjustment on the fuel/air mix? Link to comment Share on other sites More sharing options...
GeneralDisorder Posted April 28, 2017 Share Posted April 28, 2017 Depends. What induction system are you running? GD Link to comment Share on other sites More sharing options...
ClassySoob Posted April 28, 2017 Author Share Posted April 28, 2017 Depends. What induction system are you running? GD Natural Link to comment Share on other sites More sharing options...
GeneralDisorder Posted April 29, 2017 Share Posted April 29, 2017 I mean carb (what type) or fuel injection, etc. GD Link to comment Share on other sites More sharing options...
ClassySoob Posted April 29, 2017 Author Share Posted April 29, 2017 Hitachi carburetor 2 barrel Link to comment Share on other sites More sharing options...
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