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Discussion Starter #1
Hey all, I'm new here so be gentle.

I have a 77 280Z california model. Heres my problem, on the freeway I get an average of 17 miles to the gallon! I get better gas mileage out of my chevy pickup with a 350. I have done quite a bit of work on the car, like new cap, rotor, plugs, wires, injectors cleaned, wire looms repaired, thermostat, adjusted valves, and other little bits and peices along the way. The car itself runs great, and has a little more power than my fathers original 240z. I really have no Idea what's wrong, the only info I can give you is that the number 2 cylinder doesn't fire for about the first 15 seconds when it's cold, after thats it's fine, second the car over heats every now and again when on the freeway. Third I've overheated this car to the point that it will start to burn 2 quarts of oil in a 15 minute run, but when it cools of it's fine and doesn't burn any oil. Well that's all, thanks for any help
 

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not really help but consolation

i know this won't really help you; but my '75 that i work on constantly and runs very well she's by no means anywhere near perfect, always gets 15 MPG. just thought i'd share just to let you know that you're not the only one baffled by this.
my.02
Chris
 

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Yo Bondorocket,
Here are a few other things you may consider doing:
Purchase a 'Valve Adjustment' wrench and then, of course, adjust your valves. The fact you state about cylinder #2 not firing when the engine is initialy started makes me think ....perhaps a valve too tight. Do Exhaust at 12 and intake at 10 unless your elevation is greater than 4000feet.....if so, then exhaust at 10 and intake at 8.
The Valve adjustment wrench, a 14mm open-end, and a remote starter switch are what you'll need to do this. Be certain to remove all spark plugs and number 'em in case you forget what cylinder that particular plug lead belonged to, also be certain to remove your distributor cap and , of course, the Valve-rocker cover. Thats basicly it. With remote starter attached to the positive lead and solinoid female post and your ignition key in the on position you are ready to begin. Bump your cam until its lobe whose valve you age going to adjust is pointed directly upward. Loosen the bottom nut with your 17mm Valve adjustment wrench, use your 14mm open-end to tighten or widen the clearance between the botom of that particular cam-lobe. Continue on all 6 cylinders, using your remote starter switch to bumb the cam so each lobe you are working on is then directly upward. Intake valves do not have any exhaust ports coming out the drivers side engine so that'll help you to determine which valve will be exhaust and which intake.
Next, after your valves are adjusted, lets look at other systems......
At your AirFlowMeter check the condition of its matiing rubber connecting to your Throttle-body. Any cracks , holes, or duck tape, then replace this rubber peice. Now the throttle body itself is a bit difficult to see its bottom allen-bolts but remove these 4 allen-bolts and remove the throttle-body unit. You will need a new gasket if not careful here where it mates to the intake manifold but you could also ' hockey-puck ' the heck out of it when reassembly time comes. Really, get a new gasket. Put grease on Z car gaskets.....at least this one, on both surfaces and this will remedy any leaking situation. Now when you checked your AFM rubber you should have taken the rubber clear off. With the rubber removed you can see into the throttle-body. Any blackness ( yes, yes, black is beautiful but just not inside the throttle body okay...) and you will need to remove the throttle body assembly unit and soak it in carb-spray and give the sucker a really good bath. Nice shineie
metal is what we want and need to see here.
And inside your AFM are some contacts. A peice of paper swiped against/between these contacts are all that is needed. Please do not be tempted to "adjust" ANYTHING inside your AFM at this time. Experimentations upon air flow meters are done upon a AFM unit you get from a junkyard and not one which you know to be working perfectly fine.
Finally , of course, check the spark-plugs for proper gap.....personally I go for a 32. And check the engine oil, air filter,and most important your fuel filter. Z fuel filters should be replaced every 3 months with daily town usage and even once a month with constance highway usage beyond 80miles a day.
You mention "overheating" . Okay, what is the condition of your engine rings?? The piston rings go first with a too hot Z car. The mention of 2quarts of oil indicate from this distance you need to do a compression check and determine what cylinder (s) are weak. Oil leaking past the compression rings are a real possibility for your baby here. If so, then the valve guides will go next. All of this contributes to poor milage in gas and generally poor performance in a Z.
Bondorocket I have several models of Z cars and none of 'em gets less than 22mph in town driving but I live in the moutains of beautiful Colorado and I average here at altitude 25- 29mpg. Work slowly and anyalize your problem. Start with correctly adjusting the valves then proceed from there. Change frrom Bosch Plugs to a correct NGK plug , for example. Look for holes in the exhaust Manifold or cracks in the plumbming of your exhaust. Be certain all injectors are indeed firing. Put a new air filter on. Change your oil to fresh, along with new oil filter. Investagate a bit more and you'll find the problem systems conspiring against your acheiment of better gas milage. Well goodluck and remember to have fun. HappyTrails. shane-
 

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Discussion Starter #4
Thanks shane for the advise, I have a couple more parameters for you that I've done, first I've already adjusted all the valves to spec, second the engine compresion checked at 130 psi with only 1-3 psi difference per cylinder, warm and cold. I did look at one thing you said though, inside my intake manifold is all black and charded. thanks for the help if you have any more please tell me.

Thanks,
Caleb
 

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how shane?

man, you are getting good gas mileage. I get about 15-17mpg in the city an 22-25 on the highway. I'm in AL so air is more dense but I should be getting better gas mileage hah? Sould I lean it?
 

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Your mileage may vary....

Yo2001, your mileage may not be that far out (depending on how hard you drive) but as a reminder to all, make sure to check the cleanliness of the coolant temp sensor connector and those two dratted bullet connectors about a foot back up the harness. Also the afm connector. Any corrosion or crud on any of the electrical sensors indicates a higher resistance to the computer, and higher resistance means a colder (or richer required mixture) to the computers way of thinking. This is ANALOG computing and unlike digital which can often get away with on/off-high/low signals it needs to know the actual voltage going through the sensors (air temp, coolant temp, and afm vane position) and any additional resistance means 'gimme more fuel'. Also on that throttle position switch, make sure that it is not making contact on the full throttle side until you are using pretty much 3/4 throttle. Back in the late 70's I saw a bunch of 'technicians' adjust this switch so that as soon as the idle switch opened, the full throttle switch would close. They often did this to 'increase performance' or to cover up an air leak. All it usually did was ruin gas mileage!
 
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