# Bad Fuel Mileage '86 z24



## Nissanman5.9 (Dec 18, 2008)

I just got a 1986 4x4 XE Nissan pickup and checked its mileage and it's only getting around 12 m.p.g. For a 4 cyl, this sucks. Any idea on why it is so terrible? It's the electro fuel injection z24 model. It also starts hard when it's cold. Everything else works perfectly. Timing is dead on. Thanks for any help. Kevin


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## Nissanman5.9 (Dec 18, 2008)

From what I've been hearing, this is sort of normal...... I think.


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## carldick (Oct 16, 2008)

My 86.5 4x2 5-speed gets 28 on the highway. My 84 4x4 5-speed gets 20-22 with average driving . If it was mine I'd start with the basics to confirm the condition of the engine. Basically, compression test, leakdown test. Once you know the internals are ok, then a proper valve adjustment followed by making sure timing is set correctly. After these steps, then I'd replace the disposables, spark plugs, possibly plug wires, PCV. If you don't get a noticeable improvement then it's time to get into the electronics. The oxygen sensor would be one of the 1st things I'd suspect. Also fuel pump pressure for the hard starting problem.


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## zanegrey (Dec 5, 2005)

nice... but read the codes first...

tire pressure , brake drag ,crap in the bed (lighten the load..).


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## brookwood61 (Aug 18, 2005)

My 86 720 4WD seems to practiaclly run on fumes,around 25mpg around town,when all is right with it. On the highway it does better.Check the truck all over,like they said above. I have the same setup as you,but mine is rated as a 1 ton payload,so it may even be geared lower,I never checked into it.And if it has been sitting,check all the grounds and connections,and make sure everything that is supposed to be grounded/mounted has a clean ground-everything.
Good Luck


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## SPEEDO (Jun 9, 2003)

tune it up first.... cap, rotor, plugs, maybe wires, fuel & air filters, oil change, check tire pressure, might also change fluids in the trans & transferr case & diffs...
I have a 86.5 2wd Z24 and it gets 22-25 in town, (I havent had it out of town for awhile) the above is all I have done to it in the last 21 years that I have owned it...


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## wolfman01 (Nov 26, 2008)

Is it still hard to start when warm? Hard to start when cold points to valves out of adjustment. I concur with the others. Give the truck a thorough going over mechanically. It sounds like it's very much due. I'm getting 21.4mpg out of mine running around town, and mine is a V6/auto. You should be easily beating me.


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## Nissanman5.9 (Dec 18, 2008)

When I got it I replaced the spark plugs and wires, cap and rotor seem fine. There is very little to no drag on the truck. I did adjust the valves when the engine was cold if that makes a difference. Bed has 5 small sand bags in the back for traction. Changed engine oil along with front, rear diff, trans case, and tranny. Runs about 3,000 rpm when going 65 to 70 mph. I just replaced the exhaust sensor on the manifold, but little difference was noticed in mileage. Both coils are shooting spark to the distributor. Thanks. Kevin


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## Nissanman5.9 (Dec 18, 2008)

Also when crawling around under it, I noticed the metal tube running from the emissions thing up front toward the back of the truck where it looks like a catylitic converter use to be. On this model how much does that stuff (emissions control equipment) actually control the fueling? Thanks.


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## zanegrey (Dec 5, 2005)

go up front and check the aiv and all its components..

i think u might find it rusted and cloogged ..

alot of us rermove it all together but it depends on if u are still tested ..


also check all filters and replace ..


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## Nissanman5.9 (Dec 18, 2008)

I was checking out the ecm diagnostic box under the pass. seat and saw that the switch was already in the ON position. I played around with it along with my Chilton manual and finished up with switching it OFF. Wonder if it being ON would cut my mileage? BTW I gutted the AIV and the other component on the inner fender. Haven't drove it real far to see if any mileage was gained.


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## zanegrey (Dec 5, 2005)

theoretically it could be on limp mode while the switch was on ..but i am not certain..

et us know how it does with the switch back to the off position...

thanks


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## SPEEDO (Jun 9, 2003)

if it was in limp mode, the rpm's wouldnt go over 2500


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## smikster (Aug 12, 2008)

some one has to say it and i just feel the urge so here goes...

Seafoam!...film it....


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## Nissanman5.9 (Dec 18, 2008)

You said it. I ran a can through the fuel tank. I need to run some through one of the vacuum lines too. CLEAN AWAY!!!


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## Nissanman5.9 (Dec 18, 2008)

Just an update on the truck. I've gutted the a.i.v. system (filter and other boxy thing connected to it. Capped off vacuum lines and taken off some other emission controllers that I knew weren't doing any good to the engine and capped their vacuum lines. Now I just need to do some more test driving and see what I've gained.


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## Nissanman5.9 (Dec 18, 2008)

Well, after doing what I stated above, I estimated that I am now getting around 16 mpg, a lot better than 11 to 12 mpg. I'm sure it will be better yet come summer time, less idling time. Thanks to all who helped out.


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## Nissanman5.9 (Dec 18, 2008)

I don't think the last post is really that accurate. I finally checked codes today and found 23 and 24 which are good to have and also came up with 13 which is the 2 terminal water temp sensor that I am going to replace Saturday. We'll see if this does something different.


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## chrisraffield (Feb 6, 2009)

I have an '86 hb z24i 5 speed that gets around 28-30 mpg. I added a K&N filter (probably doesn't do much) and messed with the idle control valve but other than that just regular tune up keeps it running great, though on cold mornings (around the 20's and 30's) it spins alot slower on a cold start than normal, and it has an optima powering the starter. Then start works better than a new one (and its original) but that's the only real problem it has. also, with more than about half throttle it bogs out like the motor just stops turning, but if I let back off the gas, it picks right back up. I've eliminated the fuel pump, pressure regulator and fuel filter...only thing left I know of is injectors. Any insight?


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## Nissanman5.9 (Dec 18, 2008)

Well, you're doing better than me already with the fuel mileage. Mine if it's 10 or bellow out, it won't start at all unless I squirt some fuel down the throttle body.


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## zanegrey (Dec 5, 2005)

4 chris ..check your secondary coil..


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