gas mileage dropped out

[MTec007]

since the installation of my tach cluster, i adjusted the idle screw so the car idles at 700 not loaded instead of 2000. bad move.

the gas mileage has gotten severly horrible since then

5/20/10 30.2
5/15/10 34.6
5/15/10 39.8 <-cluster / idle adjusted
5/15/10 43.0
4/11/10 40.8
4/11/10 45.3


what did i do wrong? what can i do to fix it besides run the idle screw back up to 2000rpms? can anything else be causing this issue?

[batstiva]

Not to ask a stupid question, but are you certain the new cluster is accurate as far as miles traveled? Can't imagine that it's not, but I can't think of anything being done during a cluster swap that would cause MPGs to drop. Short of not hooking something up all the way, so it's only getting a partial reading. That does seem to be a pretty excessive drop in fuel economy.

Edit. I also can't see correcting the idle causing the fuel economy to drop. I would think adjusting the idle down would save gas being wasted by the high idle.

[wybnrml]

Not to ask a stupid question, but are you certain the new cluster is accurate as far as miles traveled? Can't imagine that it's not, but I can't think of anything being done during a cluster swap that would cause MPGs to drop.

Thats a good thought.

Mtec, didn't you say the gas gauge and the temp gauge wasn't working properly, maybe there is something wrong with the Cluster not reading the mileage right like Batstiva said.

[MTec007]

its not really the cluster that is at fault it happened after i turned the idle down.

also, unless something else, a sensor maybe, isnt working right... but i dont know where to start to check for things that arent working right.

the temp gauge and gas gauge both work, unlike my earlier post (i assume that was your reference) stating that i thought they were not working right

the only other thing ive done besides the idle is im currently doing a radiator flush which doesnt (or shouldnt any way lol!) effect the gas mileage. the odom seems to be working fine as far as keeping an accurate count on miles per miles traveled

[batstiva]

So, you swapped the cluster, ran it for a while, and then backed off on the idle? Or swapped and adjusted the idle at the same time? And if you, say, out on the interstate and check at mile markers, you are accurate as far as that goes?

I hate to tell you to crank the idle back up just to see what happens, but....

[MTec007]

correct.

yeah im going to have to do that, against my better judgement. will report back in a few tanks

[batstiva]

I really can't see lowering the idle causing that large a drop in fuel economy. Really has to be something else going on there. You're up to date on plugs/filters/etc. Correct?

[MTec007]

nope, my oil filter may need to be changed but my oil is self changing. air filter is clean. never checked plugs, plug wires, or what ever else needs to be checked (no clue on any thing else there).

[FB71]

it was idling @ 2k because you most likely have an intake manifold gasket leak, driving the engine lean, which grossly increases idle speed and reduces fuel economy.

[MTec007]

well im going to be buying a head gasket set soon, and im pretty sure thats one of them that comes with it

heres the link, can you confirm its there?

http://www.oreillyauto.com/site/c/detail/FEL0/HS9555B.oap?year=1988&make=Ford&model=Festiva&vi=1128079&keyword=head+gasket+set&forcedVehicle=true

[batstiva]

it was idling @ 2k because you most likely have an intake manifold gasket leak, driving the engine lean, which grossly increases idle speed and reduces fuel economy.

That's along the lines that I was thinking, but he's saying his fuel economy was better at high idle than closer to correct idle. That's what I'm having a hard time getting my head around.

[MTec007]

im going to run a few more tanks on the current setting just to make sure there wasnt any other variables. if its still south i will put it back at 2000 and try it again

[92festie]

well im going to be buying a head gasket set soon, and im pretty sure thats one of them that comes with it

heres the link, can you confirm its there?

http://www.oreillyauto.com/site/c/de...edVehicle=true

btw to answer you question, yes both the intake and exhaust gaskets are there

[MTec007]

good to know. but after talking to my brother in law, i might but a master rebuild kit if i can find one with over sized pistons and rings, and have the motor checked over and worked to match the over sized parts

[92festie]

good to know. but after talking to my brother in law, i might but a master rebuild kit if i can find one with over sized pistons and rings, and have the motor checked over and worked to match the over sized parts

ok this might be a dumb question but, wouldnt the oversized pistons and rings hurt you mpg's?? and just curious why do you wanna go that route??