Really Bad Gas Mileage, running rich

[kyle1911]

what can cause my ka24e i give me such bad gas milage.

I filled it a quarter tank and it is on empty now with only 20-30km on the clock.

O2 sensor or somthing major?

only mod i have is z32 Fuel Filter if you want to call it a mod.

suggestions are wanted !

[navysnail]

o2 sensor is a definate possibility, do a full tune up and clean your maf with brake cleaner, just dont spray it directly on the hotwire, it is sensitive

[MikeMurphy]

You may have a fuel leak along one of your fuel lines....

I dont *think* an o2 sensor can correct enough to empty that much that quickly.

[Fighto78]

I have a KA240DE and I'm getting 19.2 MPG. When I calculated it, I couldn't help asking myself why is my 4 cylinder getting such horrible gas mileage. The only mods I've done is a MSD 6A Box (which should help!), Custom 2-1/4 Exhaust, K&N stock replacement air filter, and a 300zx fuel filter.

What's going on?

[kyle1911]

its runing rich after it warms up. once the thurmostat comes to dead center in the gauge that when it starts to run really rich. it doesnt appear to be leaking as i cannot smell gas.

what would be the best way to check the lines?

[SoCalS14]

I just cleaned my MAF with eltornics cleaner and I have to say, the car runs better now. More responsive, the idle is constant (needle does not bounce) and the mileage improved.

Oh yea...taking your foot off the pedal helps.

[kyle1911]

im moderately heavy on the accelerator, i didnt go above 5k so i dont think that would have that much of an effect on it.

[SoCalS14]

Well, when the factory calculates those ratings, they professional drivers, driving at "ideal" speeds for gas consumption. I can only imgaine how it differs from the every day schmoe...

[Arrow]

right now on my 90 240 I am getting consistantly about 22 MPG on an engine with 168k miles, but earlier I got about 18-20 MPG... A simple fix could be to change your oil.... I also cleaned my AIV and MAF that helped a lot... I have noticed that w/ the older 240's the intake boot that connects the plastic tube to the throttle body often gets dry-rotted and cracks. That really made my car run rich. So rich in fact that my spark plugs were completely fouled and the car wouldn't hold idle... Bought a new boot and fixed the problem completely! FYI after about 2/3 throttle 240's run rich anyway... But you still should get better mileage than you have been getting.

[kyle1911]

I changed my oil like ~300km ago.I'm thinking of removing that useless piece that recirculates exhaust back through my engine, whatever its called i forget.Is brake cleaner to strong for cleaning the MAF?

Ill check that tube out, why would that cause it to run rich though? there are no sensors around it to affect the fuel/air ratio that i am aware of it would only be sucking dirty air.

i think im going to pull the plugs and take a look.

[Arrow]

The cracks caused air to get into the throttle body without traveling through the MAF... Air will travel the path of least resistance, and if there is more resistance with the air that has to travle through the air filter and down the tube and there is a path of less resistance, then the air will come from easier sources... Such as cracks in the tube! This caused the engine to become completely out of wack... The MAF said there was 'X' amount of air the throttle body saw "Y" amount causing the air/fuel ration to get messed up a lot!

I just cleaned the AIV (the device that recirculates air from the exhuast) There is a thread on here on how to clean it, and there is one that also shows how to remove it... Just search for either cleaning AIV or removing AIV that should find it...

And I cleaned my MAF with carb cleaner.... Just be VERY careful. I completely removed the sensor and sprayed it down and let it air dry for awhile (make sure it is completely dry before reassembling it)

The only problem that I had (which still confuses me though I don't have it anymore) is that after cleaning the MAF, the intake tube, and the throttle plate my tach was wacked! The tach was VERY over sensitive and incorrect... The tach said I was idling at 2500 RPM but the engine sounded like it was at 800 RPM... But after a few trips down town and letting it sit some time inbetween the problem stopped and I haven't seen it again since... Very strange....

Hope this helps...

[kyle1911]

it does, ah its the AIV not the EGR lol thats my search problems

[SoCalS14]

I used electronics cleaner to clean mine. Some that removes oil, grease and dirt. I did not take it apart, I just sprayed it as a whole.

I spoke to a Nissan mechanic awhile ago, and he told me some very interesting stuff about aftermarket, especially cleanable, filters. He said that filters that use oils to catch dirt often end up slightly coating the MAF sensor, making for a jumpy needle/eradic idle.

After I cleaned my MAF, my needle has been solid...

[Arrow]

Well to tell you the truth I found a mistake in my previous post... The EGR DOES recirculate exhuast gas into the intake to be re burned... But the connection is on the back of the throttle body not by the filter... The second smaller connection to the Filter box is for the AIV. Which DOES NOT recirculate exhuast gas to the intake... Well it isn't suppose to... As the AIV gets older sometimes b/c of being dirty or worn out it allows exhuast gas to go into the intake (that is why some people remove it.) But the purpose of the AIV is in reality to warm up the exhaust manifold/header faster... It is suppose to allow filtered air into the exhaust system to help burn some of the unburned gasses and heat up the exhaust system to its proper running conditions... So it really isn't too important b/c once the exhaust system heats up there is no purpose for the AIV...

Sorry for my error!

[pmkls2]

Something to also consider is wear on the timing chain. I had done just about everyhting mentioned in this post and more ( fuel filter, tune-up, removed AIV, replaced EGR, cleaned the entire fuel system and decarboned engine with sea foam via the fuel rail, intake, gas tank, and oil, k&n replacement air filter, o2 sensor,replaced TPS, cleaned MAF,replaced coolant temp sensor, consistent oil changes and oil flush ) and I was still having a lot of problems which included poor gas mileage until I finally changed my timing chain which was original. My '90 240 has 147,000 miles on it and I drive it an average of 700 miles a week and most of that is on curvy country roads. Now a couple of months after the timing chain change I am still getting a consistent 24-25 mpg and I have a very heavy foot ( I'm talking redlining the tach a lot ). I drive the car hard enough that I have burned 2 sets of tires off of it in a year's time ( trust me thats not bragging, I'm actually about to cry when I buy this next set which is coming real soon ) Just my 2 cents worth but its something to look into if nothing more simple helps.

[rousie13]

I'm getting between 25-32mpg, depending how i drive on my 91 with 169k on the clock. I just changed the O2 sensor, coolant temp sensor, plugs, and wires at the beginning of the summer.

[Arrow]

not bad, Those numbers are quite impressive... What octane do you use? I use 89 to get the best mileage to cost benifit...

[kyle1911]

damn, i dont want to deal with the timing chain now.i try some more options to kind of help since the timing chain kit is expensive and very time consuming.

[pmkls2]

Well, I would definately try the cheaper and simpler things first anyways. Only consider the timing chain if nothing else helps. And I would imagine that I could get better numbers if I get rid of the lead foot lol

[rousie13]

not bad, Those numbers are quite impressive... What octane do you use? I use 89 to get the best mileage to cost benifit...

currently using 87

[kyle1911]

k, so the hose coming off the throttle body before the vacuum hoses are cracked and broken. is there any way i could fix it without buying a new one? of is that just ridiculous?

[kyle1911]

400mph duct tape is a temp fix.

[Arrow]

I tried not only the duct tape idea but also the electrical tape thing too.... My suggestion would be to put on the duct tape first to hold it all tightly together, then cover that w/ electrical tape.

When I tried just the duct tape it seemed that the vaccum was still lost in the intake and it didn't help much (but adding the electrical tape over it did help more...)

Although, even after that I still had some problems with it... Don't know why (might have been plugs, or the whole in my filter box (which I did tape closed...)) It was wierd but buying a new boot, and for me a new air fliter box top, helped everything out a whole lot more than patching it.

I personally got ripped off in buying a new one (should have looked at a junk yard first) But for sure I wouldn't pay more than say $80 for a brand new one from the factory (I know that sounds pricey, which it is, but it is brand new and I don't have to worry about it any more!) You might be able to find one at a junk yard that is in good condition for a good price though (just make sure it is for the SOHC engine not the newer DOHC (the boots are different between the models))

Hope you find this helpful!

[SunshineAcid]

try your o2 man.these things are notorious for blowing them.not to mention, if youre been running rich for quite some time now, you prolly need to replace your plugs as well.

[kyle1911]

o2 sensor is the in the exaust manifold correct? i was under the car today and the only sensor that i could see was on it.

the 400mph stuff seems to work quite well, it has tar like compound under the plastic surface. im also pulling the plugs soon.

there was alot of grime and grease in the throttle body WTF is up with that? im think im buy a newer KA and transmission soon though.

[rousie13]

You can see the sensor from the top of the car. It sticks out of the manifold pretty noticeably. Get some throttle body cleaner and clean that bad boy out.

[Arrow]

It probably has NEVER been cleaned and has how many miles on it?? I'd say at least 150k.... It gets nasty! One of the reasons for that is the EGR and the Valve cover breather.... Both of those put either unburned gas or oil into the throttle body (kind of stupid if you ask me... but thats emissions standards for ya!)

Yeah the O2 sensor probably should be changed... Only about a $30 investment. Even if it isn't bad it is probably the one from the factory and it never hurts to replace it (expecially one with over 100k miles on it!)

[kyle1911]

i have 217xxxKM on my engine. so thats prolly why its so dirty

yeah ill change the o2 sensor soon.

[Celeborn]

I was getting poor performance (irregular idle, running rich) and terrible mileage (like 12-14mpg), and I threw in a 300zx/z32 fuel filter and a new O2 sensor, and my mileage is double what it was and she runs like a dream, and the throttle response is better with the filter.So yes, O2 sensor has tht much of an effect on mileage, at least 10mpg less with a bad one for me.