z32 bad gas mileage

[dsastr_clan]

im having the worst gas mileage in my z32 ever! my car isn't passing emissions too, i filled up the tank 2 days ago and only driven the car for about 50 miles and my tank is almost half full, how much mpg are u guys experiencing with your z32??

i have a n/a 1990 z32 converted to manual. What could it be?? i have replaced both of the o2 sensors about 4 months ago with brand new ones, the spark plugs are about 8 months old and i havent really driven the car much because i did the auto to manual conversion then we did a rebuilt on the N/A motor. i have not driven the car hard since i dont wanna waste gas i dont drive over 3k rpm, any ideas are appreciated it

[NolimitZ32]

1) what spark plugs did you put in?
2) are all of your injectors functioning properly (one may be stuck)
3) do you have any codes?
4) This belongs in tech section, I'm sure once Aaron comes across this it will be moved so don't be surprised if it disappears from general and reappears in Tech.

[dsastr_clan]

1) what spark plugs did you put in?
2) are all of your injectors functioning properly (one may be stuck)
3) do you have any codes?
4) This belongs in tech section, I'm sure once Aaron comes across this it will be moved so don't be surprised if it disappears from general and reappears in Tech.

oh, i was debating where to post this, my bad i have NGK plugs just the OEM ones. All injectors work they have in between 12 to 14 ohms and they all tic at the same paste (screwdriver test) i havent checked the codes yet

[Z-owned]

Do you smell gas at all? half a tank in 50 miles seems like alot of gas to not show any symptoms of running super SUPER rich lol.

[dsastr_clan]

Do you smell gas at all? half a tank in 50 miles seems like alot of gas to not show any symptoms of running super SUPER rich lol.

there is no fuel leaks, sometimes when i turn the car on in the morning when is cold i can feel a very very small smell of gas but very minimal, then it goes away when the car is warmed up. i tight the clamps today i dont think it'll smell again

[300ZXttZMAN]

I would say either a fuel leak along the lines somewhere... Or your injectors can still be ohming correctly but also be stuck open ..

I have experienced the injectors being stuck open just gotta do a plenum pull change it out after you figure out which one is stuck.. (do the screw driver trick like you mentioned)

[NolimitZ32]

These engines tend to have a lot of ticks because of nvcs and hydraulic lifters, I would suggest the FSM method for testing the injectors, pull the CAS and with the key in the on position )CAS plugged in) and slowly turn the CAS you should hear each injector click separately, this will 100% let you know they are at least mechanically functioning, also if the injector lower o-ring rots out you will continuously leak fuel into the lower plenum and into the combustion chamber. other than that is it possible that your fuel gauge is just screwed up, have you actually recorded how much fuel it will take after a 50 mile drive? The gauge pickup sensor could be on its way out and causing bad readings.

[Mr300ZX]

I'm thinking like the previous posts mentioned, you are running REALLY rich. My Z is running a little rich, but not like that.

[dsastr_clan]

I think i just jinxed myself, i went to start my car in the morning and noticed a smell of gas thru the vents but when i pulled over to the side the car was warmed up already and the gas smelled stopped, i didnt see any fuel or leaks. i think i may have a small leak coming from one of the fuel regulators hoses, i have replaced the clamps and the fuel hoses so many times on the drive side one.

Im gonna replace the spark plugs when i get home, im just gonna get some NGK v powers and im gonna clean the MAF, when i went to get my emissions the mechanic told me that he thought that my computer was reading my o2 sensors. My harness is pretty messed up but i have tried to save it by replacing the broken plugs and re rewired it, the cars runs great and idles fine but what if my wiring is messed up and the ecu doesnt read the o2 sensors? how can i check this?

tnx for all the replies guys

[dsastr_clan]

I'm thinking like the previous posts mentioned, you are running REALLY rich. My Z is running a little rich, but not like that.

if im running rich, i should be able to tell by looking at the plugs when i pulled them out right? how can i fix that?

[NolimitZ32]

Plugs should hint at it if you are running rich, do not put regular plugs in your car, use only the factory plugs, these cars are very specific about the plugs they like.

[dsastr_clan]

the plugs looked brand new when i pulled them out, but i noticed they were gapped at .40 i replaced them anyways, would this affect my fuel mileage ?

[Ace2cool]

No one has called out cats yet? Does the car feel sluggish at all? What exactly was it failing emissions for, or did the mechanic tell you?

And yes, tech section for any "I need help with ......?" threads.

[NolimitZ32]

I don't have cats on any of my cars so I have no experience with em

[McShanks]

Don't know bout cats, but sometimes I take my dog for a ride... In all seriousness, though, you have to consider there may be multiple issues here, and there is probably not one quick easy item to fix or replace and call it good. If you are smelling gas at ANY time other than refueling your car, you have a leak somewhere, and that is NOT good and NOT safe. FIND IT ASAP. Take it to a shop if you have to. You don't want your precious Z to catch fire, or cause you to pass out or die from Carbon Monoxide fumes!

[dsastr_clan]

No one has called out cats yet? Does the car feel sluggish at all? What exactly was it failing emissions for, or did the mechanic tell you?

And yes, tech section for any "I need help with ......?" threads.

ill post the sheet of the results from the emission test today, im going to give it another try after im off from work, the mechanic that rebuilt the car said that it could be the cats but he wasnt sure, i dont wanna spend 300 bucks on cats if i dont have to the car feels fine when i drive it

[es.biggs]

yeah post that emission test sheet that will help a little so we can tell whats coming out of your tail pipes

[dsastr_clan]

i forgot the emission sheets at the shop, will pick them up tomorrow

[dsastr_clan]

here is the emission sheet, what do u guys think

[NolimitZ32]

Looks like your AFR is bad due to either the MAF or O2s reading bad, the tps being adjusted wrong, or the cats being completely trashed.

[dsastr_clan]

Looks like your AFR is bad due to either the MAF or O2s reading bad, the tps being adjusted wrong, or the cats being completely trashed.

is there anyways for me to single out what the problem is>?? what im gonna do is just replace my wiring & harness since my harness its all messed up, i have a brand new one already, what do u guys think

[NolimitZ32]

Multimeter and FSM and go to work testing each wire separately, first check if your O2s are switching or if you have access to a consult cable use that to see whats up (freeware versions of conzult and other interfaces are available all over the internet. all you need is the cable which runs $60-$100 depending on whom you purchase from.

[dsastr_clan]

so i was thinking about what NolimitZ32 was saying about the fuel sending unit going out, so i started to pay attention more to it. i notices that when my tank was half full it only took 3.9 gallons to get filled up with 62 miles, so i led the tank to E (no gas light came on) and it only took 11.5 gallons to get filled up with 165 miles, thats not bad right ??? the z32's tank is about 19 gallons big?

[NolimitZ32]

Its 14 at the least, check the capacities in the FSM or google that isht. my subaru will do this thing where it will run for ~80 miles on F and then slowly start going down, by the time its on 1/2 theres actually only 4 or 5 gallons left in the tank and on 1/4 it usually has only 2 gallons (it s a14 gallon tank)

[dsastr_clan]

im gonna drive the car till the gas light comes on, BTW all i did was replaced the sparkplugs and make sure they were gap alright

[Ace2cool]

It's 16 gallons with a 3 gallon reserve on the 2+2, so 19, and 13 or 14 with a 3 gallon reserve on the 2 seater.

I'd agree with what Anton said about cats, O2 sensors, or TPS being the culprit. Perform the Mode II (Heated O2 sensor test) and see if the sensors are switching between lean and rich.

http://www.ttzd.com/tech/diagnostic/diagnostic.html

That's a good write-up. Also get a multimeter and test your TPS for proper voltage. Specs in EC section of FSM, can't remember off the top of my head, but should be somewhere around .5V.

If neither are failing, I'd say the cats would be the issue.

[NolimitZ32]

Yeah I had a O2 no response issue and was blowing liquid fuel out the exhaust (I'm cat-less )

[dsastr_clan]

UPDATE, im getting 16 city and 24/25 hgwy with nice driving. Thats not bad! i hooked the knock sensor

[Ace2cool]

Wait, you didn't have the Knock sensor hooked up?

[Sdavne]

This is happening to me as well and i think it is just the float in the tank because the tank is around a 18 gallon tank when it says i am empty and i fill up the most i have put in is around 14 gallons. at first i thought i was getting horrible gas mileage as well also because i have parts that use more fuel, bigger injectors, egr delete full cat back with gutted cats. ect...