I have a 03 m/t Z. i recently just installed a 5/16 plenum spacer and k&n drop in filter. My gas milage has went to ****. I am tracking 14-16 mpg with normal driving when i used to see 22+

also sometimes after driving for sometime, when i start the Z, the rpms go up like normal and then stalls out ( this only happens sometimes, but witha little gas at crank she starts and idles just fine( also idles fine from a stop. no rough idle..

I have done the following:

check all bolts are tight on plenum
left the factory gasket in the plenum (motordyne said it would seal properly wit both in there)
although i do hear a hissing sound from the left side which i read was normal but i don't know exactly how loud it should be,

also did and ecu reset, tb reset as well..

i am puzzled and i can't figure out anything

any help would be much appreciated from those of you who have seen or might know what i can do to get this problem solved!

 

you could get some starting spray and spray it around your manifold and see if the rpms rise. If it does, it means you've got a leak around there.

 

Not sure what the problem is, but I have the same year/model Z, and it does the stalling problem every once in a while too however the only mod I have on it is the K&N drop in filter.

 

Just a suggestion. Put a subject in the subject line like

Squeaking brakes

instead of

Help

Need help immediately

or

If you don't help right away I will die!

 

Sounds like you messed up some sensor stuff. Mess with the throttle body or MAF when doing your installs? You should have disconnected your battery when you did your plenum spacer install, did you remember to do that? If you didn't, your throttle body could have been screwed.

 

Sounds like a vacuumm leak , break out the starting fluid and check it as mentioned above.

 

when i bought my z, the previous owner had been using an extremely outdated K&N filter. those things let off oil into the injection system at tiny bits at a time. especially old ones. I had the same problem (car revs up to about 1.5k at start then goes straight down to 0 and stalls when you turn it on. but revving helps it)

SO how did i fix it? you have to get a fuel injection system cleaning. nissan did mine for $145 i think. although you can buy a liquid to put in in place of your gas that should do the same.

 

That is probably all that Nissan did for that $145, lol. I would almost guarantee that they did not pull the injectors for cleaning at that price.....
OP - pretty sure that the hissing is a vaccum leak - definitely not normal.

 

The install was relatively straightforward. In my opinion, there are only very few instances where somebody can mess up and problems arise:
- Didn't torque bolts to right spec
- Rubber funnel around the oil cap stuck between upper and lower plenum
- Forgot to plug all hoses back in
- Didn't align clamps exactly how they were when you took them off (important for a good seal)
- Didn't take off battery when doing install and messed up some electronics (either MAF or Throttle Body, both are VERY sensitive)

 

I'm going to try some MAF cleaner and also go to vatozone to see if i'm throwing a code somewhere.

I did take the (-) off my battery before install, but i accidently started my car with the MAF sensor out of the plug and threw a cel. thats why i did the reset.

if there is any other suggestions please let me know!
i definately appreciate all the help

 

triple check the the tb cable is still connected.

 

you're probably right haha. I decided to just go with it. It was becoming a big problem so I was just happy it was over with

 

make sure your vacume and pcv valve lines are still sealing properly. i installed a kenetix velocity plenum and tripple checked everything reset the ecu throatle posstion relearn a millions times and it turned out pcv valve vacume line was bearly bearly bearly not sealing.

 

+1

Also the 350 is a electric throttle there is no cable except for the connector.

 

+2
^^^ Ive actually seen this happen.

How many miles does your Z33 have?,... has it ever been cleaned out off gunk/crap residue( ie..sea foamed)??

 

this is exactly what i was going to say, therefore hes correct. haha.

BTW, you increased the airflow, so there will be more gas, and you will also be driving ti harder now that yo bought parts.. you probably did not reset the gas mileage meter, and did not rely on the normal method which is done by hand w gallos at fill up to miles driven.

deal w all of the above, and you will be fine.

 

You have an intake leak. Find it.