KyleW707

Alright I have a 97 Z28 automatic. When I bought it I fixed a broken fuel line (2 places) and two different exhaust leaks along with a misfire cause by burnt wire from touching the header. I was getting this kind of gas mileage but then replaced the coolant temp. sensor in the water pump. For a couple of days I got normal gas mileage, mid twenties on the highway and 15-20 in town, but now I'm back down, WAY down. When I took out the original sensor one of the prongs where you insert the plug was rusted and bad, so today I replaced the plug-in too just in case but no luck, still getting bad mileage. The only code I have is P1351, igniton control module if I remember right. Any ideas on why I'm getting this bad of mileage? Also before I replaced the sensor the car would have warm start problems and was running really rich. Now its still running a little rich and bad gas mileage but no starting problems. HELP!

nitrous2fast

iTrader: (2)

put a scanner on it and run live data. cross check the Coolant temp between the scanner and what it would should be at. like a big difference 50-100* would mean the sensor isn't working properly.

Next check the wire that got burnt before to be sure it didn't burn again. lol

Badazz 97 TA

iTrader: (18)

i would be looking at the ICM if your getting a code. pretty important sensor.


http://shbox.com/1/4th_gen_tech2.html#opti_test

KyleW707

the wire isnt burned again, i checked it. i put a sleeve around it and not even a hint of burning yet. My temp gauge was showing 230-240 after a highway drive before i changed the sensor, now it stays under 200. I'm thinking maybe the wire is shorting out somewhere.

KyleW707

But would that cause the gas mileage problem?

jaycenk

iTrader: (1)

The sensor in the water pump only sends temp to PCM. There is another sensor in the side of the driver side head (one Prong sensor) that goes to the temp gauge.

KyleW707

Yes but when the sensor in the waterpump is bad the pcm reads that the car is 40 degrees cooler than it is, which ultimately throws the air/fuel ratio off. The reason it was getting that hot is because it was at 230 degrees but pcm thought it was at 190 or so and the fans were never coming on

jaycenk

iTrader: (1)

I've run plenty of these things on the highway here in FL in the summer and I have never had one get that hot while cruising. Fans don't usually run when your cruising at 35+mph unless you have the A/C on. And even still I have never had one get that hot while moving for any period of time. If you still have that code you may have a coil or Icm problem. I would sort out all the problems first and then take a look at other things such as plugs, wires, cap and rotor, Primary O2's. All things that will affect fuel eco. A live data stream will tell you if all of the engine sensors are reading right or you could just use a multi meter to test resistance down the wire to see if the plug and sensor are fine.

KyleW707

Okay update, and i am even more stumped. So I put $10 in it and got around 40 miles (12.7 mpg) on the highway, when i got to my destination the gas gauge had went from 1/2 tank to between empty and 1/4th. Now the strange part. Before my 35 mile trip back home i put another $10 in it but by the time i got home i only used about 1/8th of a tank. Car didnt act any different just got better mileage. I have no idea whats going on!

ahritchie

iTrader: (1)

The Lt1 gas gauge is notoriously unaccurate....especially when below half a tank. You cannot trust it at all; once mine gets to a "quarter" tank I have to find a gas station QUICK. You have to run a whole tank of gas to accurately measure MPG on these cars. FWIW...I was getting 12 MPG in my 6spd car until I changed plugs; now 18 MPG.

KyleW707

I know but comparing the two times i put gas in it i got a lot better mileage on the way home. Even though its not accurate the gauge went from half to past 1/4th when i exited the highway the first time, the second time i started at 1/2 and ended up at about half way between 1/4th and 1/2

camar0corey

iTrader: (22)

You have an icm code and it runs rich? Replace the icm. If it still runs rich pull the vacuum line off the fuel pressure regulator, see if there is fuel in there. Turn the key to on, no fuel should come out of the regulator. I mention this as I had similar too rich issues and this seems to be an overlooked avenue, (this problem solution came from efi live forums and not here ).

ahritchie

iTrader: (1)

My gas gauge fluctuates up and down 1/4 tank at a time sometimes; I have to say it's the most inaccurate gas gauge in any car I've driven (well, possibly tied with damn digital gauge in my Dad's old 92 Vette which also had a LT1). My LS1 Firehawk does not have the same problem.

05HD

You have absolutely no idea how much fuel you are using with that method.

Put a FULL tank of gas in it. Reset the trip odometer and drive until it gets low. Then, put another FULL tank of gas in it. What it says on the pump is how many gallons you used and you can use the trip odometer to figure out your average MPG for that tank.

KyleW707

I'll replace the icm soon, as for the gas mileage estimate i am going off of what the pump says. And resetting my trip too. If i put 10 in it thats a little above 3 gallons. I should not be able to go only 40 miles with on the highway.

Jerry Clayton

Is this new math???? why don't you try using liters and kilometers???

05HD

You still don't understand. You are relying upon the accuracy of the notoriously inaccurate gas gauge to estimate your fuel economy. That is never going to work.

bluedelphium

yes. you MUST start from a full tank, reset your trip odometer, and calculate your gas mileage at the pump next time you fill up. this is the ONLY way to accurately determine your miles per gallon. the fuel guage is inaccurate and worthless.

ahritchie

iTrader: (1)

LOL dude STILL doesn't get it!

KyleW707

Uh...yeah i do get it. I realize you have to put a full tank in it to get the real average im not an idiot. But what im saying is, i put $10 in it once and gauge says i used almost half a tank (and yes i realize i didnt really have half a tank) but the next time i put $10 in it the gauge only showed that i used 1/8th of a tank. I dont think yall understand what im saying