View Full Version : Performance and Fuel Economy Issue

09-14-2006, 06:29 AM
OK, i recently got an s13 and im having some issues with it. I have tested a few things and well this might get a lil long.

The car right now is wasting crazy amounts of gas, and when say crazy i mean like 200 miles to the tank type crazy and this is driving at 3k RPM and shifting no higher than 3k. So i hooked up a scaner to it, o2 reading is between .2 and .8, so thats good. The Engine/Coolant Temp however doesnt seem to want to go up pass 176deg, yesterday i started the car and it was at 176deg the whole time, then poked around, check the sensor, found that the sensor was unplugged, plugged it back in, so now i start the car, i go from 145deg to 176deg in about 15 to 20 mins. Now, i was advised that the temps are to be around 200deg, so i check the sensor, i have good resistance, the temp housing was about 131deg and i got about 616ohm when testing for resistance. Then i tested from the plug to the ecu, well i got .2ohm, so those 2 check out fine. the teacher suggested that it could be a bad ecu stuck on the 176deg "safe" mode and that is affecting the gas milage due to the ecu reading the incorrect temps and setting the incorrect fuel setting.

So, do you guys have any other ideas that i can try, or if anything can help me confirm that this is indeed the problem, i dont feel like buying an ecu, well i dont know the prices for it.

the car is 91 240SX-LE Model, KA24DE

09-14-2006, 07:59 AM
...is ur check engine light on?

u can get a KA ecu for like $20? on ebay

09-14-2006, 08:04 AM
I have a #10 (I believe its a 10, but it is definitely auto KA and worked fine) KA automatic ECU in my garage that I'll give you for the cost of shipping and a sandwich... PM if interested

Also, can you test the KA ecu's for trouble codes? (I never tried on the KA)

09-14-2006, 10:38 AM
I have no CEL, which it would make sense since the Coolant temp sensor is working, i think that the ECU is not allowing it to go higher than 176, do you guys happen to know if 176 is the normal operatin temp for the 240, i wouldnt think it is since more thermostats are 195deg, but then again im new to the 240's.

broken240, are you sure that a Auto would fit a 5speed car, would have think that the fuel trims are a little different, but if it would run OK, then im deff interested.

09-14-2006, 04:16 PM
How fast is the O2 sensor oscillating?
Should be ~5 times per second.
Auto ECU will work but you may throw a code - many people use them on 5 speed swaps.

Take a look at the FSM ( check the proper operation temperature.

09-14-2006, 05:29 PM
the o2 is cycling correctly, i do see it jump back and forth... cant really tell you the correctly cycling becuase i dont remember off hand.

The FSM says that the account has been suspended..

I red about the auto ecu on the s13 is consider an upgrade i guess. I pmed Broken240sx about his, so lets see what happens.

THanks for all the replies guys.

09-14-2006, 06:54 PM
I saw a fuel economy improvement after I did the following.

1) cleaned intake piping and throttle body and ofcourse new filter
2) switched to syntheic oil *love my royal purple*
3) cleaned the coolant out of the radiator and cleaned the engine block as well, the refilled. New thermostat and cap were applied as well
4) started running 91 octane and did a fuel injection cleaner.
5) got new spark plugs and changed the rotor and cap on my distrobutor.
6) new fuel filter helps
7) yes a proper o2 sensor helps as well.

did all that and went from 18mpg to 26mpg on a SOHC ka *known to not be as great as a 95 DOHC ka*

Siberian Husky
09-14-2006, 07:22 PM
^^^ im with stupid..

i'd do all them little tedious things before switchin out the ecu...almost anything can effect gas milage

09-14-2006, 11:07 PM
if your coolant temp is not raising 1st ting to do is check ya thermostat it may be stuck open because if the thermostat is stuck open coolant temps dont rise very well to operating temp and it takes a long time if it does. if tha isnt the prob the coolant temp sensor may be your problem.

09-14-2006, 11:10 PM
could be your coolant temperature sensor (not the one going into the cluster). if your sensor is shitty/old/corroded, it may not accurately read temp, thinking the car is always cold. it will then dump more fuel to make the engine warm up faster.

just a possibility.

fyi, i got pretty shitty gas mileage on my old sohc, ~230-250 miles to the tank. didn't really maintain it other than oil changes though.

09-15-2006, 12:46 AM
Yes coolant temp sensor!!!

pull it and most nissan dealers have it in stock around the 20 dolla mark (MSRP) so hit them up. for the most part provide them info regarding weather its a two prong or single prong connection to ensure you get the right part. There are two different temp sensors on 240's thats why I said that.

09-15-2006, 06:55 AM
The coolant temp sensor tested good. I did a resistance test and it came out good, the numbers were according to the info on Mitchell 5. The temp of the block was about 131 and i got 616ohm of resistance, which is pretty good and close since the 176 temp was suppose to be 300 to 330ohm in resistance.

09-17-2006, 02:30 PM
have you checked the thermostat as yet? it may be stuck open.