Fuel Trim Affected by Bad Coolant Temp Sensor? [Archive] - DSM Forums: Mitsubishi Eclipse, Plymouth Laser, and Eagle Talon Forum: DSMtalk.com

: Fuel Trim Affected by Bad Coolant Temp Sensor?


mooky
06-13-2005, 05:12 PM
I'm getting bad gas mileage in my stock '95 Tsi (OBDII). Pulled some codes, the descriptions were that the fuel trim wasn't adjustable because of a faulty coolant temperature sensor. Engine runs in open loop ALL the time. Runs very fat, too, as you could imagine. I replaced the CTS with one I had from another car. Same thing. Before I go off to spend $$$ on a sensor I won't be able to return, I'd like to find out the specs on the CTS. What resistance values for which temps on this thing? I've searched the forums, I can't find it in the manual I have. Nothin' but 1g info out there (seems like it anyway). Does anyone know?

Thanks!

-mooky

iowaboostin
06-13-2005, 07:07 PM
Weird.. I've been getting mad fuel cut and my CTS is also busted. I JUST got back in from installing a new one, that'd be the best if it fixed my fuel problem :cool:

It's kinda hard to see how the two are related, keep your fingers crossed though.

stevep
06-13-2005, 08:27 PM
2G turbo ECT resistance:

68F 2.1k to 2.7k ohms
176F 260 to 360 ohms

From the 2G FSM.

Steve

SLO_smiley
06-13-2005, 10:52 PM
actually, the computer cannot really copensate fuel trim when in open loop...there are 3 things that trigger closed loop and one of those is engine temperature. when it goes to closed loop, the computer is able to make an output decision to command the injectors and all the fuel related components depending on the input it gets from the appropriate sensors like the Coolant temp sensor, MAF, O2 sensor....etc.

mooky
06-17-2005, 02:52 PM
The plot thickens....

I bought a new coolant temperature sensor from Advance Auto. I installed it first thing in the morning yesterday (before I ran the car). I cleared the codes by disconnecting the battery. I reconnected the battery and started it up. I went in the house to get ready for work. When I came back out, the car was overheating. The cooling fan never came on. I shut the car down and let it cool off for a while.

Later, I leave for work. It idles at 2k, the engine fan never comes on, there's no CEL and my fuel mileage is still bad. This morning, I slammed the old sensor back in. The car idles normally and the engine fan comes on when it should. I didn't get a CEL until 65 miles into my commute. I'm not sure about the fuel mileage. I'll check the codes at Advance when I take the CTS back. I'm pretty sure it's junk.

Why would a supposedly bad CTS work well enough to trigger the engine fan. The new CTS won't. I'm guessing the CTS is good. But is it good enough to trigger the fan but not good enough to trim the fuel? WTH?

I need a diagnostic flow chart.

-mooky

SLO_smiley
06-18-2005, 12:02 AM
the sensor itself is a resistor...so there is a chance it could have been a bad one...we got a bad blower motor sensor our of the box at work..uggh..anyways...but is the wiring ok? if you take voltage readings does it go to its 5volt reference like it should? it shodl also go to 5volts when the senosr is unplugged....that makes sure your wiring checks good.

mooky
06-19-2005, 04:31 PM
the sensor itself is a resistor...so there is a chance it could have been a bad one...we got a bad blower motor sensor our of the box at work..uggh..anyways...but is the wiring ok? if you take voltage readings does it go to its 5volt reference like it should? it shodl also go to 5volts when the senosr is unplugged....that makes sure your wiring checks good.


The wiring seems OK. Is 4.7V close enough?

The code for the coolant temp sensor seems to have gone away, now. The one and only code being set is: P0170 Fuel Trim Malfunction. Sounds like a hard error. The ECU is an EPROM unit w/105 degree C caps. They aren't leaking.

Anyone have any insight on this code?

Thanks!

-mooky

mooky
06-28-2005, 03:07 PM
GOT IT!

It was the O2 sensor. I went to Advance Auto and picked up a Bosch 4 wire universal O2 sensor. The install was painless. The connector/adapter they give you makes it possible to keep your factory connectors on the harness side. Really slick. Installation was even more effortless after I removed the driver side engine fan (don't know if that's in a FAQ somewhere...thought I'd mention it).

Looks like my fuel mileage is better than it ever was and the throttle response makes things a whole bunch more fun.

-mooky