false temp readings

[dripley]

Some of you will remember my thread on my engine over cooling problem that turned out to be the gauge reading improperly. It got worse some time after that and started affecting the way the truck ran. I am going to be tearing into it pretty soon and want to see if any you might have experienced anything like this or just have some suggestions. At the time I was lucky to see the low 170's on the gauge. As long as it stayed there every thing worked fine but some times it would drop into the high 160's and the Banks chip would start operating weakly. The low 160's and it got worse and the gauges(pyro and boost)would act up a little. Some times it would drop into the 150's and below. At these low readings the gauges would just drop out and the Banks would just stop working. I bought a Scan Gauge II and it is reading the same temps as the gauge. There is no rhyme or reason to the temp swings. It can do it while cold or hot outside. Cruising down the interstate reading in the 170.s and then slowly drop into the 140;s or somewhere in between. I installed a mechanical gauge under the hood and anytime I look at it, it reads near 190 no matter what the gauge says. It is installed about midway in one of the plugs in the head. I took voltage readings at the sensor and the sender is putting out the right signal, it is just going crazy somewhere between the sender and the gauge. It finally got to where the gauge would not hardly get out of the the 160's and the Banks chip got so erratic I took it out thinking maybe that was causing. The temps on the gauge did go up on average about 8* but it still swings up and down. I have had this problem for quite some time and it has slowly gotten worse to the state it is in now. Cant seem to find anyone who has had this problem any where and thought I would throw it out here. With all the new members maybe one of you might have experienced it.

[dripley]

Let me add a little something to the mix. About 3 years ago when my ECM went out I got some advice from someone on how to trouble shoot the problems I was having. This involved cutting wires to check for shorts and what have you. I cut the wires on the ect sensor and at the ecm. Some other wires to the tps were also cut. I did spice all of these back together and the temp gauge problem was there prior to the cutting of the wires, though not to the extreme they are now. I replaced the pigtail on the ect and soldered everything. Greased and shrink wrapped all of it also. The ecm connections are butt spliced with heat shrink splices and dielectric grease. I would have thought if the connections were going bad I would have more resistance and show higher temps instead of lower temps. I am an electrical neophyte and am basing this on the lower voltage from the sensor equaling higher temps.

[IBMobile]

The coolant temp sensor is a variable resistor type. All of the sensors I work with, coolant, oil, or air temp sensors, are the NTP variable type. With this type of sensor as the temp go up the resistance goes down. If you get a poor contact you get high resistance and a lower temp reading. The best way to test the sensor is with an OHM meter. Take reading on cold engine, note the reading, then take a reading at pin #11 (ground, black/light blue wire)and pin #14 (power supply, tan/black) at the ECM connector. If they are the same you may have a bad temp sensor, if the reading at the ECM connector is higher then you have a wire problem. Note: pin #11 is also the ground for the oil pressure, manifold air pressure , water in fuel, and accelerator pedal position sensors. I couldn't find the specks for OHM reading on the sensors so I took a reading of my truck. Cold engine temp 81f degrees (it's a warm day here), 11000 OHMs.

[dripley]

I replaced the sender a while back and at the time tested the sensor reading volts and not ohms. At one time I had a chart for volts=temp. but cant seem to find it any more. The time the sensor was reading properly at that time. I never checked it at the ECM. Mike has a chart for ohms posted here some where, I will round it up and try reading both ends. The thing I dont quite understand is the swings in the readings. I would think with a bad wire/connector I would see the false reading but why the crazy swings. I have seen as much as a 40* swing just riding down the interstate at a constant speed. My exhaust brake is tied into the ect sensor pigtail. On cold start up it kicks on and is supposed to shut off at 140*. The scan gauge is showing it cut off at 118* every time and the mechanical gauge is reading right at 140*. This makes me agree with what you are saying about the sensor or wiring being the issue, the swings baffle me.

[diesel4life]

Can you temporarily put your mechanical gauge into the port where your coolant sensor is to verify your seeing steady 190* there? Do you have any type of a high idle mod that plugs into the coolant sensor that may be giving you a fit? JR

[dripley]

I will look and see it it will fit there, not sure the hole is large enough. No high idle on my truck but the e-brake taps the signal wire for temp reading. The problem predates the e-brake install.

[Mopar1973Man]

Might for the sake of testing dis connect the Ebrake signal wire for a short period. See if that is causing a issue.

[dripley]

I disconnected the e-brake and no change in the temp readings except it did hold around 180 most of the way home. Fluctuated between 184 and 179, not to unusual.No swings down low on this trip, but have seen that in the past also. It dropped to 170 when I pulled into the grocery store parking lot and I read the sensor with my dvm at 1.107 ohms. That seems to match the IAT sensor chart Mike has, I believe the IAT and ECT work the same. In my brilliant moment I forgot to look at the mechanical temp gauge to see what it was reading. I did just walk out to the truck and look at the mech gauge and it read 150(been sitting in the driveway for 45 minutes) so I started the engine and the scan gauge actually agreed with the mech gauge. Not sure what to think about that, it is the first time I have seen them agree. Makes me think I am not watching that mech gauge as well as I should be. I have an electric tranny temp gauge. Will it work the same as an engine temp gauge? If so I could hook it up and see it in the cab and watch it more closely. So for now I will leave the e-brake disconnected and see if it holds steady for the trip back to work. If so I will hook it up for the return home and see if the fluctuation comes back.

[Mopar1973Man]

Not to :hijack:This is one of the the reason I don't exactly like the Bank module and the Edge Juice. Being both modules work the same way but get different inputs to do the same output. But the point is this one module is tapping in all over the engine getting input for all its output stacked or coupling to sensors. In any rate is it possible the Bank module is screwing up the ECM feeds? Is there possibility that the Bank module has finally having issues and its pulling down the ECM inputs? (Either directly or through the CANBUS if used?)

[dripley]

If by module you mean the tuner and not the ebrake you could be right and thats why I removed the tuner. The temps came up about 8* overall but still fluctuated between the high 150's(though not often that low) to the low 180's. That made me think the tuner was part of the problem. I disconnected the wire from the ect to the ebrake and the temp is holding between 179 and 184. I have not seen it swing but forget to look at it sometimes. It has been like that for the 2 days I have had it disconnected. I am going to reconnect the wire for the drive home and see if it swings.As far as the tuner is concerned it was connected to the MAP, TPS, and the VP. I am pretty sure there is one more tap under the dash but I cant remember for sure, but will check that out soon. The only thing the ebrake is connected to is the ECT(for cold start up) and the PCM for a speed signal. Cant remember which wire I tapped.