1990 Lumina temp guage problem
dwalmop
10-13-2004, 04:18 PM
I just swapped engines in my 1990 lumina. Everything was picture perfect except that the temp guage doesn't work, the oil press. guage is pegged, and the coolant fans don't come on anymore. I tried swapping both the ecm temp. sensor by the thermostat housing AND the guage sensor in the right cyl. head, and nothing has changed. Someone please help!
jeffcoslacker
10-13-2004, 04:40 PM
Check your grounds.
richtazz
10-14-2004, 12:30 PM
did you use the sensors out of your old engine or new ones. If the engine donor car had idiot lights instead of guages, they use different sensors that won't work with your guages. Also, did you properly bleed the cooling system. If there is air caught in the system, it would cause your guage to not operate.
dwalmop
10-14-2004, 09:32 PM
Ok, here's the deal. I took the old guage sensor from the old cyl. head and plugged it into the the new the wire. I put the guage into nearly boiling water to see if guage would react inside car (yes, the ignition was on) and nothing happened. Is this a valid test? It sounds kinda stupid but I thought it'd be a way to see if the problem was the sensor or not. Also, would the ECM sensor be different too if the donor engine car had idiot lights? Oh, and just to make sure, the ECM temp. sensor is by the therm. housing and the guage sensor is on one of the heads, right? Or do I have it backwards?
Kooterskkar
10-14-2004, 11:45 PM
The cylinder head temp sensor is for the ECM. IT tells the ecm when the engien is warm enough for it to come out of open loop. The one by the thermostat is the one you should test.
jeffcoslacker
10-15-2004, 07:48 AM
Grounding the wire directly to the motor should give a full gauge/computer response.
dwalmop
10-15-2004, 07:55 AM
Ok one last question - I am used to working on old engines where the radiator is positioned so that the cooling system needs not to be bled. What is the correct procedure to bleed these things? I also have a 96 monte carlo that I will need to do this to because it needs a thermostat.
dwalmop
10-15-2004, 07:57 AM
BTW - which wire should I try grounding to the motor? On the one sensor, there is black and yellow, on the other there is a dk. green wire.
jeffcoslacker
10-15-2004, 09:14 AM
On the one-wire, you simply ground it. On the two-wire, you connect them. That black wire should be a ground at some point. Might wanna investigate that. Try a test light if it still doesn't work right.
jeffcoslacker
10-15-2004, 09:19 AM
There is at least one, possibly two bleeder screws, at the little tower above the water pump, and at the t-stat. I like to take the screws out, and fill the radiator 'till coolant comes from both, then start and allow to warm to operating temp, shut down and wait 15 minutes or so, and crack the bleeders again and refill to purge any air. Then road test, as usually they will idle all day and not get hot, but heat up rapidly when driven if air is trapped. Make sure the engine stays normal temp, then let idle 'till fans come on, and all should be good.
jeffcoslacker
10-15-2004, 09:33 AM
When chasing glitches like this, I've found it helpful to always verify that everything that should be grounded, is grounded. There is usually a point on the motor where several grounds come together at one spot. If that's corroded, it will make things not work. If it's clean, but the motor isn't properly grounded due to a broken or missing ground strap, same thing. Nothing electrical can function properly without a ground. Can save a lot of head-scratching and tail-chasing.
dwalmop
10-15-2004, 09:39 AM
Thanks for the advice everyone. I won't have time to really try anything until sunday, so we'll see what happens.
richtazz
10-15-2004, 11:09 AM
one last hing, Kooter, you have the sensors backward. The one in the rear head with the single green/black wire is the guage sensor, the one near the t-stat is the ECM sensor. The boiling water test didn't work because the sensor has to be grounded to the engine.
dwalmop
10-15-2004, 12:41 PM
I was wondering about the grounding to the engine part. But I questioned the which sensor is which as well and I looked on the schematic. richtazz is correct.
Kooterskkar
10-16-2004, 12:58 AM
one last hing, Kooter, you have the sensors backward. The one in the rear head with the single green/black wire is the guage sensor, the one near the t-stat is the ECM sensor. The boiling water test didn't work because the sensor has to be grounded to the engine. Ahh, your right. I keep getting those backwards for some reason. :screwy:
richtazz
10-16-2004, 09:27 PM
that's ok Kooter, we all have a brain fart occasionally. You normally give good sound advice, so don't sweat it.
dwalmop
10-18-2004, 01:20 PM
Ok I tried to ground both sensors and no response. As long as the ignition is on, I should get some kind of response, right? If I ground the ECM sensor the fan should kick on if it's working? I just want to make sure I understand correctly.
Kooterskkar
10-18-2004, 03:47 PM
Ground it with a wire, then stick it in the hot water. The coolant temp sensors are thermoresistors. The hotter it gets the less resistance.
dwalmop
10-18-2004, 04:12 PM
Oh yeah! I forgot about that fundamental law of physics dealing with resistance and voltage! How embarrasing, I'm an engineer. Got the gauge figured out, now onto why the hell the coolant fans don't want to come on.....
dwalmop
10-18-2004, 04:15 PM
Can anybody tell me where the oil. press. sender is on this thing? (3.1 mpi) that doesn't work either, since the donor engine had idiot lights, and I need to swap that thing.
richtazz
10-19-2004, 02:55 PM
The oil pressure sender is on the front of the engine just above and to the right of the oil filter.
dwalmop
10-19-2004, 04:07 PM
Thanks again
richtazz
10-19-2004, 06:54 PM
anytime, that's what we're here for.
dwalmop
10-19-2004, 11:08 PM
I would like to make sure I'm bleeding cooling sys. properly. I didn't lose much coolant replacing the sensors, so I opened the valve on top the t-stat housing and unscrewed the cap on the transfer hose and dumped coolant in radiator, but nothing came out of the openings on engine. After spilling all over out the top of the radiator, I started the engine and let it run until the gauge went down a bit (from t-stat opening) and waited a bit and repeated the process. I don't think anything happened, I actually think more air got in the system. Should I have been doing anything while the engine was running? When I drive it the gauge doesn't bounce around at all like I've seen when there's air in the system, but it does seem to heat up quickly when I'm driving it. I feel kinda stupid with this thing, it seems like it should be a simple process, and my haynes manual doesn't say anything about cooling system bleeding. Once again, I appreciate everyone's help.
quaddriver
10-19-2004, 11:18 PM
Ok lets slow down a little bit and go over the pertinent W-body wiring step by step.
The entire engine harness EXCEPT KS is contained in the large 2-connector cable that plugs in by the passenger side headlight.
I am leaving out the crank sensor harness which passes under the left hand side (facing) motor mount.
The cooling fans are NOT part of the engine wiring harness at any point. You can pull relay 1 and 2 and jumper the fan lead to hot with a pair of needle nose pliers and test the fans to come on. IF they do and the relays are not bad (you can test for relay fire with 2 pieces of wire) then it is up to the ECM. both relay coil lines will have voltage at them if the fans are off (key on, engine off, engine cold, ac off) - the ecm supplies ground.
For the coolant sensors GM ALWAYS uses the one in the head for the coolant gauge and ALWAYS uses one in the intake for CTS (old ECT). The one in the intake is ALWAYS 2 wires and the ECM measures a variable resistance. The one in the head is either 1 or 2 wires, but the second wire (if equipped) ALWAYS goes to ground and this sensor sinks voltage to ground, more voltage = hotter = higher gauge reading.
the sensors may look similar, they may screw in the same holes, but electrically thay are not the same.
What you want to do is plug in a scan tool, start her up and watch the temp climb. If the ECM is not seeing temp after a calculated run-time, then a code in MALFLG1 will be set for 'CTS too low'.
If the ECM is reading temp, then the problem is in the gauge module (check the gauge fuse?)
But next, for grins, lets check the grounds.
T codes have a couple grounding places that it is EASY to overlook - did you connect the ground strap BEHIND the motor where the left side (facing) tranny output shaft housing is bolted to the motor? 2 wires there I think. Then there is a nest of wires on the tranny bellhousing bolts, bolt 2 and 3 I think both have a number of wires that connect.
A few notes about the cooling fan, the flag for fan 1 will be set at a certain temp (I am not by my manual) OR AC demand. The flag for fan 2 is not set until its REALLY hot AND AC demand.
Using same scan tool, do not blame the ecm, fans or relays until you see the flags change on the scan screen, and the fans dont come on.
and no, autozone, advance, pepboys etc do not have nor any longer sell the proper scan tool
The entire engine harness EXCEPT KS is contained in the large 2-connector cable that plugs in by the passenger side headlight.
I am leaving out the crank sensor harness which passes under the left hand side (facing) motor mount.
The cooling fans are NOT part of the engine wiring harness at any point. You can pull relay 1 and 2 and jumper the fan lead to hot with a pair of needle nose pliers and test the fans to come on. IF they do and the relays are not bad (you can test for relay fire with 2 pieces of wire) then it is up to the ECM. both relay coil lines will have voltage at them if the fans are off (key on, engine off, engine cold, ac off) - the ecm supplies ground.
For the coolant sensors GM ALWAYS uses the one in the head for the coolant gauge and ALWAYS uses one in the intake for CTS (old ECT). The one in the intake is ALWAYS 2 wires and the ECM measures a variable resistance. The one in the head is either 1 or 2 wires, but the second wire (if equipped) ALWAYS goes to ground and this sensor sinks voltage to ground, more voltage = hotter = higher gauge reading.
the sensors may look similar, they may screw in the same holes, but electrically thay are not the same.
What you want to do is plug in a scan tool, start her up and watch the temp climb. If the ECM is not seeing temp after a calculated run-time, then a code in MALFLG1 will be set for 'CTS too low'.
If the ECM is reading temp, then the problem is in the gauge module (check the gauge fuse?)
But next, for grins, lets check the grounds.
T codes have a couple grounding places that it is EASY to overlook - did you connect the ground strap BEHIND the motor where the left side (facing) tranny output shaft housing is bolted to the motor? 2 wires there I think. Then there is a nest of wires on the tranny bellhousing bolts, bolt 2 and 3 I think both have a number of wires that connect.
A few notes about the cooling fan, the flag for fan 1 will be set at a certain temp (I am not by my manual) OR AC demand. The flag for fan 2 is not set until its REALLY hot AND AC demand.
Using same scan tool, do not blame the ecm, fans or relays until you see the flags change on the scan screen, and the fans dont come on.
and no, autozone, advance, pepboys etc do not have nor any longer sell the proper scan tool
dwalmop
10-20-2004, 12:07 PM
Wow I never knew there was so much to it. Everything in my car is working fine now, but for future reference, when jumpering the fan lead to hot, which 2 is that? I've noticed the terminals are numbered. If you're not sure which ones without looking at it don't waste your time, I'm sure I could find a manual or something to let me know. BTW, the primary fan kick-on temp is 230. Thanks everyone for all the help again.
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