1990 Lumina temp guage problem

[dwalmop]

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]

Check your grounds.

[richtazz]

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]

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]

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]

Grounding the wire directly to the motor should give a full gauge/computer response.

[dwalmop]

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]

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]

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]

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]

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]

Thanks for the advice everyone. I won't have time to really try anything until sunday, so we'll see what happens.

[richtazz]

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]

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]

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.