JTB91RS

I have a '91 Camaro RS, which was originally a 3.1L v6. After an engine swap to a carbed 350 (it will eventually be TPI, but until then, it is a bit of a mutt with the electronic HEI distributor), the temperature gauge is not working, and the fan does not seem to be kicking on. I found that the ground loop for the fan relay was not connected. Fixed that, relay and fan seem to work, but still won't kick on automatically.

I discovered that the CTS was missing a pin, so I pulled the old one off the V6, but still nothing. The engine must be warmer than 160 deg F because coolant is circulating through the upper hose. I ran continuity tests on the yellow and black wires from the sensor to the ECU, and both passed. I also ran a test from the black wire at the sensor (gnd) to the chasis, and that passed, but when I turned on the ignition and ran the same test, it failed. I was wondering if there may be a bad ground, or if maybe there is a problem with the MAP sensor since they share the same gnd.

I believe the ECU (7730) is working properly, since it is controlling the fuel pump
correctly. Any thoughts?

Thanks,

John

BigBadLou

iTrader: (3)

Yes, I would check the grounds. They are usually at the back of the heads or block which is a pain to get to but if you're missing one, it could be the source of your problem.

You could measure the resistance on the black and yellow wires at the ECM but disconnect it first. Refer to the CTS resistance table for proper values.

Hope this helps.
Lou
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BTW, I just noticed your location. I'm flying to Orlando tomorrow. If you're in the Melbourne area, I can look at it if you want. I'll be sitting at the hotel most of the nights anyway.

Lou

JTB91RS

Yeah, it seems like every time I turn around I find another forgotten ground. Unfortunately, I won't have a chance to look at the car for a few days since it is across town, but I will give it another look. I also plan on repeating the last test with the MAP disconnected to see if that has anything to do with it, as well as trying an alternate ECM (a 7749 with a custom v8 prom).

Could you please tell me where to find the CTS resistance tables? I came across one earlier on another site, but it really didn't seem to be too good since it only had about 5 data points.

Thanks,

John

BigBadLou

iTrader: (3)

I found this: https://www.thirdgen.org/forums/atta...ase-ctsmat.gif

Can't vouch for 100% vcorrectness but it should tell you whether your CTS is bad or not. Mine was and it was making my engine run rich.

Lou

JTB91RS

Thanks! This table is a LOT better than the one I saw earlier. I will check the numbers sometime this weekend and let you know.

JTB91RS

OK, I checked the wiring again and found 2 more ground loops. I connected those and took it for a test drive. Once again, the gauge didn't change. Got back and tested the resistance across the CTS. It measured 356 Ohms (about 175 deg F), which seems reasonable considering that I only went for about 1.5 miles. I am at a loss. Any suggestions?

BigBadLou

iTrader: (3)

Hmm, since you don't have a workin gauge, how do you measure the engine temps? Infrared thermometer? Because you'd have to get it up to operating temps (10 minutes of driving) and then let it idle for another 10 minutes to let it reach hot enough point where the ECM would turn on the fan.

If the gauge is not working, check the sensor between the first and second spark plugs on the driver side and also check the green wire. Turn the key on and disconnect the wire and watch the gauge, then ground the wire on the block and look at the gauge again. Did it change at all?

Lou

JTB91RS

Bingo, just found it! that sensor was not installed on the new motor, and the green wire was just free hanging. I am going to install it now, but I won't get a chance to test run it again until tomorrow (still need to get it to an exhaust shop and don't want to upset the neighbors this late). The temperature I gave was not actually measured, it was estimated based on the resistance value across the CTS, but hopefully with the second sensor installed, I can use the gauge for the next reading. I will try again getting it up to temperature tomorrow and let you know. Thanks again.

JTB91RS

OK, the new issue related to this is... I went to remove the plug from the driver's side head between Cyl #s 1 & 3, and discovered that it does not take an allen key. OK, no problem, I will just try my 3/8" rachet and that will fit just like a normal plug, right? Well, it is not that simple it appears... Chevy decided to use a plug that has a 5/16" square hole (#&@%!). I have attached a picture of the same sized plug that I found on my old engine. Anyways, I was wondering if there is a particular tool I can use to remove the plug, or if I should just try removing it with a pirce of 5/16" bar stock and an open ended wrench. Any thoughts?

JTB91RS

OK, I tried using a 5/16" piece of square bar stock today, but that fitting was stubborn and rounded the bar. Since I am replacing the LO5 heads in another month or two anyways, I opted to temporarily put the other sensor on the intake manifold as well. I can now see a temperature reading, so I let the car warm up, and the fan kicks on now. Looks like the ground loops that were not connected most likely were the culprits after all.

Thanks again,

John