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Unread 01-09-2015, 08:16 PM   #1
acts1013
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Help With ECT Sensor and Purge Solenoid

Hey all...Google has been directing me to this site's wealth of information for years when I've run into issues. Figure it's time to join up and come here directly.

Got two questions about my 95 Grand Cherokee Laredo, 5.2 V8, ZJ (Dunno if these need to be separate threads)...

1. Ever since I had the water pump replaced (it was 7 degrees and had to be done that night or I would have handled it myself) my Jeep has been throwing the code for the Engine Coolant Temperature Sensor. I replaced the sensor but it's still throwing the code for the ECT sensor and the Jeep is still having trouble starting and running crappy. I think the two-wire plug to the ECT is bad, was put back on backwards, damaged, etc. Now, I'm thinking about switching the plug around to see if that fixes it or potentially rebuilding the plug (it doesn't appear to be one-directional). My question is, if the two wires get backwards or crossed what will happen? Will anything be damaged?

2. In the process of working on the ECT sensor, I noticed the purge solenoid wasn't mounted on its bracket. While trying to put it on the bracket, I broke the two plastic hoses that come out of the solenoid (It was 2 degrees). I've been trying to find pictures online of how these are supposed to be routed. One goes to a splitter and one does not. Can someone please take a picture of which hose goes to the splitter and which does not please?

Thanks a ton in advance for the potential responses and potential help!

<><------------<<<
Acts 10:13

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Unread 01-09-2015, 09:33 PM   #2
ZeeJay1997
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Quote:
Originally Posted by acts1013 View Post
My question is, if the two wires get backwards or crossed what will happen? Will anything be damaged?
no. the sensor is a thermistor and the PCM sends a ground to it on one wire and reads the output on the other wire.

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Originally Posted by acts1013 View Post
how these are supposed to be routed.
check the sticker near the radiator... maybe on the fan cowl
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Unread 01-09-2015, 09:41 PM   #3
kg6mov
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On a 95 there are two sensors. Did you replace both?
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1998 ZJ Platinum Limited 5.9, New engine and trans, no front driveshaft, but it's pretty

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Unread 01-10-2015, 02:53 AM   #4
Uniblurb
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Originally Posted by kg6mov View Post
On a 95 there are two sensors. Did you replace both?
Curious where this 2nd ECT sensor is located on the 5.2 since can't find it in the 95 FSM? I know the front one is located next to the thermostat housing in a water passage in the intake manifold.

I remember on some older engines where there was a 2nd coolant temp sensor near the rear of the intake just for the coolant temp gauge. Since the one next to the T-stat housing is communicating with the PCM I would think this would be the one causing a code, or the wiring itself, if faulty. Besides it would make the engine run bad if faulty since info supplied to the PCM adjusts injector pulse width and timing.
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-Stalling ZJ? 12 things to check before replacing a sensor; the Dirty Dozen
-Crankshaft position sensor multimeter test. & video of testing.
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Unread 01-10-2015, 07:49 AM   #5
acts1013
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Quote:
Originally Posted by ZeeJay1997 View Post
no. the sensor is a thermistor and the PCM sends a ground to it on one wire and reads the output on the other wire.

check the sticker near the radiator... maybe on the fan cowl
Thanks for the info on the ECT wiring. I knew that it channeled very little power (like 5 ohms or something). But I just wanted to make sure!

On the purge solenoid hose routing, I'll check for any info under the hood today.

Quote:
Originally Posted by kg6mov View Post
On a 95 there are two sensors. Did you replace both?
On my ZJ, there's only one sensor. But there is another nearly identical looking part that isn't a sensor but is a sender for the heat gauge. The sensor has two wires and the sender only has one. And the wiring isn't piggy backed off one another (in sequence). My heat guage is working fine so I have not replaced the sender.
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Unread 01-10-2015, 07:50 AM   #6
acts1013
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Any other input here? Especially on the purge solenoid hose routing?
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Unread 01-10-2015, 10:53 AM   #7
Uniblurb
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Quote:
Originally Posted by acts1013 View Post
Any other input here? Especially on the purge solenoid hose routing?
Couldn't find any emissions hose routing in the 95 FSM last night. But in the 94-96 ZJ parts list they're showing the top purge solenoid line routed down, which must connect to the charcoal canister because of the fitting on the end, and the bottom line which must connect to the intake manifold for vacuum where the emissions fumes are drawn in to be burnt.

No splitter shown but it may be after the left #2 line in the below diagram. Most just replace the plastic line with fuel resistant hose since the plastic becomes so brittle as you know. Good luck.
zj-94-96-5.2-purge-solenoid-hose-routing-650x300-p.-25-460-94-96-parts-list.jpg

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-Stalling ZJ? 12 things to check before replacing a sensor; the Dirty Dozen
-Crankshaft position sensor multimeter test. & video of testing.
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Unread 01-10-2015, 09:07 PM   #8
acts1013
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Fixed!

Quote:
Originally Posted by Uniblurb View Post
Couldn't find any emissions hose routing in the 95 FSM last night. But in the 94-96 ZJ parts list they're showing the top purge solenoid line routed down, which must connect to the charcoal canister because of the fitting on the end, and the bottom line which must connect to the intake manifold for vacuum where the emissions fumes are drawn in to be burnt.

No splitter shown but it may be after the left #2 line in the below diagram. Most just replace the plastic line with fuel resistant hose since the plastic becomes so brittle as you know. Good luck.
Thanks for that diagram. That's the clearest pic I've seen thus far. I went out and checked to make sure I had them rerouted correctly and I got it right. And I did exactly what you're saying...replaced with fuel resistant hose that will hold up in the cold a lot better in the future.

Anyway, finally solved the ECT Sensor mystery. I replaced the sensor. No dice. Was prepared to use some radio shack parts, some solder, and some electrical tape to make my own pigtail for the sensor (hence all the questions earlier). When I pulled the old pigtail off and tried to route it outside the engine so I could access it easily I found the problem. The friend that replaced my water pump and thermostat housing gasket must have removed the power steering pump to get clearance. And when he put it back he pinched the ECT wires and basically broke one of the wires in two.

Easy fix...use some bullet terminals, shrink wrap, solder, and electrical tape and did it right. No more Check Engine light. And man does she run way better with the correct fuel/air mixture for the temperature!
ect-wires-pic.jpg  
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Unread 01-10-2015, 10:50 PM   #9
Uniblurb
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Good deal and glad you got it fixed!
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-Stalling ZJ? 12 things to check before replacing a sensor; the Dirty Dozen
-Crankshaft position sensor multimeter test. & video of testing.
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