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Old 05-14-2010, 08:43 PM   #1 (permalink)
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Default Fifth sensor

What is the Fifth sensor on the transmission used for and can I do without it?
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Old 05-16-2010, 01:02 AM   #2 (permalink)
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the "fifth gear" switch turns the EGR off. The EGR valve sends a small amount of exhaust back into the engine. this lower the combustion tempeture and reduces NOX, a smog forming compound, but the trade off is that the engine produce less power. In fifth gear the samurai needs every bit of power it has. you can drive just fine without the switch as long as you stay in the right lane and out of my way
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Old 05-16-2010, 06:59 PM   #3 (permalink)
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The EGR also acts to enrich the fuel mixture by adding inert exhaust gas to the air being drawn into the intake.

I've always assumed the ECM turns the EGR off when it goes into overdrive.

I've noticed however that my rig stinks of fuel ever since I broke the wire to my fifth gear sensor. Now I'm wondering.... Does it tell the ECM when the car is NOT in fifth gear to turn the EGR on? If so, it will always think it's in overdrive and leave the EGR off all the time.

Anyone know for sure which way it works?
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Old 05-17-2010, 07:20 AM   #4 (permalink)
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That is why I asked this question. I don't have much smog equipment left on this vehicle. I discovered this Fifth switch while troubleshooting the back-up light problem. The wire from the Fifth switch goes directly to the ECM. What it does from there I don't have a clue. Anyway....thanks for the return answers.



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Old 05-17-2010, 09:33 AM   #5 (permalink)
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a lot of the switches on the samurai are ground switches. If it switches to ground I can just ground it while it's running and see if the EGR valve does anything...

edit: anyone know what temp the EGR valve opens at? I assume it has to be above high idle too.
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Old 05-17-2010, 12:02 PM   #6 (permalink)
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Quote:
Originally Posted by Baratacus View Post
Now I'm wondering.... Does it tell the ECM when the car is NOT in fifth gear to turn the EGR on? If so, it will always think it's in overdrive and leave the EGR off all the time.
The 5th gear switch tells the ECU that its in 5th gear, theoretically if there is no switch then the ECU will always assume that its in another gear. However, there is a fault code for the 5th switch so the ECU must make some check, maybe VSS v RPM.
There is no 5th switch on other models, the EGR switching is based on primarily on load, temperature and vehicle speed.
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Old 05-17-2010, 02:16 PM   #7 (permalink)
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the fifth gear switch completes a ground circuit when trans is in fifth gear. If you are trying to fool ecm and turn off egr , you will need to ground the wire.
the Samurai ,even when new, used outdate engine control system. A modern engine control uses sensors like throttle posision, air flow sensor and engine/vehicle speed sensor to determine load and turn off and on the egr.

the thermostatic vacuum valve opens at 149 F , the vacuum source is above the throttle plate so no vacuum unless throttle is part open. the egr system has a back pressure valve to stop vacuum at idle . to verify egr opperation you will need a vacuum gage with a long hose so you can see it while driving.
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Old 05-17-2010, 04:53 PM   #8 (permalink)
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could you just bring your throttle up above high idle? Thanks for the info. So far it's looking like my problem only coincidentally started around the time my 5th gear switch came disconnected, but this will definitely help me find out for certain.
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Old 05-17-2010, 09:32 PM   #9 (permalink)
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Another option is to make a block off plate for the EGR. There are two bolts that connect the EGR value to the intake manifold. Just remove the two bolts and unhook the rubber lines, make a plate out of aluminum or an old license plate to cover the opening into the intake, apply some gray rtv to the non-gasket side of the plate, and reinstall.

I have a 1.6 8v with EFI, so I can use 5th at 40mph with no problems. And since it is disengaged in 5th anyway, what is the harm of not having it available at all. Not sure what effect it will have on NOX emissions, but will find out in Sept when I have to do the emissions test.

I suspect that the EGR might have been stuck open. When I blocked off the EGR, I also removed the stock fan and clutch and replaced it with an electric fan. After making those two changes, I did have more power. There is a hill that I travel each week to visit my parents and before I made the two changes, I would have to downshift at 40mph after starting out at 45mph. After the changes, I was able to maintain speed without downshifting.
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Old 05-18-2010, 12:43 AM   #10 (permalink)
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most places wont pass you if you don't have an EGR valve. some states and counties don't do a visual inspection and have pretty relaxed emissions requirements. More and more areas are going to CARB standards though and you need the EGR for those places. The 1.6L engine on the trackers/sidekicks didn't use a 5th gear switch to shut off the EGR valve. They use a temp sensor and their engine management is a lot more sophisticated than the 1.3L engine. So if you're running EFI you shouldn't have a hook up for the 5th gear switch on your ECU.
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