# Crossed jumper cables, poor gas mileage



## Guest (Jun 30, 2003)

Just wanted to ask the experts. I crossed my jumper cables a while back when I was trying to jumpstart my 89 sentra in a panic to make it to work on time. I thought the fusible link was the only thing damaged after I did that, since after I replaced the black fusible link the car seemed to run fine. Now, I have run a few tanks of gas through it and she seems to be getting really poor mileage around town. On the highway, I am not so sure, since I don't drive much on the highways anymore. I checked the EGR valve and it doesn't seem to move when I rev the engine. I also read in my FSM that if the polarity is crossed on the EGR canister control valve that it will cease to function. Could crossing my jumper cables have caused this valve to break and that could be the reason for the poor mileage around town? Thanks in advance


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## gophrsplatter (Apr 11, 2003)

i don't know anything about that polarity crap but my 90 sentra was sucking down gas like my friends 305 until i put some gas treatment/fuel injector cleaner into it and it is back to normal...i have to do that every half month or around that b/c gas mileage gets so bad i can't afford to buy anymore gas.....just try that see if it helps any.


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## Guest (Jun 30, 2003)

I took a long trip a while ago and dumped in a lot of the chevron techron fuel injector cleaner. I seemed to get better and better mileage on the highway, but then when I got back to driving around town, my mileage dropped back to what it was before the trip. Now I am getting about 200 miles or less out of a tank of gas, when I used to get in the low 300's. My EGR valve doesn't seem to be moving, and I don't really feel any vacuum when I rev the engine and put my finger over the vacuum hose going to the EGR.


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## WhiteFox (Sep 4, 2002)

Check the O2 sensor. Mine was bad when I got roughly 200 miles to the tank before.. I hear those things are sensative to electrical fubars.


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## Guest (Jun 30, 2003)

Thanks, I was wondering about that too. I figured the O2 sensor would be OK, since I replaced it just before crossing the jumper cables and the car seemed to run ok, and the computer only has a code 55 in it, meaning everything is fine. I think I have my old O2 sensor from when I replaced it last. Do you think it would be ok, to replace it with my old one, as a test?


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## WhiteFox (Sep 4, 2002)

I'd guess the O2 is okay then. Try out diagnostic modes 1 and 2 if you want to see it in action. If it was nuked, I'd think it wouldn't be working right or giving another code.
Scratch that idea then..


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## Guest (Jun 30, 2003)

Thanks, I will do that when I get a chance. I still think the EGR valve isn't working correctly though. I felt underneath it and pressed on the diaphragm and the engine will start to die, but when I rev the engine, I don't feel the valve move at all. Can a broken EGR system cause a severe drop in mileage? Thanks again for all of your help.


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## blownb310 (Jun 10, 2002)

BSHAPLEY said:


> *Can a broken EGR system cause a severe drop in mileage?*


 ***** No. Like Whitefox said, check to make sure the O2 sensor is working right. Put the ecu into diag mode 2 [oxygen sensor] and hold the rpms at about 2,500 [fully warmed up] and see that the led goes on and off more than 10 times in ten seconds. It should.


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## Guest (Jul 2, 2003)

Thanks, I am going out of town tomorrow, so I will check it out on Sunday night. I'll let you know what I find. Thanks again


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