Check engine light in 97 Expy?
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New User
Joined: Jun 2004
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Check engine light in 97 Expy?
Hey guys. I was driving cross country this weekend and my check engine light came on. Now, I checked all of the fluids and nothing was low. The ruck was still running GREAT as it usually does but I was just worried. The wierd part was that it was off and then I stopped to get gas. Once I turned the truck back on is when the light came back on. Does anyone have any ideas on what might be wrong?
Also, I noticed that right before the light came on I started to get poorer gas mileage. I have 103,000 miles on the truck. Is it maybe time for a tune up? Is that why the light went on? Thanks in advance for any help. I love this site!!!
Also, I noticed that right before the light came on I started to get poorer gas mileage. I have 103,000 miles on the truck. Is it maybe time for a tune up? Is that why the light went on? Thanks in advance for any help. I love this site!!!
Elder User
Joined: Jun 2004
Posts: 679
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From: Orlando, Fla
You have four o2 sensors, two just aft of the exhaust manifold, which is probably the problem ones. Plus two more aft of the catylitic converters, these rarely have problems. The Passenger side one is a bear, but doable by the home mechanic, make sure you use an o2 socket to remove them. You can pick one up at the auto store after you have verified it is the sensors.
Elder User
Joined: Jun 2004
Posts: 679
Likes: 0
From: Orlando, Fla
You bet, the o2's collect exhaust gas info and send it to the computer to correct richness or leanness. If one goes down, then your computer goes into a default so the truck will run, the default is an estimate fuel/air mixture to get you to where you can get it repaired. You probably noticed a bit of a rough idle and sluggish throttle response in return.
It is time for a new plugs, shouldn't go over 120k, be sure to replace with recommended plugs, don't use Bosch double platinums. If you haven't done this yet on an Expy, I suggest you read about it first. The process is easy as far as undoing the coilpack screw, unplugging the c'pack, pulling it and the boot out then undoing the plug. The hard part is getting to them, there are "reads" you can check out by using a search here on site. The first time I did it, it took 3.5hrs. I have it down to 2.5 without removing the fuel rails.
One suggestion, after removing the coilpack/boot, blow out the recess with air to get the dirt out before removing the plug. This way you don't get any dirt in the cylinder. Usually the dirt that gets in there is the sand type and motors don't like sand.
It is time for a new plugs, shouldn't go over 120k, be sure to replace with recommended plugs, don't use Bosch double platinums. If you haven't done this yet on an Expy, I suggest you read about it first. The process is easy as far as undoing the coilpack screw, unplugging the c'pack, pulling it and the boot out then undoing the plug. The hard part is getting to them, there are "reads" you can check out by using a search here on site. The first time I did it, it took 3.5hrs. I have it down to 2.5 without removing the fuel rails.
One suggestion, after removing the coilpack/boot, blow out the recess with air to get the dirt out before removing the plug. This way you don't get any dirt in the cylinder. Usually the dirt that gets in there is the sand type and motors don't like sand.
New User
Joined: Jun 2004
Posts: 15
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Gas Mileage and O2 Sensors
You know, when my O2 sensor was bad, I got great mileage. I was running so lean that I was getting 3 to 4 more miles a gallon. Of course, sometimes the miss was not worth it. I got the front two and all was good.
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Elder User
Joined: Jun 2004
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From: Orlando, Fla
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