4.0 troubleshooting
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Joined: Jun 2004
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4.0 troubleshooting
Hi everyone! I am new to this site and you probably heard or seen this before but I am stumped. I have a 1992 Explorer with a 4.0 engine and a 5-speed transmission. My problem started about 2 months ago when the check engine soon light came on. I took it to AutoZone had them test it and it was sending the throttle position sensor code, so I got an new one and put it on and cleared the codes. Well the next time I went some ware guess what it came back on. I went and got it checked again and it was the O2 sensor this time. The O2 that was in there was not even a year old. I changed that and cleared the codes again. With all of this going on I lost some power and my gas mileage went down the pooper. I went from getting 260 mile to a tank to just about 175 mile. It has a very rough start up idle and smells realy rich warm or cold. Any one have any thoughts on what could be the problem. I really need the help!!
Posting Guru
Joined: Aug 2000
Posts: 1,984
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NY, when it rains, it pours! 
Sounds like you're keeping on top of things with parts replacment and keeping that pesky CEL off.
Try removing the vacuum line to the fuel pressure regulator, and see if it's wet with fuel inside. The diaphram on these things tends to rupture, letting raw fuel into the intake manifold through the vacuum line. This causes a very rich mixture, and kills mpg. It might need a new FPR......
Sounds like you're keeping on top of things with parts replacment and keeping that pesky CEL off.Try removing the vacuum line to the fuel pressure regulator, and see if it's wet with fuel inside. The diaphram on these things tends to rupture, letting raw fuel into the intake manifold through the vacuum line. This causes a very rich mixture, and kills mpg. It might need a new FPR......
Postmaster
Joined: Dec 2001
Posts: 3,742
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From: UT
Has the CEL stayed off? All codes pass codes now? Thing to remember when troubleshooting computer trouble codes, is that the computer can only see faults in circuits, not components. For example, an O2 sensor code could easily be due to a broken wire instead of a bad O2 sensor. Rerun the self-tests, check the FPR as suggested, and maybe even put a fuel pressure gauge on the fuel rail.
FYI, you don't need to take it to Autozone to pull the codes. Can be done at home with nothing more specialized than a paper clip. See www.dalidesign.com/hbook/eectest.html for instructions. Codes are output as flashes of the CEL.
FYI, you don't need to take it to Autozone to pull the codes. Can be done at home with nothing more specialized than a paper clip. See www.dalidesign.com/hbook/eectest.html for instructions. Codes are output as flashes of the CEL.
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