check engine lt. only on long trips

[geo95xlt]

my check engine light comes on during long highway trips.i went to datona last month,driving from cleveland it came on about 4 hours into the trip.it has happened on all other trips in the past.this time i noticed the temp. gauge would go up and down about 25% of the temp range in 20-30 second cycles non-stop.i cant believe the temp would actually rise and fall that quickly that often.help!

 

[Rhett]

Mine did that on a long trip too. And the truck ran poorly when the light was on. I figured it was something heating up too much, since I had to run several hours on the interstate before it started happening. It scared me so I stopped and got a hamburger to let it cool off. Once back on the road (after a 45 min meal stop) the light stayed off and the truck ran fine. But then after about another hour of driving the light came on again, and it ran poorly again. I made it back to Missouri but never could figure out what that was.

I have attributed it to bad gas. But then again, I have not taken such a long trip since that time. That was a trip from Georgia to Missouri. Since then I have only gone on 2 hour trips here in Missouri, and the chk engine has stayed off. So, I am dumbfounded...

However; I am still not convinced it was a bad tank of gas...I guess next time I take a long trip I will find out.

My guess is that an O2 sensor was getting a lot of carbon blown by it, fouling it's reading. The truck acted like it didn't know what gear to go into because it was having trouble with the air/fuel mixture. It would "lug" and "bog down" on hills, staying in overdrive when it needed to downshift. I had to punch it to make it downshift like it was supposed to. To the uninformed observer this may sound like a transmission problem, but in reality it is a mixture problem; the PCM (computer) was not getting good info from the sensors, most likely O2.

Hope my info and experience with it helps you...
P.s. do a search here, as there are lots of messages about the chk engine light on long trips.

 

[geo95xlt]

thanks for the info,i'll look around.

 

[KillerXLT]

Deja Vu! My grilfriend went to school in Maryland and I go to Seton Hall. I would make the four hour trip in my explorer every other week. I had the same problem. The temp gauge would fluxuate while the check engine light was on. I would turn the heat on b/c I was in fear that it was over heating. That didn't help so I shut off the whole thing all together and froze my a$$ off. Then I stopped at a rest stop as well to get a bite to eat to let it cool down and it came back on an hour later after driving.. Enough of the boring story. When I went to the STEALERSHIP they told me that it was an 02 sensor and they replaced it. Have not had a problem since then.

 

[mdrut]

That's how mine started..Fuel Pressure Regulator..It will stick it high speeds, High pressure...Changed it, the O2, and throttle position sensor and have not had a problem since..lol

 

[jimbo74]

same thing happened to me when i went to the snow last month. havent had a problem since only on the higher altitudes, maybe that did it ?! lack of air and all

 

[bcorff]

I'm pretty sure it's the O2 sensors. I had the same problem with my '95 except I didn't have the strange temp. gauge activity. I tried changing the fuel pressure regulator and the problem persisted. Then I changed the O2 sensors and haven't had a problem since. Don't forget to reset your computer (disconnect the battery) after you change them.

 

[Rhett]

In my case, there is no fuel in the vac lines which makes me think the fuel pressure regulator is ok...but it could still be stuck I suppose..

 

[mdrut]

Rhett, There was no fuel in mine either..Ran the codes and everything pointed to the O2, replaced and still happened..Someone on site told me thottle pos. sen, replaced still happened..researched the post and read up on fuel pressure reg. and B.I.N.G.O. All better now..

 

[kps36]

The only time my CEL went on was on a non-stop trip from St. Augustine FL to Western Carolina Univ in the Smokys. After filling the tank about 1 hr away, the Check Engine Light went on. stayed on till arrival at WCU. Next morning gone.
Why? This is what I got from knowledable sources. The trip from sea level to @3400ft above in a short period of time without stopping for any length caused the computer to fail to compensate for the air density change and caused the CEL to go on. After cool down, the PCM read the new conditions, not gone on since.
How sensitive is that ?

 

[Rhett]

mdrut I think you have a good point; I ran the codes and it had stored '76' which didn't make any sense to me.

I think I will work to replace the fpr, both O2s, and the fuel filter pretty soon. TPS maybe too if it's not too tough to change.

 

[geo95xlt]

semms the O2's are the prob.are they the sensors on the exhaust manifolds?i've never delt with them before.and in regards to the fuel filter ,how on earth do you get that thing off?iv'e looked at it a dozen times and i still have no idea whats going on there!

 

[93 & 96 EB & XLT]

.just getting on in this post. I just replaced the FPR. still getting about 12mpg was getting 6mpg.

 

[Rhett]

Yea the O2's are on the exhaust pipes, above the cat array most likely on your 95, but I am not sure. My 1994 has 2 O2 sensors, one on each pipe leaving the engine. From what I understand, different years have different numbers of O2's. The later models have "upstream" and "downstream" O2s. The early models (such as 91-92's) seem to only have 1 O2 sensor from what I know about them.

As far as the fuel filter goes, it has a "quick disconnect" type thing in it. There might be a special tool that is nice to have for it. I am going to have to do a little searching on the forum here to find more info, and you might want to do that as well since there has been tons of threads about it in the past...

I think I may bite the bullet and change all of this stuff (FPR, fuel filter, both O2's) and see if I can't restore a little pep and mileage. Only thing is it will cost me about $200 for the O2's and FPR and fuel filter.