Hi.

Well, I feel I have a sensor that my be not working properly as I am not getting that great of mileage. I have the 5.2L engine and am only getting 9-10mpg per tank (I am currently at 210 miles and in need of a fill up), which I feel is a bit low. Also, the exhaust smells bad (not cold starts, when hot) and my smog numbers are relatively high (HC PPM 106, NO PPM 889 at 15mph and 80/662 at 25mph, I brought the truck in hot too).

I just did the plenum plate (it was definitely blown) and timing chain and I was expecting to get better results, but I did not really see that big of gains. The smog numbers were from before I did the plenum, so they may be slightly better.

I figured that the issue was from the cat being clogged, however I did a pressure test at the pre-cat o2 sensor and was getting next to 0PSI. That didn't satisfy me, so I borescoped in and the cat looked very clean. Also there are about 4 welds directly after the cat so it looks like it had been replaced at least once at one point. The front o2 sensor was replaced about 2 years ago (before the plenum was done) and I don't think that that would be enough time for the plenum to ruin it, right? Also, there are no codes being thrown, so I don't think the o2 sensor is faulty. Is there any way to test the o2 sensors?

I feel that there is a sensor screwing up somewhere and making it run lean, but I'm not too sure. Could this be faulty/dirty injectors? I was reading about replacing the injectors with 4 hole injectors, would they help with this issue?

I really have no idea where to start when it comes to these sensors, so I was just looking for some help.

Thanks!

 

You should be able to do better than single digit fuel economy...... Since plenum, and timing set have already been done, I would take a long, hard, look at the front O2 sensor. Any idea what brand it is? What size tires ya running? What gears in the diffs? How many miles on the truck?

 

Dealer window sheet for my '92 Ramcharger - with 318 Magnum and A518 automatic sez - "11mpg city/13 mpg highway." And I get around 10mpg in mine. We're average.

 

with an automatic trans:
12 MPG combined city/highway
11 MPG city
15 MPG highway

with the manual trans:
14 MPG combined city/highway
12 MPG city
16 MPG highway

From what I have read the PCM sometimes will compensate for a faulty O2 sensor by adjusting the voltage to the sensor. You might try resetting the PCM (disconnecting the battery) to see if it will throw a code after it resets and you drive it for awhile. Doesn't cost anything but some time to give it a try.

 

The O2 sensor is a Bosch 13399, it is an OE fit. Tires are 265/75/16 with 3.55 gears. The truck is also just shy of 200k.

I was doing a bit of reading and it looks like 15mpg is what it is rated for on the highway, and considering I drive it very lightly, especially now since I have yet to fix the wild vents problem and in these hot days I need my AC, I feel that I should be getting much closer, or is a 30-40% loss in mileage to be expected in this old of a truck?

 

Bosch was stock?

 

No, bosch simply fits. Denso was stock.

Replace your bosch sensor with a Denso, or NTK sensor. I bet your fuel economy improves.

 

I just ordered an NTK, I'll install as soon as I get it and report back. Thanks!

 

Be sure to reset the PCM after you install it. Let it relearn the engine. Let us know how it turns out.

 

Just curious (and a tad lazy), what part number did you find for the upstream sensor? I found a couple.