GorgeRunner

My 1990 22RE pickup has been having gas mileage issues. I was getting about 20mpg when it should be getting about 28mpg. I found a vacuum leak that brought it up to 24-25mpg, but something is still not right, so now I'm thinking one of the O2 sensors may be going bad. There is no Check Engine light on or diagnostic codes, so I'm working on an educated guess.

The truck has about 152K miles and I replaced both tailpipe O2 sensors at 90K in 2006 when the Check Engine light came on and diagnostic codes indicated a bad O2 sensor. It's a "California Emissions" engine so I replaced the upstream tailpipe sensor first, but the Check Engine light was still coming on intermittently, so I replaced the downstream sensor and that did the job.

The replacement sensors are NTK and I'm wondering if ten years and 60K miles is about the lifespan of those units. Is an O2 sensor going bad sound like a good place to start fixing the mileage issue? Which sensor would you replace first, or would you do both at the same time?

wyoming9

iTrader: (1)

Where are you getting the 28mpg figure ??

I get between 15 and 18 and I was quite happy

I never ever saw 20mpg in any 4x4 with my use of said vehicles

GorgeRunner

Forgot to mention it's a 2WD. It's been getting about 28mpg since the day I bought it.

I had a 4Runner so I know what you mean about the gas mileage....

wyoming9

iTrader: (1)

Yes that makes a difference

GorgeRunner

I bought the upstream O2 sensor, hopefully that will do the trick...

Terrys87

iTrader: (1)

I would go with Denso sensors. I get mine from sparkplugs,com and get the exact replacement if you are going to change sensors. Then I would do a complete tune up using factory replacement parts.

When was the last time the Intake was cleaned to remove all the carbon? When was the last time all of the vacuum lines were replaced? Are they in great shape?

GorgeRunner

I got a Denso sensor from sparkplugs.com to replace the NGK sensors in there now. The truck has been tuned up recently, new air filter. Fuel filter replaced not that long ago. Checked all the vacuum lines carefully, pretty sure they are good. Since it has been running rich, I may run SeaFoam through the intake to clean everything out before I replace the sensor.

Terrys87

iTrader: (1)

If you want to read the following pages https://www.yotatech.com/forums/f199...l#post52147101 to get an idea of what all gets carbon clogging things up. With the amount of miles you have on your truck, Seafoam will help with some but I am willing to bet your EGR, port holes and some vacuum lines are clogged up.

That carbon get hard as concrete in some places. I operate a drill bit with my fingers to get some of the lines cleared out. Inside the Intake, I use a long screw driver to break up the big chunks and then when I get as much as I can broke loose, I take the Intake to the carwash and spray it out with high pressure.

I see you have changed a few parts out but when I work on a truck that has high miles or been neglected on maintenance I do one big job at once. First I can check a few places to see how bad the carbon is to get an idea if I need to pull the Intake. If that is the case I Pull and Clean Intake, Pull the EGR, Clean the EGR, on the EGR not only are the vacuum lines clogged but the Plunger inside the EGR can have carbon build up that the Plunger can not move.

With a long vacuum line I can suck on the hose and you can hear and see the plunger move like it should. I don't have to deal with emissions test but I have always gotten and EGR to operate and function as it should when done. To get the EGR operating can take liquid cleaners, coat hangers, drill bits and lots of patience.

It takes me about 3-4 hours Cleaning the Intake, cleaning the EGR, a complete tune up with factory parts, clean all the sensors that are in the Intake as the ones that are operating in the antifreeze gets a hard water build up on them. (I have fixed some cold start issues by cleaning the Cold Start Injector Timing Switch this way) setting the valves.

Not knowing the history of the truck and going by experience, your truck will have carbon everywhere, hard water build up on the sensors, (just use a brass tooth brush to clean the sensors until they are brass shiney) several lines clogged with carbon including the EGR Modulator.

Once you get the system cleaned and new tune up parts installed, follow either Haynes or Factory Service Manual for the Timing and Tune up steps. To do it correctly really is not as bad as it sounds. Just do not mess with the Throttle Body Position Sensor. Leave it attached to the Throttle Body. Just remove the Throttle Bodys 3 bolts and 1 nut from the Plenum and clean the air hole in the Throttle Body to Plenums and carbon off of the back side. Do Not mess with the TPS adjustment screws and you will be okay.

To pull the Plenum you should replace the brass washers on the Cold Start Injector, not saying I always do but you should especially if this is the first time you have taken an Intake off. Anytime you remove the Cold Start Injector from the Plenum and on Start up always check to make sure there are no leaks as there is lots of pressure.

Another thing I just remembered is that I have never gotten a Check Engine Light for the Air Flow Meter. The only time you will get a CEL is if you leave the electrical cable disconnected. I have had some badddd AFMs and never turned on the light. Get a multi meter and follow the resistance checks outlined in the manual. Make sure the flapper moves freely as well.

GorgeRunner

You're right, a vehicle this old is going to have more than usual maintenance. I've taken good care of it and run Berrymans B12 in the gas tank every few months, I don't know if that will help carbon buildup or not, hoping it has had some positive effect. Cleaning the sensors is a good idea, I may clean the temp sensors, easy enough job. Hoping I don't have to remove the intake, but if a new O2 sensor doesn't help with the gas mileage, I may have to.

Terrys87

iTrader: (1)

If you have to clean the carbon out, just pull it down to the Plenum. Leave the lower Intake on. You wont need to pull the Injectors or Fuel Rail either. With some of the pictures in the above link that I posted, if you find the EGR and some of the other ports clogged, you should pull the Plenum and clean everything out.

I have been into enough of these trucks and the 22re that with the above steps done from cleaning, parts and correct timing, you can have a motor that will start with in one revolution of the motor.

If you go thru any of my threads below, you will see the fuel system is one of the first things I normally start on. You will see the fuel tank have so much build up in it in most cases that it looks like rust. It is not rust, but a chemical build up in the tank from the fuel additives in the tank. I don't suggest running fuel cleaner thru the tank as I have seen it break down the build up and clog fuel filters and I have seen it clog injectors.

The rubber line coming off of the back of the fuel rail that goes to the metal line usually on the fire wall but could be on the inner fender depending on where Toyota places it in some years, the Fuel Return Line, I see clogged more time then not. I would say 3 out of 5 trucks the Return Line is clogged. The line can be clogged all the way from the fire wall to the "J" line on the Fuel Pump Assembly Bracket.

I just run SeaFoam thru the Intake and in the crank case when I want to give it a good cleaning to avoid breaking up the crud in the fuel system and causing problems. Todays fuel is junk. In my opinion, with todays fuel, there is enough ethanol in the fuel to help keep water out of the tank. Here in the Midwest, corn is a fuel subsidy and a certain percent is required to be added to the fuel. The corn growers are wanting a higher percent added to fuel. I wish they would do away with the ethanol myself.

I see you have the 4 speed transmission. If you are wanting a little better mileage, I would swap in a truck 5 speed transmission or I have even installed a transmission out of an 83 Celica and it is a direct bolt in fit with no issues. It has to be a 91 or older transmission as the older ones are mechanical driven speedometers and the 92 and newer are electrically driven. Just to make you aware of that if you wanted to go that route at a later time.

highonpottery

iTrader: (1)

I'd do all that work mentioned in the engine bay and then I'd maybe repack the wheel bearings and drain/fill your gear oils - when's the last time you gave those any service?

GorgeRunner

Wheel bearings were serviced about six months ago, fluids are changed every 30K. Even though this truck is a somewhat modest vehicle, it is well taken care of.

GorgeRunner

I've done more to try and solve this poor gas mileage problem, but am not having much success. As suggested in this thread that some of the air intake lines might be plugged, I checked a couple of the lines pictured in the thread and they showed no sign of being plugged. I did not remove any of the EGR lines, so they may be plugged up, but after seeing the condition of the other intake lines, I think that may be possible, but not probable. I cleaned the water temperature sensors. Installed new spark plug wires, inspected and cleaned a number of major electrical connections.

Still only getting 21 mpg when the engine has been at 28 mpg since it was new. The thing is, the spark plugs do not indicate a rich running engine and the truck runs fine. If I was not keeping track of the gas mileage, I would not even know there was some kind of problem. With such a significant loss of fuel efficiency, one might think the CEL would be on or at least throw out an error code, but there is no indication of a problem. The fact that the gas mileage drop was relatively sudden leads me to think more along the line of a failed component rather than a problem that develops over a period of time(like the air intake lines slowly clogging up with carbon). I think I will have to have a look at things I don't really care to mess with, like the AFM or TPS. Maybe there's a leaking injector or something. Nobody likes to see the Check Engine light, but I'm almost wishing whatever is not right would fail completely, kick out an error code and I could get this problem solved.