2002 Tacoma "Pig Mode"

Hey, everyone. I'm making the message board rounds trying to solicit ideas for a problem I'm having. This has been a tough one to search because it involves fuel mileage, and any search immediately brings up fuel economy specs or questions about oversized tires, not problems pertaining to fuel economy issues under certain conditions.

I have a 2wd 2002 Tacoma with a 2RZ-FE and manual transmission. Managed to score a 2wd extended cab with small tires, and not the 4wd Pre runner with the big tires. Have around 150,000 miles.

Been frustrated with the fuel economy and power on the highway, lately. Actually, I've suspected it for a while, but only really became sure of it,recently, when I started making long regular weekend trips. Around town I get about 25+mpg, but on the highway I get about 18 and can't get out of my own way. When I have my 200lb dirt bike in the back, I have to floor it to hold 75mph up hills. Seems like it enters this "Pig Mode" as soon as I reach 60mph, as I can hear the engine take a more labored tone. In fact, if I keep to driving around 55mph, like on back roads, it does great, just when it gets over that 60mph mark, we're in "Pig Mode" and it sucks gas.

I have a suspicion that this happens at a specific engine speed, rather than highway speed because, once, when I tried to beat someone to an entrance ramp from a light, they were able to motor around me in this clapped out Saturn when I tried running a couple of gears up in the RPM's before shifting. It took off the line well and I could keep ahead early, but when I stretched the gears out, there she went. This was surprising because, when I first got the truck, I REALLY pissed off an early 00's Mustang GT driver doing a similar thing, because this truck really had legs in the upper RPM's. Seems like around 2100 RPM (maybe a little more) is when all this "piggy-ness" starts to happen, which is where I'm at for 60mph.

Maintenance items I've checked/replaced/adjusted so far:
New NGK Spark plugs (gapped)
Valve lash (tried loose end of range, tight end, and now am in the middle-ish)
Tire pressures (rotate every other run down the highway)
Air Filter
PCV valve* (see O2 sensor below)

Checked codes last week (no light): None

Did the "Spray carb cleaner around vacuum sources" thing: Nothing

*O2 sensors were replaced around 125K when the light came on and city mileage dropped. Light went off on its own after replacement, city mileage was better (about 23mpg) until I replaced the PCV valve, then city mileage came all the way back. Highway mileage was having this issue before the O2 sensors, I believe, and still does.

Tried resetting ECU a couple of times: No change

Looked at the Mass Air sensor, but the whole intake tract looks spotless (I don't run an oiled air filter)

I finally gave up and called the local mechanic. He asked what I had done and, when I gave him the above, he said "Take it to Toyota. You've already done what we'll do" and apologized. Would really prefer NOT to take it to Toyota because, besides being about 30 miles away and would be needing to take time off, last time I went for something they just told me the problem I told them I was having, and that was it. (though, I need to look into the ball joint recall, anyway)

Last thing: I have a fuel filter I've been dreading trying to put in since I realized Toyota decided the 22RE fuel filter on my '89 was too easy to get to, and made this one tougher.

Thanks!

 

Now check for a plugged CAT.

 

yep, what he said, loss of power at higher rpm is indicative of a plugged cat, you'll eventually get codes for it, but lots of people report similar issues without a code.

if you feel adventurous you could drop the exhaust from the cat through the tail pipe and see how it runs then.

 

Have had this issue myself for quite some time. Same exact symptoms. I was convinced it was my cats. Got whole new exhaust system with a high flow cat and no change. So make sure you check your cat. A laser thermometer before and after cat sometimes gives a clue. otherwise you could get a back pressure gauge to tell for sure. I'm starting to wonder if it may be a transmission issue with 4th. But I know almost nothing about transmissions. Seems to be shifting fine.. Idk. I've replaced the maf too and no change. All the usual tune up suspects.. Except a/f sensor... So I'm subbing in hopes of other options to check out.

 

I'm really not trying to be an ass about your problem OP, but couldn't it just be that the 2RZ is a dog on the highway? The biggest thing that would disprove that is if you saw an abrupt drop in mileage and/or power recently, but I didn't see you directly reference that.

I had a 1996 4wd manual w/ the 3RZ engine and it was terribly slow on the highway with both stock tires and 32s. I have never driven a 2wd/2RZ Tacoma so I really can't speak from direct experience, but the Xtra cab trucks coupled with a 4cyl engine aren't about to win any races or fuel economy awards.

Anyways, I wish I could be more helpful but nobody else had offered that answer yet. Looks like you've been thorough so far and good luck with it.

 

Something is definitely wrong. I have a 96 taco, 2rz 5speed reg cab. It's gets 27mpg highway. And can run 75-80 no problem. In fact, it will run all the way to the speed limiter. It also has 258k on it. Like mentioned above, check your cat. It could be blocked.

 

So, it's been a couple of years, and I've been screwing around with this the entire time. I'm now 90% sure I know what this issue is: dust ingestion.

I've gone through pretty much every system possible in this truck, including the cats (checked those two ways), unnecessarily replaced a number of things, and bought all kinds of diagnostic tools (except a leak tester). How I came to the conclusion it was dust damage was, while fooling around with the intake tract looking for a vacuum leak, I discovered a prominent dusting of Georgia red clay on the sides of the air filter box on the "clean side" of the air filter, suggesting the rubber seal on the filter didn't seat right at one time and let it a lot of junk when I went to a couple of my dirt bike races. I confirmed it with a compression test, finding that cylinders 2 and 3 were a fair amount lower than the others. Before the compression test, I had bought a Blue Driver OBD Scan tool that let me monitor the ECU in real time and npoticed I had a large negative fuel trim, running about -15% or more, meaning the ECU was reading way rich and trying to compensate. I think, then, the engine would run lean, start to detonate, and the ECU would pull the timing back, completely choking the power. The valves leaking into the exhaust explains this, so this engine is definitely mechanically hosed. I'm now annoyed at Toyota for, among other things, not using the V6 air filter box, which is a slide-in style of loading the air filter. I mean, they use the same oil filter on every damn engine they make, but they couldn't use the same easier-to-load-and-check-for-seal air filter on all of their Tacomas?

Anyway, there was also a secondary issue of a clogged fuel filter I caught early on, I presume, caused by the ethanol in today's fuel absorbing some water and corroding fittings, since this is a pre-ethanol truck that wasn't my primary driver. Changing that early on bumped up the power and mileage a little. I then followed with some cleaned injectors, but that didn't contribute any gains. A fuel pressure gauge showed the fuel pump was fine.

I'm not going to go into everything I've done since realizing the issue, but I was able to get back a lot of the mileage and drive-ability with two things: running premium gas, and increasing the valve lash on the exhaust side of the two lowest compression cylinders to the max I had shims available for, which was about 0.014-0.015in.

I now run between 24 and 25mpg, the higher mark having been reached hauling a bed and cab full of camping gear and coolers, and with a passenger, down the highway. It actually handled that quite well. The gains come with caveats, though, such as not having the guts it used to in higher rpm's, not rewarding large or sudden throttle inputs with a lot more action, and struggling to hold its speed with the cruise control. I guess the ECU tries to dump more fuel in with large TPS inputs, then wigs out when it picks up extra gas in the O2 sensors. It really likes the below 2000RPM range, long steady pulls of gears, and half throttle, but I can merge on the highway pretty well, still, if I roll on the throttle steadily. It's definitely a different beast and I do miss how it used to run.

From here, I've been trying to get it out of my mind and get my '89 pickup back on the road so I have the option of working on this one. Since first-gen Tacomas are so old, now, and starting to get hard to find, the most reasonable course of action, if I keep this, would be to pull the engine and rebuild it. I'm considering finding a 3RZ and rebuilding that. I've also seen JDM 3RZ's on ebay, but don't know how trustworthy those engines are.

The other course is to buy another truck, but, holy crap, are these things huge and expensive, now. They've all be re-made to cater to the lifted/big tire crowd and leave poor choices to those like me who want to haul things down the highway without breaking the bank in gas and tires.

 

damn... she just might be wore out. 2RZ-FE... is this a distributor cap rotor ignition system? if so, part of the mpg issue could be a mismatch rotor/cap. My dad had an old Mazda pickup and during the tune up couldnt the parts shop had brand x cap and brand y rotor... mpg droped by a few mpg after replacing plugs, wires etc. Got to thinking about it and put the old cap rotor on for a test and the mpg came back. The air gap between the mismatched cap rotor was enough to cause the loss in mpg.

 

No, this is the later coil pack version. While messing around with it I've come to realize it's a pretty sophisticated system, always trying to bump up the timing to max out what it can get, unlike my '89 22RE which is more like the old school set-with-the-timing-light-and-that's-all-you've-got.