Throwing Code 21 in my 165 and wont boost past 5 need advice

[KillBill]

When I bought the car, the engine light was on. It was throwing codes 23 and 21. I had a general tune up at the Toyota dealership and they also replaced the O2 sensor with a new sensor. Now i'm just throwing code 21. The car runs like a champ but has never boosted past 5. I'm going off the reading on the boost gauge on the instrument panel and an aftermarket gauge. They are both showing 5 at full boost. Any advise on what to do next?

[KillBill]

If the pre-cat was gutted, would the engine light be on...throwing code 21?

[underscore]

what is code 21 for on the 165? The way these older cars work, with the single pre-cat O2, I don't think removing the cats makes a difference as I literally only have a muffler.

[alltracman78]

IIRC code 21 means you're running lean.
It may be a bad O2 signal to the ECU [damage to the wiring], it could also be a bad AFM.

That's one big problem with these old ECUs, the diagnostics aren't that great.

[underscore]

lean could also be intake leaks, or bad O2 wiring.

[88gt4DE]

run mine de-cat and never throws any codes. I'd be looking for vaccum leaks to since you only boost to 5psi ... maybe wastegate stuck open a little er something ....

[alltracman78]

lean could also be intake leaks, or bad O2 wiring.

IIRC code 21 means you're running lean.
It may be a bad O2 signal to the ECU [damage to the wiring], it could also be a bad AFM.

;)

Cat has nothing to do with it on these cars, the cat only effects the catalytic efficiency monitor on OBDII cars.

If it had a vacuum leak that could def cause a lean code, but it would also cause a low idle.
If the idle is fine there probably aren't any leaks.

An open WG actuator wouldn't cause code 21, it would just cause low power [and low boost].

It is possible there are 2 separate problems.

Time for some troubleshooting...

[underscore]

well if it has a CEL it won't boost past 4-5 PSI anyways, so once he fixes the code 21 he should be able to hit the normal 7psi

[88gt4DE]

I think I'd be looking for cooked / melted / broken wires over the alternator first since he's got the new 02 sensor installed ... I've had issues with my brothers with alternator wiring issues there and that same car is now setting an intermitten 21 , just havent been back to re-wire it since reported to me ...

[KillBill]

Dam, you guys rock...thanks for all the responses.

[KillBill]

Is it true that whatever code you throw, the boost wont go past 4 or 5? The car runs great for only going up to 5...I dont even know what it is like to have full boost so I may just leave it as is.