Cpasour

Ok so here is what happened, my truck ran hot but I cut it off before it ever got to the red. Now it runs good till it warms up then sometimes it runs good and sometimes it runs like crap. Hesitation, has a miss at low RPMs. This problem comes and goes. Did not have any problems till ran hot. I cannot figure it out HELP please

Sturmcrow

These engines are known to have head gasket issues after overheating. Not getting to red does not mean it did not overheat, since you need water flowing through the engine to get a good read on the temp. I am assuming that your water was not flowing, hence the overheating.

Do you have any other head gasket problem signs? Oil in the radiator? Bubbles in the radiator? Coolant reservoir smelling like exhaust when you pop the top? Milky brown oil (from coolant mixing in)? White smoke from the tailpipe?

Cpasour

I have checked every sign of leaking head gasket except compression test. All other signs say that no leak.

Sturmcrow

Good news. Did you need to refill the cooling system? I believe that leaving an air bubble trapped in there can cause some of the problems you are having. Did you go through the procedure of warming up the engine with the rad. cap off to get all the air out?

I've only been a yota truck guy for 8 months. Hopefully someone with more longevity than myself will come on soon and point you to some easy solutions.

Cpasour

The the water was flowing, my electric fan died on me and didn't know it till it ran hot. I going to try and burp the coolant tomorrow. If it has a leaking head gasket would it run bad all the time. My problems come and go. Is there any sensor that could get messed up if it over heats? I am getting cel code 21 and the light goes off and on. I think 21 is the 02 sensor but I wouldn't think an 02 sensor would make it run that bad but I don't really know ˟˟˟˟ about Toyotas this is my first one

Sturmcrow

Ok, that is good news. As long as some water was in there, you are probably in the clear with HG problems.

The O2 sensor can really mess these trucks up. Countless recommendations have been to stick with OEM too (I think it is the DENSO model). Definitely do not put a Bosch in.

That said, sometimes the O2 sensor code comes up when you actually have a wiring problem. You could check that you have continuity in the wires. All in all, you could not go wrong by putting in a new O2 sensor either way, as they really do make the truck run better in the long run and will likely improve your fuel economy.

Cpasour

Ok thanks for the info, the 02 sensor on the truck looks new but I didn't put it on and I don't know what brand I haven't looked. I will check the wiring and is there any way to check the 02 sensor?

Cpasour

I checked my 02 sensor at the diagnostic connector under the hood I put 1 probe in the ox1 and the other in b1 and at idle and at about 2500 rpms it's reading 8.4 in trying to find out if I have bad connection, bad 02 or tested wrong

Sturmcrow

Here's the FSM section that deals with diagnosing the oxygen sensor in our trucks.

http://personal.utulsa.edu/~nathan-b...42oxygense.pdf

Good luck with that. Its a fairly complicated flow chart. I do not see any mention of ox1 or b1, so you may have been testing incorrectly before. In case it is not clear from the page, you can test the O2 sensor heater circuit by disconnecting the O2 sensor wire and measuring resistance across two of the pins.

I think I may check out my own O2 sensor when I get a chance. I like better fuel economy after all.

Cpasour

Thanks for the link I hope I can get this truck figured out

Cpasour

Ok so I got my meter out check everything I could find and found that the coolant temp sensor was bad. I replaced it and it ran like a new truck for about a day then started getting code 52 and 21. It has had code 21 since I bought the truck. Now it runs like crap, I replaced the knock sensor pigtail and still code 52. The cel light only comes on when the truck warms up, when its cold it runs great and no light. I just don't really know what to do without tearing it back apart to replace the KS but I don't really want to buy a $130 sensor if its not bad. Is there anything else that may cause code 52?

Cpasour

Also it runs fine and power returns when I hit about 3k rpms

Sturmcrow

It may be possible to check the KS. I was just watching a video yesterday where a fellow check the resistance through the KS and used that as a metric for whether it was good or needed replacement. You may have to check the FSM for the procedure, if it exists. If you are lucky, you might be able to check the resistance from somewhere outside of the pigtail, since it would suck to have to pull the whole plenum again.

Kinda a long shot, but have you checked your engine electrical grounds?

Gamefreakgc

The code 52 can be a side effect of your engine running poorly. I had a bad distributor and it threw a code 52, cleared up after fixing the dizzy.

EDIT: didn't see at first that you electrical fan quit on you. Do you not have a mechanical fan? If your fan quit, that'll overheat your truck in a hurry. Check that first before doing anything else (you might still want to check coolant though).

I'd hold off on getting too deep until you fix the overheating issue. First, you'll want to make sure you have good coolant. You are supposed to replace coolant every 5 years (unless you have some odd long-life stuff in there, doubt it). Drain some out in a container. You should not see any debris. If it's green coolant, it should be fluorescent in sunlight and not show any signs of rust or reddish brown color. If you have red coolant, make sure it does not look brownish. If you do need to replace the coolant, do a complete flush, not just draining the radiator. This involves heating up the truck to operating temperature (be sure to make sure it doesn't overheat!) opening the drain cock on the radiator and constantly pouring water (distilled water if your tap water is hard) in the radiator until only fresh water is coming out. This flushes out the other half of coolant that is in the engine that a radiator flush doesn't change. You can google "coolant flush" for how-to's.

Also, you may have a thermostat that is going bad. It's located downstream of the lower radiator hose. I think there's three bolts holding it in. You'll need to drain the coolant (good time to replace/flush if needed afterwards). See below:

http://personal.utulsa.edu/~nathan-b...10thermost.pdf

Some people have had issue with aftermarket t-stats. I used a Duralast one from Autozone with no issues but if you like to play it safe get it from your Toyota dealer. This job is very simple and straight forward to do. Make sure you truck is COLD though, or you could get some nasty burns from hot coolant. I never could find the lower drain cock on the engine block, too much grime on my engine...

If that doesn't clear up your overheating issues, then you've got either a water pump going bad, blockage, or a bad radiator. There's only so many issues that cause overheating, all of them coolant related. Good coolant keeps everything running smoothly.

Gamefreakgc

The fact that it's fine when cold tells you something. When the engine is cold, it runs in open loop, meaning it runs off preset values that do not change. Once it reaches normal operating temperature it switches to closed loop. In closed loop, the ECU adjust things such as fuel mixture, air, timing, etc. to perform at it's best, based off imput it receives from the various sensors located throughout your engine. Seeing that your issues are only when warm, you've got something that is malfunctioning, probably a sensor, causing the issues. Your issues sound a lot like mine when I first got my truck. I've done so much work on mine though... hope you like working on your truck!

Code 21 is bad heated oxygen sensor circuit. A heated oxygen sensor means that it has a small current the flows through the sensor, literally heating it up so it can accurately read oxygen levels. Older vehicles don't and instead need to be warmed up before the sensor works. Since most of the heating circuitry is in the sensor, replacing it fixes it 90% of the time. Rarely, you'll have a wiring issue but a quick visual check of the wire (just follow it up to the ECU) will clue you in. Any damage on the wire indicates a possible short.

Our trucks don't like cheapo off-brands, try and get a DENSO oxygen sensor, will run you about $90. If not, try a BOSCH but beware, you might have issues.

Then don't buy it. I'm not convinced your knock sensor is bad, I think there's something else causing the engine to run poorly and as a side effect, throwing a 52.

Cpasour

The overheating issues is fixed it only did it one time when the electric fan died. I was thinking that it maybe something with the dizzy but I had a new one when I got the truck. Not sure if it is my only problem but I was going to take the dizzy cap off and the end fell off one of my plug wires so I gonna get some wires and replace the cap and rotor also I have my fingers crossed. Also does anyone know where I can get the blade for the mechanical fan, I hate the electric fan

TNRabbit

Do you need the plastic blade only or the entire fan clutch unit?

There's a local Pick-A-Part in Fredericksburg, MD, that has an entire fan & clutch unit in the 4 runner there....you could probably get it for $25 or less.

Cpasour

Thanks TNRabbit but MD is a little to far for me to drive for a fan but I do need the whole assem. or just the plastic blade I can buy the clutch at about any parts house but nobody sells the blade

Cpasour

Ok so new wires, cap, rotor and still running like crap. Misfiring and backfiring through the intake when running below 3000 rpm. I'm so sick of this truck it had to be the worst truck I have seen to trouble shoot and work on it is my first experience with a Toyota and will damn sure be my last if I ever get it running good it will be gone

Gamefreakgc

Haha, calm down there. We've all felt like that at one point or another. In reality, these trucks are some of the most reliable and longest lasting trucks out there. I'm nearing 300k miles on mine and expect many more.


I would have a compression test done on all cylinders. I had a shop do this for me for free. It only takes a few minutes of their time (compression tests can be done wrong and some meters just plain suck). It sounds like you may have a intake valve that is stuck open. What that means is during the compression cycle, the valve that lets air into the engine is still open and allowing the flame and pressure to escape back out through the intake. Once you hit higher rotations per minute, the valves open and close faster so the issue is lessened. This would explain what you experience while driving.

It could only mean a valve adjustment (did that one myself) or a valve job which included pulling off the cylinder heads and replacing valves and resurfacing the heads (more labor intensive).