I have a '96 4runner with a 2 gen S/C with URD pulley and fuel upgrade kit(not 7th injector). I am having a problem when I am driving around city, highway, or trail, and I let off the gas, the truck will run super rich, in the low 12's on the air/fuel ratio gauge. It gets too the point where I can smell the fuel going through the exhaust system, probably destroying the inside of my cat. Sometimes, I will get a P0172 CEL, which is a rich mixture reading code. And If I am going down a hill, while in gear, the truck will go right into open loop and run lean like it should, but as soon as it goes below a certain RPM, and the motor goes into closed loop, it will be rich again, untill I give it gas. Is this a problem with the tune? Maybe an 02 sensor? Any help would be awesome.

 

Well, first I would check the OBDII outputs and see what they are doing when this happens. See if the O2 seconds are reading funny or anything else jumps out at you.

Next I would check for boost/vacuum leaks, general tune up and then check the TPS sensor.

Also clean and check the MAF sensor as well.

 

As far as tune up goes, the motor maybe has 5,000 miles on it, and everything is brand new, including every sensor except for 02 sensor, TPS, and IAC. I start by testing those. I know how to test the TPS, are you able to test the 02 without a good scanner? Some how to do it with a DMM maybe?

 

Check the MAF anyways, it is the most important sensor besides the crank position sensor.

The O2 output is not a voltage, it is a wave pattern. So only way to really see what is going on there is with a scanner. They have them now for laptops and even bluetooth versions for phones.

 

I cleaned the MAF sensor recently. And the problem did not change. So I need to plug it in to a scanner, and the O2 wave forms should be showing 450mV-800mV, probably on the high end of the scale since its running so rich. But I feel like if the 02 sensor is working like it should, it should be telling the PCM to correct the problem to go back to stoichiometric air-fuel ratio. Now that I think about it more, I am pretty sure the primary 02 was "glazed over" with a white coating when I put it back in. Probably due to the the overheating before the block cracked.

 

A white chalk type coating is not that uncommon for O2 sensors, just depends on how the motor runs.

It should throw a code if the O2 sensor is bad which is why I am not saying jump to replacing it. It is possible for it to go bad and not through a code but also uncommon.

 

Okay good to know, I will check the TPS and MAF.

If the TPS is bad, wouldn't the truck hesitate on accleration? What about the IAC?

 

All possible, the temp sensor is another possibility. It is just really hard to know until you get an OBDII scanner to at least rule some stuff out.

 

I have a scan gauge 2 hooked up all the time. It shows coolant temp, and it float around 197-211 degress. I think it also shows a load percentage, can I use that to test my TPS?

 

That load calculation is not the TPS but just a calculation that the ECU does.

There should be a place for the TPS voltage/percentage in the scanner though. Check that, the O2 sensor output along with everything else to see if anything stands out when it is messing up.

Compare it to when it is running properly.

 

Ill try that. Thanks ace, you the man.

 

Live data from the scanner, at idle

ECT 195 degress
short term fuel trim -2.3 to 2.3
Long term fuel trim -18.0
O2 sensor 1 0.130 to .795
O2 sensor 2 0.065 to .870
TPS @ idle 12
Load % 14.1

My long term fuel trim is really fat, but why? Under WOT A/R is between 11.8-12.1, depending on load. Its only when I am idling down the road, like coming up to a stop light, when the truck running rich, like 11.2-11.8. If I put it in neutral and roll to the stop light, it will be very rich, then slowly lean itself out to 14.7-15.1.

No CEL.

 

Sounds like a slow responding O2 sensor to me. It wont throw a code, and the numbers will look normal. Do you know what your EGT's are?

 

Sounds like for some reason you are getting too much fuel, you are at the limit of the ECU pulling fuel out.

This could be due to a clogged air filter or something else that is reducing airflow. Or a bad FPR.

Something you could try to lean it out some would be to connect the FPR to a vacuum source. In the stock setup it just runs the same pressure all the time but if you connect the FPR to vacuum it will lower pressure at idle and in turn lean you out. Worth a shot.

 

Clogged cat? Leaky/slow injector? What is your fuel upgrade kit? How is it controlled?

 

Other possible causes^

 

So I have a vacuum hose coming off the FPR to a copper compression fitting T, with one of the hoses going to the vacuum/boost gauge, then the top one goes to the back of the supercharger's "boost port". SO the FPR should have vacuum. If the FPR looses vacumm, it will put too much fuel in the rails?

 

Hmm, well there goes that theory.

Maybe the 7th injector is leaking or is not tuned right like suggested above?

 

Truck has 218K on it(motor only has about 4k) and I dont know if the cat has ever been replaced, I doubt it. But I think I mentioned above that I can smell fuel being burned up in the cat. I cant imagine thats good for it.

Fuel upgrade kit..

http://www.urdusa.com/Fuel-Upgrades-...duct_info.html

 

If the cat was clogged, my vacuum would increase in the manifold if I blimp the throttle. That does not happen.

And I dont have a 7th injector kit, the kit I have uses bigger bosh injectors.