I have been experiencing a problem with my stock fuel system. Under partial throttle while in vacuum (turbo), my air-fuel ratios are very rich (9-10's). I have narrowed it down to the stock fuel system (unhooked the URD port fueler and it still is happening).

Here are some deatils on my set-up:

99 5vz-fe, Auto, 4WD
Turbo with URD port fueler and Split Second Additional Injector Controller
Split Second ESC1 (02 signal conditioner) and MAF Hard Voltage Clamp
Split Second FTC to Pull Timing Only (values in fuel map all set at 10)
New MAF sensor and Both 02 sensors

It happens intermitently but happens all the time after I go WOT.

A couple things I have thought of:

1. Cracked injector?- I do not smell gas though..

2. Stock Fuel Pressure Regulator? - The vaccum tube to it is tapped into my manifold not the Silencer box like stock.

3. 255lph Walboro Fuel Pump - to much pressure for stock injectors to compensate for?

4. Shorting of wire harness on stock injectors? - it Idles right at 14.7:1 though like it should.

Any ideas? Thanks!

 

are you using a wideband O2 sensor to get the readings?

 

This occurs on many supercharged 4Runners from what I understand. I suspect it has to do with the engine having more intake resistance (when the supercharger is not boosting) so it pulls less air than it is expecting, causing a rich condition. Since you have an intercooler, I would say this is possible in your case as well. The answer is dialing back the fuel in those areas, but you have to be careful because these map values are generally close to your idle as well.

I would recommend looking at your fuel trims when the engine goes really rich, I suspect they will be large negative values. This will be a dead giveaway for the fact that you need to dial back on the fuel with the FTC.

I still have to get some decel values tuned in on my 4Runner, it will go to about 12:1 or 13:1 when I let off the gas for a small hill or coasting.

 

Yes - I am using the Innovative LC-1 / XD gauge combo.

Mastacox - thanks, I was considering dialing out some fuel but was worried that it would be just covering up the problem instead of fixing it. I will hook up my scan tool tonight and check out my trims. Thanks.

Anybody else with forced induction experiencing this?

 

It looks like this expains why the mixture goes rich in coasting or decel:

it looks like fuel trims won't have anything to do with it. Since the ECU can be in open loop for decel and coasting, you will need to manually adjust the fuel a little bit to make up for the modified intake system because the computer isn't using the O2 sensor and doesn't know how much air it's really getting.

Actually, I'm kind of curious if people with stock 3.4's and the deckplate/ISR or aftermarket intakes are inadvertently creating a lean condition during mild deceleration?

 

I read that in the U-tune guide too but my situation is occuring when I apply throttle while still in vaccum. When I let off and decel, it goes back to 14.7. Also, the stock fuel system "should" still be using the 02 while in vacuum as the esc1 and port fueler are not set to kick in untill I'm in boost.

Also, since the stock system is running rich like this, I assume that it "thinks" it's at 14.7:1 even though my wideband says different. If I try and pull fuel out while in closed loop, won't it just try to add it back in to get to what it thinks it should be? Only one way to find out I guess and I will try it tonight.

Could it be as simple as an injector sticking open or being cracked?

 

Well, I'd say the first step is to use your OBD-II scan tool to see if you are in open or closed loop when this occurs.

But if the ECU is in open loop it is putting in a specific amount of fuel based on predetermined values, not on the O2 sensor. Of course, it could be the engine's O2 sensor is bad... but lets not jump to any conclusions.

 

Very true. The 02 sensor is good, just put a new one in a week ago (MAF too). I will let you know what I find out. Thanks for your help!