I have a question that I hope I will get some insight on. I have an 89 N/A with a street port, 3mm apex seals, no emissions/air pump, filter off the MAF, stock exhaust manifold, no cats, 3 inch cat back cork sport exhaust and a walbro 255 liter fuel pump. I am monitoring the afr with an auto meter AF gauge. It doesn’t even register at idle or cruising around. It will only start to register at about 30% throttle. Then at about 45-50% throttle it will get up to stoic/rich. But the car smells like it is running rich. Also it sounds like it is missing when holding the throttle in a fixed position on the freeway. Any suggestions would be very helpful.

 

Um, when you are cruising around the gauge should kinda do a scan back and forth. This is closed loop mode where the o2 sensor is assiting the ecu to find the leanest mixture to run the car. Closest to 14.7:1 ratio.

When you get on it....very close to 30% in my TII the blinky light should go from scanning to a solid led. That is open loop mode where it goes to the preset mixture for best power.

Possibly your oxygen sensor is having issues. It may show something at idle. But at cruise it should scan from lean to rich.

Sorry, you are not going to be able to tune your car via your nose What makes you think it is running rich?

Just do the basic tune up stuff. Plugs, wires, and check your timing. Also, look for vacuum leaks.

I am sure you will find this with a little digging. But the a/f gauges that use narrow band sensors (What we have stock in the 7) are worthless. They should not be used as the finally athority in tuning. The sensor in your car is only designed for one thing. Crusing, and getting best ecomomy mixture. The sensor does nothing at high rpms and high load. It is not accurate in that area and there is where you want it to be accurate in your application. There is a sensor called a Wideband oxygen sensor. Using that it is accurate from full rich to full lean.

Mine will be running in the car tomorrow! I can't freaking wait *drool*.

James

 

take your walbro out it's probably running way to rich from that... get a stock turbo II pump.

also a/f gauges are garbage...

 

Thanks for the info. The AF gauge doesn't scan at all. It was new about 4 months ago. A wide band o2 would be cool but don't have the money. The exhaust smells like gas, that’s what makes me think that it is running rich. I will however change the plugs and wires and check the timing tomorrow

 

You wont even need the TII fuel pump just use your stock one.

 

Duh, you dont have any cats. That is exactly why you smell gas coming from the exhaust. You could be lean and it would still smell like gas.

 

How bad is your gas milage? Are you getting any check engine lights? The reason I ask is because of the lack of scanning on your gauge. Your o2 sensor may have problems.

If you know how to use a voltmeter check out this site. It tells you how to test your sensor in car and out of the car. http://www.mr2.com/TEXT/O2_Sensor.html

James

 

Uh, my exhaust doesn't smell like gas, it smells like exhaust. I doubt a lean condition would make it smell like gas, because you're burning all the gas.

Where did you ground your A/F meter sensor? I grounded mine at the ECU. I wouldn't trust it much anyway, the only thing I use mine for is to monitor if I'm in open or closed loop.

 

A/F guages are not worthless. They just aren't for tuning.

The reading on the A/F guage will be either full lean, or one or two bars rich at idle, depending on how much of your emissions systems you have left. During cruise, it should bounce back and forth between lean and rich as the ECU uses the O2 sensor to adjust the fuel mixture. Accellerating should put it a few bars rich.

Start by putting your stock fuel pump back in. The stocker is good for 250HP, and you aren't making close to that. Then, replace your O2 sensor.

Also, the guage will act weird until the O2 sensor has warmed up, and the sensor often cools down at idle.

 

Thanks for all of the input on the subject. I am going to test the o2 sensor and not even look at the AFR gauge. I am thinking of getting an EGT to help out. Racing beat says that the exhaust is at about 1700-2000 F. Greddy is the only one that goes up that high. All of the emission stuff is gone. The only other question I have is why does the fuel pump even matter. In my understanding of it I have a return line that brings the gas that isn't used to the gas tank. It isn’t putting any more presser on the fuel system, and the injectors are still staying open for the same amount of time as stock. I am getting more fuel to the rail but that much more comes back to the tank. That’s my understanding of it. Set me straight if I have some thing wrong. Thanks