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O2 signals Posted by Ari [Email]  (#2847) [Profile/Gallery]
(more from Ari) on Thu, 10 Feb 2005 05:38:47
In Reply to: Re: No, Rmc, Wed, 9 Feb 2005 21:22:02 Members do not see ads below this line. - Help Keep This Site Online - Signup |
The O2 sensor provides an output. If you disconnect the O2 sensor from the ECU, you will get a voltage on the ECU side of the wire, but it's meaningless. You're just seeing a fairly random voltage depending on the input circuitry. Since it's very high impedance (looks like a BIG resistor), the voltage you read on the ECU side (with O2 sensor disconnected) may move around a bit. Ignore it.
The voltage out of the O2 sensor when the O2 sensor is disconnected is also misleading. The ECU uses the O2 sensor as one of the inputs to adjust fuel flow; if it doesn't see an O2 signal, it will go to a default value, and that's usually a little rich. That's the trouble with trying to troubleshoot a closed-loop system that isn't working right- It's like tyring to diagnose your sick cat by taking it apart and examining the pieces. It doesn't work apart. (Don't try this at home.)
When testing the O2 sensor, the car must be warmed up. The exhaust must be too hot to touch, because the O2 sensor doesn't start working until it's warmed up. If the heater is working, that's about 2 minutes.
Can you read out any fault codes? That will help some.
As to the injectors, I haven't had a lot of trouble with injectors, but I'm very careful about fuel, and have probably been lucky. There are shops that can clean injectors. I'm not quite sure that I'd take a toothbrush too them. The injector has a little pin at the end that pokes out through a hole. The injector works by pulling the pin back and letting fuel squirt out. The best way to clean them is with the pin pulled back, which means energized. And that's not something you want to do for a long time (heat buildup). I'd stick with chemical methods through the fuel. Removing the injectors will only add more variables. If only one cylinder was running rich, I'd recommend pulling the injectors, but not if all are.
If you're up to it, checking the FPR pressure would be a nice touch. You'll need to plumb in your gauge. Remember, the system is under pressure, so before opening up the system, start the car and pull the fuel pump fuse until the engine dies. With a lumpy idle, manifold vacuum will be all over the place and not much help.
If the O2 sensor is reading 0.8 and the plugs are looking rich, then they both agree. So I'd leave the O2 sensor alone for a while. As to the AMM - how driveable is the car? Can you drive it? Does it accelerate smoothly when you press the gas, or does it seem to ignore you? If the engine reacts quickly to throttle changes, then the AMM is working. The sign of a bad AMM is an engine that ignores small gas pedal changes, and requires near full throttle to do anything.
Adjusting the AMM with no response is not good. It implies that you're getting too much fuel. That keeps pointing to FPR or injectors. I'd go after the FPR. If nothing else, pull the thin hose from the FPR to the throttle body off at the throttle body, and suck on it. It should hold vacuum, AND you shouldn't get a mouthful of gas. If it tastes strongly of gas (there will be some gas taste - this IS an engine), that can be a cracked FPR diaphram, and it's sending out too much gas. If it passes that test, I'd check the pressure.
posted by 192.249....
, Wed, 9 Feb 2005 20:19:38, Thu, 10 Feb 2005 05:38:47 <-- Viewing This Message
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