I raced in the Viper Vette circuit at Thompson two weeks ago and after a trial run the car was hard to hold at idle, it wanted to stall. When I brought it back and ran it on the street the idle was still terrible. After a short time the idle hang started happening, it would go up to 2000 and then on it own drop back to 700.
At this point I put the scan tool on the car and drove it, I found that one of the O2 sensors had a voltage of 1.5 volts at or near idle, that equates to an a/f ratio of close to 10 on that bank. I continued to monitor the O2 voltage and the short/long term adaptives. I also read the diagnostics manual where it relates to the O2 system, here are some observations and finding:
1. I replaced one O2 with a Bosch #13100 ($60 at NAPA), be careful there is a mistake in the Bosch cross reference, depending on which year the cross is it could give you another number.
2. The new O2 sensor stopped the idle issue and the idle hang problem.
3. The idle is now better then it has ever been, this O2 must have had issue for some time.
4. For some reason the O2 voltage on the bad sensor was only out of range at or near idle, if it deviated at other rpms I didn't catch it.
5.The reason the idle was so bad was that the O2 sensor was showing 1.5 volts or extremely rich, therefore, the PCM was pulling fuel at idle, my aftermarket a/f gauge showed extremely lean because of the fuel being pulled.
6. A hard code was never set, probably I didn't run it long enough. They were soft codes set showing a rich condition, but, you wouldn't see them without a scan tool.
7. There are some gray comments in the diagnostics manual, but, what it seems to say is, a hard code won't be set unless the O2 voltage is over 1.5 volts. I sure there are other ways to set a over-rich code, but, strictly based on O2 voltage, they are looking at greater than 1.5 volts.
8. If you have a scan tool, the O2 voltage at 14.7 s .458 volts and the voltage should be in a plus/minus 0.2 volts.
9. Another interesting item is the fact that all the adaptives are purged when clearing the over-rich DTC. I am not sure whether this is all DTC's or just those dealing with a/f. I have a new (second) scan tool and it gave a warning (never seen on the old scan tool)that all adaptives were going to be purged with the clearing of the DTC.
10. The car has Ballangers and the O2 location is a little further from the male connector at the motor mount. I have to pull the male connector off of the mount to make it work originally. On my car the Ballangers also position the the O2 sensor a little higher and closer to the the heat deflector. The O2 wires are uncomfortably close to the that plate.
The Bosch sensor is actually 1/4" higher than the NTK oem sensor, it might have worked, but, I didn't want the wires rubbing on the plate, so I used a hole saw to cut a hole where the sensor is positioned.
One last item, after this surging and idle hang episode it started me thinking about the number of SC and Turbo cars that have this problem. This may be a stretch, but, my car is proof that the O2's can cause the idle hang and surging. It is also the nature of the narrow band O2 sensor that it is not accurate under high pressure and/or high heat, in other words on high hp cars they shouldn't be as close to the engine as they are - is the idle hang problem as simple as a temporary malfunction of the O2?
Front 02's only Jack? If I just replace my front 02's I wonder if my idle hang will dissapear.
What about the guys with no 02's, simulators etc, I wonder if they have a problem?
There are no guarantees, replacing the sensor on my car fixed the idle hang. It was immediate, the idle quality improved and the idle hang was gone. As far as which O2's to replace, the rear O2 sensors only set a code they don't control the PCM. The fronts are giving input to the PCM at all times except during WOT.
I have been logging the O2 outputs and have somemore intertesting data. I don't want to mislead anyone, a malfunctioning O2 sensor will not help WOT performance, but, it will help drivability and may clear up the hanging idle.
I have one new Bosch sensor and the original NTK with 20,000 miles on the sensor. I can tell you this, the Bosch is far more stable than the NTK. This is probably age and abuse related. Below I posted a comparison graph of a narrow band O2 sensor applied at different temperatures. This graph was made to show why a NB sensor is so inaccurate. It basically only works at or near 14.7. In other words, on the lean side the voltage output drops to zero at just a little above 14.7, it acts like a switch, unlike a wideband that has a range.
In my comment above I indicated how erratic the older NTK is, it also always shows a higher voltage (richer) than the new sensor. that also shows up in the long-term trim, it is pulling fuel whereas the new Bosch is at or near zero.
One could look at my comment and say the O2 is just doing its job, but I believe you can verfy its accurcy fairly easy. When you engine brake the a/f should be 20.9 because the engine is now an air pump. For those of you that have wide-band sensors that is one way to check the accuracy. An a/f ratio of 20.9 will also force a narrow band down to zero volts, actually less than 20.9 will get you zero, look at the graph. Therefore, is is very simple, find a long hill, pick upsome speed and start to engine brake in 4th gear, watch the scanner and see where the voltage on both O2 sensors lands. In my case the new sensor falls to zero immediately and the old oem sensor goes no further than .2 volts.
Maybe someone can find a fault with this logic, but, it is really kind of simple. Think about it this way, the narrow band sensor should be reading 14.7 at about 1/2 volt, that is the null point or the center point, if it starts out reading 40% (.2/.5) high, that can't be good. Does it cause idle hang, who knows, is it good for the car, that it can't be.
Thanks Jack for the information, it wouldn't hurt to ty it I guess because this idle hang I have is really annoying and nothing seems to cure it, I am running a roe blower with 12#s, water/methanol inj, corsa exhaust with 666 RWHP, these mods must of enhanced the idle hang that everyone seems to get now and then on there stock vipers but its getting to the point of not wanting to drive the car anymore, I counted a 12 sec delay the other day until it dropped to normal idle, 5 secs other times and more or less on & off, really irritating, I don't want to do the dowl trick that shawn says does work but this is just a bandaid.
thanks again
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