fbgh2o

So all of a sudden the car is running rich - way rich (tons of soot now coats the tail pipe). Fuel mileage is down 20% at least. The plugs are thoroughly coked (I guess that's better than washing them with gas).

The block temperature sensor is new within the last 5,000 miles.

The car was in the shop last week and they said that O2 sensor was pegged full rich. Is this a symptom of a failing O2 sensor?

I have done an intake pressure test and found a couple of small leaks. There appears to be one under the cycling valve - although it is not the cycling valve itself (new last summer). I can feel and hear the air moving under the cycling valve mount. What might be leaking there (ISV, AOS?)

This condition has appeared since I installed my Vitesse MAF (although the first 1,000 miles I got 26 mpg+ highway) and an Innovate wideband (which is not yet working correctly). John from Vitesse has been super helpful so far, but I feel as though I am imposing, so the thoughts of the experts here would be much appreciated.

Rock

Is the car a California car?

Did you pull any jumper wires under the passenger side footwell while trying to install the MAF?

Is the vac line off of the fuel pressure regulator connected? If not, it wont pull the fuel pressure back down.

tyro

Last time my O2 sensor failed, my wideband showed rich - 11:1 while cruising down the highway.

fast951

Fergus, As we discussed in our emails. Since you ran fine for a 1000 miles after installing the MAF, then something changed causing the rich condition and the drop is gas mileage. It's a matter of finding what did change.

Some of the things that could cause a rich mixture (on any 951 and not in any order):
- Faulty O2 sensor
- Faulty Engine Temp Sensor or its wiring
- Bad grounds (cause faulty signals)
- Incorrect Fuel Pressure
- Faulty TPS:
* If it's not signaling idle when it should, it causes rich idle.
* If it's incorrectly signaling a WOT signal to the DME, it will run rich as WOT is supposed to run richer

- Bad Injector(s) or wiring - You can usually tell from the way the engine idles.

fbgh2o

Thanks John.

edh

I had a similar problem with mine recently - the Vitesse MAF (white wire) was reading +0.8V at idle, not idling smoothly & running rich. I fixed it by re-doing the intake pipework & re-making the +12v and ground wires for the MAF. Not sure which part of this did the job, but I suspect the ground. I'd suggest the first thing is to make sure your have a really good ground connection.

fbgh2o

Thanks. I think the ground is solid... Car idles fine, just runs rich, but to be sure I will check again.

fbgh2o

Here is an update (for future users)

- Faulty O2 sensor (to be tested)
- Faulty Engine Temp Sensor or its wiring (it is new and operating correctly)
- Bad grounds (checked and they seem fine)
- Incorrect Fuel Pressure (to be checked - but vacuum is good 18 in. HG at warm idle)
- Faulty TPS (checked out fine as per Clark's Garage)

Tom M'Guinn

Not sure I've followed along completely -- but was this fixed? If not, then yes, a bad O2 sensor will throw off the air-fuel ratio. "Pegged full rich" would make the dme try to lean out the motor, but maybe he meant pegged in a way that causes the motor to run full rich -- either way, it needs to be replaced if you haven't already done so. Make sure the harness to it is ok also -- sometimes they hit the exhaust and melt/short, etc.

KuHL 951

Exactly what I think happened to my one week old O2 installed by a shop along with a new cat. I left the place running great with no exhaust smell at all. Drove to the smog retest, dyno broke down, drove home, waited 3 days to retest, noticed the car smelled even richer than before the repairs, took it back for retest and emissions were worse than the first test by a big margin. I'm routing my own wires this time once I pull the old O2 off.

sebastian944

are those BBS wheels? They look good in black.

fbgh2o

First answer - Not yet. John's support is awesome - especially since I don't think that this is related to the MAF and therefore not his problem.

I think that he meant running full rich...

(1) Voltage MAF to Battery + terminal
Ignition off 12.37V
Ignition on 12.15V
Engine running 13.6V

(2) MAF voltage from 12V source to ground
Ignition on, not running = 12.2V
Engine running = 13.4V

(3) O2 sensor disconnected makes no difference to vehicle operation. Idle unchanged.

(4) TPS
Initially cold with following results (engine at 43C using my handheld thermometer)
DME terminal 2
Throttle closed = 1.2 Ohms (within spec of 0 to 10 Ohms)
Goes infinite with throttle open
KLR terminals 22 to 23
Throttle close 565 Ohms (within spec of 320 - 670 Ohms)
Full open resistance 4.2K Ohms (within spec of 2.7K to 4.7K Ohms)

Retested Hot (engine @ 80C)
DME terminal 2
Throttle closed = 0.9 Ohms (within spec of 0 to 10 Ohms)
Goes infinite with throttle open
KLR terminals 22 to 23
Throttle close 610 Ohms (within spec of 320 - 670 Ohms)
Full resistance 3.9K Ohms

(5) DME Temperature Sensor
@ ~43C 875 Ohms (seems reasonable based on Clark's Garage with says that 30C = 1.46K Ohms)
@ ~80C 350 Ohms (right on the money for the Clark's Garage spec of 280 to 360 Ohms)


So what this says to me is that

(1) DME temperature sensor is operating correctly
(2) TPS is within spec
(3) O2 sensor does not appear to have any impact.

Based on the symptoms described in Clark's Garage

Engine surges or hesitates (not really)
Strong smell of gas from the exhaust (yes, I though I had a fuel leak)
Poor fuel economy (yes)
Failed emissions due to high CO or high HC levels (no test, but evidence of hydrocarbon visible in exhaust)
Catalytic converter (if equipped) becomes prematurely clogged (No cat)

I am inclined to have the O2 sensor replaced (at the same time I will have them check fuel pressure).

Tom M'Guinn

Did you tap into the O2 sensor line to monitor it with the SMT6? If so, check to see what the signal looks like. Unless you do that or tap into it with a multimeter to see the signal, you (and your mechanic) cannot know for sure.

Keep in mind that the ISV keeps the idle speed steady, so when you disconnected the O2 sensor, it may have changed the AFR even though the ISV kept it idling at the same rpm.

fbgh2o

Do not have one.... I am heading out to travel for a couple of days and will check the voltages on the O2 when I get back. John, still wants me to check the grounds, but they were cleaned about 12 months ago.

KuHL 951

17" CCW Classics, Track Series, black anodized centers