Need your Help! Guys!

[LeeS97Z28]

Hi Guys!

Would O2 sensor going bad cause my car to sputter from idle to about 1700 RPM's if you ease down on the gas it will pop a little in the exhaust until it reaches 1900 Rpm's.

I have changed plugs and wires used ACDELCO and put a brand new ACDELCO EGR Valve on it. Almost forgot, I changed the IAT Sensor. I also Cleaned the Mass Airflow sensor along with the Throttle Body. I checked the Fuel Pressure Keyon Engine off 47 psi. I checked it with the engine running it was 39-40psi.

I even unpluged the vacuum line to the Fuel Pressure regulator to see if gas might be comming from the regular it wasn't.


It still does it.

I haven't changed the O2 Sensors or map sensor.

I did have a leak from the weep hole in the water pump!

What do you guys think


Thanks Lee!

[Christopherrr]

well, i don't know the answer for the other questions, but I do know that a leaking weep hole means your water pump is about to go. Get that replaced soon...and a thermostat while you're at it...

Oh welcome aboard...

[Joe 1320]

And the weep from from the water pump usually goes right onto the optispark. Corrosion of the connections from water contamination is typical and can exhibit signs like what you describe. How many miles on the motor, plugs, wires and optispark? Are we to assume that the plug and wire change was just done? Did you notice any corrosion on the terminals of the optispark and wires?

[LeeS97Z28]

Plugs and wires done two weeks ago by my dealership. I slipped the guys an extra $100.00 Dollars to do a super job for me!

I had him replace the water pump about six months ago.

The car is a 1997Z28 with 75,000 miles on it!

[Deanz92z28]

O2 sensor replacement

Dude, I got a 1992 z28 with 65000 miles on it. It had the check engine light on when I bought it, traced that back to the O2 sensor , which was still threaded into exhaust pipe, but CRACKED IN-Half. Car was not running as rough as you say yours is.
In my car, if the computer senses the O2 sensor is bad, It just went to an open-loop mode instsead of adjuting to the feedback provided by the sensor.
I'm no expert, but I paid $18 for the sensor and replaced it in less than a half-Hour. I think GM suggests replacement at 60,000 mi. So, Why not just replace it and eliminate it as a possibility?

[Jeff_in_Atl]

What Dean said made me think. If you unplug the sensor, it should run in open loop mode. If it still runs bad, I wouldn't think the problem is the O2 sensor.

After the problems I have had with the OPTI, I would bet the farm that is the problem. Especially since you had water drip on it.

If you can get to it, unplug the OPTI and look for corrosion on the connector and the harness.

Neither of these will cost anything.

[LeeS97Z28]

Thanks Guys!

I'll check out the O2 sensors and see!


Is it very hard to get them out of the exhaust manifolds?

Should I soak it over night or do it when it is hot?


Thanks Lee!

[Joe 1320]

Unfortunately, if you soak them in penetrant, you will kill them if they aren't already dead.

[Jeff_in_Atl]

I didn't have any problems getting it out cold.

[Jason97T/A]

Originally posted by Jeff 95 Z28
What Dean said made me think. If you unplug the sensor, it should run in open loop mode. If it still runs bad, I wouldn't think the problem is the O2 sensor.

Hey Jeff, Are you sayin if you perhaps have a rough idle and a rich condition caused by a bad O2 sensor......if you unplug them the car should run better but just set off the SES light? Sorry if I misunderstood but just got me thinkin? I figured it would make it run worse.....
Jason

[Joe 1320]

When the sensors are in place and the engine is up to temperature, the computer is in closed loop. Readings from the 02 sensors are used to correct fuel mixture. If the sensors are unplugged, the computer goes into open loop just like a cold start. The 02 readings aren't used (can't be anyway since they are unplugged) , the mixtures are based on tables contained within the program of the PCM. Overall performance won't be as good as open loop, but it would run better than if the sensors were totally fouled.

[Jeff_in_Atl]

Took the words right out of my mouth.

[Jason97T/A]

So it really wouldnt cause the car to run like total crap if the sensors were unplugged....but the computer would have a harder time getting to the ideal A/F mixture? And your rough idle would be fixed?

[Joe 1320]

Originally posted by Jason97T/A
So it really wouldnt cause the car to run like total crap if the sensors were unplugged....but the computer would have a harder time getting to the ideal A/F mixture? And your rough idle would be fixed?

Maybe yes, maybe no... and no and maybe yes, maybe no.
This will isolate whether the sensors are fouled and at fault or not. If something else is causing the problem, this ain't the ticket. Again, all this does is take the fuel correction that the 02 sensors are used for out of the equation. As a rule of thumb, if it runs like crap as soon as you fire it up on a cold start, it ain't the 02 sensors as they are not used duing an open loop cold start.


Reading the sensors in real time or capturing the data with a scan device could tell more of the story. I'm still thinking it's ignition related.

[FRMLAV8]

Based on the fact that the car stumbles and sputters - I am betting on the Optispark. Especially considering the mileage and the fact that the water pump went out. That weep hole leads right to the Optispark.

If I was a betting man - my money would definitely be on the Opti! If I were you I would look there first. Replacing the O2's is a good idea, maintenance wise, but it isn't causing your problem.

Randy