RocketSapp

So, due to funds, getting married, moving, and a slew of other things my 89 has been setting without being started for quite a while. Like 5 years or so.... Sad I know... But thanks to a new job a year ago the wife and I are now debt free (except for the house) and I now have the money to not only start restoring and making my 76 C3 into the Hot Rod I always wanted, I can afford to bring my C4 back home to get it running and drive it again.

When I parked the car it was because I could not get it to pass inspection here in the DFW area. I think it was due to the Heated O2 sensor going bad but it could have been other things. It is a heated O2, a Bosh 13077, because I replaced all of the exhaust and added long tube headers. It was running great for the two or three years leading up to it not passing and it being parked.

So with all that said, my parents put the Vette on the car trailer and brought it down to me last weekend. On Saturday my dad and I put in a new battery, changed the fuel pump and strainer, and the fuel filter. I drained 18 gallons of old gas from the car, which was all that I could get out of it. I added around 5 to 7 gallons of new gas to the tank and with a little help from starter fluid and removing the clogged air filter we got it running and moved back to my driveway.

Now, after it comes up to temp it starts to run rough and seeks idle part of the time. This is when the coolant is running over 200 degrees. It also appears to be missing from time to time. I put the scanner on it and I am showing the 02 sensor returning a value of 463 mVolts which makes me that it is operational. I would think that if it was not hot enough then it would be reading something much lower.

The scanner is showing that I am still in Open loop and that the O2 sensor is not ready. This is after the 5 minutes of running at an idle where the system is waiting on the O2 sensor. It just says that the O2 sensor is not ready. It is showing that the car is running lean, so it appears to just be running in limp mode.


So, question... When running in Open loop based off the computer settings, does the computer override the O2 values that it would be sending to the scanner? It does not appear to move around very much from the .463 reading so I am starting to think that it's the computers desired value and not the value from the actual O2 sensor.

I have a new O2 sensor setting in the garage that I just bought but I don't want to just start swapping out parts in hopes that I fix it. I would rather return the O2 sensor if I can and use the money on other parts for the cars. :-)

Tim

SunCr

Steady O2 means it ain't working. Should be showing a 13. '89 uses a one wire, non heated O2.

Roughness after sitting for an eon may be bad gas or a plugged up filter or injectors, maybe a bad MAF. Remove the fuel inlet at the rail and clamp a hose to it. Put the hose in a coffee can and turn on the key. Should squirt half a can. Pour the can into a clear glass and let it sit. If there's water, it'll separate out. Unplug the MAF and see if runs ok - if so replace the MAF.

RocketSapp

You are correct that the 89 normally has a one wire O2 sensor. However, I went to long tube headers and I had to switch to a heated O2. Since the O2 sensor gets moved further back, the exhaust cools down too much for the stock sensor to get to it's operational temperature.

It has not thrown a code telling me that the sensor is bad though. I have not been running the car a long time, and not driving it, so it may not have had time to set the code yet.

The more I think about it the more I am leaning towards the heating element of the O2 sensor may have gone out. If it never reaches operating temperature it would run bad, and probably throw a code.


Yeah the gas setting for so long can really cause some issues. That's the reason for the new fuel pump, strainer, and fuel filter. I may add a fuel additive tonight and run it for a while to see how it does. Most of the additives will have denatured alcohol in it to pull the water through the system, and I hope if it's an injector issue that it's just the gas varnish on it. Most additives will help clean the varnish off as well.


If the additive and the new O2 sensor does not resolve the issue I may be pulling the injectors to give them a good cleaning. If cleaning them does not work then I may get new ones... (Might be a good time to upgrade to larger injectors. But then I will want a larger throttle body as well. )

Tim

96GS#007

The o2 sensor is not working as mentioned above. Check the wiring to the sensor...5 years is a long time to sit, so you never know when/if a critter happened to stumble by and decided it needed a quick meal of wiring.

The injectors are an easy check. Pull the connectors off them and ohm test each one. If they're the stock Multecs, they should be 15-17 ohms each (later '92 & up Multecs are 12 ohms). You'll want to check them hot and cold. Sitting that long, it wouldn't surprise me if the coil windings are bad in a couple of them.

Most likely a new o2 sensor will get you into Closed Loop. It just may clear up the rest of the issues as well.

Cliff Harris

The ECM waits until it sees more than 0.195 VDC or less than 0.686 VDC from the O2 sensor to go to closed loop mode (my '86 -- yours might be slightly different).

According to my BUA firmware, 0.443 VDC is the default value if the ECM can't get a reading from the O2 sensor. You said you're seeing 4.63 volts (not possible -- the O2 sensor output never goes over 1 volt) -- maybe that's 0.463 volts? That could be the default for your ECM firmware or you've got a problem in the O2 sensor circuit.

RocketSapp

Thanks... I was thinking that might have been the issue. So I replaced it last night, along with an oil change, and a set of new plugs.

So now when I plug in the scanner I am getting an O2 reading that moves around as I apply throttle. It's moving between .42x and around .48x with one flash of it hitting a .51x before the pulse duration changed.

I am still showing that it's running lean though. I have not gotten an error message on my dash from the computer throwing a code, but I did have the scanner to check for codes and it found one. It is telling me "MAF Voltage Low", I don't remember the actual code number but I think it's a Code 34. I pulled my air filter off thinking it might not be clean enough and it did make a difference but it's still showing the code and seeking idle. I THINK the voltage on that one was around 1.6xV before I pulled the air filter and then it went to around 1.8 or 1.9. But I was looking at a lot of numbers last night and I might be wrong about that.


The scanner is still showing O2 Sensor not read as well. But that might be a flag that it sets low until it knows that everything is ready.


I was going to grab a sheet of paper and write down all the sensor values so I could check them against the expected max and mix values. But I was running the car in the garage with the doors open and my wife came and told me that it was 11:00pm and the car was a bit loud. Yeah while I love the sound, but I am sure the neighbors were not enjoying it as much as I was. So I had to shut down for the night. I'll do that today once I get home and if I can't find anything I'll post the values here in this thread.


Tim

BTW, the first time I mentioned the voltage I said 463 mVolts which converts to .463 Volts. Sorry about that... I have worked in electronics in the past and it's a habit at times. I did notice that I fat fingered the voltage the next time I typed the voltage and put the decimal in the right place. I'll go correct that now for any future readers.

Cliff Harris

It still sounds like you're never going into closed loop mode. The O2 sensor output should vary between roughly 0.200 volts (or 200mV if you like) and 0.800 volts.

When you're in closed loop mode the ECM richens the mixture (by increasing the pulse width of the injector pulses) and then waits for the O2 sensor to report a rich mixture. Then it leans out the mixture and waits for the O2 sensor to report a lean mixture. It alternates continuously between rich and lean in a cycle that takes about 1 to 2 seconds.

I suggest looking at what the ECM is seeing from the CTS (Coolant Temperature Sensor). The ECM requires a minimum coolant temperature for a certain length of time before it will go into closed loop mode. There are some other conditions but I never went through the exercise of figuring out exactly what parameters had to be reading what to go into closed loop mode.

One more: High TPS will also keep you out of closed loop mode (the ECM thinks you're at WOT).