My 89 IROC is idling very rough. It jump from 500 to 1000 rpm. I can barely keep the car still with the brakes. I plug up a scan tool and it shows the O2 volts at a constant .962. This value didn't change at all. This O2 sensor is only a week old. The weird thing is that the computer doesn't display a rich condition engine error code after running the car for a few minutes. Also, last week, I was unable to clear the error codes. I had to disconnect the battery. Can I have a bad computer or should I just replace the O2 again?

Another question...I am using the throttle body from my 91 TA with SD. Is the IAC and TPS sensors the same between SD and MAF cars?

Thanks

 

What else is the scan tool showing you. Are you getting closed loop? Coolant temp? With that info you'd know a lot more.

And no problems with the TPS with SD. AFAIK the IAC should be OK too.

 

Thanks for the TB info. I'm not sure what AFIAK means, but I'll assume that the two sensors are ok.

And yes, that was in closed loop.

Here are some more detailed info from the scan tool:

OPEN LOOP at idle
Spark Adv 14
MAT 59
MAF 10-12
IAC 50-60
RMP 750-1000

CLOSED LOOP at idle (Car immediatly begins to run very rough)
Spark Adv 16-20
MAT 59
MAF 15-16
IAC 150-160
RPM 575-800
O2 .96 (Doesn't change)
BLM 108 (Is this as low as it will go?)

CLOSED LOOP drivin around
Spark Adv 19-30
MAT 62
MAF 14-60 (My last car was SD, I have no clue how the MAF works)
IAC 90-160
O2 and BLM stay the same


Do you think my O2 is bad? or am I running sooo rich, that it can't be measured? I can get more info if ya need it.

Thanks for the help bro

 

If you are in closed loop and your O2 millivolt readings are not changing at all then you have a dead O2 sensor. I had Bosch one go once only a week old also. At idle in closed loop the millivolts should cycle all the way from 950-0 over and over and over in a loop.

 

The SD TB's do not allow TPS adjustments because the TPS sensor is not "slotted".

What is the TPS voltage at idle? You're car (MAF) requires .54v+/- .075??

What I notice by some of the info you posted, is the IAC counts seem pretty high in closed loop...as does the MAF reading..could be due to surging and the scan tool not being fast enough to see it, not sure.

I'd first check the TPS voltage, then assuming it's okay for grins, unplug the electrical connector under the MAF sensor.

I don't think the O2 sensor is at fault, I think by some of the info you've posted, the engine is going rich...and the O2 sensor is telling you that.

Is the ECM reporting any error codes at all? Also, monitor the O2 voltage on a cold start to closed loop...does it rise up and up to tthe .9xxx? Or just jump up there? another thing, any O2 cross counts?

Also (while I'm asking questions) try unplugging the O2 sensor, you should get like 450mv and it should stay there rock solid.

One last thing, the the battery have a good charge? I/e you didn't have to jump it to get it running and now you're running off the Alternator?

I know, lotsa Q's... but report back.

Oh, AFAIK= As Far As I Know or And For All I Know...IIRC= If I Recall Correctly.

 

My TSP voltage is .64 at idle and 4.27 at WOT. That seems to be correct, right?

Unless the engine is constantly running soo rich that to O2 is maxed out, there has to be something wrong with the O2 circut. There are no cross counts. The voltage stays at .96 in open and closed loop. It never changed from the reading. Either a bad sensor/bad computer/grounded wire maybe? The O2 is the simplist thing to change right now. If that doesn't work...I'm lost.

Someone mentioned that a bad cat might screw up the backpressure enough...does that sound right?

And I don't know what the MAF or IAC should be reading at...so does anybody know whats ideal?

The alternator is brand new, no charging problems.

Thanks

 

Your O2 sensor readings should definitely be moving. Even if the car was really rich it would still alter a little bit. If the value is totally static (not moving) I would start there.

 

Do you have the MAT relocated? That reading seems cool.

Anyhow, something is making you way rich, the 108 BLM tells you that the computer is taking out as much fuel as it can and it is still rich. And you can see why it thinks it is rich because the O2 is steady way rich.

So, think about it. Old injectors, could have a leaky one. Even a misfire from needing a tune-up could make it do that. Or maybe you have the fuel pressure cranked up. Or bigger injectors and a stock chip. Or could just be a bad O2 sensor. They can be bad, even out of the box. Or maybe you're really that rich and thats what is killing them.

 

Seems strange that the O2 sensor reads constant, I've never seen that happen. I'd check the wiring to it and try another sensor.

If you're burning a lot of coolant or oil, that could kill the oxygen sensor pretty quickly.

 

I replaced the O2 sensor...same thing... .96v. I unplugged the sensor and my scan tool also displayed .96v

Any suggestions?


When in open loop, should the O2 sensor voltage vary? Or does it only do this in closed loop?

 

With the 02 sensor unplugged, you should read right at 450mv (.450v)...this is the bias voltage from the ECM. I don't normally say this, but it seems the ECM may be the culprit.

What you could do to confirm this, remove the O2 wire from the ECM plug, and probe the connector...if voltage still stays at .96, you've found your problem, if drops to the correct voltage of 450mv, then you probably have chaffed wires somewhere.

But, I must now toss in my "disclaimer"....my car is an '89 and MAF, which uses a different ECM, and I have no actual scantool experience plugging into the '90-92's SD system....so what I would consider fubar on mine, may be okay on yours...even though I think it should operate the same.

Maybe you can ask someone who has a SD TPI to look through their Helms manual and see, or maybe they'll be nice and unplug the O2 sensor and get a read for you.

 

Thanks Mike....but actually, this problem is on my 89 MAF camaro...the same as you. So if the scantool shows .96 volts with the o2 sensor wire unplugged your thinking its the ecm? Would a break or short in the o2 wire cause this same condition?

Can you please explain the removing the O2 from the ECM in more detail. How do I do this? Do you mean pull the O2 wire directly from the ECM itself and see if the volts drop to .45? Do I need to buy the Helms manual to find this wire?

Thanks

 

Sounds like you want to disconnect the wire from the ecm and check the o2 voltage. If it drops, you know that the problem is in the wiring between the sensor and where you disconnected it. If not, the ecm is causing the problem.

 

yea, now I just gotta figure out which wire is the O2. Can anyone let me know where I can get the diagram at?

 

Dang, all I had to do was re-read the first post ('89).


Pin D7 (purple wire) into the ECM is the 02 sensor line you want to remove.

What I'd do, is head to the local discount AP store, and get a "pin pusher", this will minimize the chances of messing up the pin or connector. I've had luck pushing the pins out of the connectors before with thin-bladed jewlers screwdrivers, but may as well be safe.

What you'll want to do is (power off) drop the ECM, pulll the plug-in connectors...get a flashlight in order to read the miniture numbers, and find D7 (purple) wire. ONce the pin is pushed from the connector, replug the big connector into the ECM and power it on and see what the scan tool reads.

 

Alright Mike, I pulled the ECM and i think i found D7 purple. The ECM connectors only have numbers on them, I can't find the letters. But number 7 on the bigger connector on the bottom row is a purple wire, so I'm sure thats it.

Now I wont be able to get to the AP store until tonight. I am going to try to push the pin myself. I do have some tiny screwdrivers. I kinda tried myself but had no luck...I don't want to break the pin. Do I just 'push' the pin from the front of the connector? Do I push from the top or bottom hole? and do I need to slide the metal pin sideways to unlatch it or something?

Or should I just cut the wire and fix it when I'm done?

Thanks

 

Naw, don't cut it...

Sounds like you've found the correct wire...it is on the larger (32??) pin connector...it's tough to read the number, they;ll be on the connector..nmot the wire...I forget which side.

What you need to do is take the small flat blade from the same side the wire goes into the connector and slightly push it back..there's a little "lip" inside that keeps the pin from pulling out...once it's pushed back a bit, then goe from the side that plugs into the ECM (while maintaining a bit of pressure still on the pin) and push the pin up.

It really takes third hand...a pin-pusher actually accomplishes this from the ECM side of the connector, the correct tool will have a fixed outter "shell", and the inside will slide up an push the pin...think of a solid bar sliding in a thin pipe.

 

Finally fixed,

I pulled the pin from the ECM and got .4 volts. I traced the wires and found the O2 and Coolant sensor wires melted together on the exhaust pipe under the manifold. I just repaired the wires and the car is running good. I'm gonna drive it around and play with it.

I appreciate you all helping me out.
Thanks!

 

Glad to have helped, hope she runs well.

One thing to think about, is I've heard (but not experienced) that splicing the O2 wire could add resistance, and cause false readings.

I'm not sure how true it is, becasue I've used several "universal" length O2 sensors that require you to crimp the connector on.