A friend/mechanic put the scan tool on my 84 it said the new O2 sensor read lean,he disconnected the air pump thinknig its getting to much air.The air pump wasnt pumping so that didnt help.
He said the car is running rich because its starving for fuel & thats making the computer tell the injectors to add fuel making the car run rich.I think he said the computer integrators or something in the computer is telling it to add fuel.

Also it reads only 12 pounds of vacume.I guess the scan tool gets that info from the MAP sensor?I need to hook up a real guage & check for vacume leaks.
Its confusing,He thinks low fuel pressure.I cant believe it.How can it give itself too much fuel if its haveing a problem getting fuel?
His only other idea is that the computer is bad or a bad ground to the computer.Also his scan tool, the red brick one, said there maybe an upgrade chip for that computer.
The fuel filter is new.Bone stock high milage 84.
Its flunking emmission, the worse #s anyone has seen,but it runs great.
Any Ideas or suggestions?
Thanks

 

Just a few questions for you-does it have cats, and have you checked fuel pressure? I thought-and someone can correct me, but isn't your vacumn supposed to be around 20? I do believe the 02 sensor sends information to the computer-which the computer sees as right, rich or lean, then compensates. I've had guys post responses on my post saying when there ECM went out their vettes went pig rich, without
any codes.

 

Yes it has a cat that is 1200 miles old.I was told they can go bad if your running rich.But we put a lazer temp gun on the front & compared the temp to the back of the cat.It is 215 in front & 315 behind, so it is lighting up.As far as its effecency,I dont know.
I have not checked fuel pressure,I plan on doing that soon.
I dont know what the vacume is supposed to read.
All I know is the scan tool said the O2 reads lean.But it is running rich.
Gas smell & black wet plugs.
Ive never heard that about the ecm & running rich,but it is pig rich.
Thanks for thinking about it for me.

 

I'm interested to find out what the problem is. My vette does the same. I have yet to find my problem. Let us know if you get it fixed.

 

Will do.
I cant see it being fuel pressure, Im leaning toward computer or bad connections.

 

If your O2 readings are living below 450mv (lean), then its telling the ECM to add fuel....then your Blms will be living above 128 most of the time. (rich) If they are at 160 then the ECM is not in control. What are the #'s your mech came up with? The problem may be an exhaust leak which is fooling the O2 into a lean condition. Any codes set? Your vacuum should be about 17-20" (stock cam) and fp about 38 -40lbs. It does sound like it is pig rich tho with your plugs gas soaked.

 

One more thing-coolant tempsensor-just might be your problem!

 

Good advice, except for the fuel pressure.The spec for your car is for between 9 and 13 PSI of fuel pressure. I agree with you, that since it is running rich, that it isn't going to be because of a lack of fuel pressure.

Do you have any codes set? The first step ought to be to follow the trouble shooting charts in your FSM to track down and correct the cause of any codes. That may be the end if it.

It is correct that if the O2 tells the ECM that the mixture is lean, the ECM will attempt to fatten it up. BUT, if the mixture truly IS lean for a lack of fuel, the ECM will not be able to richen the mixture and your plugs wouldn't be fouling.

Your vacuum is very low, if that is a true reading. You might stick a vacuum gauge on it to confirm. Since it is running rich, you might want to try a back pressure test on that new cat. You may have plugged it up already. If the vacuum gauge doesn't agree with the scan tool, you might want to trouble shoot the MAP. That could be the whole problem. Otherwise look for vacuum leaks or sources of false air that could cause the O2 to read lean.

RACE ON!!!

 

If your engine is running rich but your O2 sensor is recording lean I think this is one of the times when the messenger may be the problem and you have to shoot the messsenger.

It sounds like your O2 sensor is not working properly, if it is sending a false signal to the ECM that there is a lean condition which is causing the ECM to fatten up the fuel delivery too much. If the O2 sensor was working properly, the ECM would cut back on the fuel delivery when the O2 sensor records the correct mixture.

If the vacium reading on the scanner is different from that recorded on a guage hooked to the manifold, you may have a bad MAP. I would check the vaciun first and troubleshoot and correct the MAP if the vacium readings are different.

If the vacium readings are the same low numbers I would check for a blocked cat.

A bad ECM could be sending too much fuel that is called for by the O2 sensor, however the O2 sensor is telling the ECM that the mixture is lean instesd of rich as shown by the plugs, therefore it appears that the O2 sensor is the problem.

There are a number if conflicting symptoms here but my money is on a bad O2 sensor.

 

What's an 03 sensor??

 

It is that thingie that comes in the mail when you hit the wrong key on your computer when you are ordering a new O2 sensor.
Thanks.

 

It doesnt have any codes.
I can be going down the highway & the check engine light will come on , then a few miles latter it will go out.I check for codes ,none.
While my friend had the scanner hooked up. it came on & the scanner said no code.
Its a brand new O2 from chevy.
How do I check the back pressure of the cat?
Did you read the cat is lighting up & heating the gasses?
Coolant sensor is about 2 years old.
I didnt get O2 reading #s just the snap on 2500 read lean all the time.
If its the MAP I just change the sensor thing on the firewall right?, Or is there more to the MAP than I know?I think I changed it years ago ,but I'll have to go thru my reciepts to be sure.
Where does the MAP get its reading?Is it just a vacume connection?
I think my computer isnt listening to my O2 sensor.
I will check for vacume leaks & the amount of vacume with a real guage,Then computer connections.
I thanks all you guys very much.
The license runs out this month, so I will be trying hard to fix it this week.

 

I forgot to add.
No exhaust leaks.
Thanks

 

The ECM sets the SES the light. If it sets a SES light and no code is found by the scan tool at the time the light comes on I'd guess the ECM. It should have shown a code if it set the light.

Doesn't mean it is working correctly. Could be installed wrong. Could be a new part that is bad.


I would agree with jerris. Either it is the messenger or the recipient. If you hadn't said in your last post that the ECM set the light with no code I'd say O2 sensor. Since the scan tool is not reading the O2 sensor directly, but reporting what the ECM "thinks" it is getting from the O2 sensor, and that value is a known false messege, either the NEW O2 sensor is off, or the ECM that set the SES light with no code present is off. I bet you need a new ECM.

It shouldn't appear to read lean all the time if you know that the mixture is actually too rich.

Bingo.

 

This is a perfect example of when NOT to shoot the messenger...Not without a trial. You may not like what the messenger is saying, but that doesn't make the messenger a liar. IF false air such as from a vacuum leak, AIR injection tree, or wherever, reaches the O2, the O2 will correctly read and transmit to the ECM that the mixture is lean. It MAY not be lean in the cylinder, but if what reaches the O2 is lean, you cannot convict the O2. If the glove doesn't ft... Then the ECM adds more fuel to make up for what the messenger, legitimately saw.



If course this is a possibility, too. Throwing a trial (testing) the O2 can accomplish two things. IF it is good, it saves a few bucks. Also, if it is good, you won't be scratching your head and wondering why it doesn't run any better with a new O2.



If and when the true, correct, unadulterated mixture ever reaches the O2.



Possibly. Just don't dismiss it out of hand. Don't shoot the messenger, regardless of who he is, without a trial. Then take the guilty party out and massacre him.

RACE ON!!!

 

[QUOTE=CFI-EFI]This is a perfect example of when NOT to shoot the messenger...Not without a trial. You may not like what the messenger is saying, but that doesn't make the messenger a liar. IF false air such as from a vacuum leak, AIR injection tree, or wherever, reaches the O2, the O2 will correctly read and transmit to the ECM that the mixture is lean. It MAY not be lean in the cylinder, but if what reaches the O2 is lean, you cannot convict the O2. If the glove doesn't ft... Then the ECM adds more fuel to make up for what the messenger, legitimately saw.


I knew I would hear from you when I said to shoot the messenger. I do agree 100% with what you said. However a vacium leak is on the intake side and would result in a lean condition inside the cylinder. There are only 3 ways that there can be rich inside the cylinder and lean inside the exhaust.
1. The airpump is dumping too much air into the exhaust manifold - He checked and eliminated this.
2. There is an exhaust leak between the head and the O2 sensor. - He reported no exhaust leak.
3. The cats are plugged and not allowing the burnt gasses to pass out the exhaust entirely. - Why I suggested he check for plugged cats. He claims he checked it with a heat gun and they appear to be working, however I do not know if this proves that they are flowing properly. I would suggest he disconnect them and then run the engine with the scanner connected to see if the O2 sensor stops reading lean.
At least this will not cost anything.

I have been thinking about this and if we assume the O2 sensor is good there is one other possibility. With the low voltage the O2 sensor puts out, a bad reading could be caused by a bad or corroded connection to the O2 pigtail. Disconnect the pigtail and examine the connector for corrosion, clean it and check the wire for bad spots. reconnect it and see if the O2 reading is now normal.

Unfortunately I do not know of a test for the O2 sensor except changing it for a known good one. Perhaps someone else can help.

If after disconnecting the cats and cleaning the connector the same problem exists, get a bigger gun and shoot the O2 sensor.

 

I have the same symptoms, rich condition, wet plugs, sooty exhaust but no codes. I have no cats or pre cats, the EGR is disconnected, fuel pressure is good. It's not happy on tick over (even stalls and stutters sometimes) I've got a cam with 110 lsa which isn't helping the vacuum situation. I've thought about changing the O2 sensor just to take it out the loop.

I'm watching this post with great interest!

 

While I agree with the excellent points made by JERRIS and CFI-EFI, I think that a significant flag is being missed. According to the 88 FSM the ECM only lights the SES light when it sets a diagnostic trouble code. There are 2 types of codes: intermittant and hard codes. Intermittant codes are often caused by a loose connection and do not always appear when working on the engine. The code is set, but disappears a soon as the engine is turned off. Hard codes are stored in the ECM memory until erased or a given number of driving cycles have passed without the code returning.

7thvet reports that they saw the SES light come on while the scan tool was attached to the vehicle. The scan tool should have been able to record the code that caused the SES light. An intermittant code can disappear as soon as the engine is turned off, but the code should have been seen and reported at the time it happened by the scan tool if the tool was working properly.

Either there is an electrical connection problem between the O2 sensor and the ECM or the ECM is faulty in that circuit. Since it should have set a code in the scan tool when the SES light came on and did not, the ECM is suspect. That needs to be figured out before you can rely on any data from the ECM.
Garbage In = Garbage Out .. Bad data is worse than no data.

A good charting scan tool would be of immeasureable help here. You might want to look into getting a scan tool from Ease, Autotap, Datamaster, etc...

 

Update!
I took off the air cleaner, last shop that looked at it left the vacume hose that runs to the air cleaner off.So all my scanner time may have been for nothing.
So that pisses me off.Anyway I dont think thats my problem.
The car has acted like this for years, like I said it runs fine.
I checked my vacume,its correct at 17 pounds.I checked with that aircleaner hose connected & disconnected it makes no difference 17 lbs vacume.
So the guys scanner said I had 12 lbs vacume so theres a difference.
Jerris ,thankyou for pointing out if there is a difference then it might be the MAP sensor.
So with the engine idleing I pulled off the vacume hose to it, the engine shook & was rough idle.
I plugged the vacume back in & it ran better.
I did the same thing to the electricle connection to the MAP & got the same results.
Does that mean its working?
Also I pulled the computer out.Its labeled as remanufactured original equipment. So I guess someone has already replaced it once.But I think I see some corrosion on the black & white plugs.
Looks hard to clean but thats my next plan.
Also I took apart the rear injector.The screen is clean rubbers are good.
I want to thank all you guys,I know how much time in thought you dedicated to help me. Thanks again.

 

Vacumn still sounds low to me. You might want to read a post I put up
about ECM symptoms.