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92 Olds (confusing problem)


5buckeye0's Avatar
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04-30-04, 03:22 PM   #1  
92 Olds (confusing problem)

Well I'm back to pick your brains again. After I cleaned the ground cables on the block my 92 Olds (3.8lt) has started setting codes once more.It went 12 days with out setting one and the other day while driving to work it set a code 13 and the next day set a code 44. Wouldn't you know I didn't have my scanner hooked up those days. My question is the oxygen sensor settles in the 650-750 mv range while I'm out on the highway going 55. ( Normally it runs the full range while in town or when I first start it up and take off in the morning till it warms up and settles in the 650-750 range. This car is running rich and I can tell by the the O2 readings and the black carboned up tailpipe. But my scanner is saying I have a 14.7 air fuel ratio. And it still sets a lean exhaust code. I don't see how it can interpret that air fuel mix with those O2 readings.I don't think its the scanner because it its only displaying what the computer is telling it. Since thats all its hooked to. Is it possible that it is reading the air flow and what ever else to come up with the ratio. And it isn't getting burned completely. Put another battery in it altho I don't expect any change. The one that was in it checked at 12.7v and the one I replaced it with only checked out at 12.8v. Think I might be grasping at straws with that one. I think I might change the negative battery cable tomorrow. It's cheap enough and it wouldn't hurt. I keep thinking it's computer related I just don't know if it's the computer itself or grounds or just a connection. I ran thru the diagnostic chart for the O2 sensor (code 13 ) and it wasn't a hard fault I did it anyway. Jumped the (412 circuit to ground) engine running and it read less than .2v on the scanner which says it's a faulty connection or O2 sensor. Went to the next step anyway and with key on engine off measured the same circuit with a dvom and came up with a .4volts which said .3v-.6v was a faulty pcm. My main question on that one is do these checks have to be done while it is in a hard fault to be accurate. If not those two checks were conflicting to me. Well sorry for being so long winded but I wanted to put as much info as I could think of. All replies are welcome and appreciated.

 
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04-30-04, 04:43 PM   #2  
If the fault is not current the tests are meaningless.I think you have already replaced the O2 sensor if I remember right.So follow the O2 wire back to the pcm and look for problems.I also mentioned if the pcm has red,white and blue connectors on it they are known to fail.Code 13 is open O2 sensor circuit so either the sensor,wiring from it to the pcm,pcm or ground for the sensor is bad.Bad wiring includes corroded ,bent or terminals with poor tension.Sometimes running a wire from the exhaust to the engine block will restore a poor ground providing you clean the area you attach it to and clean the rust from the exhaust where the O2 sensor mounts.

 
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04-30-04, 04:58 PM   #3  
have you replaced the o2 sensor?
the fault has to be present when performing a flow chart test although it may reveal a problem when it is not present, most of the time it may ask you to clear codes and see if code returns within set amount of time if it does then tells you to either perform flow chart test or problem is intermitant.
.4 volts on the o2 wire with it disconnected and key on is about where it should be and does not indicate a problem, the only reason i would suspect that the test might suggest possible bad ecm, would be at the end of the flow chart where they have eliminated all other possible causes.
if you have a scanner you should be able to tell whether the vehicle is operating in closed or open loop, in open loop the computer does not use the o2 sensor for fuel ratio control so the o2 readings should not really even be looked at until it has went into closed loop.the computer will go back into open loop after code 44 or 13 sets as the computer has tried to compensate by using the readings of the o2 sensor and still has recieved very little change in o2 sensor voltage to indicate it is having any effect on the fuel air ratio.
sounds to me like just a bad o2 sensor if you havent changed it recently suggest having it done if just as maintence.
as per your battery voltage if its with the engine off any voltage around 11.5 - 13 volts is ok.

 
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04-30-04, 05:43 PM   #4  
Thanks Davo

I did replace the O2, and the connectors for my PCM are (female connectors green and black ) ( male connectors are blue and gray). I'll have to due a little more Detective work on the wires and grounds. If I unplug the computer I should be able to do a continuity test on the O2 wire. And if that tests out I'll run an additional ground from the exhaust to the block. I'll post later with results.Thanks

 
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04-30-04, 05:56 PM   #5  
Thanks Bejay

You must have been posting while I was answering Davo. I wondered if those flow charts were credable without it being a hard fault. I just replaced the battery because I know how sensative the electronics are to proper voltage. And I had that battery in another car and it is almost new. So like I told Davo I've got some more searching to do. By the way do you guys strip apart the harnesses when you are trying to locate broken wires and shorts. Or due you rely more on a continuity test from one end to another.Thanks and I'll get back with you.

 
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04-30-04, 10:16 PM   #6  
mike from nj
i just want to add one thing. the air/fuel ratio you see (14.7 ) is the commanded value. it is not an actual reading. it is what the computer is striving for and has little value to you as a diagnostic value. on cold starts it might be 10:1 and at full throttle might be different too. don't use it as a direct reading, the sensor voltages are the reading you should be following. (someone correct me if i'm wrong please)

second other thing: some gm cars are just finicky when it comes to aftermarket sensors, i think you used a bosch sensor. you might have the one car in a hundred that has problems with this style sensor. on my GM car, i only use a/c delco O2 sensors(all of $25).

and another thing: while cruising on the highway, the sensor should be always switching, it shouldn't settle at 650 to 750 volts. try holding the gas pedal all the way down, and the sensor should hold a high value(above 850) until you lift completely, then it should read low, like 100 or less, then resume switching.


see what happens

 
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05-01-04, 12:03 PM   #7  
Thanks Mike

First thing I am going to do is double check the computer wires to make sure I don't have an open in those.Then see if I can find an AC/Delco O2 sensor. Next thing I try will be the grounds ( battery cable and chassis cable). Then clean the exhaust where the O2 sensor mounts and maybe try an additional ground from the exhaust to the block. I'll try the test with the full throttle and letting off. I was assuming the air / fuel ratio was what it was. Because at different times I do see it change mostly slight movments but occasionally to 16.5:1 and that range Though not to often. Thanks again



PS this is an edit:

Couldn't Find an ac/delco at any suppliers that were open. (autozone etc.) If NAPA doesn't have one then I'll have to wait till monday to get one from the dealer.In the mean time I switched the O2 sensor with the one I pulled out, and it's the same thing with either one. I also pulled the negative cable of and did a resistance test. Tried every connection and had 000 resistance on my meter. So I don't think a new battery cable would really help. If anyone thinks differently let me know. When this car sits and idles it shows the full range of movment, Just shows high when driving highway. I was wondering if may be it is showing the true readings and there is some other reason it may be not getting good combustion and running rich ( maybe not enough spark or somthing else )or is the computer supposed to compensate for that.


Last edited by 5buckeye0; 05-01-04 at 04:39 PM.
 
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05-01-04, 04:22 PM   #8  
Flow charts assume the fault is current or hard so don't follow the chart.I have a gut feeling a pcm is in your future but I hope I'm wrong.Check all grounds on the vehicle,Flow charts assume that you have tested all grounds and power before you get to the chart in the first place and it is a hard or current failure.Terminal tension is very important,loose connections(or corroded) cause false data to the pcm resulting in failures or repeat failures of the sensor or pcm.What happens is little arcs form and cause bad connections on the microscopic level.I have fixed cars that had terminal fretting or corrosion with the help of my eye loupes.A jewelers tool available very cheaply.

 
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05-01-04, 04:53 PM   #9  
Thanks Davo

You were replying while I was editting my post. I agree that it might be my PCM which would be alright if that would fix the problem. NAPA sells a remanufactured unit for 85.00 with exchange.You would think after all the years they have had computers in cars they would have come up with a reliable system to bench test them at the dealer by now. I mean they have to test them when they rebuild them don't they. And I imagine it would be a lot easiewr one you pros too if you could determine a bad PCM without all of the flow chart tests you guys have to go thru everytime to determine a bad PCM. Well enough gripeing (that isn't solving my problem). If you check my editted post you can see what I did so far. Thanks for the reply.

 
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05-02-04, 06:50 AM   #10  
The O2 sensor is not the problem,it is the wire to the O2 from the pcm or the pcm.Code 13 is OPEN O2 sensor circuit.Open means the electrical circuit is broken at some point,you have tried a different O2 sensor so you have narrowed the cause.You are checking for an intermittant open circuit.Replace the wire between the O2 and pcm and see if that works.If you can not find a problem with the wires using my suggestions replace the pcm.I would get the reman pcm from the dealer because I have seen aftermarkets be worse than what I took out.

 
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05-02-04, 09:41 AM   #11  
Thanks Davo

I did a continuity test on the O2 wire this morning and couldn't get it to break connection while I was shaking the wiring harness. I understand the importance of the terminal connections, but the ends are buried in the plastic connectors. Do you splice a new wire onto the old connectors ( I wouldn't think that would solve the problem of terminal connections) or do you replace terminals and all. Can you purchase an already made up wire from the dealer and somehow get it into the computer connectors( it looks like the connectors dissassemble but there sure are a lot of wires in it) without very much wire play or room to work. Thats where I'm at right now. I agree that the dealer reman. would probably be better. Since they don't want to keep doing work over. It looks like that maybe the harness comes out where it goes through the firewall I pulled back the weather protection and it's mounted with screws in a bracket. If I can get the wire harness out that looks like an easier way to tackle the repair, how do you pros do it? I'm going out now to check the computer ground for the O2 now. It seems to me that what might be happenning since the O2 works its full range when first started that maybe when the PCM gets warm it starts going wacko. Although it does still go into closed loop. I know I've had other electronics work fine when cold then fail when warmed up And I've been told thats usually because of solder cracks at the connections.

 
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05-03-04, 03:45 PM   #12  
Monday

Well I checked the ground for the O2 and it checked ok too. I decided to pull the plugs and take a look at them (they're only 6 weeks old) they were slightly carboned from the engine running rich. But not all that bad. Just not as good as a well running engines plugs. So I cleaned them and reinstalled them and went for a test drive and it started to pop on acceleration. So I figured I had'nt got one of the boots back on quite right. My scanner has a reading for (weak cylinder) and it said #2 ( usually it says none ). Any way I checked it and turns out I had cracked it ( luckily I never throw my last change out for awhile} so I replaced it and took for test drive and the O2 read in The upper 500 to the mid 600 mv range which is lower but still not a lot of movement at cruising speed, also slow cross counts. From everything I've read and you guys say the computer shouldn't go into closed loop till the engine warms up quite a bit but mine will go into closed loop probably within the time it takes to back out of the garage and drive 500 feet to the stop sign. Well when I left work tonight the O2 stayed real low for about 5 miles ( 100-200 mv) and set a code 44 and then straightened out and drove its normal self. Like I said in my post above I've got some questions about wire replacement. Another thing I noticed tonight on my scanner while driving home was the (weak cylinder) flashed #6 occasionally. I've noticed it a couple of other times but I really didn't know what it meant ( it isn't listed as one of the parameters in the manual that came with my scanner or with the parameters from my alldata disk. But after it showed #2 on the plug I cracked I quess it must read a misfire. Thats one parameter I don't watch very much ( usually the O2 and the closed loop indicaters) Does anyone have an idea what that #6 cylinder might be doing. Well thanks for any and all replies

 
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05-03-04, 04:33 PM   #13  
The wire can be spliced because you won't have the proper tools to do it.#6 misfire can be diagnosed by swapping parts cylinder to cylinder 1 at a time.I would just back probe the O2 connections at both ends before cutting any wire though.Don't always take scan tool data as gospel because sometimes the scan tool makes the car run worse,been there and chased my tail.

 
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