Getting codes 41 and 91

S

sd_iconoclast

Registered User
I just rebuilt my '89 SC. My mods were:
Slightly wilder cam from Schneider
Kooks headers
SCP exhaust
roller rockers
10% blower overdrive pulley
Forged pistons w/ slightly lower compression (8.0:1)
heads mildly ported. Mostly port matching but this required alot of grinding on the exhaust side
BHJ balancer
ARP head studs, main studs, and con rod bolts
balanced rotating assembly
42lb injectors
C&L MAF sensor to match the injectors.

Now I get engine codes 41 and 91 continuously when I cruise on the freeway.
From what I read they mean that both O2 sensors are reading lean.
It sure looks like they are both connected properly.

Does this mean that my mods worked and now I need a chip?
Or does it just mean I did something stupid?

I hear that XR7 Dave does chips for these cars. Is that true Dave?
 
Did you have to rebuild your engine because of a head gasket failure? If so your o2's could be bad. There is a test to check them out by removing them and using a propane torch.

Quote: Use a high impedence DC voltmeter . Clamp the sensor in a vice, or use a plier or vice-grip to hold it. Clamp your negative voltmeter lead to the case, and the positive to the output wire. Use a propane torch set to high and the inner blue flame tip to heat the fluted or perforated area of the sensor. You should see a DC voltage of at least 0.6 within 20 seconds. If not, most likely cause is open circuit internally or lead fouling. If OK so far, remove from flame. You should see a drop to under 0.1 volt within 4 seconds. If not likely silicone fouled. If still OK, heat for two full minutes and watch for drops in voltage. Sometimes, the internal connections will open up under heat. This is the same a loose wire and is a failure. If the sensor is OK at this point, and will switch from high to low quickly as you move the flame, the sensor is good. Bear in mind that good or bad is relative, with port fuel injection needing faster information than carbureted systems.

ANY O2 sensor that will generate 0.9 volts or more when heated, show 0.1 volts or less within one second of flame removal, AND pass the two minute heat test is good regardless of age. When replacing a sensor, don't miss the opportunity to use the test above on the replacement. This will calibrate your evaluation skills and save you money in the future. There is almost always *no* benefit in replacing an oxygen sensor that will pass the test in the first line of this paragraph

(information source unknown--something I had on my computer in a word file.)

Eric

PS Yes Dave does chips contact him through his email that is under any of his posts.
 
shotbirdsc said:
Did you have to rebuild your engine because of a head gasket failure? If so your o2's could be bad.
Click to expand...

Actually, I rebuilt the engine because my balancer broke and the engine had alot
of miles.

My O2 sensors are new.
 
sd_iconoclast said:
I just rebuilt my '89 SC. My mods were:
Slightly wilder cam from Schneider
Kooks headers
SCP exhaust
roller rockers
10% blower overdrive pulley
Forged pistons w/ slightly lower compression (8.0:1)
heads mildly ported. Mostly port matching but this required alot of grinding on the exhaust side
BHJ balancer
ARP head studs, main studs, and con rod bolts
balanced rotating assembly
42lb injectors
C&L MAF sensor to match the injectors.

Now I get engine codes 41 and 91 continuously when I cruise on the freeway.
From what I read they mean that both O2 sensors are reading lean.
It sure looks like they are both connected properly.

Does this mean that my mods worked and now I need a chip?
Or does it just mean I did something stupid?

I hear that XR7 Dave does chips for these cars. Is that true Dave?
Click to expand...

You port matched your exhaust ports? Hmmm, I have always read on here that this is a BAD thing and will hurt the flow. I don't think this would be causing the codes you are getting, but just the same... I was under the impression that port matching the exhaust ports was a bad idea.

Anyone else care to chime in that knows a little more about it???
 
Willing to bet you forgot to ground out the wire on the back of the engine, I got the exact same symptons when I forgot to ground the o2 wire on the back of the head.

Fix that and I bet your problem is solved with the 41 and 91 codes.

-B
 
Funny you should mention the ground wires.
The problem I just fixed is that I forgot the big ground wires that go to the engine mounts. Car would not start, but turned over for a while then stopped.
I wonder if I burnt up the wire(s) you are talking about.

This souonds suspiciously relevant. Thanks.

Is it one wire or two?
Where do they connect to?
 
Thanks 90Coug.
That was exactly the problem.
I looked at the back of the driver's side head and I could see the ground wires
just dangling there.
I bolted them to the head and the problem was solved.
 
i know this is an old thread, but i think i may have a similar problem. i'm getting an o2 code after rebuilding my engine, and I remember having a short ground cable left over. Could anybody tell me where the two ends of this go?
 
blueblur89 said:
i know this is an old thread, but i think i may have a similar problem. i'm getting an o2 code after rebuilding my engine, and I remember having a short ground cable left over. Could anybody tell me where the two ends of this go?
Click to expand...

The one they were referring to on this thread was a ring terminal wire that actually is bolted in by the same bolt that holds the back side of the fuel injector rail to the driver side head I believe. Took me a little while to figure this out when i put mine back together also. Mine is an 89, they eliminated that grounding point in 90 or 91 if I remember correctly.
 
You must log in or register to reply here.
Back
Top