Codes 41 and 91, is the computer maxed out or something???

Black1987Stang · Feb 12, 2006

My friend is getting codes 41 and 91 which are both HEGO (HO2S) sensor signal out of range/system lean codes...This is his mod list
Probe forged pistons

GT40P heads

10.5:1 compression

4.10 gears

73mm MAF

70mm TB

24# injectors

A9L EEC-IV conversion

MSD ignition

MAC shorty headers

BBK X-pipe

Flowmaster force II cat-back

3-core radiator

Stainless flex-a-lite fan

Underdriven crank pully

X303 cam

1.6 aluminum RR's

Typhoon intake

Kirban FPR at 45psi

190 lph walbro fuel pump

He is wanting to go carb to fix his cold morning starts, it wont idle, dies, etc. and i think he is a simple problem, his fp is at 45psi right now and he said when he puts it down to 40 the plugs are pure white and has SLIGHT specks of detonation on the plugs so thats why he turned it up. I had a thread about about the plug color and Michael Y and others were saying the plugs were supposed to be White.This is the thread... http://forums.stangnet.com/showthread.php?t=615169
Hes saying the computer is maxed out and so he is going carb to eliminate his problems.
I think hes got something going on since I have a similiar combo and Im at 42psi AND still have the stock 19lb injectors and mine runs awesome, when he has 24s and higher fuel pressure....Anybody got any suggestions? anything know what exactly the codes might be hinting him too? :SNSign:

Raginstang · Feb 12, 2006

yeah, he needs to replace the o2 sensors. most likely, they are very old. when the sensor goes bad, I think it makes the car run rich. if the computer cant read the sensor, you will have all kinds of problems due to incorrect a/f mixture. he may just need to set is idle screw under the throttle body. and remember to reset the tps if you do this.

sunil6784 · Feb 12, 2006

41 and 91 are both 02 sensor codes, that they are out of range. When's the last time he changed them ?

HISSIN50 · Feb 12, 2006

A vac leak, out of cal' ACT or ECT, and other issues can also toss lean codes. I would not simply assume it is the O2's. It could be, or it is that the O2's simply are taking the blame for another issue.

Good luck.

Michael Yount · Feb 12, 2006

What kind of maf? Did it ever run right (no codes, no mixture issues) after the mass air conversion?

Black1987Stang · Feb 12, 2006

HISSIN50 said:
A vac leak, out of cal' ACT or ECT, and other issues can also toss lean codes. I would not simply assume it is the O2's. It could be, or it is that the O2's simply are taking the blame for another issue.

Good luck.

They are new ECT and ACT sensors...the 02 sensors are pretty old though

Hes running a Pro-M 75mm meter calibrated for the 24lb. injectors...he did the maf conversion along with the new motor. The problem started happening a few weeks ago, so it has ran good for a while with everthing. Dont flame me for this but could he use a air/fuel ratio gauge hooked up to the 02 sensor to see if the 02's are going from rich to lean (not to tune it by), just as an indicator to see if its stuck at one setting (real lean or rich)? Hes sick of it and getting ready to order parts for a carb conversion. Hes saying the plugs should be tan not white(electrode arm) and he said when he upped the fuel pressure(45psi) the plugs now have a tan electrode arm?(compared to 40psi and white electrode arm)...my idea was theres so much fuel going in (higher fp and 24lbs) that the computers trying to lean it out but cant?? When u say white plugs do u also mean the electrode arm or just the insulator?

Michael Yount · Feb 12, 2006

They're likely tan cause it's running richer than it should -- perhaps he's upped the fuel pressure so much the O2's can't keep it within range anymore.

The a/f gauges run off the O2 readout are pretty useless. He needs a wideband to get useful a/f data.

If he's this frustrated with it, perhaps a switch to a carb would be a good thing for him. Too bad....

Michael Yount · Feb 12, 2006

White - insulator...

Monsterbishi · Feb 12, 2006

It would be a crying shame to throw a carb on a motor as a bandaid fix.

That, and by the time he forks out for the carb conversion parts, he could have a aftermarket ecu in and tuned for the same price, giving much better results.

Black1987Stang · Feb 12, 2006

Michael Yount said:
They're likely tan cause it's running richer than it should -- perhaps he's upped the fuel pressure so much the O2's can't keep it within range anymore.

QUOTE]

Yea thats what I was thinking, he wont turn down the fuel pressure back to 40 because he said it shows SLIGHT signs of detonation so he doesnt want to mess up anything, hes set on going to carb.

joel5.0 · Feb 12, 2006

41 and 91 = Engine always lean (both banks)

You can monitor what the O2's are reading by hooking a DVOM to the signal wire of either side.....Quick Q,..... is he running a breather on a valve cover?...if so, that's a cause to force a lean condition in the system. You would be surprised to find out what that little ornament can do to the A/F setting in the system.

If the O2's are old (2-3 yrs), it's recommended to have them replaced. Another way to check if they're working, is to force an abvious rich condition in the engine while doing a KOER self-test...disconnecting the ECT or ACT sensor (and ignoring the code this will generate) and running a KOER self-test comes to mind, if the lean codes are still there, the O2's need to be replaced. My 2¢.

Codes 41 and 91, is the computer maxed out or something???

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