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Unread 09-12-2011   #1 (permalink)
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Default 92 Mustang running lean

I disconnected my battery to erase some codes. I burped the cooling system at the ECT sensor and applied dielectric grease to it (I had been getting code 51) and the 10-pin connectors. I had hoped that once I got the ECT code corrected that it would take care of my problems. The codes that remain are: KOEO 85-84-33 KOER 41-91-33. The 41 & 91 appeared after I installed a 255lph fuel pump. What can be done to correct the lean condition(it is running lean, it's backfiring)? New injectors?
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Unread 09-12-2011   #2 (permalink)
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41&91 are codes for the o2 sensors..slightly misleading,they fail "always lean" so the computer tries to correct for it and adds fuel,usually resulting in a rich condition...

a new fuel pump should not cause those to show...false 41&91 could also appear due to a vacuum leak,or faulty wiring

how old are your o2 sensors?
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Unread 09-12-2011   #3 (permalink)
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The 41 & 91 are most likely your thermactor system malfunctioning(tab & tad) solenoids. The 33 is most likely your egr control solenoid above your tab & tad solenoids at pass shock tower. Discount your egr control solenoid vac line from manifold and attach direct to egr and rerun codes. If 33 becomes 34 you need a new egr control solenoid( it's not applying vac to open egr anymore) if 33 remains it is most likely evp sensor on back of egr, or egr itself. I would bet it's the control solenoid. I just fixed a friends car yesterday with same issue.

The 41 & 91 are not because your new fuel pump. It is your deverter sending unmetered air into the heads most likely.

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Unread 09-12-2011   #4 (permalink)
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Need4speed 90-The left o2 sensor is relatively new, the right one? was on the car when I got it. Would this cause the engine to backfire under load? It had been wrecked when I got it. The reason the left side one was replaced is that it was broken and the connection had been pulled out of it. I'll check the wiring tomorrow.

Black87-The car was wrecked when I got it and doesn't have the air pump or canister. I have plugged the vacuum line to the canister. Can I remove the EGR valve with a plate with no adverse effects?
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Last edited by eds92; 09-12-2011 at 07:12 PM. Reason: new info.
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Unread 09-13-2011   #5 (permalink)
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Ok, Did you plug the thermactor system holes on the back of the heads? when the system was removed? I assume you did.

I would not eliminate the EGR, It doesn't give you much if any performance improvement. But it does lower combustion chamber temps(Nox) while it's functioning. Just do the checks I posted to find your egr problem(Usually a pretty cheap code to fix).

As for the 41 & 91, I am doubtful of the o2's causing this. With one new one and one unknown aged one it just doesn't make sense. If it was the 1 O2 sensor you would get either a 41 or a 91 depending on what side the o2 failed on. You are getting a 41 & 91 which means both banks(Both Sides) are Lean!

When you put the new Pump in, Did you also do an adjustable Fuel Pressure Regulator? Did you set this right(Vac Unplugged)???? Set to about 37-38 with vac unplugged?

Only things that can cause this are lack of fuel, or to much air(Intake gasket Leak-Can find quickly with brake clean or something sprayed around gaskets. Listen for Idle change or stumbling). Unless your exhaust pipes are blowing black smoke and stink of fuel(Rich) Like Need mentioned, then I would doubt the O2's imo.
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Unread 09-13-2011   #6 (permalink)
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Yes, Kirban adj. regulator @ 39 with vacuun hose disconnected. I've used a couple of cans of carb cleaner trying to find a vac leak. I'll work on the egr code tomorrow. I'll update status then.
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