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Discussion Starter · #1 ·
I have a 1989 Mustang Lx with a 5.0L. I rebuilt the engine in September of 2010. its a standar bore 302 with edelbrock heads, a b303 cam and a gt40 tubular intake, also its a 5speed The car has run fine ever since the rebuild. Then one weekend it ran very poorly until it warmed up to temperature, its done this sever times, and now it runs bad all the time, its worse during acceleration than anytime. I have a new fuel pump and filter, fuel relays are new. I have new plugs, wires, cap, rotor, distributor, and coil, also timing is correct. I have checked my MAF sensor, my TPS, the Idle air control, i have changed my coolant temp sensor as well. my car as long as ive had it has never had O2 sensors. its ran fine for a year without them. When i unplug the MAP/BAP sensor there is no change in the idel or when i rev it up. Is it possible that its bad without causing the check engine light to come on? I have pulled the codes as well if anyone needs them here they are. my KOEO codes are 67 85 87. My memory codes are 14 22 29 33 41 51 66 97 91 95. please any help would be greatly appreciated. Im starting to get fed up with this car lol.
 

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DUDE thats alot of codes! Sounds like a major electric issue maybe 89coupe can help.
 

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Discussion Starter · #3 ·
most of the codes are things like a/c and neutral switch, and random things like that. also whenever you unplug any sensor while the engine is running and it throws a code, the computer will remember it. so.... im just lost. thanks for the lead, ill get in contact with him.
 

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You need to run the codes with the engine running. So first step is to get rid of code 67. We can get to the correct way later on. For now, unplug the white connector from the clutch pedal switch. It will have 2 blue/yellow wires and 2 black/white wires. Find your normal size blade fuse and insert it in the connector. Then setup to run the codes with the engine running. But you need to have to 02 up and running to diagnose the problem correctly. No way around it. Since with them not being there it will show false lean codes( your code 91 and 41 in memory). This is also keeping the computer in Open Loop.

So installing 02s should be your first step. Also, if the 02 harness is not plugged up, then you will get code 67 also.

Ive ran without 02's plenty of times myself, and thats not a problem unless something goes wrong elsewhere.
 

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Discussion Starter · #6 ·
Can a sensor go bad without throwing a check engine light? At first the car only ran bad for a few seconds, maybe a minute at a time every great once in awhile.
 
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