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Hey, I stepped into a real POS. I have a 93 Mercury Grand Marquis, 4.6L. No CEL's, runs great at WOT, but stumbles and hessitates on cruise and barely runs at idle. this car was at another shop, they did IAC, MAF, and plugs/wires. No change. STFT -99%, both banks Say rich, but Bank1 switches, Bank2 stays at 0.00V. I can run propane into the intake and the engine starts to idle fine, the O2s come to life, but still reads RICH both banks, sensors switch or read high Voltage. Scoped the Bank2 sensor and my scope reads what the scan tool says voltage wise. Sometimes the Bank2 sensor jumps to 1.15V and stays there for several min, then drops to 0V. I smoked for Vacuum leaks, and did a compression check...all ok. PCV valve is good, I am lost on this car...and loosing my rearend. PCM? Bad O2s? Both? Please help, Chris
 

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I would check to see what the Injection system is doing I have heard of injectors just collasping and it would run great on WOT but, suck everywhere its something that is a rare case but still happens.


Jeffery
 

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Wait, both banks say rich, but when you add fuel the idle evens out? That would indicate its running lean. What did the plugs look like when you pulled them out for the compression check? Did it look like they were running rich or lean, or about right? If it is actually running rich, look into maybe a fuel pressure issue, or leaking injectors. If its running lean, look for a vacuum leak somewhere. If its neither rich nor lean, maybe look for clogged up cats. That's where I would go with it. Let me know what you find out.

Mike
 
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