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Old 02-01-2010, 03:32 PM
oldbogie oldbogie is offline
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Quote:
Originally Posted by bowhunterml
ok, so heres the story. 1994 chevy truck, 350 thats throwin a code 32. it has headers, and true dual exhaust. now the o2 sensor is only on 1 of the pipes, instead of reading all the exhaust it reads half(one side) . would this confuse my truck and cause it to throw this code? i have replaced the egr valve and the egr solenoid. i have checked for vacuum leaks, but cannot find anything. any easy idead/cheap ideas ? also, it like "surges" at about 50-60 mph, and kinda seems like it misses, but not really, its weird.

thanks for the help
You should add an H pipe and put the O2 sensor there. This will give an average reading for the entire engine instead of one bank, so any unique cylinder to cylinder mixture problems are balanced out.

Code 32 on TBI engines with headers and duals is a pretty common event. The reduced exhaust back pressure from these "improvements" also reduces the flow of exhaust gases thru the EGR valve. The system reads this and trips Code 32.

The misfire/lean operation is also a likely consequence of the headers and duals. I'd bet it only does this below 160 degrees of engine temp, which is where the EGR is not functional at all and the cold start enrichment is operating. When the EGR comes on there isn't enough exhaust flow into the intake, this makes a lean mixture as the air replaces the missing exhaust. The computer would attempt to make this up if it can. The data it gets from the O2 sensor is what it uses to trim the mixture. If it doesn't, either the O2 sensor is defective, or not seeing exhaust flow. Or the engine's components are wearing out, like timing chain and gears or fuel pressure regulator as examples, so the total needed adjustment to the mixture exceeds the computer's authority to manage.

You could jam up the exhaust with a rag and see if the increased back-pressure makes a difference. If it doesn't then digging deeper will be in order. A fuel line pressure check, voltage out of the O2 sensor, and whether the cam is timing correctly to the crank (not an ignition timing check). If the cam and crank are going their separate ways as happens with wear in the timing gears and chain, twisting the distributor while bringing the timing correct to the crank, leaves the ignition out of sequence to the cam which is out of sequence to the crank.

Other tricks are drilling the EGR valves orifice ever so slightly larger, this will let more exhaust to pass the valve with less back-pressure, but this is sensitive the engine cannot swallow a lot of exhust. Also, replacing the stock fuel pressure regulator in the TBI body with an aftermarket variable pressure unit so you can manually trim fuel delivery is help full and less expensive than a new chip in the computer. Hopefully you don't have to pass an emissions test as this will make the engine rich enough to fail the unburnt HCs and CO ratio part of the test.

Bogie
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