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Discussion Starter · #1 ·
The details

`1997 Z28, 6 speed with only 35,000 actual miles. After being laid up last winter it began to run rough, misfire, backfire and throw code 300, random multi-cylinder misfire and code 132 high voltage o2 Sensor1 , Bank 1, It tends to start fine but when it goes into close loop the problems show up. It kind of bucks under acceleration then catches up and starts bucking again. I have a scan tool and see that problem is on back one , cylinders 1,3,5,&&. I get NO wave form on the O2 sensor that's stuck at .8. After warm up the short-term negative fuel trim is as high as 36% on bank 1.

Here's what I have done so far:

Replaced the fuel injectors
Replaced the plugs and wires on bank1
New Opti Spark
Checked fuel pressure 45 psi
Checked for vacuum leaks
Checked for exhaust leaks with Seafoam found one downstream of rear O2 sensor so shouldn't matter
The scan tool shows all components like MAS, MAP and Coolant Temp Sensor are working.
Replaced O2 Sensor B1S1
Tested B1S1 Sensor wires from ECM to Sensor for continuity and checked out OK
Did not do a compression test, ( would be impossible do to confines) but did a manifold vacuum test and got 20 and no crazy fluctuations or low readings associated with bad rings or valves.
Also visually inspected plugs when I pulled them; no sign of oil from bad rings or leaky valve stems.
Pulled valve cover off to check for broken valve springs and observed valve train while motor was running everything was OK.
Pulled left side cat off and looked for blocked/melted honeycomb; didn't see any issues.

In sum, this LT1 runs rich only on Bank 1, misfires and backfires. I cant for the life of me figure out why? I have talked to several mechanics who have suggested things like checking the O2 sensor wires etc. but nobody has nailed the problem. About the only thing left, I would think is the ECM but if it failed wouldn't it affect both cylinder banks? Has anyone else out there had this problem?

105 Posts
I would look at the injectors being “Stuck” open, do you have “noid” lights? Basically,
You plug these into the injector harness plug, turn the engine over and the light will pulse with the PCM firing the injectors. Also, check your fuses for the injectors (Under hood fusebox) use an Ohm meter to check the fuses, just looking at them can deceive you, ask me How I know...... the PCM grounds the injectors, they have 12v with the key on, but if the fuse for the right bank is open, no fire. Since the left bank is firing, i’d be willing to bet the injectors are stuck though.
Also, take the vacuum hose off your fuel pressure regulator, and see if fuel comes out of the vacuum line, if it does, your fuel pressure regulator is shot. It will make it smoke black, excessive cranking and a pain in the but to change(under the cowl above the intake manifold, be prepared for scratched knuckles)
Hope this helps!
Ben Smith
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