Mechanics

HELP

1996 Chevrolet Truck • V8 4WD Automatic • 197,000 miles

I have a 1996 Z71 pickup & it stumbles, & misfires at light to moderate throttle, but full throttle seems to be the same.I've replaced plugs, dist. Cap, & rotor still have same problem had it tested at auto zone & both oxy sensors showed failing. Does this sound like oxy sensor problem or could it just be starving for fuel causing the misfire & bringing up the oxy failure? I need help please!
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Jack Carpenter Jr
February 12, 2011.



You changed everything except plug wires. This prob usually is plug wires not always but certainly they have to be eliminated and fuel filter. What you are doing is called a diagnostic tune up. So if it were mine I would do the wires and fuel filter

do you have an idle prob also?

Billymac
Feb 12, 2011.
No I don't have an idle problem just driving range, normal driving that is.

Tiny
Jack Carpenter Jr
Feb 14, 2011.
Well yes this could be 02 sensor failure but could also be the driveability prob causeing a false code. Also a carboned egr valve pintle can cause a stumble or miss generally this incorporated with a idle prob. But not always. It is worth pulling the egr and looking at the bottom of it if it is carboned up clean it.

But we are still leaning toward wires since this is the most common prob.

Billymac
Feb 14, 2011.
I change the wires & still have a little stumble & it actually backfires like once or twice when I barely give it gas, but when I put a little foot in the pedal it'll take right off & sound great just like a new one.I drove for about 20 mins on the highway & it felt like I was surging very, very minuitly, but my check engine lite never flashed this time.I thought this was weird the minuit surging cause my overdrive to kick out so I stopped & shut my truck off & counted to ten & started my truck back up took off & it started taking off kinda of sluggish & my overdrive kicked in way to soon causing my truck to ping (engine knock) like bad gas or something. Does any of this sound like anything you can think off? I don't have a lot of money to just throw at it so I appreciate all the advice I can get.

Tiny
Jack Carpenter Jr
Feb 15, 2011.
YES I UNDERSTAND THE MONEY SITUATION WE ARE ALL THERE TOGETHER. But it sounds like the wires was an improvement. Are you positive the fireing order is right recheck it. I have got a wire crossed many times very easy to do.

Check all vacum hoses to be sure they are connected and no holes in them.

Check intake manafold for vac leak. Fuel pressure very important on this eng. When you press the accell and eng backfires it is not getting enough fuel. Did you replace the fuel filter?

Summary
fuel filter
fuel pressure
vac leaks at hoses
vac leaks at intake manafold
determine which cylinder is misfireing
this could be a fuel injection controller
remove intake look for broken plastic lines for poppet valves
look for raw fuel inside the plantum chamber
the vortec has a fuel injection controller it fuels the cylinders through poppet valves these valves opening and closeing right depends on fuel pressure being exact to specs. This is a tough one to diagnose and a new controller is a couple hundred dollars.

This is why you need to pin this prob down to only the cylinder misfireing.

Billymac
Feb 15, 2011.
I added some fuel injection/carb cleaner to the fuel & took it for a drive & low & behold my truck is running back to normal for now how long I don't know.I've had this truck for only 8 months & I've replaced the alternator, heater core, water pump, thermostat, fuel pump, & the fuel filter so I'm crossing my fingers. The Heads were replaced with new ones 6 months before I bought it, so it really doesn't run bad.I really like the truck or I would've done sold it by now lol especially with this luck. Do you think that actually fix the problem or am I just experiencing some luck for a change.

Tiny
Jack Carpenter Jr
Feb 16, 2011.
Well it is possible the injection system had some type of restriction. And it is over it. I guess you just hope for the best good luck thanks for asking 2carpros.

Billymac
Feb 18, 2011.