Bad cat? Off road y-pipe?

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Schurkey

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Most fuel pressure gauges have a button on the side leading to a clear plastic hose. You push the button, gasoline vents down the hose, hopefully into a drain pan.

So if you're idling and have good fuel pressure...push and hold the button, let fuel dump into your drain pan. You've just tested the fuel pressure "under load". The fuel vented down the hose is about the same as the engine would use at heavy throttle. If the pump maintains reasonable pressure...you should be good.

What pushing the button does NOT simulate, is the loss of vacuum with heavy throttle...which would cause a vacuum-referenced fuel pressure regulator to increase fuel pressure. Not an issue on TBIs that don't have a vacuum connection on the regulator.
 
El Tigre

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The idea of taping to windshield is when depressing throttle. Gauge reading should increase ,not decrease. Never seen gauges w/button ,etc.
 
Schurkey

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El Tigre said:
Never seen gauges w/button
Click to expand...
www.amazon.com/Actron-CP7818-Fuel-Pressure-Tester/dp/B0006V2BI2/ref=sr_1_32?keywords=fuel+pressure+gauge&qid=1637469579&sr=8-32

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www.amazon.com/OTC-5630-Fuel-Pressure-Test/dp/B000R5IASC/ref=sr_1_33?keywords=fuel+pressure+gauge&qid=1637469579&sr=8-33

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www.amazon.com/ATP-Injection-Injector-Pressure-Gasoline/dp/B07GH2YK71/ref=sr_1_55?keywords=fuel+pressure+gauge&qid=1637469784&sr=8-55

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www.amazon.com/ATD-Tools-5578-Injection-Pressure/dp/B000OUZBZK/ref=sr_1_19?keywords=fuel+injection+pressure+gauge&qid=1637470235&sr=8-19

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Plus about thirty more junk-Chinese brands.
 
1-8-4-3-6-5-7-2

1-8-4-3-6-5-7-2

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1-8-4-3-6-5-7-2 said:
1997 C1500 4.3 auto

If I run the engine hard like merging onto an interstate the engine will start to miss out real bad like it's running on only 2 cylinders. Imagine putting the power on a light switch and flipping it on and off real fast, that's what it feels like. It's like the power is on-off-on-off-on and so on. I let off the gas and keep the pedal at a normal cruise speed and it bucks for about 20 to 30 seconds and then it clears up.

Plugs, wires, cap, rotor were replaced about 2 years ago with all AC Delco stuff. (plug wires may have been another brand, but still decent. I don't buy crap wires lol)

Checked the fuel pressure a year or two ago when this problem started and it was a couple pounds under spec but that could be my cheap gauge not being accurate.

Now on a cold start I can hear a horrible loud rattle noise coming from the catalytic converter area. I don't think it's the transmission making the noise, but it's hard to tell for sure. After the engine warms up the noise gets much quieter and is only heard at a certain RPM when beginning to accelerate.

Codes are p0147 (rear o2 heater circuit) and p0304 (cylinder 4 misfire)

Based on that info, what are the chances I have a bad catalytic converter?

If the cat is bad, anybody know if there is an off-road y-pipe available for the 4.3 Vortec? I used one years ago on my 96 Burb 5.7 but can't find one for this truck.
Click to expand...
As I mentioned in this OP the catalytic converter sounds like it is rattling. I didn’t think it was the transmission but it was hard to tell if the noise was for sure coming from the catalytic converter or the torque converter area of the transmission.

This morning I got under there to change the oil and I could hit the catalytic converter and hear a noise like something is loose inside of it. The noise is definitely inside the convert and not resonating from somewhere else.

I’m guessing catalytic converters aren’t supposed to do this? :anitoof::anitoof:

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Frank Enstein

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Yup ya got yerself a door stop right there.

Now you need to find out what murdered the cat or you will replace it again.

Over-fueling(misfire, lazy O2 sensor, or leaky injector), Burning oil, Coolant contamination, and impact are the most common causes.
 
1-8-4-3-6-5-7-2

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I just took the pipe off and there’s a lot of stuff rattling around inside it, so yeah, definitely bad. I tilted it forward and a small chunk of honeycomb came out of the right side down pipe.

I think it’s been messed up from before I bought the truck a couple years ago since it never has ran right. When I got it I put new plugs, wires, cap, and rotor on and a new fuel filter and air filter. The truck runs fine when driving normal but messes up if I go above 3k rpm.
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highwaystar

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Welcome to the club! My '94 did this last week. I put a Flowmaster Y-Cat on 8 yrs ago. Heard rattling, cat crumbled and blew pieces into the muffler. Replaced with a Walker Cat & new Flowmaster muffler. Mine would dead miss as yours at a load.
 
Fast_Z71

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If you’ve replaced all the ignition components I’d probably look at the spider injector. I’ve had to replace the on on my 94 Jimmy with the W 4.3 several times, but that trucks also got 465k on the odometer. If I’m not mistaken jegs sells a off-road y pipe for the 4.3 full size trucks. However if you’ve got pieces rattling around in your cat it’s probably bad.
 
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