Resumed troubleshooting the ‘99 Suburban...

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travis
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Resumed troubleshooting the ‘99 Suburban...

Post by travis »

798C31CE-3D00-4035-BA07-FD62800583A3.jpeg
I walked away from this for a few weeks out of frustration ...now trying to figure this thing out again.

1999 3/4 ton suburban, 350 Vortec engine, who knows how many miles (supposedly rebuilt at some point in the past but I’m dubious...).

Driving home from work one morning the thing suddenly loses a lot of power and will barely pull itself down the road. Pops out the exhaust if you bury your foot in it. Fuel pressure is good, scan tool readings show the passenger side bank is running full rich. It starts and idles “ok”, but the exhaust note is definitely softer and there is a slight miss. Compression test shows 180 in most cylinders, 150-155 in 3 holes (some on both banks). I know this isn’t great but there are no dead cylinders. Plug wires ohmed out really good and the plugs are firing but I replaced them anyway. Passenger side bank plugs all show seriously rich except for the one pictured above which looks quite strange. Intake gaskets and injectors and O2 sensors replaced...no change. No loss of coolant or bubbles in the rad like a bad head gasket.

Troubleshooting today I’m noticing some pretty bad lifter noise on the passenger bank. It’s always had a lifter that randomly was noisy on startup like it was bleeding down excessively, but when it did happen it would quiet down after 20-30 seconds. It’s not quieting down completely now, so after it cools down I’m going to yank the pushrods and see if one is bent.

Can a hydraulic roller lifter be the cause of my problem all along? Would it still crank 150-180 psi with a bad lifter?
The plug pictured above came out of cylinder 6, which was also slow to pump up to 150 psi.
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prairiehotrodder
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Re: Resumed troubleshooting the ‘99 Suburban...

Post by prairiehotrodder »

could just the O2 sensor be bad on the one side ? or plugged cat ?

I see you replaced the O2 sensors. I've been fooled by fuel pumps before, and fuel pressure gages. Put your ear beside the gas cap and listen if the pump sounds normal.
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BB70
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Re: Resumed troubleshooting the ‘99 Suburban...

Post by BB70 »

I would take a fuel sample in a Gatorade bottle and let it sit awhile.
If that passes do a coil output test to see how healthy- long a spark .
Start with the basics .
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Re: Resumed troubleshooting the ‘99 Suburban...

Post by CharlieB53 »

I agree/ testing exh pressure to rule out a plugged cat

Also test temp sensor as out of range can cause a false rich when the computer thinks the eng is cold but sensor not so far out as to give a check engine light.

May be more than one temp sensor. Desperate sensors for gauges and ecu. Make sure which one is which.
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