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04 z71 New Knock Sensors and Fuel Pump = Bad Results

smokinfish

SM 2005
Full Member
Joined
Oct 8, 2004
Messages
255
Location
Dallas, TX
Took my 2004 AV Z71 in to have the fuel pump, two knock sensors and harness, Coolant hoses all replaced. They do the work and then spend four days chasing a misfire code. They say it?s the flattening of two cam heads. I get the AV back and the idle is tougher than previously and the acceleration is sluggish.

Any ideas?
 
Were the replacement knock sensors and harness OEM parts or aftermarket?

There have been reports of aftermarket sensors not working as well as they should.

I insist on OEM parts for repairs I do not care to have to revisit any time soon.

Also, I would recommend using Fel-Pro intake manifold gaskets.

I would hope they at least replaced the old gaskets as these engine are well known for leaking intakes.

Leaking intake gaskets are also known to creating various havoc, including misfire situations.
 
did they replace CAM? or leave it?

Not enough info to solve.
 
Thank you for the reply?s...

I took the truck in because one of my radiator hoses was leaking. I was also having issues with a slow engine starts, and the CEL was on because of the knock sensors.

They checked and said the fuel pump was holding pressure while running and then not after the engine was shut off. I asked them to fix it all.

They used all OEM AC Delco parts. new gasket, knock sensors harness, gasket, and fuel pump.

They noticed the rough idle and CEL is now lit up because of the misfire. They did random test and exploration and found the cam heads flattening.

They did not replace the cam.

At idle in drive with the brake applied the truck has a suttle pronounced shake that it didn?t have before. It also seems sluggish when accelerating.

The truck is a 04 z71 178k miles.. Spark plugs and wires were replaced in 2015, 50k miles ago.

Is there a way to see if they cracked the gasket by over tightening, without taking the manifold off?

I have a Bosch Code tool and I?ve cleared the knock sensor code in the past it would eventually come back on. But now if you clear the CEL the light comes back on sooner.
 
What is the exact CEL code?
 
Take it somewhere else....

They should not have done a fuel pump because you lost pressure.... Fuel pumps either work or they don't.
There may be a check valve in the pump assembly to prevent the fuel from flowing backwards but the pump its self was likely fine.

Losing pressure is likely due to a fuel injector sticking open. Your best bet is to send the injectors off to be cleaned/flowed and checked. This will make them as good as new and if you have a problem with one you will know very quickly. You can pull the injectors yourself and expect to be down 1-2 weeks while it is getting done. Now that you have a stronger fuel pump you are injecting more fuel into the cylinders with bad injectors...

I HIGHLY doubt you have a CAM issue...

But again, I would strongly suggest taking it somewhere else if you have someone else do the work. That place may be good intentioned and just suck or they are purposely trying to suck you dry.

 
HOw did they determine CAM LOBES wearing flat?

 
The CEL light was on when I picked it up with the following codes:
C0223 Right Front Wheel Speed Signal Erratic, ABS$29 (history)
P0161 Oxygen Sensor Heater, Circuit Bank 2, Sensor 2, MOD$10 (confirmed)
P0300 Random Multiple Misfire Detected, MOD$10 (confirmed)
P0161 Oxygen Sensor Heater, Circuit Bank 2, Sensor 2, MOD$10 (pending)
P0300 Random Multiple Misfire Detected, MOD$10 (pending)

I cleared those and drove 25 miles No CEL, parked let it sit for 10 minutes started it up and the CEL came on with the following codes:
C0223 Right Front Wheel Speed Signal Erratic, ABS$29 (history)
P0161 Oxygen Sensor Heater, Circuit Bank 2, Sensor 2, MOD$10 (confirmed)
P0300 Random Multiple Misfire Detected, MOD$10 (pending)


I?m not sure how they checked the cams they mentioned having the valve covers off.



 
Cam is buried inside engine and one would have to remove lifters and maybe use scope to see lobes or remove cam altogether...

Second opinion might be helpful?
 
When I had the P0161 error on my engine, I found the wire going to the driver's side rear O2 sensor was totally GONE.

Something must have got a hold of it somehow and ripped it completely off.

We bought a new pigtail and installed it and the error went away.

It could also be a bad O2 sensor.

The P0300 error might be from those 5 year old spark plugs and/or wires, especially if non-OEM parts were used.

Given they have been in service for 5 years now, it may not be a bad idea to replace the plugs and wires with new OEM parts.

These engines don't seem to tolerate non-OEM spark plugs very well.

The random misfire could still be caused by an intake leak, as well.

I would start with the new plugs and wires and having a look and possibly replacing that O2 sensor.

Replacing the right front wheel bearing hub with included ABS speed sensor will probably get rid of that C0223 error.

Actually, clearing the C0223 error from the history may be enough to get rid of that one if the ABS speed sensor in that hub is OK.

That might just be an old error.

I'm calling BS on the cam issue.

Possible, I suppose, but not very likely.
 
I looked at the throttle body and MAF and both look clean. I?m going to change the spark plugs this weekend. I?m also wondering if the CAT maybe stopped up. At 178k is it worth it putting in a new Magnaflow CAT system with new O2 sensors? Or would you just change the O2 sensor first?
 
Changing out the O2 sensors on an engine that old is never a bad thing.

Perhaps just changing out the one O2 sensor indicated in the error code will be enough to take care of that CEL.

Use only OEM parts.

A closer inspection for some kind of vacuum leak would still be a good idea.

If you are certain the leak is not from the intake manifold, then perhaps one of the two PCV hoses might have developed a leak when they were removed to uninstall and then reinstall the intake.

Recent work I performed on my engine found both of the OEM rubber end parts of both of my plastic PCV hoses had gotten old and were cracked and leaking.

I never heard a vacuum leak, but the hose connection on the driver's side valve cover was cracked enough to leak oil down the back of the engine.

I replaced the hoses on both sides of the engine with standard 3/8" rubber fuel/PCV hose.

Theses hoses will fit perfectly and tight enough and you do not need hose clamps.

One other thing to look for is some sort of air leak on any of the air ducting upstream of the throttle body.

I recall one owner finding a small crack in the bellows of that air duct that was producing a misfire situation.

I just feel if you are convinced the intake manifold is not the source of your leak, then it would be a good idea to look elsewhere.

There are many Youtube videos on how to test for a clogged catalytic converter without removing the device from the truck.

Since this repair is going to be more involved and certainly more expensive, I would make sure every other possibility is explored first.
 
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