Drivability issue with Silverado

fillupread · #1 07-25-2007, 11:51 AM

Hey guys,,,, New here and need some help.

I have spend years working for GM as a Tech and my own truck has got me stumped! I could use some help.

2002 Silverado 2wd half ton with the 5.3. 150000 miles.

The engine spark knocks light to heavy, gets real heavy after 3000 rpm.. The knock retards the timing but I can feel the truck hunting for timing before the knock becomes severe. I have a huge loss of power when this happens. If I drive it light it isnt a problem but I can still feel it faintly. If I drive medium to heavy it knocks like mad causing the timing issue. I cannot tell if it is a timing issue causing the knock or knock causing the timing issue.

It isnt consistant either. Some times it will run up to 4000rpm and then start its problem. Some times it will start around 2000.

If I push it during the knock the CEL will flash but not set a hard code. I will find a P300 random cyl misfire soft code. It has not set anyother code. When it sets the misfire code, it usually sets 2 of them each time.

It only does this under load. I find nothing wrong at idle. However if I rev it hard while in park I can hear a ping or two.

What I have done so far:

Last winter I installed a new intake gasket because the original was sucking air when cold. Typical problem. The engine ran fine before the intake gasket and fine since.

For this problem I installed a new rear Knock Sensor. I found the Knock Sensor TSB and the description sounded similar to what I was having. However I felt that my issue was more severe that what was described in the TSB.

New fuel filter has been installed.

Fuel pressure was 50 psi at idle. I installed a new fuel pump and it still reads 50 psi. Guess I need to calibrate my fuel pressure gauge! After the new pump was installed the problem didn't go away

Original plugs were replaced with factory replacements at 100,000k

I have noticed a light vibration at or around 2000 rpm's while driving (engine under light load). This vibration is actually more like a designated cyl miss. However my scanner is not picking up a cyl miss but just the random Cyl misfire.

HELP!

2000CAYukon · #2 07-25-2007, 01:28 PM

Do you still have the original plug wires on it? If so, I would replace those. Seems ignition related to me. Maybe a bad coil pack or two.

//2000CAYukon

silverado122775 · #3 07-25-2007, 01:39 PM

You could have a bad ECM, causing the bad timing. But to be honest this sounds like something GM Merlin could answer.

fillupread · #4 07-25-2007, 01:45 PM

Coil wires have been ohmed and even given the soap test, all good there.

The PCM has potential but not comfirmed yet.

I have a bud that does work for GM tell me they have seen a ton of high milage silverado's getting contamination in the fuel rail from a fuel line deteriorationg. He said that the gunk fills the bank one rail and sometimes cloggs up #7 injector and causes performance issues across the board. Because fuel is still delivered it doesnt always set a specific code.

Injector cleaner is snake oil mostly from my own experience. He stated this needs to be removed and cleaned out by hand.

I dont know if this is what is happening to mine but it sure would be nice to have my truck back 100%.

I share this now for info purposes for the rest of you here. I will let you know if it fixes my truck. I plan on pulling the injectors and rails tonight.

Thanks so far.

fillupread · #5 07-25-2007, 04:35 PM

I have confirmed a common problem with the silverado of the fuel lines rusting on the inside due to moisture entering the fuel system through the EVAP system.

The corrosion/rust clogs the screen on the injectors, mostly #7 and has been known to clog in the fuel rails.

From what I have learned replacement of the injectors and rail is not necessary as a good cleaning by hand will fix the problem but the corroded fuel lines will need to be located and replaced.

The TSB is #00-06-04-024 and will discuss the moisture entering the EVAP system.

I have not had the chance to pull the fuel rail on my truck today but I will reply what I find tonight once I have a chance.

fillupread · #6 07-26-2007, 02:07 AM

DAMN!
I pulled the injectors, CLEAN as can be. No rust or gunk in the rail or a trace on the injectors. Checked the pressure reg and it was clean also.
Got my bro's burban over and swaped the MAF and crank position sensor and still have no luck.
However I did get a misfire on #7 code. I pulled the plugs and they still look good.
Im stumped!

fillupread · #7 08-04-2007, 10:58 PM

Figured I would give an update.

I took my brothers burban and swapped some parts (both have the same engine)

I have exchanged the coils, plugs, wires, fuel pressure reg, cam position sensor and nothing has changed!

WTF!

The injectors ohm correct but I am going to swap them tonight and see if that does anything.

Anyone heard of a TSB of moisture getting trapped in the purge canister? I have heard that this will add water to the fuel supply.

rrousou · #8 08-11-2007, 09:26 PM

Are you running high quality gas, namely top tier brands. If not I'd run several tanks of that through and see what happens. As a GM tech I assume you have access to the shops diagnostic equipment.

fillupread · #9 08-12-2007, 12:02 PM

Quote:

Originally Posted by rrousou

Are you running high quality gas, namely top tier brands. If not I'd run several tanks of that through and see what happens. As a GM tech I assume you have access to the shops diagnostic equipment.

I havent spun a wrench in 7 years but I still got access to everything except a Tech 2!

UPDATE***

I took the forward set of 02's out and checked forward exhaust pressure (infront of the converters) It should be around 1psi between idle and 2000rpms. Bank 2 was right at 1.5 but bank 1 was bumping over 4.

I left the 02's out and took it for a test drive. It was loud but ran like a new truck. So now I need to find a Y pipe with converters. Anyone got a set laying around?!?!?!?!

horse482 · #10 08-12-2007, 07:15 PM

Not exactly cheep, but you can buy new bolt ons from www.magnaflow.com

kenny-1907 · #11 08-13-2007, 12:48 PM

Just a thought, but with 150,000 miles on her could it possibly be a stretched timing chain ?

fillupread · #12 08-15-2007, 03:19 PM

I gutted the cats this past weekend. Fixed the problem and made it sound mean!

Prob is about every 3 days I get a cat below threshhold code. I just clear it and keep on going. Wish there was a way to fool the computer to not throw that code. When I replace the cats I doubt I will enjoy it anymore!

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