Draftman

Hello,

Please bare with me as this is my first post.

I have a 2001 Chevy Silverado, 1500, 4x4, automatic, 5.3 V8.

While pulling into the parking lot at work, my truck just died. It was as if someone turned the key to run. I still had battery as the instruments and lights were all working. I managed to push it into the parking lot and test a few things. I was able to start the truck Only if i put the pedal to the floor and cranked for a while. After I got it started, it ran as if i was only firing on 3 or 4 cylinders. I ended up towing it home and was able to check all the basics. Here is what i have done so far:

With an OBD II scanner i was able to read codes and it gave me a P0300 Random Cylinder Misfire.

I changed out plugs and wires about a year ago. I checked to make sure i had spark at each plug. I pulled spark plugs one at a time and found that about 5 of them were wet with fuel however each plug was getting spark. I was able to check the coils by swapping coils with my dads truck (same truck only two years newer). Doing this made no difference.


I swapped MAF sensor...no difference. I swapped MAP sensor...no difference. I tested and bypassed the EGR Valve and this made no difference.

I tested fuel. Fuel was about 57 PSI sitting with key in the on position. I let it sit with the gauge on there for an hour and the pressure still held. I then checked it with engine running (barely). Fuel pressure was about the same.

I replaced the camshaft sensor and crankshaft sensor which made no difference.

I also checked compression in all cylinders and found that all cylinders except one had about 170 lbs comp. Cylinder # 6 had zero lbs. I tested this cylinder with compressed air and heard air in both the exhaust and the intake.

Because the truck is running like it is out of time, do you think the timing chain slipped a couple of teeth or could I have a broken or burned valve in cylinder 6. And if it is a broken valve, would it mess up all the rest of the cylinders and make my truck sound like the timing is way out of wack? Sorry for being long-winded. I just want to try to cover everything i have done so far. Any help would be greatly appreciated.

Thank you

2000CAYukon

What does the fuel pressure do when you turn the key off? I would pull the vacuum hose off of the fuel pressure regulator and see if you have fuel in the vacuum hose.

The fact that the plugs are wet means it is getting to much fuel. Either a leaking FRP or bad ECT sensor.

//2000CAYukon

Draftman

Fuel pressure Regulator is dry (no gas in hose, and gas doesn't come out of FPR). Fuel pressure is steady. I was able to pull the valve cover and found a broken intake valve spring. Would this cause the entire truck to sound like it is out of time though?

JOSH...BAMF

I do not know about the spring, but I just replaced the timing chain on my truck this weekend and the stock one was very wimpy looking. I have 120,000 and there was alot of slack in the chain. The replacement chain and gear was about twice as thick as the stock one.

j cAT

with the intake valve not working the intake manifold pressure was not correct .......this causes the MAP to instruct the pcm/computer to dump more fuel into the combustion chamber..

the map with a vac of 20inches will produce a voltage of 1-2 volts at idle...when the vac drops on increasing the throttle, the vac. drops . then the voltage increases , and this then tells the computer to increase the fuel demanded ...


why do you think the valve spring was broken ????

Draftman

Thanks for the info. As far as why the spring broke in the first place, that is a good question. Everything i have been hearing on the 5.3 has been pretty positive. It is supposed to be a durable engine but who knows. Maybe this was a fluke and my engine was one that got a faulty spring? I am going to try to pick up parts and get the beast running. Any suggestions on springs? Go with dealer parts or would an aftermarket spring work?

j cAT

If you can't explain this failure .....replace ALL springs....