Misfire Code

[nozzle936]

I have a 2001 Silverado 2wd 4.3L with ~130K and I have been chasing my tale with a misfire codes.

Took the truck to the garage with PO300 code and a small oil leak from the lower intake...they said to replace the intake gasket...done

~ 2 weeks after the intake job, the truck became hard to start when it was damp out. Replaced the cap, rotor, plugs, and wires. The truck started easier but then flashed the SEL when running with a PO300 on my scanner.

Back to the garage with a diagnosis of the distributor gear was worn on only some of the teeth. (4 teeth were worn ~75%). Replaced the gear.

Had the truck back ~1 hr with the SEL blinking PO300. Now with a crankshaft sensor failure. Garage replaced the sensor with no luck. Found a tsb to shim the sensor with a .020" shim. Put the old sensor back in with the shim. Misfire history is showing problems with #4 and #2. Replaced the wires on #4 and #2. Now get PO304 only. Swapped the #4 plug out with #2 to see if problem followed. No luck. The spider ohmed out fine.

I change the fuel pump, fuel filter, fuel treatment, K&N recharge were done ~2mo prior to my marathon.

The truck seems a little slugish during acceleration, no misfire sound. SEL will flash at high idle. At low idle ~600, the light goes out.

Any ideas?

[MT-2500]

Originally Posted by nozzle936

I have a 2001 Silverado 2wd 4.3L with ~130K and I have been chasing my tale with a misfire codes.

Took the truck to the garage with PO300 code and a small oil leak from the lower intake...they said to replace the intake gasket...done

~ 2 weeks after the intake job, the truck became hard to start when it was damp out. Replaced the cap, rotor, plugs, and wires. The truck started easier but then flashed the SEL when running with a PO300 on my scanner.

Back to the garage with a diagnosis of the distributor gear was worn on only some of the teeth. (4 teeth were worn ~75%). Replaced the gear.

Had the truck back ~1 hr with the SEL blinking PO300. Now with a crankshaft sensor failure. Garage replaced the sensor with no luck. Found a tsb to shim the sensor with a .020" shim. Put the old sensor back in with the shim. Misfire history is showing problems with #4 and #2. Replaced the wires on #4 and #2. Now get PO304 only. Swapped the #4 plug out with #2 to see if problem followed. No luck. The spider ohmed out fine.

I change the fuel pump, fuel filter, fuel treatment, K&N recharge were done ~2mo prior to my marathon.

The truck seems a little slugish during acceleration, no misfire sound. SEL will flash at high idle. At low idle ~600, the light goes out.

Any ideas?

Low fuel pressure and MAF sensor and Camshaft retard setting and cap and rotor are main causes of missfire codes.

Got good spark and good AC delco cap and plugs?
Good compression?
What is fuel pressure readings and camshaft retard setting reading?
Any other codes?

[j cAT]

I would replace the ignition control module after carefully checking all plug wires with ohm meter for correct resistance and all connections to coil including the ground wires there and at the VCM/computer..

when replacing the cranksensor there is a re-learn proceedure...


the cap and rotor should be replaced with new distributor.

[nozzle936]

I have 66 psi at the test point. Cap, Rotor, Plugs, Wires are all new from the Chevy Dealer.

Cam Retard reads -18 degrees. the garage told me the timing chain had a little slack in it because they could rock the crank pulley. Although the slack, they did not believe this was causing my misfire problem because it would be happening on all cylinders.

I will check the compression tomorrow.

No other codes

[j cAT]

Originally Posted by nozzle936

I have 66 psi at the test point. Cap, Rotor, Plugs, Wires are all new from the Chevy Dealer.

Cam Retard reads -18 degrees. the garage told me the timing chain had a little slack in it because they could rock the crank pulley. Although the slack, they did not believe this was causing my misfire problem because it would be happening on all cylinders.

I will check the compression tomorrow.

No other codes

new wires don't mean good wires...coil and connections .. grounding of computer also ..if this has been "arcing ", the ignition module is suspect,,,I would have replaced it if the distributor was worn out..

[MT-2500]

Originally Posted by nozzle936

I have 66 psi at the test point. Cap, Rotor, Plugs, Wires are all new from the Chevy Dealer.

Cam Retard reads -18 degrees. the garage told me the timing chain had a little slack in it because they could rock the crank pulley. Although the slack, they did not believe this was causing my misfire problem because it would be happening on all cylinders.

I will check the compression tomorrow.

No other codes

Cam shaft retard at -18 will give you many problems.
Including miss fires and burned cap and rotor and to hot of ing spark.
At -18 it is firing 18 degrees from plug wire terminal.
Wide gap for spark to jump.

If dist is set right.
http://files.automotiveforums.com/ga...hp?photo=51302

And if a locked solid dist plate.
The dist gear may need turned 190 degrees to make it come out right.
Or hold down plate slotted some.
It needs to be at -0 or as close as you can get it.

[nozzle936]

I have between 155 and 160 on the compression. The plug on #4 had a lot of black carbon.

What is the chance that the injector on #4 is bad and dumping to much fuel?

[j cAT]

Originally Posted by nozzle936

I have between 155 and 160 on the compression. The plug on #4 had a lot of black carbon.

What is the chance that the injector on #4 is bad and dumping to much fuel?

if the injector is leaking down the fuel pressure will drop quickly on engine shut down..

measure wire resistance replace plug if carbon fouled see if it repeats..

ever use techron fuel cleaner ? I use this every 5,ooomi works good..

[MT-2500]

You need to get the camshaft retard corrected.
That much off will give you many problems.
On the injector.
A fuel pressure gauge and the scanner you used to check camshaft retard should have a injector leak down/balance test.

Also make sure you have good injector pulse to no 4.