P0304 2001 4.3 2WD. Several months and attempts
 

Hello,

I've mentioned this problem in other threads addressing other issues that are now fixed; however, the P0304 remains! Registration expires in nine days and I can't get it to pass emissions to register!

Last summer this code appeared. The car starts good cold and idles well. It also accelerates/cruises well. There is a small skip at idle when warm.

What I have done:

Checked Fuel pressure (good)
Swapped plugs.
Swapped wires.
Changes Plugs
Changed Wires.
Ran Sea Foam a couple of times.
Replaced LIM (Due to leakage)
Replaced Rotor
Replaced Distributor cap
All this was done last Fall.
P0304 remained.

Recently:
Went into plenum-

Cleaned #4 injector (destroyed it in the process).
Replaced #4 injector (funds prevented MFI swap)
Replaced plenum gaskets.

The above was done Saturday.
I drove it a total of 100 miles (3 trips) and no SES. I was happy!
Drove it 25 miles to work this morning. No SES. Happy!

About 10:30 I started it and before getting out of the parking lot...P0304 is back! ARRRGGHHHHHHH!!!!

Ever since last summer you can reset the ECM and can get several miles and 2-3 trips before the code would return. It usually would not return until a few seconds after starting up.

This last attempt lasted the longest. I though it was cured.


What else should I look at?

I do know I need to do a compression test. I guess I'll buy one of those.

Thanks!

I believe the evaporator canister purge valve vents into number 4 intake port. If the valve is stuck open maybe would cause you a problem. You should check compression. A leaky valve or head gasket could cause this. I've also had a crankshaft relearn procedure fix a phantom miss in number 4, but this wasnt a real miss, it couldn't be felt. I'd do compression and leak down tests next.

+1^ @Lancelot....hopefully this will help in finding the issue

If you can't pass emissions, there is a way to pass with a "waiver" ....it's all about the money...
I see you are from Atlanta, so I assume Georgia

"The need for full compliance with the vehicle emissions standard of the Georgia I/M program can be deferred with an emissions Repair Waiver. If your vehicle does not pass the initial inspection and the re-inspection after repairs are made, your vehicle may be eligible for a Repair Waiver if certain criteria are met. Note: The initial inspection cannot be more than one year old (12 months) or associated with a previous Repair Waiver or registration renewal."

Excerpt is taken from http://www.cleanairforce.com/motoris...epair-waivers/ and more info is on that link.

Thank you both.


This ECS. I've had it off for both plenum removals. How do I check it? Where is the 'intake' for it? 2wd 2001 here.

Again, Thanks!

You don't have to remove the upper intake/plenum to remove the lower intake, that being said...this is an image of it.

Backtracking to post #1, you stated that you never updated to MPFI? correct? This will also produce mysterious misfires on only 1 cylinder. I'm just trying to go over everything and hopefully keep you from spending cash where you may not need to. Do a compression test, if it checks out OK, then upgrade 1st, and verify P0304 fix. If it isn't resolved then continue on to ESC ports into the manifold. The following info applies to the X (8th vin #) 4.3ltr --->The purge solenoid doesn't feed directly into the manifold where it attaches. There is a passage cast into the manifold that takes the vapor to a tube in the front of the manifold floor directly under the TB.

Before spending money on the upgrade I would unplug the harness from the top of the upper intake and make sure all the injector pins are fully extended and not bent. I would also get the pin out for the vcm connections and check the wires for injector 4. Check for continuity between both end and check for shorts to positive and negative or voltage and ground. The blazer I have now had a bad injector wire. Those spider injectors are replaceable individually and many people have extras in there garage. The last 6 trucks I've had with those injectors did great. I replaced individual ones after a mechanic told me it was the problem only to find out he was wrong. Expensive. Those injectors can also be bench tested for leaks and proper function.

Well. time is about up and I think I have found the answer, but can not properly repair by the registration deadline.

I wished I'd purchased a compression tester long ago.

I only removed plugs #2 (known good) and #4 (P0304 coded miss). I left the remaining ones installed. I unplugged the fuel injector connector and ignition module. I hooked the tester to Cyl 2 and got 170 psi. I connected to 4 and got 130. I added a small amount of oil for a wet test and got about 135-140 psi. Is this enough increase to rule worn out piston rings? Valves burnt/sticking?


In short, is there any 'miracle' cure I can try? At least to raise the compression until I can pass the smog test in a couple of days? Can the valves possibly be cleaned with just the valve cover removed? I did the Seafoam fog method twice a couple of days ago. I've also read about adding a quart of ATF to the oil to un stick lifters.

Any other futile attempts of desperation you can recommend?

as always, thanks!

You could possibly try running a hotter spark plug in the problem cylinder.

Thanks.

What would that do?

Here in Atlanta for OBD2 they do not do a tail pipe sniff, just do a visual, check gas cap and hook up to your ecm whilst vehicle is running. Any codes and you fail. You'll also fail in 'Not Ready' in more than 1 category.


I also want to add that when the number 4 plug is shorted, the engine speed remains the same at idle. When number 2 plug is shortly, significant decrease in speed/rougher idle.

I am getting 130 psi in cylinder 4. Even though it is lower than number 2, should this still not be enough for it to contribute at least something?

Thanks,
Joey

Hotter plug may help if the heat from compression is low. The heat to some extent could be made up for in the plug.