Hello everyone, hopefully all is well. Im stumped here guys. I drive a 2000 Blazer 2wd model. Ive replaced the whole distributor assembly, all new plus, wires as well. Couple of days ago i replaced my spider injector assembly (the new updated multiport injectors) and im broke and still have a misfire on cylinder 4... haha. I dont want to go to a mechanic but this here has me stumped. If anyone has any ideas that would be excellent. My next thought was to have a compression test. Would a bent valve cause a misfire?

 

Is it an actual felt misfire, or is it just turning on the SES light with a P0304?

Of course a bent valve will cause misfire, as will many other things. But first ..... you need to determine if it is a real misfire?

 

When im driving it feels as if theres nothing wrong. But at an idle you can definitely tell theres a dead miss

 

OK - so the misfire is real. Is it setting a P0304? Why do you say cylinder #4? Do you have a scanner? If so, which one and will it display live misfire counts?

Sometimes misfire detection gets jacked up and reports cylinders out of order. We can test that. Just want to make absolutely sure which cylinder we are working on and to know what your capabilities are.

Or you can jump ahead and do that compression test and screw in a new set of spark plugs - but when you do it I would recommend that you test all 6 (not just the cylinder that you think is missing). Wire the throttle open some when you are testing compression - it makes a difference.

You can get a loaner (with deposit) compression gauge and fuel pressure gauge from your local parts store (AutoZone, Advance Auto Parts, O'Reileys, etc).

Good luck and best wishes for a successful repair.

 

How is everyone today? Im getting a code for p0304 in my 2000 4 door 2wd. It comes and goes... its weird, my friends call it the self healing chevy haha. But it came back today after running good for a week. Then itll misfire for a few days to a week or so and go back to normal. With that being said, i recently purchased a inline spark tester, and I STILL HAVE SPARK!? Im stumped. I dont have a fancy scanner to see live misfire, just a little cheap bluetooth one. Ive replaced everything dealing with fuel and spark. The new updated multiport injectors, ignition coil, distributor assembly (granted its not an ac delco even tho its still the same symptoms), and the best plugs and wires. Its still the best running truck ive picked up for $400 hands down.

 

Could be a sticking valve. Maybe check compression in #4 next time it acts up?

 

Do the compression test on all cylinders and report. One may be on the verge of low enough compression to misfire at idle. Is it worse when the vehicle is cold?

If you already have the Bluetooth OBD2 dongle, get Car Gauge Pro ($8.99). It will read the live misfire counters + the all important Cam Sensor Retard (should be 0° ± 2°).

 

I have a sticky valve on the blazer right now. And found a pair of heads for a relly good price. But its off of a '95 truck and i have a '00 blazer

 

I did the compression test. All cylinders had 134-135 psi, but cylinder 4 had 55. Im happy im getting closer to the problem. im looking around for a pair of used heads, and going to get them acid washed and resurfaced if it needs it. And them swap them out. =]

 

Yep, that's the cylinder causing the problem. Not enough compression to fire at idle. Squirt a little oil into the cylinder to make sure it's not the rings (and that it is a valve) - or alternatively you can pressurize the cylinder with air and listen at the intake and exhaust and the crankcase (second choice is more definitive).

To fix (if a valve), just buy a pair of rebuilt heads off ebay or somewhere. Probably about the same price as buying and surfacing a pair of used heads. Make sure you get the right ones for your engine (by casting number). Here's an example - free ship no core. Gaskets and TTY head bolts for these engines are reasonably expensive, so price that too. Go with the metal/rubber Felpro intake gaskets for sure.

https://www.ebay.com/itm/4-3-GM-CHEV...4AAOSwepZXRITI