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Is it possible for a catalytic convertor to go bad without showing a code? Is there a way to check other than on a machine? I hit it with a rubber mallet and it sounds fine.

95 Blazer 4.3 Votec type W engine 160,000 miles, 4 dr, 4wd, auto trans. New tune up parts about a year ago - plugs, wires, cap, rotor. New fuel pressure regulator and nut kit last year - leaking. Replaced the muffler with one from a junker 6 months ago. New oxygen sensor a month ago; bank 1 sensor 1 - P0135.

Failed the hydrocarbon portion of the state emission test. I'm going to start checking things tomorrow. It runs rough at idle but smooths out at highway speeds. Sometimes the SEL comes on. It is always P0305. Light goes off after a bit of highway driving. Been this way for over a year. Last year it passed the test. Light must have been off at the time. ha ha.

Things I plan to check: Fuel pressure, vacumn leaks, plugs, dist. cap, wires and EGR. I plan to take the coil, ignition control module, TPS, MAF and any other sensors they will check to Advanced Auto Parts or Autozone. And I plan to do a compression test on cylinder 5. Anything else I missed?

If I fail the emission test again I can get a waiver as long as I can show I spent $150 trying to fix the problem. I bought this car at auction and don't plan to put a lot of money into it. But it would be nice to pass the test.

Thanks
Mike

 

yes it is, friends cat was clogged, due to lack of money, he gutted it untill he had some coin for a new one... took 6 month to throw a code.

that being said, p305 is a cyl 5 misfire, and seeings as you failed on hydrocarbons(usually unburn fuel) I would say it's getting a weak spark(noticable more at idle) or you are getting to much fuel, mainly into that cyl.


you pretty much have the diagnositcs figured out. most likely maf, leaking gas into cylinder(s), and/or cap/rotor/plugs/wires

possible it's one of the o2 sensors as well, if they think your truck is running lean it will deliver more fuel

 

P0305 is Misfire #5. Sounds like #5 plug, wire or dist. cap. If converter is not rattling, it should be okay. Misfire will make it fail test.

 

remove the O2 sensor that is located before the catalytic convertor and start the truck. if it runs better then your convertor clogged. also you can do a leak down test on cylinder # 5 to pin point exactly if its in good working order... also how is your EGR valve?

 

Thanks all. I figured the misfire is the cause of the failed test. Chasing this problem for over a year I think it must be a problem with the #5 cylinder. I'll see what the compression test shows. I've checked most everything else in the past with no improvement. I didn't get a chance to work on it today. It will have to wait until the weekend.

Plug, wire and cap all look fine. I'll check the spark

I cleaned the EGR before last years test but I'll check it again.

Thanks for the tip on the O2 sensor

I'll post after I've had a chance to do some tests.

Thanks
Mike

 

Back from testing.

compression test:
#1 - 185
#3 - 190
#5 - 125

#2 - 165
#4 - 165
#6 - 165

All cylinders took 4 to 5 strokes to build pressure. A little history I forgot the first time. When I first got the car, I would get white smoke out of the exhaust first thing in the morning. I put some stuff in the radiator that is supposed to seal a leaking head gasket. The smoke stopped.

I did a vacuum test. It read a steady 14.5 inches. Is that a little low or within range? When I would snap the throttle open it would drop to near zero and then jump to 20 before returning to 14.5.

Fuel pressure test, - 59 psi key on , engine off. Held at 59 psi for 10 minutes. 55 psi running.

I tested the TPS and it is good.

I put in new tune up parts - plugs, wires, cap, rotor, all AC Delco. It runs exactly the same as it did - rough idle, smooth at highway speeds. So it looks like I have either a valve or gasket problem on the left side. Cylinder 5 is the one with the misfire. Not sure if it is worth trying to fix or not. I'm not a mechanic and I don't have a good place to work on it.

Thanks for looking
Mike

 

two things, that puff of smoke when you first start in the morning is probably your valve guide seals which is an easy fix. and how do you know for sure you have a bad head gasket? have you done a leak down test on cylinder #5 to pin point the leak?

 

Thanks for the reply.

No, I don't know I have a gasket problem but it is what I suspect.

The white smoke was last year and it was more than a puff. It would last maybe 10 or 15 minutes and had a sweet smell so I suspected coolant. After putting the stop leak in the radiator the smoke went away.

I don't know how to do a leak down test. Are there instructions on line somewhere?

Mike

 

so if you think it mught be coolant burning in the morning when you forst start it, have you checked to see if your low on antifreeze coolant from time to time?

and here is a how to video i found on using a harbor freight leak down tester, check it out:

http://www.youtube.com/watch?v=ofSiTGeLXvc

here is another video for you:

http://www.youtube.com/watch?v=QA7KVQq9vKA

 

Thanks for the videos. I'll check them out.

The coolant burning problem stopped over a year ago. And yes, at that time, it did seem to be loosing coolant. Only it was a very small amount. But like I said that was last year. No coolant problems since then.

Mike