Ive tried everything

[97chevy350]

I have a 97 350, missing and hesitating very badly, but it is intermittent. Code P0300, mult misfire is all im gettin. Cap and Rotor are fine, new wires, and just put on a brand new AC fuel pressure regulator. I need my truck and I am runnin out of patience. Can someone help?

[asilverblazer]

Plugs?

 

Bad, distributor parts (new parts aren't always good parts), goes for the wires too...

 

I'd try the plugs first.

[97chevy350]

I guess I ruled out plugs from the start cuz it was intermittent, but Im gonna go check them out anyway. I found out that it is missin on 3 and 6, so I will go pull those first

[97chevy350]

Plugs are fine.

[asilverblazer]

My Blazer had an intermittent hesitation, a full tune up cured it. If you are confident in the ignition components look at fuel delivery. Since it is only 2 specific cylinders, I still lean towards ignition. A fuel delivery would affect them all. Are you using a high quality plug wire? What about putting a test light on the 3 and 6 cylinder wires to make sure they are getting consistent spark?

[bronyaur]

I once had a cap with a hairline crack in it. When it warmed up I started getting a really bad miss. After letting it cool everything was fine. The crack was hard to see, and I didn't find it until I had replaced the cap and solved the problem. Then I went back and went over the cap with a fine toothed comb.

 

Just a thought.

[mmmikkke]

A miss, and then also a hesitation. I'm assuming they both come and go at the same time.

 

Hesitation is usually from a lean condition.

 

How did you determine it's missing on 3 and 6? Pulled one wire at a time and drove it to see if it was worse or not?

 

I'd say you have a vacuum leak. Fill up a spray bottle with water and spray it on the edges of the intake manifold (where it contacts the heads) while the miss is happening. See if the temporary presense of water seals the vacuum leak and corrects the miss.

 

My '95 350 needed a new intake manifold gasket at 100,000 miles, about 2 years ago. Is yours still the original gasket?

[97chevy350]

Found the misses on a scanner, new intake gaskets, also sprayed break cleaner around them to look for vacuum leaks.

[mmmikkke]

Any vacuum lines that go to plastic connectors? Spray those too. Also try disconnecting your power brakes vacuum line and plugging it.

 

I'm about out of cheap things to try.

 

PS: Did you add the new intake gaskets after the problem started or before? Could you have the wrong gaskets? New, incorrect gaskets could leak from underneath. You'd have little chance of plugging a lower side leak with water or brakleen.

[97chevy350]

Any vacuum lines that go to plastic connectors?  Spray those too.  Also try disconnecting your power brakes vacuum line and plugging it.

 

I'm about out of cheap things to try.

 

PS:  Did you add the new intake gaskets after the problem started or before?  Could you have the wrong gaskets?  New, incorrect gaskets could leak from underneath.  You'd have little chance of plugging a lower side leak with water or brakleen.

 

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New gaskets were put on about a year ago. I look for plastic connectors. I will also try plugging hte booster, you think it might be leaking there?

[ManyCamaroz]

I have a 97 350, missing and hesitating very badly, but it is intermittent.  Code P0300, mult misfire is all im gettin.  Cap and Rotor are fine, new wires, and just put on a brand new AC fuel pressure regulator.  I need my truck and I am runnin out of patience.  Can someone help?

 

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My guess.... An injector(s) is misfiring intermittently.

[billcar9999]

I had a 95 that started with symptoms like. After about 2 weeks it got much worse. It would die and not restart afterwards. It turned out to be the temp sensors. I don't remember what the codes were but it stumped me and the mechanics for a while. It was not an expensive fix.

 

Bill

[Mr. Smith]

If you are using Bosch plugs especially the plats, I would look at them real careful. I recently fixed a misfire code on a 99 cav due to the center electrode recessed up in the porcelain. The car ran but missed like hell and run like crap on the road.

[97chevy350]

I have AC plugs and I also checked them out. From what I hear bosch plugs are not good for our trucks, they say original AC's are the best things for them.

[OUMike]

I have AC plugs and I also checked them out.  From what I hear bosch plugs are not good for our trucks, they say original AC's are the best things for them.

 

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97chevy. You are describing the IDENTICAL problem that I had with my 94 4.3L. I took it to a shop and they went through everything and could not find the problem. After charging me only a dignostics fee (which was crap) they gave it back to me unfixed. I took it to my local Ponitac dealer (our Chevy dealer sucks) and it was the distributor.

 

A distritbutor can cause intermitant miss. It felt to me like I was out of power at certain RPMs and it would stutter bad. Thats the first thing I would try. Might as well stick a set of plugs and wires while your in there. The dealer was also very presistant on using ONLY AC Delco plugs in Chevrolet trucks. I know there more expensive, but those guys have never done me wrong so my trucks will always have delco plugs.

 

Hope this helps.