Engine Misfire, Need advice on moving forward

Discussion in 'Chevy Truck Talk & GM News' started by Mr. Ruz, Mar 26, 2012.

  1. Mr. Ruz

    Mr. Ruz New Member

    (I'm not sure if this is the correct place to post this... Monitor, feel free to move.)

    Hi everyone, I'm new to this forum, and relatively new to the auto world. However, I do have some experience with doing semi basic repairs.

    I purchased a '93 Chevy K 1500, V6, 4.3L about a month ago and have steadily been working on common repairs (since the vehicle has been neglected for what appears to be years). The first problem that I had to get fixed was an exhaust leak. It had two leaks, one at the donuts and another on the manifold exhaust gasket. The former I repaired quickly, but I am still waiting to get it into the shop for repairing the latter. (I don't want to deal with taking apart the manifold exhaust myself).

    Anyway, when the mechanic looked at the truck and repaired the donuts (and did some welding) he told me that the engine also had a misfire on the right side of the engine. He was of the mindset that the chamber most likely had a leaking seal and that oil was fowling up the spark plugs. After I did some research and talked to a few people I replaced the plugs, wires, and cap. It desperately needed it too. Although my mileage increased with the new plugs and the first exhaust issue repaired, the misfire seems to stick around.

    I looked up how to get into the "check engine light" and got a code 33 and a code 45. That is, MAP signal voltage high and rich exhaust, respectively. After some research, I found that these issues can sometimes be related to an engine misfire, so I checked the MAP sensor and it came out okay. So I reset the ECM and that particular code went away. However, code 45 and the misfire are all still present.

    In trying to address code 45, I ended up replacing the EGR valve. It seems to run slightly better, but not significantly.

    My questions are these:
    1. Do you think that code 45 and the misfire might be related? If so, could it be a fuel pressure/EVAP/injector issue?
    2. Is there some possibility that the manifold exhaust leak scrambles the sensors and messes everything up? How can I verify a misfire and be sure that I'm not just hearing an exhaust "pop"? (although I think the mechanic was honest, I want to be sure myself, too).
    3. What does it tell me that the misfire is on one side of the engine and not random?
    4. Is it possible that it is a vacuum leak?
    5. If it is a seal within the engine and oil is getting into the chamber, how big of a repair is that? Can/should I do that myself?
    6. Finally, what should I look at first?

    I apologize for the length of this post, but I greatly appreciate any guidance at all. Whether it be what to look for, what to ask the mechanic, or how to address the repair.

    Last edited: Mar 26, 2012
  2. moogvo

    moogvo Epic Member 5+ Years 1000 Posts

    Welcome to the forum.

    I am sure your code could be related to your misfire. You probably have a rich condition BECAUSE of the misfire. So here are a couple of questions. What kind of plugs and wires did you use? If they are not AC Delco, then those can also be a problem.

    Answer to question 2: No.
    3: several factors can cause a misfire. Fouled plug, low compression, bad plug/wire, burned valve, etc. there are MANY reasons that it would not be random.
    4: probably not. It would likely appear on random cylinders if it were caused by a vacuum leak.
    5: depends on your level of experience and how mechanically inclined you are. This probably wouldn't be something you could tackle without help.
    6. First, make sure your plug and wire are good. Then go for a compression check.

    Finally, everything I have said here is based on one single misfiring cylinder, and not random misfires. Good luck and keep us posted.
  3. Revredneck

    Revredneck Rockstar 100 Posts

    Go for the simple and basic here. Take a very hard look at the vacuum lines where they attach to the ports on the intake manifold and TBI unit. I've seen lots of misses fixed by repairing a split vacuum hose. One way to test is to start the engine and spray some carb cleaner around the base of the TBI and around the vac. hoses at the manifold. HTH
    Good Luck and God Bless
  4. Mr. Ruz

    Mr. Ruz New Member

    Hey thanks guys! Sorry for the very late reply... I've had an extraordinarily busy week. I will try that pressure check within the next couple of days and post back with some results. (I've already checked the vacuum lines and can't find anything. Also, I changed the plugs to AC Delcos and saw no change in performance.)

    On a side note, I've noticed that the misfire seems to go away after the vehicle warms up and then sits for a while in warm weather. (That is to say, is can't get TOO cold). It's been starting up at colder temperatures then it's used to because the previous owner always put it in the garage. I'm thinking off the top of my head that perhaps it's a head gasket leak, and when its cold it leaks but when it warms up and then sits and dries out it seals again... Of course, the pressure check will tell us more. SOON TO COME!

    Thanks again

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