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  • Cylinder Miss

    I have a miss on# 5 cylinder on a 1998 GMC 5.7 engine. Does any one know what might be causing this?

  • #2
    Re: Cylinder Miss

    Have you checked the usual suspects? Does it have a ignition cap, spark plug wire, spark plug? Can you plug in an OB2 tester, find a code?

    Comment


    • #3
      Re: Cylinder Miss

      Does it misfire idling, under load, or all the time?

      "Great" later model vehicles (Yes I consider 1998 later models. ) can exhibit misfires or skipping for a ton of reasons other than the electrical system. Older vehicles with skips or misfires were consistently fixed most of the time dealing with the plugs, wires, distributor. So you can replace them, & it might be where I would start as well, but the likelihood that it will correct the problem is lower.

      Also try the knock sensor.
      Check pressure at #5 injector.
      Cleaning or replacing EGR & MAP.

      Hope it's not a sticking valve.

      Comment


      • #4
        Re: Cylinder Miss

        Originally posted by Frankiarmz View Post
        Have you checked the usual suspects? Does it have a ignition cap, spark plug wire, spark plug? Can you plug in an OB2 tester, find a code?
        I have,Truck has them all,all has been replaced by myself,by a auto mech.,OB2 tester said miss on cylinder 5.

        Comment


        • #5
          Re: Cylinder Miss

          Originally posted by BobsPlumbing View Post
          Does it misfire idling, under load, or all the time?

          "Great" later model vehicles (Yes I consider 1998 later models. ) can exhibit misfires or skipping for a ton of reasons other than the electrical system. Older vehicles with skips or misfires were consistently fixed most of the time dealing with the plugs, wires, distributor. So you can replace them, & it might be where I would start as well, but the likelihood that it will correct the problem is lower.

          Also try the knock sensor.
          Check pressure at #5 injector.
          Cleaning or replacing EGR & MAP.

          Hope it's not a sticking valve.
          Truck misfires mostly at idle or stop lights,Some times the service engine light goes away and so does the miss, but mostly stays on. If I find time to check all yo suggest or I will try to contact someone to do so for me.

          Comment


          • #6
            Re: Cylinder Miss

            Originally posted by red1234 View Post
            Truck misfires mostly at idle or stop lights,Some times the service engine light goes away and so does the miss, but mostly stays on. If I find time to check all yo suggest or I will try to contact someone to do so for me.
            Useful information! The fact that it does not misfire sometimes leads me to believe it is not mechanical, or fuel related, and that leaves electrical.Intermittent problems can be tough, bad harness, connector, sensor, and worst of all, computer related. Computers do go bad, they are expensive. Consider spending the money to go to a really good diagnostic tech, someone far beyond an OB2 tester. They are out there and can discover much more than a code.

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            • #7
              Re: Cylinder Miss

              start with the plugs and the wires
              Push sticks/blocks Save Fingers
              ~~~~~~~~~~~~~~~~~~~
              "The true measure of a man is how he treats someone who can do him absolutely no good."
              attributed to Samuel Johnson
              ~~~~~~~~~~~~~~~~~~~
              PUBLIC NOTICE: Due to recent budget cuts, the rising cost of electricity, gas, and oil...plus the current state of the economy............the light at the end of the tunnel, has been turned off.

              Comment


              • #8
                Re: Cylinder Miss

                I'm no engine mechanic, but from my limited experience I'd start by pulling the plug to see if it is fouled. Clean the plug, check the gap and adjust if necessary. Then I'd look at the wire: how old is it, they don't last forever? I had a Mercury once that had terrible problems when it was moist. You could turn the lights off it the garage and on trying to start you could see a lot of arcing off the wire. While the car was only four years old, almost everything in it was cheaply defective. New wire and the problem went away.

                Beyond that, I'd have to look to a good garage mechanic. But that's where I would start.

                CWS

                Comment


                • #9
                  Re: Cylinder Miss

                  I have a old spark plug machine (sold by champion), and it has a test chamber and you put the plug in it and push the button and it arcs the plug and via a little window you can watch the arcing of the plug, the second part of the test is you add air pressure to the chamber it is arcing in and it interesting to watch when the plug blows out, (yes the voltage is low in the machine compared to the modern system)

                  but at one time plugs were changed ever 10,000 miles, now many are not changed for 100,000 miles, many of the plugs are wore out even if they look OK, (I really do nt understand the why but there not up to par),

                  also the wires break down, with oil and time, (in time they can cross fire even ).

                  and from what I have read it will in time cause the coil to go out and some times the module that controls the coil,

                  thus a few dollars on the spark plugs and wires may save you on expensive repairs on coil and other parts,

                  while the plug is out do a compression test and see if it is up to specifications,

                  but pull the plug and see if there is oil fouling and any other signs of other problems,

                  I do not see this said but is a check engine light coming on? if so see if some one can read the code for you and go by the recommendations to fix the problem.

                  P0305 Code - Cylinder #5 Misfire

                  Technical Description

                  Cylinder #5 Misfire Detected

                  What does that mean?

                  A P0305 code means that the the car's computer has detected that one of the engine's cylinders is not firing properly. In this case it's cylinder #5.

                  Symptoms
                  Symptoms may include: •the engine may be harder to start
                  •the engine may stumble / stumble, and/or hesitate
                  •other symptoms may also be present

                  Causes

                  A code P0305 may mean that one or more of the following has happened:
                  •Faulty spark plug or wire
                  •Faulty coil (pack)
                  •Faulty oxygen sensor(s)
                  •Faulty fuel injector
                  •Burned exhaust valve
                  •Faulty catalytic converter(s)
                  •Running out of fuel
                  •Poor compression
                  •Defective computer

                  Possible Solutions

                  If there are no symptoms, the simplest thing to do is to reset the code and see if it comes back.

                  If there are symptoms such as the engine is stumbling or hesitating, check all wiring and connectors that lead to the cylinders (i.e. spark plugs). Depending on how long the ignition components have been in the car, it may be a good idea to replace them as part of your regular maintenance schedule. I would suggest spark plugs, spark plug wires, distributor cap, and rotor (if applicable). Otherwise, check the coils (a.k.a. coil packs). In some cases, the catalytic converter has gone bad. If you smell rotten eggs in the exhaust, your cat converter needs to be replaced. I've also heard in other cases the problems were faulty fuel injectors.

                  OBD-II Trouble Code: P0305 Cylinder 5 Five Misfire Detected
                  on some things by swapping the components one can single it down to an area or an item, (by causing the problem to go else where). But on plugs and wires replace the set, if they have not been done before, the coil packs swapping them around may be worth the effort.
                  Last edited by BHD; 10-31-2013, 11:11 AM.
                  Push sticks/blocks Save Fingers
                  ~~~~~~~~~~~~~~~~~~~
                  "The true measure of a man is how he treats someone who can do him absolutely no good."
                  attributed to Samuel Johnson
                  ~~~~~~~~~~~~~~~~~~~
                  PUBLIC NOTICE: Due to recent budget cuts, the rising cost of electricity, gas, and oil...plus the current state of the economy............the light at the end of the tunnel, has been turned off.

                  Comment


                  • #10
                    Re: Cylinder Miss

                    Ok, I've seen some good advice and some that really doesn't apply in the responses above. Before I tell you anything else, let me say that I was an auto service tech at a chevy dealer for 5 years in the early 2000's before I quit and found something better, and I serviced a LOT of these trucks. Hooking it up to a scanner will likely get you nowhere since you already know what codes the computer is storing. Your problem could really be almost anything, but I will list the possible causes in the most likely order, and ask some questions to help try to narrow it down for you. The most likely cause is probably ignition(plugs, wires, dist. cap, or possibly even wrong firing order due to wires mixed up). 2nd up would be injector dirty/clogged. This is a fairly common occurrence, and can sometimes be fixed by a simple injector cleaning. These are the most common issues, but I have seen others cause this. Anything from bad valves/engine to the distributor being out of time (do NOT try to set the distributor timing yourself, as you need a decent scan tool that gives you the cam/crank sensor correlation value to do so) Did this start on it's own or did it start after some type of service work was done? Does it give you any other codes than the misfire code?
                    Last edited by d_slat; 11-01-2013, 12:29 AM.

                    Comment


                    • #11
                      Re: Cylinder Miss

                      "Truck misfires mostly at idle or stop lights,Some times the service engine light goes away and so does the miss, but mostly stays on" Quote red1234

                      Mechanical (bad valves), and fuel related problems(clogged injectors) don't go from bad to good, allowing a smooth idle and check engine light to go on and off. I'm pretty sure it's electrical. Even good mechanics will take this sort of problem to a diagnostic expert after they try replacing parts( ignition , O2 sensors, etc).

                      Comment


                      • #12
                        Re: Cylinder Miss

                        Originally posted by Frankiarmz View Post
                        Mechanical (bad valves), and fuel related problems(clogged injectors) don't go from bad to good, allowing a smooth idle and check engine light to go on and off. I'm pretty sure it's electrical. Even good mechanics will take this sort of problem to a diagnostic expert after they try replacing parts( ignition , O2 sensors, etc).
                        Actually, depending on the circumstances, both mechanical and fuel related issues can seem to come and go. Just for example, a dirty fuel injector can seem to be just fine until the truck warms up and the computer goes into closed loop. When it is in open loop, the computer overfuels, just like having the choke on, until the O2 sensor temp and the ECT come up enough. This overfueling can make it seem like the problem is gone, but in reality it hasn't gone anywhere, and is just hiding behind the circumstances at the time. I'm not saying that the problem is mechanical or fuel related, but I will not also say that it isn't by the amount of info given. I also didn't tell the OP not to take it to a diagnostic expert, I only stated that hooking the truck up to another scan tool wasn't likely to tell him anything other than what he already knew. Diagnostic experts do much more than hook up a scan tool and read codes to tell you what's wrong with your vehicle.

                        Comment


                        • #13
                          Re: Cylinder Miss

                          Originally posted by d_slat View Post
                          Actually, depending on the circumstances, both mechanical and fuel related issues can seem to come and go. Just for example, a dirty fuel injector can seem to be just fine until the truck warms up and the computer goes into closed loop. When it is in open loop, the computer overfuels, just like having the choke on, until the O2 sensor temp and the ECT come up enough. This overfueling can make it seem like the problem is gone, but in reality it hasn't gone anywhere, and is just hiding behind the circumstances at the time. I'm not saying that the problem is mechanical or fuel related, but I will not also say that it isn't by the amount of info given. I also didn't tell the OP not to take it to a diagnostic expert, I only stated that hooking the truck up to another scan tool wasn't likely to tell him anything other than what he already knew. Diagnostic experts do much more than hook up a scan tool and read codes to tell you what's wrong with your vehicle.
                          I'm glad you are weighing in on this thread, you just brought up some things I never knew. I figured it had to be electrical because even with the over fueling scenario you mentioned, wouldn't it take a while running well for the computer to lose the trouble code an erase the check engine light? I'm glad you didn't nix a diagnostic expert, and I hope he does get back to us, I hate mysteries and want to know what's causing the problem. A buddy of mine has a 99 Mustang and after changing coil packs and some other parts, his mechanic sent him to an expert. Turned out to be a bad computer, think it cost around $700 or more to repair and the guy said they had to send his computer out. He said it had to be year and model specific, does that sound right? Thanks, Frank.

                          Comment


                          • #14
                            Re: Cylinder Miss

                            Originally posted by Frankiarmz View Post
                            Turned out to be a bad computer, think it cost around $700 or more to repair and the guy said they had to send his computer out. He said it had to be year and model specific, does that sound right? Thanks, Frank.
                            yup, that's about right. The computers aren't cheap, and they need to be programmed to the vin# to accommodate whatever options the car has. As far as driving awhile for the light to go out, I believe it takes somewhere around 3-5 key cycles without the fault for the light to go out. So in the scenario I shared about the clogged fuel injector, if the truck would make several short trips of 5 min. or so and be turned off for a bit between trips, it can easily be enough to turn off the light. Or if it only seems to really miss at idle in gear, if you don't idle it the computer won't see the miss. It monitors crankshaft speed, and looks for a drop in speed at certain times to detect the miss and figure out which cyl. is missing, so a real slight miss might not be detected at idle when not in gear, but might be detected when in gear because the added load will slow the engine much more.

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                            • #15
                              Re: Cylinder Miss

                              Thanks to everone for pitching in, when I have the time to focus on this issue,I will inform everyone.Might be a while.

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