P0200, misfire, backfire, VERY rich, lack of power after cam swap in 04 LQ4(6.0)

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    P0200, misfire, backfire, VERY rich, lack of power after cam swap in 04 LQ4(6.0)

    2004 Silverado 2500HD 6.0L LQ4 swapped into a Land Cruiser with now under 70k miles on it. It WAS running mostly fine completely stock. The stock harness was reworked. I had a valve rattle at higher RPMs so I decided on a cam swap while I fixed the valve springs: cam is a fairly mild one. <snip company>
    208/216 | .561"/.561" | LSA113+4

    I also upgraded the valve springs to BTR #SK001S.

    After a long time sitting, I tried to fire it up with a TON of misfiring. I found most of the stock injectors(25317628) were stuck. I replaced them with OEM Delphi injectors with part number 25343789. This resolved a large part of the misfire issue and it was 'mostly' drivable. As it turns out, the new injectors are for an 8.1L and not the 6.0L.

    It feels like a misfire, for sure backfire out tailpipe when I let off the gas, super rich running to the point a car several car lengths behind me could smell it while doing 55mph, bad lack of power, and it is throwing up a code of p0200 occasionally. Almost 'zero' power if I go WOT at 2000 RPM... I get more seat of pants g-force from a miserable 4.3L with the same test.

    I've thrown a noid light on five out of eight injectors and I can barely see it flashing. I have verified that power at the injector is exactly the same as the battery.

    I have tried swapping PCMs with no change. The tuner adjusted the tune for the 8.1L injectors and it is still not running correctly.

    The stock harness that came with the engine had been worked many times. I thought that maybe some of the work I did wouldn't have made the computer happy (shorter wires, longer wires, combined power) so I just wrapped up reworking a completely stock harness. I kept the grounds as is in the stock locations on the block(three) I also kept the power circuits as original(INJ1, INJ2, MAF/PCM, o2) I also kept the routing stock except for the MAF sensor.

    The cam sensor is new(AC Delco) as are the o2 sensors.

    I am watching the PCM with HP Tuner VCM Scanner.

    Currently, the long term fuel trim too often gets stuck at high negative(-18%) The MAF at idle is 0.8x lb/min at idle. The MAP is 37.x kPa. It runs at a solid 210 degree F.

    Questions in red to help id question from background info:
    1) I am using a stock 2004 Silverado 2500 6.0L harness. I only reworked it for power, MIL, tach, and speedo(ie things that normally head into the cab/fuse box) The grounds are in the default location with stock bolts. My battery ground goes to one of the motor mount bolts. For the power, they are fused/split apart similar to stock(INJ1, INJ2, etc) For the grounds, should I sand the block where they are bolted? Should I add a secondary ground from the harness 'bolts' to the battery ground?
    2) Cam sensor is new. I replaced '50k mile' old one with ACDelco 213-363. Is it a junk brand?
    3) I am not running the rear o2 sensor(ie cat scan). I am running the front one which is ~4 years old and minimal miles on it. The new one is ACDelco 213-1161. Again, is it a junk brand? Could running pig rich fowl it up bad enough for false readings?
    4) Both knock sensors are also ~3 years old along with the knock harness. The new ones are ACDelco 213-3521.
    5) The crank sensor is the original 2004 unit with ~50k miles. Scanning shows it to be working fine.
    6) I may have replaced the MAF/IAT sensor with ACDelco 19330121. I'd have to triple check that this didn't end up on another project. Would a bad maf cause issues without throwing a code?
    7) Would a vacuum leak cause this bad of a drivability issue? I have one suspect area BUT the MAP sensor readings aren't showing something that looks out of the ordinary. I'm assuming that a vacuum leak bad enough to fawk up drivability this bad would be very obvious on a MAP sensor.

    Anyone have a good resource or thought on how to use HP Tuner VCM Scanner to diagnose 'hardware' issues? So far, none of the signals look to be stuck.
    Last edited by Lil'John; 08-12-2020, 09:45 PM. Reason: removed company ;)

    #2
    Start back at the beginning, double check cam timing and get a set of 6.0 injectors. Remove as many variables as you can and get it as close to how it was before the problems as you can. The 8.1 injectors are probably set so low in their duty cycle that they're barely firing, how's fuel pressure look? Depending on the pressure you're feeding them they could be running between 30-40lb/hr which is quite a bit more than the 6.0 injectors. If I had to guess, you have a tuning issue with the new injectors

    Comment


      #3
      There really isn't any 'timing' that can be done on the cam. My understanding for non-super high performance cams is just point the dots together and go. I double checked after this issue popped up. The dots(cam and crank) line up as they should.

      On the injectors, they can be tuned. From my reading, one can swap injectors to anything you desire without changing the 'main' tune as long as the 3-4 injector items are adjusted. I've seen reports of doing this with Deka 80lbs with my pcm style. I've checked the old/new tunes vs 6.0L and 8.1L tunes for the injector items. From what I've seen, the injector sections match up.

      I checked the fuel pressure early on and it was in the 50psi range(I think that was the number)

      On replacing injectors vs just tune against them, I think it will be cheaper to just tune against them especially now that it is looking like I will delve more into tuning that I wanted. I've been doing lots of research.

      Right now, I'm trying to ensure that wiring and sensors are in good shape before I blame the tune.
      As noted, one concern is grounds. The grounds are untouched and in stock location. So I'm concerned maybe the bolts aren't doing a good job grounding to the block or maybe I need a ground 'strap' run from the harness grounding locations to the battery ground location.

      Another concern is whether the AC Delco replacement sensors are junk.

      Last concern is whether a vacuum leak could cause this level of problems but not be notable in the map sensor or some other readable parameter.

      Here is the rig in question(green):
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      Comment


        #4
        MAF, MAP numbers look normal. a vaccum leak would not be noticed at WOT unless is was ginormous and between the throttle valve and MAF sensor. Fuel trims at -18% would very likely not cause a severe seat of the pants feeling type problem. Rich means too much fuel OR not enough air. It can also mean an exhaust restriction. I have had many "custom tuned cam swapped whatevers" come in the shop 9 out of 10 it was a simple thing that some one missed. The other 10% were a tune issue that I told them to take back to who ever did it.
        If this was in my bay I would do a relative compression test followed by looking at the misfire data at idle and under load. if you feel it is not spark related you can do an injector balance test. these easy things can be done with a Snap on Verus or Zeus. Do you know anyone with one? Do you have a power probe 4 its wayyy better than a noid light but not a scope.

        Comment


          #5
          gmcxt Thank you for the reply.

          As you note, I am expecting something on my end is screwed up and not the tune now that the tuner adjusted for the 8.1L injectors.

          I forget what size the crossover pipe diameter is... it is at least 2". They merge into a 3" exhaust all the way out. The muffler is in good shape... it has offset inlet/outlet and I can see all the way through.

          I will check the compression. How would compression issue cause rich issue?

          I will put this picture of HP Tuner scan with 'bad injector' tune:
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          The intake air temp will pull timing out but the engine coolant temp and RPM bring it down to maybe 3-4 degrees pulled.
          Attached Files

          Comment


            #6
            I'd figure out why you keep getting a P0200. That is directly an injector issue. Wiring, not plugged in, bad injector, bad fuse, etc. Why test 5 and not all 8?
            Hartwig Motorsports 4516, Team Yukon Gear and Axle
            www.150Tunes.com
            www.DiffsOnly.com

            Comment


              #7
              Originally posted by waynehartwig View Post
              I'd figure out why you keep getting a P0200. That is directly an injector issue. Wiring, not plugged in, bad injector, bad fuse, etc. Why test 5 and not all 8?
              Thank you very much for reply here and Pirate. If you would like, you can leave the Pirate thread alone.

              The current installed harness is a VERY lightly touched stock harness. I did not touch the ground circuits(stock location and uncut) or any of the wires left to the PCM. I combined the power wires as they were stock(INJ1, INJ2, etc) Before I installed the harness, I did the following:
              1. Checked power continuity. All eight passed.
              2. Checked power resistance (injector to fuse) They were all ~0.3 ohm
              3. Checked voltage at injector. All matched battery voltage. Obviously after install.
              4. Check pcm to injector continuity. All eight passed.
              5. Check pcm to injector resistance. They were all ~0.3 ohm
              6. Checked pcm grounds continuity((Blue 1, 24, 27,40, 64 and 67/Green 1 and 40) All passed.
              7. Checked pcm grounds resistance. They were all ~0.3 ohm
              My understanding with a noid light is it should be visible without required complete darkness. I checked only five of the eight injector circuits with a noid light because all five were barely visible in shady conditions. I saw no point in going with three more since I've got five giving me junk results. This somewhat says wiring issue but the above checks don't show the harness itself being an issue.

              A further test of the harness was checking the pcm side grounds for continuity to the battery ground. They also passed.

              I've tried two different PCMs. One was directly tuned by the tuner with no changes. The other was flashed with the tune. The results were the same. If needed, I've got two more PCMs on the shelf I could do the same test with.

              I would hope the new injectors aren't the problem. But unlike the old injectors, I didn't run +12v across the terminals to double check.

              Comment


                #8
                It all depends on how you test. No load, a bad wire/connection can still show 12v and be bad. Start unplugging injectors and see which doesn't change the idle. Do the same with coils. In fact, unplug your o2's and MAF, also, and leave them unplugged for now. That way they can't influence anything... Reset your fuel trims with your scanner afterwards, also...

                As someone above stated, larger injectors will have a smaller duty cycle at idle and possibly won't even trigger a light. The fact you have a light flash at idle is a good thing. Confirm all 8. They should all flash the same and consistent.
                Hartwig Motorsports 4516, Team Yukon Gear and Axle
                www.150Tunes.com
                www.DiffsOnly.com

                Comment


                  #9
                  Here is a quick 1 minute video showing drivability... go to the last 10 seconds or so to hear the back firing.

                  This was pre-8.1L injector tune. At the last 10 seconds, you can hear a downshift to third gear, acceleration, and then left off the gas/back firing. In middle of back firing, I upshift to 4th gear. (NV4500 tranny)

                  My expectation is that from a stop, the 6.0L should be able to at a bare minimum pegleg burnout a 35" tire with 4.56 gears.

                  Comment


                    #10
                    Do you have a screen shot at idle and one at 5000RPM? If you could set it to graph mode instead of gauges that would be better.

                    ​​​​Id you had an intake valve that did not open as much as the others it would let less air into the cylinder. That cylinder would be rich because the same amount of fuel would be delivered to that entire bank of injectors. Your air to fuel ratio in that moment on that cylinder would be less than 14.7:1 or a Lambda of less than 1. Too much fuel or not enough air is considered rich. That cylinder would also have a little less compression relative to the others.

                    Comment


                      #11
                      I'll have to make another run for a 5k rpm shot. But here are two graphs of slightly higher rpm and idle rpm I pulled from a recent run(I can't 100% say this is the new 8.1L tune or the 6.0L tune)
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ID:	7274 This run was monitoring the misfire current and history counts. At no point during the run did it show a misfire.

                      I did do a visual verification that the rockers were moving... nothing really stood out at me watching each side while cranking the engine.
                      Attached Files

                      Comment


                        #12
                        50 psi? KOEO or KOER? If KOEO I think your fuel pressure is a bit low.

                        Comment


                          #13
                          Originally posted by waynehartwig View Post
                          It all depends on how you test. No load, a bad wire/connection can still show 12v and be bad. Start unplugging injectors and see which doesn't change the idle. Do the same with coils. In fact, unplug your o2's and MAF, also, and leave them unplugged for now. That way they can't influence anything... Reset your fuel trims with your scanner afterwards, also...

                          As someone above stated, larger injectors will have a smaller duty cycle at idle and possibly won't even trigger a light. The fact you have a light flash at idle is a good thing. Confirm all 8. They should all flash the same and consistent.
                          I missed this.

                          Thank you for description of NOID. I will go through and check again on all of them this time. The five that I did check were all same brightness and consistent.

                          When I was checking voltage at the injector, I did it without the engine running. I pulled the plug and hooked the volt meter on it. Then while I was still connected I man-handled the harness/plug to see if anything changed.

                          When you say unplug o2's and MAF, are you basically talking about putting it into a speed density tune only?

                          I will give the injector/coil unplugging a try but I don't recall finding a difference when I tried earlier.

                          Originally posted by shortbus4x4 View Post
                          50 psi? KOEO or KOER? If KOEO I think your fuel pressure is a bit low.
                          I'm not sure what your abbreviations mean

                          I will go double check the fuel pressure number. But it was 50s at idle. The fuel pump is a stock 99 Camaro(actually using whole assembly)

                          Comment


                            #14
                            Key On Engine Off is KOEO, I'll let you guess what KOER is. Take a fuel pressure reading with KOEO, my guess is it should be around 60-70 psi and it probably will be. Check fuel volume too, I've only experienced it a couple times where fuel pressure was in spec but the pump wasn't moving enough volume.

                            Comment


                              #15
                              I've done a few tests mentioned above.

                              Fuel pump pressure:
                              Key On Engine Off: 53/54 psi
                              Idle and ~4500rpm: 59 psi

                              Voltage @ injector plug: 14.1xV each. Battery was 14.2xV.

                              Noid light: VERY hard to tell with as dim as it was. Passenger side bank all looked consistent with brightness and frequency. Front injector on driverside was VERY hard to tell. I will give it another test. The other three looked consistent with brightness and frequency. Due to dimness, it is hard to tell if passenger and driver banks were consistent.

                              Disconnect injectors: As I disconnected the injector plugs for the noid test and the voltage test, I noticed no real difference in idle.

                              Disconnect coils: As I disconnected the coil plugs, I noticed no real difference in idle.

                              Comment

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