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Need help from Professional VP Mechanics

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  • Need help from Professional VP Mechanics

    I posted last year reference a 2008 5.7 Volvo Penta motor issue which resulted in water ingestion into motor.

    Motor is a Volvo Penta 5.7L Gi-G

    Motor has now been replaced with a brand new VP motor with new VP heads & new exhaust (not a remanufactured motor but a VP motor (orig intake was swapped to new motor). Boat now runs flawless with the exception of an idle issue. This issue has existed since day one of the new engine install.

    Once motor has warmed up & out of closed loop mode, idle starts fluctuating 200-250 rpms, almost sounding like it has a small cam in it, up down loping. Sometimes it will smooth out for a couple minutes then right back into the loping. When in gear, it does not show this symptom, only when it's in neutral.

    Motor was installed by a VP authorized repair shop & who has been assisting me in trying to figure it out but to date, weve been unsuccessful.

    Things that have been done thus far:
    * engine scanned by VP dealer for codes (No Codes)
    * new IAC & operating correctly according to VP
    * new Crank Senor installed & operating correctly
    * new rotor & cap
    * TPS operating within parameters according to VP
    * no binding on throttle cable at throttle body
    * PCV valve in valve cover operating correctly
    * both hi & low pressure fuel pumps within specs
    * fuel pressure regulator is operating correctly according to VP
    * Fuel injectors were cleaned and flowed by VP dealer at time of engine install.

    A video clip of motor running was captured on the VP dealers diagnostic laptop and sent out to Volvo Penta and the reply back was that all seems to be operating within parameters.

    VP dealer and I are now scratching our heads. It happens everytime motor comes out of closed loop mode, just after warm up. Sometimes it will smooth out for a couple minutes but ends up going back into idle issue. The idle issue makes it difficult to shift smoothly because of the rpms.
    If anyone can chim in on this, or if you know someone experienced in diagnosing VP motor issues who you can point me towards, I would greatly appreciate it.

  • #2
    According to my VP dealer who said they sent the diagnostic video clip to Volvo Penta; it was told to me that according to VOLVO PENTA, other than rpm fluctuations, everything appears to be operating correctly.....& they offered no suggestions 🤔
    Last edited by Regal1973; August 16th, 2019, 06:04 AM.


    • #3
      Typical unstable idle is a vacuum leak somewhere in the intake tract. Have to look at everything above the cylinder heads. Typical IAC is reacting to the crank speed dropping by opening quickly. The small leak is overwhelmed by the influx of air and so idle must drop back by the IAC closing down some. Its also wise to make sure the entire IAC passage is clean and not coked up with carbon.

      Also help me understand the "closed loop" mode that you refer to...what I know from vehicle apps is closed-loop operation takes place when the air-fuel control is adjusted by feedback from what the oxygen sensor is measuring. The engine starts in "open loop" mode where its pure speed-density, the injector pulsewidth is calculated from a lookup table. And after appropriate coolant temp has been achieved then closed-loop operation is started. In closed loop operation I'm speaking of, O2 sensor trace is going to be a sine wave output (toggling) as the engine runs slightly on both sides of the optimum air-fuel range, by design.

      And I am certainly no pro, just a shadetree mechanic for sure.


      • #4
        Saline Marina, I recant my last statement about closed and open loop, as I do believe you're correct. The idle issue starts immediately at the point of warm up and when the rpms "should be settling in" around 600.
        The IAC & passage appear to be whistle clean and entire intake manifold was cleaned prior to install. Motor has approx 15 total hours.
        I've attempted to spray carb cleaner around the intake and base of the throttle body to see if I hear any change in the idle but no increase in rpm when doing this.
        If it were vacuum related (and your diagnosis makes complete sense to me hence why I tried to spray carb cleaner) would it come and go, or would it be a constant? I guess it could come and go as parts & gaskets etc heat up, expand, cool and shrink as motor temps fluctuate.
        Last edited by Regal1973; August 16th, 2019, 07:06 AM.


        • #5
          Closed loop/open loop was terminology used to refer to engines with O2 sensors where during warm up the EFI system is regulated by set parameters not the upstream O2 sensor, then as the coolant temp reaches normal the upstream O2 sensor is used to regulate fuel mixture. If this engine has no cat converter or O2 sensors the distinctions between open and closed loop may not mean the same thing. I'm not familiar with marine EFI being an old school Quadrajet or Holley guy but it seems that it runs OK till it comes off of the cold enrichment circuit then possibly a vacuum leak is allowing in too much air for the EFI system to handle because it does not have adaptive control like an auto system with O2 sensors.

          What you describe does sound like a vacuum leak, what intake gaskets did they use? GM did have some problems with the OE ones on the Vortec engines. I think Fel/Pro makes very good gaskets, I would look carefully at all the gaskets in the intake system. If the intake has a manifold vacuum fitting hook up a vacuum gauge to it and see what it is reading and if it drops in sync with the rpm fluctuations.


          Last edited by Lou C; August 16th, 2019, 07:35 AM.
          1988 Four Winns 200 Horizon
          4.3 OMC Cobra

          98 Jeep Grand Cherokee 4.0 Selectrac
          07 Jeep Grand Cherokee Limited 5.7 Quadradrive II

          "While air doesn't freeze....rust never sleeps"


          • #6
            Lou C, I know the VP technician that came out to my home to trouble shoot the issue did put a vacuum gauge on the motor.
            If I recall correctly, he appeared to be somewhat initially concerned with the vacuum readings ( I dont know what the #'s were) but after making a phone call to his shop, and speaking with the owner, this concern seemed to immediately disappear. That was when he was directed to install the new crank sensor.

            after the crank sensor install, it seemed like the rpms started to settle down and he thought he had fixed the issue ( just a coincidence & one of those odd times the rpms decided to settle down I'm thinking). He left and about 30 minutes later, I decided to restart the motor. After about 1minute of run time on the hose, the idle issue started up again.
            after notifying them of this, that's when they decided to send out the captured data on their laptop to VP.

            I dont know what brand of gaskets were used. Maybe I should suggest my VP shop pull the intake, clean all surfaces and install a total intake manifold & throttle body gasket kit from fel-pro?


            • #7
              If you can try running it and the squirt a light oil (like auto trans fluid) in the joint between the intake and cyl heads on both sides, same with the other gaskets. See if doing that causes it to temporarily smooth out as the oil gets sucked in. Normal manifold vacuum should be approx 18-21” (measures in inches of mercury). I wonder what the tech saw that made him concerned?
              1988 Four Winns 200 Horizon
              4.3 OMC Cobra

              98 Jeep Grand Cherokee 4.0 Selectrac
              07 Jeep Grand Cherokee Limited 5.7 Quadradrive II

              "While air doesn't freeze....rust never sleeps"


              • #8
                Have you ever tried disconnecting the IAC when the engine starts surging? I am curious. If the engine continues to run but at a low RPM and holds steady then there is a signal triggering the IAC causing the surging. I wonder if the throttle body could be slightly distorted from being over tightened and the throttle blade is not seating inside the bore.
                Get your own vacuum gauge and connect it so that you are getting the reading from the same line connected to the fuel pressure regulator to see what the reading is when the engine starts surging. Another handy tool to have is a fuel pressure test gauge. They sell them at all the popular auto stores. Check that the fuel pressure holding steady at idle.
                Kenner, Louisiana 1980 Donzi 18'. 2+3 6.2 MPI Alpha 1


                • #9
                  Lou C, I will give that a try next time!

                  Kenny Nunez, I'm pretty sure I've attempted disconnecting the IAC in the past, but I dont completely recall the outcome. I'll try that again and make note of the engines response to it being disconnected.

                  I have a fuel pressure gauge and both the low and hi pressure pumps are steady and within spec at idle and cruising.

                  I dont have a vacuum gauge ( how I've made it all these years without one only God knows lol) I'll have one by this weekend though haha

                  I had a moment where I was wondering about the throttle body & blade but the more I thought about it; if it was torqued out of spec and distorted, wouldnt it happen all the time no matter what? The rpms settle down from time to time, for a couple minutes, but then goes back into the loping idle.


                  • #10
                    As I'm thinking this through, if it's a vacuum leak (which all makes sense as a possibility), the only way I can see it going from idle issue, to normal idle, then back to idle issue and so forth, is if parts are expanding due to rising temperatures and allowing for the "leak" to seal up temporarily. Then upon cooling & contracting (such as when the thermostat opens up) the cooling parts slightly open up the leak again.....am I off base here with this train of thought?
                    I've dealt with vacuum leaks that were so obvious a 10yr old could find them, but not intermittent ones 😁


                    • #11
                      As far as my thoughts on the throttle body, if the blade was not seating then the IAC would be trying to compensate for an unstable vacuum signal.
                      You probably have the PCV valve on one side and 1 or 2 hoses from the valve covers to the flame arrestor.
                      If there is a small crack in the intake manifold it may be on the underside. Try this, remove the PCV valve from the valve cover, remove the hoses from the plastic nipples and plug them. After you get the vacuum gauge run the engine until it starts to surge then install the hose from the vacuum gauge in the PCV bung in the valve cover with a good seal. You should not get a vacuum on the gauge but if it does happen then the manifold is cracked. I have seen this happen when the intake manifold gasket was leaking into the crankcase . Try disconnecting the IAC first just to be sure since it is the easiest thing to try.
                      Kenner, Louisiana 1980 Donzi 18'. 2+3 6.2 MPI Alpha 1


                      • #12
                        Kenny Nunez, thanks for the insight & suggestions!
                        I'll try that as soon as I get a break in this NOT so SUNNY Florida rainy weekend.


                        • #13
                          If you are certain the IAC is known to be good...an excellent suggestion above is defo the way to go..in spraying some WD40 or similar (don’t think transmission fluid is volatile enough to work) around the intake manifold etc.
                          Good luck.


                          • #14
                            QBhoy, I'm almost certain the IAC is operating correctly. I originally replaced the factory one with a new authentic VP IAC thinking that might have been my issue. There was no change when looking at it on the scanner, so I went ahead and put the orig one back in....no use putting a $100+ part in when the orig is working fine lol
                            I'll try squirting wd40 in around all gaskets & seals where the manifold meets the heads & block, as well as the throttle body and sensors. Hope I run across somewhere that affects the idle.....this has become one of those times you just wanna start cursing the motor and flinging wrenches across the driveway LOL jk, but its been very aggravating to say the least, especially when my VP shop cant even seem to figure it out 🤨......I'm just a shade tree guy, so I have excuses LOL😁


                            • #15
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                              Ok, this is whats been attempted today and what I've learned.

                              I started motor and let it warm up. Once the motor started idling up & down (about 90 seconds after start up), I pulled the connector at the IAC and the motor ran smooth. I advanced the throttle a few times and each time it settled back down without idle issues. The dash alarm was beeping when disconnected as it should. Plugged it back in and idle issues started up again.

                              I sprayed wd40 on every sensor attached to the throttle body and intake, I sprayed all manifold to block mating surfaces & on each fuel injector port....nothing changed.

                              THEN... sometimes i noticed it would settle into a smooth idle briefly. I started wondering why it would just do this out of the blue, so I began watching the gauges and it started to paint a picture for me...an abstract one which I have no idea what it is but this is what I'm learning:
                              When the temp is between 160ish - 170°, the motor starts its idling up and down. If I advance the throttle and get the thermostat to open and the temp starts soaring downward, once it gets below 150-160ish, the idle goes smooth. The temp will drop all the way down to 100 on gauge and then once it slowly comes back up over approx 160+, it starts its idle issue again!

                              I spoke with the VP shop today who did the motor installation. He called VP directly and after sharing this info, he was told that because the motor was replaced, the computer is trying to adjust the idle fuel burn rate because it was set to the orig factory motor. Said that the new motor would have different pistons, a different bore etc etc.
                              I explained to the VP shop that the motor I purchased was a brand new ( not remanufactured) Volvo Penta 5.7L Gi-G motor. I even contacted the reputable company I purchased the motor from and they verified it to be a brand new VP motor all factory spec., not a remanufactured one.

                              Now I'm back at square one, other than I see that there seems to be a relationship between temp and idle issues. The motor never gets above 170° on the hose and I've never seen it over 175°.

                              Anyone have anymore ideas 🤔
                              & Thanks for all the help so far👍