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Re: G3606 A4 units

I don't have any inside info on the parts shortages.  About the only thing I can say is that either the parts needs orders were miscalculated or the vendor has had production issues.  It could be a bit of both.  There is a shortage of G3500 cylinder heads also, I hear.

 

Best Regards,

Al Hunt

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Re: G3606 A4 units

I agree with Al. If the W/G is sticking at all, even for 10 seconds, the air fuel ratio is not going to track well and the NOx will be thrown off. Once the W/G breaks free the control system is going to have to have to try and recover from this upset which may take a little bit. During this process the control may over compensate one way or the other causing the swing in NOx.

 

Al, do you know anything about the world wide back order on the A3 VTC and TPS W/G shafts?? are there issues with the shafts again?

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Re: G3606 A4 units

For awhile, we were pulling and rebuilding the wastegate anually but we were finding nothing wrong with them when we pulled them at 8,600 hrs. We now are only messing with them on an "as needed" basis. Nobody wants to mess with the blanket or the very unsafe position to remove them on our 3606s. It will be dissapointing if we have to repair wastegates every 2k on the A4's.
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Re: G3606 A4 units

Sorry, I wasn't as clear as I should have been. The unit I found the sticking wastegate is the same unit I started this thread about with the swinging NOx.

I was working on the unit beside this one when I heard it start struggling.

I have a short video of the wastegate twitching but I need to upload it before I can post a link. I will try to get to it tomorrow but I will have it uploaded the beginning of next week.
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Re: G3606 A4 units

The A4 uses a different wastegate than the A3, but is similar in construction.  The A4 is running about 10 psi more inlet manifold pressure and is running hotter exhaust temps than the A3.  So I think the A4 WG environment is more severe than the A3.  If you had that long a WG life on the A3, then I say you are the exception.  Most customers had to service the A3 WG from 5K-8K hours.  I had one customer who said he could set his calendar; WG service right at 5K hrs, just like the OMM.  And your A4 are at 3K.  The A4 OMM says Inspect the WG at 5K hrs, just like the A3.

 

If the WG stuck any, it would certainly affect the NOx as the ECM is using the air flow to maintain air fuel ratio against the required fuel flow to maintain desired engine speed.  And this may just be telling you what the service interval might need to be at your site conditions, since you found another WG stuck.

Best Regards,

Al Hunt

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Re: G3606 A4 units

CatGasMech, I have had sticking wastegate issues on our A3 units and agree on how they act. This is different as I actually watch the wastegate go from 15% to 90%. When at 90%, the choke closes to around 50% then back open. After that, the wastegate closes to 15% again and you can see the boost climb 10~psi and audibly hear the turbo pick up speed.

Al, I should have thought to verify hydrax pressure but did not. I will the next time I am at that site. As far as the servos, I can do that but all 5 units have this twitch yet not all of them are swinging the RPM and NOx.

Just Wed, while I was working on a unit beside the one that is bad on swinging the NOx, it started to really struggle. I went over to the unit and quickly realized the wastegate was sticking when it went full closed. It would take a few seconds for it to pop free but after only 4-5 times sticking, it stuck and remained stuck. I used the back of my adjustable wrench and tapped it. It popped open and stuck again. After doing this three times, it seemed to settle down and it stopped chasing the NOx.

So, with that, I am wondering if the wastegate sticking is causing the swinging NOx, which is what you are saying also. I also wonder if the twitching is causing the wastegate to wear and bind up prematurely.

I haven't opened up the exhaust blanket on our A4's yet so I don't know if the same wastegate was carried over from the A3 but we have ran 3 years on a wastegate on a A3 without issue.
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Re: G3606 A4 units

If adjusting the gains lower (less active) hasn’t stopped the WG movement, I might just first make sure that the hydrax pressure is properly set. It should be 225 ± 5 psi. I probably should have suggested checking this first in my last email. The hydrax pressure usually doesn’t contribute to instability unless the pressure relief valve is bad or if the hydrax pump is bad, causing uneven flow in the system. Then I would probably swap the servo valves on the end of the actuator. I would swap the choke with the wastegate; the choke has less movement when the engine is in the working load mode. This valve is held on to the actuator cylinder with 4 machine screws and there is an o-ring seal under the servo. Swap these out and see if the movement goes with the WG actuator. If it does not, then we have to concentrate on the WG system.

You do need to make sure that the WG shaft is not binding up when it gets hot. WG binding could cause the ECM to begin using the choke to try to control the engine air flow, although this usually doesn’t work very well when the engine is loaded.

The WG is fully open at 100% and fully closed at 0 %. The software prevents the WG from opening greater than 50, in order to have better response when moving from choke air fuel ratio control to WG air fuel ratio control under load. As the engine picks up the load the WG will move more closed, toward 0%, until it closes to the correct position for the load on the engine. I don’t know just where the normal WG position is since I have not been around the A4 much yet. I would think that it should be near35-40% near 100% load.

Having the air cleaners outside the building should not be a problem unless the ambient temperature stays below freezing for a long, continuous time. Under these conditions, icing may occur and cause some operational problems. Many engines that operate in cold temperatures have some sort of mechanism to utilize the exhaust heat to warm the engine inlet air to above freezing.

The current Flash File for the G4606 A4, 1875 hp @ 1000 rpm, 130 deg F A/C is 525-9998.

 

Please let me know how you progress in resolving this issue.  Thanks.

Best Regards,

Al Hunt

New member

Re: G3606 A4 units

Have you confirmed that the wastegate is actually opening? We had one unit that was running on the choke above 90% load because the wastegate was seizing up when it got hot. It seemed fine when the unit was down but when it got hot it would tighen up to the point where the actuator could not control the position. This resulted in the choke starting to close to control air manifold pressure. Although the ECM said the wastegate was commanded all the way open it was actaully stuck at 30% open.

 

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Re: G3606 A4 units

I have lowered both gains down to the minimum of 10% and it still has not stopped the twitching. It does slow down how fast the ECM will react to the changing NOx. I have also lowered the max choke position to try and minimize the swing in NOx but that hasn't shown much improvement either. I want to say the FCF has drifted past 102 when the air temp starts to dip. we have the air filters mounted outside of the building on these unit (a first for us) and it might cause us some growing pains. Even if I get the NOx to stop swinging, the wastegate will stil twitch and likely cause premature shaft/bushing wear. the twitching is noticeable on all five of our A4's even though only two are swinging the NOx.

 

Thanks for the suggestions and I will try some of that. I wish I had a serial number handy but I do not at the time of me writing this. If we have an updated FF, do you think CAT might look into a new FF to remove the twitching from the wastegate acuator?

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Re: G3606 A4 units

If the wastegate is not still during loaded operation, I would certainly make some adjustments to the settings.  The WG gain adjustments has been changed to the AFR gains adjustment.  I would first try to calm the WG down by reducing the proportional amount and see if this helps; it should as this will slow the ECM correction command speed down, making the WG reaction slower.  Let the EG performance guide you here;  stop reducing the setting when it no longer has an effect.  If you reduce the Integral setting, this will act as a "drag" on all of the WG action.  I use the example of reducing the Integral setting as wading into deeper and deeper water; the deeper the water is, the slower you are able to walk.

 

Working with these two settings should help tame the WG.  This was an issue in the early (first few) G3600 A4 and was corrected.  If your changing the gain settings doesn't settle the WG down, it may take a new flash file.  I don't remember if there was a specific change to the FF for this issue or not.  If making these adjustment value changes does not help, I would suggest that you contact Scott Double at Cleveland Bros. Cat Dealer in Erie, PA.

 

As for the NOx drifting,  Cat recommends that the Fuel Correction Factor be kept in the range between 98-102.  This should enable the A4 engine work at its best.  This is a different philosophy than for the G3600 A3, where the FCF did not have a target; it was strictly an indicator of how much adjustment the ECM had made to the AFR to maintain emissions.  The A4 philosophy is different in that there is a target range for the FCF.  This range adjustment is adjusted by adjusting the BTU value in the Configuration screen when the engine is loaded operating in the NOx feedback mode.  Reduce the BTU to raise the FCF toward 100; raise the BTU to lower the FCF toward 100.  This will not affect the ECM controlling the NOx; it will continue to attempt to keep the actual NOx equal to the desired NOx.  This might be part of your NOx drift.

 

You should perform the NOx calibration procedure, maybe coinciding with a maintenance interval.  Many of the maintenance actions do affect combustion which will affect NOx output.

 

You didn't state the start choke position or the maximum position settings.  It might be that you will want to reduce the maximum choke settting.  This choke feedback map is not as developed and sometimes the ECM needs a little "help" to prevent overchoking the engine.  Overchoking could maybe cause the ECM to start hunting, although the choke should be wide open "100%) with 90% load.  You also want to make sure that the specific gravity and specific heat ratio values are correct for the fuel the engine is using.  You also didn't state what the inlet air manifold temperature is doing with these cooler ambient temps.  If the IMAT is going cool, it may be that the auxiliary cooler is oversized.  On the A3, the ECM started richening up the AFR when the IMAT got too cool.  I am not sure if the A4 does this or not but I would guess that it does.

 

I think these things might help the engine performance.  I haven't had a lot of G3600 A4 experience so I am also still learning this engine.  Please let me know how you come out with these suggestions.

 

Best Regards,

Al Hunt