Reply
Visitor

Re: G3606 A4 units

There are several A4 units in our area that have had W/G's seize in the last month or so. Doesn't seem to matter if the engine is an inline or a vee. It appears to be a clearance issue between the shaft and the bushing. Adding 0.010" clearance to the ID of the bushing once installed seems to have resolved the issues. Another contact of mine went the other way and turned the shaft down at the bushing contact area 0.010". Either way the result is the same. More cleance helps.

Contributor

Re: G3606 A4 units

Yes, sorry Al, I forgot you had mentioned that earlier. I will definitely look into the pressure and report back.

Yes, Cat did remove the dynamic adjustments of the wastegate and the choke but they added adjustement to the air fuel control which slows down both the wastegate and the choke. However, it never took the twitching away even when reduced to 10%. I started to wonder if the adjustment was just slowing the ecm down in making its calculations but not really changing the execution.

I guess I get to mess with them a little longer.
Trusted Contributor
Trusted Contributor

Re: G3606 A4 units

One thing you want to do is make sure the hydrax pressure is set correctly to 225 psi.  There is some thought that the higher pressure might contribute to the instability of the actuator.  I saw one on a G3606 this past week twitching a bit.  The hydrax pressure was set to 270 psi; reset it to 225 but don't know how it will affect the stability.  Couldn't stay on site very long.  Should be able to adjust the dynamics to settle it down but Cat took the dynamics adjustment capability off the wastegate; should put it back.  I am recommending that.

 

Best Regards,

Al Hunt

Contributor

Re: G3606 A4 units

Well, we have had the wastegate shafts replaced (awhile ago) and it helped remedy the NOx fluctuation. The only problem is, even when new, the wastegate was twitching a lot. I can't help but think the twitching is leading to failing wastegate shafts prematurely. I have not been to this particular site for about a month now but I will get over to it soon and see what is going on.

Highlighted
Trusted Contributor
Trusted Contributor

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

Visitor

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?

Contributor

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.
Contributor

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.
Trusted Contributor
Trusted Contributor

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

Contributor

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.