Turbo problems on the Tundra

The saga continues; we found a guy called Braam- this fellow has been tuning engines since he was 15 and then also went and got a mechanical engineering degree, so he has the theoretical background and the practical experience.  And he wasn’t scared to come out and have a bash at the engine.  He did a pretty good job and helped James and I understand a bit more of what is going on.  We also discovered two new problems.. sigh.

The first was that the turbo does not seem to be delivering sufficient boost to the manifold.  An MGL manifold sensor indicated that the maximum pressure that we were getting in the manifold was 1.3 bar, or roughly 1.3 times atmospheric pressure (a bit more than that up here at the highveld at 5000 feet).  We’re expecting around 2 bar- atmospheric pressure PLUS 1 bar of boost.

So off came the turbo and I lugged it to a helpful pilot, in the form of Brian Williams at Turbo Exchange.  He determined that the waste gate controller was opening at around 0.4 bar boost- very low.  This might mean that the exhaust gasses were bypassing the turbine wheel of the compressor too soon so that we would not bet sufficient compression at the other end of the turbo.  A quick internet search gave us the idea that the turbo should be good for 280HP with this engine at 1.2 bar boost pressure- we’re only getting around 0.5 bar boost (local pressure is around 0.8 bar and manifold pressure 1.3 bar, hence 0.5 bar boost).

Brian suggested that I either change the waste gate actuator or modify it to be able to adjust the amount of ‘pre-load’ on it, which is what I decided to do.  In the photo you can see the original connecting arm from the waste gate actuator, on the left, to the waste gate arm, via this bent connector.  The barrel bolt you see was spot welded to lock it in postion.

I cut the bent part off and turned a new barrel connection and then extended the waste gate arm.  This meant that the ball rod-end could now be screwed in and out to adjust the preload.  That was a good afternoons work…

 

Back to Brian and we tested again; now the waste gate cracks open at 0.8 bar; so we may have improved the output boost- we still have to see.

 

That’s when the second problem got analised.  We’d seen that the Manifold Absolute Pressure (MAP) sensor on the engine gave us a reading of almost 1 bar higher than the MGL MAP output.  We new that the MGL was correct as we had a few others and compared the ambient pressures.  Checking the calibration of the MAP sensor we sensed that there was something funny going on, so we pulled the MAP sensor off the engine and ran one of those nifty and fantastic internet searches again.  Sure enough, Crossflow had pulled off another fast one on us- the MAP sensor maximum pressure was 1 bar; fine for a normally aspirated engine, but useless for a turbo-boosted one.  We need at least up to 2 bar, or 3 bar.  So that’s on order and should be here next week.  Then we try again.  The turbo’s back in and waiting….