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High Elevation Turbo Boost Anomaly
We were climbing out of Phoenix area towards Flagstaff on I17. We were in 4th gear around 1950rpm and 25psi boost when at about 6000 feet elevation both my boost gauges went to zero.
I have the usual analog boost gauge in the dash, the digital boost info is the DDEC data displayed on my VMSPC computer. First I thought I had blown one of the aftercooler hoses but the engine kept pulling and there was no black smoke from the exhaust. It seemed the turbo was still producing boost but the gauges were not showing it.
I did not want to stop to investigate out of concern that I might not be able to restart the engine. The forecast was for significant snow and low temperatures. That area was not a good place to linger.
We eventually climbed up to the Arizona divide on I40 around 7300 feet with the boost and related info (fuel consumption, load) being zero or unreliable but the engine working fine. Once we came down below 6000 feet on the other side, the boost gauge etc behaved normally again.
I’m not complaining that the engine continued working but I was surprised that the DDEC III would continue to produce full power with zero boost indicated. Fuel injected should be proportional to boost; zero boost should imply very little power. No fault code was thrown during this episode.
Has anybody experienced something similar? Is this a software bug in the DDEC III displaying the wrong boost info at high elevations? But how does one explain the analog gauge being at zero too?
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8 Replies
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I have no clue what critical altitude is for our turbo systems, which is the point at which the turbo is losing boost proportional to the loss of atmospheric pressure, but it seems 6000 is way too low.
I cannot think of a single reason why you would see the drop off of reported boost, while the engine performed as if it had sufficient boost.
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What has me stumped is that both the digital and analog gauges read zero boost but the engine was operating ok.
I looked at the intake manifold. I can see three sensors, one is the analog boost sensor with a small air line going to the dash (I assume). The other two are digital senders, one probably for air intake temp (which were normal) and the other for boost pressure. Nothing obviously amiss.
I found an old thread with a similar problem. According to that a bad barometric pressure sender can cause the turbo boost to read zero.
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Gary & Peggy Stevens09-27-2009, 08:48 AMOn my D60 I was having intermittent Turbo Boost Failure.While driving I would notice the Turbo Boost Gauge would go to 0 and a light on the dash would come on. I took the bus to Stewart & Stevenson, and they determined I needed a New Style Barometric Pressure Sensor. and ReProgram the ECM to the correct software level.
$700 later I haven’t had any problems with the Turbo Boost.
Gary S.
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There seems to be a possible interaction between the barometric pressure and the boost sensors. The baro sensor is supposed to reduce fuel at elevations above 6500 feet due to less oxygen content and that is pretty much the elevation the boost reading started to misbehave.
Newer engines (2000/2001 model years) had a campaign to replace the baro/boost sensor harness but my engine predates that change.
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Made it back home without any further issues. All gauges were normal. Clearly, the coach is telling me to stay below 6000-7000 feet during winter. Maybe, the DDEC3 is smarter than I am.
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I know for a fact my turbo boost gauge does not reflect boost pressure accurately and I suspect it is an intentional situation.
On my EGR engine, when the engine is running and the EGR has not cycled on, max displayed boost is about 30 PSI at full power, and that is confirmed with my DDEC reader. When the EGR kicks on and I am still seeing 30 PSI on the boost gauge, but my DDEC reader shows almost 50 PSI of boost.
That might have been by design so owners would not be lined up wanting their boost gauge replaced because it was going up and down which is what happens when the EGR valve is open and sending exhaust gas into the engine. When that happens the DDEC sends more fuel into the engine to compensate for the loss of power that would occur with the introduction of exhaust into a cylinder and the added boost via a multi speed turbo is needed to burn the extra fuel. All this is done to reduce NOX by cooling down the internal cylinder temps.
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That barometric sensor harness drove me nuts, similar symptoms as you are having and mine was changed twice.
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Could you tell me were the sensor is on my D60 maybe I should have mine checked
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Scroll down on the post, there is a link to the harness.
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Thanks
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