[Lee]

At least we are now all on the same page understanding there is something very wrong. There is no intake air restriction and no exhaust restriction from the turbo downstream and the turbo is working properly. Here’s the sequence. The problem did not exist….. the coach was parked for 30 days…….. the problem was immediately apparent upon departure…….. nothing changed with intake or exhaust. Where does that leave us?

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Those numbers are under no load.

I cannot access the bulletin without a password but I really want to see Detroit Diesel expressing a limit on the pyros.

On a plane I had the engine manufacturer had no limit on the TIT (turbo inlet temperature) which is akin to the pyro temps because there was no combination of manifold pressure (boost) or fuel flow that could create temps that would damage the turbo.

It might be possible DDEC I has a limit for the EGT, but if it does it is more likely that limit is to protect the turbo than the engine. The blades expand with heat and at some temp they begin to come in contact with the housing.

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Jon, I oversee 2 generators here both 12v92-750 kw units under load they run around 850 to 900 degrees with 15 lbs of boost churning out 780 hp with turbos on each manifold neither has pryometers I plug my Alnor into the test ports on each side I haven’t figured out how to do it with a Pro/Link yet it’s only been 8 years now

These are dual ECM’s as the DDEC IV will only support 8 cylinders both of these ECM’s are programed to shut the engine down when the EGT reaches 1200 degrees keep in mine these are off road engines his could be the same The DDEC 111 and IV will read the temperture for each cylinder under the TMP if is it to high it will shut down

good luck

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Over the last few years I’ve read several diesel performance
forums. What they all say is 1200 degrees on your longest hardest pull
is a safe number. It doesn’t seem to matter which brand or what size the
engine is. I read that the competition pulling trucks and tractors can reach 1600
to 2000 degrees for those short runs. These are all four stroke engines.
I have no ideal how the 1200 number was determined. I used it on two
very different diesel engines that I own, a mechanical 5.9 Cummins and a 14 liter
Detroit and neither has destroyed itself so far. I have a friend that tunes on the road trucks every day, he uses the same number and has no early engine failures.

My 8V92 was 500 HP, DDEC II and would run about 1100 degrees on a long hard pull at about 28 lbs of boost.

These temperatures are taken in the exhaust manifold before the turbo.

Ken

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From everything I have read and understood a high exhaust gas temperature is a result of either an air fuel mixture that reaches or approaches peak (which is where the maximum power is) or high cylinder pressures. An engine can have high cylinder pressures without producing peak power due to timing.

Operating an engine at peak power is not necessarily damaging but fuel economy and engine life suffer which is why our diesel engines run well below and on the lean side of peak EGT. Peak EGT as a result of combustion is when the fuel / air mixture is nearly perfect. If you operate an engine on the rich side of peak EGT you have to lean the engine by reducing fuel flow, and as the fuel amount is reduced the EGT climbs, eventually reaching its peak or highest value. If the fuel flow is further reduced, the EGT begins to drop and the engine is being operated on the lean side of peak EGT. Continuing to lean the engine eventually shuts it down. The reverse is also going to shut an engine down in that if there is too much fuel for the available air it also will shut down.

Varying the fuel / air ratio affects how the power is delivered, and in the case of a lean mixture the combustion is more of a longer event pushing down the piston and is likely to have significantly lower internal cylinder pressures. A mixture at peak or slightly rich of peak is a more explosive combustion event and it results in high internal cylinder pressures. The danger in running an engine at or very near peak EGT is greatly increased stresses on the engine and higher probability of detonation (think of engine “ping” but far more violent).

The EGT can be a measure of those stresses which might be why DDEC is set up to shut down an engine at a certain value. As the fuel / air mixture varies the combustion timing also varies and it is likely the Detroit engineers are protecting the engine using EGT as the trigger. I have no clue how DDEC is set up, or if it has any ability to adjust all the parameters that affect EGT.

The final consideration regarding EGT is usually the turbocharger. By its nature the rotor outside diameter is only slightly smaller than the inside diameter of the housing. As it heats up from the exhaust the rotor expands and at some point it can expand enough to contact the housing at which point it will seize until it cools down. Usually there is some value of EGT that becomes the limit for the turbo. That is established by the turbo manufacturer. If DDEC is shutting down an engine at 1200 EGT for example then it could be a turbo limitation as opposed to a limitation based on internal cylinder pressures or to prevent detonation.

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I tell you guys what is strange the 3406E Cat will run at almost 1100 degrees no load and won’t climb a 100 degrees under a heavy load 1035 degrees is the norm for the 3406 I have a 6.5 chevy diesel that will sound the alram @ 1000 degrees and goes back to idle @ 1150 degrees sometimes it is a PITA with the goose neck and the 416 Cat backhoe on long pulls

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We had over 200 trucks and NONE of them had a pyro. I think the last trucks we had that did have them were in the 70’s. I can’t even remember where they ran at….