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DDEC I blues
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That sounds like not enough air. Previously you had
mentioned about 15 lbs of boost under full load. That seems low compared to my
old 8V92, it would be in the mid 20’s. Are you still around 15 lbs of boost?
Exhaust temp goes up downhill with the Jakes on? I can’t think of anything that would cause that other than a clogged exhaust.
Clifford, tell me what I’m missing.
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I really agree with Ken on this. He and I have had conversations about diesel engines running lean and my 87 with DDEC I could be driven like I stole it and my EGT readings on the pyro would peak at 1100.
The EGT does go up to about 300 on the Jake on a long steep downhill so that is normal. That is only the heat of compression.
One thing that might be a contributing factor that hasn’t been mentioned is the intercooler. Has anyone verified it is OK? If it is leaking or plugged it is going to definitely reduce air which brings the air / fuel mixture closer to peak and is driving the EGT (pyrometers) up. The only problem with that theory is typically the greatest power output comes close to peak EGT although that is the hardest on the engine but if the DDEC meters fuel relative to turbo boost that would explain why low air is also low power.
This is just a brain dump and may not be worth the bandwidth it is written on.
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Does the 8V92 of this vintage have the blower bypass valves? They are supposed to open when turbo boost exceeds roots blower pressure. I had one of the bypass valves stick on my 6V92TIA boat engines. This will prevent full boost pressure reaching the intake. Just an idea.
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Bill, later models had air to air CACs, the 8V92 has an internal coolant to air intercooler.
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I’m about out of guesses. I read back through the 4 or 5 paragraphs
I had written and realized that’s about everything I think I know, kinda surprised
it took that much room. It seems at this
point fuel delivery is not the problem. It may be 2 different problems. I even
thought, who ever built the current engine could have got the cam timing off a tooth.
I’ve never seen a DDEC III, IV or V (don’t know about DDEC II) that will display
injector timing when using the factory dialogistic software unless the stock
ECM program has been modified. It’s odd that the DDEC I diagnostic tool will display injector
timing. Would that show if the cam timing was off a tooth? I don’t know. I do know if
the cam timing is off a tooth on current DDEC V 14 liters you’ll get no
indication from the diagnostic software, that’s even if the ECM program has been modified to allow monitoring
of the injection timing when using the factory diagnostic software. I think everyone has had good
logical suggestions. I hope you’re able to find an answer.Ken
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Bill,
the temp rise during compression / jake brake use seems normal. They are called compression ignition engines for a reason. In the cylinder you’d see air temps of 450deg C just compressing the charge air 22:1 or so. The EGT gauge just sees an average after some decompression and will be lower.
A quick check to eliminate any air obstruction would be to put a gauge after the turbo and in the air inlet gallery (there should be an access plate with a nipple) and compare the two pressure readings at full load. There should be just a few psi difference as the air flows around the blower and through the aftercooler.
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Bill,
Two things….if in fact you are not getting all the air to the engine (you said low turbo boost) your engine may be running richer. I believe diesel engines run lean of peak EGT and as the mixture richens due to less air you approach peak EGT and that is driving the pyrometers up. What we don’t know because I have never seen it anywhere is if Detroit specifies an upper EGT limit. I have seen drivers say they limit theirs to XXXX, usually 1000 or less but nobody actually has ever shown that or any higher temp to be at or exceeding the limit. As a point of information there is an absolute limit on planes, usually the turbo inlet temperature because once temps reach the limit and beyond the expansion of the rotor from temps causes it to hit the case and damages it. EGTs are also limited but usually due to potential valve damage.
You have to understand you can run an internal combustion engine rich or lean of peak. If you are going to screw with fuel and air flows you need to understand where the engine is running because usually continued operation of any engine near or at peak is damaging to the engine and in some cases causes detonation. This is not a short topic to discuss or explain.
Trust me, if your Jake was functioning your EGT as shown on the pyros would definitely show an increase in temp above idle or no throttle temps. On my 87 I could see one or both banks register about 300 degrees when the Jake was finctioning for an extended period such as a long downhill. My pyros also showed my peak when I was driving it like I stole it of around 1100 degrees for each bank.
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I know this subject has been beaten to death, but I can’t find anywhere where it is mentioned if you have pulled your intake piping off and inspected every inch of it. I know you said you replaced air filters, but have you, or anyone else actually looked at all the piping? Including anything prior to the filter housing. Just wondering….
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Bill, I have been watching this thread.. Sad to see all the time and monies that you have spent.. One thing that no one has mentioned is.. Have you inspected your turbocharger. When I see the high EGT’s, I would make the recommendation to check your turbine wheel for FOD.. It doesn’t take much to knock the tips off the OD of the turbine. You will have to pull the turbocharger, and remove the turbine housing to properly inspect the blade tips..
Disclaimer, I only recommend this when everything else “electrically” checks out.
It is also my “opinion” that you might want to start looking at moving towards a complete DDEC 3 configuration or backdate to a 100% mechanical setup.
It’s nice driving down the road seeing all the engine sensors on a display.
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