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DDEC I blues
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Bill,
I really hope you find the problem. I can’t
imagine how bad you want it fixed. Grounds that are not connected or
that provide a partial ground are commonly over looked. Everyone always looks at the power suppy side.Ken
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Bill,
It is evident that you need to quit what job you are doing and open a PREVOST repair facility!
Hope that the new maunal fixes your problem. You have waited WAY TOO long for a fix.
Good luck,
Mark
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I would take that to mean you have a ground that is not connected. You
have an incomplete circuit. For a complete circuit you must have a
power supply, the work (bulb, sensor or whatever) and a ground or
sometimes refereed to as a return. A short to most people means the
power is accidentally connect to a ground before it gets to the work. Sometimes because the power wire has a place where the insulation is
damaged and it’s agaist a ground source like the chassis or a screw or
nail shot through the power wire into a groud source. A short usually pops a fuse or breaker
that’s why it’s easy to find. A faulty ground does not pop fuses that why
it’s sometimes overlooked. -
Bill, how many miles on your chassis!
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Another way to interpret that open ground could also mean that the
sensor circuit (boost sensor or any sensor) does not have good return or signal back
to the ECM.I hope I’m not confusing the issue.
Ken
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when inslalling any sensor did someone use teflon tape. It has upon more than one case created a bad ground situation! I know the theory that the threads should cut threw the tape and make ground. FWIW Since I had this problem I do not use any tape on sensors.
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Bob,
That’s a good point
about the Teflon tape. Since this sensor has its own ground I don’t think it
would matter.Bill,
Remove
some insulation from the 452 ground wire close to the sensor. Take a jumper
from there to a known good ground. If that works you can make that a perment ground or if you want, with some luck we can trace down the exact point where the ground is not connected. Keep in mind you’ll have to repair that insulation.
Ken
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Keep us posted. I’ll try to help. A boost sensor that’s not giving the correct information to the ECM could certainly result in low power.
Ken
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Just because the ECM is not setting the code doesn’t mean
the sensor or harness doesn’t have a problem. Just a few weeks ago I was trying
to help a friend over the phone. He had a Series 60 DDEC IV that had low power
with no codes. He had checked the fuel supply system and confirmed there was no
air in the system and the pressure was correct. He was watching the boost
pressure with the diagnostic software and noticed that the boost was lower than
normal. Low boost, low power, good fuel supply and no codes. The truck had no
EGT gauge so he couldn’t check that. I suggested trying a new boost sensor.
“But it has no codes. How could it could it be bad?” Finally I
convinced him to try a new boost sensor and it fixed the problem. I know you
have already replaced the boost sensor but it can be any of the sensor wires
that are partly grounded or not completing the circuit. The majority of the ECM
program is the diagnostics, the part that makes the engine run is relatively
small. In the program every sensor has a set of parameters for that particular
sensor. The parameters include the lowest voltage the sensor should send back to
the ECM, the highest voltage and if these voltages are out of range how long
can they be out before the check engine light is turned on? A millisecond, 30
seconds, It depends on what the sensor is reading. You can imagine it’s
impossible for the diagnostic program to always be correct. In a previous post
you mentioned 300 to 500 degrees for your EGT. If that reading is in long hard
pull it seems low. I remember something like 800 near sea level and 1100 at high
altitudes like 8000 or 10,000 feet. I’m suspicious of the boost sensor circuit
even though there is no code. It has set a code in the past. A problem with it could
result low power and low EGTs. Keep in mind when checking a circuit with an OHM
meter the meter can display zero ohms indicating the circuit you’re testing is good but the Ohm meter does not load the circuit. Here’s one example, suppose a rodent has partly chewed through
a multi strand wire only leaving 1 or 2
strands. That’s enough to show a complete circuit using an Ohm meter but on a
low voltage circuit like sensor it may cause a voltage drop resulting in a
false reading getting back to ECM. I bring up these long shots because several
people have worked on this and failed to find the problem. I would not rule out
any possibility. I would ground that 452 wire just in case, it’s not too hard
to do and make another test run.Did you say the exhaust system had been checked and was not restricted?
Also the wrong boost sensor will cause the same problem, no codes but low power.
Ken
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