False boost pressure reading

[chtree]

Hey Guys,

I've been getting a check engine light when boost guage reads no boost. It throws high input on the computer. We put a new sensor on and checked for continuity. I was hoping that you'd seen this before and we were missing something simple. When the check engine light is on it de rates the motor. That's a real pain when your a 100 mi. from home. Please, any ideas will be appreciated.

Chris

[Petervs]

Hey Chris,

Your post is not very clear.
First off, are you talking series 60 or 8V92?

DDEC II, III or IV?

And when you hook up a code reader to the DDEC , you will never get an output that says "It throws high input on the computer".

It might say "manifold pressure high" or "oil pressure low" or some such. If you are asking for input from the gurus here, please state the actual output verbiage, it will help us diagnose more sensibly.

Just as one idea, there may be a fault in the DDEC system, and it could be a sensor, but it can also be a wiring item. If a wire chafes through and comes in contact with a part of the engine or chassis that acts as a ground, it can fool the DDEC into a false signal, and changing the sensor will not repair it.

If you have replaced the sensor, and there is no change, then you must verify the continuity and integrity of the wiring to that sensor.

[chtree]

Peter,

The bus is a 2003 shell with a DDEC III. The computer reads high input voltage. The problem is it doesn't do it all the time. We ran great for 200 mi. then it started acting up again. The ck eng light will come on and the boost guage will read 0 or max boost. At zero the engine derates itself, at max reading it operates ok until the guage drops to zero. We were thinkig short or corrosion also, but its hard to find unless it fails while we have the tester hooked up. The ck eng light might come on and off 10 to 20 times over a 100miles then stay off for a 100mi. Any ideas?

Chris

[Jon Wehrenberg]

Find the closest Detroit Diesel and turn the problem over to them.

Finding intermittent problems like you describe is almost impossible. The techs will hook up the reader and start driving to see if they can get it to occur.

Finding the cause almost requires the problem to be there when the reader is connected. It sounds like something simple such as a faulty ground or bad connector plug, but that is the stuff that will drive a person crazy.

I had a four pin connector assembled when the bus was new with one of the pins bent making a bad contact. The bus was 10 years old and had about 150,000 miles before the problem popped up. It all of a sudden would not go past idle. After a few minutes of turning the engine on and off it started working again. It was luck that a Prevost tech found the problem by pulling apart every connector in the engine control system because when they started chasing the problem the bus was running perfectly.

[Gary & Peggy Stevens]

Chris, when I first got my bus I had what sounds to be the same intermittent problem you had.

The bus would run fine down the road, and then the check engine light would come on and off, and I noticed the Turbo Boost Gauge would not register any output. It was intermittent, but I knew that something wasn't right, so i took it to our local Stewart and Stevenson.

They determined I needed to replace the Barometric Turbo Boost Sensor with a new Dual Barometric sensor. They were getting a Code 86 on the reader, which translated into a High Voltage Barometric Calculations Code Error?

They checked all codes and reset them after this install, and I haven't had the problem since.

Gary S.

[chtree]

Thanks for all the info guys! Our local detroit guy mentioned hooking the computer on and then going for a ride. also I will ask about the dual barometric boost sensor.

Thanks again,

Chris

[Petervs]

Chris,

Just clarification. The computer is your DDEC control unit. The service guys attach a "code reader" to your DDEC wiring so they can read the output from your computer to see what is going on. They can also attach a printer for a record of the situation.

Some of us have purchased used code readers so we can do it ourselves. Only a couple hundred bucks .

Semantics only.....

[JIM CHALOUPKA]

Detroit diesel service is phasing into using laptop computers for diagnostic work as well as changing the parameters of the DDEC onboard engine computer.

The software is available for purchase by others than employees of Detroit diesel.

JIM

[chtree]

Hey Guys,


I talked to our Detroit mech. and he thought we might try Gary's idea about the dual barometric boost sensor. I'll let you all know when installed and tested.

Thanks again!

Chris

[Joe Cannarozzi]

Way to coach that DD tech Gary.