Low boost, wastegate error code.... Can anyone help

[Iceman23]

Hi guys, I am new to the forum and wonder if anyone can give me a hand.

We have a 2003 mack with. Cx613.

Here's what the truck is doing...

- while pulling a full load and 100% throttle and with a scanner hooked up, the ecm shows 100% engine load and approximately 19-20 psi boost.

- after maybe 10-15 secs or so, error code sid 32 fmi 2 (wastegate output error) will come up and engine light and ecm shows an engine load of about 80% and boost drops down to around 14psi or so.

- the error code remains active and engine light stays on until the truck speed drops down to only a few mph. Occasionally another code will accommodate the one mentioned earlier....that one is spn 288 fmi 2.

Ok here are my thoughts...

- I believe the sid32 fmi2 which is turning on the CEL may be causing a derate. Now I check the wastegate actuator for function under test setup which I set a pressure regulator for 35psi. The actuator functioned properly and seemed to open and close the wastegate lever just fine.

- the wastgate actuation appears to be very straightforward. Intake pressure reaches XX psi and that air actuates the actuator piston in the wastegate and overcomes its internal spring and actuates the wastegate lever. No sensors, no solenoids..etc. So the only thing I can imagine to trigger a wastegate code in the ecm is excessive boost pressure and thats not the case as I never get more than 20psi under full load.

-Lastly, why doesnt the truck build more than 20psi before the CEL comes on and is THIS the REAL problem which is somehow turning on the wastegate code.

- I also noticed that the inlet air pressure was around 33psi and the boost was around 20psi. Forgive my ignorance but where and what is the inlet air pressure/sensor?

Well, any comments or suggestions is greatly appreciated.

Thanks

Chris

[Mackpro]

SID-32 is the Mack 4-5 code, check out these to Mack service bulletins.

wastegate 1.pdf

wastegate 2.pdf

[rsb502]

That fisrt bulletin looks like the winner, 20psi is low and if the intake pressure was 33 and the boost pressure was 20 the two sensors are not reading inside the set variance so they are triggering a derate and fault code until you are no longer in a hard pull, looks like (and I am not sure on this engine) the intake pressure of 33 may be measured at the turbo and the boost pressure of 20 may be measured at the intake manifold. If so you have a charge air leak and therefore the sensor on the intake tells the computer to derate because there is a problem, hook up a mechanical boost guage on the intake manifold (cold) side and see what you get (a low mpressure air press guage that reads in the 5 lb or less increments will work if no boost guage is handy. If you get a lower reading on the mechanical guage than the ecm reading you have a charge air leak, or just get a spray bottle with soapy water in it and run the truck at about 1000rpm and spray the charge air system down looking for bubbles. Other than that it would be a bad sensor and I would guess it was the boost sensor (if there are two sensors) again I dont know this engine that well Im just using mechanical deductive reasoning from older Mack's.