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Ask Clayton Your Own Question
Clayton, Mechanic
Category: Heavy Equipment
Satisfied Customers: 755
Experience:  5+ Years at Freightliner, Detroit & MBE Certified, ATD, and Electrical
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I am loosing power on Freightliner Classic XL Detroit. Help

Customer Question

I have a Detroit 14L 515HP - Engine serial#  06R0802208. Turbo is having this loud whistling noise and turbo PSI is higher than normal when I step on it. I loose power, no signs of smoke but check engine comes on. I had this problem before but after a big hiccup, it was back to normal, now it seems to be permanent. Changed the egr valve/turbo almost 2 years ago. Seems like the turbo is getting overboosted, PSI is around 50, turbo is spinning faster louder than normal. I got fault codes from the dash, There are so many codes, might be an electrical problem?

Submitted: 5 years ago.
Category: Heavy Equipment
Expert:  JANECZFJ replied 5 years ago.


46 – ECM battery low voltage

77 - Anything from turbo boost high to oil pressure high

72 - Vehicle over speed

63 – PMW issue

44 - Coolant, oil or intake temp high

34 -Turbo boost sensor intake voltage pressure low

21- TPS input voltage high

47- Turbo boost or air inlet pressure high

49- Turbo compressor out pressure high

51- Turbo compressor out temp high

31- aux output short to ground

Without PID, SID or FMI codes I cannot be more specific. But I do think it's something electrical like a bad ground, loose connector or possible bad ECM.

I will be here to answer any follow up questions.

Customer :

What are the PID, SID, FMI codes?


These are more detailed codes that can only be retrieved with a reader. They give a more specific reason for the flash.

Expert:  Clayton replied 5 years ago.


Welcome to Just Answer.

The fact that the turbo is making noise is leading me to a turbo, I know it is 2yrs old, but the actuator on the turbo controls your boost, you should NEVER see 50psi under a load, also, if you are revving the engine with it unloaded, and you boost more than 14psi, than the VNT veins are sticking.

There are a few checks that need to be done. But I am 99 percent sure your turbo is bad.

You need to pressure check the charge air cooler, block one side, pressure it up to around 25-30 psi, and see how much it leaks down. Should not leak no more than 5 psi in 1 minute. If your charge air cooler is silver, it is most likely going to leak. The silver charge air coolers were bad around leaking around the seam. I have changed LOTS. If yours is BLACK, they are less prone.

Next is the VNT actuator. This controls the boost. These leak, but usually if they are bad enough, you can hear it, and it won't build much boost. If the Veins stick closed, the boost will be uncontrollable, and the engine will DERATE and throw THESE faults.

You can check to see if the Veins are sticking by removing the pin on the actuator that connects the linkage. The linkage is on the exhaust side of the turbo, it moves up and down with the actuator. If you see black soot around the shaft, if you can move it in and out.

47- Turbo boost or air inlet pressure high

49- Turbo compressor out pressure high

51- Turbo compressor out temp high

39- VNT Veins not respond ( unknown FMI )

What is bad about high mileage EGR Detroits is when they rack up the miles, the EGR components start going out. When you replace one EGR component, you are back in the shop replacing something else. When I get one in the shop that has symptoms like yours, I check everything that will fail. This usually leads to a very high bill. Parts prices are about like this.

EGR Valve- $900

Turbo- $2000

Charge air Cooler- $800

Customer: replied 5 years ago.

I moved the linkage on the turbo up and down with the actuator disconnected and they move freely. I took the egr valve out and the valve was stuck closed, couldn't close or open. I had to put pressure on the valve to open it. Put a little bit of wd40 and it moves freely again. I never had this problem before when I replaced the egr valve like 2 years ago. Check engine light came on. I had no power and black smoke occurred. But this time, check engine comes on. I loose power but not as bad as before and there is no smoke and the turbo seems to over boost and cause this loud whistling noise. I sprayed soap and water, on all the hoses, on the vpod for leaks and no leaks. I checked the turbo on both ends for shaft play and its ok, blades are ok, turbo is only 1.5 years old. So hopefully what was wrong was the egr valve.

Expert:  Clayton replied 5 years ago.

Most times you have an overboosting condition, the turbo is the problem. Put the actuator back on the linkage, put 65 psi to the actuator. Any more than this and the results will be inaccurate. Take a .004 feeler gauge and stick it between the linkage and the stop. If you cannot get it in there, the turbo is junk, if it is very loose, go up to .008, if you can get an .008 in there, the turbo is junk. I think you have two problems. Egr valve and turbo. Watch the actuator while you rev the engine, check to see if there is any hesitation for it to come down. The egr valve is oil actuated, if it hangs up, it is junk. Blow out your egr cooler also while you have the egr valve off. If the egr valve sticks open, you won't build much boost. The system is designed to close the egr valve when it is in boost mode. Also, check the plate under the delta p sensor, they like to crack. It is located on top of the thermostat housing.

Customer: replied 5 years ago.

My turbo boost psi gauge on the dash board seems to be malfunctioning. When I start to have boost, it takes the while for the boost gauge to go up and it gives bad psi reading. What could be the problem with this other than the gauge?

Expert:  Clayton replied 5 years ago.

I am about 99 percent sure it is datalink driven. Pull the gauge and if there is a plastic tube in the back of it, it is mechanical. If it does end up being datalink driven, the boost sensor is what tells the gauge what the boost is.

Customer: replied 5 years ago.

I took the truck to a local mechanic shop and they put the scanner on it- it had 21 codes, so he deleted it so I can go run it so the check engine light would turn on and give a current code. I ran it and no check engine light turned on because I was empty, wasn't under a heavy load, so there aren't any active codes. I'm afraid to take it to a Freightliner/Detroit because I have had bad experiences with them and besides its not giving me a code. I'm going to check for leaks starting at the intercooler towards the engine again. Also I forget to mention, the vacuum psi gauge that I have on the dash that I believe is for the air filter restriction or whatever, when I step on the gas pedal, that gauge rises abnormally, that never happened to me before, and again, I have no smoke, no signs of oil leakage but I have poor fuel mileage. I'm thinking of buying some sensors that maybe might most likely lead to my problem. Which one would be closest to the problem, the MAP Sensor? Coolant Temp sensor? Turbo speed sensor? Throttle position sensor? Fuel pump, coupling? EGR cooler if its leaking/dirty? Fuel check valve? Is there a way to test the turbo actuator manually to see if its bad?

Expert:  Clayton replied 5 years ago.

Well, the restriction gauge should go up if there is a restriction in the intake due to a dirty air filter, but you said you changed it.

Make sure your boost gauge is not mechanical, if it is, a boost sensor may not help you.

I would put a manual gauge on it to see what your ACTUAL boost is.

Poor fuel mileage could be leaking charge air cooler, hoses, intake manifold gaskets, egr hoses, fuel leak, problem in the EGR system, bad injector or injectors (typically causes a miss).

I would have them pressure check the entire system, and not block off the charge air cooler. Just pressure it up to around 30 psi and start spraying connections with soap solution. Then block off the other side of the charge air cooler, and pressure it up and see if it holds.

My prediction is if it throws a fault code, it will be fault code 39.

Customer: replied 5 years ago.

When I was driving, check engine light came on and I got code 39. I disconnected the delta p sensor and the turbo works normal, it doesn't whistle too loud. Could it be the delta p sensor? Is it bad to drive with it disconnected?

Expert:  Clayton replied 5 years ago.

It will eventually throw a fault code that may derate you. It is also possible, it is bad, but you will not know until you hook it up to a scanner and see what the delta P counts are. The plastic plate that the delta p sensor bolts to are bad about cracking, something you might want to look for. Also, the venturi tubes are also bad about getting carboned up.

Customer: replied 5 years ago.

If I buy the delta p sensor, would it have to be calibrated at a dealer or is it already auto calibrated?

Expert:  Clayton replied 5 years ago.

To be honest, it depends on your software level if it can be calibrated. I am sure it can, but I am not 100% sure if it is necessary. I work at a dealership, and we always calibrate it, but since you do not have access to the tool, it is up to you. I would probably calibrate it because you are trying to troubleshoot the problem, not calibrating it might keep you running in circles.