L90H Loss of engine power.

[Innocent bystander]

I have a Volvo L90H Loader that has low power below 1500 RPM. if at idle and you give it throttle in gear it will go up to about 1000 RPM and either goes no higher or very slowly up to 1500 then take off normally from there. Especially if you are already moving then slow down, as the RPMs drop down to around 1000 as you lay back into the throttle the RPMs will just hang out around 1000 and wont go no higher. I have PTT and Prosis and have been through everything that I could find including passing all tests in PTT.

-No fault codes
-TPS in Data always shows actual(Shows 100% when stuck at 1000)
-Engine is not bogging down or missing
-It will always rev up if in neutral. In gear under load is when it acts up
-Fuel supply is in spec and never drops off
-Rail pressure always equals commanded
-I have a sister machine that I have compared all data and cant find anything out of range except fuel injection mass.
If I floor the throttle in gear on sister machine injection mass goes almost instantly to 65.
If I do the same with problem machine it goes up to 35 and hangs there for a bit and slowly builds up to 65-70 as it builds power. I assume injection mass is calculated but not sure or how it calculates it.

 

[Ben Witter]

Have you checked your turbocharger and boost pressure?

 

[Innocent bystander]

Yes cant find anything wrong with turbo and boost seems pretty close to sister machine, the problem seems to be pre boost. Solid black line is boost and red dotted is fuel injection mass.

 

[funwithfuel]

How about your inlet throttle valve? They have a tendency to get lazy when on their way out. When power is off and unplugged, you should be able to push it open and it should gently "bounce" shut when you let it go. The same with EGR. If you have high EGR, it would/could display similar symptoms.

 

[Ben Witter]

Worry less about rail pressure and FCV current and look more at
Inlet throttle position
EGR valve position and target
EGR temp and differential pressure
Fuel feed pressure
Exhaust gas pressure
Inlet manifold temp and press
Engine speed, load and torque values

Compare these to reference values especially at high idle and under torque converter stall.

Also don't forget the exhaust aftertreatment system. I have seen excessively plugged DPF's cause this very symptom

 

[AristoTruckTech]

Yes! Don’t forget to check for any partial clogging.
It's possible that the ECM’s fuel map or calibration has drifted or isn’t optimized for the conditions. Even if it's not throwing an error code, there could be an issue in how the ECM calculates the required fuel mass based on sensor inputs.
Comparing the ECM calibrations between the two machines could reveal discrepancies. If the ECM software is outdated, consider a reflash or update to see if it resolves the issue.

 

[Innocent bystander]

Thanks for all your replies! Has new throttle valve and shows open during loss of power and new EGR valve, I had the EGR cooler cleaned.
I installed test ECM and ACM module
All parameters are in spec except EGR differential pressure goes way high under load and if I remove EGR Diff pressure sensor machine runs normally. What would cause such high EGR diff pressure?

 

[funwithfuel]

Unwanted EGR. The sensor is on a venturi. As exhaust gasses pass by, the flow is monitored by the delta of the two orifice. Did you clean built up carbon from sensing passages?

 

[Innocent bystander]

Yes the ports are not plugged, the are pretty short on this if I recall.

 

[Innocent bystander]

The EGR pressure goes off the chart even at 0% EGR valve. I dont get it.

 

[Ben Witter]

Sounds like the ECR valve is stuck open

 

[Innocent bystander]

I thought so also, has brand new one, took it back off today and inspect and couldn't find anything wrong with it. even pressure tested the cooler thinking it had internal leakage

 

[funwithfuel]

On the venturi tube where the sensor is mounted, the one passage is a reduced diameter drilling on an angle towards the skinny side. Blow through that and chase with a pipe cleaner. If you have any EGR with no differential, it'll read high. Have you swapped sensors with the good donor?
Did you physically exercise the actuator of the EGR? When your EGR shows high, what does the EGR position show? Is the plate securely attached to the shaft? Did you check the silicone hoses for cracks or tears? Are the clamps tight with no evidence of soot escaping?

 

[Innocent bystander]

Well I got it fixed.... the intake port side to the EGR diff pressure was still partially plugged up.