The Dispatch | Expert | Scudo Hub

tee_cee

Member

Registered: 2016-03-18

Posts: 634

Regen problem diagnosis (with help from gemini)

So 40k miles after a new dpf, pressure sensor, catalyst topup, turbo, intake manifold and injectors, the dpf regens are starting every 120-150 miles instead of 300 +/- 50 miles.

The normal process is for the the ecu to monitor the amount of calculated soot in the dpf, until it hits 5g/l. The regen then runs until this figure drops to 1g/l, and the the heat built up usually clears this down to 0g.
I had noticed that some regens were kicking off at less than 5g/l and then continuing on after the calculated soot had dropped to zero, sometimes for another 15 or 20 minutes.
As time went on the regen were always starting at 2-2.5g/l, so it looked the soot was building up at twice the predicted rate.
So I tried a couple of bottles of Forte injector cleaner, cleaned the MAF sensor, and swapped out the pressure sensor, did a smoke test to locate and fix a small leak at the air intake - no change. Got the injectors pulled and all tested good. Finally got a hydrogen carbon clean, which caused an extra long regen cycle on the way home, for 45 mins.

Time to do some proper analysis, with my new friend gemini, torque pro and several 6km test drives

1) Drive at a steady 50 mph (EGR will be open, MAF will be relatively low), then floor the accelerator.
The moment you floor it, the EGR graph must drop to 0% instantly. As it drops, the MAF graph must jump up cleanly. If the EGR line hesitates, or if the MAF line shows a "dip" or a lazy curve before climbing, your EGR valve is mechanically sticking open under exhaust pressure. This starves the engine of fresh oxygen for a few critical seconds, creating a massive pulse of black soot every time you accelerate.

PASS - The test event occurs at Sample Point 185 (10:23:09). Analysis confirms that the engine ECU and associated mechanical actuators are functioning cleanly with zero abnormal delays or airflow
discrepancies. egr_test_report.pdf

2) Graph Turbo Boost against your O2 Sensor / Lambda. Do a full throttle pull in 3rd gear from 1,500 to 3,500 RPM.
Watch the peak values. On the DW10CD, boost should hit and hold roughly 1.2 to 1.5 bar (1200–1500 mbar above atmospheric). At that exact moment of peak boost, Lambda should settle around 1.15 to 1.25. If your boost is struggling to hit its target, or if Lambda dips hard down toward 1.05 or lower, you have a classic intercooler/boost pipe split. The engine is calculating fuel based on the air the MAF saw, but because that air is leaking out of a split hose, the cylinder runs way too rich.

PASS -- The live data confirms that the turbocharger core (CHRA) is operating at full performance with immediate response times. No intake boost leaks or shaft drag detected.
turbo_diagnostic_report.pdf

3) Check for turbo lag - set and measured values for turbo position/pressure and air mixer plus maf, O2 & rpm

FAIL: Data log analysis confirms a direct causality between air doser butterfly valve sticking, intake air throttling starvation, and transient underboost (turbo lag)

Bingo vehicle_diagnostic_report.pdf