by metalworker0 » Sun Jul 12, 2026 7:06 pm
this is a long post hope it covers most things .
Three things that can cause it other than injectors
Egr sticking open or gears in the egr motor stripped
Hole in the boost pipes near the alternator(common - rubs on bolt)
Turbo actuator .. again plastic gears - or stuck actuator.. but if youve replasced not applicable
maf air flow sensor .. but only after checking first 3 first
non of them do the injector cylinder balance test with forscan, followed by leak off test
Egr and turbo actuator can be tested with forscan - choose pids - commanded and actual .. they should follow closely
cylinder balance test
copied from another post i made
Because i know so little - Here's what AI says about cylinder balance .
Cylinder balance PIDs (Parameter IDs) measure the power contribution of each engine cylinder. The Engine Control Unit (ECU) monitors tiny changes in crankshaft speed to determine if each cylinder is firing evenly. If a cylinder is underperforming, the ECU compensates by adding or removing fuel.
For a visual breakdown of how a car's computer watches the rhythm of the engine and flags uneven cylinder performance:
Cylinder to Cylinder Power Imbalance ·
Viewing live data on an OBD2 scanner, you will generally see numbers associated with fuel contribution, RPM, or torque.
The Baseline:
All cylinders should be close to 0 (or a neutral baseline like 90). Ideally, no single cylinder should be drastically different from the others.
Positive Numbers (+): If you see a positive number, it means the ECU is adding fuel or adjusting timing to force an underperforming cylinder to pull its weight.
Negative Numbers (-): If you see a negative number, the ECU is pulling fuel to calm down a cylinder that is working too hard.
What the Numbers Mean (Troubleshooting)
If one or two cylinders have high positive or negative values while the others are perfectly balanced, it is pointing you directly to one of three common issues:
1. Poor Fuel Delivery
The Data: A high positive value (e.g., +4.0 mg/str) or negative value (e.g., -3.0 mg/str).The Problem: A clogged, stuck, or leaking fuel injector is either starving or flooding the cylinder.
.3. Low Mechanical Compression The Data:
Consistently high positive balance on a single cylinder.The Problem: Burnt/leaking valves or worn piston rings mean the cylinder cannot hold pressure, resulting in a severe drop in power.
cylinder balance .. question into google
Diesel, what is considered very high and very low in a cylinder balance test?
In a diesel engine, a cylinder balance test (often called an injector balance rate test) tracks the fuel compensation needed to keep a smooth idle. "Very low" or negative numbers indicate the cylinder is producing too much power (over-fueling), while "very high" positive numbers mean it is under-performing and requires extra fuel.
Normal vs. Extreme Ranges (Measured in mm³ per stroke)
While ideal limits vary by manufacturer and engine type, general guidelines for a fully warmed-up engine at idle include:
Excellent/Normal: Between -2.0 and +2.0 (depending on your model, this is the expected factory sweet spot).Acceptable/Tolerable: Usually up to ± 3.0 or ± 4.0.Very Low (Over-fueling): Anything below -3.0 or -4.0.
A negative rate means the engine's computer is taking fuel away from that cylinder because it's running too strong or the injector is leaking/worn.Very High (Under-fueling): Anything above +3.0 or +4.0.
A positive rate means the computer is adding fuel because the cylinder is weak and needs help to fire evenly with the others.
Absolute Limits:
Readings exceeding ± 15.0 are considered the absolute maximum limits and often immediately trigger fault codes or "limp mode".
What the Extremes Mean
Balance rates highlight relative performance, not just the health of the fuel injector. If you see extreme numbers, the culprits generally include:
High Positive Rates (+): Often caused by a clogged or restricted injector, low compression (due to worn rings or a bad valve), or low fuel pressure.
Low/Negative Rates (-): Typically caused by a physically worn, stuck-open, or over-delivering injector that is dumping too much fuel into the cylinder.
Because these tests only measure a vehicle’s cylinder contribution at idle, they are best paired with manual diagnostics. - injector leak off test
I could be wrong ! So going by that, yours are all within the normal range -2 to +2.. only differing by tenths rather than whole numbers .. well that's my interpretation of it. no extremes.
now if a leak down test proved otherwise, .. then it makes the cylinder balance test a non item
all the best.mark
