Renault 0.9 TCE Misfire
Discussion
Car is a Dacia Logan with the Renault H4B 900cc turbo three pot, port injected. It has 37k miles on it, has regularly serviced and has been utterly reliable for the last three years or so.
Recently my wife complained of it sounding lumpy and hesitating when cold, and I could hear a definite misfire under cold idle. As the engine warmed and the idle speed dropped, the misfire disappeared.
There are no engine codes present, either OBD2 or Renault specific. Looking at the misfire counters in the live data, I see misfires being detected between 1300-1500RPM under no load, at engine speeds above and below and above this the misfire disappears. If I bring the engine up to 2000RPM or so and pull the speed down by slipping the clutch, I don't see any misfires.
With the engine cold the misfire counts are mostly on cylinders 1 and 3, with the middle cylinder showing about 1/4 of the outer values. Once the engine has warmed the misfire count is predominantly on cylinder 3. Additionally the accumulated knock detection counters are showing about 20% more on cylinder 3.
The plug change interval isn't too far off so they were replaced, but it made no difference. Moving the coils didn't move the warm misfire count to a different cylinder, and just to be certain I borrowed a good set of coils which also made no difference, so it seems unlikely this is ignition related.
The fuel trim in closed loop at warm idle is +4.7% long term, and between -8% to -10% short term, so a net reduction in fuelling. The oxygen sensor is switching quite happily at idle, though obviously flatlines at 0v when misfiring occurs.
I'm thinking this is possibly a fuel delivery problem on injector 3 which is working especially poorly at low duty cycles pulse widths, but this wouldn't explain why it idles smoothly when warm, and I would have expected greater positive fuel trims?
Recently my wife complained of it sounding lumpy and hesitating when cold, and I could hear a definite misfire under cold idle. As the engine warmed and the idle speed dropped, the misfire disappeared.
There are no engine codes present, either OBD2 or Renault specific. Looking at the misfire counters in the live data, I see misfires being detected between 1300-1500RPM under no load, at engine speeds above and below and above this the misfire disappears. If I bring the engine up to 2000RPM or so and pull the speed down by slipping the clutch, I don't see any misfires.
With the engine cold the misfire counts are mostly on cylinders 1 and 3, with the middle cylinder showing about 1/4 of the outer values. Once the engine has warmed the misfire count is predominantly on cylinder 3. Additionally the accumulated knock detection counters are showing about 20% more on cylinder 3.
The plug change interval isn't too far off so they were replaced, but it made no difference. Moving the coils didn't move the warm misfire count to a different cylinder, and just to be certain I borrowed a good set of coils which also made no difference, so it seems unlikely this is ignition related.
The fuel trim in closed loop at warm idle is +4.7% long term, and between -8% to -10% short term, so a net reduction in fuelling. The oxygen sensor is switching quite happily at idle, though obviously flatlines at 0v when misfiring occurs.
I'm thinking this is possibly a fuel delivery problem on injector 3 which is working especially poorly at low duty cycles pulse widths, but this wouldn't explain why it idles smoothly when warm, and I would have expected greater positive fuel trims?
stevieturbo said:
LimSlip said:
FWIW a set of injectors from a very low mileage engine fixed this issue.
very unusual.Did you get the injectors tested to see what was actually wrong ?
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