Advice sought, high revs miss-fire
Discussion
Seeking a little guidance from the Pistonheads knowledge pot please.
We've been running a BMW S1000rr engine for a while now using the stock ecu. We decided to go for an aftermarket ecu (don't want to name names yet simply to avoid prejudiced views).
On the dyno we had a very specific and very repeatable high revs miss-fire. We replaced the plugs and COPS so can hopefully count those out. At elevated revs the dyno guy could not put enough ignition advance on to get the best power. If he applied the advance the engine needed the engine developed a miss, the more advance dialed in the sooner in the rev range the miss started. There is no detonation. We spent a fair amount of time experimenting with the coil charge time, this made no difference, ignition is running sequentially so the coils have plenty of off/rest time.
For example:
at 32 degrees of advance at top end, engine will rev out cleanly to 14500rpm, this produced c175bhp
at 36 degrees of advance at top end, engine will start to miss fire at 13500ish rpm, at 13500 rpm power is up to c177bhp.
at 40 degrees of advance at top end, engine will start to miss fire at 12500ish rpm, at 12500 rpm power is up tp c178bhp.
The miss-fire is a bit like a soft cut on a rev limit, it almost sounds as if the spark is being blown out. If the throttle is held open revs will gradually increase though the miss to the actual soft cut at 14500rpm. This was on a fresh engine using fresh fuel.
The dyno guy spent an age looking for reasons as to why this could be happening without resolve. We involved the ecu supplier whilst on the dyno via Teamviewer to see if they could see any reason for it without resolve.
Any opinions or diagnostic directions would be gratefully recieved.
Thanks for reading.
We've been running a BMW S1000rr engine for a while now using the stock ecu. We decided to go for an aftermarket ecu (don't want to name names yet simply to avoid prejudiced views).
On the dyno we had a very specific and very repeatable high revs miss-fire. We replaced the plugs and COPS so can hopefully count those out. At elevated revs the dyno guy could not put enough ignition advance on to get the best power. If he applied the advance the engine needed the engine developed a miss, the more advance dialed in the sooner in the rev range the miss started. There is no detonation. We spent a fair amount of time experimenting with the coil charge time, this made no difference, ignition is running sequentially so the coils have plenty of off/rest time.
For example:
at 32 degrees of advance at top end, engine will rev out cleanly to 14500rpm, this produced c175bhp
at 36 degrees of advance at top end, engine will start to miss fire at 13500ish rpm, at 13500 rpm power is up to c177bhp.
at 40 degrees of advance at top end, engine will start to miss fire at 12500ish rpm, at 12500 rpm power is up tp c178bhp.
The miss-fire is a bit like a soft cut on a rev limit, it almost sounds as if the spark is being blown out. If the throttle is held open revs will gradually increase though the miss to the actual soft cut at 14500rpm. This was on a fresh engine using fresh fuel.
The dyno guy spent an age looking for reasons as to why this could be happening without resolve. We involved the ecu supplier whilst on the dyno via Teamviewer to see if they could see any reason for it without resolve.
Any opinions or diagnostic directions would be gratefully recieved.
Thanks for reading.
Edited by Borla on Saturday 29th December 03:00
Thanks for reply, no the dyno didn't have a 'scope, so unfortunately didn't have the opportunity to look for any interference. I think that will be our next step.
As for the coils wiring, I took the wire sizes from the BMW wiring diagram (off the top of my head I think they were 0.75mm sq for pos and neg and the signal was 0.5mm sq. and the runs are similar length to as they were on the stock harness.
As for the coils wiring, I took the wire sizes from the BMW wiring diagram (off the top of my head I think they were 0.75mm sq for pos and neg and the signal was 0.5mm sq. and the runs are similar length to as they were on the stock harness.
Borla said:
Thanks for reply, no the dyno didn't have a 'scope, so unfortunately didn't have the opportunity to look for any interference. I think that will be our next step.
As for the coils wiring, I took the wire sizes from the BMW wiring diagram (off the top of my head I think they were 0.75mm sq for pos and neg and the signal was 0.5mm sq. and the runs are similar length to as they were on the stock harness.
3 wire coils with the driver in them shouldn't have that problem, But it would still be worth a try to see they are getting the correct signal. Smaller gap can help too, when i upped the boost on my lpg audi 1.8t i had to run a smaller gap.As for the coils wiring, I took the wire sizes from the BMW wiring diagram (off the top of my head I think they were 0.75mm sq for pos and neg and the signal was 0.5mm sq. and the runs are similar length to as they were on the stock harness.
Thanks for all the suggestions guys, couple of other things I should mention, all of the injection system bar the fuel pump is stock. The miss-fire will occur at any throttle demand, so doesn't appear to be related to the tps. We have had this engine previously on this dyno at 189bhp at (IIRC) 13800rpm ish.
To answer the questions in order;
Have we looked at fuel flow and pulse widths? The engine runs two injectors per cylinder, I don't know how the BMW ecu drove them but the ecu we are using they can be configured in numerous ways. The dyno guy has a lot of experience so I left the decision on how they sequence up to him. I do recall he said neither upper or lower is exceeding 60% duty cycle.
New plugs but what gap? Again the guy on the dyno fitted the new plugs just in case one had gone. He checked the gap of both old ones coming out and new ones going back in. As above the spec of components or engine hasn't changed, but closing the gap is something we could try.
Have we monitored fuel pressure? Put simply, yes. There is a permenant fuel pressure guage mounted adjacent to the fuel pressure regulator (set at 3 bar) and the engine has a fuel pressure sensor that we have calibrated and can be monitored via the ecu software. Fuel pressure stays solid at 3 bar.
Thanks so far.
To answer the questions in order;
Have we looked at fuel flow and pulse widths? The engine runs two injectors per cylinder, I don't know how the BMW ecu drove them but the ecu we are using they can be configured in numerous ways. The dyno guy has a lot of experience so I left the decision on how they sequence up to him. I do recall he said neither upper or lower is exceeding 60% duty cycle.
New plugs but what gap? Again the guy on the dyno fitted the new plugs just in case one had gone. He checked the gap of both old ones coming out and new ones going back in. As above the spec of components or engine hasn't changed, but closing the gap is something we could try.
Have we monitored fuel pressure? Put simply, yes. There is a permenant fuel pressure guage mounted adjacent to the fuel pressure regulator (set at 3 bar) and the engine has a fuel pressure sensor that we have calibrated and can be monitored via the ecu software. Fuel pressure stays solid at 3 bar.
Thanks so far.
HedgeyGedgey said:
Check the plug gaps as mentioned. If you were on the dyno have you got the AFR plot? That will show if it's a fuelling issue, I'd put my money on it being ignition side tbh tho. Change plugs and regap them, cheapest and easiest option atm
Thanks for input, yes he gave us an afr plot which shows no fuelling issues. Like you say all things point towards the ignition. Fault was the same on 2 sets of plugs running stock gap that is proven in this engine. Will try massaging the gap a little though.Sorry this is a long dead thread but I just thought I'd post cause of problem in case anyone else needs to know. After the dyno we looked at the data log to see if we could identify a cause and we notice there was slight interference on the TPS signal. We did a lot of work involving shielded cables and loom re-routing without success. In the end it turned out to be the OE BMW throttle position sensor not being happy working with a different ecu.
The BMW tps is a hall effect jobbie, we tried a couple (including a brand new one) of replacements and all displayed the same issue. We ended up replacing it with a good old fashioned mechanical wiper type tps (from a MG ZR IIRC!) and all has been happy for the last season and a half.
The BMW tps is a hall effect jobbie, we tried a couple (including a brand new one) of replacements and all displayed the same issue. We ended up replacing it with a good old fashioned mechanical wiper type tps (from a MG ZR IIRC!) and all has been happy for the last season and a half.
.
Its good to hear what actually solved the problem. Borla said:
In the end it turned out to be the OE BMW throttle position sensor not being happy working with a different ecu.
Or the ECU not being happy with a completely different design of throttle position sensor? For the ECU to get the right signal, the sensor would have to be electrically compatible with the OEM one. It's easy to imagine a hall effect sensor having completely different electrical characteristics to a resistor track sensor, for example.Mignon said:
It's still a bit of a puzzler to me why a TPS would cause a misfire. Maybe some light can be shed.
Depends on "misfire".When TPS does have control over fueling ( and sparks ), including accel enrichments, overun fuel cuts, idle control off/on etc... It wouldnt be too hard to see why it could cause issues if it was spiking one way or another causing rapid and large changes when there should be none.
The running issues could be perceived as a misfire, when perhaps they arent quite that. A datalog would have should any anomalies with the sensor at a fairly early stage though ( if logged at a fast enough rate...ie no generic OBD crap )
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