Engine won't rev past 5k rpm
Discussion
I recently put my car back on the road after being off it for around two years, in that time the engine was wrapped up sitting in the corner of the garage. Before it was taken out it was running fine with no problems but now it is back in I have a problem that it won't rev beyond 5k. Regardless of load it bounces at 5k in a rev limiter fashion. It is a 4 cylinder turbo engine on aftermarket engine management and aftermarket cam.
I have checked the Soft Limiter, Hard Limiter and Boost threshold limiter settings in the ECU software and it doesn't appear to be hitting these (doing so results in a big red popup on the laptop screen normally). I've also set them all artificially high to test but it makes no difference.
The only changes to the engine apart from everything being disconnected and reconnected was a minor adjustment to the cam timing (within the range of the vernier pulley), tappet clearances and exhaust manifold port sizes. The car drives fine up to 5k and idles ok at 1k, the rpm read out in the laptop software also seems to be correct. At the '5k rev limit' it still reads 5k in the software. The engine charges up to 5k and then immediately refuses to go further, it isn't a progressive loss of power.
My thoughts on possible causes are:
- The cam timing adjustment
- Faulty crank position sensor ( I doubt this because the reading on the laptop is fine)
- ECU problem
Has anyone ever had a similar problem? Could cam timing being slightly out really cause this rev limit effect?
Cheers,
NISaxoVTR
I have checked the Soft Limiter, Hard Limiter and Boost threshold limiter settings in the ECU software and it doesn't appear to be hitting these (doing so results in a big red popup on the laptop screen normally). I've also set them all artificially high to test but it makes no difference.
The only changes to the engine apart from everything being disconnected and reconnected was a minor adjustment to the cam timing (within the range of the vernier pulley), tappet clearances and exhaust manifold port sizes. The car drives fine up to 5k and idles ok at 1k, the rpm read out in the laptop software also seems to be correct. At the '5k rev limit' it still reads 5k in the software. The engine charges up to 5k and then immediately refuses to go further, it isn't a progressive loss of power.
My thoughts on possible causes are:
- The cam timing adjustment
- Faulty crank position sensor ( I doubt this because the reading on the laptop is fine)
- ECU problem
Has anyone ever had a similar problem? Could cam timing being slightly out really cause this rev limit effect?
Cheers,
NISaxoVTR
ECU is a KMS MP25 on a TU5JP engine. It's pretty basic and doesn't have any proper data logging software as far as I'm aware. Sensor wise, the throttle body sensors are from a MK1 106 Rallye, Map sensor is a 2 bar Magnetti Marelli, crank sensor is the standard one from a Saxo VTR and lambda sensor is a bosch 5.2. The car doesn't have a cat installed at the moment.
Everything looks in order with the valve springs and rocker gear. Not that it's any guarantee but its only done 3000 miles. The inlet pressure reads a pretty steady 8psi at idle and doesn't vary by more than .3/.4 psi. Same with lambda, it sits steady at idle.
I thought perhaps it was a problem with the coil pack / spark plugs. I remembered that my 'helper' adjusted the electrode gaps on the spark plugs while the engine was out so pulled these out for a look. They were around 1mm, i've adjusted then back to 0.7mm. They are NGK BCR8ES plugs. I don't think this made any difference but noticed when testing that if I give the car a sharp kick from idle it will rev round to 7k, but if I try to bring the revs up slowly it limits at 5k.
I think there may be a problem with the throttle position sensor. The 'auto' calibration fails with a 'range too narrow' error when you try to configure the min and max throttle positions, and when you hold the pedal half way down the reading on the lap top doesn't seem stable. I'm going to look at picking up a new sensor/throttle body and give that a go.
Everything looks in order with the valve springs and rocker gear. Not that it's any guarantee but its only done 3000 miles. The inlet pressure reads a pretty steady 8psi at idle and doesn't vary by more than .3/.4 psi. Same with lambda, it sits steady at idle.
I thought perhaps it was a problem with the coil pack / spark plugs. I remembered that my 'helper' adjusted the electrode gaps on the spark plugs while the engine was out so pulled these out for a look. They were around 1mm, i've adjusted then back to 0.7mm. They are NGK BCR8ES plugs. I don't think this made any difference but noticed when testing that if I give the car a sharp kick from idle it will rev round to 7k, but if I try to bring the revs up slowly it limits at 5k.
I think there may be a problem with the throttle position sensor. The 'auto' calibration fails with a 'range too narrow' error when you try to configure the min and max throttle positions, and when you hold the pedal half way down the reading on the lap top doesn't seem stable. I'm going to look at picking up a new sensor/throttle body and give that a go.
Kokkolanpoika said:
Dead valve spring? I have got similar problem with my RV8 when i use Real steel single coil spring witch has got 1 coil less.. Just like hitting soft rev limiter approx 5500rpm. Those springs lose over 40KG open pressure in couple of year and approx 7000km..
They aren't properly heat treated then and will be losing free length and therefore fitted load. Full lift load over the cam nose isn't the issue here. It's the fitted load when the valves are shut. If this load is insufficient the valve doesn't close onto the seat properly. It just bounces up and down and prevents the next engine cycle commencing properly.With stock weight components on that engine you probably want about 90 to 100 lbs fitted load in an ideal world.
NISaxoVTR said:
Everything looks in order with the valve springs and rocker gear.
You mean you've actually taken the rocker cover off and checked properly since I posted that or you're just guessing? Either a broken spring or ones that have lost their tension and fitted load give exactly your symptoms. Check again.Found this error on the diagnostics page of the ECU software at the weekend:
Throttle Position Sensor:
TPS short circuit: 00:28:52,5 h:m:s
TPS open circuit: 00:00:00,0 h:m:s
Lowest TPS value (TPS < min load 33): -33%
Highest TPS value (TPS > max load 0): ---%
I measured the signal wire of the TPS at min and max loads (engine off) and it showed:
Min Throttle: 0.69v
Max Throttle: 1.92v
I'm not sure if this is an unusually small range? Its this range which is too narrow for the ECU to auto calibrate so I've had to enter the TPS range values manually. I tested another sensor (different style so can't use on car and it ranged from 0.15v to 2.5v). The throttle position is broken into 16 units in the map, 0.0 to 15.9. It seems to cycle through this range ok relative to pedal position when the engine isn't running but the ignition is turned on (same with cycling from 0.69v to 1.92v). It behaves differently when the engine is running though and the throttle position stays at 0.0 unless its pressed down a large amount. I'm not sure why it would be different with the engine running or not. It seems something is interfering with it.
I checked the continuity of all the sensor wires from their individual plugs to the main ecu plug and they seemed fine. Each only beeped on their own wire. When the engine is 'limiting' at 5000 revs the TPS is showing 0.0, I think the overrun fuel cut is kicking in which is set to happen > 5000 revs and < 0.5 TPS. I've ordered a new TPS sensor which should arrive in a couple of days.
Throttle Position Sensor:
TPS short circuit: 00:28:52,5 h:m:s
TPS open circuit: 00:00:00,0 h:m:s
Lowest TPS value (TPS < min load 33): -33%
Highest TPS value (TPS > max load 0): ---%
I measured the signal wire of the TPS at min and max loads (engine off) and it showed:
Min Throttle: 0.69v
Max Throttle: 1.92v
I'm not sure if this is an unusually small range? Its this range which is too narrow for the ECU to auto calibrate so I've had to enter the TPS range values manually. I tested another sensor (different style so can't use on car and it ranged from 0.15v to 2.5v). The throttle position is broken into 16 units in the map, 0.0 to 15.9. It seems to cycle through this range ok relative to pedal position when the engine isn't running but the ignition is turned on (same with cycling from 0.69v to 1.92v). It behaves differently when the engine is running though and the throttle position stays at 0.0 unless its pressed down a large amount. I'm not sure why it would be different with the engine running or not. It seems something is interfering with it.
I checked the continuity of all the sensor wires from their individual plugs to the main ecu plug and they seemed fine. Each only beeped on their own wire. When the engine is 'limiting' at 5000 revs the TPS is showing 0.0, I think the overrun fuel cut is kicking in which is set to happen > 5000 revs and < 0.5 TPS. I've ordered a new TPS sensor which should arrive in a couple of days.
Edited by NISaxoVTR on Sunday 15th September 22:56
.My old 106 Rallye certainly needed a replacement TPS in its (shortened) lifetime.
In the past I've had rev limiters appear by accident when I used a borrowed map.
When it hits the limiter what does the spark advance do? My car would work fine and then advance went off at xxx rpm and it turned out to be that the map I'd borrowed had either traction control or launch enabled.
In the past I've had rev limiters appear by accident when I used a borrowed map.
When it hits the limiter what does the spark advance do? My car would work fine and then advance went off at xxx rpm and it turned out to be that the map I'd borrowed had either traction control or launch enabled.
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