Speed increased when mode changed from EV to Hybird Drive

[csp]

I recently experienced a strange effect from my Mk4 Jazz Hybrid; not long after starting off from cold travelling slowly up hill in EV mode the car speed increased when the engine started up, I had to apply the brakes since I was approaching a junction. The engine seems to run faster when starting from cold than when it is warm, although at low speed the engine should just be charging the battery so it should not directly effect the car speed.

I have only experienced this effect once.

Also see post below concerning MK2 Hybrid
https://clubjazz.org/forum/index.php?topic=12334.0

[John Ratsey]

I've not noticed this problem yet but I think the engine always starts and runs at 2000? rpm when doing a cold start at home as the last part of a journey home is slightly downhill and done in EV mode thus leaving the battery below 60%. The car's priority is to get the engine warmed up quickly by putting some charge into the battery as well as moving the vehicle (the engine may run for less than a minute to get the battery to 60%). When I set up an improvised tachometer using OBDII reader and phone I noticed that the preferred engine speed was 2000 rpm (or higher if more power needed) but went below 2000 prm when in direct drive (about 1600 rpm at 42mph and then increased in proportion to vehicle speed). 

So far I have found the transition between different drive modes to be completely smooth. I wonder if the extra fuel used for the starting of a cold engine resulted in a brief power surge. Perhaps you should mention your observation to your dealer to pass on to Honda as you might have encountered a situation where the transition isn't so smooth.

[Muldoon]

I would be concerned over any odd behaviour and the complexity of this system. It seems a full EV or old fashioned petrol have less potential for anomaly than hybrid.

[Mellorshark]

John, wouldn't your findings on engine speed suggest that the use of 98 RON could be beneficial?

[John Ratsey]

I would be concerned over any odd behaviour and the complexity of this system. It seems a full EV or old fashioned petrol have less potential for anomaly than hybrid.

Any modern vehicle depends on a lot of computer software. The new Jazz's hybrid system should be fairly well debugged as it's a slightly scaled down version of the system in the CR-V hybrid that has been on sale for well over a year. However, going back to the reported problem, the engine starting shouldn't cause any change in vehicle speed which is determined by the electronics driving the motor.

John, wouldn't your findings on engine speed suggest that the use of 98 RON could be beneficial?

Please explain your reasoning behind this suggestion?

[Mellorshark]

I was under the impression that the effect of higher octane fuel on a non "performance " engine was higher  torque at lower engine revs. But it's only what I have read ( honest john ). I used Shell V Power in the mk3 because it went up hills better and where I live you can't go anywhere without going uphill.  I don't want to start a debate about super  v supermarket fuel.

[John Ratsey]

I used Shell V Power in the mk3 because it went up hills better and where I live you can't go anywhere without going uphill.  I don't want to start a debate about super  v supermarket fuel.

The Mk. 4 has the electric motor to provide the torque which the Mk 3 noticeably lacked at lower revs. There are plenty of threads about the merits of different fuel tyres. This is one https://clubjazz.org/forum/index.php?topic=12269.0 . Personally, I buy Redex from Wilko when it's on offer and give the car some when the tank gets refilled (with standard 95 octane, usually supermarket stuff) but my objective is to keep the fuel system clean and the cheap fuel might not have all the additives of more expensive fuel.