Talk Morgan Forums Morgan Sports Cars Classic Morgans (pre-CX) GDI Plus 4 Throttle response

Does anyone else have a hair-trigger throttle response on their GDI Plus 4 when cold?

The slightest touch of the pedal seems to send the revs soaring like I've just given it a good stab on the pedal. Setting off becomes pretty tricky, as you have to time hitting the bite point with the flare of revs just starting to keep it all under control, and not sounding like a learner on their first lesson...

It gets better as it warms up, then is perfectly fine when fully up to temperature.

I know there was a re-flash of the ECU, but I think the car should be late enough to have that already.

RedMogT,

I have a GDI ( build week 24/15 )but I have not suffered the problem you have.
They all seem to rev up when first starting without touching the throttle and even with the ECU flash, there is still a short period of high revs which quickly settle down to around 1000/1100r.p.m whilst warming finally going down to 800r.p.m when warm.
It may well be worth going to your nearest dealer to see if the ECU flash has been done, it certainly improved my car no end.

The short run up to high revs on startup is common to many fly-by-wire throttle cars, it's perfectly normal and nothing to be concerned about. Here's what I believe is happening:

The ECU uses three different ignition maps to fuel the car during startup.

The cranking map ensures there's fuel and sparks available and that everything is ok, then it transitions to the ignition map which provides a richer mix for startup (like putting on the choke), then once the engine has fired it transitions out of the ignition map into the main running map.

Meanwhile the ECU is checking for a valid throttle position site signal from the pedal sensor so it knows the throttle is working correctly.

Until it gets this, the engine is effectively in limp mode - the throttle setting is defaulted to a value which allows the car to be driven without a working throttle pedal - so the revs go to about 2k or so. As soon as the valid throttle site signal is detected, the revs die back down as the ECU hunts for the target idle speed by adjusting the fuelling and advance. The ECU is operating in Open loop mode here, it won't be taking any notice of the Lambda sensors as the engine is still too cold.

The length of time a car spends in each map is set in the ECU programming. On my car, we have set the ECU to hold the crank map for a minimum of 3 seconds in order to start building oil pressure before the engine is allowed to fire, but many engines will exit crank mode as soon as the ECU has got a valid response from the crank sensor and the injectors. I think the logic is that people prefer their car to start immediately and aren't that worried about building oil pressure.

Yes - it also revs up to ~2k after starting. It's a bit weird in that it "spools up", rather than "flares up" giving the impression it is going to run away with itself, but I'd read in other threads that it was perfectly normal and it dies back soon enough not to be an issue. The theory makes sense that this is to allow it to move without a pedal signal.

The issue I have is with the hypersensitivity to throttle inputs that makes the first 5 minutes or so driving an absolute bu**er!! I'll drop over to the dealership for the later map, see if it helps/has it already - interesting that no-one else is commenting on having that problem.

Driving it exclusively it is possible to work around, but after driving other cars it takes some serious re-adjustment.

Not sure why Morgan couldn't use the Ford ECU... Ford probably spend tens of millions on that mapping and fine tuning!!

Still, adds a bit of character!

The problem with the manufacturers ecu is that the code is locked and cannot be changed. This is an issue because the stock ecu depends on all sorts of sensors and inputs like airbags that the Morgan simply doesn't have. Ergo, an aftermarket ecu is needed.

Don't have that problem on mine at all.

Mine is not like that at all. Start up is unexceptional. A quick blip and it settles down. When cold my throttle response is linear. But when it warms up it becomes hair trigger. I'm getting used to it and I might have the flash, but BHM weren't convinced it would improve it.

Yes - I don't think we need to be in any doubt that these are still Morgans!! Yours hair-trigger hot, mine hair-trigger cold, and others are just right...

Worried about having the flash now. I'd rather have hair-trigger cold than hot.

It's rev specific though. It rockets from 1k to 3k then seems to calm down. Now I'm over 2000 miles, I'm using full throttle at times to see if the ECU will learn the full movement.

Tim,

This explains something that I have noticed for years my existing and previous Subaru's take a while to start while our Mazda's vy comparision appear to start instantly.

I guess from you post, that the Subaru ECU waits a number of seconds to allow the engine to transfer to the first starting map to allow the Oil Pressure to build up before starting while Mazda may be less concerned on this point or use a more instantly responding oil circulation system.