MX5 Turbo - Hesitation on Boost
Discussion
fatjon said:
Thanks for the excellent tip. I will get plugged in at the weekend and pull a bit of timing and up the duty cycle on the idle valve a little. I can see the logic of the argument. I think I may be limited by cooling system if I go too far with it though. It heats up pretty quick if it gets too much retard. That said, I have room for a second fan on the radiator and I can live with that solution for a cleaner idle. The symptoms certainly fit your description, in particular the very non linear behaviour of the injectors at idle with variations in electrical load. The ECU has a compensation figure for a change in voltage but as you say, the variation is so non linear that it is all but useless as a method of controlling the amount injected at idle. My typical idle PW at 900 RPM and 14:1 AFR is 1.5ms at it maxes out on full boost at around 80% duty cycle so I don't have a lot of scope for a change of injector size even tough it's a rather short idle pulse width.
Had a similar but unrelated problem on my Cerbera. It had an intake harmonic at very low RPM with fuel standoff when running at very small throttle angles at low speed. Made it shunt and was a very unpleasant drive. Same cure though, I pulled some timing and that means you naturally open the throttle a little more which solved the problem. That tip came from Dave Walker at Emerald, now there's a man that knows his stuff. Just didn't want to double the value of my MX5 by adding one of his ecu's.
That worked really well. I pulled 10 degrees out of the timing and opened up the idle a little and it now idles like clockwork. The open time for the injectors went up from 1.5 to 1.8 and seems to have dropped into a more linear and controllable area. The AFR is now a very stable 14.5 and the EGO control is having no trouble stabilising it as electrical load changes occur. Not having any heat problems either.Had a similar but unrelated problem on my Cerbera. It had an intake harmonic at very low RPM with fuel standoff when running at very small throttle angles at low speed. Made it shunt and was a very unpleasant drive. Same cure though, I pulled some timing and that means you naturally open the throttle a little more which solved the problem. That tip came from Dave Walker at Emerald, now there's a man that knows his stuff. Just didn't want to double the value of my MX5 by adding one of his ecu's.
fatjon said:
That worked really well. I pulled 10 degrees out of the timing and opened up the idle a little and it now idles like clockwork. The open time for the injectors went up from 1.5 to 1.8 and seems to have dropped into a more linear and controllable area. The AFR is now a very stable 14.5 and the EGO control is having no trouble stabilising it as electrical load changes occur. Not having any heat problems either.
Struth. One of those once every three months lucky guesses from Max paid off eh? So it's not a total waste of time having him in here then 
Sorry for the bump but this problem still isn't fixed, it's simply better than it was. This was due to an injector leak which is now fixed - all seals on the injectors replaced and they have been flow benched and cleaned.
Any other ideas?
Factually i know it can't be the injectors, fuel filter, spark plugs, air filter, am very doubtful it's the leads, fuel pump, coil pack and I don't think it's the mapping, turbo or boost leaks? At a loss with it.
Any other ideas?
Factually i know it can't be the injectors, fuel filter, spark plugs, air filter, am very doubtful it's the leads, fuel pump, coil pack and I don't think it's the mapping, turbo or boost leaks? At a loss with it.
Edited by Buzzkill on Thursday 1st August 19:01
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