Getting the duty cycle percentage down.

[RICHARD]

hi people.
can anyone help out there with the problem i've got as regards getting the duty cycle percentage down. I've got the engine running quite well but at around 5500 6500 rpm the duty cycle gose off the gauge at around 118, acouding to a couple of data logs i,ve done. It as though it's got a rev-limiter. The set up i've got is a EDIS set up running a set of throttel bodies on a 1300cc vauxhall engine using 1400cc injectors.
many thanks Rich

[RICHARD]

hi jim
got a fuel presure gauge fitted and the presure is maitaining at 45psi. It's also fitted with a adjustable presure regulater. The injectors are out of a 1400cc engine not rated at 140cc. Don't realy know what the ratting is. Got the car running on the rolling road some mounths ago by ower tunning man that deals with omex alot. Wasn't to bad on the rolling road but when it came to the open road things were a bit different. The engine i know can rev to 6800rpm and can push out 125bhp at 4600 rpm at the fly wheel. My thoughts are that the injectors maybe a bit to small. Have tried larger ones but can not seem to get the engine to rev. I have a wideband o2 sensor fitted with a digital gauge fitted. The read out is a bit hard to judge because it moves so fast at top end of the rev range and when the engine starts with the miss fire/rev limiter efect it just goes mad.
I have also tried putting the fuel presure up and also down, but don't seem to see a difference. Bottom end reving is ok upto around 4500 then a flat spot up to 5000 then a rev limitering thing happens at 5500/6500.

cheers Rich

[RICHARD]

hi jim
thanks for the info on what i could try to get the thing running better. I have got a set of 200cc injectors that i'll try next wkend. Do i have to play around with the fuel map or can the change be done by changing the fuel required in the constants bit???
cheers rich
ps if i have managed to up load a data log have a quick look to see what you think cheers.

[efahl]

Unfortunately , it will probably require both a
Required Fuel adjustment and re-tuning your VE Table some .

Can you explain why?

[efahl]

Good explanation, Jim. I was hoping I wouldn't have to type all that stuff in again (since MS is more an educational project than anything else, I always like to see explanations detailing why something is the case).

Two related items come to mind:

1) Some tuning parameters are pure-time injection durations, and will always need changes when changing injectors. For instance, cranking PWs are specified in ms and hence can be scaled by

Code: Select all

   newPW = (oldPW-oldIOC) * newFlow/oldFlow + newIOC

where
   PW   = pulsewidth
   IOC  = injector open/close time
   Flow = flow rate

2) There have been many threads on this, it has been implemented in code by several people (I recall Tony Bitzanis writing a perl script to do this about five years ago, it might still be hanging around) and Lance probably has it in the manual, but you can accurately figure out the IOC of an injector by tuning to a known AFR (stoich is usually easiest) at a given set of constant conditions (temps, RPM and MAP), then changing the number of injection events and retuning to that same AFR. The difference in VE is, as you explain above, due to error in IOC.

Eric