amcinstaller wrote:if some ecus run bank fire (fire an entire injector bank at once) then injector timing cant be all that critical.
Can someone please explain (if injector timing cannot be adjusted) why when turning the dizzy on a running engine. One extreme (say clockwise) causes the engine to run rough and then turning the dizzy CCW results in the engine stumbling again ? The sweet spot being somewhere between these to extremes.
I have had the dizzy turned in such a way (misadjusted) that the engine would kick back-like the ingition timing was to far advanced-while cranking ?
Another part of Benny and my conversation was his comment that whenever Hesco gets a 4.0 in for service. One of the first things they do is loosen the dizzy and find that sweet spot again. All in the name of readjusting the CMP for a worn timing chain. Which he claims often makes for smoother running engine.
Turning the dizzy simply changes the timing events of when the CMP goes high and low. If the flywheel (CKP) sequence for #3 has entered its timing notches, or # 5 has not yet finished, the ECU gets confused and does not know which cylinders is to be fired next, creating a rough running situation. I had a several page thread going on how my engine was breaking up at a very specific RPM range, but idled smooth and revved up to 2500 RPM smooth, but from 2500 to 3000 it would cough and miss and break up, over 3000 was ok. I adjusted my dizzy as per some help with a member on here, and it completely solved my issues. It just had to do with the sequence of events between the CMP and CKP.
amcinstaller wrote:if some ecus run bank fire (fire an entire injector bank at once) then injector timing cant be all that critical. i tihnk actually the magic number is in the injector pulse width rather than the timing.
Maybe so, but the 4.0 system is a sequential fuel injection system, which fires each injector individually.
oletshot wrote:....and silvolites are only cast not hypericantspellits.
From what I've read sequential systems show small improvements in fuel efficiency and power at very low RPM's after a couple thousand RPM's batch fire does just as well. Once the engine is really spinning It really is the amount of fuel available being correct that's more important than the timing of the spray.
From what I've read on max effort engines putting the injector further up stream often helps power. This means that a precise injector opening event, timed to fire down the open valve are impossible. Appearently even though the fuel is displacing air, it is also cooling it, and it's getting turned into a finer more homogeneous mixture that burns more evenly. On the extreme side of this there are even setups where an IR intake is fed by an injector that's actually above the radius entry to the intake runner (in other words you can watch the fuel spray into the mouth of the intake) Kind of like a Fancy TBI injector only for an individual runner intake... There are also setups that have the injector mid way in the runner facing the wrong direction so it fires BACKWARD into the oncoming air stream, to break up the spray droplets with the shearing forces.
In my opinion one of the reasons Carburetors still dominate drag racing is that the cooling effects of many types of race fuel cooling the entire intake charge from the Carb on down is a significant benefit outweighing the slight displacement of air. Whereas most port injection setups will have a dry (and hot) manifold... Under normal part throttle conditions with normal street gasoline, this is not big deal and the perfect idle and fast starting and better fuel efficiency of port injection, wins hands down. At Wide Open Throttle with better fuels, the better mixture, and the cooling effect wins out for power.
[quote="Mgardiner1"]Turning the dizzy simply changes the timing events of when the CMP goes high and low. If the flywheel (CKP) sequence for #3 has entered its timing notches, or # 5 has not yet finished, the ECU gets confused and does not know which cylinders is to be fired next, creating a rough running situation. I had a several page thread going on how my engine was breaking up at a very specific RPM range, but idled smooth and revved up to 2500 RPM smooth, but from 2500 to 3000 it would cough and miss and break up, over 3000 was ok. I adjusted my dizzy as per some help with a member on here, and it completely solved my issues. It just had to do with the sequence of events between the CMP and CKP.
Side note
Interesting as this is an "event" I run into also. The strange part is that it is not always present. Reducing fuel pressure seemed to help, a little. Just a little lower mid range stumble as the engine seems to be "coming up on the cam" Best way to describe it would be that the engine feels a little loaded up for a couple of seconds. Then clears its throat and moves on.
Still plan on taking a look at modding a CKP for more timing and trying a lower octane fuel to see if we can tolerate a faster flame front.
