MicroSquirt.com read only forum (Jan.15,2018)

Greetings from Florida.

I've got a turbocharged 20V silvertop Toyota engine on which I've installed MSII V3 w/EDIS. With the thorough information in the technical manuals and the breadth of knowledge on this site, I've been able to get the car running very well and I've had a great time along the way! The car runs really well under all conditions: idle, cruise, acceleration enrichment and WOT w/8 psi of boost. It runs at least as good as my stock cars .

Up to this point I have run the factory 330 cc/min high impedance injectors. When tuning I reached a point at which my duty cycle reached 100% in 4th gear under full boost. So I knew an injector upgrade was necessary. Compatible side feed injectors typically come in 440, 550 and 660 cc/min. After checking the calculations for injector sizing on this site I felt the 440s would just come shy of allowing me to meet my desired target of 280 HP without exceeding 80% duty cycle, so I selected 550s.

I checked the idle PW calculation, as clearly outlined in the MS technical manual as follows:

PW = REQ_FUEL * VE * MAP * E + accel + Injector_open_time
PW = 4.9 msec * 30% * (25 kPa / 100 kPa) + 1.0 msec = 1.36 msec

I realized this was getting very small for the idle PW but after reading all the posts on this forum I saw several people say they have been able to get good idle control on similar sized engines using 550 cc/min or larger injectors.

But I can't . After reducing my VE table to 1%, my idle AFR is still incredibly rich and the car will no longer idle. I have to feather the throttle to keep the engine running at which time it just revs from 1k to 2.5k and back down again. With the 330 injectors my ReqFuel was around 13ms. The calculator computed a value of 4.9ms for these 550 cc/min injectors and I figured I could always reduce it further if I had a problem. But I’ve tried reducing the ReqFuel to 3 or 1 ms and that has no perceptible effect on AFR or idle stability.

To make sure I wasn't doing something silly, I swapped the 330's back in, reloaded my old tune and the car idled and ran like a clock again (to my relief ;)). I then ordered a second set of 550's thinking perhaps there was a problem with the first batch, but there's not much difference (if any). When trying to tune the idle, I've disabled EGO and the acceleration & decel enrichment but I still can't get the car anywhere near an acceptable AFR or eliminate the wild hunting.

So I'm wondering if I'm just trying to get way too large of an injector to meter the small amount of fuel required to idle or if there are additional items I can check and adjust to fix this problem. I am using the standard IOT of 1ms and I've tried 1 and 2 squirt strategies.

Would low impedance injectors be of any benefit? Or should I just throw in the towel, purchase 440s and just accept the HP limitation of those injectors? Thank you in advance for any assistance you can provide. I apologize if this question has been answered elsewhere on this site, as I have searched and searched and cannot find any more ideas to explore. Alternatively, I would like to hear from some of you who have relatively small engines using 550 or larger injectors with a ReqFuel of 5 ms or less IF you've been able to get your engine to idle at anything better than 10:1 AFR . Thanks!

do you perhaps need to alter the opening time parameter? it make be set too long and too much fuel gets in not related to the req fuel amount..

Duncan

From everything I've read it's very rare that injector opening times are lower than 1ms but no, I haven't tried that. I will give it a shot. Thanks.

Mike

I remember finding numbers of 0.5ms for some injectors at some battery voltages. because the opening time is actually 'opening time' - 'closing time' it's possible (although not seen except for quite high battery voltages where the opening time is quick and the closing time slow) to have a setting of 0 if the opening time and closing time are equal. Maybe the parameter could be better termed 'travel time' or 'injector latency', but I digress.

Hope you find your gremlin...

cheers,
Duncan

440cc injectors should easily have made the kind of power you're looking for, and if you needed more flow you could increase fuel pressure a bit.

Perhaps you should try the 2.5 beta code? It had very high resolution fueling code, although I'm not sure whether that already made it into the normal code base.

Matt,

Using the calculation example from the manual I get the following:

InjectorSize = (HorsePower * BSFC) / (#Injectors * DutyCycle)
(280 HP * 0.65 lb/hr/HP) / (4*.85) = 53.5 lb/hr ~ 560 cc/min

I realize .65 might be a tad on the high side, but from what I've read it's a pretty good rule of thumb for turbocharged engines with high(er) compression that rely on a running a little rich to keep the piston crown temperatures under control. I was thinking the same as you that I could run a rising rate fuel pressure regulator to get a little more out of the 440s but I've thought of that as a band-aid for improper tuning/injector selection in the past. I also don't like the idea of supplying higher pressure to the injectors since it reduces their operating life. Thanks for the input!

Mike

what's your compression? 10:1+?

whatever it is, running way high AFRs isn't gonna help you much. I don't buy that whole fuel cooling buisness... from what I've seen it's just retarding the combustion so much that you're making less pressure in the cylinder (and such less heat). Drop the fuel a smidge, reduce boost by like half a psi and pull a degree of timing or so, and it seems like you'd make the same torque anyway.

Maybe I'm completely off though.

Matt, the compression is 10.5:1. When using the standard equation to size the injectors I don't see how I can get 280 HP out of even a N/A 4 cylinder (BSFC~.55) with 440 cc/min injectors and a duty cycle of 85%:

InjectorSize = (HorsePower * BSFC) / (#Injectors * DutyCycle)
(280 HP * 0.55 lb/hr/HP) / (4*.85) = 45.2 lb/hr ~ 470 cc/min

As for the other point about cooling, you are right in that the power lies in the timing; a few degrees can change the torque quite a lot. However, you can change the AFR plus or minus 1-2 points and have little if any affect on power (ie cylinder pressure). But if you monitor temperatures through EGTs, etc. you will see changing the AFR has a huge effect on the heat generated. This heat has to go somewhere: out the exhaust, into the combustion chamber, into the valves and into the piston crown. This temperature (and thus heat transfer) can be significantly lowered by running proper AFRs at high cylinder pressures. This is one of the reasons forced induction engines have worse BSFC numbers.

Mike

Thinking about it further, I think I'm starting to understand my error(s). My previous calculation for idle pulsewidth looked like this:

PW = REQ_FUEL * VE * MAP * E + accel + Injector_open_time
PW = 4.9 ms * 30% * (25 kPa / 100 kPa) + 1.0 ms = 1.36 ms

My logic was wrong when I said I figured I could lower the ReqFuel (4.9ms) or idle VE (~30%) if I had problems. But that won't help anything. Both of these only serve to lower the idle PW further, which certainly isn't going to help if I'm already commanding idle PWs which are too small! It seems the injector opening time of the 550s is just too large to allow them to meter a small enough quantity of fuel at idle on this small engine (1.6T). This has been discussed a lot on this site and in the manual, however I just didn't make the connection until running up against this wall for myself .

Looks like it's time to trade for some 440s...

Mike

So you tried a smaller opening time and that didn't help?