Lower my fuel pressure to help w/fuel injectors.., ...being too large??? Options

[Mueller]

Running 2.0 injectors on my stock 1.8, new fuel injection fires all 4 at one time (batch), I have a feeling new injectors are too much....anyone lower their fuel pressure to compensate for large injectors??

I'm wondering how low can I go yet still retain a nice reliable pattern?????

[TimT]

if I remember Link 1 you can fire injectors 180 apart... so all injectors dont fire at the same time..

you can make two sets of injectors and reduce the dwell time they are on

[TimT]

Also keep your fuel pressure constant...

thsi eliminates a variable..

rising rate FPRs (IMG:http://www.914world.com/bbs2/html/emoticons/bootyshake.gif)

[snflupigus]

is there a removable programable chip in these ecms? or is there some manual pots or something in there to do what you're talking about with injector pulse duration and timing.

[0396]

Running 2.0 injectors on my stock 1.8,

Interesting idea..hope you can figure it out. Because I can you use that on my 1.8 too.

Thanks and hope all is well (IMG:http://www.914world.com/bbs2/html/emoticons/cool.gif)

[DNHunt]

Mike

I know you can lower them a little but, I seem to remmember that it is not a lot. If I remember correctly, because of the large pintel (sp) the spray pattern will suffer.

Here's a link to a pretty good paper on injectors available. I've played with a Borg Warner aftermarket 0 280 150 151 that flows 240 cc's per minute. They gave me a pulsewidth of 2.0 ms at idle. If you d decide to use any Borg Warner injectors, put hose clamps over the hose on the barbs. It appears they are swedged on bot I had a hose come off.

Dave

[airsix]

Mike,
What pressure are you running? Have you modified your fuel-pressure reg yet (added a manifold pressure port)? When modified for boost-signal pressure compensation the regulator will actually LOWER pressure under high vacuum. I found this useful because it allowed me to widen the pulsewidths at idle.

-Ben M.

[Mark Henry]

I'm running 2.0 injectors on my stock 1.8 right now!

No issues, but my fuel values are a tad low.

[Mueller]

QUOTE (snflupigus @ Jun 13 2005, 12:05 AM)

is there a removable programable chip in these ecms? or is there some manual pots or something in there to do what you're talking about with injector pulse duration and timing.

I hit a button on my laptop computer to change the pulse widths and everything else for it (IMG:http://www.914world.com/bbs2/html/emoticons/smile.gif) (IMG:http://www.914world.com/bbs2/html/emoticons/type.gif)


It appears I have an ignition problem, I'm still getting the erractic miss running just the cdi and distributor taking the Link off of the duty of controlling the ignition...I only had time to pull the plugs last night and boy, are they filthy, looks like I dipped them in charcol dust....my next step will to clean them up, gap them and try it again. If I still have the miss, then I'll remove the CDI box from the equation.

For my pulse width at idle, I am at 4.5ms, stock fuel pressure regulator, fuel pressure set at I think 32psi

I've run these injectors with my D-Jet on the 1.8 with no signs of problems, so I'm a little confused as to why I'm having an issue now, but it might all be ignition related now that I am headed down that path of troubleshooting...thanks all...

[airsix]

Mike,
Since the 2.0 (and 1.7) injectors are 3.5 ohm you ought to be able to run really short pulse widths with no problem. Just going from memory I think my minimum pulsewidth is just 1.75 ms. 4.5 sounds like an eternity. If you have a scope you could easily measure the minimum time to open the injector by looking at the current spike. It should initially spike and then fall to a point and plateau. Time from start to the plateau after the spike is the time for the injector to fully open and thats the minimum pulsewidth you should use. I'm pretty sure it will be 2ms or less.

If you are having trouble with your fuel numbers getting too small to work with on the fuel map screen, have you looked to see if there is a "fuel multiplier" in the Link settings that can be changed? My MIC3 has this and it allows me to move all of the map values into a useful range if the numbers are too high or low. It doesn't change the actual fuel volume being delivered, it just changes the range of values on the tuning map that you work with. Think of it like zeroing the dial on your mill or lathe. I hope that makes sense.

-Ben M.

[Mueller]

QUOTE

If you are having trouble with your fuel numbers getting too small to work with on the fuel map screen, have you looked to see if there is a "fuel multiplier" in the Link settings that can be changed? My MIC3 has this and it allows me to move all of the map values into a useful range if the numbers are too high or low. It doesn't change the actual fuel volume being delivered, it just changes the range of values on the tuning map that you work with. Think of it like zeroing the dial on your mill or lathe. I hope that makes sense.

yep, makes sense, in the fact the instructions for the Link mention something to that effect.....I re-read the tuning/config manual and I'm going to start at square one, I jumped ahead with tuning, now I have a better grasp of how to set it up.....I'm hoping the cleaning of the overly fouled plugs helps some (IMG:http://www.914world.com/bbs2/html/emoticons/smile.gif)

[lapuwali]

You have to be careful on open/close times. The numbers I've seen quoted for "modern" injectors is 1.25-1.75ms just to open the injector fully. That's not a low v. high impendance issue, just a time for the pintle to move from fully closed to fully open. The close times are similar.

One thing I've not figured out yet is if the pulsewidth includes the open and close times, or only the open time, or neither. Electrically, I'd expect it to include the open time (pulse goes high, injector starts to open, pulse goes low, injector STARTS to close). If that guess is correct, then 1.75ms is a reasonable minimum time, and the fuel flow only includes whatever comes out while the injector is opening and closing, with no "fully open" time (other than whatever is there from the inertia of the pintle reversing direction). I'd bet there would be little to no measurable difference between a 1.5ms pulsewidth and a 2.0ms pulsewidth on most injectors. Operating in this area is also going to give high inconsistent fuelling from cycle to cycle, since the open and close times aren't fixed, but vary by 0.1-0.2ms each time.

Even if I'm wrong, and the pulsewidth only includes the fully open time, the fuzziness introduced by the variable open/close times will still be a very significant portion of the total fuel injected. If the times both vary by 0.2ms each, then at 1.75ms, fuel flow is going to vary by as much as 10% from cycle to cycle. (0.4ms/1.75ms is 23%, but there's not 100% of fuel flow while opening or closing, so take a swag at a bit less than half of full flow over the variation in times).

Perhaps none of this makes any practical difference (who knows how bad carbs are in flow variation?), but there's certainly going to be some lower limit. I'd expect 1.75ms to be very close if not over that limit. Dave Hunt noticed that, when running 2.0 injectors on a 2.0 with MS, that only 0.1ms in pulsewidth made a noticable difference to idle quality.

Here's a quote from John De Armond, who's forgotten more about EFI than any of us ever knew:

under normal conditions, the injector spends so much time opening
and closing. A typical injector can open in a millisecond. It
takes a similar amount of time to close. During the opening
process, the flow goes from zero to full flow in a very non-linear
fashion. High speed photographic studies I've done on the old style
Pintle injector (where the valve pintle is visible) shows that the
flow doesn't start until about 750 microseconds into the open
event. The closing process is also nonlinear but of a different
shape. During idle and cruise, the injector is running with an open
period of from about 0.5 ms to perhaps 1.5 ms. Under these
conditions, the injector is continuously either opening or closing,
never reaching the full open state (or just barely doing so.)

I'll note that the D-Jet injectors are the "old-style pintle" injectors he's referring to.

[snflupigus]

GM tbi injectors often go "static" - meaning they stay constant open because by the time they might close they are opening again because the fuel needs still havent been met... we've had a lot of problems making power with the system. They go static pretty quick because they are such large injectors and they take so long to open and close. We've used vacuum adjustable regulators so that fuel pressure is low at high vac and high at no vac. The pressure has to be increased at WOT and pulse width messed with a TON so as to still correctly meter fuel down at low rpm, while at WOT they can go static and be in full open but still delivering the right a/f ratio for peak power.

Mind you these small block chevy engines are running about 350hp+ with only 2X80lb/hr injectors at twice the rated fuel pressure.

I thought you guys were referring to tuning the stock djet system. I was getting excited for a moment thinking that my old prom burner might come into use again LOL

[airsix]

QUOTE (lapuwali @ Jun 13 2005, 10:32 AM)

Perhaps none of this makes any practical difference (who knows how bad carbs are in flow variation?), but there's certainly going to be some lower limit. I'd expect 1.75ms to be very close if not over that limit. Dave Hunt noticed that, when running 2.0 injectors on a 2.0 with MS, that only 0.1ms in pulsewidth made a noticable difference to idle quality.

Since there were so few production automobiles using solenoid injectors in the early '70s I'm convinced that Porsche/VW/Bosch "made due" with what was on the shelf - grossly oversized injectors. By today's standards our injectors are HUGE for our per-cyl displacement. Take for example the Subaru 1.8L-Turbo injectors I was using - they flow about 25% LESS than the D-jet 1.7 injectors. Lucky for us, our D-jet injectors are very low impedence and the coils charge quickly, so you can tune your PEFI to use super-short pulse-widths just like the factory did with D-jet. If the PEFI doesn't have the sufficient resolution to work with such short pulse-widths then the only logical alternative IMHO is smaller injectors. I think Mike's dillema is that he's adding forced induction, so he will probably need to keep the large injectors. It's almost a cake-and-eat-it situation. Hopefully his Link system will be able to work with the very-short pulse-widths at idle. I'm guessing it will since the Link is very popular with the WRX tuners.

-Ben M.

[Dave_Darling]

Mike, I recall reading on the Rennlist a year or so ago that you can probably drop the fuel pressure by up to 5 PSI and still have a half-decent spray pattern.

For what that's worth.

--DD

[airsix]

QUOTE (Dave_Darling @ Jun 14 2005, 09:00 AM)

Mike, I recall reading on the Rennlist a year or so ago that you can probably drop the fuel pressure by up to 5 PSI and still have a half-decent spray pattern. For what that's worth. --DD

That's what I was talking about earlier. When I put a boost-port on my fuel pressure regulator the result was linear pressure increase equal to boost pressure, but at idle the vacuum pulls the pressure down about 5 psi. from where it runs when vacuum is low or neutral. Tuning the PEFI for the fuel-pressure change was very easy and only took a minute or two since only idle mixuture was affected.

-Ben M.

[lapuwali]

The idea here basically being to try to keep the fuel pressure across the injector constant. With a fixed reference FPR, pressure across the injector goes DOWN as the manifold pressure rises, which is the opposite of what you want to happen. With only 2 bar of pressure to start with, at WOT, the pressure across the injector is only 1 bar. With a rising rate FPR, you can keep the pressure at 2 bar from idle to WOT. This flattens the pulsewidth curve substantially, raising it at idle and lowering it at WOT, so you can run longer pulsewidths at idle, and have more headroom for a richer mixture at WOT.

In a turbo application, this would be pretty close to necessary, as there'd be almost no way you'd get the necessary dynamic range out of a single set of injectors for off-boost idle to on-boost WOT.