Injector dead time and pulsewidth

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craig903
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ECU Model: S80 Pro
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Injector dead time and pulsewidth

Post by craig903 »

Hi, I'm having a few issues and have a few questions.

I'm using a dta s80 ecu, Alpha N setup and I've been running around on a base map for a while to put some mileage on my car before going on a dyno. I've been trying to get a steady idle and I've succeeded to a point. She idles around 1050 rpm but fluctuates 50rpm up and down. Recently I've noticed that when coming to a stop the afr's are running into the 17's/18's just before idle rpm is reached. Fuel cut is off. I've now pinpointed that the issue lies on the pulse width. Siemens deka 630cc injectors. on idle the manifold vacuum is around 0.30/0.40 kpa. when coming to a stop the vacuum is reaching 0.30 and with the map compensations its lowering the pulse width down to a final pulse which varies between 1.1-1.5(including dead time and other compensations) and my injectors can't cope that low. generally around idle it seems to be good at 1.55ms pulse. When temperature compensations come to play ie sitting in a carpark this lowers the pulse further and then I get rough idle with lean air/fuel ratio, again 17's/18's

I've generally been aiming for 14-14.7 for idle, If I aim richer this should increase the pulse width on idle, my question being what AFR should I be happy running on idle and what would be classed as too low, and should I say reduce timing down to 5 degree's on idle, which should mean less power, so needing more fuel/air to maintain idle rpm?

I've been trying to dial in the dead time aswell but every time I try I'm getting different results. I have lambda control and battery comps off but every time using the test i'm getting different results. Light throttle and I can run the test and lambda may fluctuate a little ie 0.2 and then other times it could be from 14 down to mid 12's Siemens deka 630cc long with the minitimer plug



thanks
Rob Stevens
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Re: Injector dead time and pulsewidth

Post by Rob Stevens »

Is it a big power motor to need those injectors?
I run about 2 degrees at idel on my k series to get good auto idle control, so less than 5 will be fine. Is there any chance your TBs are not always settling the same and you have a good air flow to each at idle. I've got those injectors on one motor set at .7ms I think
Rob Stevens
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Re: Injector dead time and pulsewidth

Post by Rob Stevens »

I target 0.99 lambda at idle
stevieturbo
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Re: Injector dead time and pulsewidth

Post by stevieturbo »

Turn off all closed loops and idle control.

Tune so idle, fuel and timing are all static at say around 1050/1100rpm. This way there should be no fluctuations from any of those aspects. With timing say around 15-20deg...again, static. Adjust throttle opening to achieve this speed.

Then with idle control on ( timing ), it should easily be able to pull the rpm down a bit.

But 630cc injectors arent overly big at all, and they do spray well. Batch or sequential ?

Ultimately, if you are not concerned about emissions, then just give the engine whatever fuel it wants to achieve the idle you want ( without going daft like say 11:1 AFR )

It'll probably be stronger in the 13-14 range than it will higher than 14.

Of course any ability to idle will be affected by many factors, so it is just a case of playing with it and see what it wants. But starting with lots of static values removes variables, letting you change one at a time to see how it affects the idle.
craig903
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Joined: Mon Apr 03, 2017 12:45 pm
ECU Model: S80 Pro
Distributor: ebay
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Re: Injector dead time and pulsewidth

Post by craig903 »

So I'm running 4 cyl low compression 8:1 with a gt30 turbo want to see 400+. Alpha N with pressure compensation, batch ignition. I thought the issue may be related to the big bosch idle valve so I've just swapped everything over to using Ignition advance and issue still existed. This is when I traced it down to the actual pulse width being too small. 1.5 is the minimum required from a datasheet I have. and 1.55 seems to be the average pulse being sent when hot. @ 40kpa but in some situations its pulling down to 30kpa and this is where the extra 10% from the manifold compensations is pulling fuel and reducing the pulse width down and then the afr's go amiss dramatically into the 17's/18's and sounds like its a cylinder or two down.
stevieturbo
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Re: Injector dead time and pulsewidth

Post by stevieturbo »

That's crazy low compression these days for only 400hp

And batch fire or sequential ? Sequential may help

But really...630cc injectors are not big at all, and if they are genuine Siemens or whatever make, should idle very well.

Have you guessed the dead time values or used the calculator/test feature ? Or plucked numbers from online ?

And I dislike using TPS as main load with boost, even if some like it.

It adds complication for no good reason in most cases. MAP vs RPM is far simpler.
katana
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Re: Injector dead time and pulsewidth

Post by katana »

What about lowering your FP, say, 0.25 bar then raise the whole map by 8.5% ? The FP will appreciate that when on boost as well!
stevieturbo
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Re: Injector dead time and pulsewidth

Post by stevieturbo »

He hasnt stated what FP he is running, and lower doesnt always help, as it can make any spray pattern worse.

There shouldnt be a problem with good quality 630cc injectors, unless it's a very very small engine or something
Alex DTA
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Re: Injector dead time and pulsewidth

Post by Alex DTA »

400 bhp with a GT30 would put it in the 2L engine capacity region.
If you are getting down to 1.5 ms total pulse width including dead time, that leaves about 0.8 ms injector opening time.
There should be no problem with that. I run 900cc with that opening time on my 2L.

Get your injectors tested to make sure they are genuine, and not clogged.
craig903
Posts: 18
Joined: Mon Apr 03, 2017 12:45 pm
ECU Model: S80 Pro
Distributor: ebay
Firmware Version: 73.01

Re: Injector dead time and pulsewidth

Post by craig903 »

Injectors are new Siemens deka and baught from a reputable place which was suggested from a tuning company.

Blocked injectors I would presume I would have to give a higher pulse.3 bar fuel pressure.

2ltr engine , it's happy idling at 1050 +-50rpm @ 1.55ms pulse there abouts. it's just situations where the vacuum gets to 0.3 and lower from let's say quick open and close of the throttle. I've had it where the compensations have baught the pulse down to 1.12ms including dead time and then yeah sounds like it's starting to miss fire. Like I said injector info states 1.5ms minimum pulse for the injectors.

I have a 3kg flywheel and lightened crank pulley and low comp so its easier to rev then a standered engine which doesn't help. Just need to fiddle and find a way of giving it more fuel. I'm going to try a 0.92 idle and see if that's better
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