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High v's Low Impedance injectors

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Hi All,

I'm having issues getting my newly build set up to run. I have built a sister car /engine combo to a mate's, it's a TA22 Celica with a 4age 20v turbo - build thread here (http://performanceforums.com/forums/showthread.php?67301392-My-TA22-Celica-track-race-car-4AGTE-20v-powered)

The engine/car is almost completely identical and shares the following components:

- Compression ratio (9:1)

- Capacity (both 0.5mm oversize)

- Cylinder head (mildly ported Silvertop head)

- Cam shafts (Std Silvertop)

- Throttles & intake plenum (Silvertop throttles w/ GTIR plenum)

- Fuel pump (Bosch 044)

- Fuel pressure regulator (Turbosmart)

- Fuel system (10mm fuel lines, return style system, surge tank, etc)

- Turbo (GT28)

- ECU (Wolf 3D v4)

- Wiring loom (to/from the ecu is identical)

So, as you can see the car is near on identical, the only thing not identical is the injectors. He runs 2JZ 440cc high impedance injectors, and i run 3SGTE 440cc low impedance injectors. The ECU supports both high and low impedance injectors, hence why i didn't think much of using different injectors on the sister car.

I loaded his map onto my ECU and the thing starts, however it runs like a dog. i can get it to idle however when the throttle is touched the thing craps itself and hesitates. I pulled the plugs and found them to be black and sooty. The real funny thing is my LM-2 wideband says it's running lean, like 20:1 when i touch the throttle. I think it needs a new sensor and/or calibration because the spark plugs say it's running rich.

Would the difference in high/low impedance make the actual injector open/close time (at the nozzle) different, if the signal pulse width from the ECU is the same - e.g. if i sent a 2.0ms pulse to both injectors, would one flow more/less?

If there is a difference, so i add or subtract pulse width at the ECU to get the fueling close? I have the dyno booked in 3 days and i want the thing running and able to drive onto the dyno.

Is there anything i should look for? The motor is totally new, and hasn't had the rings bedded in as yet. I'm simply trying to get it to a running state.

Thanks,

Dave.

With older generation injectors the low impedance design was implemented to help improve response or latency. This needed to be coupled with a peak & hold injector driver that allowed the current to the injector to be controlled accurately. Ultimately if your ECU is able to correctly control a low impedance injector then there should be minimal difference. The latency values between the two sets of injectors will almost certainly be different though which needs to be accounted for.

What you're explaining doesn't quite add up. Provided the injectors are all clean and flowing evenly I would only expect a relatively small difference between the maps for a high and low impedance injector (assuming the actual flow rates do really match). I would be confirming everything in the mechanical package first - Cam timing, base ignition timing etc

Hi Andre,

Thanks for the reply. Yes something is not right in the set up. I will double check all the basics, throw a new set of plugs in and then start playing with the tune again.

I found some info on the net about the two different injectors from this site (http://paulr33.com/powerfc-faq/inj_side-en.htm):

My mate's tune is for the #17 injector, Denso # 23250-4604 (2JZ-GTE), 14.2Ohms, 0.97ms "invalid injection time", 470cc @ 3.05bar

My injectors are the #14 injector, Denso # 23250-74090 (3S-GTE), 3.3Ohms, 0.55ms "invalid injection time", 455cc @ 3.05bar

Is there anything alarming about the difference in the "invalid injection time". I'm not too concerned with the slight difference in flow, as that's easily adjusted. I don't know a whole heap about injectors.

Thanks,

Dave

By 'Invalid Injection Time' I'll assume the guy means latency. Listing a single value will again make me assume that this is measured at 14V but that's a bunch of assumptions.I'd be a little wary of those values anyway as for the #14 injector, the latency appears to barely change as the fuel pressure is increased - This doesn't match reality.

That being said, provided the data is remotely accurate, it shows the #17 injector's latency is getting on towards double that of the #14 injector. If this isn't accounted for in the tune, it will have an impact on the fuel delivery regardless which way you are swapping injectors.

Thanks again for the reply Andre.

I have a feeling my low impedence injectors are much more responsive and dumping way more fuel in given the same pulse length from the ecu. The fuel pressures are the same and i've taken the overall trim from 48% down to 15% and the mixtures are coming down from way rich to about right. Got it to idle with a little throttle input at 1200rpm and 14.7:1 AFR. I can slowely bring the revs up with the throttle and get it to run cleanly. I think it's heading in the right direction.

I think the fouling is now due to the throttle pump (acceleration enrichment) being completely out, throwing in way too much fuel with the throttle is opened.I have another question regarding transient tuning, but i'll post in the course specific area.

Cheers

Glad to hear you are getting on top of the tune. Keep up the good work!