Injector Latency and Current Draw

[grimreaper]

Few things bouncing around between the ears..

According to the attachment, Stock 440cc injector coils saturate at 2.3-2.4 amps. Theoretically this current would never be reached.
3 ohm resistor pack in series with 2 injectors at 2.9 ohms = Rt 4.45ohm (ideal)
voltage across resistor pack is 9.45v and then 4.56v for the injectors at 14v from alt/batt.
Current It= 3.15a and each injector is seeing roughly 1.58a.

My question is how this current effects aftermarket injectors and latency. RC pl8-550cc's call for 4 amp peak /1.5amp hold and ohm out at 2.9ohms at room temp. Rc tech support said they will work fine with the stock system regardless of the current but did confirm that 4 amps is supposed to be the minimum opening current.

If stock injectors work on a 1.5a peak/.5a hold how would the latency have to be adjusted? thinking increased but current is still limited regardless.

The other option is to change the resistor pack to provide the current the injectors are rated for. Dont know if the ecu drivers can handle more current though.
Maybe im overlooking something, please advise.

 

[Maple191]

The 3 ohms from the resistor pack, is that the resistance of each branch or the total resistance?

 

[Nick M]

The 3 ohms from the resistor pack, is that the resistance of each branch or the total resistance?

http://www.cygnusx1.net/Supra/Library/TEWD/MK3/manual.aspx?S=Main&P=46

 

[Dirgle]

Few things bouncing around between the ears..

According to the attachment, Stock 440cc injector coils saturate at 2.3-2.4 amps. Theoretically this current would never be reached.
3 ohm resistor pack in series with 2 injectors at 2.9 ohms = Rt 4.45ohm (ideal)
voltage across resistor pack is 9.45v and then 4.56v for the injectors at 14v from alt/batt.
Current It= 3.15a and each injector is seeing roughly 1.58a.

My question is how this current effects aftermarket injectors and latency. RC pl8-550cc's call for 4 amp peak /1.5amp hold and ohm out at 2.9ohms at room temp. Rc tech support said they will work fine with the stock system regardless of the current but did confirm that 4 amps is supposed to be the minimum opening current.

If stock injectors work on a 1.5a peak/.5a hold how would the latency have to be adjusted? thinking increased but current is still limited regardless.

The other option is to change the resistor pack to provide the current the injectors are rated for. Dont know if the ecu drivers can handle more current though.
Maybe im overlooking something, please advise.

Interesting questions. I double checked your math and it looks good. A couple curious things. Even though at a baseline fuel pressure(250kpa) the hold amperage is .5a, that is only concerning what the stock injector requires. Whatever the hold amperage allowed from the ECU is, it is probably different. And to be honest I don't think the TCCS uses a peak and hold driver for it's injectors circuits. Even though they are low impedance injectors. I think it's a saturation style driver, as evidenced by the ballast resistor. So this means that the injector would see total current for the duration of the PWM cycle, 1.58a in this case.

Concerning the RC injectors, the amperage number you gave are probably calculated for the max PSI the injectors are designed for. At lower pressures the current requirements are probably lower. And hence why they operate fine on the stock system. Though I haven't seen the data sheet for the injectors so I'm not sure.

And while differences in latency are probably there, the TCCS should have enough room in the fuel trims to compensate for it.

Interesting questions indeed.

 

[Dan_Gyoba]

Some experimentation would be needed on the injector resistor pack.

If the injector resistors are wirewound, which is in fact the most common format for relatively low resistance devices in existence, then it can be assumed that there is a relatively high amount of inductance in the total resistance, and that there would be an inrush current which is higher than that which will stabilize. I suppose I will use that term, as it applies to inductors. In order to measure it, one would need an oscilliscope on the output line, watching amperage as voltage is applied, or I suppose one could recalculate it with an inductance meter.

Alternately, one could disassemble the resistor pack to see how the resistors are formatted, but you'd still need to measure, I suppose.

It wouldn't surprise me to see a "spike" at the front end of the current when the injector signals fire.

 

[jetjock]

The TCCS manuals cover much of this. In a nutshell the injectors on both flavors of 7M are saturated driven, voltage controlled (hence either the resistor pack or high impedance to limit current), and latency is automatically compensated for. It's old school. Current controlled injection is the norm these days and although Toyota had it back in the day it was never deployed on any USDM model.

 

[3p141592654]

And while differences in latency are probably there, the TCCS should have enough room in the fuel trims to compensate for it.

It is tough for the TCCS to compensate for this with a fuel trim. Dean and I have been discussing this offline, but the latency corrections are only done for battery voltage. Since latency is a y-intercept problem, and fuel trim is a slope correction, fuel trim cannot solve the problem properly, but will do its best over the three bands that are compensated for.

The proper correction is to modify the TCCS table for latency, which is where we are going with this.

 

[grimreaper]

Thanks for the replies guys.

Dirgle- I could see the current draw being for a peak pressure situation. What concerns me is that there are several varieties of low resistance injectors that usually fall into a 2.5a peak/.5a hold or 4a peak / 1.5a hold. The common P&H drivers seem to accept a 4:1 ratio for current limiting. So if we swap in aftermarket injectors that are barely reaching their field energy levels, any benefit of P&H is going out the window. It would appear that injectors rated for 2.5a /.5a would be best suited for the stock saturated drivers. All theory though.

Thanks Jetjock, the efi articles spell it out clear as day. Wish they gave up the hard data though.

Attached are the 2 best correlations to the stock drivers data sheets. No luck finding one from NEC but these appear close. The stock drivers should be adequate to handle a higher current but it doesn't appear there is any additional current sensing in the ecu. So A drop in the resistor value would leave the injector coil or driver to handle the constant current in a saturated form. Meaning a lot more heat..

NEC- D1590 K driver, 8 amp continuous, 12 amp pulsed..

I spoke with RC eng. again. Nice enough guys.
Low R PL8(-M)-550cc:
10v - 0.920ms
11v - 0.810ms
12v - 0.680ms
13v - 0.590ms
14v - 0.510ms
15v - 0.400ms

High R 550cc's
10v - 1.070ms
11v - 0.880ms
12v - 0.780ms
13v - 0.670ms
14v - 0.550ms
15v - 0.460ms

Im guessing our latency table for the low r inj will fall in between but much closer to the high r inj. There is also a constant to aid in the latency correction. Guessing that is to cover the expected lag from a saturated driver.

 

[grimreaper]

Im looking into P&H circuits for add ons down the road. Several posts from injector manufactures state that a true P&H driver/low r inj vs a Sat driver/low r inj can have significant effects on fueling. I've seen statements of needing 8-15% less fuel with the P&H drivers due to opening times. A higher resolution is also gained. Trying to find actual test to confirm these statements though.

Any body have access to SAE papers that can share? Looking for the document numbers now..

and to add to what Jon posted, the stock ecu does a good job correcting within its capabilities. When you see the logs and actually look at the data, things are a bit off though. You end up with some reverse fueling errors like to much at idle, not enough up top etc.. Fuel pressure compensations that shouldnt be needed and such. If you wanted to re-tune the whole map to take into account the latency issues you could, but youd be hosed when you turned on the head lights or ac..

 

[grimreaper]

this time with the data sheets

View attachment d1590.pdfView attachment IC-ON-LINE.CN_d1590_614188.pdf

 

[3p141592654]

This is the 7MGE injector driver. Pretty sure the GTE is no different, but will check. It is obviously nothing special.

 

[jetjock]

A Darlington Jon? Really?

 

[grimreaper]

Heres what I found in my stock, 89 grey plug, 7mgte tccs.

Small change in the resistor value for the injector snubber. What is interesting is the TC40H157p. It appears to control the injector signal source. Im guessing the MF166 (ND) is the backup IC in case of a failure in the 64pin Denso(failsafe). Something else I noticed is that 2/3 of the inj circuits connect to the same pin on the MF166(ND) indicating asynchronous injection during failsafe. Have not traced the third inj circuit but would assume its the same.

Datasheets attached for what I could find.
View attachment IC-ON-LINE.CN_td62706p-h_4229440.pdfView attachment TC40H157P.pdf