Peak 'n' Hold 1227749

Last night I swapped my high Z injectors for low Z injectors (32 to 42 lbs/hr). It was too late, or too early to actually start the car (1:30 AM), and didn't want to piss off my neighbours. So this morning I tried it, and not good results, It was as if half the injectors were not firing.


When I swapped the injectors, I swapped in my modified ECM, that I installed .07 ohm sense resistors, and the jumpers as per the Sunbird wiring. I removed the two grounds for saturated injector driving. I did have the injector grounds wired as a '7730 in pins D6 and D7. It has been this way for 4 years. The Sy/Ty shows pins D6 and C13 for injector grounds.




Anyway, really lean, running rough, tried a few changes to the BPC, and no change in the way the engine was running.




So I decided to switch it back to saturated mode (leaving the low-Z injectors in place, as a test). While the engine idles fine, I can not drive it, it goes really lean with load, no boost, just simple accel.


This was on a good running bin with the smaller injectors and the only change is to the BPC vs EGR table to account for the larger injector size.




Is there anything besides, the jumpers needed to switch between saturated and peak and hold injector firing modes?




I used the ideas here: http://home.comcast.net/~p-928/749mods.html for resistor modification. I did not change the injector driver itself however, since the part number given in that link is a discontinued item and can't find a matching replacement.




Car details:
Nissan 2.8L I6
1227749 ECM Sensose resistor modification for 6 cyl.
Code59 ($59)
Mopar injectors (will get part number later)


I will try swapping back to my old injectors tonight, but I'm looking for ideas.

perhaps the injectors have a vastly different voltage and min pw offset requirements compared to what your calibration is setup for?

Possible, but the problem is more than just incorrect voltage compensation.

Sounds like it must have been a long night.

SYTY drives six high impedance injectors on one driver. SYTY wiring shows injector returns on C11 and C12 which are bridged internally, same as D6 and D7.

Sunbird drives two banks of two low impy injectors. Bank one injector return on C11, jumper from D5 to D6. Bank two injector return on C10, jumper from C13 to C15.

Change wiring and report back.

So I missed the part about the injector driver output at C12 needing to be moved to C10...

I'm in my car warming up with a fairly stable idle and 42 lbs/hr injectors using the peak and hold wiring.

Thanks Shannen, for giving me the kick in the head I needed.

I'll wait for it to warm up then take it for a drive.

So I've gone back to my old high-Z injectors, since it seems that they weren't causing the issue I was experiencing. I was also having a bit of a hard time tuning them out, in the time that I have available to do so, especially without a proper offset table for them.

I have noticed that I needed to move the injector output back from C10 to C12, not sure why, but it is what it is.

So, it is very possible to run 6 low-Z injectors from a '7749, using both drivers and .07 ohm sense resistors (internal modification), wired correctly. The car ran well this way, just needed more time than I have to tune them.

Good to know. I hear ya regarding time...

Achievement unlocked: Thread necromancer...

I recently reinstalled the 42 lbs/hr injectors, this time I gave them more time and attention. After adjusting the injector offsets vs battery voltage, they have a stable idle and work well.

The more I adjust the offset table vs battery voltage the more linear my VE table can get. When I first started with these injectors there was quite the deviation between idle and even cruise cells, but bringing the injector offset table more inline with similar injector offsets I see for other injectors (I can't find a proper table for these exact injectors), the less deviation there is and the easier is is to tune them. My car has NEVER pulled like this, even at higher boost with the 30 lbs/hr injectors. I'm currently at 14 PSIG of boost above 40 MPH.

The other thing I've noticed that the injector offset table seemed to affect was the effectiveness of DFCO. For the last while I had my 30 lbs.hr injectors in and for the first bit with the 42 lbs/hr injectors I had no or little in teh way of DFCO. Usually only seeing a max of low to mid 20 AFR when DFCO was enabled, when I would see up to 99:1 AFR a while ago. (14point7.com WBO2 controllers have a display range of 10.27 to 99:1 AFR). Now that my offset table is coming inline, I am getting up to mid 90s for AFR in DFCO, I love it, I have real DFCO again. Also the transition between DFCO and disabling DFCO is smoother than it was previously.

So what am I trying to say in this post, injector offset vs battery voltage settings is of paramount importance when it comes to port injection, and can effect a lot of parameters in the tune, along with drive-ability.

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So what am I trying to say in this post, injector offset vs battery voltage settings is of paramount importance when it comes to port injection, and can effect a lot of parameters in the tune, along with drive-ability.

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Good to hear you found a path to success. The P&H injector is very sensitive to voltage corrections ime. And the more flow the injector is designed to deliver, the less room there is for error. What will really compound problems is a charging system that provides minimal charging at or just below idle. This combination can cause endless tail chasing.

hey six shorter, I'm tossing around the idea of a 749 sswap onto a car that has stock low z injectors, that I know nothing about. not even flow ratings anywhere I can find haha. what kinda strategy did you use to help dial in the voltage offset?