Modern injectors, new fuel rail - no heat soak problem

[AK260]

Not sure that a carb setup would be a direct comparison, however that is good to note. I'm not likely to be buying a new aluminum rad yet, as I will need to reverse the rad flow / hose locations when I do the VQ35DE conversion.
 
Edit - just noticed you are in Surrey. I was born & lived in Kingston-Upon-Thames until I was 10, after that we moved around various countries. Where are you?

Small world. I’m on Oxted - JCT6 of M25!


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[HusseinHolland]

7 hours ago, AK260 said:

Small world. I’m on Oxted - JCT6 of M25!


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One of my sisters lives in Tunbridge Wells - so you are about 1/2 way between the two

[AK260]

Very small world! 😉

[HusseinHolland]

On 11/13/2023 at 9:13 PM, Zed Head said:

Those 712's are high impedance.  You'll want to remove the dropping resistors, I'd guess.  Although I ran high impedance on my engine and they worked fine either way.  Looks like you might be a hair rich with those.  Good luck.

@Zed Head - just to revisit this - you left the injector ballast pack in place, and ran with high imp. injectors for an extended period? Can't find any definitive on line info on leaving the system this way. I don't want to run into issues down the road due to the reduced current to the injectors. It certainly starts (shorter crank time) & runs much better with this setup. No sign of heat soak, however I'm still going to make an additional heat shield to protect the composite injectors. The only reason I am reticent to touch them is potential need for re-wiring that end of the harness due to the age & exposure of the terminals/housings (if it ain't broke, don't fix it)

Edited November 16, 2023 by HusseinHolland

[Zed Head]

I did.  When I first put the system together I left the resistors in place as I tested it.  Then I removed them and jumped the wires, just because.  Then I think that I put them back just in case a future owner wanted to swap back to the original setup.

I thought about the possibility of low current causing delayed opening times but decided that the EFI system is so crude that it probably didn't matter.  It's a semi-batch fire system with no O2 sensor trimming.  It just squirts a gob of fuel every rotation to all cylinders at the same time.

But, with your AFR gauge you could easily run a simple test.  Extra resistance won't hurt the ECU.  Worst case you see some leaning at idle, where injector open duration is lowest and delayed opening time might have an impact.

[HusseinHolland]

1 hour ago, Zed Head said:

I did.  When I first put the system together I left the resistors in place as I tested it.  Then I removed them and jumped the wires, just because.  Then I think that I put them back just in case a future owner wanted to swap back to the original setup.

I thought about the possibility of low current causing delayed opening times but decided that the EFI system is so crude that it probably didn't matter.  It's a semi-batch fire system with no O2 sensor trimming.  It just squirts a gob of fuel every rotation to all cylinders at the same time.

But, with your AFR gauge you could easily run a simple test.  Extra resistance won't hurt the ECU.  Worst case you see some leaning at idle, where injector open duration is lowest and delayed opening time might have an impact.

Thanks for the input - I do actually see a little leaner idle once the engine is fully warmed (15.7 range instead of 14.7) when idling after a drive. I can always adjust the potentiometer to compensate, but then it's not a hands-free system. I guess I will make a jumper for the two connectors & see if it changes that aspect. Otherwise, I don't see any reason to alter it, it feels much smoother overall, and as mentioned, the hot or cold crank times are MUCH better with this setup than the old.

Edited November 16, 2023 by HusseinHolland

[Captain Obvious]

I'm thinking that the higher the injector impedence is, the less impact the dropping resistors will have. What's the static resistance of the new injectors? In other words, if you put an Ohmeter across the new injectors and then do the same with the old, what are the resistances at DC? 

That dropping resistors would still be in series in the circuit with the "high impedence" injectors, but depending on the resistances, they may be overshadowed by the resistance of the injectors themselves. Voltage divider and all that.

For example... If the dropping resistors are 1 Ohm and the injectors are 100 Ohm, it won't really matter whether they are included or not.  That may be why you guys aren't seeing much of an impact whether the dropping resistors are installed or bypassed.

[HusseinHolland]

11 minutes ago, Captain Obvious said:

I'm thinking that the higher the injector impedance is, the less impact the dropping resistors will have. What's the static resistance of the new injectors? In other words, if you put an Ohmmeter across the new injectors and then do the same with the old, what are the resistances at DC? 

That dropping resistors would still be in series in the circuit with the "high impedance" injectors, but depending on the resistances, they may be overshadowed by the resistance of the injectors themselves. Voltage divider and all that.

For example... If the dropping resistors are 1 Ohm and the injectors are 100 Ohm, it won't really matter whether they are included or not.  That may be why you guys aren't seeing much of an impact whether the dropping resistors are installed or bypassed.

Good thoughts there. I can easily measure the two sets of injectors & note the resistance values. As with the Clock thread, I always get ker-fuddled when doing the math on resistance values, although in this case it would simply be addition, since the ballast & injector are in series, not parallel. Then use Ohm's Law to figure out the Voltage or Current passing?

 

EDIT  -I was just looking in the service manual, it doesn't actually give a test value for the resistor, just whether there is a voltage continuity in each individual injector circuit.

Edited November 16, 2023 by HusseinHolland

[Zed Head]

29 minutes ago, HusseinHolland said:

Thanks for the input - I do actually see a little leaner idle once the engine is fully warmed (15.7 range instead of 14.7) when idling after a drive

Leaner with the new injectors or with and without the resistors, same injectors?

I think that you'd need to do a one-to-one comparison as far conditions to really know.  Engine temperature, air temperature, etc.  With and without resistors.  Otherwise it's just conjecture. 

[Zed Head]

Aren't we comparing  about 16 + 6, to 16?   22 to 16.  I just pulled those numbers from memory, the more precise numbers are out there somewhere.

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Edited November 16, 2023 by Zed Head
+?

[HusseinHolland]

On 11/16/2023 at 1:33 PM, Zed Head said:

Leaner with the new injectors or with and without the resistors, same injectors?

I think that you'd need to do a one-to-one comparison as far conditions to really know.  Engine temperature, air temperature, etc.  With and without resistors.  Otherwise it's just conjecture. 

Just to come back to this - I was referring to the new injectors & rail with the stock ballasts. I haven't played around with combinations.

I did find that the lean warm idle I have been seeing the past few days was actually due to my cutting 2 of the lower injector seals upon installation. I'll put the details in my engine bay fuel thread.

[Captain Obvious]

On 11/16/2023 at 1:07 PM, HusseinHolland said:

I can easily measure the two sets of injectors & note the resistance values.

EDIT  -I was just looking in the service manual, it doesn't actually give a test value for the resistor, just whether there is a voltage continuity in each individual injector circuit.

Page EF-56 of the 76 Manual says the dropping resistors should be 6 Ohms. I have not measured anything to verify.

And I didn't find a spec for the injectors, but I measured a couple here and came up with about 2.4 Ohms. No accounting for the absolute accuracy (or inacuracy) of my meter, but that's what I got.

Do you know the resistance of the high impedance injectors you are using?