No idea why my car keeps killing injectors

[180sxdan]

Near the start of the year I went from stock 370cc injectors to a set of Nismo 740cc's for my S13 SR20DET.
About 2 months ago I noticed my wideband was reading full rich and I found cylinders 2 and 4 were running very rich based on the spark plugs. Swapping injectors around cylinders moved the problem so I know they were the fault.
So I bought 2 new injectors from japan put them in and again they ran fine for a month at least. Now I've just finished putting in a new turbocharger, I go to check my wideband and again I'm getting full rich so I check my spark plugs again and find both 2 and 4 are very rich even though the bad injectors were replaced previously.

I have no idea what could be causing this other than maybe some sort of electrical problem, my ECU is a Haltech E6X if it makes any difference, but I don't understand why it was never an issue with the stock injectors but these Nismo's aren't working well at all. If anyone has any info or help at all I'd really appreciate it, this is a problem I'd like to fix very soon as it's my daily driver and I have no idea where to start.

Cheers.

[Hijacker]

Do you happen to know what your fuel pressure is?

It's an odd problem for sure. I would also double check that you're not overdrawing current on the injectors as well as ensuring the voltage isn't going over 12 V by too terribly much.

Also, make sure the injectors are testing between 10 and 14 ohms. Brand new, they should be around 11 ohms.

[180sxdan]

I don't have a fuel pressure gauge so unfortunately I don't, my pump is a walbro 255lph I believe, and I would think if fuel pressure was an issue it wouldn't be cylinder specific. But just incase my fuel filter is also fairly new replaced only a couple of months ago.

I did check resistance across all 4 injectors last time when I noticed 2 were getting stuck open and I remember they were all the same resistance. I'm not sure exactly what resistance they were as I can't remember but 11 ohms sounds about right and none of them stood out as having an odd value, they were definitely within the range you've specified.

Are you saying to check voltage at each individual injector when the car is running? For current draw I would have to get a meter to run in series with the injector so I'm not sure how I'd measure that.

[blkvrtswp]

You could give Wiring Specialties a call - they might have some good advice. I'm sure they have seen some odd problems!

[Hijacker]

You don't need the car running to check voltage at the plugs. There's a hot wire that stays hot all the time, and the ECU grounds the injectors when it's time to spray fuel. So you can leave the car turned off and just check the hot wire with ground and see what you get. It should be battery voltage. I would also double check with the car running what the voltage of that line is just to be certain it's staying around battery voltage (my guess is yes, otherwise the alt regulator is going bad, and you'd have other problems surrounding that). Each injector should be fed off the same hot wire.

To check current, run a jumper for one pin of the plug to the injector and bridge the other connector with your DMM. You're checking to see if an overcurrent draw is happening on those two cylinders. I would definitely check all four injectors so you can compare the two problem children.

Since you have two injectors that aren't dying, my guess is that maybe you've had bad luck with duds. The service manual only has you check the voltage, resistance of the injector, and ensure you have good continuity. It doesn't have you check current, but it's the last thing I can think of that would kill 2 out of 4 and it's consistent. If you do notice a larger draw on those two circuits, I'd start tracing wires from the injectors to the ECU and make sure there isn't a short to a hot wire somewhere.

I'm hesitant to blame the Haltech since you said the previously failed injectors weren't dependent on the cylinder they were placed in to run rich. If the ECU was at fault, I'd imagine that it would be a fuel timing issue and the running rich wouldn't follow the injectors.

My worst case I can think of is that you get two new injectors, but swap them into 1 and 3, and put your old, operating properly injectors in 2 and 4 and see if the problem occurs again. But that's kind of an expensive diagnostic test.

[PapaSmurf2k3]

Also make sure your fuel filter isn't garbage and letting trash get through to clog your injectors.

...but if you said the resistance of the bad ones was different than the good ones, then you're probably right that its purely electrical. You don't have some kind of acid or corrosion on the mating connectors do you?

[180sxdan]

I just checked resistance across all 4 injectors and they all read 11.4-5 ohms, voltage at all of them is 12.7V with the car off which is the same as the battery. Voltage when running is 14.6 on all of them with battery voltage at 14.2-3.

I also checked resistance between injectors at the ECU connector and got 23 ohms between all of them, ofcourse because 11.5*2=23 and I'm essentially measuring between 2 injectors plugged in.

I haven't checked current draw yet but I plan on it soon.

[180sxdan]

With the same voltage and resistance I'm inclined to believe the current draw will be the same but I will check to confirm tomorrow once i make up a couple of wires to run in series with the injector and a multimeter which can measure current around 1A.

The purpose of checking resistance across the wires from the ECU was to see if there was a short anywhere along the wires. I also checked there's 0 ohms between all the injectors and both the 12v supply and ground pins. Because all injectors read the same values I would say theres no problems there.

I'm just curious if anyone has any idea if a mechanical problem could cause this issue.

[180sxdan]

ok I checked current draw of cylinders 1 and 2, both were 80mA at idle when the car just turned on. Now remember my issue is with cyl 2 and 4 so I was able to test a cylinder without the problem (1) and a cylinder with it (2). Since they were the same I'm confident the rest would be too.

Unfortunately when I went to test the next cylinder my Eng Cont fuse blew, something must've shorted with the ammeter as the connections weren't very stable so now obviously the car won't start without that fuse in as the injector live wire is only at 3.6V. I know this in fact because there's an identical fuse next to it rated the same, I swapped it in and the injectors get their usual 12.5V with the car off however I have not started it like this yet and would like to get another fuse before I do.

Anyway in addition I used an insulation tester across all injector signal wires to ground with the ECU unplugged and there was no sign of a short. I checked resistance between the live wires and ground which gave 21 mega ohms for all.

Something worth noting aswell is my ECU seems to forget its base map after a while of daily driving, sometimes when I get on it I notice the maps set to default and I have to load mine again on there.