Last Updated: 09/23/2025 @ 07:29 am
Credit: Ahmed H.
This is something I posted in another group. Here is a small informative write up on something I ran into little while back.
Here are two different GTR injectors. One is claimed to be as “remanufactured GTR injector” and the other one is as real GTR fuel injector that I removed from a customers car.
As a tuner we often have cars brought in and deal with different brands of fuel injectors which is fine as long as the injectors are consistent across the board and it is incredibly helpful if they are normally supplied with a data sheet. Such as flow matching, minimal injector pulse with, fuel injector dead time, injector PW compensation, pressure differential dead time etc.
This customer asked me to tune their G37 with “reman” GTR injectors but I had requested that I would see them prior to installing them.
Just looking them over, you can clearly tell which one is the fake “GTR” injector. The molding is different, the brand logo is slightly off, the area where the Oring sits is very off, the spray pattern cap isn’t drilled at the correct angle, and what really gave it away as soon as I took it out of the box was the electrical terminals and connector.
So why is it important to run a known matched/reputable set of injectors? For many reasons, but one of which is drivability. As a tuner, we can tune a set of injectors on the dyno, to try to give you as much of the OEM drivability and consistency as possible. But with low quality fuel injector, you will end up with sporadic drivability after the car is off the dyno and in real world driving conditions. Some of the issues that can be encountered with knock offs are fuel trims will constantly change (sporadic), check engine light DTC, power loss, misfires, lean conditions, per cylinder fueling will be off etc. the list of issues can be very long.
Couple of the reasons for these knock off parts causes these issues is their inconsistency of performance due to voltage change, temperatures change, and being closely flow matched at low injector duty cycle such as idle, light throttle, cruising conditions, etc.
Here’s an example: let’s say at idles, your engine needs 2 milliseconds worth of fueling. Your tuner has input all the right data for the injector on the dyno. After getting the engine warmed up, now your tuner will adjusts the fuel table to get a good idles and stable fuel trims.
Let’s also say you bought the knock off injectors you were warned not to buy. Looking at the data, you’re idling at 2 milli seconds when the engine is warm. You drive the car home, next morning you start the car and it cranks for a while before it starts then after it starts you get weird misfires. Knock injectors can easily change in operation by .5 milliseconds. Doesn’t sound like much but that 25% of your fueling at idle. Things get works when you turn on the A/C, radio, and defroster.
The cars ECU can usually accommodate up to 25% of fueling at low loads, but will worsen as voltage changes and engine operating temperature changes. The reason is the injectors are performing different at different temperatures. This is why OEM and quality brands spend so much time developing their injectors. to give you that optimal consistent cold start, hot start, idle, drivability etc.
Just remember, the reason your car has poor drivability is probably because of your knock offs injectors, not necessarily your tuners fault.
The fueling will be much closer to target fueling under WOT as this .5 milliseconds becomes a much smaller percentage and less noticeable. This is something to look into if your car only runs great at WOT and nowhere else.
Hope this helps saves you from having to deal with a future hassle. P.S. of course Fb took a lot of the resolution away from these pics. Also, the real injector is on the left of you have noticed.
Cheers!
Fake
Real
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