liquidus

Okay, so I got an RB20 project car. It has a tough time starting up and runs super lean (18:1+). If I unplug the MAF, the car starts right up, runs at 11:1 (the car came with larger injectors).

So, my first thought was bad MAF. My cousin had an RB25 MAF, and after looking online they seemed to be the same. Tried it and had the exact same problem.

Next I looked at my SAFC under the sensor check screen, and saw that at idle the MAF was sending about 1.1V, and if I pressed the gas a bit it goes up to 2+V (I don't dare press the gas to much at this A/F ratio). This seems to indicate the the MAF is functioning properly.

Thinking that the SAFC may be causing a problem, I disconnected it from it's plug, and jumped the white and yellow wires on the plug, so that the MAF signal would go straight to the ECU, instead of going to the SAFC for modification. Doesn't fix it.

My boost gauge shows about -17, so I don't think there are any vacuum leaks, and to be sure there were no leaks in front of the throttle, I connected the MAF directly to the first bend coming out of the throttle body, bypassing the turbo, bov, FMIC, and all couplers. Still runs ultra lean.

Now I'm starting to run out of ideas. If I max out the amount of fuel I can add with the SAFC, I can get it to idle at about 15:1, but if I press the gas at all it goes back up. Something is definitely wrong here.

Please help!

JSimpson

If i had to guess... I'd say the car got an ecu tuned for the bigger injectors somewhere along the line. Rb20s stock usually run pig rich.

Sileighty_85

check for leaks After the MAF on the rubber intake pipe to the turbo

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liquidus

@Sileighty85 I have checked pretty diligently for leaks, by inspecting tubes and by spraying carb cleaner. Also, I did hook the MAF up at the first bend of the pipe coming out of the throttle body, bypassing the turbo, FMIC, BOV, etc, so I'm pretty confident it's not that.

Also, I've done some more work. From inspection it seems like the injectors are actually stock, despite the fact that I was lead to believe they were much larger. It was pretty dumb for me to not check this earlier.

I've searched for the number on the injector but came up with zero results. They have a red ring facing out and say 5L31 2108, with a little nissan symbol outline in between the 5L31 and the 2180. If anyone can confirm what injectors these are I would greatly appreciate it.

I also got a fuel pressure tester and am seeing around 40psi, so it's not the fuel pump/lines.

Based on this info here is what I am thinking:

1. The injectors are wired wrong? The fact that it idles so well with no MAF, and that by adding fuel with the SAFC with the MAF on I can get the A/F to 15:1, seems to indicate that this isn't true, but I'm not sure on this though, please let me know.

2. This ECU has fuel maps for larger injectors? If these are in fact stock RB20DET stock injectors, maybe the ECU has fuel maps for larger ones, causing the lean A/F. Unfortunately, I have no idea how to test for this.

3. The injectors are N/A RB or KA injectors? Since I haven't been able to confirm the number on the injectors, and that I think that this engine used to have larger injectors, is it possible the injectors were replaced by ones that are too small? Not sure here either.

Based on this info, what do you guys think. If you can help me test/rule out any of these, I would really appreciate it.

Thanks,
Rob

JSimpson

Just run the bigger injectors the car came with...