RB20 Lean with MAF

[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!

[Yellow4g63]

Are the injectors stock? do you have a FPR on it?

[Sil240]

Hey,

Sucks to hear.
I think the output in the ecu was fried.
I got a new harness and had CarlH from Blackbox tuning wire it for me and it was plug and play.
The dbag who wired it for me the first time majorly focked meand he probably fried that part of my ecu's (4). Don't put another ecu on your harness.

Contact Carlh

Good luck bro!!!
Hope it works out for you

[Liquidus]

Okay, so 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 kinda 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 the idles so well with no MAF, and that by adding fuel with the SAFC I can get the A/F to 15:1, seems to indicate that this isn't true, but I though I remembered reading that in limp mode the ecu fires all the injectors simultaneously. 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

[Yellow4g63]

stock RB20 injectors are 270cc which should be the same size as the KA with top feed injectors. I think the stock RB20 injector is red in color (can't rem since I upgraded). You need a consult cable and nissan datascan or one of the other free consult programs to pull the bin from the ecu so you can see if it's modified. If you have a chip burner you could just open up the ecu and see if it's been chipped. If it idles better with the maf unplugged then the prob could be the maf, unplugging the maf loads a limp mode program into the computer.

[placham]

Yep 5L31 3210 is stock RB20 injectors. got a set sitting right here that came out of my 20. 5L31 is part#
get DJ50 2415d those are stock RB26 injectors 444cc should probably help out with AFR, but you'll need resistor pack. DJ50 part#
What ever injectors you get you should retune your ECU just in case, unless you know what its exactly tuned for.
By the way 444c Rb26 are a drop in with minor mod to injector harness, also Denso/Greddy will work, out of many out there.

But try what was posted earlier first.

[Liquidus]

Thanks for the reply guys. It's not the MAF itself, I've tried two different MAFs, and I've also watched the voltage they both send using my SAFC's sensor check screen, so the MAF itself works.

On confirming the part #'s, mine say 5L31 2108, and you said the stock rb20 injectors are 5L31 3210. That's a different second number, are you sure they're the same?

I'm wondering if it could be a bad o2 sensor, if unplugging the MAF puts it into limp mode, it probably stops worrying about the stock o2 sensor. So I'm gonna try that next. As far as getting a CONSULT cable, I've seen some on ebay, but I'm not really sure if those are legit or not. If you can give me any info on a good place to get that I would appreciate it.

Thanks,
Rob

[placham]

Their the same as long as the first number is 5L31-**** , which could be 5L31-2108 or 5L31-3210.
Last set of numbers is batch number first set is model number.

And to clarify GTR injectors are 0j50 not Dj50 like I posted above, sorry for that. Looked at it wrong.

I was thinking O2 too, since u unplug MAF throws it into limp and goes into "open loop mode", but apparently underload ecu kicks out of "closed loop mode", it only runs under cruise (And I think idle) in "closed loop mode". So ether way u should see some change in AFR if the 02 is bad.

Matt.

[Liquidus]

Thanks for clearing that up for me. I couldn't believe that googling that number didn't come up with anything. I really appreciate the info. I'm going to check the o2 sensor next. After that it's down to the ecu or wiring.

I'll do some more testing tomorrow and get back to you, thanks again!

-Rob

[Liquidus]

Swapped out the o2 for an RB25 o2 sensor. I read that they were the same sensor, just different length wire coming out of it. Doesn't fix it. Considering it runs 11:1 with no MAF, is it even possible it's the fuel injectors themselves, or does the 11:1 w/ no MAF eliminate that.

Thanks,
Rob

[Yellow4g63]

Did you pull any codes from the ecu?

[Liquidus]

I actually just went and pulled codes from the ECU just now. It's throwing code 12, bad MAF. This doesn't make sense though. Does the ECU store codes until you manually reset it? As I said I did unplug the MAF, but when I put the ECU into mode 3 it was plugged in. Doesn't seem to make sense....

When I was doing this, I evidently messed something up, because now when I try and start the car it makes really fast clicking noises and the wipers turn themselves on.

Evidently I shorted some wires together or something?

So now:

1. Does the ECU store error codes from when I unplugged the MAF in the past.
2. What could I have done to make the car not start, click really loud and fast, and to make the wipers turn themselves on.

Thanks,
Rob

[Yellow4g63]

Yes it will have the code from the maf been unplugged stored in there.

[Liquidus]

Okay, that makes sense then. However, the not starting, fast clicking, self activated wipers.....No idea. Maybe I shorted something out? idk....

[Yellow4g63]

sounds like a short.

[Liquidus]

Okay, so the short is sorted. Reset the ECU and checked for codes, showed 55, all good.

I found a thread online about a similar problem, and the solution ended up being that the aftermarket air filter caused strange airflow/turbulence, causing the MAF to read improperly. Thinking it was a long shot, but worth a try, I took off my aftermarket air filter/intake thing. Then, I put my KA air filter up to it. I couldn't make it fit in there quite right, but I got it hooked up well enough.

Imagine my surprise when the A/F went to around 13~15. I'm thinking the MAF is hooked up too close to the turbo and/or too close to this big aftermarket intake/filter thing, causing turbulent air and an incorrect measurement by the MAF. As you can hopefully see from this pic, there's a small bend out of the turbo, then the MAF, then the filter. I'm thinking that is the problem.

Is this a decent possibility. It certainly seems like it to me. Anyone have a similar experience?

[Yellow4g63]

Wish I could help but I don't have any pics of how long the stock intake tube is.

[Liquidus]

Awesome, thanks guys. That seems to validate my idea. Considering the current piping for the front mount, it's gonna take a bit of work to get the piping right to move the MAF farther away, and I'm going to use a different air filter. I'll post my results once I get it taken care of.