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!

[compactfean]

What is your fuel pressure at?

[Liquidus]

I hadn't checked the fuel pressure yet because it seemed to run so well with no MAF, but I just talked to a friend on facebook, plus your reply, make me think that I need to start looking into fuel delivery. Will get that done sometime this weekend and will post again. In the mean time if you have any other ideas let me know.

Thanks,
Rob

[compactfean]

I find it amazing how many people have motor swaps and don't know the vitals of there car. When I diagnose, I never assume anything is good. Lol. some things to check when tuning or diagnosing, tps voltage, maf voltage, timing, fuel pressure, and if cts is within spec. Also a boost leak test. I feal that all of these should be checked, and done with any swap before ever driving the car. Also ...the most important is check codes. After this check list has been covered than its to monitoring afrs/tuning /boost controller adjustments etc.

[Liquidus]

@compatfean. If you read my post, you saw that I tested the MAF voltage and boost leak. TPS voltage was also checked on my and is fine, and I don't think that would cause lean conditions, but idk, I'm not a master mechanic and don't have a bunch of tools, but I love cars and am trying to learn as I go. Your post isn't really helpful in any way. Do you just copy and paste that into every post asking for help with an engine swap? Useless.

To the more helpful people:

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 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

[compactfean]

If you find it useless, oh well. But at least you have cleared some things up. You still haven't checked the cts or timing. Some other things to check is the brake booster for leaks, (will pass a boost leak test because of the check valve but can still leak under vacuum), also what voltage is your stock o2 sensor telling your ecu? Is your wide band also your narrow band signal? And if so how do you have your analog outputs programmed?

[Liquidus]

Hey compactfean, it seems I owe you an apology. Sometimes there are douchey people on forums, and when I read your post it came out as that sort of thing. But your other posts with more suggestions were really helpful. It's also impossible to tell the inflection of a message since it's only text and not spoken word, so maybe it came out wrong when I read it. Please accept my sincere apology, and sincere thanks for giving me more suggestions.

I actually just capped off the port for the brake booster, so it's not that. My wideband isn't my narrowband, I'm running the stock o2 sensor as well.

I have not checked the timing, but I'll do that as well. But, considering it runs fine with no MAF, is it even possible that it's the timing?

Thanks again for the additional suggestions, I'll test some more stuff and get back to you.

Thanks,
Rob

[compactfean]

Timing can affect afr but usually you would notice it running odd. (playing with timing on my emu it took about 7 degrees advanced to start affecting afrs.) When i said ” it a amazes me” I was saying that in general. Actually my favorite thing to post is ” refer to fsm” jk. You actually have checked more than most. Its all good. As far as your theory about the bigger injectors I don't think that is the case because with the maf disconnected the ecu puts out the amount of fuel needed according to the other factors the ecu uses for tp value.

[Liquidus]

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

[compactfean]

As for the code, it should remember it until it is cleared. So I would clear it and disregard until your next drive. As for the not starting, does it crank?

[Liquidus]

No, it doesn't. No cranking, just loud fast clicking, and magic windshield wipers. I'm thinking that either:

A. When I unplugged the battery to reset the ecu, I accidently unhooked a ground near the battery??

B. When moving the ECU around to look at the error codes, a wire shorted somewhere? Maybe one of the wires where the SAFC is spliced in?

I'm going to go try and figure that out after work today. As long as I didn't actually damage anything when one of those things happened, it shouldn't be too hard to figure out. I hope.

[compactfean]

I would say you messed up somewhere asking the line with the battery. The fast clicking indicates poor connections to the battery, or a, dead battery. I would do a voltage drop test and see where your at.