SR20DET MAF adventure

Paint, body preparation and modification, interior work and electrical
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jovial_cynic
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Re: SR20DET MAF adventure

Postby jovial_cynic » 27 Mar 2015 10:03

Cool. I don't have a consult cable yet, but I may end up getting one.

However, it looks like I can test a few things without it. I haven't ran voltage or continuity checks all the way down to the ECU yet so I'll do that tonight when I get back home. I FEEL like those checks will all pass, though, on account of the 1.7v that I can throw into the mix; I'm pulling power and ground directly from the plug that goes into the MAF... so it's only logical that the power and the ground are good, and that the MAF signal wire has continuity on account of my ability to adjust the O2 readings by adjusting the voltage I'm injecting down the plug.

I'll make all the checks tonight though, just to make sure. And then I'll run my LED test as well. It just seems odd that my MAF will bench-test just fine, and when in the car, the signal terminal on the MAF shows that it's pumping out 1.7v... which is exactly where I have my voltage injection circuit providing... but when the MAF signal terminal is actually connected the signal wire on the plug, it's like the voltage bottoms out. I can't see it bottoming out, and since I'm only testing between the MAF signal terminal and ground, I suppose I'm not taking into account any resistance that may be dropping the current between the MAF and the ECU (weakening the signal?), and while my voltage injection circuit has plenty of current going through it, maybe the MAF has a lower current supply...

Being stuck at work and not working on the car is frustrating! :?
71 510 2-door SR20DET (S13)
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http://www.myagentjosh.com
http://www.newprotest.org/510

akara
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Re: SR20DET MAF adventure

Postby akara » 27 Mar 2015 16:12

dislexicdime wrote:Do you have a consult cable? Best thing i ever bought for trouble shooting my sr

I second this, absolutely get a Consult cable! It's great for checking that you have a clean voltage sweep through the TPS and MAF.
1.7v sounds high to me, my car with Z32 maf runs at 1.1v at idle.
Notice the FSM page 115 says it should be .8 to 1.5v at idle with the factory MAF.
I also want to note that I also had this leaning out issue before!, what caused it was my MAF being too close to my turbo, causing more air to be sucked AROUND the hotwire element than past it directly.
The SR20DET in my experience is very sensitive to MAF positioning in the intake tract. You need the sensor to be at least 18" away from the turbo inlet, and a couple bends might help create some turbulance to even out the reading.
It was a NIGHT AND DAY difference from when I had the MAF attached directly to the compressor inlet vs the intake I made pictured here: Image
Heres another one someone else made in a 510:Image

That intake changed the car from undriveable to almost stock feeling.

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jovial_cynic
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Re: SR20DET MAF adventure

Postby jovial_cynic » 27 Mar 2015 16:57

I thought about that a bit too, actually. If you see this video of my engine running, you can see how the intake is set up. It was warmed up already. This was before I had my O2 sensor to know that it was running lean.

https://www.youtube.com/watch?v=clTib9NbIy0

I may have a little less than 18" there... so I'll fiddle with that to see if that has an impact.

As far as the voltage goes... I have noticed that with the 1.7v direct injection, the O2 has creeped a little rich on me, moving into the 12:1 range. However, the reading on the MAF says 1.2v with no airflow at all (ie., engine not even running), so I'm really curious about your reading. Have you tried seeing what your sensor output voltage is without it running?
71 510 2-door SR20DET (S13)
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PoorMtnKid
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Re: SR20DET MAF adventure

Postby PoorMtnKid » 27 Mar 2015 19:00

Are you not running an intercooler? Could that have anything to do with it?
looking for pass. side arm rest

Ash510
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Re: SR20DET MAF adventure

Postby Ash510 » 27 Mar 2015 19:48

Just a little info that I found when doing my car, is that the o2 sensor should be at least 18
inches down stream from the turbo, so that it gets a cleaner more consistent flow over it.

this may be an issue or not , just an idea

Aron

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Re: SR20DET MAF adventure

Postby jovial_cynic » 27 Mar 2015 21:51

Well, following the FSM, I've confirmed the following:

A. Battery voltage between "B" on the terminal and ground. [CHECK]
B. Continuity between "C" on the terminal and ECU pin 26. [FAIL]
C. Continuity between "D" on the terminal and ECU pin 27. [FAIL]

And then I decided to check the pinout for the S13 Redtop ECU that I have and wondered why on earth would the MAF have continuity to the Exhaust Temp Sensor (pin 26) and the Detonation/Knock Sensor (pin 27), and remembered that the S13 and the S14 have different ECUs, so...

A. Battery voltage between "B" on the terminal and ground. [CHECK]
B. Continuity between "C" on the terminal and ECU pin 17. [CHECK]
C. Continuity between "D" on the terminal and ECU pin 16. [CHECK]

Per the FSM, I'm now clearing the ECU by disconnecting the battery for 24 hours. I've also cracked open the ECU entirely to make sure there are no visible breaks in the wires internally, and that looks good, too. So I have to put that together now with a little bit of solder...

I am a little curious about the the 1.7v coming out of it at idle, now that I have seen that the FSM suggests that it should be between 0.8v and 1.5v at idle. That's for the S14, but I imagine the S13 is going to be similar.

I'm going to try some different tubing before and after the MAF to see if there is some weird improper air flow/restriction around the MAF sensor. That really shouldn't be the case, though, since I can watch the MAF sensor voltage increase from 1.2v to the 1.7v when the car idles with the voltage circuit injecting an appropriate amount of voltage to the ECU. Yes, I'm in agreement that 1.7v should provide a rich condition... but in the real world, the 1.7v from the MAF isn't making it to the ECU. I can't figure that out.

Sigh.

I really do wish that the MAF isn't the problem. I like it when tweaking and wrenching provides a solution. I don't like it when "buy another one" is the solution.
71 510 2-door SR20DET (S13)
------------------
http://www.myagentjosh.com
http://www.newprotest.org/510

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Re: SR20DET MAF adventure

Postby jovial_cynic » 28 Mar 2015 10:35

Oh, side note: When the engine is warmed up, plugging the MAF back in does not cause the engine to die, but it does lean out, and giving it some gas causes the O2 sensor to detect a slight richening of the exhaust gas, but not enough for me to feel comfortable stomping on the gas. The fact that the engine even CAN rev above idle means that there is some additional voltage from the MAF getting to the ECU.

So what we have is a consistently low voltage signal from the MAF. If the voltage did not increase at all, the engine wouldn't be able to go above idle. I know this because when I'm injecting 1.7v to the ECU directly, you can't rev the engine at all with it bogging and dying on account of the injectors not opening up any more than at idle.

Again - with the MAF plugged in and the engine warmed up, the engine runs, but very lean. Revving it allows the RPMs to increase, but it stays very lean... and this tells me that the MAF is working... but not very well. There is a constant low voltage considition going to the ECU from the MAF.
71 510 2-door SR20DET (S13)
------------------
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http://www.newprotest.org/510

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okayfine
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Re: SR20DET MAF adventure

Postby okayfine » 28 Mar 2015 11:02

jovial_cynic wrote:Again - with the MAF plugged in and the engine warmed up, the engine runs, but very lean. Revving it allows the RPMs to increase, but it stays very lean... and this tells me that the MAF is working...


Does it? Or just it just happen to mirror what happens when starting a cold, carb'ed engine: You need choke. Once the carb'ed engine is warm, you don't need the extra enrichment. So your situation is that the engine's lean when cold, but is able to run once warm. Unless you've checked the voltages revving/warm versus idle/cold, but you didn't state values above, so...

For kicks, have you checked through the fueling? IIRC you had wanted to reinstall the factory emissions stuff on your engine. Perhaps there's a completely different issue (dying pump, pulling vac in the tank, kink in the line, bad regulator, plugged injectors), and the fuel supply is somehow inadequate? Above-spec MAF readings aside, you don't want to focus too much on a single problem when you're not sure that's the problem.
Because when you spend a silly amount of money on a silly, trivial thing that will help you not one jot, you are demonstrating that you have a soul and a heart and that you are the sort of person who has no time for Which? magazine. – Jeremy Clarkson

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James
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Re: SR20DET MAF adventure

Postby James » 28 Mar 2015 13:38

Test post…..
Finished is better than perfect......

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jovial_cynic
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Re: SR20DET MAF adventure

Postby jovial_cynic » 28 Mar 2015 14:01

okayfine - I'll pull voltage from the MAF later this afternoon while revving to see if it is swinging up with the additional air intake. That'll give me a more definitive answer on that. I hadn't even though of the whole choke scenario. Isn't the starter-enrichment wire supposed to handle that?

As for emissions stuff, I never got around to touching any of that. The fuel supply, though... since the engine idles properly when I force-feed the ECU the 1.7v, doesn't that automatically mean that fuel isn't the issue, considering that the MAF is (in theory) providing the same voltage to the ECU? I installed an inline fuel pressure sensor, so I'll pull signal off of that and see what I'm reading, so hopefully that'll give me some clarity on that as well.
71 510 2-door SR20DET (S13)
------------------
http://www.myagentjosh.com
http://www.newprotest.org/510

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okayfine
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Re: SR20DET MAF adventure

Postby okayfine » 28 Mar 2015 15:42

Cold-start valve is still pulling air through the MAF. I wasn't speaking specifically of additional fuel/air, more than a warm engine will tolerate leaner air/fuel than a cold engine.
Because when you spend a silly amount of money on a silly, trivial thing that will help you not one jot, you are demonstrating that you have a soul and a heart and that you are the sort of person who has no time for Which? magazine. – Jeremy Clarkson

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Re: SR20DET MAF adventure

Postby jovial_cynic » 28 Mar 2015 17:16

Ok. Pulled voltage from the MAF while revving the engine in limp mode. Voltage on MAF signal output definitely increases w/ increased airflow. RPMs can't get too high in limp mode, but as WOT as possible, it was pushing nearly 3v.

So weird. I just can't figure out this.
71 510 2-door SR20DET (S13)
------------------
http://www.myagentjosh.com
http://www.newprotest.org/510

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Re: SR20DET MAF adventure

Postby jovial_cynic » 28 Mar 2015 18:26

Ok. LED test revealed something interesting.

When testing an LED with my injector circuit, using the 12v and ground wires from the MAF plug, but using a 1.7v output to the LED, and then grounding it back through the MAF plug, the LED light up and stayed lit.

When testing the same LED with the signal from the MAF, the LED lit up for a brief second when flipping the ignition switch, and immediately died. I turned the ignition off, turned it back on again, and the LED lit up for a split second and then quickly died again.

I ran voltage across the LED, and instead of being at 1.7v like it was before I was testing the LED, it dropped down to 0.2v. And that 0.2v is consistent with a lean condition that I was experiencing.

But this gets weirder. Keep in mind that I have 12v going to the MAF through the MAF connector plug. I also have grounded the MAF through the MAF connector plug. When I DISCONNECT the ground wire, the LED lights back up and stays lit.

WHAT IS GOING ON?
71 510 2-door SR20DET (S13)
------------------
http://www.myagentjosh.com
http://www.newprotest.org/510

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jovial_cynic
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Re: SR20DET MAF adventure

Postby jovial_cynic » 28 Mar 2015 18:39

AND THEN...

I checked voltage from the sensor wire from the MAF. Apparently, when you disconnect the ground, you get TEN VOLTS from the MAF signal wire.

No clue. Head hurts.
71 510 2-door SR20DET (S13)
------------------
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http://www.newprotest.org/510

akara
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Re: SR20DET MAF adventure

Postby akara » 28 Mar 2015 18:42

I think it might be worth it for you to try another maf
the maf sensor is not like the o2 sensor which just affects trims on a base map under only certain conditions, the maf sensor and tps are directly used to calculate load by the ecu and the signals must be free of noise and correct.
i took a look in my tuning software what some values should be for different nissan MAF
heres your s13 maf
http://i.imgur.com/FrIqET4.jpg

an S14 maf:
http://i.imgur.com/CvsVvYY.gif

and finally my Z32 maf:
http://i.imgur.com/vpQoTvK.jpg

It looks like no matter what nissan maf you have 1.7v is going to make the ECU calculate about 10 percent load so I think its worth checking out!
Grounding is important and many people recommend regrounding the MAF instead of relying on the poor quality factory nissan ground splices placed throughout the harness.
Do you have a vacuum/boost gauge? You should be seeing 20in of vacuum at idle, any less means you have a vac leak!


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