Kingtal0n

then try a SOHC KA maf element next, cheap and easy to find. DO the cheap easy things first.

NGK BKR7E I think, is the stock plug. They should be cheap~ $2 each?

heres what I would do if I had it in front of me right now.

1.check the timing with a gun
2. unplug the fuel regulator
3. unplug the O2 narrowband (to force open loop)
4. drive the car see if the problem still occurs.

If it still happens, and fuel pressure remains high, then, you have it narrowed down to:
ECU, Injectors, MAF, wiring (sorry but wiring is always suspect no matter what) For the MOST PART, as we are taking for granted that the engine is truly running lean. I would be able to tell but I am afraid you might not be able to. So I am just taking for granted the a/f ratio at this point.

__________________
5.3/4l80e/turbo 240sx playthrough:
https://tinyurl.com/turbo240

Nikzilla

Autolite Copper/Spark Plug (3924) | AutoZone.com

Trying spark plugs I get, but MAF?

We can see the MAF voltage and there is a perfect correlation to TP and RPM.
Is there really any doubt?

Cuz ya kno, autozone MAF's are like $70 and finding a 240 in a junk yard will take me a month lol.

Kingtal0n

Is the correlation perfect? should the maf voltage be higher? we dont know. If the maf is reading low- it would cause your symptoms. We can not tell if it's reading low without testing another maf. I used to have a bunch of spare sensors. I might have one around somewhere Ill look. but I doubt it. I kept a spare in my glove box for years.

definetelly dont buy one for more than $10. For now you can still try what I just recommended.

__________________
5.3/4l80e/turbo 240sx playthrough:
https://tinyurl.com/turbo240

Nikzilla

I am 95% certain it is truly lean. I just can't explain why the narrowband disagrees.

I recently set the timing, I'll check it again when I get home.

You mean pull the vacuum hose off? I have a fuel pressure gauge FYI, so shoot questions about fuel pressure if you got em, but fuel pressure seems pretty good to my eyes.

If unplug the O2 (like I mentioned in the original post), the car doesn't have the same problem. The difference is, with the O2, it slowly leans out until it bottoms out the gauge. With the O2 unplugged, it just runs generally lean when cruising. Like at 16-16.6. Wot under boost still yield the normal 11 AFR though.

Nikzilla

Damn you make good fucking points

However, there are certain specs for MAF voltage at idle and WOT. From what I just looked up, idle is supposed to be ~.8 and WOT is 5.12 max. I can check to see if I match, however I can't rule out the possibility of the MAF crapping out only in certain voltage ranges.

Also, how do I get a MAF without junkyarding?

Kingtal0n

Ok, so your maf is sort of bad, and your O2 sensor is garbage. Case closed I think.

this is what your post sort of says:
1. the maf reads wrong, 16:1 is too lean even for a cruise. So its no good, or you have a vacuum leak. One or the other. Ok, or the ECU is bad, or the wiring is bad. (of course).

2. the O2 is causing you to run lean during closed* loop. It "disagrees" and shows "rich" because its garbage (bad) and that is exactly why the ECU is pulling more and more fuel. What I dont understand is why that doesn't show up on your data tool. Sounds like the data tool is mis informing you as well.


So for now, unplug the O2 and swap the maf when you get a chance. Next maf reads 16:1 also? You have a vacuum leak, a voltage drop between the MAF and ECU (bad wiring), or a bad computer.
your maf wire HAD to have been extended. Maybe investigate how that was done. There is a shield wire that should be in place, and may have something to do with your problem. Check to make sure that whoever did the job used an OEM maf wire with the big white grounded shield. Follow it back to the "wiring job" to make sure the ground was actually attached. In fact check it for ground (the shield wire is usually grounded to the ECU iirc)

__________________
5.3/4l80e/turbo 240sx playthrough:
https://tinyurl.com/turbo240

Kingtal0n

Ok, mafs have a parabolic voltage curve. Did you ever take any college algebra? Im not picking on you, just curious because it explains how a maf works. In that math class they show you parabola. Its a U-shape. The MAF has to operate on the U-shape, and if you ever noticed a parabola has a much greater slope (rate of change) on its edges, rather than in it's center. So a maf operating in the center has much more resolution, that is, the quality of the fueling is better, more consistent. On the edges, the fueling is worse, but thats fine because at WOT you arn't trying to nail a very specific A/F ratio, just anywhere around 11.something is fine.

Furthermore, 5V is MAX, meaning that you have run out of MAF hot-wire, your ECU would fuel cut to prevent damage (its supposed to anyways. Some don't...). You wont get near 5V with a stock turbo on 7psi. in fact you can unplug the wastegate of the T-25, watch it spike to 18+psi and it wont even hit fuel cut (most of the time!). So if you stuck a multimeter on the maf and went to wide open throttle your max voltage would probably be around 3.8-4.1 volts, Just a guess.

In the middle, you cant tell where you are supposed to be. But thats ok, because SOHC KA maf hot-wires are cheap. If you cant source one, I am sure I could find one no worry.

__________________
5.3/4l80e/turbo 240sx playthrough:
https://tinyurl.com/turbo240

Nikzilla

just checked MAF voltages from a log. These specs are from an S14 SR20DET FSM.
Idle voltage spec is 0.8-1.5V. Mine is 1.6V.
3,000 RPM voltage spec is 1.2-2.0V. Mine is 3.2V (25% throttle).

This is the opposite of your theory of low MAF voltage, I am dumbstruck.
WHY IS EVERYTHING BACKWARDS IN TIIIIS ENGUUUUUN.

What do you mean by the MAF reads 16:1?

Dude, this O2 sensor is quite literally 2 days old. I replaced it because I thought this issues was caused by a bad sensor, but no change in symptoms.

Nikzilla

I took Differential Calculus freshman year, thanks

That was just some shit I quoted from a thread. Used the actual FSM values. Hope the S14 and S13 blacktop share an MAF lol.

Can you actually buy hotwires without the whole MAF housing at autozone?

Kingtal0n

no, S13 and S14 maf are completely different. There are also 2 different S14 maf sensors, and the S15 sensor which I think is the same as the 98 S14 sensor. its been too long...

Anyways. sorry you cant use the S14 numbers.

And no, I just goto a U-pull-it (do they have those around you?) And take out the hot-wire portion from the maf sensors when I see S13 SOHC KA cars sitting around. I used to have a few but no clue where they all went...

The engine is fairly simple. the maf reads airflow, the ecu reads the maf, the ecu sends an injector pulse. If the pulse is not big enough... (or if the fuel pressure is low. Or if the injectors are clogged.) There wont be enough fuel.

Your engine isnt getting enough fuel. And you verified the fuel pressure. So either the injector pulse is too short (maf reading wrong/O2 reading wrong) or the injectors are all clogged.
or there is an air leak after the maf. (or the ecu is bad -unlikely)


notice that "bad wiring" also falls under "maf reading wrong". So does "air leak" because that also causes a maf to "read wrong".

__________________
5.3/4l80e/turbo 240sx playthrough:
https://tinyurl.com/turbo240

Nikzilla

Welp S13 SR20DET FSM's don't exist in english.

However, according to this thread: http://www.freshalloy.com/showthread...ltage-too-High

S13 MAF should read ~.25 above S14, which puts my idle well in spec, but my 3,000 RPM, not so much.

But I also just realized that that read is under load. I think the FSM spec implies no load. Brb diving back into the logs.

Nikzilla

Just ran down and did a quick test. Holding 3,000 RPM in neutral, MAF reads 2.34, which is again, more than spec, not less. Sigh.

We do have junkyards. I visit 2 every month. I have yet to find a 240 lol. Closest I've come was a Z31. I'm going again this weekend though.

It's opposite. If I had vacuum leak, MAF would read lower. If I had wiring issues, MAF would read lower. I'm confused.

EDIT: Shit I just realized the O2 was unplugged during that test. Does that really matter?

Kingtal0n

you have no point of reference so checking the maf voltage can not tell you anything. It doesnt matter what the maf voltage is; it matters what the air fuel ratio is.

__________________
5.3/4l80e/turbo 240sx playthrough:
https://tinyurl.com/turbo240

Nikzilla

How are you calcuating the air/fuel?

Kingtal0n

YOUR wideband is telling us the air fuel. I have not and could not possibly calculate how much actual gasoline is leaving your injectors, no matter what sort of maths exist in the known universe, since we have NO idea how much fuel they actually flow, and no way to determine how much air is entering the engine, and what percentage of it is reacting with gasoline...

__________________
5.3/4l80e/turbo 240sx playthrough:
https://tinyurl.com/turbo240

Nikzilla

Ahh, from what you said I thought you were getting it from the graphs. Tripped me out.

I just got the spark plugs. I'm going to put them in right now.

Nikzilla

BIG UPDATE:

So I swapped the plugs (they were gapped to ~.37), started the car, put the ECU into base idle adjustment mode (locks timing to 15) and put a timing light to it.

It read -30. Fuck. CAS must have slipped. I set it to 15 and re-torqued it, bumped up the IACV to match as well.

It's almost undrivable.

Here is what happens.

Low RPM, low throttle, it drives fine. As soon as I let ANY boost build, the timing gets pulled back to 0, my fuel pressure spikes to 60psi, wideband dives down to 12, and the car makes no power. It's slower under boost than without boost.

As far as I can tell, the previous issue is still there, but it's really sorta hard to tell because of how fucked everything is right now. If I just try to hold it at 2500 RPM, the narrowband spikes rich and wideband spikes lean. The shit part is, I can't correct it by spiking the throttle anymore, because then it builds boost. It was impossible to get the car past 3,000 RPM.

But, GOOD NEWS! The duty cycle started behaving!

Here is the data log:


The only thing I can think of, is that the .37 plug gap is somehow reacting with the boost.

Fuel:
Walbro 255lph
Z32 filter
Stock FPR (But I have a Tomei Adjustable sitting in my garage which I haven't installed yet)

P.S. When I pulled the spark plugs, they looked dry, with a bit of powdery white on them, which is a big change from black when I was running rich a month ago.

Kingtal0n

Your timing could not have been -30, i think you have the timing light backwards. Most timing lights have an arrow pointing towards the plug. Does yours? If you hook the pickup on backwards, the timing will read wrong, like yours did. I do not think the engine would have idled at all with -30 degrees of timing.

If you have advanced your timing to 45+ now there is no doubt your knock sensor is pulling out timing, like yours is doing.

I always take my timing from the #1 cylinder coil pack, not the loop at the back.

You should fix the timing, and stop using that data-scan tool of yours. Do what I said in post #36 as this issue has been solved I am 99% certain. Just in case you missed it,

1. Unplug your O2 sensor
2. Find a SOHC KA maf
3. Find a 1-wire O2 sensor for $8 from a local pep-boys or auto store.

If you cannot locate the 1-wire sensor or the KA maf I will locate them for you.
Once you fix your timing your engine should run normal again. If possibly bump your fuel pressure by ~5psi to help your lean cruise out slightly.
And buy some injector cleaner just for the heck of it.

__________________
5.3/4l80e/turbo 240sx playthrough:
https://tinyurl.com/turbo240

Nikzilla

-30 means BTDC right? Not ATDC.

Do timing lights have directions? I thought the way they work is the induction loop just activates a relay that turns the light on. Direction shouldn't matter.
I have the basic $30 light from autozone. It has really good pickup from the induction loop. From what I read, the fancy digital lights have problems with the loop in the back because they are too sensitive, and the other wires interfere with them, but the cheap light works fine.

I'm going to the junkyard this Sunday, I'll get a MAF.

Kingtal0n

Wait, your engine was running fairly normal, then suddenly after you "fixed" your timing with a $30 light now the ECU is pulling timing and the engine runs like crap?

Yeah, the pickup was backwards.

__________________
5.3/4l80e/turbo 240sx playthrough:
https://tinyurl.com/turbo240

Nikzilla

man fuck. Goddamnit. Shit. No one ever told me there fucking directions on the induction pickup.

I'm gunna run home and check my timing in every way possible now.

Nikzilla

Ok, you were right. The timing read -15, then I flipped the pickup, it read -5. Adjusted it to -15 again. Then I tried to read it off the coil pack. It read -15 either way I flipped it.

Anyways, while doing all this, I noticed TWO FUCKING GROUNDS THAT WERE NOT SCREWED IN. I stole 2 bolts off my tool cart, and guess fucking what, THE CAR IS DEAD ON.

Jesus fucking christ I laughed like a maniac. That made my valentines.

This is what happens when you let your friend put the intake manifold back in while you do the valvetrain.

Thank you my man, for all your help. You have no idea how much I appreciate it, and I wish there was someway I could return the favor.

Case Closed.

tom_sr20

i have this stumbling problem too. many keep telling me its a ignition related problem. so i changed all my coils packs, cas and plugs. all new oem parts by the way. still no fix. now i too feel like its an ignition problem but since i replaced most of the ignition components im starting to lean towards what powers the them which is the alternator. i run dual electric fans, gauges, hid,sounds and ac. im guessing the coils arent getting enough juice. im gona go for a quest alternator upgrade next and see wat happens.

Nikzilla

My 5 cents:

Instead of throwing parts, run better diagnostics.

Can you define your stumbling problem? Is it a misfire, or just lack of power? If you're concerned about your ignition system, you can run a test to determine if your plugs are missing. Unplug your injectors, take out the coil packs and spark plugs, put the plugs in the coil packs, and ground the electrodes. Then have a friend crank the car and you can physically see if your plugs are firing.

tom_sr20

engine stumbles during boost. 3k above. idles perfectly fine. if u were to put a volt meter on your battery with the car running, where does the voltage sit at? mine stays on the low 13's.

Nikzilla

What kind of data can you monitor?

Sounds like something in your car can't keep up with power. Check your fuel pressure, check your timing, check your plug gap. Wideband would be extremely helpful.

tom_sr20

i need a wide band to see if its lean or rich on stumble. no tools to monitor

Nikzilla

Without any data you're kinda just poking in the dark.

Need more data

tom_sr20

yup. but if u have time can you check where ur battery voltage sits with car on. with light and ac on too. should it be in the 14 volt range? mine is in the low 13's

Nikzilla

Mine is low 13's with nothing on. I don't have AC. I have a small battery though cuz of intercooler.