Danger_Dorn

Ok so this has been driving me nuts. No matter how I drive I get 10 mpg (shifting before 3k, staying out of boost)

Engine is a redtop with 2k on OEM rebuild with 32 ecu and Man. Trans.

I have adjusted my TPS to .45 volts and verified with my wideband that I'm running normal fuel mixtures. (It is reading lean due to an exhaust leak but that's getting fixed this weekend)

I think I may have a gas tank leak because when I fill up gas pours out of the top of the tank so I'll be investigating that this weekend also.

Also my 02 sensor may be shot but I haven't found a fool proof way to troubleshoot it. Anyone know the voltage at idle with normal AFR's?

Also installed a AFPR and Z32 FF @ 43.5 psi vac unplugged. Air filter is clean with new maf and injectors spray evenly.

I have my coilpacks grounded with the OEM grounding point (good or bad?)
I have a ground from the Intake manifold to firewall, and a ground from near exhaust to fenderwell. Maf is grounded to fenderwell with 2mv resistance.

My sparkplugs are autolites (bkr7e equivalent) gapped to .28

Ignition timing is set to 15btdc. (oem)

93 octane. WS harness

What else can I do to try and get better mileage? I have read a few threads but nothing too helpful/recently up to date.

ultimateirving

Ok so i get about 22mpg average with 91 on my tune. You are definitely off quite a bit.
I would investigate for any leaks, especially if something is leaking when you fill up, its possible your gas can evaporate.
Also I believe the system is supposed to be sealed so that could be having some impact on your fuel woes.

Next the 02 sensor plays a large part in the gas consumption when not WOT. So if you dont think it is working then you need to do a few small tests to make sure its hooked up. Easiest way is to turn the ignition on and wait like 5 mins to see if the o2 sensor gets hot. That means it has power and is at least functioning.
Next i would check to make sure that the signal wire has continuity to the ecu.
And i hope someone else can chime in to explain better how to test the o2 unit beyond that.

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Z32 with lq4 swap
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Danger_Dorn

Thanks Irving. So the points of the gas tank that are sealable are the cap, fuel cap, the in and out lines...What about that line that runs under the tranny tunnel? Whatever that vent thing is...should I cap that? Ill have to find that crack by feeling around in the tank considering I don't really have time or resources to drop it.

From what I understand with the o2 sensor is that under 3k it controls your AFR's but in WOT it has no effect. Also at idle it will have between 0 and 1V which is determined by the resistance it detects via sniffing the fuel in the exhaust right? IIRC 0v is lean and 1v is rich so to test my o2 sensor I would probe it and watch my voltages in relation to my AFR on the wideband right? I just read somewhere the medium for o2's is .45 and anywhere below or above that is lean or rich.

Sorry just thinking aloud and if it's right it will be a good future reference...opinions?

ultimateirving

Your technique sounds like it is fine, I do not know what the voltages are for stock 02.

Do you have a consult port? That would instantly solve the guessing games.

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Danger_Dorn

No I dont have a console port but I would be interested in one. Is there a write up anywhere? I just searched google and returned nothing. I will also post up the results of my new o2 sensor voltages for future referance. And what about the gas tank line thing? Some people leave it open to the engine bay but that concerns me considering that gas fumes could vent out. I think I might put a vac cap over it and give it a week.

Mikester

I know this varies... but my base timing has always been 17BTDC. Not that 2* is a big deal, but in your case, every little bit will help lol.

Gap your plugs to .030

As far as the third line coming off your tank, it does not go into the tranny tunnel, it goes to a check valve; and then to the hardlines along the passenger frame rail... and you do NOT want to cap it off. Your tank needs to 'breathe' in order to maintain proper pressure between the indise of the tank and ambient... That line is your evap line that helps perform this function; as well as allowing excess fumes to be sucked into the intake manifold... reducing explosion hazard and adding to fuel economy.

You are leaking fuel. Find & fix the leak(s).

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Danger_Dorn

Thanks mikester. There is a line that comes out next to the fuel lines that looks like it goes to the fuel tank. I dont have the canister hooked up or anything. Are we talking about the same line? It is simply just open currently...no bueno?

Mikester

Follow the lines from the fuel tank, there should be 3. 2 go to the fuel feed/return, the 3rd goes to a small check valve bolted to the unibody just fwd of the spare tire well.

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Danger_Dorn

So today I went and adjusted all 4 corners of my coilovers since when I put them on I just threw them on to be done with it. I also got my new o2 sensor in. It made a small difference but since I sealed up my exhaust leak I am now running lean. 15.5 at idle unless it does its weird thing where it revs low and leans to 17. It is at like 14.5 in cruise AND BOOST! Sometimes it will go to 13.5 but I have checked EVERYTHING including moving my fuel pressure up to 40 with vac plugged in so like 47 unplugged. What else can I try besides the above

ultimateirving

Who wired your fuel pump? I've heard of problems with stock wiring not being up to par

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Z32 with lq4 swap
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Danger_Dorn

Really? hmm...I wired my own but I just cut and installed the new one

Danger_Dorn

Well I'm not too sure what else to do about my fp wiring. I just went an checked it and I soldered and shrink/heat wrapped it before. I could do a full hardwire but I'm not sure if its necessary and I haven't been able to find a white up

inopsey

your maf is grounded internally to the ecu, not sure why you added another ground to that. what do you have grounded from near the exhaust to the fenderwell. i doubt you need extra grounds above what factory gives you provided you have good contact at oem locations and good wire.

Danger_Dorn

A lot of people re ground their maf because it reduces resistance and gives better response. I have extra grounds because they never hurt and I have read that people found they benefit.

ultimateirving

Hey dorn check the voltage at the fuel pump wires if you can with the car idling, I've read in other posts that the stock wiring isn't up to par or some shit. Dunno why that would be the case, buttt low voltage to the pump could be a problem all around

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Z32 with lq4 swap
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inopsey

when you make things more complicated than they have to be you might be causing other problems. if you brought it to me to fix first thing i would do is remove your ghetto wiring mods.

Danger_Dorn

There is nothing ghetto about it lol just like the coil packs have a chassis ground. Its just grounding the MAF to the chassis so you reduce resistance from .9 to .2 ohms.

Also as far as my fuel leak, turns out my fuel tank access hole gasket was rotted away so I RTV'd until i get a new one. Still running lean though. I turned up fuel pressure and it helped a little but still not in the 11-12s at boost. Is that goal for tuned cars or oem ones too? I run like 14 and richer in boost but nothing more than 13.5

Mikester

^^Definitely lean^^

Your ECU is #32? What is that? Isn't a redtop ECU 62, or was that a typo in the OP?

When you did the OEM rebuild, did you go to 86.5mm pistons; have any machine work done? OEM turbine & head gasket? Anything at all that would affect AFR's?

If you are losing fuel somewhere between the tank and the rail; adding fuel pressure will only exacerbate the problem. Best thing you can do is either set the FP to stock; or put on a stock regulator.

As far as adding a ground to your MAFS, perfectly fine. WS harnesses come with a chassis ground on the MAFS pigtail. I like the added security of knowing my MAFS ground is spot-on- and there is nothing ghetto about it.


Going back to the fuel pump... Do you have an aftermarket pump?

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fullthrottle

He has a hole in his tank. That's it. It's very common. It's probably cracked or rusted through like a 1/4 of the way up your tank.

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Danger_Dorn

This will be a long one....When the motor was rebuilt I re-used my stock rods and pistons with new rings. I had the head and blocked decked and the appropriate cosworth metal headgasket installed with ARP's. Everything else internally is new oem. I have a walbro 255 fuel pump which is wired correctly via solder and shrink wrap and I checked it last night to make sure it was still in tact. My fuel tank "hole" was just the rubber o-ring on top was worn so I RTV'd it until my new one gets here. I filled up last night and no leaks. I'm running the stock t25 turbo and when the shop had it they said it was perfectly healthy for its age. No oil seepage or bad blades. I am running the 62 ecu yes it was a typo. I just installed a new SKINNY oem 02 sensor 2 nights ago and it kind of helped a little. I also had an exhaust leak from my t-elbow to the DP which I fixed with a new thick gasket. I am now running great while cruising but it still leans out at idle sometimes and its still around 13-14 in boost @ 12psi. My spark plugs are clean and gapped correctly. Next I might try cleaning my maf again, checking my TPS, MAF, and anywhere else for voltage/resistance. I am seriously about out of ideas other than my vacuum leak since my gauge reads -8 instead of -15 or whatevs. I made a smoke machine a few days ago but I dont know if it will work. Thanks again for the ideas! PS my ws harness did not come with a second ground but I made my own so nbd.

NoPistons!

Sucking in unmetered air would cause you to go lean for sure.

Check everything between the maf and the head.


All else fails do a compression test. Blowby will throw your afr's off also.

Also see if your cas walked from where you clocked it at. Timing also effects afr.


Only other thing i could tell you to check is your injectors. Take em out the rail, disconnect the coil packs, let the injectors (still in rail) rest in a drip pan and watch the spray pattern.


Best of luck. Good thing you have a wideband. Best purchase you can make for a turbo car.

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Just another broke ass drifter

Danger_Dorn

Ok so I've done alot of searching and finally have a list of things I need to do to fix my problems. I think its lean because of a vac leak probably in my intake manifold so I borrowed an air compressor to check it. Also it starts rough in the morning and I figured my starter signal switch, the one from your ignition to the ecu to enter "start mode" might not be connected (not sure if WS does this wire or not)

Danger_Dorn

Ok just went and did almost everything to try and figure this out. Tried my extra maf and no change. Maf is 1.5-1.6V at idle 8-900 rpm. Vac is still like -8. I used an air compressor and plugged it up to my maf location and sealed all leaks. I tested it up to 15 psi and heard no other leaks besides one small charge pipe one and the nipple under the TB which I fixed and still -8 vac. My tps is .50 volts and I tried .45 and .55 and there was no difference. I listened to all 4 injectors and they sound good and consistent. My last resort might be to buy a consult port and see if that yields anything. Anyone else have any ideas? I might try to plug my pcv and see if that changes anything. I know it rattles so thats not a problem.

Still having issues and it better not be my rings/lands because they were just inspected and re-ringed about 2.5k miles ago by a respectable shop.

Danger_Dorn

Sometimes at idle it will stay at 14.5 afr but it only does it once in a while and its at random. Then other times it will come to a stop, no matter how, and it just straight leans out. Any ideas? I dont think CTS has anything to do with it considering it does it cold and warm and my dash gauge reads pretty close.

Davidna2fi

Consult works wonders when diagnosing the nissan ECU systems for SRs. I see everything, and if you look at the manual for refrence points it'll pin point what areas are not reading right and possibly either a wiring issue or sensor is bad. Spend some coin and order one. I've used mine for years and it helps so much with any nissan engine.

Danger_Dorn

Cool Jackpot! Looks like i'll be getting one of them. Whats the best free program

Davidna2fi

Best program is ECUtalk, it can do a text type data logging file and it'll spit it out like this. Only get the USB type consult port, not the serial ones.

Consult Diagnostic OBD USB Interface 14 Pins Scanner Tool for Nissan | eBay I use this one.

Danger_Dorn

this is the one you bought? Cool. I just downloaded ecutalk. I hope I dont have like 30 engine codes lol. My light and CEL dont work.

Danger_Dorn

so I just went in a re-soldered my ecu light. Now I'm throwing 12 MAF, 13 CTS, and 34 Knock sensor. This is confusing because I'm not running rich...normally 2 of these would cause a rich condition. Strange. I'm soldering my maf ground back to stock to see if it still gets the code. Its weird because my maf voltage is within spec so I think the ground is whats causing the code. I checked my cts resistance and its 4.1 k ohms at 80 deg. F so thats within spec...knock sensor? who knows why that went off. Maybe its from having hard suspension

Diehardsr20

Is your cts specific for that year car/chassis? If I remember correctly when I last checked my cts (the 2 prong next to the single prong underneath intake runner number 1(the single prong is just the dash unit, doesn't affect ecu)) at 80f outside before first initial startup was 2.6 kilo ohms to normal operating temps at 0.8 kilo ohms.

You can bypass the knock sensor buy installing a 1 k ohm resistor into the pigtails just until you can figure out the problem. From what I've read nissan knock sensors are constantly sensitive and it gets worse with stiffer suspension, etc. Just keep an eye on those wideband readings. You go lean you grenade your engine.

I had the same problem recently with mpg and I have to say its a vacuum/boost leak somewhere. After I installed an afpr (walbro 255 instal) and found my leak (normal op temps @ idle should be 15inhg), it doesn't take a quarter of a tank to drive 30 miles now. Before finding my leaking pcv I was @ 9inhg at idle with normal temps. Also, with the leak my startups were crap. After the leak was fixed startup improved.
My 2 cents. Hope it helps you.