Any help with another GTIR problem...

that looks nasty....fix that first.

pull the codes

no, the maf is gtir specific and costs about 600$ at the dealer for a new one. best bet would be to buy a used one or buy and rewire a 300zx one (you will need a retune here).

duct tape and hammers... oh my

maybe best to leave it with a shop

hmm, if u had a consult cable , some datalogging would help decipher your problem

knowing if your various sensor voltages are in spec or even returning values at all

First time poster here, resurrecting an old thread.

I just bought this GTIR off of the OP, and later stumbled across this post.  If anyone is interested in continuing to troubleshoot I'd love a hand.

Thus far, I have attempted to rig up a ka24e maf (the sohc KA's have a maf with a similar voltage curve, not perfect, but close enough to run) and the little GTIR that couldn't quite is still showing the same symptoms. 

I am going to rig the stock one back in and clean up that nasty connection as best I can, run a consult and report back.

At idle, what is the nominal voltage that should be registering from the MAF to the ECU?

No :) he gave me full disclosure. I credit him for that. I accepted that I would be probably able to resolve the issue, with a lil help from my forumites ;)

alright and btw, I wouldnt use anything besides a gtir maf on this car ... lol

See if it opened a fuse, possibly the engine control fuse.  Would check that before condemning an ECM.

Sure is, but it's one of the best cars I've ever owned.

Well, all the fuses are fine. All good, have a spare link ecu sitting around gathering dust. That's one way to bypass a faulty maf :p

too hard to look at the wonderful reflection off your screen

could you create a google spreadsheet doc  and post the link here with the datalog

what is the maf ground wire's resistance? it should be sub 10mv.

o2 its quite normal to see the 02 sensor do nothing at idle, mine does it all the time, once u get on throttle, it will bump voltage back n forth which is normal as well.

your batt voltage is really low its sub 12, your battery healthy? alternator healthy? grounds ok for the battery and engine to body?

have u tested injectors, make sure they're functional and spraying fuel, not leaking, clipped tight

whens the last time u changed plugs, fuel filter, cap rotor?

are you missing the throttle body vacuum port caps? if so tee them all together similar to the BOV vacuum hose install.

have u completed a vacuum leak test, probably will need a smoke machine to help. the connections to the factory bov good? your bov leaking?

Excellent Nick, I will run a quick datalog tonight and export it for comparo.  Thanks for the baseline!

Yeah, reflection was ok on review, but the resolution of this here iphone is junk for recording a screen.  Apologies for that.

As to the rest of your questions:

Maf is regrounded, to the body.

All caps in place on the plenum/throttle body.

My 02 reads a flat zero at idle, but what I will do is datalog it and see if there are any dead spots or other strange variances in waveform.

Battery voltage is low due to me almost killing it during other phases of this operation.  It seems to be coming to a more happy place as I run it more, but if it doesn't achieve above a baseline of 12 I will test out my charging system to see what I can see.

I had suspected injectors might be at issue, and was going down that path, but idle is smooth and startup is good now, no black smoke or fouled plugs.

Fuel filter is new, I may do plugs just because they are fairly cheap, and have had a big beating during the rich running test phase.  Will pull the cap to determine condition.

As to blow off leaking, I will plumb up an actual vaccuum gauge and advise further.  Assuming that I should be on the look out for an arbitrary drop in boost at the manifold under wot/near wot? 

Hit up the pick n pull for an alternator, or get it rebuilt.  The OP's location is Edmonton, so if you're in Alberta, Calgary's got 2 1991 NXs, but it doesn't say if they're equipped with the  SR20.  If you're really feeling limber, get it swap the guts and return it. :)

Should be an 80 AMP Hitachi.  I stripped an NX pretty bare.  It had a Bosch reman in it.  I believe Nick also noted the B15 Sentra 2.0 SE model has a 100 A alternator with its SR and should work.  It may also be worthwhile to try pricing it out because sometimes rebuilding can be just as expensive.

Would you happen to know if it's the same as a P11 one?

Just thought I'd put in my 2 cents.

From what I've read (other than the alternator failing) I think it would be best if you checked the fuel pressure as all the previous symptoms that were mentioned on this thread would point me in the direction of fuel delivery and not enough of it. This is mostly from experience of cases like this and a pressure guage on you fuel line would answer it right away wether or not your having pressure issues (and that doesn't mean the fuel pump isn't reliable and priming... just tired and not supplying enough fuel pressure/volume under load)

So here's the train of thought. Vehicle always starts up perfectly reliably since the pump primes before each and every start up.  (Not much needed in the way of starting as the injectors will open a lot more than usual during a cold start situation under low volume and no load circumstances)

Now the vehicle runs abnormally at idle as the computer takes in the measured airflow and calculates what the injector pulse width should be for that amount of air under the current temp of air and engine condition. Now you could have a couple of problems as being such an old car the voltage of the O2 should be varying up and down during idle to give you a better stoichiometric reading which will generally be read by the ECU as a rich then lean condition (the faster the cycles the better the O2 is working as they tend to slow down after old age). You should also be checking the amount of vacuum at the fuel pressure regulator as these cars would NEVER have a vacuum leak (Check and replace all hoses with fresh ones and a bag of small zip ties will be your best friend as you need 2 ties for every hose.... one at either end) Again you can check the handy fuel pressure guage for pressure regularity by removing the vacuum line from the regulator which should show up as 3 bars or about 45lbs of pressure with no vacuum on the regulator. When you attach the vacuum line again with engine running of course then the vacuum should lower the fuel pressure as it's meant to. The O2 may not be dead yet so you may not see a code from the ECU and if it's fuel pressure related then it won't pop up a code other then knock when you get fuel starvation.

Now the reason it may run smoother when the MAF is disconnected is because you've removed a calculation value from the ECU to read and so it does what any good ECU does and tries to protect the motor which is by running it a bit rich with the preprogrammed "SAFER" map in the memory in case "anything should go wrong" like your MAF has just been disconnected. It will also supply more than enough fuel for say ...vacuum leaks....Hope this makes sense to anyone bothering to read this longass explanation.

Now the reason the engine won't rev past 3000-4000 rpm is because if the fuel pump is old and tired in the more then 2 decade old vehicle we have. The pump motor is running but in the years of life it's had who knows if it's sat for awhile... gotten rust in the tank.... run that rust grit through the fuel pump impellor wheels and ruined the clearances which would effect the total volume and pressure it would create in the fuel system (not to mention all the crap stuck in the filter). Since the fuel filter may have been changed by the previous owner then you may not know of the crap from the tank. Now the car starts reliably and it can run under load (as the knock sensor and O2 are working overtime to protect the motor with ignition retardation and as much fuel enrichment as possible for the ECU parameters) but now it cannot create boost under any rpm levels. This would be because under boost our fuel pressure increases at a 1-1 rate meaning for every pound of boost we run than we get one more pound of fuel pressure (as this isn't some cheap fuel pressure riser system like on a homemade turbo Honda) So since we know that the fuel pressure regulator will run the pressure at 3 bar or 45lbs of pressure with no vacuum we can also know that under 7lbs of boost we should also see about 52lbs of fuel pressure.

OK, here are some answers now. The engine when increased to 3000-4000 rpm under load will open the injectors for a given rate of "known fuel pressure" but if the fuel pressure/volume can't keep up then it shows up as loss of fuel pressure and then the motor coughs and stumbles as you starve the damn thing for fuel. Of course the second you let off it again it goes back to your crappy idle again (unless you've fixed that now too).  So you try and drive it again thinking maybe if I can keep it under 3000 I'll try and hit boost..... unfortunately you've just made it even worse again as when revving the motor up you've dropped the vacuum and the regulator is trying to up the pressure to the non-vacuum setting of 45lbs and when you try and hit boost it just does this even more quickly which again can result in fuel starvation quite quickly. This again unless thoroughly abusive (which most of us aren't as this would like destroy the motor quickly), we usually let off and never really create enough trigger points to trip the check engine as we know somethings wrong already by the way it runs.

Now how do I check for fuel pressure when it revs all the way up when sitting there(since it needs so little in fuel with no load)... well really long fuel line with the guage where you can see it while driving would show you the drop  (which is really the only way) or a really expensive electric guage so you never worry about loss of fuel pressure without some way of diagnosing it mounted inside the cabin.

I have run into one situation where although more unlikely (after you've checked fuel pressure is good) I've found fine rust particulates gathering on the filters right above the injectors which effectively starves individual cylinders but usually should up as the motor running under 2 or 3 cylinders (if it runs at all). Luckily in this case I don't think this is what's happening

Hope this helps and makes sense. I'll take any criticisms but there are a lot of other way's of having these problems.... I just think from what I'm hearing that this would possibly be the most likely in this case.

Ok, lets tie this knot into a pretty little bow.

First, Nick, the alternator you listed worked like a charm, direct fit save having to widen one eyelet so it would fit over the larger diameter b+ bolt.  As well, the r&r was very simple.  If you have an FMIC, pull that pipe out of the way, take off the waterbox, and it is a very quick in and out through the top.

Second, Khrys,  Very informative post.  I went through it line by line and have the following updates based upon your suggestions. The vaccuum side of things was ok.  I did however have a broken bolt from the output side of the turbo to the hotpipe that goes out to the FMIC.  Resolved that, and clamped it all down a lot more securely than it had be.  Resolved.  NO more air leaks from what I can see.  When I have the time to get to a garage with warmth, heat, and light, I will replace all my vac lines as able.

As to the fuel pump, I have some of my own knowledge to bring to the table from my days of tuning old turbo 8 valve cars that came with a pretty wimpy pump that would live forever if not abused.  What I found is that over time, the pump will work fine at cold idle and start, but as the injector pulsewidth narrowed as the vehicles would warm to optemp the pumps would have a hard time and overheat due to the additional back pressure.  I mention this because it's a very simple and oft overlooked thing.  In the case of this GTIR, the previous previous owner fitted a walbro 255, so we know that unless that has burnt out in less than 20k, the fuel pump is a known good variable in the system.  The injectors themselves are wired tight, and not leaking, as far as I know.  I can back that up with a fair degree of certainty because the usual injector leaking symptom (nasty black cold starts, megarich AF when the maf checks out as good, and there are noair  leaks.  When I have time, I may pull the rail just to make good and sure (as well as to replace the o-rings preventatively, but I'm ok with assuming that they are on the up and up.  Further, another forum post suggested checking the top rail to injector seal as well as internal leakage by priming it a few times and having a sniff for fuel smell at the rail where it joins the injectors.  No problems there.  I will also check the tops of the injectors for the prefilter rust you mentioned.

Now, as to the current state.  The new alternator solved all the issues I was having post maf replacement.  Just went and drove around for a good hour or two and put the metal down very hard.  Solid pulls well into the red zone.  The backfire has gone, and I believe that it was in part due to the fouled plugs clearing themselves out and the AAC unsticking after the car having sat for so long.  The ABS light has gone out as well, likely due to that alternator finally providing decent charge.

I have never owned a more fun car, save perhaps the r32 or r33, but those are givens.

Oh yeah, my stars, what an AMAZING car when it runs. 

Y'all are very lucky owners.  I am now, too.  Definitely infatuated with what I've got.  We had our first real dusting of snow today.  Extremely timely repair job.

The brakes need attention to be sure.  I think, I don't know, but intuit that they need to be at least bled.  The pads and rotes are pretty new, but seem pretty damn soft to the pedal.  Will investigate.  Also, anyone have a good tap on balljoints and bushings?  USDM equivalents?