Q45. Run it into the ground or try to repair?

Mom won't drive the Infiniti anymore. Stalled one too many times for her to trust. I like it. The air blows cold, Bose stereo kicks, actually passes people, can take car seats. So. 
 

1996 Q45. 197k. White. 
it has a misfire. The car shakes at idle and sometimes will die at stoplights, but only when up to temp. Put a foot down, and it's magically fixed. Tires are new, ac just serviced, compression check ok, new plugs, new MAF.
No codes.

I can not detect any vacuum leaks. Best I can tell, #8 is slightly fouled. Possibly a leaking injector? I haven't tried putting a stethoscope on it, not sure I can. 
 

questions

1) can I even replace an injector without opening a can of worms? (Vacuum leaks, gaskets that might be nla) that is, if I determine that to actually be the issue  

2) should I even bother? It runs just fine most of the time, I can't afford to sink any real money into it, and with 200k and being 25 years old... maybe drive till it won't, and walk away?

*edit, I should note, should I decide I want the car, it'll be cheaper than most of the Qs on this board. So it literally owes me nothing. 

IMHO a Q45 likes it rough.  Abuse the hell outta it and laugh the whole time.

In reply to barefootskater :

I never experienced the problem but as i understand it, one of the Achilles heels of the Gen1 Q45 is knock sensors. The actual knock sensor is the same sensor as used in the Maxima so the availability of the part is not the problem.  The problem is accessibility.  

These sensors reside deep in the V of the V8.  Getting to them requires the removal of coolant connectors, fuel connectors, air connectors and electrical connectors.  Lots of heat in that V area over the years.  The risk is that it is expected that one of those connectors will break during the  job and many parts are no longer available.  

EDIT: but, you have a '96, that means you have OBD2.  Is the car throwing any codes?  

Should you bother?  Sure, why not?  That is, if you are willing to accept that the car might not make it through the surgery.  

I  can't imagine parts being NLA.  Last year I redid the top end of an 91 Sentra and everyone had parts.  Auto Zone, Rock Auto, Amazon.  Once the aftermarket adds a part to its arsenal, they hold on to the dies/stamps/cnc so they can always provide them.  Even if they stop fabbing and stocking a certain part, they usually still accept orders for them.  Injectors and o-rings are pretty universal.  They're like tires.  You just get the right inlet, outlet, o-ring, electrical connector, flow, and height.  Or just have yours rebuilt.

Do a compression test first.  It's possible you have a valve or ring issue which shows up at lower speeds but becomes less noticeable at higher loads.  From there, move on to obvious electrical/ignition things.  Move the coil/plug/wire to another cylinder and see if OBD notices the misfire on the same cylinder or the one that the stuff was moved to.

Diagnosis is pretty easy.  If it's an injector, replace or rebuild it.  Ignition components are cheap.  If it's a scratched bore or cracked ring, drive it until it explodes and then donate it or sell it here as a challenge car.

Did you check the intake boot?  Down in the folds of those bellows they often dry rot and crack.  Because it's after the MAF it gets all kinds of confused because the MAF doesn't agree with the O2s.  It will often throw a lean code because it reaches max enrichment to try to satisfy the O2.

Did you try checking coil packs?

It did throw a knock sensor code once a couple months ago. That said, I don't see how a knock sensor could have anything to do with a misfire. 
 

The intake boots are good, and it shows no sign of a vacuum leak, though I haven't tried putting smoke in it. Idling and spraying carb clean at all the usual places didn't reveal anything. 
 

Parents did pay a guy to diagnose it, and he claims to have done a compression check and everything was ok. Not a guarantee, but I trust the guy. He's the one who replaced the MAF, as it was throwing a MAF code at the time. 
 

imma just drive it for now. Like I said, most of the time it runs fine. Just shakes like it's having withdrawals, but only at idle. My mustang shakes (2.3) so I'm used to it. 

In reply to barefootskater :

Real dumb solution- can you turn the idle up high enough to avoid the shakes?

In reply to Tom Suddard :

Yes, or, tried swapping coils around. The problem seems to stay with #8 though the only real sign is a slightly fouled plug. No misfire codes, not since my parents picked the car up, just one instance of a knock sensor code and MAF. Mechanic replaced MAF and when the problem didn't go away my folks decided not to spend any more money. 

Oh, and the steering fluid falls out. Needs a few ounces of fluid every week or so. All the hoses are super grungy, so hard to say where it's coming from. 

I had some pin fit issues on my 94's MAF that caused some issues. Clean the pins up and tighten them up a bit with a little pick.

NICO was a great forum for tech support on my Q45 years ago but I honestly have no idea if the cars are still popular enough to have the dedicated following they did 15 years ago

I've always had a liking for those cars.  It sounds like it has some good attributes for you.  If the body and interior are in decent shape I think it would be worth keeping to going.

Just drove it across town again. New (to me) issue. It bucks. If I had to describe it, I'd say it feels like it's fuel starving. But again, applying a boot makes it act normal. Still no codes. Mom says "oh it's always done that." No surging, just feels like no more gas. 
 

On the bright side, I thought the sliding roof was busted.  Nope! Works great. That's a huge plus. 

I did have to resolder some joints in the fuel pump driver at one point for bucking which was not unheard of. I was fond of the theory that as the fuel pump aged drew more current it eventually exceeded the thermal capacity of the factory solder joints.

In reply to psychic_mechanic :

The driver? In the ecu?

And it died three times on my way home. Twice while driving, throttle on. All my experience is screaming fuel pressure issues, maybe time to buy a gauge. 

In reply to barefootskater :

IIRC it was behind the rear seat, a seperate module hanging underneath the parcel shelf. Depending on the engine load it varies the voltage to the fuel pump like a blower motor resistor to 3 different levels.

NICO thread

In reply to psychic_mechanic :

That thread is gold. I poked around on that forum earlier but couldn't find anything. The problem described is exactly what I'm experiencing, even down to the engine shaking at low rpm. And it doesn't sound hard to repair. Awesome sauce. Thanks!

Well shoot. I tried bypassing the FPCU but it made no difference at all. The fuel pump runs great. It is a regulated return system, and I should put a new filter in because that was one of the things the p/o did, and I don't trust it. Especially with the amount of fuel cleaner they ran through it. 
 

The issue is definitely worse when it's hot out. Still no codes, despite it running pretty rough and dying a bunch. Hard to start back up the last few times too. Guess I'll keep plugging away. 
 

Dad thinks is plugged cats. But, he always thinks it's plugged cats. 

In reply to barefootskater :

They sound great with an open exhaust so can't hurt anything.

In reply to Stampie (FS) :

Except for emissions. And chances of getting it registered anywhere that checks emissions. I generally don't mind that kind of thing, it's not like I'm driving that much anyway. But I generally take great caution not to do anything I can't undo cheaply later. "Coring" or removing cats falls under that category. 
 

Plus, I don't think that's the issue anyway. 

So does it run and start ok when cold but once it warms up it starts to run rough?  If so that sounds like a closed loop/open loop type issue. Can you disconnect the O2 sensor and see if it smooths out?  I'm not familiar with the Q45 and if there's a way to force it to stay in open loop for diagnostic purposes but if it runs well when in open loop it is likely sensor feedback.  For what it's worth I know on my LS1 equipped Chevy's I can disconnect the MAF sensor to force it into open loop operations.  Not a fix but can help chase down a problem if you can't actively read the sensor inputs.

Try an Italian tune up on it and run it hard for 3-5 min with a couple solid pulls to redline?

So. I've had a vehicle buck like this before. It was a bad throttle position sensor. I'm still getting no codes, but something is wrong. 
 

So, on the closed/open loop thing, I'm thinking this may be helpful. If I unplug the MAF, that should force it into open loop and run essentially on throttle position only right? I know relatively little about EFI. 

Swap injectors beteeen 8 and the one next to it?