Edit to add: No idle issues. RPM needle doesn't bounce, just seems to be an issue upon start up and acceleration

Current Miles 88785
I'm back, this time with an issue that's stressing and bugging me real bad right now. I can't seem to get rid of code p0171. I've been told a ton of stuff needed to be replaced like the O2 sensors, Fuel injectors, Coil packs, spark plugs, spark plug wires, MAF sensor, fuel filter, Fuel pump, and throttle body. I have taken the throttle body off and cleaned it with throttle body and air intake cleaner, MAF sensor was cleaned with MAF sensor cleaner.

I went ahead and replaced the spark plugs as 1 started misfiring 2-6 were fine but replaced them anyway I didn't want old and new spark plugs in the motor, the O2 Sensors, fuel injectors (kept the old ones as well as have a spare set), air filter, MAF sensor (I even snagged two extra MAF sensors off two other 3.8's bless those owners for letting me take them) and the coil pack for bank 1 (I kept my old part incase it wasn't that). It's still throwing the p0171 code so I'm putting my old pack back on and sending the new one back. I'm now being told to replace my fuel pump, thought I'd turn to you guys as the shops keep giving me different things to replace and they are all things that's already been replaced so I feel like they are just pulling stuff out of the air.

Injector 1, if you count when I originally replaced them, has been replaced 2 times now. Thinking it could have been a spark plug and spark plug wiring issue, 1 and 5's wires were switched both have new spark plugs, it still dinged on one. Coil pack with 1 on it was replaced because they claimed it had a short. The code came right back on.

When she starts, she starts fine sometimes but sometimes will chug a little and then settle out the chugging sometimes happens during acceleration as well. My Fuel pressure gauge is working properly so I'm a little hesitant on replacing that unless you guys deem it necessary because they are trying to charge me 400+ for just the part, not including labor. I looked up how to replace it and it doesn't seem that hard, if it's possibly that, would y'all recommend that as a DIY? I have the tools I'd need to get it off.

Also wondering if I should get a non-locking gas cap? It's an AC Delco so I didn't think it'd be an issue, people like to syphon gas in this area so I thought it's give me a lil extra protection in that area.

Things replaced so far, all have been AC Delco/Delphi parts*
Both O2 sensors
Spark plugs
Coil pack* (Duralast I couldn't find any AC Delco/Delphi ones on short notice, It's going to be returned as it doesn't seem to have fixed my issue. If y'all recommend keeping it, I do plan to replace it with AC delco later down the line.)
Air filter
MAF Sensor
Fuel filter
Gas cap (AC Delco locking gas cap from Rock auto)

Things that haven't yet been replaced (That I know of, the car spent dang near it's whole life couped in a garage)
Spark plug wires (Replacements are on the way)
Fuel pump
Manifold Gaskets
Fuel Pressure regulator
Throttle body

Everything, aside from the stuff I have replaced is 22yrs old, the MAF sensor was replaced because I could just pull the top off it and I did not like that one bit. There is no gas smell when she starts or when she's running. Gas mileage doesn't seem that bad as a full tank will last me 2 1/2 weeks going to work and back and my weekly movie.

Sorry for the long wall of text, I wanted to be as detailed as possible with what's been done and what hasn't regarding that code. I think that's everything, I hope it's coherent. If anyone wonders why I'm replacing other stuff, I'm pretty sure none of this stuff has been replaced in this cars 22yrs. It doesn't have records of spark plugs and all that but it does have a spotless oil change record. I travel sometimes and I don't want to be stranded in the middle of no where should one of those old parts decide to give out on me

 

Don't have much time to reply at the moment, but the first step is to not keep shotgun replacing parts in the hopes the problem goes away.

You need to take a step back and diagnose it. Get a cheap scan tool that reads live sensor data and see whats happening. If you think its the fuel pump- rent a pressure gauge from Autozone and confirm that before going throguh all the hassle of pulling it.

 

I used my friends scan tool and all it does it tell me that it's running lean. I don't believe it's my fuel pump as it's not doing anything weird. That's why I'm hesitant to replace it and why I've turned to you guys. Different shops either can't read it because they say it has a different program, they are trying to say it's things I've already replaced, or try to say it's my manifold gaskets claiming they smell gas when no one else does. When its pointed out no one else smells gas they then try to blame other things.

It was taken to the dealership for a diagnosis, they said it was misfiring on all cylinders as well as a laundry list of other problems. When I started it, it was jerking badly and the idle was terrible. I told them it wasn't doing that before I gave it to them. The guy that diagnosis kept trying to say its having misfires, the cats shot, my fuel pump is bad and the gaskets needed replacing. I told them I wanted a second opinion and had it towed home because I didn't want to drive it like that. When I got it home I looked under the hood, they didn't put the spark plug wires back where they were supposed to be and one of them wasn't even on the spark plug it was just hanging off the oil cap. So I'm paranoid now about having others mess with it if the dealer was willing to do that during diagnosis

I have sense put them back where they belong, the idle returned to normal, she's back to normal it just that code now that comes and goes as it pleases

When I do test my fuel pump with the voltmeter, what numbers should I be on the look out for?

 

How does it run with the MAF completely unplugged? You usually need the AC Delco MAFs. Ive come home with 5 off brand ones from the junkyard and had every one of them make the car run worse...

I would check the intake gaskets with an unlit propane torch. What is your vacuum reading?

 

I haven't tried it with the MAF sensor unplugged, it did have an aftermarket on there after I replaced it the first time. I took it off, cleaned the original and slapped it back on there. I can try unplugging it at lunch and I'll get back to you on what it does

I do not have a propane torch or any propane accessories so I will have to get my hands on one. Im going take it up to Autozone and Oriellys today to check the vacuum on it.

 

School me on this, What's the procedure on this? I've never heard of this.

Thanks

 

It just exposes any vacuum leak you might have. If it sucks in propane thru a vac leak, idle will become erratic. It will alternate between wanting to die and high idle.

Nothing short of a life saver on my 300zx.

 

As propane is a fuel itself, the engine will respond if any is sucked in. Depending on the size of the vac leak on the engine, the results will vary in severity, but even the slightest leak will usually be enough to disturb the idle speed and show up in fuel trim correction when you pass the area with a leak. When you're at idle, the engine isn't using much gasoline / air - so it doesn't take much to upset that balance with an external fuel.

Personally, I feel more comfortable using some kind of smoke instead - especially if youre just starting out diagnosing a car that doesn't run well. Reason being is that ignition system failures are relatively common and can lead to external sparking (especially on cars like these with actual spark plug wires). Given propane is heavier than air, it'll naturally roll down over the side of the engine towards the floor and could ignite on a bad plug wire thats arcing to the head or something.

The trick with smoke is controlling the volume so that theres enough present to see air movement where its being ingested, but not so much that it obscures your view.

 

Back in the day, I used starter fluid (ether) for that. Now, I smoke everything.