1996 2.7l p0171 rough idle, shakes and dies under WOT

I’m having real trouble with a p0171 code on my truck. Read through a bunch of the threads already on this issue but I’m still stuck. I have ST trims at +19.5% and LT trims at +25-30%. If I rev it out and then push in the clutch it will stall. At high engine loads it will die off and start bucking/sputtering. So far I’ve replaced the MAF, both o2 sensors, and the intake (all OEM except intake, it’s a volant). Fuel pressure at idle is right around 50, I smoked the intake and found zero leaks. Catalytic converters is good. Blocked the EGR and test drove with no difference in fuel trims (reset after blocking it). Really the only thing I haven’t messed with is the injectors but before I buy those Itd be great if I could get some other input from guys more experienced than me

 

What brand of O2 sensors and MAF? Check you PCV valve and hose. What do the spark plugs look, black or clean white?

 

O2 sensors are denso, MAF is toyota OEM,PCV valve is good, no intake leaks, plus are blackish if I remember right (they have 10k miles on them, I checked them a couple weeks ago). Yesterday I blocked the EGR and it feels like it runs a lot better, no sputtering or stalling, but fuel trims are still reading way lean

 

run a compression test I bet you have a bad cylinder.

 

200 on cylinder 1, 180 on the other 3

 

Check fuel pressure, most chain parts stores have a kit you can borrow. Test pressure at idle and ~3000 RPMs. Should read between 43-45psi and no fluctuation, do some research to get the exact number.

If fuel pressure is low or fluctuating, it's either your filter, pump, or pressure regulator.

If fuel pressure is normal, it's time to pull the injectors and have a shop flow-test them on a bench. Avoid buying "rebuilt" or aftermarket replacements as they tend to be chinese knockoffs and problematic in my experience.

Good luck and keep us posted on progress!

 

Seem like you have a major vacuum leak in your system in my opinion.

 

It’s been about a month or so, but I did check the pressure and if I remember right it was around 45-49 with no change at 3k RPM/ no load.

 

I don’t think so, smoke tested my intake a few times from a few different places with no signs of leaks. Also sprayed brake cleaner everywhere with no change at idle

 

OP, did you ever get this solved?
i have a question for you: when you smoke tested for Vac leaks, did your EGR vacuum modulator leak smoke?

 

No still working on it, no smoke anywhere with test. I’m thinking it’s an open/burnt wire on primary o2 heater circuit. We’ll see

 

how did you smoke test it? I made an adapter that goes on the MAF end of the air tube then I prop the throttle plate open and then I squeeze all the rubber hoses/lines.
If there wasnt a massive vacuum intake leak she should run in closed loop mode just fine.
Is your OBDII tester capable of Live Data?

 

I had same problem, bought the actual coil packs only swapped those out on misfire and was good to go..!

 

Found the problem, made a post in another thread on it. My Auto ECU is been using was corroded from having water in the truck (high humidity=corrosion I’m assuming) the o2 signal wires were basically melted off the board so the ecu wasn’t seeing any voltage and just pegging the injectors out to try and compensate. Had another MT ecu sitting in the garage for a couple years so I swapped all the harnesses and tried running it on that one, kept getting p1600 for battery voltage fault. Turns out that ECU was corroded too, just on the BATT+ terminal. Pictures attached. 1 mint condition eBay ecu later and the truck is running mostly perfect, getting about 17-18 MPG coming from 11MPG before. No lean codes, no coolant temp codes. EGR is stuck open a little probably from it running so rich for the last year or 2.