the dreaded PO171 after serious engine work

[bonniebird]

my 98 bonnie as you may have read before pretty much a good part of the engine was flooded with radiator fluids due to a hairline crack in a tank that started to spew and thus was sucked in thru the intake..wound up overheated and never seen such fried head gaskets...anyway got the heads all dipped and fluxed and valve job..all new UIM/LIM upgraded gaskets for LIM,plugs,wires,new map sensor (I lost old one) new radiator of course,etc...took a while but its back together and running great just like before other than the first day out it threw a PO133 code (slow response bank 1 ) cleared that and now its always PO171 (lean bank 1) the code never comes at start up its always after its warmed up about 5 or 10 mins.....sprayed carb cleaner @ vac points and found a good leak and took care of it but still codes..tested O2 sensor in live data and when you spray carb cleaner right @ disconnected vac the volts shot right up past .900 like its supposed to...I have almost 150k on the engine and im pretty sure its the original o2 sensor ...can it check good and still be bad? right in the middle of the firewall is what I think is some hexagon shaped thing having to do with the a/c and we broke some black plastic stuff off of there as we were attempting exhaust manifold removal (very fun btw!!!!!!) Could that cause the code? I've read so much on this in the past 2 weeks that my head is spinning and I'd like to aim my S&W 45Colt at that *dang* illuminated silly engine on the dash!!! But I'll gladly listen to your thoughts..Thanks guys

[zuper8]

One time I had the same problem, it ended up being the EGR tube that goes into the intake manifold. It cracks at the flange and is pretty much impossible to see until you take it off. Worth checking, they are very delicate.

[Jfridge92]

^ +1 on the EGR tube. Mine is likely cracked there for my P0171, I just don't feel like draining some coolant to pull the throttle body hahaha.

[bonniebird]

Is there anyway to diagnose if the fault of the po171 is due to a cracked egr pipe - such as spraying some carb cleaner near there and listening for a surge?? Just hate to have to tackle the tb removal again unless I'm pretty sure...

Thanks guys,
bonniebird (Melanie)

[Jfridge92]

You can try and spray carb cleaner, but the location of the tube can be really hard to check with it on the car. Typically it's best to remove it, cover one end, and shine a light through it in a darker room. You'll be able to see the cracks easier that way. It's a pain to check, so try carb cleaner first, but that's not guaranteed to find the leak there. I wish it was in an easier spot myself haha.

[bonniebird]

In this never ending quest of trying to track down this PO171 - I sprayed carb cleaner under the throttle body aiming it at where the egr tube goes into the manifold - - did this 3 different times and every time it caused the engine to die immediately...is this telling me this is where the vac leak is??

[haro1225]

Usually it will rev up when the carb cleaner goes in but if that's the only place that causes any change when you spray there, you may have found the problem.

[bonniebird]

When we were checking for vac leaks the other day the engine certainly did rev up when we found a leak...but it just died when sprayed at the egr tube @ the lim...I may try and smear some sort of copper rtv or some such goop to try and isolate it further before pulling off the tb for no reason...this is just so aggravating ....*dang* po171!! Grrrrr!!!!

Thanks again guys for your helpful input

[KM AXer]

A quick note about the cleaners....

Some are formulated these days to be quite "Non-Flammable". The vapors from a spray at a leak may cause the rpm to rise if the stuff used will readily burn, but may cause the stalling or stumbling described if it is more like a fire extinguisher in composition.

[bonniebird]

Going crazy trying to pin down this PO171 - - and driving hubby crazy in the process....after we got the engine all back together after the head gasket/valve job/uim/lim - it ran great but the first code was po133 (slow response oxygen sensor 1) we cleared that and then for the last 2 weeks or so its always been the po171 and would pretty much pop the code within 15 miles or so - but the last 2 days its been 50 and 70 miles before it coded ...today when I checked the scanner there was also a pending code PO137 (oxygen sensor 2 low voltage ) I guess theyre all related to a lean condition...I was really thinking that we probably have an air leak somewhere in the egr tube the part that goes to the intake manifold - but now I'm wondering if it could possibly be a bad MAF sensor...when I took it out to check it last week it looked totally clean but I sprayed it anyway with some carb cleaner, let dry, reinstall...but you know prior to all this my whole engine was awash in coolant water because of the ruptured radiator tank -- my maf readings at the time the code (po171) sets seem weirdly low...0.01..0.05..0.07......in the service manual it says I can disconnect the maf sensor and if that corrects the problem then of course replace the maf....it just doesn't seem like the car would even run without the maf, but I'll try it..seems like it would code instantly...now my head is spinning...any thoughts from you folks are most appreciated.

Melanie (I just wanna get back to my 67 firebird 400 rebuild!!!!!!!!!!!)

[bonniebird]

I disconnected the maf and of course it threw a 103 code...so I guess the maf is good ? ...guess I'm still looking at a possible egr tube crack..just wish it was easier to get at...just don't understand why maf readings are so low and the short and long term trims were pretty high (16.4) but in the last day the short trims look more normal (3.1) but long still high...I think I'm overthinking this whole mess since I'm so ocd!! Thanks for your patience with my ranting...

Melanie

[KM AXer]

I wish I had any more advice to offer. Keep at it, you'll figure it out.

As for the Firebird, one of my buds in HS had a '68 400, one hell of a fun time it was!

[zuper8]

I know it seems like a pain in the butt to take off the throttle body, esp. if you have old vac connectors threatening to break, but if you're really at your wits end it's worth it just to check. Only a little coolant will spill. If you sprayed cleaner on the area and the engine died, well, to me that says it's sucking in there no doubt. Those suckers are so easy to crack I don't know how anyone manages not to crack them when doing the LIM job. I was able to fix the crack with JB weld on one of my Bonnevilles. Wish so badly I could source a new one.