Thread: P0171 (yes i've read the other posts)

I haven't driven my car for a year and recently transplanted the engine into a new body. I'm pretty sure before the car was running fine. Long story why I haven't driven for a year. Lady was passing a car going up a hill, I was on the other side coming over on my motorbike. She hit me head on and I lost my leg. So over the past 6 months, I've been rebuilding a car from the bottom -> up keeping busy

P0171. Pegged STFT and LTFT


Engine specs
T66 turbo with 3" downpipe
Lt1 MAF with min-afc set to 82%
HV3
#130 springs
ST5 cam
2 fuel pumps
#80 injectors
PCV system with catch can & smog pump. (I have this capped off until I can find out why my the car is lean, before i introduce more unmetered air into my intake)

First I replaced my egr stove pipe with a good one I had laying around while the engine was out. Once I pressurized my intake and used soap and water, found the second one is cracked at the seal too. So I RTV and put in a penny to close it up for good. No more EGR to worry about leaking. Also closed up the egr at the exhaust side but left everything in for emission checking. The motor is still plugged in, so no codes set.

I put in 10psi into the intake from a vacuum hose and it holds and slowly goes down. I'm confident it's not a vac leak on how slow it drops down to zero (but i've been known to be wrong sometimes). I can take a video of my gauge if I think it's slow, some may not. If I remember correctly from an hour ago, 5 seconds to drop to 5psi then maybe another 8-9 seconds to drop close to zero.

IAC counts are 35 at warm idle. (I've read 40 is normal, but I do have an aggressive cam). It will increase if I rev the rpm, and come back down to 35 at idle.

-12 psi vacuum at idle

Fuel pressure is 44 at idle, 52 with fpr pulled. I do notice the system doesn't hold a pressure, when turning the key to 'on', the system will pressurize and my aeroforce gauge will go back to zero as soon as the pump stops priming. Don’t think this is an issue causing me to go lean because it runs at idle fine. Just takes a few cranks to get it going, something to do with my dual aftermarket pumps. Again, I don’t think it’s an issue for this right now.

When I unplug the MAF, the STFT will go into the negative and the LTFT will starts to come down. The car will surge and eventually die after 10 seconds or so. I’ve cleaned the maf with electrical cleaner and special q-tips for electronics.

I've done the big 3 upgrade, so I don't think it's a grounding issue. Tomorrow I’m going to disconnect my big 3 and play around with the grounds, maybe too many is bad somehow.. ?

I'm puzzled.
Thanks everyone.

Let me know if you figure it out. Seems like the exact same issue my car is having. Except my LTFTs are pegged and my STFTs seem to fluctuate.

Going to change out my pump and put a rewire on tomorrow and see what happens.

I just took my big 3 off before this issue started happening and am considering putting it back on now.

The MAF is reading 1# per minute (7-6grams per second) at idle.
If I just touch the gas a hair at idle, the LTFT will move closer to 0. STFT will not.
Wideband agrees with O2, 16.5 to --- reading.

It's a LT1 MAF, not sure how else to test it.

My WOT make the LTFT dead on zero (OverKill tuned pcm)

Can I not use a scantool instead? Little fuzy how to check for a bad maf when its reporting values

Aeroforce and Alexpeper. I can monitor the HZ & #perminute, I just don't know what to compare them too. At first glance, they seem to be intact. My min-afc is set to scale down the singal 82%.

I think my MAF is ok. At hot idle, 2.25HZ at the MAF. 1.87HZ at the afc/pcm side. So the afc is doing its job at the 82% level I have set. Scangauge also reads 1.87HZ. If I slowly turn up the afc to bring it to 2.HZ at idle, the trims start to level off. (2 out of 3 times i did) I'm thinking I just need a tune for some fine adjustments. I added a bigger I/C and 3" downpipe since the last tune. (I'm turbo).

The only thing I don't get is when I unplugged the MAF, the trims start to move closer to zero (somtimes, sometimes it does, sometimes it doesn't). Maybe that puts it in a speed density mode instead? Ithought I read when you unplug the MAF and your trims level off, it's a bad MAF.

Thanks Rico for your help.

I just put on air breathers for the PCV. The EGR is just closed up for now to help diagnose the issue aswell. I'll deal with any SES codes until I can get them tuned out. I'm not sure what my RPM's are set to, but yes setting the rpm low really cuts your timing chain life in half. (But the car sounds soo cooool) I took my fuel pumps out and notice 1 bleeds off the pressure. Again not to concerned with it, 1 is always on and 1 turns on under boost. Turning them both on at idle, results in 60psi.

1. I'm using the stock L67 MAP
2. I think my #80 are from zzp, which i think is Mototron
3. I don't have a stock L67 MAF anymore. I did "borrow" another LT1 MAF but same results as before.
4. L67 TB on L26 top end, so there is a coupler infront to the 85mm LT1 MAF
5. I'm from Ontario, so Will (OverKill) is a friend. He's done my many in car tunings.

The car's last tune, i'm pretty sure we wouldn't of left it with high ltft at idle/cruise. I'm confident the MAF is tuned correctly (WOT still locks in at long term fuels at zero) Since the last tune, I put the engine in my new body and upgraded to a larger incooler and larger downpipe. Everything else shouldn't of effected the tune. I'm feeling around all the exhaust joints for any air blowing out.

I start over again with the vaccum tests. I'll take a video of my boost gauge to see how long it bleeds off when i pressure the system and go from there.
One pic on my phone.

Sorry for the late reply, kind of got a body cold all weekend and barely moved. I'm going to work on some speaker boxes the next few days to give me a break on this car. lol.

I did pull the manifolds off, cleaned them and put them back on while the engine was out of the car. So I'm sure they are sealed fine, as doing this all with the engine out is a piece of cake. In the car, I've lossen all the turbo/downpipe/cross over bolts and re did them to see if anything was offset while installing them. I'm actually going to look into a smoke machine (or make one out of a party fog machine) to check for exhaust leaks.

I've taken out the IAC and cleaned it, wasn't that dirty though. It does move back and forth and the scan gauge shows values withit it's range. I forget off the top of my head, I'll rescan it though but I think it was around 35 at idle. I also scanned the MAP and BARO and they are showing the right values. Plus if you substract the BARO from MAP, it gives you the vaccum, which my boost gauge is confirming. The MAP is sitting at the back of the UIM. I tapped in some barb fittings into the UIM to run the devices. In the picture above, you can see by the FPR I have a barb fitting just for it.

The BOV of the turbo, Hobb switch and the MAP are off a barb fitting. FPR is on its own barb fitting. The boost controller and wastegate are off the brake booster, and the HVAC/boost gauge is off another barb fitting.


I'll take some more pictures in a few days, I have a fever of 102F so I'm bed resting it for now.

OK I took the week off from cars and watched a heck of a lot of movies. Feeling better. This weekend I'm going to tackle it agian.

I quickly plugged up the pcv system shut and put a boost gauge on the oil stick spout. It does actually goes postive 1-2psi and oil starts to burn out the exhaust. Turn on my smog pump and it starts to pull a few psi right away. I'm confident my pcv system is sealed from the intake.

When I started to burn oil, I noticed some smoke coming from the rear of the engine. I'm not sure if it was the wind blowing it back to the front of the car from the exhaust or if there is a leak back there. So I bought a fog machine. I'll plug up the exhaust and throw on the smoke machine and see if there's any leaks. I'll also try on the intake too.

Is 1 valve always shut compared to the other? In my mind, if I smoke the exhaust there should be no traces of smoke in the intake system. Two valves should never be open at the same time.?

This has plagued me for months and when I lay in bed it haunts my dreams. I'm testing everything, 8 times over. What have I done to the car, which upgrades all at once that would cause this. Bigger intake/IC piping, sucking more air in? No cause the MAF will take care of that. Bigger exhaust, maybe a leak in the pipes because it's hard to fit 3" of turbo exhaust in the car. Ok buy a smoke machine and check for exhaust leaks... No leaks. Go back and check intake again, it slowly holds pressure at an acceptable rate. grrr. Maybe it's a bad sensor, bad ground, bad wiring...

Putting on a smaller brake booster to fit in the 3" exhaust piping, my brakes were mushy and you had to put a little bit of force on them. I thought, I haven't driven a grandprix in a year since tha accident, i'm using my left foot now, this new car has 13" brakes upfront, 12" on the rear, smaller brake booster, SS lines instead of plastic, it just must be a little more soft then normal. A few times it's crossed my mind to plug the brake booster line to cancel that equation out of the system, because I've plugged every other vacuum source. Then I'd fall alseep and forget.

My trims are starting to move back to zero. Dam the brake booster.

Yes it's actually the brake booster itself. At the end where the metal arm comes out to the brake peddle. It's not audible because of the foam stuffed in there. Put an air compressor to it and you can tell.

I feel like an idiot, the softer peddle should of been my main hint. But so many things were new to me, GXP brakes all around, smaller booster, SS lines, etc.. Plus I should of pulled the hose off after the car was running and noticed there was so 'suction' left in the booster. Off to the wreckers today.