Reposted to hopefully the correct section--

Car is 2001 T/A, 6sp, 136k miles, BBK SSI Intake w/BBK 85mm TB, SLP Lid w/stock paper filter, stock exhaust, new NGK plugs and MSD wires

First off, thanks to everyone on this site for amount of knowledge you all share. I've done quite a few searches and solved most of my problems, but I'm getting stumped and need some help! Sorry for the long post explaining what I've done and where I'm at...

I first had SES Codes P0171 and P0174, lean both banks, and a slight ratlle/knocking noise, but only at operating temp (I thought it was trans/clutch rattle since I know it has a cheap clutch in it). I had already fixed a vac leak (HVAC--thanks ls1tech!) and couldn't find another, so I took it to a shop that didn't come off as retarded. I figured the o2's were bad based off some research/opinions, so I had them checked. The upstreams (ex manifolds) were dead, but the shop didn't think that was the root of my problems; the ones at the cat were "lazy". Checked MAF--perfect. Ran a smoke test for vacuum leaks, and found that the nipple on back of the MAP sensor had broken, so broken MAP sensor and vacuum leak. Fixed, no more leaks. I went ahead and ordered the upstream o2's anyway.

The car was running like a champ, but the SES light cane on a couple days later. Still ran great, and no rattle/knocking noise. I have them scan it--lean both banks again, but the light goes out on its own later on. My upstream o2's arrive, pop them in, runs even better. No light.

About 2 hours later--SES light comes on, knocking noise is back (under load below 2k rpm, then goes away--just like before), lost a little power, and oil pressure dropped ~10 psi (hovers below 40 instead of above 40--this is a new problem). First scan it was just Lean Bank 2, but scanned later and it was Lean Both Banks as well as P1626-Theft Deterrent Fuel Enable Signal Not Received. All this happened at once, and I'm not sure where to start.

EDIT Took it back to the shop today to have them do some diag. The fuel filter is new, 44K has gone through it, and I had checked the fuel pressure before (only when cold) and it was fine. The shop had also checked it cold when they first had it and it was fine then too. However, I took it to them while hot today and the fuel pressure would not hold; you could just watch the gauge steadily drop. They're going to try and isolate whether it's a leaky injector, or more likely a bad fuel pump/module. That makes a little sense because the car fires right up in the mornings, but after it sits in the afternoon it cranks for about 5 seconds before it fires, but could that P1626 code be related? Could that be cutting the fuel and causing it to run lean?

Any/all help is appreciated, and thank you if you're still reading this!

 

Seems like you are on track to finding it. I don't hear of injectors being an issue but rather pumps going bad.

Are they able to put a volt meter on the pump itself to see if the low pressure is caused by the PUMP not being able to put enough power out or is the signal TO the pump not high enough.

Also that you said BOTH banks are lean leads me to believe a pump issue and less of a injector issue. I would think an faulty injector would cause issues on one side only and be read as lean by the o2 sensor.

Either that or there a good vacuum leak after the MAF which air is getting in and tripping both banks to go lean.

There are some good youtube videos explaining how to read o2 sensor signals while revving the car to determine whether it is a fuel issue or vacuum leak issue. I had a similar issue with my 99 Cobra. After replacing 2 o2 sensors (which did not fix my problem) I decided to attack it systematically and narrow it down. Came to be a vacuum leak b/w upp and lwr intake manifold. I had my long term fuel trims constantly rise to the max of adding fuel...so I knew the fuel pump wasn't an issue. Lead me back to a vacuum leak problem.

I used these types of videos to help understand diagnosing my issue.


This video shows the Long Term Fuel Trim (LTFT's) are HIGH meaning the computer is demanding more and more fuel to the point that it will eventually max out, but the system STILL needs more fuel. Which will trip a "lean" condition....hence caused by a vacuum leak. Your situation may be different where you see LOW LTFT values because the pump can not supply the required fuel amount.

 

Thanks for the response. The shop got back with me today after a few hours of diag and informed me that the check-valve in the fuel pump is what is bad, luckily not the pump itself. To alleviate my hot-start issues I can just turn the key a couple times before firing, which I can deal with for now since the pump is delivering fuel while running as it should. They ended up troubleshooting the lean condition to the MAF itself. I wasn't able to talk to the tech today to find out exactly why, so I don't know what exactly is wrong with it. I know it is clean and looked good, but I never tested it myself. I did ask if they were sure there are no vacuum leaks and they said it smoke-tests just fine.

Glad I don't need a pump/injectors right now, and a MAF was kind of on the list already. If I do need to replace it, should I just replace it with a stock 78 or get an 85mm to go with my intake/throttle body? And if I do go bigger, is a tune necessary even with a stock gm 85?

 

i went through p0171/4 on my truck, along with P0101 MAF.
if you're still stock except for the intake manifold and throttle body, i think basic diagnostic procedures will work- when you change significant things from stock like larger/different MAF sensor or descreen it, different cam, headers, or reprogram the PCM then it makes it much harder. Generally P0171/4 if you consistently get both means it's air intrusion upstream of the intake that's affecting both left and right O2 sensor. the dtc means the o2 sensor read lean for excessive amount of time, 2 min i think. what generally causes this is emissions equipment such as the fuel vapor purge solenoid that allows fuel canister vapors into the intake under certain conditions, and AIR pump solenoid that goes to the exhaust which pumps fresh air into exhaust to help the catalytic converters preheat. you're looking for anywhere air can enter into the intake and throw off the fueling calucations causing a lean condition, or into the exhaust piping causing a lean condition. very common those solenoids over time are prone to not sealing and leak air past them, they don't go bad electrically so they won't throw a specific DTC, but the PCM has no way to know they are leaking other than seeing the affect at the O2 sensor. And with the evap system i believe there's a solenoid between the evap caninster and the intake, then there's another between the canister and outside air. so you would want to replace both there. on my truck it was nice because the one solenoid was right on the intake behind the throttle body, was $7 rockauto. sorry i don't know specifically on the f-body, i believe a lot of it in on top of the gas tank so you'll have to drop it.
the other thing is the PCV system, the little stub hose between pcv valve throttle body is prone to cracking and leaking, so check all those hoses between the valve covers to the throttle body. and don't overlook the oil filler cap and dipstick sealing, or elsewhere on the motor that air can enter the crankcase. i don't know on the LS1 if the PCV system draws fresh air into the crankcase after the MAF, i know it did on the 8.1L in my truck in which case it's air calculated for by the PCM- if extra air enters in not accounted for by the MAF then that can be a problem.

for over 10 years and 136k miles my money is on what i described, i wouldn't touch the MAF sensor at this point unless you get P0101 or other specific MAF dtc.

 

I don't think your check-valve in the fuel pump will cause you to run lean. It allows the fuel pressure to bleed down but once the car is running, the pump should supply enough pressure.

I'm betting you have leaking intake gaskets if they haven't been done. That or your MAF is bad.

 

Does the BBK intake do away with the EGR inlet like the LS6 and FAST do??

That is one major source of un-metered air/vacuum leak from that o ring gasket being bad, or unseated, IF there is still an EGR system/pipe on the car.

 

You're right, it's not causing the lean condition but the pressure is bleeding down. The pump is working fine otherwise. I also checked for leaks around the intake itself and can't find any--the gaskets were a thought early on.

EGR is still there, and I don't think that has been checked (I never did and my mechanic didn't metion it.) I will be looking into that before I buy a new MAF.

 

Not sure what I was thinking of, but the car does not have EGR. However, I pulled off the block-off plate and there is no O-ring. I found the instructions for installing the BBK and it says there is an O-ring that goes under the block-off plate. Could this be my problem? That the block-off plate isn't sealing?

 

Yes it could if BBK says there should be an o-ring gasket there.

Also make sure that plate is torqued to spec (BBK should have that available somewhere), and I would even Loc-Tite it with the red stuff.

I still have my stock factory EGR setup, and EVERY time my car starts behaving like what you've described, I KNOW it is THAT stupid little gasket o-ring which has become unseated from and shifted on the EGR pipe, causing a MAJOR vacuum leak.
It has gotten to the point that I carry around a ratchet with a 10mm socket on it and a spare o-ring AND some of that self sealing, non-adhesive silicone wrap stuff to fix this on the run.

I guess this is just one more reason so many do away with the EGR system, and go to LS6/FAST intakes which do not even have that port/opening in them.

 

I broke out the carb cleaner, and sure enough it was leaking from there. Found a O-ring that fit the groove and coupled with a little red RTV, it is sealed for sure. Couldn't find torque specs, but it's tight.

However...there's two male fittings on both lower sides of the intake in the same area--I believe PCV on the pass side and EVAP on the drivers side. Carb cleaner tells me that BOTH are leaking. I think the PCV side is just a bad hose, but I'm 99% sure the EVAP fitting is leaking where the fitting is joined with the intake. Is there a way to seal that? Maybe from the inside? Is this a problem with BBK intakes?

 

Your mechanic missed a lot of stuff or just didn't do any work when you asked for a vacuum leak test. I bet the guy at the counter knows his stuff but the mechanic is lacking. Call and give them friendly feedback.

The pcv and breather fitting are on the passengers side and evap on the drivers. If they are leaking try to get some hose clamps to help seal them to the male nipple. The evap is a quick connect fitting you may need to purchase from the dealer

I believe the bbk's suffered leaks from the manifold gaskets in the early models. I think they changed the design a while back and new ones have rubber inserts where as the initial designs were stamped aluminum for gaskets that would eventually leak.

 

Damn...this is why I don't trust anyone to work on my car...

All this time it took spraying **** down with carb cleaner to find THREE vacuum leaks!

OP, now is the time you take your car back and do a lot of legwork on your own car. If you find a problem you can't fix, THEN bring it to the "mechanic" to simple fix that one issue. The time you are paying him to "diagnose" issues clearly is not well spent lol.

 

Yes, I'm going to attempt to fix these issues tomorrow. I went back to the mechanic and pointed them out, and he swore up and down that they did not smoke and that the smoke ran all the way through the system as it should. He did admit that he did not spray it with anything, which I probably would have done first if I were him...

I'm not too upset since they've found/fixed legitimate issues that I did not know about and/or did not want to do myself. Also, after I still had issues they T/S it for no charge and didn't screw me on a fuel pump, so good on them. It's just annoything that every time something gets fixed the next thing in line breaks!

 

Well good thing they seem to be treating you right. A decent scanner/code reader with live data feed works wonders to diagnosing issues like this.

I suggest you pick one up to use in the future.

 

Little update:

Fixed the few vacuum leaks I found, not much of a change. It's still running great when it's cold, but when it warms up it has a slight knock under load below 2k rpm, and when it starts doing that the oil pressure is still dropping 10-15 psi. I can't narrow down any more vacuum leaks, the upstream o2's are new, MAP sensor new, PCV valve new, MAF clean (one shop said it was "weird" and another guy said it was fine), new paper air filter, just Seafoam'd it, fuel system is good.

I said I can't narrow down any vacuum leaks, but if I fog some carb cleaner toward the front of the intake it occasionally stumbles. I can't make it repeat itself though, it's just random, so there may be a small small leak, but I don't think that would cause my oil pressure to drop and all that, and it actually seems to be affected more when it's cold and running well. I'm really at a loss now. Keep in mind that for a couple days 2 weeks ago it ran absolutely perfectly after a big vacuum leak was fixed due to the broke MAP sensor. Possibly a closed-loop issue? Any other sensors I should check/replace before I pull the intake and re-seal it for lack of anything better to do?

 

Ok, so I got the Torque app and one of those bluetooth OBDII readers and have been observing my LTFT's and o2 sensor activity. At idle, my LTFT's are both at 25%, with the STFT adding another few percent. While accelerating the LTFT's drop ~5%, but don't stay there long. All of this indicates a lean condition, hence me having P0171 and P0174, lean both banks. STFT never strays too far from 0 in either direction.

My front o2's (new) are working as they should, but I noticed that the rear o2's stay around 700mv almost all the time, occasionally going to ~600 or 800. Very occasionally they would drop to ~2-300, but almost never. I wanted to see if they'd respond to a big vacuum leak, so I pulled the EVAP hose and they instantly dropped to 0-100mv range just like they should. Either they're working properly, or they happened to wake up for this test.

So my fuel trims indicate a constant lean condition and SES, but my rear o2's are indicating an almost constant rich condition. Does anyone have any insight as to what my problems could be? I'm thinking it could be my cats, but really hoping not. It still runs awesome when it's cold, but once it's good and warm it starts rattling/detonating under load. Idle/revving sounds pretty perfect all the time.

Also, my alternator is reading like it's a little weak, showing high 13.6-14.0V range. My coolant is also in the 220-230 range and I plan on changing the thermostat. Could either of these be tied in to all this?

 

Having the 02's reading rich and the LTFT's showing 25 go hand in hand. The car is always adding fuel (LTFT's showing 25 and 02's reading high voltage) because something (un-metered air) is getting into the system and the car adds fuel to compensate.

When the car hits it's max allowable fuel levels it will trigger a SES for a "lean" condition saying "hey bro I'm adding all the fuel I can and STILL can't get the fuel trims in spec". Somehow air is getting in, the car compensates and adds fuel until it can't anymore.

When you say the front O2's are working correctly, what are they doing? If they fluctuate up and down like a sine wave then that's good. What do the front 02's do when you pull a vacuum hose? Do they flat-line as well?

If the O2's are the same kind front and back then try switching them around. Put the fronts on the rear and rears up front and see what happens. Kinda like chasing a misfire.

The fact that you have BOTH banks reading rich (indicating a lean condition) makes me believe a vacuum leak or crappy 02's giving false signals to the computer. AFAIK the computer only listens to the 02's when the car enters closed loop = engine is up to operating temp. Monitor the 02's as the car warms up looking at the water temp and 02's together.

Do you have L/T's? Check for a loose connection in the exhaust pipes before the 02 sensors. Or if you have a loose EGR tube letting air in/out etc.

The oil pressure drop is interesting...factory oil pressure gauge? I wouldn't be surprised if it is shitting the bed on you giving a false reading if you have 136K mi...

 

Sounds like you still have a vacuum leak. I would get rid of the bbk intake and put your stock one back on or a friends if they have one laying around.

Have you verified the pcv valve and hoses are good? If the valve is bad you could just be sucking un metered air through there

 

Thanks for the responses!

The fronts are up and down like a sine wave, and they dropped the exact same as the rear when I pulled the vacuum hose. They're brand new Denso's. I haven't swapped them, but I'll probably end up getting new Denso's for the rear while I'm at this. No L/T's, all stock with egr deleted from the intake. I watched the o2's while in open-loop today and everything appeared normal, but in closed-loop is when it runs like crap. And it's right at that same time that the oil drops. Like as soon as it goes closed, all hell breaks loose. Stranger yet, the gauge operates smoothly when in open-loop, but when it's messing up the gauge kinda jumps from its idle reading to its under load reading, and lags behind what the engine is doing. Again, when cold/open-loop, it works perfect.


If I do have a vacuum leak still, which I very well could, I'm having a hard time finding it. The pcv valve is new, and I RTV'd it inside the tube to help it seal. The tube appears to be fine, and I've sprayed carb cleaner all over it and get nothing. If I had a stock/ls6 intake laying around I'd probably go that route, but I think I'm going to pull the BBK and re-install it since I'm losing faith in the guys that put it on.

 

When did you start having this issue? Randomly or was it shortly after a modification was done? It will typically take 3+ driving cycles to have codes pop up.

I would look to see if there is a crushed gasket on one of the intake port runner openings (if the BBK has them) Or some crack on the backside/bottom of the intake.