Satans DTC P0171 P0174

Hello everyone. First off, I'm brand new to forums in general and especially new to this one. I've searched high and low across the Internet and have even talked with the service techs at the Pep Boys I work at. I've been driven to join you all here and ask for help with my trucks trouble codes that will not die.

1997 Silverado 5.7 Vortec

It all started (or came to light) after I had to swap a junk yard transmission. First the MAF sensor was bad, so I replaced it. Also, it was time to replace the cats, so I did that. After all of that work I got two new codes.

P0171 and P0174. These codes must come from Hell itself. I understand the appear from a lean condition, whether real or perceived by the computer. To help you get an idea of the frustration and hell I've been through, here is a list of what I've done so far. I have replaced...

The MAF sensor
Both upstream O2 sensors
Fuel Filter
Fuel pump
Intake manifold gaskets both upper and lower as well as the throttle body and fuel injector module gaskets.

I've also checked for and sealed pretty much any area where air could leak in, such as...

Around the MAF sensor
PCV valve
PCV grommet
PCV elbow
Intake hose to throttle body
Oil dipstick o-ring
Brake booster hose
Valve covers
Oil fill cap.

But wait! There's more! I've looked to see if there are any air leaks after the engine in places like...

Where the headers meet the block
Pipes to header
Cats to muffler flange
And anywhere else around the O2 sensors themselves.

Before being as drastic as throwing parts at this, I used both my coworkers scan tool at the shop to read the codes and then research their causes and possible fixes as well as one I went out and bought for myself. I checked for good readings on every sensor, I measured fuel pressure, I've checked for ground on nearly everything.

After close to 6 months and three tickets later for expired inspection and registration stickers because of the Devils Service Engine Soon light, I am at wits (and wallets) end. As of posting I have scanned my truck again and have found things are just *********** and I've now ended up the following codes:

P0171
P0174
P0151
P1345

I don't even know how the hell the last one is showing up, both the crank and cam position sensors have been replaced already (well before this psychological torture started).

So my question is, what could it possibly be? What should I do now? Was my co worker right, should I grab a new ECM/PCM? A there any fixing this? Should I put my truck out of its misery? Myself, lol? I am the only person in my family that currently has a job. I am only 22, and making $10/hr, I can't afford anymore tickets, and I need a reliable ride.

Let's get back to basics.

Did you do a compression test? ( Y/N ) If so, what were the dry and wet results?

Did you do a leak down test? ( Y/N )

Add a vacuum "T" and a vacuum gauge that you can read with a nice big gauge. Start the engine.
Is it 'bouncing'?

Convertors can fail for many reasons. Replacement ones can fail if the engine is excessively lean or rich as well.

Who replaced the cam and crank sensors? GM? Was the offset set correctly with a Tech 2 Scan tool?
If not, that will cause you a whole host of issues.

Good you have already checked and cleaned grounds.

Excessive slack in the timing chain can cause erratic cam / crank sensor correlation.

I would hesitate to spend any more money throwing parts at it without a proper diagnosis.

Without knowing your full financial burden, you may be better off with a small inexpensive new car, if you qualify for financing. It was not mentioned if you require a truck for work. If not then, a car ( 4 door sedan if you have a young family ) is your best bet.

Pros - brand new - routine oil changes is likely the only maintenance you will need for the first few years, depending on the amount you drive. Tires may last you 3 years or so if you are a city dweller and have a short commute. Brakes - your mileage may vary there.... there are people that could cook off pads and rotors in a half year, and others that can go years on brake parts doing the same drive.
Warranty - peace of mind. Likely much better fuel economy.

Cons - Constant payments, higher insurance. High depreciation in a few years. The constant payments can let you get back on your feet, as you have no hidden 'surprise' repairs that will empty your wallet time after time.

If you 'need' a vehicle and have no credit, you need to build credit first. In that case, a cheap running vehicle is your best bet. Save up and pay cash for it. Get a credit card, talk to your bank and get the lowest interest option card to start, and use it wisely.

Absolutely do not fall into the trap of 'financing for everyone, guaranteed'. Interest rates from these 'high risk lenders' are just shy of the criminal rate of interest, basically like a legal loan shark.

Most used car loans are at least triple the financing or more than a new car loan, especially if you qualify for low interest financing at a dealership.

As always, you must decide what is best for you and your unique situation. Hope that helps.

michael hurd said:

Let's get back to basics.

Did you do a compression test? ( Y/N ) If so, what were the dry and wet results?

Did you do a leak down test? ( Y/N )

Add a vacuum "T" and a vacuum gauge that you can read with a nice big gauge. Start the engine.
Is it 'bouncing'?

Convertors can fail for many reasons. Replacement ones can fail if the engine is excessively lean or rich as well.

Who replaced the cam and crank sensors? GM? Was the offset set correctly with a Tech 2 Scan tool?
If not, that will cause you a whole host of issues.

Good you have already checked and cleaned grounds.

Excessive slack in the timing chain can cause erratic cam / crank sensor correlation.

I would hesitate to spend any more money throwing parts at it without a proper diagnosis.

Without knowing your full financial burden, you may be better off with a small inexpensive new car, if you qualify for financing. It was not mentioned if you require a truck for work. If not then, a car ( 4 door sedan if you have a young family ) is your best bet.

Pros - brand new - routine oil changes is likely the only maintenance you will need for the first few years, depending on the amount you drive. Tires may last you 3 years or so if you are a city dweller and have a short commute. Brakes - your mileage may vary there.... there are people that could cook off pads and rotors in a half year, and others that can go years on brake parts doing the same drive.
Warranty - peace of mind. Likely much better fuel economy.

Cons - Constant payments, higher insurance. High depreciation in a few years. The constant payments can let you get back on your feet, as you have no hidden 'surprise' repairs that will empty your wallet time after time.

If you 'need' a vehicle and have no credit, you need to build credit first. In that case, a cheap running vehicle is your best bet. Save up and pay cash for it. Get a credit card, talk to your bank and get the lowest interest option card to start, and use it wisely.

Absolutely do not fall into the trap of 'financing for everyone, guaranteed'. Interest rates from these 'high risk lenders' are just shy of the criminal rate of interest, basically like a legal loan shark.

Most used car loans are at least triple the financing or more than a new car loan, especially if you qualify for low interest financing at a dealership.

As always, you must decide what is best for you and your unique situation. Hope that helps.

Click to expand...

Well, I very much appreciate your help, as well as your reply. I did not expect an answer so quickly lol! I think at this point I need to follow your advice with further testing. As far as I know the computer was never relearned when either sensor was replaced, and I did the replacement with O'Reillys parts. That is all I know so far. From here I guess all I can do is rent the necessary tools and test the compression and vacuum. Also, as much as I'd love to buy a new car, (sort of have my heart set on a turbo chevy sonic) I can't really afford it yet. But maybe one day...

I just wanted to check in. I have not gotten a chance to test the compression or the vacuum yet. However, I wanted to give you a little more information if I could. First off, my truck now has 192,030 miles on it. Also, the truck is a 1997, but technically it's a 1996 (I guess, it was built in 11/1996) and the engine is SFI. Now, the mileage is for the Cam/Crank correlation fault P1345. Out of all of those miles, as far as I know, it has the original timing chain, lol, could that be the cause? Keep mind, both sensors, cam and crank, have been replaced, as well as the distributor, and the timing was set using a scanner at a garage, but there was no mention of a Cam/Crank relearn, I'm pretty sure they didn't have the tool to do it, or felt they didn't need to.

Second, When I first start my truck (after several minutes of cranking, resting, spraying with ether, and grabbing jumper cables) I hear a very clearly audible and loud hissing sound that slowly dies down as the engine warms up. As far as I can tell, it's coming from the throttle body, and I swear when I laid myself over the engine bay and put my ear directly over the throttle body that the sound was coming from around the TPS and IAC valve. When I tried to cover the IAC valve wiring and plug, I was certain I could feel air being sucked in from there, and when I listened using an old stethoscope, the sound was loudest in that area.

I took the serpentine belt off so the fan and other accessories wouldn't make much more noise, and so the fan would not blow any smoke away while my father blew cigarette smoke over the engine so I could see if that was where a potential vacuum leak could be. Unfortunately, the engine had warmed up enough that the sound was gone, and I could no longer feel any air being sucked in.

From what I've read, and from what I've felt, I don't think the IAC valve is failing on its own. Some cold mornings when I get out onto the road and hold my speed at a dead steady speed around 50-60 mph, I feel the truck jerking and bucking. Once I've driven long and far enough, the jerking goes away. But there haven't been any real issues with idle, stalling, nothing. The only thing that really happens is when the engine is cold from sitting overnight, if I tap the throttle, the engine sputters before it picks up. Same thing when in gear. When leaving my driveway in the morning and pulling onto the road I've tried flooring it to see how it responds and the engine starts chugging and sputtering until it dies. Even when trying to accelerate normally, I have to watch how much throttle I give or I might accidentally stall the engine. But after it's warmed up, by the time I get to work, and by lunch time, it starts fine on the first crank just like always and the throttle responds like normal.

Final thought, the issue with the low power and struggling under heavy throttle really started when a friend of mine's father replaced the transmission in it. I never got a chance to scan the codes to find out if there truly was an issue with P0171 or P0174 when it felt that way, but I felt like sharing that, just in case you guys could think of any way on Earth a "simple" transmission swap could trigger something like that.

That is about all the additional information I can provide at this time until I perform the two tests I have yet to do. I thank you all for any and all help and information you provide, it is very much appreciated.

11/96 = 97 model year

If you had lean codes, something is amiss. Sounds like un-metered air, however you have pretty much tried everything that would possibly give the engine air that is not measured by the MAF. Worn throttle shaft in the throttle body?? That may explain that and driveablity issues.

Check for the ground on the back of the passenger side cylinder head, and the condition of the one going to the body. Not just a physical, "looks ok" but rather, measure the resistance.


Do you know for certain what year and model the transmission was out of? That will not explain the perceived or actual lean condition the computer was trying to correct though.

The wrong lock up converter clutch material may cause driveability issues though.

Hope that helps. If compression is good, and a vacuum gauge doesn't wildly swing, I would look at the throttle body for wear around the shaft.

Do you have a friend / co-worker or anyone you know with a good running 96-98 or classic - 00 truck with that throttle body you could try to see if that helps clean up the starting and other issues?

michael hurd said:

11/96 = 97 model year

If you had lean codes, something is amiss. Sounds like un-metered air, however you have pretty much tried everything that would possibly give the engine air that is not measured by the MAF. Worn throttle shaft in the throttle body?? That may explain that and driveablity issues.

Check for the ground on the back of the passenger side cylinder head, and the condition of the one going to the body. Not just a physical, "looks ok" but rather, measure the resistance.


Do you know for certain what year and model the transmission was out of? That will not explain the perceived or actual lean condition the computer was trying to correct though.

The wrong lock up converter clutch material may cause driveability issues though.

Hope that helps. If compression is good, and a vacuum gauge doesn't wildly swing, I would look at the throttle body for wear around the shaft.

Do you have a friend / co-worker or anyone you know with a good running 96-98 or classic - 00 truck with that throttle body you could try to see if that helps clean up the starting and other issues?

Click to expand...

Well, after doing some more reading I decided to pull my IAC valve and clean the piss out of it, where it plugs into the throttle body, and the contact pins where the harness plugs in. I popped it back in with a slightly thicker, new o-ring around it and fired it up. Started almost instantly. Grabbed the the throttle from under the hood and slammed it to WOT and it revved up nice, quick and responsive. I have no clue if that is the fix though. For now I've reset the codes and it runs okay. I will know much more after tomorrow as it is now driveable enough to get me to work on time and back home again, just need to let the computer perform it's drive cycle.

The ground I have not checked for resistance, however, I did do a thorough cleaning to the wire and its spot where it connects to the engine, but I don't know about the one on the inside of the fender, I've never touched that one.

As for the transmission, I actually put in a fair bit of research to satisfy my curiosity of...

1. Why it was so hard to find one from a junk yard that was in working condition that'd fit my truck.
2. Where the hell the one in the truck came from (it was a rebuilt transmission put in around 2005 and was trans no. 2, I'm now on 3.)
And 3, what the hell my original one was.

Now I have the answers for all of those.

What was in my truck was a rebuilt unit from a GMC van 2500 was 6WHD. The original was 7CJD. The one I got from the yard myself and swapped I can't really find a true code for. The case is stamped with 24207965 and the tail housing is 25208015-4. This was a newer style transmission with a bolt on full bell housing and it had a six bolt tail housing instead of the old four bolt that my previous two had. This one ended up fitting (although a tight fit) but I knew it would, since I got it out of a 96 that was set up like my truck, extended cab, short bed, 5.7. When I got that transmission I used the torque converter that came with it since mine was already cooked.

That's about all I know so far. I want to guess that my lean codes will come back again, regardless of how much better the engine runs and starts. On my scan tool the LTFTs are around 21-23 on both banks when the engine is warm and at operating temp. I honestly do not know if that is good or not, but from what I've read, it isn't what I want.

After doing intake gaskets you have to set the distributor with an advanced scan tool that can read the timing. You can't just put it close the same spot it came out. This is not negotiable. Have you done this?

For the 1998 model year and some late 1997 from my research was a bolt on bellhousing. I have not seen reference to 1996 with bolt on bell housing, so it was likely a replacement transmission.

The valve body would be the same as 1997 and compatible with your truck.

mistaake said:

After doing intake gaskets you have to set the distributor with an advanced scan tool that can read the timing. You can't just put it close the same spot it came out. This is not negotiable. Have you done this?

Click to expand...

It was set with a scan tool. That's how they got it to sit just right in order to keep the check engine light at bay. But they never mentioned anything about a relearn.

michael hurd said:

For the 1998 model year and some late 1997 from my research was a bolt on bellhousing. I have not seen reference to 1996 with bolt on bell housing, so it was likely a replacement transmission.

The valve body would be the same as 1997 and compatible with your truck.

Click to expand...

That junkyard transmission was definitely a replacement for the truck it was in. From what I could find online the numbers on the case indicate it could be from a 2001 4x4, but I'm not certain on that, and the numbers on the tail housing don't pull up anything.