odd engine code (P0174)

Anybody have any experience with this code? Check engine light comes on and stays on for a few trips, then disappears for a few trips. then comes back. I have not noticed any change in engine behavior.

When I had them run the code at OReilly, it came back as "P0174 System Too Lean (Bank 2) DTC severity 2 out of 3. "

Though it hasn't effected driveability, I'm thinking it's a fuel injection issue. Any ideas?
I will need to resolve it by February so the car can pass state inspection. Thanks for any tips!

If you can get a reader that displays real time data (which you should have anyway), look at the 4 O2 sensor signals. If the traces are quite active, the lean condition is probably real. If the signal is relatively quiet, the sensor itself might be on its way out.

Have you fixed your exhaust manifold leaks yet?  They warp outwards on the the front and rear cylinders, usually cracking the rear bolts and then you get air leaks that cause false leans.  Every LT1 owner should take off their exhaust manifolds, have them planed flat at a machine shop (it's cheap) and then reinstall with new Grade 5 flange cap bolts (3/8-16, 1.25" center and 1.5" outer).

""Grade 5 flange cap bolts (3/8-16, 1.25" center and 1.5" outer).""

Or the Stainless Steel stud kit from ARP.

Either one is good. I'm not going to argue with you, only to say that the exhaust manifold bolts get probably the most heat cycling of any bolt on the car. To me it's cheap insurance just to replace them with regular grade 5 every 5 years. Another trick is to only torque them to 20 ftlbs instead of 30ftlbs. It's not a high pressure joint, and the cast iron [You must be registered and logged in to see this link.] as mild steel so it's a wash. This does not apply to stainless steel - some grades of stainless expand at close to twice the rate of cast iron so they would need the full 30 ftlbs for sure. It's not obvious which grade the ARP stainless kit is, so I leave it to you to figure that out, or just torque them to 30 and be done.

sherlock9c1 wrote:

Either one is good. I'm not going to argue with you, only to say that the exhaust manifold bolts get probably the most heat cycling of any bolt on the car.  To me it's cheap insurance just to replace them with regular grade 5 every 5 years. Another trick is to only torque them to 20 ftlbs instead of 30ftlbs.  It's not a high pressure joint, and the cast iron [You must be registered and logged in to see this link.] as mild steel so it's a wash. This does not apply to stainless steel - some grades of stainless expand at close to twice the rate of cast iron so they would need the full 30 ftlbs for sure. It's not obvious which grade the ARP stainless kit is, so I leave it to you to figure that out, or just torque them to 30 and be done.

I am trying to decide now just what to use on my engine upgrade that is in process. The engine had 140K on it and appeared to have original bolts and gaskets in it. It did show exhaust leak tracking on both sides rear bolt locations.

On most engines I have found that the bolts seem to run slightly cooler than the manifolds, so will actually get a bit tighter as the manifold heat increases. You can test that by measuring breakaway torque cold and hot. I found this out very obviously on my Mopar V8 turbo engines I built. They ran hot manifolds because of the turbo restriction and the double horsepower I was making and would break bolts like crazy and also leak. Grade 8 broke very fast, grade 5 lasted a while, grade 3 stretched and leaked but didn't break. Went to stainless socket head cap screws in type 304 stainless and nearly all the issues went away. I think what was going on was that the higher thermal expansion rate of the stainless offset the lower temp that they ran at than the manifolds so the torque stayed more even during cycling.

Will studs fit with these manifolds with regular nuts or do you need to make/find tall nuts? Stainless studs if available to fit would be my choice, I think.

""Will studs fit with these manifolds with regular nuts""

The 170,000 psi stainless ARP set comes with studs, 12 point nuts, and washers. Been doing fine for twenty years.

I confirmed that the rearmost bolt on the driver side exhaust manifold is broken off. Now I am finally planning to do something about it!

Does anybody have a kit number or good source that has these bolts prepackaged and easy to order? I couldn't find the kit on the ARP (American Racing Products) site. I found one on Summit which was over $100, which is A LOT more than I would have expected to pay.

Get the appropriate bolt(s) in grade 8 from the local hardware store.

I just had the same code show up on my 96 RMW. Happened to be the rubber elbow that connects the metal PCV line to the PCV valve itself. The only way I found it I was changing out my PCV valve anyway, and when I took the old one out the rubber elbow had melted on the inside of the curve. Sometimes its better to be lucky than good...

BobD wrote:

I just had the same code show up on my 96 RMW. Happened to be the rubber elbow that connects the metal PCV line to the PCV valve itself. The only way I found it I was changing out my PCV valve anyway, and when I took the old one out the rubber elbow had melted on the inside of the curve. Sometimes its better to be lucky than good...

I will have to check that out thanks!

I just finished repairing the broken exhaust manifold bolt (see post in exhaust section). The good news is that the repair went well and it's totally tight and quiet. The bad news is that the 174 code is still there.

I will look into the PCV angle. Autozone ran the code and it came up with recommending the fuel pump be replaced. That seems unlikely, since the pump has been replaced not long ago. There are no driveability issues and that code never came up when the fuel pump died before (twice). I was thinking maybe replace fuel filter, it could be restricting flow?

"" it could be restricting flow?""

Any restriction in the fuel delivery system would probably affect both banks. The pump and filter side of the system is easily checked with a fuel rail pressure gage.

If the code is always on one side of the engine, it indicates an inlet manifold leak or injector problem as suspect.

So, I am pretty sure I resolved this engine code issue. Turns out Bob D. had it nailed in the comment above. Appears to be from a hole in my PCV elbow, just like he said.

On the inside curve, not readily visible, was a large opening in the rubber. I didn't see it or feel it until I removed the elbow and examined it. Didn't look torn. Maybe melted, but I don't know why it would melt there. It's far from the exhaust. Not sure where to get a new elbow besides a junkyard. I used sone rubber cement for now, see how long it lasts.

After reseting the codes,.they haven't come back after several drives. Thanks for all the suggestions!