5.0 Lean codes after Torque Monsters and Intake Spacer Install

[WitchCityMounty]

Hey guys I am hoping you can through some light on how I might fix my 2000 v8 mountaineer. Last week I got from sea and installed Torque Monster Headers, a 1” Phenolic upper intake manifold spacer and a high amp alternator. I did the plugs and wires while I was at it. I already have a Flowmaster 40 series cat back and a MAC intake. The problem is that the truck has not run right since I did the install. The mounty is throwing 2 codes with the check engine light: P 0171 and P 0174. I believe these are too lean on the O2 sensors, but I am not sure which 2 because there are 4 sensors. I changed out all 4 of the O2 sensors two days ago and reset the computer (again) and the codes came back. The truck is running real strange, particularly at idle. She either idles very high, 1500-1900 or extremely low 600. When she is at 600 she sounds awful, kind of a thrumming sound like an old hot rod out that isn’t tuned up. At speed she smoothes out a little but when I take my foot off the gas she will not go down to 1000rpm, ever. She stays up at 1500 and is shifting poorly as a result. I know I did something to cause this when I put everything back together but I can’t figure out what. I took the entire upper intake manifold off and checked all the vacuum hoses. They all seem fine. My next thought are to pull each plug off the coil and see if the she stumbles more or stays the same and try to track down a bag plug and wire. Any ideas on where else I should look for my problem? Any input is greatly appreciated.

 

[stangman82]

sounds like a vacuum leak. my guess would be the new plenum spacer leaking, but it could be anything that was moved during the swap. also generally a misfire will throw its own code, not a lean code

 

[Turdle]

My guess is the gaskets to the spacer are not sealing well, or you may have knocked the PCV seal at the rear of intake loose. There is a grommet in the hole, and the seal should be tight. This is often overlooked

 

[WitchCityMounty]

My guess is the gaskets to the spacer are not sealing well, or you may have knocked the PCV seal at the rear of intake loose. There is a grommet in the hole, and the seal should be tight. This is often overlooked

I RTVed both gaskets to the spacer so I know it is in the right place, I have torqued everything down there and taken that on and off twice with no luck. I appreciate the input any other ideas? If it all comes off again what do you think about RTV between the gasket and plenum and between the gasket and lower intake manifold?

 

[Turdle]

The pcv is at the rear of the lower intake-and very hard to reach. Is it tight?

 

[WitchCityMounty]

The pcv is at the rear of the lower intake-and very hard to reach. Is it tight?

It is. I had to modify it's top vacuum line so that it would sit right with the spacer.

 

[JCat]

At speed she smoothes out a little but when I take my foot off the gas she will not go down to 1000rpm, ever. She stays up at 1500 and is shifting poorly as a result

Sure sounds like a vacuum leak. Spray starting fluid around your connections and see if the RPMs change.