Pdavy10

I have a 6.0 gen 3 LS swapped into a 1996 c1500. I needed to swap out the oil pressure sensor so I could read the oil pressure on the dash. I pulled the whole intake to get to it. I reinstalled the intake, rails, injectors, brake booster line, the line from the intake to the passenger valve cover, and reconnected all the plugs. It ran perfectly fine before hand. I know the intake has a supply and return for the fuel on the intake also. But now it runs like crap and I can’t figure out why.

Racer-X-

The first thing to do is hook up a scan tool and check everything. Any codes present? Are all the sensor values in range and about what you expect? What are the fuel trims running?

Pdavy10

Yes I’ve checked everything and now it’s throwing a P1514 “No DTC definition found” and a P0106 “MAP/BP sensor”. And I took it all back apart and put it back together and now it’s like I can hear a vac leak or something.

Racer-X-

Is the MAP sensor properly installed in the manifold? Is it connected? Are all the vacuum lines connected?

P1514 is a big mismatch between throttle position and MAP sensor readings. It happens when there's a huge vacuum leak, or a problem with the MAP sensor, or possibly when the throttle plate is broken or has a mechanical malfunction not caught by the sensors. It means there's a lot more air getting into the intake manifold (30% more I think is the threshold) than the PCM expects for the current throttle position.

P0106 means the MAP sensor is either disconnected, or it's reading a pressure that's way out of range for the conditions the engine is operating in. For example, if the MAP sensor is hanging on the wiring harness, connected, but not installed in the manifold, you'll get this code (don't ask me how I know that).

BTW, if it's the rubber seal on the MAP sensor (missing or degraded), those are easy to find if you know the part number (GM 16194007), but can be difficult to find by the vehicle because that part comes from the "GM Performance" catalog and isn't associated with any years or models in the normal parts catalog.

Pdavy10

it has a very mild base tune, all the lines are installed correctly that I know of, and the MAP sensor seal isn’t terrible but it also isn’t the best. I did find the hose from the front of the intake to the passenger side valve cover was split and replaced it. I removed the intake again and it seems like it sealed correctly that time. But it’s still running rough. Maybe it needs to re-tuned? I have no clue what would cause it to just randomly start acting like this. But I’ll try to replace the seal for the MAP sensor and see what that will do.

G Atsma

Yeah, make sure you have NO leaks anywhere. Go over everything carefully.
ONE issue I can think of is if it was tuned with an unknown vacuum leak. Hey, it happens...

Pdavy10

That’s kind of what I was thinking. Because the brake booster, PCV hose, the new hose I installed, the MAP sensor, the injectors, and rails are all connected. When I get time off from work again I’ll re-check everything with a fresh set of eyes.

Racer-X-

If you need to go looking for vacuum leaks, the O2 sensors (graph the voltages with the scan tool/ap) are more sensitive than your ears when spraying throttle body cleaner around the injector seals and gaskets and such. Hook up the scan tool, run the engine until it's warmed up (some) and the O2 sensor voltages are in a normal oscillating rhythm. Watch those voltages with a graph on your scan tool/app. Start spraying to find the leak and watch the O2 sensor voltages. When you hit a leak with the cleaner, the O2 sensor will go way rich and you'll see the oscillating wave form pattern get disrupted.

Pdavy10

Okay, I’ll have to try that around the intake gaskets, all the hoses, and injector ports.