MAP dives during WOT. Anyone else seeing this?

[Ellwein Engines]

I've seen this happen on numerous (3 or 4) customer vehicles in the past and just figured it was a bad Manifold Air Pressure sensor.
Recently: No crazy combo. I have a bone stock customer LT1 with a simple TorqHead conversion. Upon 100% throttle the MAP comes up to 90kpa very slowly and stays there for a while but 1/2 way through the WOT it starts diving down from 90kpa to 30kpa. (30kpa at 100% throttle...think of that).
Anyone else see this? Do you think it is in anyway related to internal wiring of the TorqHead PCM? On the LT1 PCM the MAP shares the 5v return to the PCM with ECT and Trans Temp. On a true stand alone P01 ECM the MAP 5v return is independent and has it's own pin into the PCM. TorqHead PCM is not a true stand alone PO1 ECM. It may have internal wiring to the PCM that works, (most of the time). I'm thinking some subtle wiring problems and or grounding.

Discuss.

Thanks,
Karl Ellwein

[blindsquirrel]

Eliminate the engine from the equation, test the MAP at key-on with a vacuum pump.

[Alvin]

I've seen this happen on numerous (3 or 4) customer vehicles in the past and just figured it was a bad Manifold Air Pressure sensor.
Recently: No crazy combo. I have a bone stock customer LT1 with a simple TorqHead conversion. Upon 100% throttle the MAP comes up to 90kpa very slowly and stays there for a while but 1/2 way through the WOT it starts diving down from 90kpa to 30kpa. (30kpa at 100% throttle...think of that).
Anyone else see this? Do you think it is in anyway related to internal wiring of the TorqHead PCM? On the LT1 PCM the MAP shares the 5v return to the PCM with ECT and Trans Temp. On a true stand alone P01 ECM the MAP 5v return is independent and has it's own pin into the PCM. TorqHead PCM is not a true stand alone PO1 ECM. It may have internal wiring to the PCM that works, (most of the time). I'm thinking some subtle wiring problems and or grounding.

Discuss.

Thanks,
Karl Ellwein

Is the car still making power when the map dips?

No chance there is a intake coupler or elbow sucking shut?

[Ellwein Engines]

Tested MAP yesterday and all tests were SAT. All wiring good. MAP voltage traces perfectly with TPS (4.5v at WOT). MAP kpa still dives even though MAP voltage is 4.5V. Weird.

[Ellwein Engines]

Car makes a bit less power because it is in a low kpa area of the fuel map. No actual intake elbow problem. one would think so. But anyway. The MAP voltage at WOT is perfect...4.5v as if it were 90+ KPA but at the same time the reported kpa is diving like a rock.

[Ellwein Engines]

Car makes a bit less power because it is in a low kpa area of the fuel map. No actual intake elbow problem. one would think so. But anyway. The MAP voltage at WOT is perfect...4.5v as if it were 90+ KPA but at the same time the reported kpa is diving like a rock.

Capture.PNG

[Ellwein Engines]

Car makes a bit less power because it is in a low kpa area of the fuel map. No actual intake elbow problem. one would think so. But anyway. The MAP voltage at WOT is perfect...4.5v as if it were 90+ KPA but at the same time the reported kpa is diving like a rock.

MAP kpa and MAP voltage screen grab.PNG This is the best screen grab with MAP voltage and MAP kpa traced together.

[blindsquirrel]

If you checked it with external vacuum applied, and it behaved as it should, at that point I'd be really fired up to put a tee in the vacuum source to the sensor and watch a manual gauge while driving. If the gauge follows what you see in the scanner, you have a plumbing/vac supply issue at wherever the sensor is mounted.

[Ellwein Engines]

Ended up being not enough sampling resolution. The MAP frequency was truncating. I put the polling at 20hz and all matches as it should. So basically a scanner operator error.

[Alvin]

Ended up being not enough sampling resolution. The MAP frequency was truncating. I put the polling at 20hz and all matches as it should. So basically a scanner operator error.

I was just about to reply the same thing. You have a lot of pids going in your channel list. Log the bare minimum. The older PCM's aren't fast enough to log so much.