About the relationship between ELD and your MAP sensor reading

[CivicIsFast]

I am having an issue with the map sensor displaying the maximum available pressure, no matter the voltage input.

A quick description of how the problem started. I was switching the wideband signal from ELD to EGRL, because the wideband would only read as rich as 11.97 even though the gauge can read to 10. Previous civic generations had issues using ELD, a resistor needed to be removed or something like that. No mention of it for 8th gens but it was just one of my trouble shooting steps.

At some point in that process, I've messed the map sensor system right up. I went to test the new wideband location and the car wouldn't start. Too much fuel from the map sensor reading approx. 40psi. Went out and unplugged the map sensor completely, still reading 40psi. I rob the stock map sensor off my brothers car, switch it in the tune, 10psi. Unplug that as well, still 10psi. Return the stock sensor to its rightful place and it works fine in the other car. Map sensor is not the issue. Here's where it get funky, I get the multimeter, with reference to the battery ground, all three map sensor connection pins show 0v. With reference to battery 12v, all three map sensor connection pins show 0v. If that's not confusing to you, read the last two sentences again, you didn't get it. I trace the 5v (yellow/red) wire to the ecu, good continuity and no damage to pin. I trace the signal wire (Green/red) to the ecu, good continuity and no damage to the pin. I don't know where the ground wire is going, so I cut it and grounded directly to the battery (also tried grounding to the injector ground on the manifold). No good results.

With no success tracing the wires, I cut the 5v off the MAF sensor since I'm not using it anymore (turbo car). Manage to confirm 5v power to the map sensor, and 1.3v signal to the ecu. Check the ecu reading through the laptop, still 10psi. I start flipping wires around to vary the signal to the ecu but nothing changes the reading in the ecu.

At some point along the way I moved the wideband to ECT2 and added a split to the ELD pin. I thought maybe having no signal to ELD was throwing off the map sensor. It was not. Sorry for the misleading title.

Any help would be great. The car has almost 400k km on it and its not worth having honda set me up with a new ecu, or going stand alone. Would rather not have to get rid of this car. ECT2 and ELD are both disabled in the tune.

08 Civic Si, stock motor with vtec killer, gt3582.

[CivicIsFast]

Today I looked into the 5v ref circuit on ecu connector c. Got some weird results. I found 5v at vcc3 from the tps connector, but nothing from vcc1 at the map sensor. I pulled the wires out of the ecu connector and put in an already cut wire so I can check the signals directly and be sure there's no short anywhere else. Same result, 0v vcc1, 5v vcc3. I grabbed a length of wire to go directly from the vcc3 output at the ecu to the map sensor power. Now there's no signal from vcc3 either, even when the circuit is disconnected.

Both tps error codes showing high still. Everything for me seems to be pointing towards ecu damage. Should I open it up to check? Anyone got any tips for getting the panel off of it?

[Spunkster]

IF the ECU is damaged, then you will need to return the ECU to stock and unlock the FlashPro. Do not try to open the ECU as there is nothing you can fix in it.

If the MAP sensor has been wired incorrectly then it will be damaged and have to be replaced. You may also have to replace the engine harness if you have a bunch of cut up and spliced wires.

[CivicIsFast]

Do you know of any available engine harness diagrams? I have not been able to find any for the Si. I lost my tach signal as well, so I'm thinking maybe all these sensors are on the same circuit with a short somewhere. But I can't confirm anything without pulling the entire harness apart.

[Spunkster]

You will need the helms manual and electrical trouble shooting manual.

www.helminc.com

[CivicIsFast]

SOLUTION:
I found a couple frayed wires a couple inches back from the ecu connectors causing a 5v short to ground. When I disconnected the ecu and pulled the connectors to look at them it would move the 5v wire away from the ground. Because of the ecu's location I couldn't get a probe behind it while the circuit was loaded.

I found a low mileage engine harness on facebook, threw it in and started right up.

Also the wideband is now in EGRL and it reads to 10.0.