Duffman9465

Hey guys. Not totally sure if this is right place to post this as I have a few things going on. I recently changed out my entire engine harness on my 04 manual z. I also replaced all of the intake gaskets because the lower intake gaskets were leaking. The old harness had some shotty and janky "repairs" done to it and that's what prompted me to get a new one. After I replaced the harness, the check engine light came one with the codes p2122 and p2127. Of course, this means I have absolutely no throttle response. The rpms start at normal cold start range and then rise to 2k. The idle does not drop from 2k after warming up. I attempted to relearn idle with datascan, but the blower motor now runs all the time no matter what, so datascan fails the relearn. I'm wondering, would all of this be due to the new engine harness? The car drove and ran kind of ok before the harness. I can't find any issues in the wiring for the accelerator position sensor, but also haven't had time to put my multimeter on it yet. The codes come back immediately when cleared

partial tldr: replaced engine harness because of many bad repairs from previous owner(s). Have both accelerator pedal codes (p2122 and p2127) with no throttle response. Warm idle is at 2k. Blower motor will not turn off on all settings, even when set to "off," so nds2 won't relearn idle.

any help would be appreciated. It's getting warmer out and my other car needs some work now too. So I need to be able to drive something

icer5160

iTrader: (4)

You only replaced the engine harness right? No other harnesses? Double check your work, sounds like there's one or multiple open data/signal circuits (or shorts). Could be as simple as a bad connection at a plug somewhere, or worst case, damaged wiring.
If you picked up a "used" harness from a salvage yard, I would check continuity with a multimeter.

Wiring can be a PITA to troubleshoot, so good luck!
-Icer

Duffman9465

Oh believe me. I know how bad wiring can get. Work with it all day at work. Yes, the harness was the only one replaced. I did not replace the harness for the injectors and knock sensors because the new harness didn't come with it. I didn't personally pick up the harness from a salvage yard. I bought it off of ebay since I can't find any part outs for z's in my area. I'm hoping it's not the ipdm because I've already replaced that due to my old one shorting out. Would the best place to check for continuity be at the throttle body? Or possibly for throttle systems at the ipdm? I have very limited free time to check things with this car

Zjum3a

Were you able to fix it?

Duffman9465

Not yet. I havent had a lot of time to get to it. I've been going over wire diagrams at work to help narrow it down. I'm thinking it's a ground issue. I'm going to try and go through the grounds near the ecu. It seems the ground distribution over there has a lot to do with all my issues. If that doesn't get me anywhere, it might be time to put a scope on it and figure out if there's any circuit issues

icer5160

iTrader: (4)

There's a major body ground right under the corner carpet, below the PCM mount location in the passenger footwell. Don't forget to check the main grounds in the engine bay, there are various locations, but most are easy to find.

Just my gut feeling, but I think there's a chance some jacketing on wiring got pinched/damaged and it's causing a short to ground somewhere. This is a common issue when pulling/routing new harnesses, all it takes is a sharp edge from sheet metal to completely ruin your day. These can be hard to detect because the cut in the jacketing can be extremely small. I would inspect all the wiring choke points around the battery box and firewall, look for damaged shielding in all areas where the harness runs against sharp corners.
Cheers!
-Icer

Duffman9465

That's what I'm thinking too. Gotta start simple. I'm thinking a ground is the issue because there's multiple things going on that weren't happening before the new harness. I know the ground you're talking about is the ground for the accelerator pedal. I'm not sure where the ground is for the blower motor issue I'm having. Kind of doubting that one is a ground issue. That one is likely a circuit issue like you're saying. I'm trying to carve out time for the z. The weather hasn't been cooperating for quite a while

i8acobra

iTrader: (6)

You sure the harness came off your year? Compare the wire colors and locations from the ECM plug on your old harness to your new harness. Make sure Nissan didn't move a pin or two. Nissan likes to do that.

Duffman9465

I did a pretty thorough comparison before installing it. Everything seemed to match up. I want to pull the ecu connector back through the firewall and just double check it and see if any if the pins are good. But my old one had a ton of work done to it at the ecu connector from before I bought the car. So I'll likely have to stare at the wiring and a diagram to figure out exactly which wires are which. I hate having to back track other people's work

Zjum3a

I'm not sure if you fixed the issue but if not, check your E10, E11, and E12 connectors. They're the 3 big connectors right next to the battery. I had the same issue after swapping my engine. Took me 8 days to see that the E11 plug ( the one in the middle) wasn't fully connected.