Overboosting - Mk2 20v - AMK
I've had this problem for longer than I've known it's been a problem - because of never driving a 1.8t before, I have no experience on how they deliver boost, power delivery etc especially in a mk2. The conversion was finished back end of november, a AMK engine on OEM managment in a MK2 golf.
Notable mods: B5 TIP, 007, N249 bypass, bypassed & simplfied some of the hoses under the manifold, assumed leak free after a smoke test revealing the above manifold hoses leaking, now being fixed. ECU is running an unknown map as I got it off ebay as the original was knackered.
After fitting a B5 Tip a few weeks back, went to erase the fault codes & had left the N75 unplugged. At the time, VCDS was saying the N249 was unplugged. After checking wires back to the ECU, turns out the electrical connector for the N249 had been plugged into the N75 & vice versa. Essentially I'd been running with the N75 unplugged for a month or so. On that night, I plugged the plugs back into their correct sensors & went for a drive...
The results were a massive 2.0bar+ Spike, (Boost gauge stops at 2.0bar) @ 2500rpm, dropping off to 1.5bar & maintaining to redline. Mental to drive but the engine internals are standard. Didn't drive the car until I'd spoke to B5 during this week to confirm all was NOT well.
Initially before I noticed the problem & still how the car acts now with the N75 unplugged it'll run at just under 0.5 bar until approx 4000rpm then gradually rise to 1.5 bar around 4500rpm & maintain to redline.
I replaced the N75 valve today with a new one & checked the correct plumbing. The valve was originally an 'F' but has been superseded to an 'E' type valve. It's made no difference.
Tomorrow I'm going to have a look at the actuator adjustment, the turbo was a recon K04-023 from Midland turbo so don't want to rule out incorrect actuator setting up from them. I've read to adjust - slacken off the nuts on the rod, push the wastegate closed, wind the nuts up to touch the arm in the closed position then +5 turns for preload & bring the second nut up to tighten?
No related fault codes at the moment. I'll post logs below but I'm struggling to work out what's actually going on. I don't understand when the N75 is unplugged that it manages to eventually build boost pressure later on, rather than just maintain actuator pressure. Also don't get where this huge spike is coming from when it's plugged back in?
First Log is of the N75 plugged in & running silly boost - 3rd gear to near redline:
Second Log is with the N75 UNplugged - 4th gear, ran out of road is why it stops at ~5k
Any ideas much appreciated, I'll report back tomorrow but decreasing time & money with other commitments means I don't have a lot of time to look into the fault.