Hi guys, I have just finished plenum pull (EGR + Water hose bypass), replaced spark plugs and whatnot. I am now having an issue where the car will run fine until I put my foot down, it will not exceed 0-2psi, it will accelerate normal and hit a barrier like a brickwall and it will instantly stop ALL accel until I ease off and on. Nothing into boost. I had a code 34 and fixed(I think) Firstly Re wiring Det sensor, the emi cover wire that is black, do i need to re connect this to the black wire of the plug or ignore it and leave it as the wire shield. (when I reconnected it I got a 34 again, now I dont have the code and black wire is disconnected, only the yellow/tan one is) Could I have not done this right, causing it to pick up incorrect detonation and cause the ECU to limit timing? Secondly what the hell is happening with the 0 boost issue.
For the det sensor the shielding wire does only connect to earth at one end, I can't remember which for certain but I think it was at the block, this gives you shielding without the shielding acting as an earth strap and hence carrying a current and causing noise in the signal. For the no boost, that is definitely more than just safety boost/limp mode which would be ~7psi. Likely causes are faulty MAF or dirty MAF connector and vacuum leaks. Maybe some more detail on how it drives, can you drive around slowly just not go full throttle? Is it a certain rev range that causes trouble? It's also possible your spark plugs are burnt out and can't hold spark with boost
The sub-harness screen earths through the connector, so the black wires should be connected to both the plug and the socket. Disconnecting the screen might cause the ECU to mis-read a detonation signal, but it shouldn't raise a code 34. That usually indicates loss of continuity on the sensor wire, which is different. Very strange.
Thanks fists + mclean I can drive around slowly, I just cant put my foot down, any approach on boost will stutter and not accelerate. Ill get my hands on a new MAF, I replaced all spark plugs yesterday. I have bypassed the plug/socket completely and shielded the wire connecting ECU side and sensor side, no change though. The sub-harness was fine when I checked the resistance. I dont see how the single wire amongst the harness would be interrupted either. Am I looking at a dead/melted sensor?
Did you do plugs before or after the problem started? If it is perfect until positive manifold pressure I would be inclined to think its a leak that develops under boost, possibly faulty PCV valves but double check all intake and vacuum piping. Is the fuel reg vac line attached? might be worth testing that it works, disconnect and block it's vacuum line while idling and the idle should change.
I replaced plugs after, one had died and was running on 4 cylinders (bad plug + bad injecotr wiring) which cleared up one of my problems but leaving my no pressure issue. Is it possible to have my idle fine, with a busted MAF? because if its possible thats what im hoping for. I will check again although I have double, triple checked for it, even engine off with compressor. I checked regulator and it appears to be running fine, this was my first thought, hoping for an easy fix!
I don't have first hand experience with a dead maf so not sure. Bit of info might help You're idle is right on 750rpm and definitely firing all six with no missing? At this stage its fairly likely you have an electrical fault somewhere so go through the list of things OZX 320 gave in your thread look them up on z32.wikispaces.com or tech.aus300zx.com and work through the diagnostics. Consult and someone experienced would help you a lot, maybe offer a local some pizza and beer to help you out Other less common things to check, you may have left a rag in your piping somewhere, check the two valves for clutch and brake boosters (one if NA or TT conversion without clutch booster) from the engine end you should be able to suck but not blow
Alright thanks Tom, Will continue exploring as directed and hopefully turn something up, ill start with Airflow sensor and continue on. Will keep posted about the topic!
A little higher maybe 800rpm, but yes all 6 firing! Theres a slight miss, but its probably due to the fact I need to re adjust TPS to spec, I also am in need of re checking all ignition timing and I now have a new problem, cranking without start, may produce backfire. Timing belt is fine so Im going to recalibrate CAS + TPS and I havent checked this from previous owner. Hopefully MAF (bad Air-fuel ratio) + Bad ignition is the only issue now!
Based on that AFM topic there's a good chance that's your problem, a known good unit is the easiest way to check, and having a good loom and a multimeter will allow you to compare and see if its a damaged wire
Alright so brand new MAF in, same problem, wont build above 2psi. The vac seems a lot stronger than usual. Meaning opening throttle wont have a strong effect on vac, and it'll suck straight back to full vac instantly. Not sure if related. Could be an improvement to before!
New theory, could it be down to a ****ed boost controller? It has a spring loaded bleed from the previous owner.
Won't be boost tee unless its making a significant vacuum leak (unlikely). If the boost controller failed you would run either 7psi or 'free boost'. Your boost meter isn't the most reliable gauge in your car and 2psi isn't going to be related to any settings or controllers so probably better to tell what rpm or throttle load it's failing at. Does it feel like a hard cut e.g. like someone has thrown on the brakes or a soft cut i.e. it just stops accelerating? Its still possible its in the MAF loom, no easy way to check without consult. Do you have a series 2 PTU? what is the wiring for it like? Actually, I just re-read your last update, check that your throttle bodies are actually opening, could be a problem with the linkage or cable.
Been reluctant to post so far given the posts have been complicated. Sounds to me like a minor vacuum leak of sorts. Wondering if you have still have an EGR and the unit is stuck open? Doesn't quite account for the Code 34 however Maybe some pics of your engine bay components that are relevant might help more here. JC
Its a medium sort of cut, its a jolt to 0ms-2, but its not so drastic itll lean me forwards. S2 PTU installed no so long ago, all connections are good. Throttle bodies are definitely opening (Somethnig works yay) No EGR, no vacuum leaks! And yes all the intake pipes are properly connected. If the code 34 is throwing it into failsafe mode. Is that just 7psi safe boost. Or is it a completely safe really low boost mode?
And I appreciate all help so dont feel reluctant to ask. Im hoping it will end up being a silly mistake that Ive made. I currently have the plenum off again replacing a coolant mess-up I made(Pipe popped off.) So Im going to remove lower plenum while im there and inspect det sensor, possibly buy a new one + sub harness.
"Knock sensor failsafe mode If the ECU detects a problem with the knock sensor circuit (i.e. code 34), it switches the knock control system into a failsafe mode. This causes the system to go full retard and permanently run at -8 degrees of knock timing which is the proper, safe thing to do. Fooling the system and bypassing the knock sensor with a resistor stops the ECU from going into this failsafe mode with potentially disastrous consequences." Just found this. What noticable effect would -8 degrees timing have?
The absolute lowest limit your boost can have, without having physical damage to the turbos or wastegate assemblies, is 7psi; this is set by the strength of the spring in the wastegate actuator. What blow off valves are you running? could be a failed spring in there, also triple check their vacuum lines are all connected to the correct sources Edit: make sure you check the PCV valves too if you haven't already
