Rough When hits 3000RPM

[phihac0123]

Hi i am now owning a 1990 twin turbo 300ZX for almost a year and during that year i might have about 3 weeks total of road time the rest was spend in the garage trying to fix it... now the latest problem that ive got beside so many others is that when the engine is cold its will idle rough for little while and then its gonne stablelise itself but then when i get on the road and the car is at working temp, when i hit around 2500-3000RPM the engine starts to back fire and really and i mean REALLY running rough like it wants to die or something... i have tried to change the fuel pressure regulator but nothing same probleme... so before i try something else in vain ill try here first thanks!

[KDS_cars]

I had similar issues but worse at all engine speeds. back fire at higher rpms and when coming down from high rpms and over all running rough. After changing everything fuel related except the fuel rail (ecm,icm,injectors,all connectors, etc) I finally found it was an injector o-ring issue. the fuel would leak past the orings and down above the intake valve. killing spark and sending fuel all though the cylinder and into the exhaust. (causing the back fire some wear between the cylinder and exhaust.) I would recommend pulling the connectors to the coils. pulling off the connector, listening for a change in idle, and then plug it back in. is you pull a connector and their is no change in the engine, that cylinder isn't firing. i'd then shut off the car. wait thirty min or so and then pull the coil and spark plug out to see if their is fuel on the plug or in the cylinder. may not be the issue but testing for a dead cylinder would at least tell you what isn't wrong. i have also has issue with the fuel damper failing causing fuel to leak into the intake manifold. that might cause slightly different issues but is easy and worth while to check. just pull the vacuum line from it with the car running and see if any fuel leaks out from the damper.

[phihac0123]

Thanks for the replie, i will definitly check that out, i have order a new fuel pump since my car isnt even starting at the moment and i notice that it was my fuel pump that died... but when that car starts again i will check for a dead cylinder.

[phihac0123]

Well ive check for a dead cylinder and turn out when i unplug my cylinder 5 coil pack my idle does not change at all so im guessing that its not firing, and i also unplug the vacuum on the fuel damper to check for fuel leak but everything is good so any suggestion on how to investigate this problem furter ?

[centralcoaster33]

I'm pretty sure you can use a voltmeter to test the resistance of your coil packs. While you're at it, you could test the resistance for your fuel injectors. Also, borrowing and using a compression test tool on each cylinder would help rule out issues.

[phihac0123]

i did swap my coil pack number 5 with my 3rd coil pack just to see if the problem would still be there and my cylinder 5 is still not firing so the problem is not my coil pack im gonna check my fuel injector next.

[phihac0123]

So here is a quick resume of what i did. i check my coilpack again 12V, i check my injector 12V, ive check the plug for my coil pack and injector a get a 12V signal, ive tested my PTU seems to works just fine, ive remove my coilpack and spark plug and grounded somewhere to SEE if there is spark there is sparks i have manually spun around my CAS to manualy hear the click of each of my injector and they all works... so now i am really lost because when i unplug my coilpack on my cylinder 5 still no change in the idle... i need some help

[centralcoaster33]

Did you check all spark plugs and injectors or just your suspicious 5th cylinder? Do you have any oil or fuel sitting in the cylinders? What is your timing set to in degrees?

[phihac0123]

i did not check all of them just the #3 and #1 and i only check the spark plugs i did not look inside the cylinder but on the spark plug of my 5th there was some gas on it but not enough to say that its not normal and my timing is set at 15 degree

[phihac0123]

Update So i went for a quick test drive and the car honestly never worked better, i was pressing the gas pedal and no back fire or miss fire at around 3000/3500RPM which was the highest i could get the car to go RPM wise, but today no backfire i was able to actually drive the car everything was going great... until i arrive home not far before i arrive i was accelerating and i heard a sort of ''pak'' noise i dont know really how to describe de sound but i heard a sound and the car just died on me. lucky for me i was close enough and had enough speed to get in my driveway but i was around 6000RPM when the engine cut off and when i fire it back up again my idle was very jumpy, barely starting and when it idle, the idle is bouncing around 300RPM and 1500RPM so im suspecting a vacuum leak...

[phihac0123]

UPDATE. SO... i check on the forum for the vaccum leak guide so i followed it and found out that the ''pak'' noise i heard was one of my inlet intercooler hose that was not tight enough so a place that back and since i had the front bumper out i check for leaks on my carbon canister and i found out to my amazement that the bottom part of the canister was missing... so i went online and check for how to deleat it and i did and i did the bypass but now when i start the car it will fire up and run for about 15 second and stall ... so i really need help on this i have no clue of what i could be... and i really want to drive the car so bad but i cant

[centralcoaster33]

Well, if the EVAP system isn't connected in the right order, or bypassed in the right order, then you'll have fuel delivery problems, so double check your bypass method maybe. Your PAK noise (that's an interesting description, just saying it doesn't sound like a sound at all, more a word, but I don't know) being a disconnected intake pipe is a big deal with vacuum of course. You're entire system should be checked for leaks I'd think. You need vacuum to control fuel pressure and to control boost, is that right? Man, I wish a Z owner or Turbo guy would help us out.

[phihac0123]

yeah, ive check all my piping afterward i found my intercooler piping that was disconnected ill double check for the bypass that i did im pretty sure i did it the right way but ill double check anyway. and yes i need vaccum to control fuel pressure and boost and well for the PAK noise i notice that it does not sound like it should be i talk french so i say it with the french canadian accent so it make sense it that context but in english it really does not hahaha i didnt notice that before haha and btw thanks for the help you and one other are the only ones who is trying to help and i appreciate that

[phihac0123]

Hi here is a video of the problem i have. Please note that i do NOT press the gas pedal at all during the video and if i did all i would have accomplish is a couple of backfires so hope this helps.

https://youtu.be/EGC3EjWrfTw

[centralcoaster33]

I gotcha on the PAK sound. The video link works well.

I think you might want to check your timing and see if you can adjust your idle speed after that. Again I guess. You said 15 BTDC, but is it steady or does it bounce around at idle? You should look into how to get codes out of your ECU. Maybe a sensor is not giving proper signal to the computer. Throttle position, Mass Airflow, Cam Angle, and Oxygen are critical sensors. Also, vacuum leak. I don't know how to check everything in vacuum, especially on a turbo car. Maybe by spraying car cleaner around any piping after the MAF. You should look it up. Sounds like you're getting close though.

[centralcoaster33]

OBD-1 cars have codes pulled from the light bulb on the back of the ECU... instructions are online for turning a screw. I haven't done it. Mine is OBD-2. They're all pretty similar. Here's an instruction set:
1991-1994-240sx-reading-computer-ecu-codes-t253912.html

[phihac0123]

i check for codes and i get a code 55 so everything is ''working'' fine...

[centralcoaster33]

Okay, 55 means all is good. Has the battery been disconnected and reconnected, basically resetting the ECU? Or, have you managed to clock some miles since the last battery disconnect and the ECU actually has data to work with? Did you check the timing and voltage of the handful of sensors I mentioned? How about that vacuum? You can look to the FSM for non-code issues and diagnoses. Maybe you still have issues with cylinder 5. Here's a link to what I believe is your car's FSM. Look to the EF & EC chapter. Page 42 has some descriptions like that.
http://www.nicoclub.com/service-manual? ... /1990/efec
All chapter links from FSM:
http://www.nicoclub.com/FSM/300zx/1990/