hi, I have problem with my car like on video. after rpm cut off my car starts shaking and run like with misfire for a while.. I'm looking for solution one year now its after replace: PTU TPS spark plug CAS injectors wiringloom ecu o2 sensors fuel regulator fuel pomp https://www.youtube.com/watch?v=BKLEOqaAmaY thats can be valve float, valve is open longer because of weak spring valve more oil going to hydraulic lifter because valve is opened longer than should be and because of too much oil in hydraulic lifter valve is opened more than should be and it's take a while back to norm but i bought second engine and also same shit happened.. two engines with weak springs? someone recognized this problem? or had similar issues..
yes it's happened when i hit rev can you explain how its possible its happened only when i hit rev limiter? and after some time its back to normal? when i clean spark plug its should help? i need just test... or this mean it's spark plug is somehow damaged? BKR7EIX or PFR6B-11B what i better to buy? i run now 17 psi stock turbos on CZP is writte: For Stock Boost Levels up to 15 psi: Use Colder Range Stock Plug PFR6B-11B, Smooth Daily Driver '7' Heat Range: Stock Turbos (15+ PSI level), Sport 500s. 530s, & 600s. Great for street use. small advice?
Dont know about the Z specifically but a lot of ecu's kill the spark when you hit the rev limiter - this means you get excessive unburnt fuel in the pistons and that can foul the plugs causing a temporary misfire, my guess is that is what the guys above are saying when they reply fouled plugs. when ignition starts up again the fuel gets burnt away and the problem comes right - Oil can cause this as well when one has bad rings or valveguides but I dont think that is your issue.
This guy posted the same thread on 3ZC I ended up wasting a lot of time trying to explain the problem and the solution, he did NOT follow instructions and simply replaced an old tired motor with another old tired motor & who would have thought - still has the exact same problem. I've been through this exact same issue as have many others who drag race RBs etc, it is caused by soft valve springs, there is so much air & heat going through an engine 7KRPM the spark plugs don't foul or become wet. I can set the rev limit to 4KRPM on my own car and sit it on the limiter for ten minutes if you like & post a vid with not even a hint of a stumble afterwards. The missfire is caused by the lack of compression caused by the incorrectly adjusted followers caused by the soft valve springs not being able to deal with the high RPM & the rev cut & the fuel burning in the exh manifold causing excessive back pressure against the valve. If a perfectly good VG did missfire after rev cut don't you think there would have been a HUGE outcry from the customers who just purchased a brand new squillion dollar car & it keeps missfiring after they touch the rev limiter between gear shifts? It's not a standard or normal thing, it's an old tired motor showing signs of its age, new springs will sort it, sometimes if you are lucky the correct grade of oil will hide it for a bit longer. I proved oil viscosity can effect this problem by changing oil to a thicker grade then having issues on the next tune with valve float at high boost, went back to a thinner grade & that problem went away, still had a missfire after rev limiter, changed valve springs for Z1 springs = problems all solved. HINT: the noises the valve train is making after the rev cut is a great indication of the condition of this motor - it's damn near F$#%^D
Mungyz i just wanna confirm this problem, because i checked valve spring and its all have almost the same values after compressed 115-114 I referenced the FSM to find out the testing specs for the stock ones (120.6 lbs. @ 1.043") so where is problem?
As far as I'm aware all stock ECUs kill fuel not spark, blowing clouds of fuel smoke is frowned upon when getting a vehicle through compliance. Carbies probably used spark cut since it's easier/more effective than attempting to cut fuel.
would that not run the risk of a lean out though? and thanks for the info, guess it show what sort of cars I have played with more lol....
Re: Fuel/Spark Cut The following is in reference to Racelogic Traction Control. Fuel Cut The idea of cutting fuel to an engine sets alarm bells ringing in engine builders, as they all know of the potential disaster of a high revving race engine running lean. Running in a lean combustion mode will elevate in-cylinder temperatures very rapidly, the denser the air/fuel charge, the more heat the lean burn can generate. Therefore it is vital that a fuel cut system will not cause a lean burn. The simplest way of preventing a lean burn is to remove more than 50% of the fuel from the pulsed delivery. A mixture will only ignite if the air/fuel ratio is within a tightly defined window, look at the efforts being put into making lean burn engines fire on very low air/fuel ratios (1:20 or more). Removing more than 50% of the fuel will cause an air fuel ratio of over 1:25 and will result in a complete miss-fire, with the unburned fuel passing out through the exhaust valve. Even if a high air/fuel ratio did manage to ignite, the energy available from the amount of petrol injected wouldn't be enough to elevate temperatures significantly. Of course the ideal system will remove 100% of the pulsed fuel delivery, allowing the cylinder to take a gulp of fresh air, and the in-cylinder temperature would remain virtually unaffected. Racelogic Traction Control operates in this manner - the complete injector pulse is removed so no possibility of lean burn can exist. Prolonged fuel cut on one particular cylinder would cause scavenging of the petrol lining, the inlet tracts, and when the next full fuel pulse arrived, it would be partially reduced in quantity by the re-wetting of these tracts. Therefore it is often important to manage a rotation of the cylinder cutting to prevent this situation from occurring. Spark Cut Cutting the spark to an engine will stop any chances of a weak mixture occurring, but it carries it's own potential problems due to a large quantity of unburned fuel travelling through the cylinder and out of the exhaust. This petrol can remove some of the oil lining the inside of the cylinder, and pass it thorough the exhaust, again this only becomes a problem if the fuel to one particular cylinder is cut for an extended time. The best way to overcome this is to rotate the order in which the cylinders are cut. The unburned fuel in the exhaust will have a catastrophic affect if there is a catalytic converter in the exhaust, as it will try to convert the unburned fuel to harmless elements, effectively burning the mixture. This causes the catalytic converter to heat up very rapidly, reaching temperatures in excess of 1000°C, and possibly melting down completely. Thus prolonged spark cut is not recommended for catalytic equipped cars. Source: http://www.pdm-racing.com/products/racelogic.html
Unfortunately not everybody gets rev limiters right, a mate did demolish the ring lands in his GT Forester by hitting the limiter on a wet pan, had heaps of mods so not sure if a stock one would have done it but definitely wasn't good. The limiter on Nissan's 90s cars is very safe though, not much point touching it in a vg but RBs and SRs can bounce off it all day, as demonstrated by your local drift clubs. SR needs rocker stoppers though.
