ECU internal circuits tend to either work or not however at this stage, it can't hurt to try. The fact that some times it will start no problem indicates everything should be OK but if the ECu is receiving incorrect input from one of the sensors, that could be the problem. Time to start changing sensors. I'd start with the CTS as its the cheapest. A failing CTS can intermittently report the wrong temps to the ECU causing it to provide the wrong fuel and spark maps. Trying to start a stone cold engine using normal operating temperature fuel/timing maps could resemble similar symptoms to yours. Remember to change only one thing at a time to baseline your work and a preventative caution to ensure the sensor wiring plug connection is also 100%. Perhaps also grab a couple datascan screenshots of before and during cranking and post up here.
Thanks Mark. Yes, I've been looking at the datascan values while attempting to start. Engine temp appears to be working fine. Been keeping a close eye on what the injectors are doing, as there is a high chance the engine is flooding.
UPDATE: Nothing really to report. I have checked spark now & all cylinders are sparking strongly & correctly. As mentioned before, fuel pressure is correct @ 41psi at idle. Another tune has been tried, but symptoms haven't changed. I am going to pull the plenum for the third time & check rail again. Will also check injector spray with the CAS out. If it still isn't obvious what is wrong, I will reinstall the old injectors and tune & see what happens then. Now I just have to find the time to do this
watching this thread very closely sim, you are right on the verge of finding out the issue, or at least it feels like it, theres not many places left it can be hiding? one thing that i was thinking is wiring harness, is it old or new.....and alarm or immobiliser? possibly shorting/failing and cutting spark or something similar, just throwing it out there
I really would encourage you to start replacing sensors one at a time. The car has worked OK for a period indicating an intermittent problem. If fuel delivery was an issue (injectors) this would be a consistent problem. I'd start with the CTS then CAS etc
Yeah, the issue only seems to be on start up. Sometimes it will start no problem, other times it needs to be cranked for a few seconds and it coughs to life, lastly sometimes it just cranks and doesn't fire at all. If this is the case & I continue to try, the spark plugs become fouled with fuel. If the car does start, it runs fine from there on out. CTS is giving a correct reading via datascan. I tried starting it will the fuel pump turned off and it was firing slightly, but not enough to start. This suggests excess fuel. I also tried starting telling the ECU engine temp was at 50 degrees, didn't seem to make any difference. Hey Ross, original wire harness. I was thinking possible faulty alarm too, but there is spark and fuel even when it doesn't start. The issue seems to be flooding (during initial start-up), now I have to find out why.
has the engine been compression tested? if some cylinders are low on compression, then they will be harder to start than others, and depending on where the engine stops after shut down, (remembering it will always stop at a different part of the engine rotation anywhere between tdc and bdc) those cylinders not firing properly will sometimes foul the others as the unburnt fuel washes through the intake.......other times the stronger compression cylinders are in the right spot and will drag the others into order so no starting issues. once warm the lower compression cylinders gain a little compression while running plus heat so no dramas..... all just a theory, but possible?......my car has similar symptons to yours but now it just never starts without cranking for eternity, hence my interest....ps, this is how mine started its problem, hard to start, got worse and worse and worse till my eventual never starts problem
Something else for you to try. Check Pin 43 on the ECU - the Start signal. A signal should be present when you turn the switch to the Start position. When the ECU sees the "Start" signal, it does three things: If the engine is cold: * it advances the timing to get maximum combustion pressure; * it over-rides the default duty cycle value held for the IACV-AAC valve to give higher RPM. Finally, * it triggers an initial injection of fuel at the point the Start position is hit followed thereafter by normal injection cycles during cranking. If your Start signal is missing, you will get none of these three things and accordingly the car will be hard to start when cold and much easier when warm. Check Pin 43 at the ECU with a multimeter and turn the ignition switch to the Start position and see if you can see the Start signal. Then check the pin fully engages with the socket to ensure the ECU gets to see it.
UPDATE: Old injectors & Eprom have been reinstalled. Car was test started this morning & fired as normal. Tested again this afternoon & normal again. Not getting my hopes up as of yet, as the car would run fine with previous setup occasionally. So at this stage time will tell & I shall keep you all updated. I will be test starting the car everyday this coming week & if she is still firing as normal come next weekend, I'll be more confident the issue was/is related to the nismo 555 injectors & tune. But again, don't want to get ahead of myself at this stage.
UPDATE: Well that was short lived... Car was test started again this morning, but same symptoms as with previous setup. Car cranks, but won't fire. Back to square one This car is really head f*#king with me now! (though I wasn't expect going back to the previous setup would change anything).
Mate I would follow Marks advice at this point and beg borrow sensors that you can swap in one at a time to try find the issue, include, AFM, CTS, CAS, PTU and ECU also if possible. Maybe also test voltage coming off the alternator. MattB
Fuel Might be Fuel pump, FPCU or Fuel Filter. Borrow from a friend any or all of these items and test, just to rule them out. If the fuel pressure drops out while the car is sitting there for a period of time, it will be hard to start when cold or might stall. There is always supposed to be a certain amount of pressure in the line, just for starting...your car might be losing this pressure. If you still have the OEM fuel pump, the check valve on them usually starts to leak from age, causing you to lose pressure when the car isn't in use and making it hard to start. The FPCU are known to fail too. If you haven't changed the fuel filter for a while, give that a change as well...a blocked one may also give you starting problems. Cheers Rob.
Hey Rob, Fuel can be eliminated as the issue. I have an inline fuel pressure gauge installed & the pressure is spot on (tad over 40psi) & holding. Also, car wouldn't start with aerostart. I have even gone as far as installing another set of injectors. It's either lack of spark, or excess of fuel.
PRVR is long gone. Little update. Car would start first attempt for the last three days (without touching/changing anything). I even took it for a short burst around the block without a hiccup (& plenty of power @8psi). This morning it started, but soon coughed and splattered till it stalled. Only to refuse to start again like it did initially in February. So it has to be a sensor/fuse/relay. Just the difficult task of finding out which one.
Have you actually tried a different PTU / CAS? when these 2 items are behaving erratically (not completely rooted, but getting there) they'll do exactly what you're describing. Not trying to sound like a broken record but it seems that's the only thing you haven't done.
I've just purchased a spare S2 PTU from member zed280zx. If you want, can contact him and get him to mail it to you first to see if it solves your problem. Have a known working CAS here as well, can send down for you to try...... polished too, so more likely to work in your car
