Cold Start Issue

[pmurr181]

Hey Guys,

Got a problem. I have an R32 GTS4 and is has issues starting in the mornings. Whenever i let the car sit over night it will not start on the first crank or even on the second unless i am pedalling the gas. Is there a cold start valve or something? I have already changed the O2 sensor and the water temp sensor which the ECU reads for start up. Also the spark plugs and coil packs are all new. Some times it is not even if i leave the car over night but if i let it cool down for a couple hours.

Reason is winter is coming and i would like to get this figured out before winter come around again, any info/suggestions would be appreciated.

Thanks

Paul Murray

[TheyKilledKenny]

Try cleaning your IAC valve, it's under your throttle body. It helps with cold starts and if its bunged up with carbon it could be the reason you're having problems. Search SAU forums for a thread about cleaning the "air regulator".

[Skym]

IACV is one cause of harding starting, but rarely the problem. o2 sensor is ignored with cold startup in morning.

When you start engine it cranks on a fairly rich table on ECU, but once you let go of key it switches to a very rich table and is the cause of revs dropping and engine stalling. A trick to use is apply throttle (opens throttlebody) when starting to allow more air into engine to combat the rich startup. Also when coolant gets colder, the rich problem will get worse.

But there are other things that contribute to hard starts, like using incorrect oil (too thick), intake hose clamps are loose (airleaks), engine has an upgraded fuelpump (need to retune ECU), startup tables are too rich (the main reason why it has trouble starting). If have hard starting problem when engine is cold or hot, then can be traced back to a faulty CAS (CAS error code on ECU).

[pmurr181]

Yeah i didn't think it was the IACV which i have already cleaned. I have brand new O2 sensor spark plugs fuel filter, not leaks and vacum lines all redone. I only have issues with the starting in the morning. Like you said soon as i blip the throttle it starts up perfectly. I have heard that it can also be the AAC valve below throttle body close to IACV on RB20. I also have cleaned that with no luck.

If it is the tune. what would i be looking at for a tune to fix this problem? Also I am wanting to get a tune for m car anyway what kinda gains can i be looking at with a rb20 with intake, full exhaust, intercooler sprayer, and boost controller tuned to 12psi? Would it be worth waiting till i have more parts on the vehicle or doing a tune for the start up and everything in general?

Thanks Once Again Skym

[Skym]

With my car, I found changing from a 10w60 to 10w40 oil made the biggest difference to cold startup. Factory is 7.5w30. Also running a decent battery (dry cell which is more powerful and lighter with weight) helps.

If have Nistune, then it's just a matter of running a wideband and noting what the A/F ratio's are during warmup. Make changes to fueling, ignition to match and next day (cold start), drive car to see if the changes are close to perfect. Repeat until you get it right. Or could leave it for half a day to cool down, but coolant probably won't be cold enough. A tuner can do this for you and probably has previous tunes he can use as a base tune to work from, which saves time, $$$.

From what I understand, roughly 15hp with stock intercooler (not enough ventilation behind stock intercooler and heat soaks back of intercooler. This raises intake, cylinder temps and reduces ignition timing that can be run before engine knocks and the hp you can create from the extra ignition timing). If have good pump gas, FMIC (cooler intake temps), more aggressive tune, then 30hp is possible. With E85 (cooler cylinder temps, higher octane / resistance to knock, so more ignition timing can be run), probably another 50hp+ (going by dynocharts I've seen) on top of that.

[blackandgrey]

pmurr181 did you find the issue yet? I have the same exact problem.

I have to pump the peddle or hold it down to the floor for it to start, as if it isn't getting enough fuel by itself on start up and needs a little help.

Let me know if you figure it out

[Pete-R33]

try priming your fuel pump boys. turn the key to ignition and then letting it sit for like 2-5 seconds then cranking it over. Gasoline, like any other liquid, evaporates less when it is cold. You have seen this -- if you pour water onto a hot sidewalk it will evaporate a lot faster than it will from a cooler place like a shady sidewalk. When it gets really cold, gasoline evaporates slowly so it is harder to burn it (the gasoline must be vaporized to burn). Sometimes you will see people spray ether into their engines in cold weather to help them start -- ether evaporates .


Also : A battery is a can full of chemicals that produce electrons. The chemical reactions inside of batteries take place more slowly when the battery is cold, so the battery produces fewer electrons. The starter motor therefore has less energy to work with when it tries to start the engine, and this causes the engine to crank slowly.

[GodziRRa]

Same banana w/ my GT-R. So to Mr. pmurr181 did you solve the problem?

[DarkCaporaL]

I'd check the engine temp sensor and AAC valve.

[pmurr181]

Alright guys do I got her figured. I re-adjusted the timing and changed my plugs. Also set my acc valve and checked my tps. I put in 94 octane instead of 91 from shell and I changed my oil to 5w30 full synthetic. The biggest change was the fuel and the oil. A full synthetic oil helps alot on cold start ups. Not that I wasn't using one but like skym said I ran a lower viscosity oil. She starts up every time now. Love the remote starter again