Car Runs Good When Cold But Crap When Warms Up

[Gameboy]

hey guys, sorry i know this isnt an import but i forgot my login details for the r31 forum.

OK, my mums car runs good when its cold but then once it warms up, runs like complete shit. It has sudden bursts of power and sitting and the lights for to long makes it stall.

I reset the ecu and (took battery off for around 3 hours) then connected it back up and the car ran fine and then started running like shit again. Now i dont know if its because the car cooled down a little or i reset the ecu.

Plugs arent to old and has had a new afm. Also, it seems to be running really rich ( smells of fuel) but doesnt blow smoke. Anyone have any ideas as to what it could be before i start buying stuff ?

Edited May 16, 2007 by Gameboy

[DRD-00F]

to reset the ECU properly, disconnect the ground and pump the brakes a few times... that will drain any power that is in the lines...

as for the rest of it, check your intake, if its sucking in a lot of hot air, it wont really like that much...

hope someone can help more

[342Four]

smell of fuel seems to suggest that either there is a fuel leak somewhere, or there is a massive over fueling issue

check the injector hoses, the fuel pressure regulator near the fuel rail for leakage, the fuel filter etc anything that is related to fuel

[SKiT_R31]

smell of fuel seems to suggest that either there is a fuel leak somewhere, or there is a massive over fueling issue

check the injector hoses, the fuel pressure regulator near the fuel rail for leakage, the fuel filter etc anything that is related to fuel

Possibly leaky injector? hows economy?

dirty afm/vacuum leak could cause the car to stall etc, but the smell of fuel would be from a leaking injector, or fuel lines somewhere (is it coming from the rear or front of the car? could be a leak from the tank lines) If its through the exhaust, could even be an ignition issue if its not blowing smoke

[MBS206]

Check the engine temp sensor resistance when cold, check it again when hot.

Sounds like a dud sensor.

[dontfeelcold]

Check the cold start air regulator, make sure it works properly. I had a similar problem, except my car was running very rich. Changed the afm, plug and removed the throttle body and cleaned it out. It takes a few seconds to start but is good on the fuel now. I had a strong fuel smell happening aswell but thats because it was running so rich.

[Gameboy]

I took it into Ultra Tune ( dont flame me ) because my mum wanted to and they said that they replaced the end of a spark lead and charged us $90. Took it home and next day it was worse. Took it back and they pretty much said that they dont know what is wrong with it.

The car is very random. My mum whent to overtake a car and when she booted it, it started breaking down and almost got into an accident. I have another R31 here (wreck) so im going to swap over some stuff and hopefully find out whats the cause of this problem. Ill will also try the things mentioned

[nismo_GTST]

I had the exact same problem. I took it to a few mechanics and they had absolutly no idea. It ended up being that my exhaust cam was stuffed. Mechanic said it was warped. If it is that, get it fixed asap cos it will start to cause a whole lot of things to go wrong. Before you know it, you will have to rebuild the top end. Good luck dude!

[342Four]

check the ignition lead from the coil to the distributer

we had that in our old r31, cause of the heat etc it had been 'destroyed' on teh inside of the lead and there was no conduction to the distributer, so it would run like shit (it was just touching, and would go alright some times, but other times not)

[Gameboy]

Just thought i would update this thread and tell you what has happened. It was the AFM all this time. Me and my bro done EVERYTHING mentioned in this thread even more!. I never suspected the AFM because it was a reco unit from UltraTune and when we took it in, they never said anything about it they just said they cant find what the problem with the car is.

Anyways, the car has been going perfect for a few weeks now and has even eliminated this really small hesitation that used to bug the hell out of me. It was like when even you will push the accelorator down from idle, it would kind of cut out for a SPLIT second but that problem was fixed by replacing the fuel preasure reg. Its so odd because we have had this car for around 8 years and has ALWAYS had that hesitation problem and now i have to get used to it not having the problem

So yeah, if you are having a strange hesitating problem, chack your fuel preasure reg

Thanks for all the help