Car woes - Won't start when it's mildly cold outside

Satsumomo

Hello!

Car in question is a B12 Sentra, it uses a fancy carburetor that can compensate for altitude above sea level.

Here's the problem, if it's cold out (less than 12ºC, which is 53.6ºF) and the car engine is completely cold, the engine will turn no problem, but it will not start. If I keep at it for a while, like turning the engine every 5 or so minutes, then I will get a sputter. This means that the next time I try, the engine will actually turn on.

If it's too cold, which is maybe less than 5ºC (41ºF) I shouldn't even try, car will not start at all.

Other symptom: When car finally starts, while driving the engine will be idling at 1500-2000 rpm. This car has a mechanism that if you press the gas fully before igniting, the car will idle for 1500rpm, until you press the gas pedal again, something like a warming up feature.

So when this happens, if I press the gas, the engine will idle to 800rpm for 2-3 seconds, go back to 1500rpm then slowly creep it's way up to 2000. Once the engine is nice and warmed up (20-25 minutes, I guess I mean completely warmed up) it will stop doing this.

What should I be looking inside? Some sort of thermostat? I have the service manual for the 1987 version, which unfortunately doesn't have the same carburetor as mine does.

I do not want to take it to the mechanic, since last 2 shops fixed vacuum leaks by stuffing bearings inside the carburetor hoses instead of replacing the damn cheap hoses. Yay Mexico.

Zeon

Sounds to me like either a vacuum leak, or the cold start mechanism is broken. Id lean more towards vacuum leak because of the seeking idle, but vacuum leaks also cause really poor cold weather starting. If its a manual choke, first thing you can do is make sure its working properly (lever works properly and closes the choke plates fully). If its an automatic choke, youd have to figure out how it works.

To check for a vacuum leak, once the car starts, spray WD40 all around the vacuum connections/hoses and any seals leading to the combusion chamber (intake manifold, around the head, etc). You can use quickstart or even straight propane as well if you dont have WD40, but be careful if the engine is hot as it could ignite. If theres a vacuum leak, the engine will rev up when you hit the leak with WD40.

The other thing it could be is clogged pilot jets. If theyre completely closed up in one or both of the carbs, that carb will try and feed itself off the mainjet (if its a CV carb, which most any modern carb outside of high performance applications are). Most of the time, this leads to really poor starting when the engine is cold (not necessarily cold outside though) and erratic idle once its warmed up, but this really depends on the carbs/engine. Some carb/engine combinations wont run at all, some will run almost as good as with clean carbs, so you wont really notice a problem. Carbs are super easy to clean yourself, just get a good set of screw drivers, a wire bristle brush, a toothbrush, and a can of carb cleaner. Set aside an afternoon and scrub the hell out of them, cleaning everything. Be extra careful with the jets though, dont send anything sharp or hard through them. Scoring them even in the slightest will make them pretty much useless. Just spray through them with carb cleaner, and if thats not working, soak them in a cup of carb cleaner over night and then blast through them with compressed air.

Satsumomo

When the car is warmed up, the idle is perfect at around 900rpm, it doesn't oscillate at all.

Thanks for the tips, I'll start with the WD40 method

IronKnuckle's Ghost

Battery voltage ok?

Spudge

I'd put money on it being an automatic choke issue

Don't know how that system works on your car though, be it a relay or a fuse or whatnot

edit: what year and engine?

Satsumomo

It's 1991, but they ceased to be sold in the US in 1990, so I guess it's the 1990 version.

It's an E16S engine. All the symptoms make think it's a problem with the choke too.

I posted this on the NissanForums, and I got this reply:

idle air solenoid on LH side of engine is bad has two wires bolts onto intake { when standing in front of car} remove as much smog hoses and simplfy as much as possible. pretend its 1968 just vacum to dist and keep your PCV get rid of everything else..

Sounds good, I've actually seen some E16S engines with very little stuff connected (Seriously mine is crazy).

Spudge

Yeah if you live in a non-emissions area that would definitely be the route to take

If not, Rockauto looks to have replacement solenoids for about 40 bucks

Satsumomo

Yeah my state does have emissions requirements, buuut since my license plates are from another state which doesn't require them, I'm actually exempt.