Quoting toybreaker:
Quoting fastasleep:
Many times, a harness problem at the ecu coolant sensor on the t-stat housing will start out with this kind of symptom.
Could you elaborate on this a little more? Like, lets say the two wires going into the coolant temp sensor are bent and exposed...
I'll give it a shot, but there's better people to answer questions like this... (maybe Keydiver could add some info/correct my errors)
A logger is really nice for troubleshooting these kinds of issues. /ubbthreads/images/graemlins/smile.gif
In order for the ecu to know when to tell the coil to throw the spark, and how much fuel to inject on each spin of the crank, it has to know a few things about what's going on.
Coolant temp, and to some extent Intake Air Temp play a large role in getting things started when it's cold outside.
When the engine is warm and in closed loop, it has some pretty sophisticated feedback from the sensors, and can adjust timing and fuel ratios to exactly match the operating conditions.
On the intial key-up, all it has is temp info.
When you engage the starter, the engine spins over and things start happeneing.
As the crank turns, now it will get airflow and rpm input, but it's pretty much just doing a look-up from the cold start maps to get the ball rolling while operating on the starter.
The numbers it uses for these calcualtions come from the iat (in teh mas) and ecu temp sender (on the t-stat housing).
If the info is accurate, good things happen, and you're sitting there warming your car up and listening to the traffic report, planning your commute.
If the info is bogus because the wires are broken/sensors bad, well, let's just say your day just got more complicated. /ubbthreads/images/graemlins/banghead.gif
The mass air flow meter will give the ecu info on how much air is entering the motor. It will also report on the barometric pressure and temperature of the incoming air. This is important because the air density will change with temperature and barometric pressure. Colder days mean more dense air (for a given volume), requiring more fuel to reach the same air/fuel ratio
The crank angle sender will give the ecu postion and rpm information from the crank and other rotating bits.
Now the ecu knows how much air entered, and how many combustion events will be expected from that quantitiy of air, so it can do some math and formulate an injector pulse width to inject the correct amount of fuel for each expected combustion event. (yea, there's a few other imputs like tps and the like, but for start up, it's mostly airflow/rpm/temp info that the ecu uses to get the ball rolling)
Because the fuel doesn't vaporise well when it's cold outside, the air fuel ratio is substantially enrichened for a cold start. Most of the fuel just stays in droplet form, and doesn't atomise well when it sprays out of the injector at low temps. Much of the little that does will re-condense into droplets on the cold intake surfaces. During cranking, the airspeed in the intake port is low, so there's not a lot of turbulance to help to mix the fuel and air together/break the droplets up. These droplets don't burn so well, so the ecu adds a sh*t ton more fuel in the hope that some of the extra mix will be in the right place at the right time to initiate combustion. (When the key is returned to the run position, the cranking enrichment is turned off)
As an aside, on higher mileage cars with lots of carbon on the backs of the valves, a substantial amount of the fuel will be absorbed by the carbon deposits, leaving the first couple of cranks on the lean side, so some engines make take a spin or two to get lit up.
At any rate, after a turn or two, there's some fuel floating around in the chamber and hopefully, a spark will light things up, and we're off to the races.
Sometimes, it doesn't, and that's when the trouble starts.
The liquid fuel will do some bad things for making happy sparkage.
It will coat the plug tip, making another path for the spark energy to take.
It takes a sh*t ton of power to ionise the air in the spark plug gap.
A dry plug will fire because the ceramic surrounding the center electrode has a very high insulative value compared to the air inbetween the spark plug electrodes.
A wet plug won't fire across the gap because the electrical energy will just take the path of least resistance thru the liquid, and just trickle along the sides of the center electrode to ground.
In addition, the liquid fuel will also dislodge a lot of loose carbon, and some of that carbon invariablly ends up bridging the gap, killing any chance of throwing a spark in that hole.
As soon as the engine lights (usually on another cylinder) turbulance will blow the carp out, she'll start hitting on all the holes, and the engine settles into a fast idle.
If all the plugs are wet, well, things aren't going to go according to plan.
Checking for spark with the plug out of the chamber is helpfull, in the sense that you can see if the secondary sysem is working. However, it's dry firing in low pressure, versus wet firing under pressure in the cylinder, so don't assume it's enough to lite things up when the spark appears weak just laying there in open air.
Many vehicles have a "clear flood" mode in their ecu programing.
When the ecu "sees" 100% throttle while cranking the starter it will turn the injectors off. I'm not completly sure those wily mitsubihi programers put that into the ecu code on these cars (Jeff ? ), but holding the throttle all the way open will at the very least get a lil more air in to dry things off if it doesn't start on the first couple of cranks.
I believe the ignition timing is also adjusted by the ecu for colder temps, so yea, step one is to make sure the ecu is seeing the correct info from the temp senders.
I've been using the rear speaker pigtails in lue of an actual t-stat pigtail, as the connector is exactly the same, (minus the rubber shroud.) It's getting really hard to find good 'stat harnesses, even on the n/a cars.
I would be happy to send you a ecu coolant temp pigtail in the mail, along with some heatshrink to make a nice, permanent repair. (just send me a pm with a shipping address)
I am ashamed I haven't done a write-up on how to replace the t-stat sender pigtail. /ubbthreads/images/graemlins/blush.gif
I've done this job for a bunch of the locals, and I never seem to have time or a camera to take pics.
Cold weather takes it's toll on the battery, so everything has to be ~tip top shape~ in order for the motor to light up.
The lower voltage/amperage available at the starter means the engine turns over more slowly and there's less voltage to work the coils/fuel pump and etc. (Thick oil won't help when it's friggin cold either /ubbthreads/images/graemlins/wink.gif )
A weak coil/corroded terminals on the plug wires, large plug gap, dirty injectors and the like take their toll on driveability when it's warm, but become an insurmountable obstacle when it's brutal cold.
Once the plugs get wet, it's gonna be a chore to get things going.
Taking a little time to get everything in good working order when you're working on the car in a nice clean garage will pay great dividends when you're trying to kick the car out of bed at 'o five thirty in sub-zero weather. /ubbthreads/images/graemlins/wink.gif
edit Sorry this post is such a mess. I'm having trouble sleeping, (day five /ubbthreads/images/graemlins/crazy.gif )
