Cold start problem

[Harley]

help!! im stumped...when its cold out..anything below 50 degrees, it will turn over but wont start. after about 6 tries, it will sputter, after 10 tries, it will start and run on what seems to be a cylinder or two for a few seconds...after several of these tries,5 or more minutes and it sputtering a few times, it will snap out of it and run fine! i have went through all the grounds,replaced the iac valve, the ect sensor and still no luck. it seems that as soon as the engine temp goes above a certain level, it runs fine....this all started happening after i changed my valve cover gaskets??? after that the dash temp gauge died and this cold start problem surfaced....any ideas are welcome

 

[RonD]

You replaced the ECT Sensor, the TWO wire "sensor" right?


There is a ONE wire Sender used for the dash board temp gauge, the two look similar but serve different purposes.

ECT sensor activates the "Choke mode" in the computer, this causes the computer to run the engine rich, with advance spark timing and higher idle.
Just like a choke plate did on carb.

The Sender is just used for the temp gauge.

A faulty ECT sensor would explain your problems, after multiple cranking tries the cylinders warm up so engine can finally start.

Cold engines need a rich mix to start and stay running, the colder they are the richer the mix needs to be.
If idle after starting isn't above 1,000 then ECT or IAC Valve may be at fault, IAC Valve needs to open more on cold starts to provide more air for the extra fuel.

This rich mix places a burden on the spark plugs/system, you need a hot spark when engine is colder.
To see if this might be the problem, the next cold morning run a jumper wire from the battery positive to the Coil +, this will give the coil full voltage for starting, which it should have via the TFI system.

If vehicle starts then check out the TFI system: http://www.therangerstation.com/tech_library/TFI_Diagnostic.shtml

Most single coil systems have separate power for the coil, 12 volts for starting, and 7 volts when engine is running, this lower voltage makes coil last longer, and extra hot spark isn't needed after engine starts.

 

[Harley]

You replaced the ECT Sensor, the TWO wire "sensor" right?


There is a ONE wire Sender used for the dash board temp gauge, the two look similar but serve different purposes.

ECT sensor activates the "Choke mode" in the computer, this causes the computer to run the engine rich, with advance spark timing and higher idle.
Just like a choke plate did on carb.

The Sender is just used for the temp gauge.

A faulty ECT sensor would explain your problems, after multiple cranking tries the cylinders warm up so engine can finally start.

Cold engines need a rich mix to start and stay running, the colder they are the richer the mix needs to be.
If idle after starting isn't above 1,000 then ECT or IAC Valve may be at fault, IAC Valve needs to open more on cold starts to provide more air for the extra fuel.

This rich mix places a burden on the spark plugs/system, you need a hot spark when engine is colder.
To see if this might be the problem, the next cold morning run a jumper wire from the battery positive to the Coil +, this will give the coil full voltage for starting, which it should have via the TFI system.

If vehicle starts then check out the TFI system: http://www.therangerstation.com/tech_library/TFI_Diagnostic.shtml

Most single coil systems have separate power for the coil, 12 volts for starting, and 7 volts when engine is running, this lower voltage makes coil last longer, and extra hot spark isn't needed after engine starts.

thanks ron, i did replace the two wire sensor and the one wire also...funny thing is, when this started, the temp gauge stopped working too. ect sensor didnt fix the problem but the temp sensor fixed the gauge. ill try the jumper wire and see if that narrows this down anymore. i agree about the temperature being involved...it seems to run better and better as it slowly heats up...very frustrating problem. was also wondering if lack of fuel pressure might be leaning it out too much causing a too lean cold start problem??

 

[RonD]

Yes, low pressure could cause that, but I would expect that to show up at highway speeds as well, after warm up.

You could test the voltage at the ECT sensor.
Use a pin to pierce one of the wires
Turn on the key
Set Voltmeter to DCvolts
Ground the meter's black lead
Touch Red lead to the pin
If voltage is above 4.7v then that is the 5volt Power wire from the computer, it also powers other sensors like the TPS, and IAT(air temp).

Move pin to the other wire
If engine is cold it should show 3volts or slightly higher
32 degF = 4.0v
65 degF = 3.0v
100 degF = 2.0v
200degF = .5v (operating temp of engine)

Computer reads this "return" voltage and uses it to set the rich mix amount based on engine temp

 

[Harley]

Yes, low pressure could cause that, but I would expect that to show up at highway speeds as well, after warm up.

You could test the voltage at the ECT sensor.
Use a pin to pierce one of the wires
Turn on the key
Set Voltmeter to DCvolts
Ground the meter's black lead
Touch Red lead to the pin
If voltage is above 4.7v then that is the 5volt Power wire from the computer, it also powers other sensors like the TPS, and IAT(air temp).

Move pin to the other wire
If engine is cold it should show 3volts or slightly higher
32 degF = 4.0v
65 degF = 3.0v
100 degF = 2.0v
200degF = .5v (operating temp of engine)

Computer reads this "return" voltage and uses it to set the rich mix amount based on engine temp

thanks ron! i will check this asap...maybe i have a broken wire leading to the coolant sensor? this problem started after i changed the valve cover gaskets and i had to move a lot of wires in the process....we will see...