502 hard to start when cold
 

I have a 2000 model 502 EFI that is hard to start cold after it has sat all week and over night. Once it starts i dont have a problem with it the rest of the day. I'm just looking for some suggestions on what it might be that i need to look into. Thanks

I found a focused effort to only use no-alcohol fuel and use of a fuel treatment improved starting and initial start smoke markedly on my carb 454.

I started with Lucas fuel treatment and had good results but switched to Conklin fuel mate plus due to it having both fuel stabilization and cleaning properties. (and a buddy was pushing the Conklin as a dealer)

one of a couple of things. the system probably has an internal leak somewhere ... an injector or something that allows the fuel pressure to bleed to zero and "dry out " the rail or rails. its pretty common. beyond fixing it is to turn the ign on and the pump will run for a few seconds. when it stops turn the ign off and on again and let the pump run again and do this a couple or three times. this will go some distance in rebuilding the pressure in the rails and make it easier to start. beyond that, make sure the water temp switch ( not the gage... the temp switch for the injection ) is good and the connections are good.

taking the injectors out and cycling them with cleaner backwards often fixes the leaking issues.

I would check the temp sensor Probably not telling the ecm that the engine is cold and not richening the fuel mixture on startup.

fuel system cleaner. could be a leak, but probably a sensor.

I'd put a fuel psi gauge on it, and see how long the fuel psi holds with engine off. Like steve says, sounds like the psi is leaking off, thru a injector, o ring, or even a valve in the fuel pump.

Having the same problem but with carb motors. Maybe fuel evaporating from bowls over extended period of shut down. Any thoughts??? Fixes??

I had the same problem, I found if I rubbed my hands together really fast then place them on a big set of boobs she fired right up. OOPS wrong thread....

Ok i've only had a chance to try turning the key on 4 or 5 times letting the pump run each time. Unfortunately this didn't help any. Still took along time to start.

Ignition control module going bad? I would have to crank and crank my engine to get it to fire unitl I just replaced it. There was also a lack of upper rpms and hesitation in the throttle.

Today i was able to check the fuel pressure. When i first turn the key on the pressure goes to 45 lbs then drops and stays at 37 to 38 lbs. When i get it started the pressure holds at 40 lbs. I think these numbers are about right.

Hey csharpo,

Did you ever have any luck tracking this down? I have a 97 with a 502 EFI and have the exact same issue. When i start from cold it takes quite a few seconds of cranking before it finally hits, once it does it runs like a top, no idle issues no top end issues. If i turn it off for a few hours at a restaurant or in cove, it fires right up no problem when i go to restart it. After it sits over night it's hard to start again. Changed Cap, Rotor, Plugs, and Wires last year, and I always put a new water seperator on every year, along with Ethanol free fuel. It's been doing this for well over a year now.

Guys what is the water temp switch/sensor? I tried to search google by these phrases and did not come up with much of anything i could use. Does it have a Mercury proper name?

Thanks,
Bill

Having the exact same problem. I had the injectors cleaned and replaced the ect sensor and problem is still there. This is on an efi motor but find giving it a little throttle helps the amount of time cranking. Been talking about this with my mechanic he thinks the fuel is going back to the tank because I don't have a fuel/water separator or anti siphon valve...could this be my problem and possibly the others. I'm not sure if mine counts as the same as the others since my motor isn't stock and has a blower? But it does have the exact same symptoms as the others...cold start problem after sitting over night-needs to be cranked a long time to get started, after started it runs perfect and refires if not sitting over night...a few hours is fine.
Thanks