mercruiser 5.0 mpi hard start when warm

[shoestring]

Re: mercruiser 5.0 mpi hard start when warm

well i have my flowbench proven injectors re-installed, I have checked my fuel pressure, 38 @ idle, 42 w/ vacuum disconnected, drops to 32 when i shut the engine off and holds solid for 10-15 min. plugged in my scanner and didn't get any codes that would support my problem, tps goes from 0% up to 99%, coolant temp matches helm gauge up to 160-could go haywire higher but 160 is all i can get on the muffs. saturday i'm going to play with the iac a little and see if something may be hanging up there. I'm not sure what the ecm should be telling the iac to do at warm start but i think it should be higher than what it is at idle if not @ 100% open during start. when i start hot or cold the engine only goes up to idle, it doesn't run up to 12-1400 and then back down to idle like most mpi cars do @ start, not sure if it is supposed to. the iac is working while it is running, between neutral and gear i can tell the engine is responding to the load, i understand the iac runs full open to full closed everytime the key is turned on, i guess it could start hanging up when it is hot. if i run into a dead end on the iac, i guess i will have to take my tools out on the water and test it out when I am having the problem. I was hoping to solve this before then. is there anything i have missed, i welcome any other sugestions anyone might have. thanks ss

 

[BOATnSC]

Re: mercruiser 5.0 mpi hard start when warm

well i have my flowbench proven injectors re-installed, I have checked my fuel pressure, 38 @ idle, 42 w/ vacuum disconnected, drops to 32 when i shut the engine off and holds solid for 10-15 min. plugged in my scanner and didn't get any codes that would support my problem, tps goes from 0% up to 99%, coolant temp matches helm gauge up to 160-could go haywire higher but 160 is all i can get on the muffs. saturday i'm going to play with the iac a little and see if something may be hanging up there. I'm not sure what the ecm should be telling the iac to do at warm start but i think it should be higher than what it is at idle if not @ 100% open during start. when i start hot or cold the engine only goes up to idle, it doesn't run up to 12-1400 and then back down to idle like most mpi cars do @ start, not sure if it is supposed to. the iac is working while it is running, between neutral and gear i can tell the engine is responding to the load, i understand the iac runs full open to full closed everytime the key is turned on, i guess it could start hanging up when it is hot. if i run into a dead end on the iac, i guess i will have to take my tools out on the water and test it out when I am having the problem. I was hoping to solve this before then. is there anything i have missed, i welcome any other sugestions anyone might have. thanks ss

I know this is a late reply, but I have a 2000 model 5.0 EFI and it was vapor locking. What happened was when you stop the engine the hot water from the block was draining back into the fuel line cooler. Once I figured this out (many days and headaches later) I installed a brass one way valve in between the fuel cooler and the block on the water line. Problem solved. Been two years without a single issue.

 

[Majesticman]

Re: mercruiser 5.0 mpi hard start when warm

I just developed this problem after we filled up at the marina. My 4,3 OMC ebbtide with 350 hrs never had a problem of any kind until then. Starts fine when cold but when warm it take about 30 secons to start. Somone told me the fuel could have acohal in it causing it to vaporlock easier. I hate to suck the fuel out but I am that point. Is there anything else to check that is not real technical or aditive to neutralize the acohol?