Cool Fuel

[badal]

Mercruiser 5.7 EFI 1999/Bravo 3 in a Bayliner 2655<br /><br />Been experiencing engine running problems, Limited WOT(3800-4000)<br />Reluctance to respond to Throttle Low/Mid Range<br />Poor or failure to warm start<br /><br />Compressions been checked, all between 175 and 195<br />New coil fitted<br />New Ignition module fitted<br /> <br /> <br />My fuel pump may be faulty. Can anyone advise, I would like to do away with the cool fuel system and install a simpler high pressure pump and Regulator system which is more accessible than the Mercruiser system<br />I live in Scotland, so High ambient temperatures are not really a problem for me. <br /><br />Any help would be greatly appreciated

 

[rodbolt]

Re: Cool Fuel

have you actually tested the fuel rail pressure? there are some other causes of the symptoms you decribe.<br /> a TBI system should run about 11 PSI and the MPI system should run about 45 PSI. but both systems also have filters in the individual injectors that can restrict fuel as well as some other components that can create a rich or lean condition.

 

[badal]

Re: Cool Fuel

thanks<br /><br />no the fuel runs from the cool fuel system directly to single point inj (carb)on top of the engine<br />The engine does not have individual injectors<br /><br />My manual says 38 psi which is regulated via the cool fuel system in a loop back through the filter

 

[rodbolt]

Re: Cool Fuel

double check your manual, most cover both systems.<br /> if you have a TBI you have 2 injectors MPI will have 8.<br />most TBI systems run significantly lower rail pressure than MPI systems.<br /> however some TBI systems will typically hold 30 PSI.<br /> there are some tests for clogged filters and the TBI system is easy to remove the injectors the MPI system is sligtly harder . but a fuel pressure test will tell you if your high pressure pump is working or not. if it is move on to the next step. the fuel pressure guage can also tell quickly is a pressure regulator is sticking open or an injector is sticking open.<br /> EFI is so much simpler than carbs but it requires a different set of testing techniques.<br /> it also requires a few test tools that without your only other option is to start replacing parts till its fixed or your broke and disgusted.

 

[badal]

Re: Cool Fuel

Hi<br />thanks again - Yes its TBI with two injectors<br /><br />I assume that I should pressure test at the joint where the fuel line meets the carb Body, and that this test should be carried out on the water through the entire rev range<br />OR<br />Can I assume that the pump will deliver constant pressure from a static test?<br /><br />I have the drive in bits so it will be a while before I can get floating, but in the meantime and with regards to my question regarding cool fuel, can I render the cool fuel system redundant and by pass it with a new HP pump and pressure regulator?<br /><br />Thanks again for so much help

 

[rodbolt]

Re: Cool Fuel

the pressure regulator is part of the TBI assy. no good way to bypass it. the system is very pressure sensitive as the ECU does not monitor fuel rail pressure. to much and it will run very rich not enough and it runs lean, usually a 4psi variance will create problems.<br /> have you ever had issues with trash or water in your fuel?<br /> and be aware that a leaking riser or riser gasket will create all sorts of drivability issues including severe spark knock and backfireing in the intake as well as a rich condition at idle.<br /> a bad IAC will create all sorts of funny problems at low speed.<br /> yes the fuel pressure gauge attaches to the inlet side of the TBI, some systems have a schrader valve and others require an adapter, no real ryme nor reason its just how merc and volvo and some others did it.

 

[badal]

Re: Cool Fuel

I'll make the suggested checks <br /><br />thanks for your help

 

[newport dave]

Re: Cool Fuel

Don't mess with the Cool Fuel system. It will be a lot easier to diagnose and repair than re-engineer. <br /><br />As Rodbolt mentioned, there are other things that can be causing those symptoms. Let the engine computer do some of the work for you - check the engines self diagnostic system for trouble codes. That may not tell you what the problem is, but at least it will eliminate some possible causes.<br /><br />Dave