engine wont idle for more than a few minutes

[imported_rosco]

1995-1996 mercruiser 8.2 EFI.
engine starts fine, will run at cruise all day long. but after its warmed up, it will not idle for more than 3 or 4 minutes before it cuts off. starts back up and dies again after a few minutes.

replaced the mechanical fuel pump, was fuel in the weep tube. didnt help
replaced the relays for the ignition and the fuel pump. didnt help.
replaced the AIC? automatic idle control/circuit. a thing on back of the mass air sensor that controlls the idle. no help.

the elecric fuel pump is getting a constant 12 to 13 volts, adn like i said, works fine at cruise. boat is currently in the shop and they are going to use another electric fuel pump and bypass the factory one to chek it, but i think they are shooting in the dark. the pump either works or not. if it quits at idle, it would also quit at cruise after a few minutes.

getting really annoying, and expensive. already have 5 hours of labor tied up with what has been done to no avail so far. by the time i hit 15 hours, i could replace the entire injection system with the money its going to cost me.

any suggestions?

last resort for me will be to strip the injection system off and put a carb on, eliminating any and all electrical components controlling the motor. already owe enough in labor to have done that .

has to be an electical problem associated mabe with the fuel, probably with the ignition. will run when its cold for a good 10 minutes before cutting out. after its warm, 3 to 4 and it dies. so it also has to be associated with something that is affected by tempature.

 

[Don S]

Re: engine wont idle for more than a few minutes

Got a Serial number? Systems are not the same on a 95 compared to a 96.

 

[imported_rosco]

Re: engine wont idle for more than a few minutes

its in the shop. but the parts list he got the other parts from were for a 1993 to 1995 group of numbers. if that helps.

would like to check the fuel pressure, as opposed to swapping out a 500.00 fuel pump, but dont see anywhere on the body to attach a pressure gauge.

coil mabe?

 

[KRS]

Re: engine wont idle for more than a few minutes

Rosco,

DonS is an absolute PRO when it comes to these motors. Follow his advice and you'll do well. He needs the serial number to tell you anything.

 

[imported_rosco]

Re: engine wont idle for more than a few minutes

it is the 1993 to 1995 502 EFI gen v engine.

dont have access to the boat right now, cant get the numbers. can get them monday probably. definatly monday. loosing faith in the shop where its at. bill is already around 600 bucks and they still havent found the problem. they charge 60 bucks an hour for diagnostics. toss in 2 relays, a 100 dollar mechanical fuel pump and an IAC motor, and im getting a bit fed up with the "replace stuff till it works" stratagy.

i dont know what its like where you live, but here in south miami, very few people want to work on inboards. the place my boat is at is probably the only place within 20 miles that will. the rest are in the downtown district, and i dont think dragging a 9 foot beam boat through downtown traffic is a good idea.

it would be really discouraging if i wasnt confident in my ability to strip the EFI system off, bolt on an aftermarket electric fuel pump and a holly marine carburator, and let the dog chew on the controll modual and the wiring and sensors that go with it.

last resort. if it gets to 1000.00 dollars and still no solution, im gona exercize it.

 

[imported_rosco]

Re: engine wont idle for more than a few minutes

did some testing with a fuel pressure gage after retrieving my boat from the cave men working on it.

pressure drops like a rock right before it dies. turn the key off and on again, a couple times the pump doesnt charge the system, after a couple tries it does.

only acts up after engine is at operating temp[ature., around 170 to 180.

definatly a fuel problem. but is it the pump? or could it be the pressure regulator? thinking the regulator myself, especially in light of the fact the friggin pump is over 500 bucks.

 

[imported_rosco]

Re: engine wont idle for more than a few minutes

well, i removed the pump. dont have a flow meter, so i filled a bucket with about 3 inches of water, put the pick up for the pump in it, and attached it to a battery charger.

what i found out,

with the charger set on 2 amps, the flow was constant but the pressure was eratic. strong, then weak, then strong then weak and so on.

with the charger set on 12 amps, the flow was constant and the pressure was constantly strong. let it run in the bucket for over a half hour and no change.

if the pump is supposed to work on less than 5 amps, it needs replacing. if the pump is supposed to work on 10 or more amps, it "might" be fine. no one at the cave had a clue as to what the amperage for the pump should be. or, as i am finding out, has a clue in general.

my next problem is to first, find out what the amperage should be. something that would have been easy to check had i checked it before i removed it. i could check the amperage coming out of the relay for the 3 second charge when you turn the key on, but i cant check the amperage when it is running unless i put it back in, and i need to do some more testing on the pump first.

the second thing i need to do is find some way to rig a pressure regulator to the bussiness end of the pump and see if it will put out a constant 30 plus lbs of pressure for a given time. something a COMPETANT mechanic could have done with a flow meter. again, the cave people not only didnt have a fuel pressure gage, but stared at me with a blank look when i asked to borrow a flow meter.

local auto parts store doesnt sell them either. i bet mercruiser does but would hate to see the price.

any suggestions on rigging a pressure regulator that will work with a liquid? rigging a fitting for the pump should be easy enough with a piece of alluminum tubing and a breakline flange tool.

 

[imported_rosco]

Re: engine wont idle for more than a few minutes

sweet. the manual, while it is quite useless for spacifics on any one component, lists the fuse for the fuel pump as 15 amps.

good bet the pump itself usses 10 amps or more for operation.

the pump "may" be good. still need to test it to see if it will put out a constant 30 to 40 lbs of pressure constantly for a given time and still pondering how im going to do that.

going on the assumption the pump is good, two more paths spring up.

1. gas is not getting to the pump.
2. the fual rail is not holding pressure.

1. already tested for blocked vent tube by operating engine with gas cap off. so thats not it. mechanical fuel pump is new, so thats not it either.
a. fuel filter is bad. possibly, have replaced it however unlikely, but havent ran engine since.
b. cam is worn out on sea water pump and not driving mechanical pump. possibly, but unlikely, sea water pump is less than a year old and looks to be new and not rebuilt. it is aftermarket however.
c. someone put an underdrive pully on sea water pump. very unlikely, but not impossible.

2. manifold not holding pressure.
a. a leak. would be no missing a fuel leak under 40 lbs of pressure, so rulling that out.
b. fuel pressure regulator is bad. no way to test this other than spending 60 to 70 bucks replacing it.

my plan, first is to somehow test the fuel pump pressure over a given time span. the pump could still be bad. my finger cant tell the differance between 20 lbs of pressure and 40 without something to compare it too.

dont know where i will be able to find a regulator that works with liquid. an air compressor regulator would be ideal, but dont know if it will work with liquid. a gas pressure gage would work if i could find one with a pressure bypass that would allow the fuel to flow through it at a given pressure. ie, a flow meter. hardware and auto stores here dont carry them.

no point in going further untill i can test the pump. and at 500 dollars, replacing it is not an option unless i KNOW its broken. right now, it doesnt look like it is.

 

[Don S]

Re: engine wont idle for more than a few minutes

Try this:

http://www.iboats.com/bbboard/bbBoard.cgi?a=viewthread;fid=24;gtid=1107009

 

[imported_rosco]

Re: engine wont idle for more than a few minutes

thanks.

i never considered blockage or restriction in the lines. i have already ruled out a blocked vent tube by opening the filler cap, but havent considered mabe air getting into the system and causing the fuel pump to run dry.

if the fuel pump checks out, this is probably something i need to check before going further.

will be ordering the vacume guage, thanks/.

 

[Starflight]

Re: engine wont idle for more than a few minutes

I'm just thinking w/ my fingers here.....wouldn't a restriction or air introduction from a leak be more of a problem while underway than at idle? He said he could run all day w/o a problem until idle.

 

[freddyray21]

Re: engine wont idle for more than a few minutes

seems to me when you are cruising your alternator is putting out max voltage letting the pump flow normally. When you idle maybe the alternator is not putting out enough to keep the pump working. The battery should compensate unless it is weak and needs replacing.

 

[imported_rosco]

Re: engine wont idle for more than a few minutes

well, star, actually the higher the RPM, the less a little extra air will affect the operation, unless the increased air increases exponantialy with the increased RPM.

you also have to consider how this bastardized system works.

the mechanical fuel pump pumps a resivior full of fuel just like a large float bowl in a carburator. thats all it does. it even has a needle valve in it just like a carburator.
the electric fuel pump sits in this resivior and pumps the fuel into the fuel rail at a set pressure. then the pressure regulator opens and allows the axcess fuel not being used from the engine to pump back into this same resivior.

it really is a backward system. like the injection part was an afterthought slapped on to a carburated motor.

if there is air getting into the system, the mechanical fuel pump wouldnt be able to keep up with the electric fuel pump and the resivior would run dry causing a loss of pressure in the fuel rail. at idle, the mechanical pump might be going to slow with the air leak, but mabe at higher RPM,s it can keepp up.

just guessing how it might happen. could very well be the fuel pump is toast. wont know untill i test the pump. cant even explore anything further untill i know for sure if the pump is good or not.

and i say "i", because evidently, the word mechanic here in miami is reserved for idiots who toss parts at a problem untill it goes away. i called 4 differant boat shops and not a one could bench test an electricc fuel pump. something that should be a no brainer for any shop that works on fuel injection systems. its sad. really sad. and unfortunatly, i know just enough to recognize an idiot when i see one. i should be ignorant and rich. that way, i would get my boat back in a couple weeks all ready to go and wouldnt sweat the bill that would probably equall my mortgage.

freddy, that is pretty much how the volvo penta injection system works. it gets its power from the alternator. but the mercruiser system goes through the ignition system. both batteries would have to be dead or dieing to affect the voltage going to the fuel pump. either way, have already tested the fuel pump with a volt meter before calling a shop. it is getting a solid 12 to 13 volts all the way through the event. something i bet the mechanics didnt do either, if they had, i wouldnt have two brand new relays. it didnt make sence to me when they told me they replaced them, but i figgured mabe they know something i didnt.

well, im dead in the water untill i can test this pump.

also toying with the idea if it is bad to pulling the mechanical pump off, and scrapping the bastardized electric fuel system and replacing it with an aftermarket high performance automotive fuel pumpp and regulator. could do the whole thing for half of what it would cost be to just replace the mercruiser pump alone. would be nice if there was an aftermarket option for replacing the factory pump and be able to keep the rest of the system. 500 bucks for a fuel pump is not only steep, its stupid.

but, cant do anything untill its tested. well, atleast i learned something about the fuel injection system on my boat out of all of this. just wish it hadnt cost be a few hundred dollars to learn it. ill let you know how it works out. mabe it will help someone to not fall into the same mechanic trap i fell into.

 

[Silvertip]

Re: engine wont idle for more than a few minutes

If you want to make a bench test setup, Holley makes a small adjustable pressure regulator and any pressure gauge available in the plumbing dept of any home improvement center could be used. I'll add my two cents worth. Have you tried running without the engine cover? Fuel percolation perhaps due to heat build-up? Electric fuel pumps are generally wired through the engine oil pressure switch for safety purposes. An oil pressure switch that has become sensitive to lower oil pressure with warm oil would shut off the pump. The trigger point is normally 5 - 6 PSI so oil pressure would have to be low or the switch no longer accurate so this is a long shot. However a bad connection to that sender would not be out of the equation. Try bypassing that sender temporarily and then test.

 

[Starflight]

Re: engine wont idle for more than a few minutes

I am not familiar with your system at all, but was thinking along with Silvertip about the oil pres. safety switch. lower oil pressure at idle tripping the fuel pump out.
Was also thinking that if the fuel system didnt have a return line, or a restricted return line, that the head pressure created could possibly cause the pump to over heat and shut off if it has a internal overload switch in the pump like most electrical motors have.
Again, I'm just thinking, and trying to learn something along the way.

 

[Starflight]

Re: engine wont idle for more than a few minutes

At air conditioning supply stores, they can have or can get glass sight glasses that have flare connections that you can create a double flare to connect to. With a sight glass you can check the fuel for air bubbles. Or if you can get by with a temporary clear flexable tubing to check the same would be helpful.
I really suspect a electrical or electro-mechanical problem. ie the oil pres sw. or the pump. I would check current and voltage at the pump when the problem happens. If the voltage still exists when the problem starts and the amps go to zero, its gotta be the pump shutting off.(internal safety switch) If the voltage dies, then I would suspect the oil sw.

 

[imported_rosco]

Re: engine wont idle for more than a few minutes

this model doesnt use an oil pressure switch, but eliminated an electrical problem with the pressure gage. fuel pressure in the rail drops to 15 lbs from 30 lbs before engine dies. definatly a fuel issue.

made a test gage with a air compressor regulator, 15 bucks, and a fuel line i cut up to use the ends as connectors, 20 bucks. worked lovely.

results on benching the pump were mixed. it ran for 2 hours non stop, but flow rate was disturbing. at 40psi, it was pumping a little over 20 gph of water. at 35psi it was pumping around 25 gph.

my ultra high tech flow meter? an empty one gallon milk jug and the stop watch feature on my timex. took 3 minutes to fill it at 40psi, and 2minutes, 30 seconds at 35psi.

granted, water is more dense than fuel, but i dont think fuel would have been that much higher. thinking the pump should atleast make 40gph at 40psi. a 502 will burn 35 to 37 gph at wot. but, 1 gph should be sufecient at idle.

replaced the fuel filter, ran the pump again with the flow meter attached at the pressure side of the pump and the pressure gage attached at the end of the fuel rail at the same time.

results, it ran fine untill it reached 180 degrees. then pump pressure dropped to 20. the rail pressure hung on for a few seconds then droped too.

not the regulator. definatly the pump.

another disturbing discovery, the fuel bowl the pump sits in was less than 1/4 full. and when i removed the pump is was really hot. two possiblitied here. the pump is overheating then loosing pressure, and or, may be bad, or the fuel bowl is running out of fuel and making the elecric pump run dry.

the mechanical pump is new, as well as the filter. i removed the anti-siphon valve and put in an open niple to eliminate that as a possibility to the bowl running dry.

same results. pressure on pump end droped and was followed shortly after by rail pressure and engine died.

removed pump and immediatly benched it again in a bucket. the GPH at 40psi was down to 15. definantly something wrong with the pump. but that doesnt explain why the bowl was not full. may be two problems going on here, or one problem the result of another, ie, the bowl is mostly empty thus leaving the pump uncovered with liquid and making it run really hot and causing it to fail.

no friggin clue why the bowl will not stay full. mechancal pump is new, filter is new, removed anti-siphon valve, and even used another pick up on the tank for second test. odly, the tank has 4 of them. some models come with twin engines, which would explain 2, mabe a generator for three, but never seen 4 before.

well, i have made a decision anyway. regualrdless, i need to replace the pump. thats 500 bucks for a factory job, plus another 70 bucks for the rubber o-ring on the lid of the bowl.

replacing the pump will do nothing about the bowl not filling though. im at a loss here. so i decided mercruiser can kiss my arse.

gona do some research, and go with an aftermarket fuel pump. edelbrock makes a nice one for 300 bucks, but still need a regulator to bring it down to 40psi, plus, it needs to be primed. ie, i need a low pressure pump to feed it. must have an anti-siphon valve by law, so will need to bring fuel to the high pressure pump via another low pressure pump or a mechanical pump.

has anyone done this before? could use some advise. like will a low pressure electric pump pull fuel through the anti-siphon valve and fuel filter?

Holly has a couple low pressure elecric pummps for marine application that look ideal, or do i need a mechanical pump to pull the fuel past the anti-siphon valve and fuel filter?

can i connect the low pressure pump directly to the high pressure pump? or do i need to use a bowl of some sort to adjust for the differances in flow rate so one doesnt starve the other out?

does anyone know of a good high pressure pump that is coast guard approved, ie, for marine application? BTW, im not above using one approved or not.

i know i can run the return line from the fuel rail back to the tank, apparently, there are plenty of places to attach one there. i also know i can use the same relays and wiring too. spliting them for a second electric pump should be easy enough also.

only thing i havent figured out is what to do with the vent on the low pressure pump.

 

[muc]

Re: engine wont idle for more than a few minutes

Got a Serial number? Systems are not the same on a 95 compared to a 96.

Don S. might have asked this question because there are 2 different VST used -- need the serial number to know what one you have.

Your fuel pump might be bad now (they are lubricated by the gas that they pump) -- not real sure if the water that you have been using for testing was a good idea?

Did you try doing the tests that Don S. suggested? That part about the clear hose could be important.

Good Luck Muc

 

[imported_rosco]

Re: engine wont idle for more than a few minutes

yea, the long block was replaced about 2 years ago, but the rest of it is 0d840650 through 0f802599 1993 to 1995 series.

and no, im sure water was not the best idea, but, didnt have a test bench, and didnt want to play around with a bucket of gas and a battery charger in close proximity. i doused it with wd40 inside and out when done.

did the vacume test. it checked out fine. and as stated before, the engine runs fine at cruise. removed the anti-siphon valve too to eliminate that for testing purposes, and ran engine with open gas cap to ensure adiquit venting.

there is no reason the float bowl should not be filling as far as i can see. the sea water pump is new, but its possible mabe the cam is worn off that drives the mechanical pump, though not probable. it is possible the pully is too large and thus underdriving the mechanical fuel pump too, it is after market, adn not sure of the diameter of the factory one, but i doubt that could be a real problem, especisally at idle.

i noticed on later models, however, that they use the same injection system minus the fuel system. the newer ones dont have a low pressure pump(mechanical), and the overflow from the electric pump is vented back to the fuel tank as opposed to recirculating in the fuel pump resivior. the newer ones also come with a fuel cooler suggesting heat was a problem with prior models.

the newer system is significantly less complicated and less expensive to replace.

either way, if i could be confident it was "just" the fuel pump, and im convinced it is faulty, i would consider replacing it even though it is twice as expensive as any top line fuel pump should be.

but i cant. recirculating the overflow from the electric pump, basically pumping heated fuel back to the pump, is a bad design to begine with. it guarentees really hot fuel at idle. the more that is bypassed, the less that is frech from the tank, ends up to a fuel cooker. it SHOULD have been vented back to the fuel tank so it could be replaced with cool fuel.

mabe the heat is causing a vapor lock situation in the resivior, i dont know. but it should be filling and its not. weather it has enough to run the elecric pump, i cant say. all i can say is, that it will idle for a good 30 minutes or better untill it reaches 180 degrees. then it doesnt. so, while its cool, everything is working fine, low GPH rate and all.

heat definatly plays some part in this fuel mystery. exactly what, im not sure.

what i am sure about is, i can eliminate the heat, the lack of fuel, the low GPH rate and any lack of confidence for less money than it would take to replace the factory pump.

unless i can find the problem definitively, mercruiser can kiss my butt. the factory formula mechanics just want to throw good parts after bad at it untill they either replace the entire system or it starts working. that, to me, is unacceptable, not to mention im sure as heck not going to dump a couple grand tyring to fix a fuel problem.

it is a poorly designed system. the heated overflow should never have been allowed to go back directly to the fuel pump to be heated again and recirculated again creating a fuel cooker.

i can fix it. i can make it stronger than it was, faster, more dependable WITHOUT spending 6 million dollars.

 

[Silvertip]

Re: engine wont idle for more than a few minutes

There is an "old" vapor lock trick you might try. Soak a towel in ice water. After getting the engine to stall. Wrap the towel around the return line. Restart the engine and see if it fails. If it does, try wrapping the towel around the resevoir. If this seems to solve the problem, Try wrapping aluminum foil around the line. Wrap it such that you create lots of relatively high ridges, creating a heat sink of sorts. Even mounting a fan so it blows on the pump and line may help. While these are obviously not ideal fixes, they at least help in the diagnosis.