Trouble with troubleshooting

[Bski]

I'm new to this forum. I have a 5.7 litre Volvo I/O that is giving me some real grief.<br /><br />The motor has 67 hours of run time on it, only used in freshwater, parked under covered storage in the winter.<br /><br />The problem I have is that I ran it at a lake the other day and it ran fine accept the idle seemed rough. After checking everything possible and cleaning out the carb it still acts like it's idling on less than all 8 cylinders. From 800 rpm to about 2000 it sputters and then it will smooth out all the way to 4000 rpm +. Even on the lake with or without a load it runs like this.<br /><br />I put in new plugs, checked the wires for any cracks or arcing, dist cap appears to be good. Fuel filters are clean. The only other thing I think that is possible is that I ran the tank down low on gas and I think I must be sucking up water. I did empty out the water separator but it still didn't make a difference. It was running fine when the tank was full on the prior trip and this time I ran it down real low.<br /><br />My main question is, if the tank is full wouldn't I still see the ill effects of water in the fuel or does it get pulled into the system when the level of fuel goes down?<br /><br />I appreciate any suggestions, I've been wrenching on cars, motorcycles, and boats for 30 years + and I can't seem to pin point this problem. <br /><br />Thanks for any help, sorry for the long post.<br /><br />P.S. Anyone have any good suggestions as to how to drain the gas tank? Considering a siphon but not sure if I can get it all the way to the bottom.

 

[Boomyal]

Re: Trouble with troubleshooting

Gas floats on water so it won't make much difference how full the tank is. It there is water in it you will pick it up. However, your seperator filter should remove it. <br /><br />I think you have a carb problem. Get a couple of cans of Seafoam, pour one and a half in the gas tank and feed the rest, slowly down the carb while running at a fast idle. Then go out and run it. Try to keep it at the rpm that it starts out running crappy and see if you get any improvement.

 

[Bski]

Re: Trouble with troubleshooting

I think you are right about the carb problem. I pulled the separator filter off and poured it into a clear jar, didn't see any sign of water at all.<br /><br />I don't believe it's electrical cause it runs too good on the top end. <br /><br />I guess it's time to take the carb off again and pull it apart and see if I can find something stuck in somewhere.<br /><br />When I figure it out I will let everyone know.<br /><br />Thanks.

 

[csanna]

Re: Trouble with troubleshooting

wait a minute // you said gas floats on water // If thats the case then he wouldnt get water in his sys till the fuel level drops. because the fuel sys pickup is very near the bottom of the tank.

 

[Wart T]

Re: Trouble with troubleshooting

Is this electronic ignition? I have seen the modules in the Volvo prestolite distributors cause that. I would suspect the idle circuit in the carb first though. But simple stuff first. Verify the idle is at the proper speed after adjusting the idle fuel mixture screws using the lean drop method. Then check the base ignition timing. Then remove the fuel filter, fill it with B-12 or BG44K fuel system cleaner. Start it up and let it idle. Dont rev it, you want the cleaner to go through the idle circuits. If that makes a difference or fixes it then voila! You have located the problem.

 

[Boomyal]

Re: Trouble with troubleshooting

Originally posted by csanna:<br /> because the fuel sys pickup is very near the bottom of the tank.

Dat's correct. That is where the heavier water is!

 

[Bski]

Re: Trouble with troubleshooting

It is electronic ignition, I'm not sure if the ignition could be the problem cause it doesn't seem to be a problem under load. How can I test the module for the distributor?<br /><br />Regarding filling the filter with B-12 or other cleaner, that sounds like a good idea except wouldn't that be a little too strong for the motor and possibly burn valves or pistons? Also, I can't get it to idle at all now, it just dies out. I did try setting the fuel mixture (lean out method) and noticed that the circuit on one side doesn't respond, which makes me suspect the idle circuit being plugged up. Timing was checked too.<br /><br />I'm going to take the carb off tonight and look over the metering block real good, I'll pull the jets out and spray cleaner through all the passageways, then use compressed air to blow it out.<br /><br />I won't discount the possibility of water yet, just going to go through the steps.<br /><br />Thanks for the replies.

 

[ron7000]

Re: Trouble with troubleshooting

in response to your other post about the prestolite distributor, no. If it was mechanical with points, then maybe if the dwell is screwed up. With electronic, they usually work 100% or not at all. What you can do is get a timing light and watch the timing mark advance on the crank when rpms increase. As for checking dwell, you'd have to get a dwell meter and since it's electronic probably reference a service manual for specific procedures. I'm not familiar with volvo.<br /><br />What year is the motor? The first, and cheapest thing you should do, is get a vacuum guage.<br />Check vacuum at idle, or as close to 800 rpms as you can get. If the needle on the guage bounces, then you're not getting good valve seal and will need a valve job. If you dont get good consistent vacuum, then the carb will never operate properly at idle. I learned this the hard way by buying a new holley 4bbl for $400 and finding it didn't solve the problem. Motor liked to run at 3000+ rpm, but would load up at idle and had a hard time accelerating smoothly and strongly through the 2000 rpm range. It's also possible the valves might only need adjusting. It's hard to diagnose without first hand experience, so take that into consideration before thinking of pulling the heads.<br /><br />If you do have good vacuum, then have you replaced the power valve on the carb? What model carb is it by the way?

 

[Bski]

Re: Trouble with troubleshooting

Ron,<br /><br />It's a 97 motor and boat, I bought it new and it only has 67 hours on it. It ran fine for a day and the next day it started acting up. I was going to measure the vacuum but after I replaced the power valve it got worse and won't even idle. Carb is a Holley 4bbl. I'm pretty sure that there is something clogging the idle circuit or something in the metering block.<br /><br />As I mentioned in the other post, I pulled the carb apart last night and shot carb cleaner through any orifice that I could find so I'm hoping when I put it back on the problem will be gone. <br /><br />I agree with the ignition, if it was points then it would be a different story. I have heard of electronic modules acting up when they get hot, but like you said usually they die altogether. <br /><br />I'll have to keep my fingers crossed and hope that when I put the carb back on the problem will be gone, if not I'll have to keep troubleshooting.

 

[highaltitude]

Re: Trouble with troubleshooting

check for an ignition miss with a timing light. test each cylinder throughout the rpm range. this will tell you if it is fuel or ignition. you can also use the timing light and shoot it down the carb throats while running the boat. this will make it easier to see if the carb if flowing fuel through all the throats. good luck.

 

[calwldlif]

Re: Trouble with troubleshooting

plugwires could look fine and still break down.<br />an ohms meter will tell you if there ok<br />the old pull a wire off 1 at a time, note<br />rpm drop, could help.<br />if the problem is elec not fuel<br />i feel for you , trouble shooting sucks.<br />rick

 

[Bski]

Re: Trouble with troubleshooting

I just put the carb back on last night. Didn't fire it off yet but will probably do it tonight when I get home. <br /><br />After cleaning the carb I don't see the possibility of this being an issue anymore.<br /><br />One interesting thing I found was that the nipple which is normally located on the upper side of the metering block was missing. This is the ported vacuum which normally kicks in above idle. The boat was new when I got it but maybe they put rebuilt Holley's on them and somewhere on the assembly line they left the nipple off.<br /><br />I made a rubber plug so I won't get a leak there.<br /><br />After I fill up with a fresh tank of fuel and put on a new water separator filter I will add a little B-12 and then fire it off.<br /><br />From here on it's time to look at the ignition again and then if worse comes to worse I need to start looking into the valve train.<br /><br />One last thing I thought of late last night, it's possible that the choke is not opening all the way, I need to look at this one more time.<br /><br />On the positive side, I know my carb is nice and clean inside <br /><br />Have a great weekend!<br /><br />P.S. highaltitude and Wildlife, I did do the pull one wire at time while the engine was running and the weird thing was that I only noticed a drop in rpm with certain wires off. The spark is there but the rpm didn't really change as much with certain cylinders shut down. I've never seen this happen before, usually there is a definite drop when a wire is pulled. This leads me to be more concerned with something internal like the valves or the camshaft. Guess I'll have to wait and see.

 

[ron7000]

Re: Trouble with troubleshooting

Originally posted by Bski:<br />P.S. highaltitude and Wildlife, I did do the pull one wire at time while the engine was running and the weird thing was that I only noticed a drop in rpm with certain wires off. The spark is there but the rpm didn't really change as much with certain cylinders shut down. I've never seen this happen before, usually there is a definite drop when a wire is pulled. This leads me to be more concerned with something internal like the valves or the camshaft. Guess I'll have to wait and see.

do that at 2000 rpms in gear, so the engine is under a load. If you don't hear and feel the difference pulling every wire then you're not getting spark. This troubleshooting method isn't good at idle in neutral.<br /><br />with the holley, if you have a 4160 model, float level should be set so float top is parallel with top of bowl. Set idle set screw 2 turns in after contacting cam which moves the main throttle plates. Idle mix screw should be opened 1.25 turns counterclockwise initially, then adjusted once motor is hot to get good idle. Sounds like you may have gotten some dirt floating in there and probably hanging up the needle valve.