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View Full Version : Is it water in the fuel?


jfw432
11-02-2012, 11:24 AM
I've been struggling with my engine more regularly lately. I always thought water was getting in the fuel because the power would start to die off, pick back up, and repeat until it eventually sputters out. After a few minutes of cranking, starting, variable revving, and dying again, the engine will start and act normal again. So water in the fuel seemed to be the most likely. It started a couple months ago and has gotten more and more frequent to point where it happens 2-3 times in an outing.

I've done a variety of things to the fuel tank vent to help eliminate water intrusion including adding an air compressor style water separator which won't allow any liquid through the line. Well I'm still getting what seems like water in the fuel and last night even unhooked the vent line completely and was still getting the problem.

I'm beginning to think this isn't a water intrusion issue at all. Would a failing mechanical fuel pump exhibit a similar problem or not wanting to rev or sputtering out?

strad
11-02-2012, 01:29 PM
Well I remember years ago our family's 86 suburban (5.7 4 bbl carb) suddenly didn't want to run properly under any load at all, but it would idle fine. When our mechanic tested fuel pressure, it was about half of spec. With a new fuel pump it ran fine again. So if it were me, to eliminate the fuel pump from the equation I would check fuel pressure, ideally while the symptoms are present.

Edit: you don't mention what exactly you're working on. That would probably help the smart ones around here lol. I assume it's carbed or you wouldn't have mentioned a mechanical fuel pump.

jfw432
11-02-2012, 03:01 PM
Yeah it's a carbed 351w with a mechanical fuel pump.

JimN
11-02-2012, 03:48 PM
I've been struggling with my engine more regularly lately. I always thought water was getting in the fuel because the power would start to die off, pick back up, and repeat until it eventually sputters out. After a few minutes of cranking, starting, variable revving, and dying again, the engine will start and act normal again. So water in the fuel seemed to be the most likely. It started a couple months ago and has gotten more and more frequent to point where it happens 2-3 times in an outing.

I've done a variety of things to the fuel tank vent to help eliminate water intrusion including adding an air compressor style water separator which won't allow any liquid through the line. Well I'm still getting what seems like water in the fuel and last night even unhooked the vent line completely and was still getting the problem.

I'm beginning to think this isn't a water intrusion issue at all. Would a failing mechanical fuel pump exhibit a similar problem or not wanting to rev or sputtering out?

If you want top rule out water in the fuel, you'll need to take a sample at the pump. You can check fuel pressure but it's never very high, anyway. All it needs to do is fill the bowl, not atomize in the cylinder- the wet manifold/vacuum handle that.

It could be a lot of things- all related to fuel delivery, or not. When it bogs, squirt some gas into the carb and see if it kills, or runs better. If it kills, it was too rich already. If it runs better, it could be a power valve, float, needle valve,....

If it revs fine in neutral but not under load, make sure the timing is correct and the gap/dwell are set to spec. If it has electronic ignition, make sure the timing is right. If you can get a spark intensity tester, use that, too.

How long since the plugs, wires, cables and rotor were replaced? Have you cleaned the flame arrester?

jfw432
11-02-2012, 04:58 PM
I am putting brand new wires, cap, plugs, and rotor on this winter but haven't replaced anything but the plugs since I bought it 2 years ago. The carb was rebuilt mid summer and it could be a problem with the rebuild kit I installed but it ran so much better after I rebuilt it that I don't really suspect that. The flame arrester is a little black but it was cleaned a couple months ago.

If I have problems, it has the same problems in nuetral and under load. When I'm trying to clear up the problem, I'll rev the engine in nuetral and when if it starts to die above around 2-2.5k rpms, I'll give it more gas and it'll rev. If it starts to die below about 2k rpms, I have to back off the throttle to keep it alive. If I squirt a little fuel in the carb prior to cranking it, it will usually run a little cleaner. Sometimes that will clean it up completely and others it will only work for a few seconds just like I had never done it.

I'm getting ready to pull the engine out of the boat for winter mods and will be doing a leakdown check fairly soon to see what else could be wrong.

jgraham37128
11-02-2012, 05:38 PM
Have you replaced the fuel filter?

jfw432
11-02-2012, 06:43 PM
Yes I replaced the fuel filter a couple months ago.

JimN
11-02-2012, 08:47 PM
I am putting brand new wires, cap, plugs, and rotor on this winter but haven't replaced anything but the plugs since I bought it 2 years ago. The carb was rebuilt mid summer and it could be a problem with the rebuild kit I installed but it ran so much better after I rebuilt it that I don't really suspect that. The flame arrester is a little black but it was cleaned a couple months ago.

If I have problems, it has the same problems in nuetral and under load. When I'm trying to clear up the problem, I'll rev the engine in nuetral and when if it starts to die above around 2-2.5k rpms, I'll give it more gas and it'll rev. If it starts to die below about 2k rpms, I have to back off the throttle to keep it alive. If I squirt a little fuel in the carb prior to cranking it, it will usually run a little cleaner. Sometimes that will clean it up completely and others it will only work for a few seconds just like I had never done it.

I'm getting ready to pull the engine out of the boat for winter mods and will be doing a leakdown check fairly soon to see what else could be wrong.

For whatever reason, I saw a lot of bad coil wires on Ford engines. Also, see if you can get Borg Warner Gold series cap and rotor- I use those on my truck and they come with a lifetime warranty. I used them when I worked on boats, too.

Judging by the fact that it runs better when you squirt gas in before starting, it sounds more like a fuel issue.

mondos829
11-02-2012, 08:57 PM
Spray wd-40 in the rotor and cap, get everything coated lightly. Fixed my issue, I was having fouling due to condensation in the cap.

jfw432
11-02-2012, 11:34 PM
Looks at the plugs today and they look really white like the engine has been running lean but I'm also used to looking at 2 stroke plugs. All of the plugs pretty much look like this. What do you think?

j.mccreight@hotmail.com
11-02-2012, 11:53 PM
Look worn out or possibly lean condition, could you detect any detonation while running? Is the insulator cracked? If carburetor or fuel pressure are not the problem you need to check initial timing and advance timing and switch to at least 89 AKI octane fuel.

jfw432
11-03-2012, 06:41 AM
Well I never noticed any deto. The plugs have maybe 100 hours on them at most. The insulator isn't cracked but it sure has a lot of deposits on it for being so new.

I'll check on the timing and adjust timing/octane requirements as necessary.

j.mccreight@hotmail.com
11-03-2012, 09:02 AM
Was there perhaps a large amount of "fuel additives" in the fuel tank, too many additives can leave deposits.

jfw432
11-04-2012, 02:50 PM
No I never put any additives in my fuel except in the winter which was probably 300 gallons ago.

cal69
11-06-2012, 12:27 PM
Can you first rule out any spark problems? I say this because I just solved a similar problem with a new to me 1992 PS 205. It would cut out after running it for about an hour or so, then not restart until it sat for 10-15 mins. I thought it was fuel and rebuilt the carb (had been sitting for 3 years prior to buying it), changed the filter, checked the tank & still the problem persisted. I checked for fuel delivery on the water when it conked out and it had a steady squirt from the carb. Put my hand on the coil and nearly burned it off. Changed out the coil and Pertronix unit and the problem went away.
Just something to consider.

jfw432
11-06-2012, 10:49 PM
Well I can't imagine spark is the issue because the engine always fires back up and the more fuel I put down the engine, the longer it will run before conking out. I have dealt with many electrical problems in the past on boats, cars, and jetskis and this doesn't resemble any of those.

Thanks for the idea though.

bsloop
11-13-2012, 09:23 PM
I installed a small liquid filled fuel pressure gauge just before the carb from Jeggs. It was maybe $30 and I can see fuel pressure at any rpm and while under load if I leave the cover off.

I was chasing a slow die condition too while at higher rpm / load. Turned out to be the anti-siphon valve was partially blocked. (small ball check valve at the fuel tank).
Under low demand conditions all was mostly ok, it was starving at higher fuel demands.

psychobilly
11-13-2012, 09:55 PM
Well I can't imagine spark is the issue because the engine always fires back up and the more fuel I put down the engine, the longer it will run before conking out. I have dealt with many electrical problems in the past on boats, cars, and jetskis and this doesn't resemble any of those.

Thanks for the idea though.

I had the simular type issue that you're have and it was the oil pressure switch that run my fuel pump.... It has run great every since I replaced it.... It would have symptoms that you're describing and I couldn't find the issue until it finally crapped out.
Edit... Dope! I just seen your second reply that it a mechanical FP.
NEXT LOL