98 Volvo 7.4 LP fuel pump whine at idle

[GHfishin]

I have read a lot of threads and haven't yet seen an answer to this one.

7.4L fuel injected. low pressure pump forward on top of the filter and high pressure pump aft on the reservoir.

Engine starts and runs for a bit till it warms up. Then it begins to whine low like its cavitating and building up a bubble. As this happens it gets warm. In a couple minutes the the pump shutters a bit and the whine stops only to start the cycle over. throttle up to 1500 RPM and the whine goes away and the pump runs fine and cool. Fuel flow and burn rate are consistent with normal operation at cruise but when I reduce to idle again the cycles starts over.

I have changed the pick up from the tank and the check valve, I have disconnected and reconnected (with locktight) everything between the tank and the pump and replaced the o rings on the pump. Still whining.

I can't be the first person to have had this problem.

 

[Don S]

Re: 98 Volvo 7.4 LP fuel pump whine at idle

Check the inlet screen on the low pressure pump. If you look at a lot of the posts in this forum over the past couple of months you will find a bunch of people with the problem.

 

[GHfishin]

Re: 98 Volvo 7.4 LP fuel pump whine at idle

Checked the screen. Removed all the fittings and resealed them with locktight. Put on a new pump. none of this solved my problem. Then I installed a clear section of hose between the end of the fuel hose and the connection to the filter bracket. ran the motor for a bit. I watched as a bubble formed at the fitting, grew larger as the whine got louder then sucked through and the whine stopped. I watched as the cycle repeated a few times. During this cycle the pump is not moving any fuel through the line it is just emptying the filter. when the fuel in the filter gets below the nipple the pump sucks the bubble out and fuel flows through the line to the filter for a bit then stops again and the cycle repeats. Also if I blead out the shrader valve for checking fuel preasure it relieves the bubble and resets the cycle also.

I think this means my problem is in the fittings connecting the hose to the filter housing. But the fact that the bleading helps may mean a vapor lock sort of thing.

Tomorrow I will try replacing the fittings for the hose connection. Unless you have a better idea.

Thansk for your help.

 

[daedge2]

Re: 98 Volvo 7.4 LP fuel pump whine at idle

check water lines that cool it if you cant blow through it they are plug pump gets hot and starts winning. Clean it out will be plugged at bottom outlet. the fitting on the cell is pressed in . take it out and clean it . mine was doing the same thing very easy fix. I bought a new one . But start talking to people and finally hit me. clean it put it back on runs great Dont have to take it all apart unless you want to

 

[GHfishin]

Re: 98 Volvo 7.4 LP fuel pump whine at idle

Update:

Still have the whine a little. The motor still runs fine so I'm just running it to see if it will get worse of fry the pump. I have changed the pump enough times now that I have it down to about 3 minutes flat. May take longer if I have to do it 50 miles off shore though.

 

[rjdurham]

Re: 98 Volvo 7.4 LP fuel pump whine at idle

I have the same problem, same symptoms you describe. Have been experiencing it since I bought my '97 two seasons ago. My engine is a 7.4GLPLKE. First pump failure was about a year ago. After replacing, new pump started whining after approximately 10 hrs and became hot at idle. At cruising speed pump stayed cool. Replaced that pump under warranty at end of last season. Replacement started same pattern after about 12 hrs this year, and is getting louder.

It seems you've done everything to correct an air leak, which is what I was about to do for mine this weekend. Before I replace the pickup, anti-siphon, hose, and seal the fittings, I am curious if you've figured out anything else?

Thanks for posting about this widespread problem that seems to have everyone baffled.

 

[GHfishin]

Re: 98 Volvo 7.4 LP fuel pump whine at idle

still whinning but not getting much worse. I have run a full tank of gas through it (140 Gal.). I will be filling it this week to see how it does with fresh gas but not holding out a lot of hope.

Like I said before I'm carrying a spare and waiting for it to die. If someone has a suggestion I'm happy to try anything.

Thanks,
Kerry

 

[dypcdiver]

Re: 98 Volvo 7.4 LP fuel pump whine at idle

How about getting a gallon can and a short hose connected directly to the filter, to eliminate the supply side.
I once had a fuel filter on a diesel motor that was not sealing on the rolled rim, took some time to find!

 

[GHfishin]

Re: 98 Volvo 7.4 LP fuel pump whine at idle

We connected a funnel (about a gallon) through a clear tube to the bottom of the pump. This bypassed the filter and still created bubbles that would periodically push down into the clear tubing, supply side of the pump.

We then connected the same funnel and clear tube to the fuel line after the low pump figuring gravity should provide about the same 3 or 4 psi as the low pump. No bubbles. I assume this isolates the problem to the pump and fuel line fitting.

I have been video taping all these tests and if we ever get this figured out I will write a report on it.

Any input is appreciated

 

[rjdurham]

Re: 98 Volvo 7.4 LP fuel pump whine at idle

I too am keeping a spare on board and hoping for the best.

I had sealed all fittings with pipe dope, tightened the hose clamps onto the barbs, replaced the anti-siphon and checked the pickup but no result. On my fuel line, the fitting at the filter housing has a compression fitting, which I did not add pipe dope to and I had wondered if it might be the weak link. But with your eliminating the filter and attaching a line directly to the pump I am stumped again.

How did you attach the hose to the pump? Directly with a barb in the hose and threaded male fitting and o-ring to the pump?

When you ran your temporary rig, was it quiet until the bubbles formed? Did it seem to labor?

 

[GHfishin]

Re: 98 Volvo 7.4 LP fuel pump whine at idle

I connected the clear hose to the nipple on the underside of the filter housing (that goes into the filter). still had the cycling whine and bubbles. Bypassed the low pump and connected strait to the fuel line using gravity. No bubbles.

Question: could the air be coming in through a bad return line connection? The high pressure pump still runs smoothly and is cool. Engine runs fine also.

 

[rjdurham]

Re: 98 Volvo 7.4 LP fuel pump whine at idle

Not following on the return. Seems you've isolated it to the o-ring that is supposed to seal the fitting at the pump. Any way to get a better seal there?

 

[Dave Dup]

Re: 98 Volvo 7.4 LP fuel pump whine at idle

Disconnect the Vapor reservoir cooling hose from the exhaust riser. Plug the riser connection start the engine and verify a steady flow of water from the hose. If not check for obstructions or kinks in the hose. If you have a decent flow leave the hose disconnected and let the engine idle for at least 30 minutes. Check to see if the pump is hot or whinning.

 

[GHfishin]

Re: 98 Volvo 7.4 LP fuel pump whine at idle

I'll try it today. Thanks

 

[GHfishin]

Re: 98 Volvo 7.4 LP fuel pump whine at idle

The low pressure pump is on the front of the engine. The reservoir is on the rear of the engine and is cooled by raw water. The pump is cooled by the fuel flow.

That said the cooling water goes through the reservoir, a small cooler for something else, an oil cooler and into the fresh water cooling heat exchanger. After that it flows through the manifolds and out the exhaust. I would think if this were blocked everything would be getting hot.

Further the high pressure pump which draws from the reservoir, and the reservoir itself, stay cool.

I appreciate your help but can't see how the reservoir cooling can be my issue if everything down line from that works fine.

 

[GHfishin]

Re: 98 Volvo 7.4 LP fuel pump whine at idle

I know it doesn't make sense but I removed the high pressure pump today and discovered the screen about 1/3 clogged with some sort of debris. I think it may be the remnants of the first low pressure pump I burnt up. I cleaned the screen and replaced the pump with new o-rings. I had just replaced the low pressure pump #4. so there is no whine now but it is still getting hot at idle. I think I may replace the high pressure pump with a new one, just because I have it, and see if that resolves the issue.

 

[GHfishin]

Re: 98 Volvo 7.4 LP fuel pump whine at idle

Replaced the high pressure pump. No improvement. Sooo, I replaced the low pressure pump/filter/assembly with this unit (http://compare.ebay.com/like/310420132943?var=lv&ltyp=AllFixedPriceItemTypes&var=sbar). Ran it around the sound a couple days and this weekend ran 40 miles for Tuna with no issues. I think it was the O-Ring on the bottom of the fuel pump but that design is stupid. This pump hooks directly to the line for and aft. I will try to post a picture when I get one.

 

[John Scott]

Re: 98 Volvo 7.4 LP fuel pump whine at idle

I will be interested to see how the new pump you purchased through eBay works out. I have the same problem ('95 7.4 OMC King Cobra w/third LP pump in 3 years) you have described with the LP fuel pump..... gets hot and whines at idle and fast idle. Contacted Volvo Penta cust. service (new Volvo pump #3857985) and was told pump is cavitating (only 12hrs on this pump) and until the fuel delivery issue is resolved, pump with continue to fail. I watched mechanic check fuel delivery to pump (air leaks and pressure/vacuum) at the last pump change and everything checked out. New pump has run for 10-12 hrs with no signs of overheating or whine. Seems if fuel delivery/air leaks was problematic, wouldn't the pump show same symptoms by now? Volvo also said that the additives put into the fuels can be the cause of problems. They claim to have tested these pumps using fresh, 10% ethanol gasoline and no problems have resulted. I tried to get the name of the brand of gas they used in these tests without success. I also tried to get vendor names for these pumps so I could contact them to try to work through this issue with them but Volvo said they could not disclose the vendor names. Perhaps I'll try several manufacturers of fuel pumps to see if I can get lucky. I remain frustrated as I continue to look for answers and carry a spare pump.

 

[JoLin]

Re: 98 Volvo 7.4 LP fuel pump whine at idle

Replaced the high pressure pump. No improvement. Sooo, I replaced the low pressure pump/filter/assembly with this unit (http://compare.ebay.com/like/310420132943?var=lv<yp=AllFixedPriceItemTypes&var=sbar). Ran it around the sound a couple days and this weekend ran 40 miles for Tuna with no issues. I think it was the O-Ring on the bottom of the fuel pump but that design is stupid. This pump hooks directly to the line for and aft. I will try to post a picture when I get one.

Question- did you tie the pump into the V-P wiring in such a way that it will stop pumping if the engine stops running (regardless of whether the ignition is 'on')? The OEM fuel setup will quit pumping if there's a delivery problem (like a broken fuel line), instead of pumping fuel into the bilge. I like your ingenuity, but it's easy to overlook built-in safety features when one 'reinvents'. Just a thought.

My .02

 

[GHfishin]

Re: 98 Volvo 7.4 LP fuel pump whine at idle

Question- did you tie the pump into the V-P wiring in such a way that it will stop pumping if the engine stops running (regardless of whether the ignition is 'on')? The OEM fuel setup will quit pumping if there's a delivery problem (like a broken fuel line), instead of pumping fuel into the bilge. I like your ingenuity, but it's easy to overlook built-in safety features when one 'reinvents'. Just a thought.

My .02

Ther are two wires leading to the fuel pump. I hooked the yellow to hot and the black to negative. I assume the safety shutoff stuff is electronic and therefore wired in before the pump. Again I assume safety things interupt the power being sent to the pump so just cutting off the plug and wiring the new pump in should leave all those in place. I don't know how a guy would test this though, if you do let me know. I have run two trips now 40 miles offshore each and the boat has run well and fuel flow has been comparable to the oem pump.

This trip we did have a situation where the high pressure pump squeeled for a second after Idling for quite a while. It sounded like it was passing a bubble but only lasted a second and was fine the rest of the day.