Volvo 7.4Gi Cuts Out - Fuel Pumps Stop

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  #1  
Old 10-12-04, 02:22 PM
parothd
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Volvo 7.4Gi Cuts Out - Fuel Pumps Stop

I have a 98 Volvo 7.4GI that for the very first time in 270 hours left me stranded. The boat ran at about 3000 RPM for 10 minutes and then cut completely out. It would crank but not start. Turning on the key revealed neither fuel pump was running based on the lack of that audible pump whine. I checked all the circuit breakers and swapped in a new fuel pump relay. I also reseated the power lead to the low pressure pump. All of a sudden the pumps started working again as if a breaker had reset. It now runs between 5 and 25 minutes and then cuts out again. When it cuts out, as before, both fuel pumps are not running. Also when it is running, the LP FP gets very hot while the HP FP stays cool. But again, the 20A breaker for the pumps does not appear to be tripping.

I know that the "pump on" signal comes from the computer. I also know the pump should not be getting as hot as it does. What I can't equate is why one pump running hot would cause both pumps to stop. Is there anything in the computer that would trip when presented with the higher load of the LP FP and perhaps shut off both fuel pumps? My issue is that if the LP FP is bad, I can understand that, but why would the HP FP also stop working?

I also thought if the computer is turning them off, perhaps there would be a DTC explaining why. Unfortunately I do not have a code extraction tool so have been unable to determine if there are any stored codes. Does anyone know how to pull the codes with a test light or something similar? I tried to decipher the wiring diagram and it looks like it's doable (based on the way we do a typical GM car) but I hesitated to begin jumpering wires and risk damaging the box.

Thanks for listening and thanks for any help or suggestitions.

Terry
 
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  #2  
Old 10-14-04, 11:57 AM
parothd
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Here's an update...

After thinking through this I "believe" there are only two fundamental things that can shut off both fuel pumps at the same time. One being the common breaker and the other the computer. I guess there could be other things, but these are the most obvious.

I have some concern that I may have inadvertently been resetting the circuit breaker during troubleshooting of the episodes. Each time it would die I was pushing the breaker reset button to see if that was the cause. With most breakers there is at least a small click when reset which I never felt In the absence of that I have been assuming it was not tripped.

As I have thought through this I have come to the conclusion that the most logical explanation for having both pumps stop together is the breaker being tripped. This could be caused by the added load of the low pressure pump which I noted to be running hot. I suspect that the breaker could be very sensitive to reset and perhaps not noticable by mere touch.

To prove this I am planning to run it until it quits and then measure the voltage at both sides of the breaker. If I don't have 12V on both sides, the breaker is tripped (open). If I do have voltage on both sides then I must have a different issue.

Heading down that second path... in searching the manual I have been unable to find any sensor or trigger that would signal the computer to turn off both pumps. The "limp" feature, triggered by low oil pressure or high engine temperature cuts cylinders but does not turn off the pumps. The only thing I could find that cuts both pumps is turning the key off. It kills the two pumps to prevent dieseling. I think if that were the case everything would reset when I try to restart it... or so it seems. Remember that it has never failed to crank, but when experiencing the problem it won't start because the fuel pumps are not running.

Hmmm...

Any thoughts or comments are appreciated.

Terry
 
  #3  
Old 10-18-04, 02:39 PM
parothd
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Here's the next installment following testing this weekend.

I let the boat run at various speeds for aver 2 hours and it never shut down on it's own. So I took her out with my wife following on our Waverunner in case I needed a tow. It ran flawlessly for about the first 35 minutes and then out of the blue died as in the past. But it's not that simple. In the past when it died and I would try to start it, I had no electric fuel pumps. This time when I turned the key off and then back in, the pumps whirred to action and the engine started right up.

After that first stall it quit another 4 times in the following hour and each time it would start right back up like nothing was wrong. The very first time this happened, when I had to be towed in, it no only wouldn't start at the scene, it still wouldn't start 3 days later. In that episode the pumps were not coming on.

So with this new twist of the pumps being active after the stall, I am leaning toward having multiple problems. I think the first may have very well been a tripped breaker that I unintentionally reset while troubleshooting. What I am trying to understand is what caused the breaker to trip and how might that be related to a secondary problem.... and what is the secondary problem?

I'm not seeing any responses to my posts so either this is boring everyone to death, you think I am a nutcase that is wondering aimlessly through the message boards trolling, or I have answered all your questions and you are just following intently to see what the outcome is. I assure you I am not trolling. This one has be puzzled and I could really use some suggestions.

Things I am now considering:

1) Something in the gas tank intermittently blocking the pick up tube causing it to run out of fuel. In this scenario I suspect that the lack of fuel might also have been the cause of the fuel pump getting hot, which in turn might have tripped the breaker. By the way, I already pulled the anti siphon valve to make sure it was not the culprit. I used to own a 21 foot Wellcraft Nova Offshore that got me towed several times before I found that the fuel filler hose was deteriorating inside and small pieces of the hose were clogging the check valve. It honestly acted very similar to this problem, but like I said, I have removed and inspected that and found no problems there.

2) Water in the fuel. Same effect as number 1 once my fuel filter is filled with water.

3) God forbid... an intermittent electrical problem. This could be anything from a loose ground to a broken ignition wire in the harness.

4) There is still the wild chance that I have a computer problem simply telling the fuel pumps to shut off for some reason. Could be related to number 3 or who knows what.

If anyone has any ideas or has had anything similar happen, please let me know and tell me how you solved it. Also if anyone knows how to pull the computer codes that would be a help too.
 
  #4  
Old 10-25-04, 05:47 AM
parothd
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Here's the latest...

It runs flawlessly, but still cuts out at random intervals. These range from 3 or 4 minutes of running to as long as 30 mintes. The bigest difference now is that it immediately starts back up. If you have read my trials here, the first time it cut out it would not restart and I had to be towed in. Through all the troubleshooting I have caused a change in the problem but not fixed it. Very puzzling!

The final test I did this weekend was to electrically disable the low pressure pump. The boat will idle in this mode forever because the high pressure pump can draw through the low pressure pump enough to support no load running. But under load that is not the case. I did this test because I wanted to see how it acted when the low pressure pump stopped working. I previously noted that this pump has been suspect and seems to run hotter than it should.

Unfortunately when I drove the boat with the low pressure pump disabled, and it finally began running out of fuel, it was very different than what I normally feel when it cuts out. With the pump disabled it ran for about a minute and then started bucking and surging before it actually quit. When the actual problem occurs the cut off is instant. No surging or bucking, just off instantly.

The search continues. Any thoughts or suggestions are welcomed.

Terry
 
  #5  
Old 08-11-05, 07:57 AM
dalee
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Same Type problem with Volvo Penta

I have a similar type problem with my Volvo Penta 7.4 GL. A couple of month's ago , I installed an Navman Fuel flow meter and it seemed that's when my problems started of starving gas to my carburator and the engine would not start. I had my mechanic look at it and he replaced the oil pressure switch and relay to the fuel pump at a cost of $ 290.00 , on the first test run after the replacement, boat started up fine and ran good. Back at the dock , my wife showed up and we then went on a ride and on throttle up, the engine cut out but did not shut down. I pulled back on the throttle and then tried again with no problems. Got back to the dock and the next day tried to go for a ride and boat would not crank. That's when my mechanic suggested that I take out the fuel flow meter which I did and I also replaced my fuel line. I then had a terrible time trying to get the engine to start, had to pump my throttle about 30 times and then just leave it wide open, when it finally cranked. It ran good for over an hour at which time we stopped for dinner and when we came back - the engine would not start. I walked over to a friend's house and got a fuel pump for a car that we wired up to connect to the battery. I installed in inline before the volvo fuel pump and heard it pump fuel to the engine. Engine cranked right up, disconnected the fuel pump from the battery and ran home over an hour with no problems. During the inital start up - we heard a sound of air escaping which we thought might be the anti sphion valve. I took that out the next day after I got back and still extremely difficult to start engine. Must pump about 30 times on the throttle and then leave wide open.

The engine and boat are about 11 years old but have never had a problem like this before. Talked to the local Volvo parts dealer/mechanic and he thinks its not the fuel pump but could be a bad dioide in the wiring harness. Guess I'll try and trouble shoot that next . I also want to install a clear hose from the tank to the fuel pump to see if I have fuel being sucked back into the tank for some reason. It seems that the fuel line each time I have unhooked it was bone dry. It should be full of fuel at all times and it is not leaking in the boat.

If you have any idea what my problem could be or let me know what the solution to your problem was, perhaps I can troubleshoot mine without my mechanic getting richer off of me. I would appreciate it.
 
  #6  
Old 08-12-05, 01:05 PM
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Join Date: Nov 2004
Posts: 74
Intrmittent

You have focused on the fuel system - Is there an ignition coil that could be failing when heating up? Not a mechanic but my experience with a auto coil was similar, cools and runs again? It finally broke down completly.
 
  #7  
Old 05-03-11, 11:15 AM
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Join Date: May 2011
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oldie but goodie

I have to resurrect this thread. I am going through this right now with my 98 cobalt 7.4 volvo. Did anyone figure this out?
 
  #8  
Old 05-03-11, 07:58 PM
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Originally Posted by mykal41 View Post
I have to resurrect this thread. I am going through this right now with my 98 cobalt 7.4 volvo. Did anyone figure this out?
What exactly is the motor doing and what have you done to diagnose it? just to get a base line.
 
  #9  
Old 06-14-11, 11:30 AM
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Join Date: Jun 2011
Location: USA
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Cool Broken power terminal (bolt) in low pressure fuel pump housing

I have a 1998 Four Winns 245 Sundowner VOLVO Penta 7.4 GI and have been having issues for the last 2 years of it running fine then cutting off for no apparent reason. Just this weekend ran it for 30 minutes then it dies on me, so i finally looked at it myself instead of paying a mechanic to do it. I finally found out WHAT it was after 45 minutes in the engine compartment. Behind the low pressure fuel pump located on the top left front of my engine behind the housing there is 2 red wires tightened to 2 seperate bolts sticking out of a black plastic housing. 1 of the bolts broke in half (assuming the factory overtorqued it) inside the paltic shrink wrap housing and was covered in green corrosion so the metal was not getting a good conenction all the time. I scratched corrosion off and stuck the bolt back in and it cranked right up and ran fine all the way back to the doc. I will replace this entire part , but this was my ghost and now it is dead. I hope this helps. Happy booating.

Scott
 
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