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2004 crusader 8.1 L running rough

Chris actually does this for a living so I would listen to him. If you look in your newly downloaded MEFI 4 manual you will see your engine should have 41-47 psi prior to start, 37-43 psi at idle and 44-48 psi WOT. So the pressure should go up, not down as the thottle is opened. And frankly your "good" engine (36 at idle, lower at WOT) sounds sub-spec as well.

Off road and hot rod guys like these marine engine controllers. Pirate 4x4 has a good article on the system with some interesting links.
CaboJohn
 
Chris,

thanks for your response. As mentioned before, I have checked everything including switching the fuel rail from one engine to the other and running the engine directly from an outside fuel tank and still the same issue. Next step as you suggested, the low pressure pump. One question. I thought that the low pressure pump either worked or not worked, but it seems not to be pushing enough fuel. Does this explain why I had low PSIs on the fuel rail?

thanks again.
 
Chris,

thanks for you posting. I have tried everything including switching the fuel rail from one engine to another and running the engine directly from a separate fuel tank and neither solved the problem. The last step as you are suggesting, is changing the low pressure fuel pump. I thought that low pressure pump either worked or didn't work, but I guess it can be somewhere in between. Does the low pressure pump not working properly explain the low fuel pressure on the fuel rail?

thanks again for your help
 
Mike305 said:
Chris,

thanks for you posting. I have tried everything including switching the fuel rail from one engine to another and running the engine directly from a separate fuel tank and neither solved the problem. The last step as you are suggesting, is changing the low pressure fuel pump. I thought that low pressure pump either worked or didn't work, but I guess it can be somewhere in between. Does the low pressure pump not working properly explain the low fuel pressure on the fuel rail?

thanks again for your help
Click to expand...
I did not say to change the low pressure pump, I said to test the low pressure pump.

If the low pressure pump is not working or is not producing enough flow you will have erratic fuel pressure on the rail.
 
Take a picture of your low pressure pump and post it. So we know what style pump you have.

After you check to see it is getting power and you check the plug on the pump You will have to remove it from the boat and test it on the bench to check flow. Safest way.

Barrel style Crusader inline fuel pumps are known to lock up with debris.
 
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Hi, I changed the low pressure fuel pump between the engines and still had the same problem. Then unplugged the spark plug cables (one a time) while the engine was running (1500 rpms). The rpms went down on all, but one cylinder and therefore I replaced the apart plug. Started the engine again and the problem continued. Then all of a sudden. The engine started running perfectly. Turn it on and off many times and everything if fine. I really do not know what I did, but it is working fine.
 
Hi guys, I was finally was able to take the boat out today. The error on the B&G instrument was still there (same engine as I had the problem with). The firts 15 minutes, the boat ran great at 3100 rpms and then, the same engine with all the problems started with the following:

- the rpms would go down to 3000 and them come back to 3100
- at one stage, the rpms went all the way down 1000
- I had the troubled engine start pulling fuel from the other tank and that did not help
- the engine would go back to 3100 run great for several minutes then start dropping to 3000 and back up to 3100

i still have the error message on the B&G "throttle pressure error"

any suggestions?

Thanks,
 
Hi,

finally got a mechanic with a machine to be able to read the engine and the issue was the:

Crankshaft Position (CKP) Sensor

purchsed and installed a new one and issue solved.

Thanks for all the help
 
I have been reading your postings with some interest since I have been having similar issues with my 2004 North River with the Marine Power 8.1L. Does anyone know for sure what the rail pressure is supposed to be and how much it is supposed to drop if any? I am seeing several values out there and have looked at a couple of different MEFI manuals that contradict themselves. The posting above says 37-43 idle, 44-48 WOT and I have seen those specs. The symptom I am having is.... normal WOT would be around 4100rpm (cruise around 3400) but recently I am only able to get 3600rpm max. We are still frozen up here in Alaska so everything at this point is in the garage. Rail pressure is 45psi and drops to around 22psi when I bleed off the pressure with the gauge (Doing the math, the max fuel amount that my gauge will let me bleed off is about half again as much as WOT fuel consumption would be). Bad high press pump, problem solved right? Comparing readings with 2 other boats I run with that are within a year of mine and the same motor yield results of 20psi and no drop when pressure released and 40psi with a slow drop to 20psi when pressure released. These other boats have had no issues and get full power. Any thoughts on this one?? I'm a bit stumped as to what my pressure is supposed to be and then I can start narrowing the problem from there....

Thanks!
INREQ
 
Why are you checking for a specified pressure when you "bleed off pressure with the gauge"? Most of us normall verify the prime pressure (KOEO), the idle pressure and then the WOT pressure....you can also do a coarse assessment for internal leaks using the pressure gauge after removing the running voltage from the pump...

I'd be hard pressed to believe an 8.1L will run under load with only 20 PSI in the fuel rail.....

I'd use the factory service manual as the reference of choice...you can always check with Crusader directly....your 45 PSI is expected but you don't specify what the condition was when it was obtained...
 
I would love to be able to check my pressure at WOT but my jet pump would probably have some issues with doing that without being in the water. Like I said, we are still all ice up here in the frozen north. What I was trying to accomplish with bleeding off the pressure was to simulate the amount of fuel being consumed at WOT. If I'm doing my math right, at 20gph (a guesstimate at what the fuel burn would be at 4100rpm) the consumption would be about 20cc per second so I was trying to bleed off about that same amount and see what the pressure dropped to. I know, not very accurate but it's all I've got to work with right now. The Marine Power manual I was finding online had copied the automotive version and put their name on it. WTF!? And the automotive version specs are up in the 60+psi range. I just looked on Marine Powers site again, I don't know if they've updated whats avail or I just missed it when I was looking a few months ago but they do have a decent manual now which is showing 38-44psi which is what I would have thought. I guess I'm going to have to break the news to my friends that their pumps are going out because at WOT they are only about 20psi on one boat and 25-30psi on the other. There's a lot more to this story but without writing a novel to explain what I've had happen and tried so far it would only get more confusing. Basically I'm on my 5th pump in 3 yrs and at $350 bucks a pop it's getting old. I may be asking for more advise soon!!!

Thanks,
INREQ
 
1) You will likely get more attention/advice if you start your own thread on your problem.
2) Since it occurs at high rpm, the pressure testing will not tell you much until you can get it in the water and run it at speed. In the meantime you can change filters, since if it is falling pressure at high flow rates that is the most likely cause.
3) You should consider pulling the injectors and having them tested/cleaned by an experienced shop. On my weak engine I found two partially clogged and one stuck wide open. Letting these gas engines sit for months really gums things up after a few years. Cost is around $20-$25 an injector but it is part of the "fun" of boat ownership.
4) Other than fuel, there are many, many possibilities on your engine for sources of the problem, and a scanner is required to find them. You mentioned two friends with the "same motor". A good opportunity for each of you to throw a buck and a quarter in the hat and buy a scanner (Rinda Techmate). Then you can really trouble shoot. Go to Pirate 4x4 on the web to read about the many MEFI inputs that could be the issue and follow the link to the manual.
CaboJohn
 
2X on testing in the water...

Most engine marinizers use the Delphi manual as it doesn't get much better and there's no extra effort (cost) involved. some change the default tuning parameters but most keep them the same...likewise, some use minimum discretes where others will go above ... either way, the troubleshooting procedure really doesn't change...

The only drawback is the few errors in the Delphi manuals get propagated...once you understand what is going on, I think they are obvious and easy to correct.
 
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