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2004 crusader 8.1 L running rough

M

Mike305

Member
Hi need help with my 2004 8.1 L Crusader engine. I have done the following to try to resolve the issue but the engine is still running rough, especially at higher rpms. If I accelerate in neutral from 0 to 3000 rpms it seems fine, but if it goes over, the engine starts running rough and back fires, tach goes up and down. Also, I ran the boat today and as long as I was below 3100 rpm it seem fine, over 3100 rpms the tach was going up and down.


- changed spark plugs
- clean fuel injectors
- new fuel filter


any suggestions?
 
Jeff,

Thanks. The bad tach would make the engine run rough? I was going to start with cleaning or replacing the puck-like fuel filter.
 
fastjeff said:
Such behavior has been reported here before, and it was a bad tach. Good luck!

Jeff
Click to expand...

Yup, Jeff is starting you out in the right direction.

I had an engine we just could not get running smoothly....ended up being a wire that was shorting out at the tach. Try the tach first...easy and quick..(prior to the find we changed all the plugs, the distributer cap, the ignition module, the rotor, the coil and it was just that damned wire up front at the tach):mad:

Good luck !!
 
Cleaning or replacing that puck style filter should be done periodically anyway. Also remove and clean the anti-siphon valve at the top of the tank. Do you have a single tank or one per engine with crossover valves? If two tanks with crossover valves, you can try to set it up to run off the opposite tank, but don't have all the valves open so that each engine is trying to draw fuel from both tanks. It sounds like a fuel starvation issue which could be caused by many things, including a clogged vent on the tank. That you can test quickly by removing the fill cover.
 
Erich, I will clean the puck filter (what should I use to clean it?). I have two tanks, so I will test with other tank or both. I will remove the fuel cover to test. Thanks for the recommendations
 
Hi,

Just cleaned the puck filters (both were dirty, but not too bad), checked the tach for loose wire and checked the fuel vents and all looks fine, but the problem continues. I have a mechanic coming on Wednesday to check fuel pressure and other. Any other suggestions? Again, I have done the following:

- Cleaned puck fuel filter
- replaced fuel filter
- Fuel injectors were sent out and cleaned and one was replaced
- Compression test - ok
- New spark plugs

Anything else I should try?

Thanks and Happy New Year!!!!
 
Like I said earlier, check the anti-siphon valve and also the tank vent. And Chris at Dockside suggested disconnecting the tach...not just checking the wires. There was an instance reported on this forum regarding a tach causing a similar problem. The tach otherwise appeared to function normally.

Another possible caused is the pump could be sucking in air from a very small leak in the fuel supply. One that is so small that it doesn't leak fuel but can suck in air during high vacuum times that are typical of higher rpm/speeds. Those valves for a crossover setup are a possible leak source. How difficult would it be to run a new dedicated fuel line direct to the tank?
 
Mike305 said:
Hi,

Just cleaned the puck filters (both were dirty, but not too bad), checked the tach for loose wire and checked the fuel vents and all looks fine, but the problem continues. I have a mechanic coming on Wednesday to check fuel pressure and other. Any other suggestions?
Thanks and Happy New Year!!!!
Click to expand...
I didn't say for you to check the tach, I said to disconnect the tach.
 
I'd get a fuel pressure gauge and make sure there is adequate pressure in the rail first...getting a scan tool hooked up would be the second step...no point in guessing or throwing parts at it given all the elctronics on that engine.
 
Chris,

disconnected the tach and still the same problem. It seems as if the engine is starving for fuel. From 900 to 2000 rpms (going up slowly), seems to run well, but if I go beyond 2000 rpms the engine misses and the rpms drop (go up and down). I have a mechanic coming out tomorrow to check the pressure on the fuel rail. What is weird is that I just had the rail and the injectors cleaned.

any other suggestions?

Thanks
 
Mike305 said:
Chris,

disconnected the tach and still the same problem. It seems as if the engine is starving for fuel. From 900 to 2000 rpms (going up slowly), seems to run well, but if I go beyond 2000 rpms the engine misses and the rpms drop (go up and down). I have a mechanic coming out tomorrow to check the pressure on the fuel rail. What is weird is that I just had the rail and the injectors cleaned.

any other suggestions?

Thanks
Click to expand...
Ok, Now that the simplest and most over looked test is done,

You can do this yourself.

You will need a fuel pressure gauge. Hook it to the fuel rail and take readings while under way or run it up at the dock. My guess is you will find high fuel pressure. This will be caused by plugged regulator. When the pressure is too high the injectors cannot open.

The regulator is easily removed for inspection and cleaning.



If you have low fuel pressure or erratic pressure, you will have to check the low pressure pump operation.
 
Last edited:
I cleaned the regulation and exchanged it with the one from the other engine and still issue is not solved. I have the mechanic coming in tomorrow. I will ask him to check the fuel pressure and pump.

thanks
 
If your mechanic shows up without a scanner and the readily available MEFI-4 manual (you should have one anyway) then he really does not know his stuff. Scans are essentual for these injected MEFI engines. There are just too many possible problems that could cause your symptoms, most of which the scanner, with the manual, will reveal. Having said that, the one most likely possibility (fuel starvation) does not show on the scanner and it needs the easily done fuel pressure test. At WOT you should have 44-48psi in a standard system and 43-46 psi in a returnless system. Those are under load. Prior to engine start the pressure should be 41-47 psi.

Good luck.
CaboJohn
 
Hi,

The mechanic ran the fuel pressure test and the engine giving me the problem had a 33psi at idle. As the RPM went up to 2500 rpms, the psi's went down around 33 and as the rpms continue to go up the needle on the psi gauge was very erratic (around the 30psi mark).

I also tested the engine that is working well and the psi at idle was 36. At higher rpms it went down slightly, but not much.

The mechanic tells me that it could either be:
1) Bad high pressure fuel pump
2) Something blocking the gas hose into the engine

Any comments/ help? Should I replace the high pressure pump?

Thanks
 
Did he only check the fuel pressure today? You should take a ride to your local Sears store and get yourself a Digital volt meter and a fuel pressure gauge. We can walk you through testing this system.

An inconclusive answer is what you paid for today.
 
Fortunately, he did not charge me.

I just transfered the high pressure fuel pump from one engine to the other and no change. So I guess is not the pump. The only thing related to fuel is either the fuel line (from the fuel switch to the engine).

I guess I can also exchange the fuel rail and injectors between the engines to see if there was something wrong with the new injectors I put in???

Any other suggestions? I am running out of things to test and the mechanic that has the scan machine is about an hour and a half from me and he is not too thrilled to come see me.

Thanks again for all the help.

Mike
 
No I did not. I did switch to pull gas from the other tank. If the anti siphon usually by the tank or is it closer to the motor.

thanks
 
Given that I switched from one tank to another, I assuming that the anti-siphon is not the problem. I will check the fuel hose from the fuel switch to the motor to see if it is blocked. I will also try the switch the fuel rod with the injector from the other engine.
 
Chris,

Given that the good high pressure pump did not work on the bad engine, should I then focus on the low pressure pump? Would a malfunctioning a low pressure pump cause the issues I am having?
 
If the low pressure pump is not working correctly the engine will not perform, It will start and run and fall on its face when the throttle is pushed up. The low pressure pump feeds the high pressure pump.

First check pump operation, when they are verified to be working correctly then you move on to checking other things. There are no shortcuts when diagnosing.
 
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