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50 GXI breaking up above 4000 rpmbs

M

md_cruiser

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"This problem has my mechanic

"This problem has my mechanic scratching his head while running up my bill simultaneously.

'03 Volvo 5.0 GXI
I have added fresh gas, new fuel water seperator, distributor, rotor. Compression checked out good when I checked it.

The problem occurs when you try to advance the boat above 4000rpms (sometimes less). It comes on plane great, then for no reason, looses power and starts breaking up and looses RPMs. If you try to push the engine for more, it starts to backfire on you. It does not power off completely, just backs down to about 2000 rpms. If you let off and try it again 30 seconds later, the whole process repeats itself.

Mechanic tells me there are no codes on the computer, that the fuel pressure with load is very good.

What should we be looking for next? Timing? ECM? Coil? Other fuel components?

The port engine runs great the entire time, so that rules out bad gas, since they both pull from one tank."
 
What condition are your exaust

What condition are your exaust manifolds in? I had a similar problem however it was on a smaller motor. Exaust manifolds were wasted and water was entering though the exaust valve.
 
Manifolds are in good conditio

Manifolds are in good condition. There wasn't water in any of the cyclinders when I pulled the plugs either.

Could the electronic protection mode kicking on? Is there a way to temporarily disable the system to see if that is what's causing it? The gauges are all reading perfect.....so at this point I have no clue.
 
Yu might try swapping electron

Yu might try swapping electronic ignition parts/ ECMs to see if the problem migrates to the other side.

JEff
 
"Electronics are so often blam

"Electronics are so often blamed for problems where in reality are very seldom the culprit! Your simptoms are a classic fuel supply . Same tank OK But am sure not same supply lines. Try running on a remote fuel tank , Use a old outboard fuel tank hooked up directly to fuel pump. This way a least you will be able to eliminate fuel supply as a problem and carry on -or go back and fix problem with fuel lines / valving etc.
Good luck
BJ"
 
"BJ-
I have been thinking th

"BJ-
I have been thinking the same thing for a week now, but, the mechanic tells me there is good fuel pressure, even when the engine cuts out. The boat is still in the water, so I will take it out when I get a break in the weather to see if the remote fuel source helps.

Actually, I think I can swap the supply lines from the different engines since they are right next to each other."
 
"Even with Good Fuel Pressure,

"Even with Good Fuel Pressure,......

You Could have Plugged Injectors,...."
 
Update:
Switched the fuel su

Update:
Switched the fuel supplies with each other and still nothing. Unplugged the high pressure pump and it ran up to 4500 RPM's and about 5 seconds later it bogged down in the bad engine again. Could not replicate the high RPM run there after. It wouldn't run above 4000 with or without the high pressure fuel pump plugged in.

Fuel tank vent is clear.

What are the next "to do's"

Would plugged injectors allow the boat to run 4500RPMs one second and not the next?

Is there a way to see if the engine protection mode is kicking in? It gives no alarms when it breaks up.
 
Volvo has a wiring system that

Volvo has a wiring system that ties in the oil gauge to the engine. I experienced this same problem when my port engine's oil pressure gauge malfunctioned. The gauge would move when the ignition was on but would not fluctuate with the engine. It just sat in the middle. I changed the oil gauge and the engine ran fine.

I would ask the mechanic about sensors. If you have a malfunctioning sensor it may also be telling your computer that there is a problem. I purchased an inexpensive volvo repair model that lists all of the sensors and how to check.
 
Warner`s reply is interesting.

Warner`s reply is interesting. Havent run into that one yet but will remember it .
Unplugging hi pressure pump and getting a spurt of 4500 rpm is downright wierd. Only thing I can think of is - hot engine - lean fuel condition = momentary run away. Not a good thing to do as tempatures in combustion chamber goes thru the roof.
Interesting also that without hi pressure pump you are able to get 4000 RPM.
Still convinced its time to go back to basics.
Try pulling the spark plugs and have a good look at them . What you are looking for is anything different in colour or burn patterns. This may help you determin which - if any pacitular cylinder is problematic.
As for rev limiter it is all in the ecm and controled by sensors.
The best way to eliminate this is as fast jeff suggested is by swaping componets.
Another thing to keep in mind is that bad grounds and low voltage ( ! ! !deep cycle batterys!!! ) have driven many a mechanic to beer and fishing.
Good luck and keep us up to date.
BJ
 
"When I pulled the plugs last

"When I pulled the plugs last week for a compression check they were all had a very nice burn color and no plugs were odd. The compression was 140ish for all 8 cyclinders.

I just put in a brand new battery for the engine after the first time I took it out and had this problem. (starting battery up to volvo specs)

Bad grounds? Voltage would be kind of an obvious one with the computer on the engine wouldn't it?

Is there anyway my volvo certified mechanic can override the sensors and the engine protection mode? I think it's best he talk to Volvo at this point. The computer scanner should allow him to diagnose this further if it's electronics related....

Warner, after I read your post on another website, I checked the gauge and it seems to be fluctuating correctly. If it's a bad sensor sending bad information to the ECM, then that is another story, hence my question about turning the protection mode here to see if we are dealing with a mechanical breakdown or if it's the computer that's causing my sleepless nights.

All the advise is greatly appreciated. Any more?"
 
"Joe, perhaps you can apply a

"Joe, perhaps you can apply a little bit of several comments. I mentioned testing the sensors and fast jeff and BJ mentioned swaping ecms. Sense you have twins just swap a few of the possible culprits and see what happens.

What other site did you see my comments on? Just curious.

If all else fails, I mentioned this problem to the lead mechanic at my local regal dealership. He is scheduled to attend a Volvo specified class early next week. Perhaps the Volvo trainers can help."
 
"This reminds me of a problem

"This reminds me of a problem that arrived when OMC introduced 'knock-sensors' in the ignition system for optimizing ignition advance. Sometimes when hitting a wave, it started acting just like You describe, and even at certain rpms. The recommendation then was to take it out, clean treads, install with loc-tite (?) or replace.
Check if there is a knock sensor in one of the heads pointing towards the transom."
 
"UPDATE!!!
BAD FUEL PUMP. Th

"UPDATE!!!
BAD FUEL PUMP. This could be the most expensive fuel pump of all time, being over a $1300 job.

Good thing the original pump "tested above average during load" (sarcasm)

When I re-read my post above about me unplugging the high pressure pump, doesn't it make sense? (even though they listed it as a failed low pressure pump?)

Luckily, warranty picked up 2/3rds of the job.
Good thing I asked the mechanic 8 times if it was the fuel pump.....

Thanks guys! I could have sworn it was a bad sensor."
 
$1300.00! Quite expensive. Do

$1300.00! Quite expensive. Does volvo cover those for four years or do you have an extended warranty? I am glad you found the problem
 
"It is the Volvo 2+4 exten

"It is the Volvo 2+4 extended protection.
Unfortunately for me, they have set amounts dedicated to each task...where a fuel pump may be 3.5 hrs labor and $599 parts. The total was $703 for parts and alot more labor. I picked up the difference."
 
They told me it was the low pr

They told me it was the low pressure pump. Does anyone need a high pressure pump? I am willing to part with it for a fair price.
 
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