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Power loss at cruising speed on 2002 8.1 port engine

bob17412

Member
Have 2002 crusaders with 8.1 mpi on a 39 Silverton MY. While at cruising speed of 3600 rpm for about 5 minutes, lost power on port engine. After slowed down, put engine back up to cruising speed and lost power again on port engine with engine ultimately failing and inability to start. This season Port engine was difficult in starting and ultimately wouldn't start at all. Pancake filter was clean. Replaced low pressure fuel pump but still wouldn't start so then replaced high pressure fuel pump. Engine started right up and took it out for run. Was running fine but only getting 3800 rpm at WOT. Replaced fuel filters in both engines and when took it out the next time experienced the problem described above with the loss of power on port engine. Checked anti siphon valve in port gas tank and had some debris in it, but did not fix problem. Mechanic then removed valve and still no fix. Replaced plugs but still same problem. Seems as if not having enough fuel pressure at high speeds which causing engine to slow down and ultimately fail. Fuel seems to be ok.

Above process has been going on for two months. Help.
 
Re: Power loss at cruising speed on 8.1 port engine

I had a similar problem once. Turned out to be sediment in the fuel tank. It clogged the pick up in the tank and restricted the fuel flow to the point the engine died. Would run at low speeds for a while but eventually wouldn't run at all. Same symptoms you describe. Fuel tank was 20 years old in that boat. If yours is newer (with an 8.1 it probably is) perhaps there's some other obstruction in the tank? Good luck. Certainly sounds like a fuel delivery problem.
 
Re: Power loss at cruising speed on 8.1 port engine

try using a fuel pressure gauge to verify that fuel delivery is the root cause. If that turns out ot be the case, a vacuum gauge can help you pinpoint any existing restriction in the pre-pump section of the line.
 
Re: Power loss at cruising speed on 8.1 port engine

Checked the pickup tube, fuel line to pancake filter, return fuel line from fcc to tank and the vent hose. All seem ok. Some sediment in pancake filter but very minimal. Put a fuel pressure gauge and had 40 psi at idle. The mechanics are scratching their heads and don't have a scan tool to hook up to the ecm. Anyone know where one can be rented. Engine idled and started ok after checking fuel lines and will take for a spin on Friday to see if issues again at 3600 rpm.. Will let you know. Thanks.
 
Re: Power loss at cruising speed on 8.1 port engine

you need to check the pressure at WOT and a couple points in between.

I doubt you'll be able to rent a scan tool unless you want to hire a mechanic; then the tool comes for free.

Personally, if the mechanic you are using doesn't have a scan tool by now I'd be lookin' for another one.....not saying they are bad just not properly equipped.
 
Re: Power loss at cruising speed on 8.1 port engine

Does the boat have to be under load to check at WOT and points in between or can it just be in neutral. Not having much luck hiring a rent a mechanic, folks want the boat at their marina and if I could get it to their marina I wouldn't need them.
 
Re: Power loss at cruising speed on 8.1 port engine

Does the boat have to be under load to check at WOT and points in between or can it just be in neutral.

To check for fuel starvation issues, you need to be flowing as much fuel as possible. The most direct way is like MM suggests using a fuel pressure gauge on the output side of the last fuel pump before the engine. A good reading here will eliminate the entire fuel system, including the pump.

If instead, you only measure fuel vacuum BEFORE the last pump, you might be able to see a fuel restriction, IF the pump is OK. Its a good way to mind the filters. It doesn't show up a air leak or bad pump so good.
 
Re: Power loss at cruising speed on 8.1 port engine

WOT, under load, to make sure the pump meets spec. Same for the reduced RPM checks.

You may want to consider just buying the DIACOM software & cable. It isn't cheap but neither is the flat rate hour charge for a mechanic to visit you. I'd view it as an investment, just like any other high quality tool. A scan tool is another option...may save a few bucks if you only want the basic features.
 
Re: Power loss at cruising speed on 8.1 port engine

Talked to Crusader distributor and indicated wouldn't waste money as Crusader adds their own software that you wouldn't get with Diacom so wouldn't see everything going on. Are they blowing smoke or is there some validity. Still having issues and mechanic wants $90 an hour that includes travel time, so have about $400 sunk cost in initial diagnostic and travel time.
 
Re: Power loss at cruising speed on 8.1 port engine

I think a 2002 still uses the regular delphi program in the ECU with Crusader determined "parameters". Being these are mass produced engines, I doubt there is little, if any, deviation from the GM provided data. Call Rinda and get their view on what you can and can not see. I've never heard of anyone that bought the package and was later disappointed by lack of capability. Rinda has supplied mercruiser with their OEM branded scan tools for decades so I would put a bit of faith in their view. While you've got them on the phone, they can explain the tradeoff between buying the DIACOM kit vs the handheld tool.
 
Re: Power loss at cruising speed on 8.1 port engine

Thanks, I will check with them. Problems continue, thought bad tach on same engine so ordered new tach and doesn't register rpm's. Wondering if tied in to engine problem????
 
Re: Power loss at cruising speed on 8.1 port engine

I'm sure a scan tool would pick up a code, but wouldn't a bad oil pressure sensor cause the same issue? Does the engine "think" the pressure is low and reducing the RPM's?
 
Re: Power loss at cruising speed on 8.1 port engine

bobct:

A good scan tool will not only provide any codes set but also allow you to monitor sensor data in real time.

The newer ECU's have a few different variations on the "how to protect the engine" logic implemented. This is one area where each OEM usually 'tweaks' the code used by the ECU. Typically, loss of oil pressure results in engine shutdown indirectly as the fuel pump is turned OFF. Continued engine operation, even at a lower power level, w/o oil pressure would likely result in catastrophic damage. imagine the resulting bad press that would flood the www sites......
 
Re: Power loss at cruising speed on 8.1 port engine

And that is the CANBus setup, right?

Yes believe it is. Took out today and same problem. fuel pressure was 44 psi at cruising 3600 rpm until engine slowed down and ultimately stalled. Would it be a bad oil pressure sensor or the switch. Thinking of replacing both. Noticed that the oil pressure gauge dropped off dramatically when the engine went into reduced power mode before stalling out. Coming back on one engine a pain. Mechanic thinking of swapping ecm's to see if problem duplicates to starboard engine.
 
Re: Power loss at cruising speed on 8.1 port engine

When you say "Until engine slowed down and ultimately stalled" did the fuel pressure drop at that time or did it remain at 40+ psi? How does this pressure compare to the other engine? Do you have any active codes? You can check for DTC codes without a Diacom setup. If you were going into RPM reduction, which you are not, you would have an alarm. Do you have any alarms sounding? Have you done a compression test?

It sounds like you need a good mechanic.
 
Re: Power loss at cruising speed on 8.1 port engine

When you say "Until engine slowed down and ultimately stalled" did the fuel pressure drop at that time or did it remain at 40+ psi? How does this pressure compare to the other engine? Do you have any active codes? You can check for DTC codes without a Diacom setup. If you were going into RPM reduction, which you are not, you would have an alarm. Do you have any alarms sounding? Have you done a compression test?

It sounds like you need a good mechanic.

no codes thrown. No alarms sounded. Mechanic was on board when it happened. How do you check for code without the Diacom? oil pressure on gauge dropped drastically at time of engine slow down.
 
Re: Power loss at cruising speed on 8.1 port engine

You didn't answer the question. Did the fuel pressure drop prior to, or as the engine started losing power? Have you done a compression test? How do you know there were no codes if you have no way to read codes?

If you have the dash engine light cluster you can jump across the A and B terminals on the data link connector on the engine, that will send a blinking code to the "Check Engine " light on the dash. You need to read the series of coded blinks. These are stored DTC codes,
 
Re: Power loss at cruising speed on 8.1 port engine

You didn't answer the question. Did the fuel pressure drop prior to, or as the engine started losing power? Have you done a compression test? How do you know there were no codes if you have no way to read codes?

If you have the dash engine light cluster you can jump across the A and B terminals on the data link connector on the engine, that will send a blinking code to the "Check Engine " light on the dash. You need to read the series of coded blinks. These are stored DTC codes,

Didn't answer question because I don't know. Mechanic was monitoring fuel pressure gauge and a diagnostic tool called Tech One (old Gm tool I guess). He was watching the Tech one and said it did not provide any codes - hence the no codes thrown comment. He said the fuel pressure was fine about a minute before the engine started to lose power. We haven't done compression test. Next step mechanic is proposing is to swap the ecm? and see if problem duplicates itself on the starboard engine, then oil pressure sender, sensor etc. to try and pinpoint the problem. Open to suggestions as boat hasn't worked right this season.
 
Re: Power loss at cruising speed on 8.1 port engine

While it may seem primitive, linesix's suggestion for the dash light codes do work well. Our trucks used to work this way years back the blinking light can direct you to the problem nicely. Looks kinda like morse code, then it repeats. You can have your answer in a very short time
 
Re: Power loss at cruising speed on 8.1 port engine

Thanks. I will check that to see if anything is stored. I know a dumb question, but where will you find what the coded blinks mean if there are any.
 
Re: Power loss at cruising speed on 8.1 port engine

The Rinda manuals have a pretty good listing of the DTCs - free off their www site.
 
Re: Power loss at cruising speed on 8.1 port engine

I have 2008 Crusader 8.1s with similar problem, symptom of fuel starvation at cruise rpm. It is a random failure occurring 2-3 hours or 1/2 hour into a trip. This model does not have the "pancake" filter. There is a filter in the Fuel Control Canister (FCC). Changed the Racor filter, fuel line, filter in the FCC and the symptom did not change. There are two fuel pumps on this engine, low pressure and high pressure. Crusader techs have advised me that the low pressure fuel pump is intermittently failing and will ultimately stop pumping. As part of the spring commisioning, I will be replacing both these pumps. Will not know if the problem is corrected until boat is floating and sea trialed.
 
I would suggest you check the fuel tank vents. I have seen this problem more than once when all other repairmaen failed. Try loosening the fuel caps and rerun your test. Bugs and corrosion can plug the screens.
 
Tough to wait months before finally, maybe, resolving an issue that's bugged you all winter! I feel your pain. If this was a crabbed motor I'd recommend having a helper manually add a bit choke when this problem occurs, but...

Good luck!

Jeff
 
I have had similiar problem with my boat. Several times I have gotten water in my fuel tank because of a faulty "o" ring on the gas cover. Everything was fine as long as the bow rise was low. As I increased power the bow rose and the water moved to the rear of the tank where the pickup tube is located. The engine would stop as the result of filling it with water. Maybe it is worth looking.

Chuck Hanson
 
Engines are '08 - same for the boat? If a repower, there could be some crud in the tank accumulating over the pickup tube's inlet screen.
 
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