2004 VP 5.7 GXI no power, popping, knocking & backfire.

Jeepen

Cadet
Joined
Sep 20, 2018
Messages
15
VP 5.7 320 GXI MPI duo prop
compression test 150 PSI on all 8 cylinders
New fuel pump assembly & filter with low side reading 10 psi High 55psi
plugs, wires, cap and rotor look great less that 20 hours on them
new fuel regulator with new style clip no screen but when replaced the screen was clean no debree.

Engine starts and idles great. when you engage drive and give it any throttle it starts popping, knocking and backfire and has no power. The thing that is weird if you don't engage drive and rev up engine it sounds great, revs up fine sounds like it has tons of power but as soon as you engage drive under load it sounds terrible. Very frustrated please help?
 

Scott Danforth

Grumpy Vintage Moderator still playing with boats
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If you have the crab cap, change your cap and rotor
 

Jeepen

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Sep 20, 2018
Messages
15
What do you mean the crab cap? The reason I don't think its in the ignition is the boat runs good out of the water. Revs to 4500/5000. Does not miss or anything. I even engaged the drive with the ears and still runs great. It seems to act up in the water under load. so crazy got me frustrated. Have you had the same problem? Mine has the MPI. I bought a cheap scanner tool that plugs into data port and flashes code. It scanned the system and did not have any issues. I appreciate your reply. I am a diesel mechanic by trade, would love to talk to someone about this issue. My phone is 435-650-4881 my name is Josh.
 

enginesilo

Petty Officer 1st Class
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Jun 9, 2008
Messages
355
What do you mean the crab cap? The reason I don't think its in the ignition is the boat runs good out of the water. Revs to 4500/5000. Does not miss or anything. I even engaged the drive with the ears and still runs great. It seems to act up in the water under load. so crazy got me frustrated. Have you had the same problem? Mine has the MPI. I bought a cheap scanner tool that plugs into data port and flashes code. It scanned the system and did not have any issues. I appreciate your reply. I am a diesel mechanic by trade, would love to talk to someone about this issue. My phone is 435-650-4881 my name is Josh.

I'd take Scott's advice and start with the cap and rotor, but I will agree it is strange if they only have 20 hours on them. I have the 5.0 GXI Fuel injected which is very similar and I was experiencing symptoms in the water as well. On the hose it ran fine and revved normal, but once I put it in the water the idle got a bit uneven, but it would rev normally when in neutral. At its worst, it wasn't revving past 3000 RPM's and I could feel as if the engine was missing.

I did a spark test before I changed the cap and rotor, and all cylinders were showing spark and firing. But as soon as the new cap and rotor went on, all the symptoms went away. I changed the cap and rotor yesterday and took it for a ride today and it was a completely different motor. Smooth idle, TONS of power out of the hole, and it revved up while under load.

Did you change the cap and rotor yourself 20 hours ago? And how long did it take those 20 hours to accumulate? If the boat sat a lot and was done by a previous owner who knows what was actually done, etc.

Could it be timing related? At the very least pop off that distributor cap and check how the points look, and the rotor contact tab.
 

Jeepen

Cadet
Joined
Sep 20, 2018
Messages
15
I appreciate the input. It has electronic ignition, no points. I did the tune up myself. We had the boat on a long weekend trip. We ran it down the lake WOT for about 1-1/2 hrs. It ran awesome. We parked on a remote sandy beach for about two hrs and whe we went to take off that’s when all my troubles started. It started fine and idled out of the canyon, but when I went to take off it sputtered and backfired and fell on its face. I shut it down checked everything I could and all looked normal. I started it and blew it out and was able to plain out but noticed a significant HP loss. After that it just got worse.

Reading through the Internet I noticed a lot of people had similar issue that were from the fuel system. So I psi tested mine and was a little low on low psi pump. So changed the whole assembly. Checked the regulator it was clean but changed anyway. With no change.

took it on test drive and it revs fine under no load. You kick it in gear and it has zero power, sputtering, and backfiring. It does sound timing related, but seems strang it revs with no load. I’m going to try new cap and rotor just to make sure. But I looked at them today and they look good. When I did the compression test the plugs looked wet like a film of fuel on them. It does seem to be running rich as well. I’m wondering if I have a cam position sensor out or bad distributor. I did put new heads on it last year but it’s ran great all summer so I can’t imagine I installed it wrong. But who knows!
 

Scott Danforth

Grumpy Vintage Moderator still playing with boats
Staff member
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Jul 23, 2011
Messages
47,304
What do you mean the crab cap? The reason I don't think its in the ignition is the boat runs good out of the water. Revs to 4500/5000. Does not miss or anything. I even engaged the drive with the ears and still runs great. It seems to act up in the water under load. so crazy got me frustrated. Have you had the same problem? Mine has the MPI. I bought a cheap scanner tool that plugs into data port and flashes code. It scanned the system and did not have any issues. I appreciate your reply. I am a diesel mechanic by trade, would love to talk to someone about this issue. My phone is 435-650-4881 my name is Josh.

this is the crab cap

rra-18-5375_ml.jpg


they are junk, and usually only last a year or so. start here, as when they go bad, they cross-talk internally

since you reved your motor to 4500/5000 out of the water, change your impeller, you toasted it.

NEVER DO THAT....EVER. 1500 RPM on the muffs is limit to the water you can supply

plus, your motor would run that fast with only 2 cylinders without load, so you did nothing but murder your impeller

what is your fuel pressure?

follow the troubleshooting guides in the manual or the stickies.
 

kenny nunez

Captain
Joined
Jun 20, 2017
Messages
3,056
Have you ever inspected the fine screens in the injectors? Volvo used plain steel for the fuel rails and rust flakes may be blocking the screens. Just something to check but worth the effort,
 

Jeepen

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Joined
Sep 20, 2018
Messages
15
Kenny, Thanks for the advise I will pull the injectors and rail next. Im not thinking that is it just because I installed a new regulator and while having it off you could see in the rail and it looked pretty clean. Also the fine screen on the regulator looked really good. But Imp at a loss so I will try anything.
 

Jeepen

Cadet
Joined
Sep 20, 2018
Messages
15
Little update, not good but here is another update. I bought a Rinda Techmate pro and plugged it in and it no stored codes and said system was functioning properly. Ugg That was some expensive useless information. Since my last post I have done the following.

Scott Danforth-I inspected my impeller pump and no damage. Thanks for the heads up on reving it out of the water on the hose. I will not do that anymore.

Fuel system-changed out my suction hose from the tank to the pump installed clear filter to observe flow and debree.
New plugs, wires, cap, rotor.
New coil, module and cam position sensor.
Removed and cleaned MAP Sensor
Inspected harness and all conections.

Anyone out there please help? So very frustrated!
 

QBhoy

Fleet Admiral
Joined
Mar 10, 2016
Messages
8,286
Hi
warm the engine up to temp, take it out into wide open space. Turn it off. Feel under the diz cap for the securing bolt or not that holds the diz gear down. Slacken it off slightly (about a 13mm spanner or imperial equivalent)
Rotate the whole assembly literally a mm or 2 clockwise, tighten up and see if it’s better.
 
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