Hesitation/bogging during hard acceleration Volvo Penta 5.0 GXi-A

[callen369]

Hope your opinion is right on the integrity of the GM bottom end :grumpy:, as I am tapped out with the new risers and manifolds....Although my new local marine mech charges a flat 500 for engine swaps; had to ask... Bet that doesn't include build up/transfer of parts. You know, just in case it isn't fixed and calls for a 383 stroker....:eagerness:

So, for tomorrow, I will install the repaired head, compression check the other side just in case, then pull that head and replace the gaskets and install the intake, and then wait patiently for the manifolds and risers to arrive...fingers crossed on a solid fix.

Thanks Saline for your input on gaskets and arms. Fel Pro it is. Not ready for the rockers just now.

 

[callen369]

Went back together without too much hassle. Just waiting for the manifolds and risers. Now I have compression on all cylinders.

 

[alldodge]

As a non-Volvo expert and reading through all the post I'll offer the following:

Fuel pressure should not immediately drop off to zero. Fuel pump should seal off and regulator should also hold pressure.

Set timing to correct setting and do not move around to see if it will help with problem. Your posting of advancing the timing and then retarding after hearing pinging means pieces of your engine were being damaged. The damage I see on the position and plug could very well be from detonation.

What are the numbers on your cylinders now?

 

[callen369]

Checked them all, 115 +- 5psi.

I questioned the fuel pressure...but was told by a guy at the marina it was ok....don't know him or his experience.... It is a throttle body setup with a return line. I have taken the regulator apart to clean, and reassembled....had a new diaphragm....but I couldn't get it to seal properly, so reinstalled the old one...

Any thoughts?

 

[alldodge]

Checked them all, 115 +- 5psi.

I questioned the fuel pressure...but was told by a guy at the marina it was ok....don't know him or his experience.... It is a throttle body setup with a return line. I have taken the regulator apart to clean, and reassembled....had a new diaphragm....but I couldn't get it to seal properly, so reinstalled the old one...

Any thoughts?

Again as a non-Volvo dude, what I have found is the GXI-A fuel pressure should be, low pressure should be 8psi +/- 4psi and high pressure should be 29psi +/- 2psi and they should be this way from idle to WOT. In your first post you listed it as 15 to 32 psi. This would tell me your regulator is probably the issue. Your gauge may or may not be accurate but the 18 psi variance is way out of range.

 

[Tail_Gunner]

AllDodge pretty much nailed it here, the fuel pressure remains constant@ the range's he posted......Again on the timing..... when you advanced it if you.... did advance it... and pinging happened the mefi knock sensors would have picked up the detonation and retarded it...how far did you advance the timing anyway's.... I still think your running rich the bog your experiencing is the TB clearing itself.

As to the timing did you short the data connector to put the circuit in base mode?? You are running a distributor system that cannot be tuned so to speak it's all been pre programmed to operate and certain level's of advance at predetermined rpm level's. You ecm has all the programming and it also determines precisely how much fuel to inject....it function's on milleseconds at 30lbs of pressure if your pressure is above that then you will run rich and boat engine's run quite rich from the factory.

 

[callen369]

On the distributor base, there is a factory white line, and I adjusted just enough where the line were about mismatched. So ballpark 1/16 inch rotation, was looking for a couple degrees either way to see if it would help.

Guess I will replace the regulator...are these the same as GM TBI springs/diaphragms? I just started looking, but having trouble finding them.

Also, running rich sounds about right....old plugs were a little more brown then I am used to.

 

[callen369]

Well, back together, and it runs. But I still have the hesitation issue...If I drop the throttle, it falls on its face for a second then starts to recover.
So to recap...

1. New cap, rotor, coil, plugs wires, pickup coil, ignition control module and base timing set to 10 BTDC
2. Fuel assy disassembled, cleaned, new filter, pressure checked good, all lines checked for obstruction/wear, anti siphon good
3. Injectors pulled and cleaned, new screens and orings installed, new MAP sensor, TPS sensor
4. heads pulled, new gaskets 115psi +-5 each cylinder
5. new manifolds and risers

I still have a pressure regulator to try out, and after the comments on fuel pressure loss after key off, I am debating a high pressure pump. Although, the fuel pressure holds steady under all throttle positions. So I would think the engine would run ok, but maybe take a couple seconds longer to start waiting for the pressure to climb.

 

[alldodge]

Well, back together, and it runs. But I still have the hesitation issue...If I drop the throttle, it falls on its face for a second then starts to recover.
So to recap...

1. New cap, rotor, coil, plugs wires, pickup coil, ignition control module and base timing set to 10 BTDC
2. Fuel assy disassembled, cleaned, new filter, pressure checked good, all lines checked for obstruction/wear, anti siphon good
3. Injectors pulled and cleaned, new screens and orings installed, new MAP sensor, TPS sensor
4. heads pulled, new gaskets 115psi +-5 each cylinder
5. new manifolds and risers

I still have a pressure regulator to try out, and after the comments on fuel pressure loss after key off, I am debating a high pressure pump. Although, the fuel pressure holds steady under all throttle positions. So I would think the engine would run ok, but maybe take a couple seconds longer to start waiting for the pressure to climb.

The pump just pumps, it doesn't change pressure when the throttle is dumped, so I don't think that is the issue. It's either the injectors or regulator that would cause a pressure drop and I'm leaning toward the regulator. The computer should just increase the pulse with when more fuel is needed. If the injector was leaking I would think you would just be getting to much fuel but that would not cause a stumble, it would just be rich. There should be a vacuum line from the regulator to the intake manifold. If the vacuum line is removed pressure should increase some, like when you drop the throttle. The increase may only be momentarily because the regulator should keep it at pressure.

Check and see what kind of vacuum you have on the line.

Another reason I don't think it's the pump is you said the engine runs fine once it is up on plane, right? If this is correct the pump is supplying sufficient fuel

 

[callen369]

Alldodge,

I have a new regulator assy to install and try this week. But as far as vacuum line, it is a throttle body, and the regulator is directly mounted to the top. there are no vacuum lines, just a small metal tube that points into the butterflies.

 

[Saline Marina]

I might have missed it in the re-reading, but did you change out the gasket under the TBI unit (TBI to intake manifold)? If compromised that can lead to a vacuum leak and an incorrect fuel pulsewidth.

 

[alldodge]

Alldodge,

I have a new regulator assy to install and try this week. But as far as vacuum line, it is a throttle body, and the regulator is directly mounted to the top. there are no vacuum lines, just a small metal tube that points into the butterflies.

As before I'm not a Volvo guy but on Mercs there is a regulator even on TBI mounted next to the high pressure fuel pump. Do you have anything mounted to your fuel pump?

 

[Tail_Gunner]

As before I'm not a Volvo guy but on Mercs there is a regulator even on TBI mounted next to the high pressure fuel pump. Do you have anything mounted to your fuel pump?

His Volvo has a low pressure pump next a high pressure pump... that's direct to the tbi, the regulator is spring loaded right in the tbi...Its a old 454 tbi.

The regulator is that casting right behind the tbi

 

[callen369]

Gunner,
Where did you find that diagram? And do you have the part number for the regulator assy? I assume these are different than those used on trucks, etc. since they run ballpark 15 psi from the fuel pump, and mine runs 34psi...

 

[Tail_Gunner]

http://boatinfo.no/lib/volvo/manuals/5057a-f.html#/0

Your going to have some trouble accessing the regulator