Switching from Volvo TBI to Carb on a 1996 5.7 GI

C

camboat

Cadet
Joined
Dec 1, 2025
Messages
12
I have recently bought a 1996 2460 pursuit with a Volvo penta 5.7 GI with TBI.

The engine only has 80 hours on a rebuild. The problem that I am having is low fuel pressure and the wiring harness is bad.

I have replaced the tank fuel tube, check valve, fuel line, both fuel filters, both fuel pumps, and had the TBI rebuilt. I'm still not getting 30lbs of fuel pressure on the high side.

The wiring harness is obsolete and can't be found anywhere. I'm sure the VST is in the same shape.

So my next step is replace the TBI with a marine carb, low pressure fuel pump, and manifold. I'm not sure if I need a new distributor. Please let me know if I need anything else.

This will get rid of all the old parts so I can have it repaired anywhere if needed.

Attached is a photo of the distributor. Not sure if this will work with the conversion.

I will have a marine mechanic do the work.

Any help would be appreciated.

Thanks!
 

Attachments

  • dist 1.jpg
    dist 1.jpg
    70.5 KB · Views: 9
  • dist 2.jpg
    dist 2.jpg
    96.4 KB · Views: 9
  • dist 3.jpg
    dist 3.jpg
    93.5 KB · Views: 9
Scott Danforth

Scott Danforth

Grumpy Vintage Moderator still playing with boats
Staff member
Joined
Jul 23, 2011
Messages
51,849
the TBI unit IS ONLY 30 lbs. if it was in a car it would be 15psi

what pressure were you looking for?
 
C

camboat

Cadet
Joined
Dec 1, 2025
Messages
12
30 psi. I’m only getting 6-8 on the high side

With the bad wiring harness it’s going to be hard to troubleshoot.
 
Scott Danforth

Scott Danforth

Grumpy Vintage Moderator still playing with boats
Staff member
Joined
Jul 23, 2011
Messages
51,849
the low pressure isnt a wiring issue. your regulator in the top of the TBI unit has debris, or your high pressure pump isnt running.
 
C

camboat

Cadet
Joined
Dec 1, 2025
Messages
12
The TBI was just rebuilt. Both pumps are working. I have a strong feeling the VST has problems. So everything is new except the VST. Not sure if I can work on it.
Thanks
 
alldodge

alldodge

Moderator
Staff member
Joined
Mar 8, 2009
Messages
43,594
Welcome
Found what I believe is you motor with HP pump on top the VST.

As Scott mentioned, it has to be the Reg or the pump with only 6-8 psi. My first thought is you have 2 LP pumps instead of 1 LP and 1 HP.

The tank only holds fuel and any fuel above what is needed by the TBI is returned to the tank. Your getting fuel pressure and it's not over flowing so it has fuel in it.
 
C

camboat

Cadet
Joined
Dec 1, 2025
Messages
12
Thanks
When it quits raining here in the PNW. I will do more troubleshooting.
 
Bt Doctur

Bt Doctur

Supreme Mariner
Joined
Aug 29, 2004
Messages
19,480
dist should swap with no issues ,I have a2 barrel vortec manifold that was on a 5.7
 
C

camboat

Cadet
Joined
Dec 1, 2025
Messages
12
Here are a couple of pictures of the STBD side ecm plug. I ended up putting heat shrink on all the bare wires. The wires seem brittle. I don’t trust it to be reliable. If I could find a used replacement plug I could splice it in.

I can find a 5.7 GL wiring harness. Would that work if I swapped over to a carburetor? It sure would clean up my wiring mess and solve my discontinued parts problem.
 

Attachments

  • IMG_6734.jpeg
    IMG_6734.jpeg
    2.2 MB · Views: 14
  • IMG_6733.jpeg
    IMG_6733.jpeg
    2.4 MB · Views: 14
Scott Danforth

Scott Danforth

Grumpy Vintage Moderator still playing with boats
Staff member
Joined
Jul 23, 2011
Messages
51,849
was the boat sunk?

the connector is available from either LADD or TE connect. you need new terminals too.

regarding a carb, simply make your own wiring harness. its like $30 worth of materials.
 
Lou C

Lou C

Supreme Mariner
Joined
Nov 10, 2002
Messages
13,796
I’d think about taking the time to replace the brittle wires of you can. Because if you can get it to work you could potentially save a lot of money. If not then see if you can find a harness for the GL model & if not you might be able to make one from the schematic.
 
Scott Danforth

Scott Danforth

Grumpy Vintage Moderator still playing with boats
Staff member
Joined
Jul 23, 2011
Messages
51,849
The green is corrosion

The brittleness is from overheating
 
C

camboat

Cadet
Joined
Dec 1, 2025
Messages
12
I have been doing a lot of research on this project. I ordered a good used 5.7 GL wiring harness. It has the relay for the single fuel pump.

Can I use the stock intake Chevy manifold (PN 14096242)? I have read that there is a plate adapter for the TBI and a Edelbrock 1409 will be a direct fit after removing the plate or would I be better off using a Edelbrock 7101 with the 1409. I have a closed cooling system not raw water. so the 7101 should be fine. (I hope)

I have my parts list.
Carb: Edelbrock 1409
Intake: Edelbrock 7101 if needed
Fuel pump: Carter electric 4-7lbs
Flame arrestor: Holley
Looks like my stock distributor should work. If not I will get a new one.
I will be adding a high temp and low oil alarm. Pretty cheap insurance. I do monitor my gauges constantly.

Looking forward to cleaning this engine up and simplifying things.

Thanks for the help and let me know if I'm headed in the right direction!

Jack
 
Lou C

Lou C

Supreme Mariner
Joined
Nov 10, 2002
Messages
13,796
Post up a pic of what your stock intake looks like. If it looks like a 2 bbl intake I would not use it. If when you remove the plate it looks like a 4bbl intake then I think it’s fine..
 
Scott Danforth

Scott Danforth

Grumpy Vintage Moderator still playing with boats
Staff member
Joined
Jul 23, 2011
Messages
51,849
Seriously, if you want more power, while ditching the TBI,

Get a bigger cam, get the marine Edelbrock carb, a 1-1/2" carb spacer and swap to a 750 cfm 4-barrel
 
You must log in or register to reply here.
Top