1998 OMC- Volvo Penta 5.0 Gi idles perfect but won't rev up especially under load

[Jinman417]

Hey guys heres my problem. About 2 months ago my low pressure fuel pump went out so I went ahead and replaced both the low pressure and high pressure pumps. Took the boat out for the first time about 3 weeks ago and within 10 minutes it was running hot. Turned around immediately and found that the thermostat was stuck closed. I replaced the thermostat and went right back out and suddenly the boat will not go!!!! It idles fine and if I very gently ease into the throttle I can get it to go but not enough to get on plane. If try to acclerate normally it bogs down and will not rev. Even when it was running hot its was still running perfectly, it would go right up on plane and not skip a beat! So over the last 3 weeks I've been going thru my Volvo Penta manual and searching the web for different ideas and here is a list of what i've done/ replaced:
New IAC valve ( i know this has no affect on acceleration but I replaced it as part of rebuilding the TBI)
New MAP sensor
New TPS sensor
New water fuel seperator
Completely rebuilt TBI
New Cap and Rotor
New Spark plugs
New Ignition module
New Ignition Coil
New water temp sensor

The fuel pressure holds steady at 14 psi
The compression is 165 to 180 on all cylinders
Ive tried running it on a seperate fuel tank with fresh fuel

IT IS NOT GOING INTO SAFE MODE!!! It wont even rev to 2500 rpm unless I gently apply throttle and that is if its on the trailer under no load. Under load it is basically impossible to make it accellerate. As soon as I give it any kind of throttle it immediately bogs down and wants to die. I dont have a scanner to look up any codes. I know I need to do that but I will probably just take it somewhere to have it scanned. I'm thinking that the ECM is probably bad I just wanted to post on here to see if anyone has any other ideas. Thanks in advance for any help.

 

[boatguya1]

Re: 1998 Volvo Penta 5.0 Gi idles perfect but won't rev up especially under load

Re: 1998 Volvo Penta 5.0 Gi idles perfect but won't rev up especially under load

Off the top of my head 14psi seems way low for your fuel pressure, what does the manual say it should be?

James

 

[Jinman417]

Re: 1998 Volvo Penta 5.0 Gi idles perfect but won't rev up especially under load

Re: 1998 Volvo Penta 5.0 Gi idles perfect but won't rev up especially under load

The manual says when I turn the ignition on I should see between 9 and 13 psi and when running it should be within 1 psi of that.... the pressure when running hovers right aroun 13 to 14 psi

 

[cobalt1999]

Re: 1998 Volvo Penta 5.0 Gi idles perfect but won't rev up especially under load

Re: 1998 Volvo Penta 5.0 Gi idles perfect but won't rev up especially under load

You need to check your high pressure fuel pump, you should have approx 29 psi.

 

[Jinman417]

Re: 1998 Volvo Penta 5.0 Gi idles perfect but won't rev up especially under load

Re: 1998 Volvo Penta 5.0 Gi idles perfect but won't rev up especially under load

You need to check your high pressure fuel pump, you should have approx 29 psi.

Then why does my Seloc manual say 9 to 13 psi? According to every google search I've done on TBI fuel pressure they all come back with 9 to 13 psi. My 1989 Chevy Blazer has the same set up (except its a 5.7) and GM factory fuel pressure is 9 to 13 psi!!! I'm not hating on your reply but please show me something that says the fuel pressure should be that high!

 

[muc]

Re: 1998 Volvo Penta 5.0 Gi idles perfect but won't rev up especially under load

Re: 1998 Volvo Penta 5.0 Gi idles perfect but won't rev up especially under load

?You need to check your high pressure fuel pump, you should have approx 29 psi.?

That is correct if he has a fuel cell but he has a 1998 that should have VST that runs much lower pressure and his reported pressure is close.

I think 98 still had exhaust flappers, maybe they burnt up with the overheat and are plugging the exhaust and causing excess back pressure?

An engine model and/or serial number would help because the engine might be the same year as the boat or it might be 2-3 years different.

You have replaced a lot of parts, might be time to do some diagnosis with a scan tool before replacing the ECM.

 

[Jinman417]

Re: 1998 Volvo Penta 5.0 Gi idles perfect but won't rev up especially under load

Re: 1998 Volvo Penta 5.0 Gi idles perfect but won't rev up especially under load

Model number is 50FBPBYC.... The first "B" may be an 8. The label is hard to read

Serial number is TO13009243

Yes it does have the VST. I will investigate the exhaust flapper theory as this is the first I've heard of this and it would make sense since the issue seems to of occured following the overheat. Thanks for the info!

 

[gbeltran]

Re: 1998 Volvo Penta 5.0 Gi idles perfect but won't rev up especially under load

Re: 1998 Volvo Penta 5.0 Gi idles perfect but won't rev up especially under load



I hope that is OK to post, if not the mods can remove it. I'm with the needs more fuel pressure crowd. I think 29 off the high pressure side. Yeah, I know a GM car with a TBI only requires about 13 psi, but your boat is different. They run on a preprogrammed fuel schedule since they don't use an O2 sensor and are a LOT more demanding of the fuel system.

(where do you live, if you are anywhere near Redondo Beach, Cali, I have a scanner I could swing by and take a look)

 

[cobalt1999]

Re: 1998 Volvo Penta 5.0 Gi idles perfect but won't rev up especially under load

Re: 1998 Volvo Penta 5.0 Gi idles perfect but won't rev up especially under load

OP's own words...........Hey guys heres my problem. About 2 months ago my low pressure fuel pump went out so I went ahead and replaced both the low pressure and high pressure pumps.

 

[Jinman417]

Re: 1998 Volvo Penta 5.0 Gi idles perfect but won't rev up especially under load

Re: 1998 Volvo Penta 5.0 Gi idles perfect but won't rev up especially under load

I've seen that chart online and it causes alot of confusion for me! According to my Seloc manual 1997 and 1998 engines run at the lower 9 to 13 psi and 1999 and newer TBI engines run in the 27 to 33 psi range. The fuel pressure test that the manual has for the 97-98 engines states a ignition on pressure of 9-13 psi and a running presure within 1 psi of that. Thanks for the offer but I live in South Florida so its probably not to easy for you to "swing by" LOL! I plan on having someone come by tomorrow and scan it. Believe me I hope its as simple as replacing the high pressure fuel pump!!! Not looking forward to having to buy a new ECM if thats whats wrong!

 

[Jinman417]

Re: 1998 Volvo Penta 5.0 Gi idles perfect but won't rev up especially under load

Re: 1998 Volvo Penta 5.0 Gi idles perfect but won't rev up especially under load

OP's own words...........Hey guys heres my problem. About 2 months ago my low pressure fuel pump went out so I went ahead and replaced both the low pressure and high pressure pumps.

What does that mean?

 

[gbeltran]

Re: 1998 Volvo Penta 5.0 Gi idles perfect but won't rev up especially under load

Re: 1998 Volvo Penta 5.0 Gi idles perfect but won't rev up especially under load

If you still have the old HP pump I'd try that. Just to cover the basics, you have checked the plug wires for proper orientation? What about timing, has that been checked? I might even be tempted to try the old coil just to rule that out also. I had a similar issue (not the overheating part, but the not wanting to rev while under load) and it was the fuel pump, but mine has that fuel cell. I looked at the manual from the Adults only section for a 5.0Gi BY version, don't know which one you have, BY, WT, etc., and it shows 11 psi +/- 2 for TBI engines, but if you keep reading when you get to the testing part it shows 11 is for the 4.3, 29 for the 5.7 and it doesn't mention the 5.0. You're guess is as good as mine on that one. Mine is a 2000 5.0Gi and it calls for 29psi.

 

[Jinman417]

Re: 1998 Volvo Penta 5.0 Gi idles perfect but won't rev up especially under load

Re: 1998 Volvo Penta 5.0 Gi idles perfect but won't rev up especially under load

If you still have the old HP pump I'd try that. Just to cover the basics, you have checked the plug wires for proper orientation? What about timing, has that been checked? I might even be tempted to try the old coil just to rule that out also. I had a similar issue (not the overheating part, but the not wanting to rev while under load) and it was the fuel pump, but mine has that fuel cell. I looked at the manual from the Adults only section for a 5.0Gi BY version, don't know which one you have, BY, WT, etc., and it shows 11 psi +/- 2 for TBI engines, but if you keep reading when you get to the testing part it shows 11 is for the 4.3, 29 for the 5.7 and it doesn't mention the 5.0. You're guess is as good as mine on that one. Mine is a 2000 5.0Gi and it calls for 29psi.

Well my model number does have "BY" in it... Not sure if that means that I have the BY version but it could be. I don't have the old pump and I haven't checked the timing only because nothing has happened tht would of changed it.Hopefully I can get it scanned today and if all is clear with the ECM then I will look into the fuel pressure dilemma. Like I said, I would be happy if it was the fuel pump!

 

[Don S]

Re: 1998 Volvo Penta 5.0 Gi idles perfect but won't rev up especially under load

Re: 1998 Volvo Penta 5.0 Gi idles perfect but won't rev up especially under load

For one thing, Seloc is an aftermarket manual, and has lots of mistakes in it. You start off in your title with "1998 Volvo Penta 5.0 Gi idles...." which tells me you have a 305 Chevy V8, but then you post the model and serial numbers, we find you have a FORD V8 nor a chevy. You also have an OMC setup, not Volvo.
If you put on aftermarket pumps for a Chevy and getting 13 Psi, then you screwed up.
Look at the chart posted above, with key on engine off, you should be seeing 39 PSI +-3psi.

 

[Jinman417]

Re: 1998 Volvo Penta 5.0 Gi idles perfect but won't rev up especially under load

Re: 1998 Volvo Penta 5.0 Gi idles perfect but won't rev up especially under load

For one thing, Seloc is an aftermarket manual, and has lots of mistakes in it. You start off in your title with "1998 Volvo Penta 5.0 Gi idles...." which tells me you have a 305 Chevy V8, but then you post the model and serial numbers, we find you have a FORD V8 nor a chevy. You also have an OMC setup, not Volvo.
If you put on aftermarket pumps for a Chevy and getting 13 Psi, then you screwed up.
Look at the chart posted above, with key on engine off, you should be seeing 39 PSI +-3psi.

It is an OMC/Volvo Penta but it is not a Ford! Not sure where you get that info but I've never seen a small block ford with a distributor in the back or with centerbolt valve covers, etc. I've never checked into the serial or model number for what every letter/ digit means but I have used them at my local Volvo Penta parts supplier and they informed me that it was an OMC Cobra / Volvo Penta combo and that most parts are interchangeable but they have never given me Ny indication that my numbers say its a Ford!!! Instead of trying to prove/show that I am some sort of idiot why don't you post the reasoning why you think I have a Ford, that would be more useful to me than you showing me your moderator ego!

 

[Don S]

Re: 1998 Volvo Penta 5.0 Gi idles perfect but won't rev up especially under load

Re: 1998 Volvo Penta 5.0 Gi idles perfect but won't rev up especially under load

50FBPBYC

In Volvo terms, that F indicates it's a Ford.

Basically you have the OMC version of the engine during the OMC/Volvo joint venture, not the Volvo version. There are parts diffeerences in some places.

Moving this thread to the OMC section. Then maybe you will receive some proper information.

than you showing me your moderator ego!

Being a mod had absolutely nothing to do with my answer, and I won't bother you any more.

 

[Jinman417]

Re: 1998 Volvo Penta 5.0 Gi idles perfect but won't rev up especially under load

Re: 1998 Volvo Penta 5.0 Gi idles perfect but won't rev up especially under load

I am happy to announce that we seemd to have found the problem!!! My combo does indeed require 27 to 31 psi to operate normally. The VST (vapor seperator tank) that the high pressure pump pulls from was full of gelled up old fuel and other debris and the intake screen on the pump was also packed full!!!! Just have to pick up a new gasket tomorrow and it should be good to go! Thanks for everyones help!

 

[perna00]

Re: 1998 Volvo Penta 5.0 Gi idles perfect but won't rev up especially under load

Re: 1998 Volvo Penta 5.0 Gi idles perfect but won't rev up especially under load

I had the same exact thing happen to my 5.0. Just make sure you pull the injectors and clean them because there will be debris in the screens of them too.