VP 8.1GXi Fuel Pressure / Hunting at Idle

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VP 8.1GXi Fuel Pressure / Hunting at Idle

Postby JNelson90 » Mon Apr 30, 2018 10:06 am

I have 2006 Volvo Penta 8.1 GXiI-F engines and had one long block (port engine) replaced over the winter do to lean burn and piston damage. Now the marina is telling me that I have low fuel pressure at 0 vacuum (with key switch on but engines not running). Should be 50-60psi but it is only showing 40psi. Both engines are exhibiting the same low value. My original engines (before the new longblock) seemed to always hunt and surge at idle but appeared to run fine at higher RPMs. When I purchased the boat (used) the surveyor indicated the idle air controller was the issue for the hunting at idle so I replaced both throttle bodies (the IAC is built into the throttle body and not a replaceable component) so I replaced both throttle bodies. This improved but did not solve the hunting at idle.

My starboard engine (original) still hunts at idle (I had the injectors cleaned and tested and was hoping for improvement) but only a 100 or 200 RPM shift. The port engine (with a new longblock, cleaned and tested injectors and cleaned out intake manifold) hunts several 100 RPMs. The marina is not sure what the issue is. They ruled out the gas tank / pickup by running from a portable gas container but the pressures and hunting were the same and they also tried a new fuel pressure regulator with no change. They commented on the input connector on the fuel pump but it seems like it is too much trial and error. I could really use some insight from the wealth of knowledge from the forum. The trial and error method is going turn me into a broke boater.
Kindest regards, Jeff

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Re: VP 8.1GXi Fuel Pressure / Hunting at Idle

Postby cbsmith » Mon Apr 30, 2018 11:21 am

I seem to recall reading on here, either from Chris In Texas or Imrich, that Volvo had a firmware update for the ECU for the 8.1 engines to fix some issues? Maybe they would have more information about this, or you could find it via a search.
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Re: VP 8.1GXi Fuel Pressure / Hunting at Idle

Postby JNelson90 » Mon Apr 30, 2018 12:24 pm

Thanks for the response - when the marina installed the new longblock they sent the ECM back to Volvo Penta in order to be updated for the new longblock. I would think this includes any potential firmware updates but you never know with VP. Thanks again!
Kindest regards, Jeff

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Re: VP 8.1GXi Fuel Pressure / Hunting at Idle

Postby ImRich » Mon Apr 30, 2018 12:37 pm

Have they checked your fuel pump?

Perhaps some of the internal screens need to be cleaned? I don't know if your engines have the issue, but some fuel pumps fail due to the E-10 fuel eating the paint on the inside of the fuel pumps, and it slowly blocks the internal screens.

My engines run smoothy, but I'm still waiting to get my ECMs updated to the latest firmware version to solve a very hard to find issue where very rarely one engine will simply quit when I'm shifting between forward or reverse (or vice versa). My mechanic keeps trying to coordinate with a local Volvo rep to get this done.
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Re: VP 8.1GXi Fuel Pressure / Hunting at Idle

Postby JNelson90 » Mon Apr 30, 2018 12:52 pm

I did read the posts about cleaning the input screen on the high pressure pump side. I relayed that information to the marina to see what they say. I think I will try that on the starboard engine to see if it works - I just ordered a fuel pressure test kit with a pressure relief valve and drain line (just to be safe). I suspect I should change the o-rings at the same time; correct?
Kindest regards, Jeff

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Re: VP 8.1GXi Fuel Pressure / Hunting at Idle

Postby ImRich » Mon Apr 30, 2018 1:12 pm

I'm not sure about the O-rings. I would hope/think that any good mechanic would know all of this and wouldn't need much help from any of us. ;)
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Re: VP 8.1GXi Fuel Pressure / Hunting at Idle

Postby JNelson90 » Mon Apr 30, 2018 2:09 pm

One would think that but I feel there is way too much trial and error and the bill keeps getting higher and higher. They are telling me since they are responsible for the warranty that I can't use the engine until they fix it. Doesn't give me many options about working with other mechanics.
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Re: VP 8.1GXi Fuel Pressure / Hunting at Idle

Postby gofast24 » Tue May 01, 2018 9:54 am

JNelson90 wrote:One would think that but I feel there is way too much trial and error and the bill keeps getting higher and higher. They are telling me since they are responsible for the warranty that I can't use the engine until they fix it. Doesn't give me many options about working with other mechanics.

Maybe turn what they are telling you around and tell them you cant pay for the repairs until it is actually fixed (able to run again)? I can really understand how frustrating this can be especially with the boating season here again! Has anyone pulled any codes from the ECM in the process of determining what is wrong?
Good luck.
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Re: VP 8.1GXi Fuel Pressure / Hunting at Idle

Postby JNelson90 » Wed May 02, 2018 7:10 am

I will check on the codes from the ECM but I doubt it. They now want to change the input nipple into the fuel cell as they believe it is too small and the elbow being sharp is restricting flow. I am not betting on this fixing things. I believe it will come down to replacing the entire fuel cell.
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Re: VP 8.1GXi Fuel Pressure / Hunting at Idle

Postby ImRich » Wed May 02, 2018 8:44 am

Also check the condition of your anti-siphon valve that may be on the fuel tank pickup line.
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Re: VP 8.1GXi Fuel Pressure / Hunting at Idle

Postby JNelson90 » Wed May 02, 2018 8:57 am

Thanks and yes another good thought. However; we think we eliminated all of the tank and fuel line issues by running on a portable tank and line with the same symptoms. Thanks again!
Kindest regards, Jeff

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Re: VP 8.1GXi Fuel Pressure / Hunting at Idle

Postby gofast24 » Wed May 02, 2018 10:57 am

Just another thought = As your having these problems at idle/no load conditions I dont think the internal fuel strainer screens being blocked would have any effect as the fuel flow at idle is minimal, i would expect fuel flow blockage thru the screens would be more likely to cause a problem at WOT or somewhere close to WOT? I know you indicated that the engines seemed to run fine under load but still had the rough idle problem. After pulling any codes that may have been logged I still suspect the IAC valve to be the problem, check the electrical connections from the IAC to the ECU > We had this rough idle problem on one engine for a few weeks but it just went away :), no problems since then (two years ago). Gosh, you replaced both throttle bodies and still the same problem? Have to ask what the throttle bodies cost?
Keep us informed when you finally figure out the solution!
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Re: VP 8.1GXi Fuel Pressure / Hunting at Idle

Postby JNelson90 » Wed May 02, 2018 11:55 am

After replacing the throttle bodies (I think I paid around $650 each) the rough idle got better. It was hunting and surging several hundred RPM and after the new throttle body (with IAC) it dropped to 1 or 200 RPM max. Much smoother but definitely not smooth. Now with the new longblock; that engine is back to hunting and surging several hundred RPM and they are blaming it on the fuel pressure (40psi). I am finding support that the correct high side fuel pressure for the 8.1 is 36-44 psi and the 50-60 psi spec is for the 5.7 liter engines. I have now emailed Volvo Penta with my engine serial numbers to get the truth from them. I have the EFI workshop manual for the 5.7 and 8.1 combined and it clearly shows (for the 5.7) the 50-60 psi spec but it does not show a spec page for the 8.1 engines.
Kindest regards, Jeff

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Re: VP 8.1GXi Fuel Pressure / Hunting at Idle

Postby gofast24 » Thu May 03, 2018 10:59 am

Jeff, your doing great! Again, did you get any codes read from the ECU? Also, at idle, as previously mentioned, the 40 PSI should be plenty of fuel pressure at idle? Have to start wondering if there was (is) any water in your fuel tanks? I know you indicated the mechanic used a portable fuel tank already which should have eliminated the problem of water but who knows? If you dont hear back from VP via e mail I would give them a call! Hopefully your VP certified dealer/ mechanic has already done that? It is strange that both engines have the same hunting problem at idle, something is funny here! Cant believe both engines have had both throttle bodies/ IAC's replaced, fueled from a separate tank, etc. and still have the same joint problem. Have you checked the throttle plate positions both at idle setting and WOT settings? It is possible that your throttle controls/cables/adjustments are not allowing the throttle plates to fully return back to the idle stop screw position?
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Re: VP 8.1GXi Fuel Pressure / Hunting at Idle

Postby JNelson90 » Thu May 03, 2018 11:29 am

Hi GoFast24 (sorry I don't have your first name) -

Fuel / water in fuel was ruled out by running on portable gas container and fuel lines. No ECU codes - I have ordered the Rinda software to get at the codes since the marina mechanics do not have a code reader. I have not heard back from Volvo Penta so I will try calling them today. The mechanic spoke with other Volvo mechanics and now they are on the paint chip issue plugging up the fuel cell. That normally shows at WOT rather than idle so I am not optimistic. I am taking into my hands as much as possible as I am not getting any where except for higher bills from the Marina. I keep saying "I Love Boating AND this is TOTALLY worth it" right?
Kindest regards, Jeff

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Re: VP 8.1GXi Fuel Pressure / Hunting at Idle

Postby gofast24 » Fri May 04, 2018 9:49 am

JNelson90 wrote:Hi GoFast24 (sorry I don't have your first name) -

Fuel / water in fuel was ruled out by running on portable gas container and fuel lines. No ECU codes - I have ordered the Rinda software to get at the codes since the marina mechanics do not have a code reader. I have not heard back from Volvo Penta so I will try calling them today. The mechanic spoke with other Volvo mechanics and now they are on the paint chip issue plugging up the fuel cell. That normally shows at WOT rather than idle so I am not optimistic. I am taking into my hands as much as possible as I am not getting any where except for higher bills from the Marina. I keep saying "I Love Boating AND this is TOTALLY worth it" right?

Jeff, my name is Bob (I had a 24' Python Cuddy Cabin with a 502 Merc I/O and straight thru hull exhausts (with Captain's Call system) about 10 years ago)), therefore the "gofast24 :)
Can't believe your "VP" mechanics dont have a OBD-M reader to pull codes from your ECU's? Check with a local Marine Surveyor, they most likely have one and could read any codes at a reasonable price?
When you completely replaced the throttle bodies (with built in IAC's) did they have the idle position throttle plate stop screw's pre set to the correct position? If they are slightly open too much that will confuse the ECU and therefore "rough/surging" idle. It is also possible that if you have defective throttle plate position sensors that could also be confusing the ECU's? I would also try disconnecting the throttle cables (if you have mechanical throttle controls?) to make sure the throttle plates are at the correct idle stop position.
Yes, boating is totally worth it (especially when everything is working correctly :)
Keep us up to speed on any progress you make!

Thanks
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Re: VP 8.1GXi Fuel Pressure / Hunting at Idle

Postby JNelson90 » Fri May 04, 2018 10:39 am

Hi Bob,

Many thanks for your post as I believe that it provided valuable insight. I followed the installation procedure for the throttle bodies from the Volvo Penta manual and it did not indicate anything about adjusting the plate / stop screw. Gives me something to investigate this weekend. I did order the Rinda Diacom Marine software and adapter so I can verify the ECM details, sensor inputs and check for error codes. I am also pretty close to confirming the the high pressure fuel side for my engines should be 40psi +/- 4psi and mine are right at 40psi. The marina has been working for 2 weeks to get it to 50psi because they think that is the spec but I have some documentation from VP and just waiting on final verification from their support team. The documentation I have shows my engine series but stops 2 years before my actual version. I suspect that the value did not change.

posted the install procedure that I had from VP on the throttle bodies below.

To install:
1. Carefully clean the throttle bore and valves. Do not use anything containing methyl ethyl ketone and do not soak it in solvent - use a spray carb/choke cleaner! If you didn't remove the TP sensor and IAC valve, make sure that you get no solvent on them during cleaning. CAREFULLY scrape any gasket material off the mating surfaces. Make sure all passages are free of dirt and completely dry before installation.
2. Install the sensor and valve if removed. Position the throttle body and new gasket on the plenum and tighten the bolts/studs to 80 inch lbs. (9 Nm). If your engine (8.1L) uses nuts, tighten them to 89 inch lbs. (10 Nm).
3. Check that the throttle lever moves freely, snapping back to the closed position and then reconnect the throttle link to the lever. Tighten the nut securely.
4. Connect the IAC and TP leads.
5. Install the flame arrestor.
6. Reconnect the battery cables.
7. Start the engine and allow it to idle for 30 seconds, turn it Off for 10 seconds and then restart the engine and check that the idle is OK.
Kindest regards, Jeff

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Re: VP 8.1GXi Fuel Pressure / Hunting at Idle

Postby gofast24 » Mon May 07, 2018 10:40 am

Big question here regarding your IAC valves are part of the throttle body and not serviceable per your previous posts? Per your #1 above from VP = "If you didn't remove the TP sensor and IAC valve" etc. They say "if you didn't remover the IAC valve" that to me means that it is removable? Where did you get the info that your IAC valve is not removable. Try going to the VP OEM parts site and input your engine serial number and look up the throttle body/IAC parts exploded view, see if it shows a removable IAC valve listed.
Good luck, there has to be some strange gremlin here somewhere!
Bob
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Re: VP 8.1GXi Fuel Pressure / Hunting at Idle

Postby JNelson90 » Mon May 07, 2018 11:13 am

I have found that the Volvo Penta service manuals are not always complete and don't always show clear differentiating facts about their different engine series. When you look at the parts schematic for my exact engines you can see that the IAC is "not serviceable" (see below showing a paste from the parts schematic), a phone call to the Marine Parts Express confirmed this along with my surveyor that told me I would need to buy the entire throttle body. Thanks for trying!

8.1GiI-G, 8.1GXiI-F
7744930 - 25 - 9064 22484 Upd: 21 NOV 2005
8.1GiI-G, 8.1GXiI-F
REF PART NO. QTY DESCRIPTION NOTES
1 3817844 1 Throttle body
1 Valveidle air control NOT SERVICED
1 Sensorthrottle position NOT SERVICED
1 Controlthrottle position NOT SERVICED

Lastly, I did not have the correct adapter for the Diacom software so I will have another update next week once I get the right DLC adapter and have a chance to get back down to my boat.

Happy boating (for those of you that have working boats - unlike mine)!
Kindest regards, Jeff

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Re: VP 8.1GXi Fuel Pressure / Hunting at Idle

Postby gofast24 » Tue May 08, 2018 10:24 am

Thanks for the info Jeff,
Yes, even though it is 2018 and everything is electronic and on line with instantly updated info some companies dont update anything, including parts lists and parts exploded views (and of course, prices).
Hopefully you will be able to connect to your ECU and see if any codes stored,still cant believe there aren't any marine mechanics in your area that dont have a code reader and you have to buy your own? FYI, our 2001 4160 is doing great for a 18 year old vessel (960 hours on the VP's) , just a lot of maintenance and service keeping it that way.
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