VP 8.1GXi Fuel Pressure / Hunting at Idle

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Re: VP 8.1GXi Fuel Pressure / Hunting at Idle

Postby cbsmith » Wed Jun 13, 2018 6:01 am

I had a vacuum leak on an old 1990’s era fuel injected Chevy car and it causes an uneven idle like you are describing. Once any throttle was applied it smoothed out.
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Re: VP 8.1GXi Fuel Pressure / Hunting at Idle

Postby JNelson90 » Wed Jun 13, 2018 7:01 am

Thanks for the tip - measuring vacuum shows a consistent vacuum but I do suspect an intake manifold air leak. I will let everyone know once the engine is fixed; I can hardly wait!
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Re: VP 8.1GXi Fuel Pressure / Hunting at Idle

Postby fatmattyd » Thu Jun 14, 2018 6:47 am

These are interesting tips... measuring vacuum shows consistent readings, but a bad sensor could still throw the ECU off the deep end.

I think we're pretty much all rooting for you at this point, it seems you've been through the ringer!
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Re: VP 8.1GXi Fuel Pressure / Hunting at Idle

Postby JNelson90 » Thu Jun 14, 2018 9:57 am

Most of the sensors were swapped with the starboard engine which did not result in any improvements. Readings on the computer seem to show accurate sensor data as well. All the time my marina and I invested in attempting to solve the problem should indicate a deeper issue than the standard issues. There are so many things that can cause hunting and surging at idle; that alone makes it somewhat complex. Ultimately, I would have been happy (but sad) if it was a quick fix that I missed so I am reserved but happy about the delay. For now; I have a floating condominium but I am happiest when driving the boat and that has only happened once in the past 10 months. This weekend, the marina that my boat is at is having a big party with a band so my wife and I will make the best of of it. Happy boating!
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Re: VP 8.1GXi Fuel Pressure / Hunting at Idle

Postby gofast24 » Thu Jun 14, 2018 10:56 am

JNelson90 wrote:Thanks for the tip - measuring vacuum shows a consistent vacuum but I do suspect an intake manifold air leak. I will let everyone know once the engine is fixed; I can hardly wait!

Assuming you measured the intake manifold vacuum on the port (surging engine) why not try measuring the vacuum on the stbd and compare the reading? A +/- 2% or so should be OK, much more than that (higher vacuum on the stbd engine than the port very well could indicate a intake air leak downstream of the throttle body. What is the vacuum scale on your vacuum gage? Inches of water (probably not) or in-Hg, PSI?
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Re: VP 8.1GXi Fuel Pressure / Hunting at Idle

Postby JNelson90 » Fri Jun 15, 2018 7:48 am

I did measure vacuum on both engines and they were very close (+/- less than 1 inch). Volvo Penta sent me a document indicating that the vacuum should be 11 inches (because of an aggressive cam per VP) but I was seeing about 14 inches on both engines. Still no updates from the marina; I can hardly wait to hear what the fix is - assuming they can actually fix it.
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Re: VP 8.1GXi Fuel Pressure / Hunting at Idle

Postby gofast24 » Fri Jun 15, 2018 10:58 am

JNelson90 wrote:I did measure vacuum on both engines and they were very close (+/- less than 1 inch). Volvo Penta sent me a document indicating that the vacuum should be 11 inches (because of an aggressive cam per VP) but I was seeing about 14 inches on both engines. Still no updates from the marina; I can hardly wait to hear what the fix is - assuming they can actually fix it.

A inch of water column (not really significant, there are 34' of water (308") or a inch of Hg (Mercury,29.92" "very significant) at sea level! These numbers are relative to "0" pressure if your in space so typically pressure or vacuum reading in the engineering community are referred to PSIG (the G meaning gage ) pressure. Anyway, sorry to bother you with this technical stuff:)
Good luck, hope you figure this out before winter!
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Re: VP 8.1GXi Fuel Pressure / Hunting at Idle

Postby JNelson90 » Fri Jun 15, 2018 12:23 pm

No worries at all; I like the technical stuff. Thanks again for all your amazing insight!
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Re: VP 8.1GXi Fuel Pressure / Hunting at Idle

Postby gofast24 » Sat Jun 16, 2018 11:09 am

JNelson90 wrote:I did measure vacuum on both engines and they were very close (+/- less than 1 inch). Volvo Penta sent me a document indicating that the vacuum should be 11 inches (because of an aggressive cam per VP) but I was seeing about 14 inches on both engines. Still no updates from the marina; I can hardly wait to hear what the fix is - assuming they can actually fix it.

With VP indicating you should have 11" (of what, inches of mercury or water column?) and you are measuring 14", just as a last resort remove your flame arrestors from the throttle body's and re measure manifold vacuum at idle! Had to pull our flame arrestors after buying our vessel as both were seriously plugged with pine pollen, dust, some paper towel chards, oily from crankcase oil vapors and other stuff you wouldn't normally find in a flame arrestor in a boats engine room , but the previous owner never cleaned anything even with over 700 hours on both engines!
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Re: VP 8.1GXi Fuel Pressure / Hunting at Idle

Postby JNelson90 » Mon Jun 18, 2018 10:59 am

Just referenced the VP email and it was 12 (not 11) and listed as [12 inHG]. I like the idea of running without the spark arrestor in place. My engine compartment is really clean and the spark arrestors look clean as well so I am not optimistic about it but certainly worth trying as it is so simple to test. I called the marina yet again this morning and I am still waiting to hear back on the status of the repair.
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Re: VP 8.1GXi Fuel Pressure / Hunting at Idle

Postby JNelson90 » Fri Jun 22, 2018 10:55 am

I finally heard a possible diagnosis for my engine problems from the marina with the certified Volvo Penta mechanics. They performed a smoke test using an endoscope and found smoke getting into the the intake plenum which probably indicates a bad gasket seal. They were not able to confirm where the smoke was getting in but they suspect removing the intake and replacing the gaskets should do the trick. I had suspected this all along but was unable to prove it. I will continue to provide updates as the repair continues to progress. I have been without a running boat now for just over 10 months now; so what will a few more days mean - actually its killing me not having a working a boat and yesterday would not be soon enough to have it repaired.
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Re: VP 8.1GXi Fuel Pressure / Hunting at Idle

Postby JNelson90 » Tue Jul 10, 2018 12:26 pm

Update.....

Another roller coaster ride for me and my wife on our engine repair. I arrived late Thursday night to the boat (June 28th) as my wife and I had 10 days off and an anniversary to celebrate and we were hoping to take a long boat trip with several stops along the way. When I got there on Thursday night the engine was fully back together and I was thinking it was fixed; however; on Friday morning the mechanic indicated that it was not fixed and redoing the intake manifold made no improvements to the issue. Apparently, the smoke test turned out to be a false lead due to some crankcase vent that allowed the smoke in and "fooled" the mechanics.

This past Friday Volvo Penta had the mechanics turn up the fuel pressure on the high side (we did not even know that was possible but there is a torx screw setting on the fuel pressure regulator that allowed them to make the change). The spec is 40psi +/- 4 psi and the current reading was 42 psi. They had them up it to 52 psi and made a comment about some replacement long blocks needing higher pressure. This change did in fact improve the idle issue as the engine now only hunts / surges about 50-100 RPM which is very similar to my other engine(s). We have not tested it to see how it impacts the engine when in use / at higher RPM's.

My question to the mechanics surrounded the potential other issues this may cause being "out of spec" and if this was a satisfactory solution per Volvo Penta and if it would impact my warranty on the new long block. The mechanics emailed VP Thursday evening and 3 times on Friday with no responses to our (the mechanics agree with my position) . On Monday they emailed their regional manager with VP and again another day with no responses. We did spend our 10 days on the boat but never left the dock - SOOOOOO frustrating. So far today; still no word from Volvo Penta - I was a fan of VP but that may be changing if they leave me out in the cold on this. I will continue to update as things change - thanks for letting me vent with my fellow Regal owners.
Kindest regards, Jeff

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Re: VP 8.1GXi Fuel Pressure / Hunting at Idle

Postby JNelson90 » Fri Jul 13, 2018 7:04 am

Update; the Volvo Penta regional service manager finally contacted the marina VP mechanics and has now confirmed that my ECM does not have latest configuration for my engine. Now keep in mind that my ECM was sent back to Volvo Penta during the initial long block installation to be re-flashed back in December. Either way; it wasn't flashed with the right code or newer code was created for my current long block configuration during the past 6 months. Who is going to be responsible for 3 1/2 months of troubleshooting this problem? I have not seen any invoices for all the troubleshooting yet, but I know they are coming. There is a small glimmer of hope that the VP service manager will get to my boat today to update the ECM so I can finally use my boat again. I am also concerned that my new long block did not go through the proper break-in procedure because all the engine running (about 3.5 hours) has been for testing and not following the VP break-in procedure. Finally, I have been saying for months now that my ECM should be re-flashed and I even sent an email to VP regarding the possibility that it needed to be re-flashed but they would not deal with me on that indicating they would only work with authorized VP mechanics. That email was back on May 23rd - almost 2 months ago.
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Re: VP 8.1GXi Fuel Pressure / Hunting at Idle

Postby gofast24 » Mon Jul 16, 2018 10:59 am

JNelson90 wrote:Just referenced the VP email and it was 12 (not 11) and listed as [12 inHG]. I like the idea of running without the spark arrestor in place. My engine compartment is really clean and the spark arrestors look clean as well so I am not optimistic about it but certainly worth trying as it is so simple to test. I called the marina yet again this morning and I am still waiting to hear back on the status of the repair.

Never run with the throttle body flame arrestor off!! Also, a little fishy that the mechanics saw smoke ? in the intake manifold? You should have a crankcase to intake manifold (PVC) positive crankcase ventilation valve to allow crankcase vapors to be ingested into the intake to allow them to be burned in the cylinders and not expelled to the atmosphere like pre 1960's car engines had. Question, why did you need a re man engine in the first place? Mechanics turning up the fuel press 10 PSI above VP recommended not too smart either, why did the tell you that that needed to be done when you already had normal fuel pump pressure? Cant believe replacement long block need a higher fuel pressure if using the original OEM engines intake manifolds and injectors?
Good luck, let us now what you finally figure out! .
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Re: VP 8.1GXi Fuel Pressure / Hunting at Idle

Postby JNelson90 » Mon Jul 16, 2018 12:15 pm

Thanks for your response and input. I know that my engine does not have the typical PCV valve and there description of the smoke test did not fully reveal to me where the smoke ended up but their conclusion was a vacuum leak at the intake manifold. I did check with the mechanics on the flame arrestor and they had run with it off to inspect the throttle body plate but that was ruled out because it did not make any difference. Last year I had a major engine failure most likely due to a lean burn condition (paint chips in the fuel cell that partially plugged it and some of my injectors) which ultimately broke off part of one of my pistons. The replacement longblock was recommended due to the fact that pieces of metal from the broken piston could have worked in to many areas in the lower part of the engine and the most direct fix was a new long block. Lastly; I don't know why Volvo Penta requested my marina mechanics to increase the fuel pressure on the high side by +12psi (they did make some comment that some long blocks needed this change) . It is definitely not in spec to my knowledge so I am hoping the updated flash on the ECM will allow the engine to idle properly while at the in spec 40psi fuel pressure. I am still waiting for the Volvo Penta regional service manager to show up to my boat to flash the computer. I will let you know as soon as they complete that step.
Kindest regards, Jeff

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