Volvo penta stalling help

[Tipafew]

Ya got a Techmate and there are no codes, good news
What about the other items folks have been asking about?

Thanks for your help. Fuel pressure checks out good. I will take another look at throttle bodies but last time I remembered them being very clean.

First year I had the boat I fogged the motors when winterizing. Later I read that you aren’t supposed to fog these so never did again after that. Is there any chance there is a small air passage that can plug or some other reason they say not to fog them?

 

[alldodge]

What does good mean?

 

[Tipafew]

What does good mean?

I checked it last year when I was hunting this problem so I would be lying if I said I remembered. I just remember at the time it was right at the spec that I had found.

Also had one pump go out last year and rebuilt both of them and no change after that with the stalling problem either.

I can check it again this weekend.

 

[tpenfield]

Just going back through this issue . . . you said it has been happening for a couple of years now. Was there something back then that may have caused it. Did it come on suddenly or gradually? both engines showing symptoms at the same time or one, then the other? Was there maintence done just before this issue appeared?

This is a situation where the ability to record the ECM data (Rinda Diacom) is valuable as you can play it back slowly and see what information is going out of its normal range.

If you cut just one throttle back quickly does just the one engine die ? . . . or do both engines die?

I'm just wondering if there is something funky going on with the engine voltage and a rapid change in the RPM is causing the ECM's to think they don't have enough voltage. (just a hunch)

 

[1000 Islands]

Really, you come from 40 years of auto background and a Manufactures manual is not worth the paper its printed on

While there not the greatest, that is way over the top for me

The OEM Volvo diagnostic service manual is indeed very poor. It reminds me of the 80's, when the automotive OE manuals were pretty poor. Current OE automotive SI is light years ahead of OE VP SI, and you aren't stuck with wrong, incomplete, etc info as it's computer-based with changes constantly being made and intel corrected. The OE auto SI is often wrong, incomplete, missing stuff, etc, on current model year stuff.

Since I am an independent automotive repair shop owner, you wouldn't think this would be an issue, but we are a go-to for many area body shops for technical repairs, such as ADAS calibrations and programming concerns, and we have worked on more current model years already this year than usual. I just had a 2022 Audi E-Tron GT in, replacement of 1 forward radar unit, and we removed component protection, program, code, and finally perform the calibration on. That was no joke! Many European platforms only have SI (outside of R2R stuff) built into their scan tool platform. They are expensive to buy, expensive for scripts, cantankerous to use, and often require LSID credentials for full capabilities.

I think the OP is in over his head. Hopefully I am wrong. I admire his fortitude. I just wish he'd clean the throttle bodies as I suggested a while ago. The cost is minimal, it's easy to do, and it's part of any 8.1L "tune-up" in auto-world. Who knows, it may even fix something.

 

[1000 Islands]

If cleaning the throttle bodies doesn't help, if memory serves there may be minimum air rate screws behind a plug on each TB. Things wear out. Pop the caps and given them a nudge in. Make sure the counts are not 0 afterwards. That will set codes. I'm sure you can find that in the VP diagnostic service manual (sarcasm).

 

[Tipafew]

Just going back through this issue . . . you said it has been happening for a couple of years now. Was there something back then that may have caused it. Did it come on suddenly or gradually? both engines showing symptoms at the same time or one, then the other? Was there maintence done just before this issue appeared?

This is a situation where the ability to record the ECM data (Rinda Diacom) is valuable as you can play it back slowly and see what information is going out of its normal range.

If you cut just one throttle back quickly does just the one engine die ? . . . or do both engines die?

I'm just wondering if there is something funky going on with the engine voltage and a rapid change in the RPM is causing the ECM's to think they don't have enough voltage. (just a hunch)

Thank you. Excellent questions.
I bought it fairly late in the season about 5 years ago. I don't remember it quitting at all that’ll first season. The next year I started having the issue. That's why I brought up the question about why they say not to use

There have been situations where just one has died and others where both have died.

If cleaning the throttle bodies doesn't help, if memory serves there may be minimum air rate screws behind a plug on each TB. Things wear out. Pop the caps and given them a nudge in. Make sure the counts are not 0 afterwards. That will set codes. I'm sure you can find that in the VP diagnostic service manual (sarcasm).

So interesting find today. Was cleaning the air intake and noticed that the throttle plates were partly open. Then realized that with the throttles all the way back that the cables were still holding the butterflies open on both engines. I know the computer is supposed to control idle and def not the cables! I backed them off so that they throttle plate could return all the way back to the idle stop and the butterflies fully close.
I DID NOT TOUCH the little set screw.

Dropped the boat in the water and both engines fired fast and when right to idle. They always take two tries to start so I was pumped.

They idled great but later while in neutral I revved them and both engines would get stuck at a really high idle like 1500 rpm.

Sitting on the boat now……. Hoping that maybe the computer needs to re-learn or something.
Fired it up again and same thing. Idles perfect but if I Rec them they won’t come back to idle. Exact same ok both engines.

 

[alldodge]

There is no re-learning
Remove throttle cables and place TB fully closed. Adjust cable so that cables just slide back on. Remove once again and turn barrel nut one more turn out so there is a slight pressure holding the Throttle plates closed

 

[Tipafew]

There is no re-learning
Remove throttle cables and place TB fully closed. Adjust cable so that cables just slide back on. Remove once again and turn barrel nut one more turn out so there is a slight pressure holding the Throttle plates closed

Yep that’s what I did. I used to race jet skis and build my own engines. I just treated it like I was adjusting throttle cables on those. It’s resting on the stop now instead of the cable. Will see….

 

[vroom ZOOM]

Thank you. Excellent questions.
I bought it fairly late in the season about 5 years ago. I don't remember it quitting at all that’ll first season. The next year I started having the issue. That's why I brought up the question about why they say not to use

There have been situations where just one has died and others where both have died.


So interesting find today. Was cleaning the air intake and noticed that the throttle plates were partly open. Then realized that with the throttles all the way back that the cables were still holding the butterflies open on both engines. I know the computer is supposed to control idle and def not the cables! I backed them off so that they throttle plate could return all the way back to the idle stop and the butterflies fully close.
I DID NOT TOUCH the little set screw.

Dropped the boat in the water and both engines fired fast and when right to idle. They always take two tries to start so I was pumped.

They idled great but later while in neutral I revved them and both engines would get stuck at a really high idle like 1500 rpm.

Sitting on the boat now……. Hoping that maybe the computer needs to re-learn or something.
Fired it up again and same thing. Idles perfect but if I Rec them they won’t come back to idle. Exact same ok both engines.

Try disconnecting the battery for a day and then hooking it back up, might not do anything since its an open loop system, but you could try. It really sounds like your IAC is not dashpotting. This is where I like the data logger graph to monitor tps, rpm, and iac position (idk about volvo, but on some motors, IAC "duty" does not refer to the actual position of the IAC, but rather how much it is moving... pretty useless IMHO in your case). I start the data logger, and run the boat so it acts up. You should see the iac open up as you rev up, and stay open as you slow down, until the motor gets the throttle closed signal from the TPS.

Generally at idle and about 20C I would want to see the IAC at about 30%. On some motors there is a way to set the IAC into service mode, which locks it in at the position where it should be at idle, and the bypass air screw (or throttle stop, if no bypass screw) is adjusted to get target idle speed. If your IAC is full open already at idle, there isn't much it can do to give more air to the motor when it slows to idle. that is why it runs at around 30% at idle, to allow a much larger range to open when the motor rapidly slows down.

For the issue where it wont return to idle, you need to watch the tps reading before and after revving it up. When you turn the key and the ecm turns on, it takes that tps reading as idle. Anything just SLIGHLTY higher (about 0.02-0.04 volts), and the motor is no longer in idle mode. As a result, the IAC opens up much further. When you get on the throttle, it always opens up, so when you snap the throttle shut, the IAC is already in the open position so the motor doesn't stall. For this issue, clean the throttle plates to ensure they are not sticking, and make sure there is preload on the throttle cable.

Sorry for it being so long, but i hope this helps

 

[Tipafew]

Try disconnecting the battery for a day and then hooking it back up, might not do anything since its an open loop system, but you could try. It really sounds like your IAC is not dashpotting. This is where I like the data logger graph to monitor tps, rpm, and iac position (idk about volvo, but on some motors, IAC "duty" does not refer to the actual position of the IAC, but rather how much it is moving... pretty useless IMHO in your case). I start the data logger, and run the boat so it acts up. You should see the iac open up as you rev up, and stay open as you slow down, until the motor gets the throttle closed signal from the TPS.

Generally at idle and about 20C I would want to see the IAC at about 30%. On some motors there is a way to set the IAC into service mode, which locks it in at the position where it should be at idle, and the bypass air screw (or throttle stop, if no bypass screw) is adjusted to get target idle speed. If your IAC is full open already at idle, there isn't much it can do to give more air to the motor when it slows to idle. that is why it runs at around 30% at idle, to allow a much larger range to open when the motor rapidly slows down.

For the issue where it wont return to idle, you need to watch the tps reading before and after revving it up. When you turn the key and the ecm turns on, it takes that tps reading as idle. Anything just SLIGHLTY higher (about 0.02-0.04 volts), and the motor is no longer in idle mode. As a result, the IAC opens up much further. When you get on the throttle, it always opens up, so when you snap the throttle shut, the IAC is already in the open position so the motor doesn't stall. For this issue, clean the throttle plates to ensure they are not sticking, and make sure there is preload on the throttle cable.

Sorry for it being so long, but i hope this helps

You are FULL of great info. Thank you!! I will play with this more over the holiday weekend and dig in deeper to some of the things you mentioned.

My idle on both engines bounces around 590-650. Its set to desired idle of 600 according to what I see on the techmate when the boat is at idle but if I have just the key on and engine not running the techmate shows desired idle speed of 668 which seems weird. IAC readings that I was getting at idle were around 105 when the idle was closer to 590 and 75 when it was closer to around 640rpm. I don't believe this is percentage though. With just the ignition on but engine not running the IAC shows 120.

I definitely have more stuff to look into. Sure seems IAC related.......It didn't stall on my once this weekend. I was trying to make it stall and the rpm would just drift down perfectly smooth to idle like they should. I love intermittent problems. One motor did still quit on me at start up though.