Volvo Penta 8.1 issue

[km1125]

I would check actual manifold vacuum and compare with the readings. Is it possible you have a vacuum leak?

You do not have O2 sensors, correct? Is there any indication in the scan parameters that indicate "closed loop" vs "open loop"?

[av8or98]

Source of the post Clearly the STBD is not happy...what was your test rpm and were the engines completely warmed up ?....appears to be little higher fuel rate for one reason or another and the IAC seems like open too far for a warm engine at idle, but sometimes therde are other reasons.

First the easy stuff, were the flame arrestors off when you tested....are they both spotless clean, check the throttle plate and clean the throat and edges of the plate....check for gouges or sticking.

There used to be seals on the GM type map sensors that can go bad . Need to find out why it showed sensor bad but what I mentioned is good to do anyway, also if there is a vacuum hose from the manifold to the fuel regulator ,check it for fuel.

This was data taken right after start so the engine was still cold. MAP wasn't showing bad. I was trying to put things in columns in the post but it didn't turn out that good.
I was thinking a blocked flame arrestor as well. They were installed when the engine was running. I took the stbd off and I could see through it but it was dirty. Same with port.
Vacuum line from manifold to fuel regulator was clear-free of fuel.
I'll let the engine warm up and take the flame arrestor off for the next run.

[av8or98]

Source of the post I would check actual manifold vacuum and compare with the readings. Is it possible you have a vacuum leak?

You do not have O2 sensors, correct? Is there any indication in the scan parameters that indicate "closed loop" vs "open loop"?

I do not have O2 sensors and I don't see anything in the data that resembles closed/open loop. It is possible that I have a vacuum leak. Wouldn't know where to start troubleshooting that. There aren't many vacuum lines other than the one going to the fuel pressure regulator.

[bud37]

Source of the post
This was data taken right after start so the engine was still cold. MAP wasn't showing bad. I was trying to put things in columns in the post but it didn't turn out that good.
I was thinking a blocked flame arrestor as well. They were installed when the engine was running. I took the stbd off and I could see through it but it was dirty. Same with port.

Good, get that stuff clean and don't forget the throttle bore and plate.......I figured the engine was cold when it showed the iac's open that far and the fuel.....like a choke.....you need to get them up to running temp and stable before you will get any useable numbers.....watch the engine temp and air inlet temp and see how the iac's react while the engines warm up.....they should close down to a reasonable number as the fuelling drops accordingly.

Remember there are only two ways for air to get in at idle.....the Idle air port and around the throttle blades ....hopefully this volvo setup is like the merc mefi system I have some understanding of.

Well lets see what happens.....

[DanM]

Take a look at this thread. It may be related:
viewtopic.php?f=8&t=2805&p=16578&hilit=DanM#p16578

[av8or98]

Okay. I've cleaned the flame arrester and verified that the idle air port is clear. No nicks in the throttle body. Let the engine warm up and did a balance power check. Interesting results. #1, #4, #6, #7 had good drops and the others had slight RPM drops. That happens to be every other cylinder in the firing order. Again, all coils and wires have been swapped to the other engine. All plugs replaced. Computers have been swapped. It seems like the ECU is shutting down every other cylinder for some reason?

[bud37]

If at this point you have exchanged all the equipment from the good running engine with no change then it is something else here, but maybe the harness i the same though.......grounding and voltage in the control harnesses are very important....have you checked all the pins ?
What do the plugs come out like after it ran with the missing....is it not firing the plugs or is there no fuel.

Here is something I came across, may help a bit....I don't know if this applies to your year but....

https://www.justanswer.com/boat/5tc0z-v ... nning.html

[av8or98]

I haven't rang wires or checked the pins. That's a possibility for sure. Based on the link that you referenced, I'm wondering if the crank position sensor may not be picking up a signal like it should. The shop manual always states to check the ground first. Other than the main ground for the engine, is there a ground for the computer and fuse box? I looked at this quickly and didn't see anything obvious.
Plugs are wet when they come out.

[bud37]

Are all 8 plugs wet or certain ones........to me that would indicate not firing or gross over fuelling...but the over fuelling should be obvious in the injector pulse width data imo.
Past the harness/pins I really don't have any more ideas, sorry. Does the manual have a diagnostic/troubleshooting work tree ? Check the function of all the sensors on that engine, Have you tried to contact Volvo about this, maybe they have a recurring problem in older engines that presents itself in the manner you are seeing.....good luck with it I hope you can pick thru this and find the glitch.

[av8or98]

Hello again. I found the issue! After changing plugs, filters, swapping wires, coils, computers, compression check, checking fuel pressure, running countless diagnostic tests, etc. I went with my first guess...fuel injectors. I was hesitant because I thought it would require a lot more effort than it really did. It took about 15 minutes to pull them and 10 to put them back in. Pulled them all and had them flow checked and cleaned. No more rough idle, it makes full power, all good. Interesting thing is the flow test didn't seem that bad. Three injectors were "different" than the others with the worst having a 6% lower flow. Thanks for all the suggestions and help!