AQ131D Won't start and backfires

[Kris McCuller]

Hello all, I'm almost out of ideas and I'm hoping someone here can point me in a new direction of diagnosing this problem. I'm a novice working on a old boat with a limited budget so keep that in mind. Horrible combination I know....

Anyway so I've got a '88 AQ131D engine with a VP275 sterndrive that I bought used a few years back. She was running fine up until this season. When I took her out of winter storage and gave her an inspection I noticed that my upper bellows (around U joint) was cracked. I decided to work on it myself after getting $500+ estimates from some local shops.

It took me awhile but I pulled the upper gear box off and slid the shaft out, replaced the bellows, and put her back together. I then I set about doing some other regular maintenance. Fresh oil and filter for the engine and stern, reinstalled freshly charged battery, checked the plugs (could probably use some new wires but $$$), changed out the antifreeze, new water fuel separator, fresh fuel, hooked the fuel lines back up, and plugged up all the raw water drains and cleaned the filter. While I was doing this I noticed my impeller was in bad shape so I replaced that too. I know a lot of this should have been done at winterization, but what can I say... I got lazy.

So after all this is done I try to start it up and it cranks just fine. After a bit I see some fuel going into the carb (ran it dry for winter) and I think I'm set. After cranking a few more times it seems like its about to start but then I hear an INCREDIBLY loud backfire and the engine dies. This is all it has done since: crank, backfire, and die. I've been working on diagnosing the problem for awhile now and I've just run out of ideas. I ran fresh fuel from an external tank, checked that the distrib was pointed to plug 1 on TDC (can't really adjust timing much without it running), rechecked spark, checked compression (one cylinder is low but acceptable range, same as last year)....

The only other thing I can think of is drive shaft alignment. I didn't mark the shaft's position when I pulled it out and I know it rotated while I was trying to reinstall the gear box. Could this be causing my issue? Any ideas on how to fix? Any of you boat geniuses have other things for me to look at?

Any advice you can contribute would be greatly appreciated.

 

[alldodge]

Hello all, I'm almost out of ideas and I'm hoping someone here can point me in a new direction of diagnosing this problem. I'm a novice working on a old boat with a limited budget so keep that in mind. Horrible combination I know....

Anyway so I've got a '88 AQ131D engine with a VP275 sterndrive that I bought used a few years back. She was running fine up until this season. When I took her out of winter storage and gave her an inspection I noticed that my upper bellows (around U joint) was cracked. I decided to work on it myself after getting $500+ estimates from some local shops.

It took me awhile but I pulled the upper gear box off and slid the shaft out, replaced the bellows, and put her back together. I then I set about doing some other regular maintenance. Fresh oil and filter for the engine and stern, reinstalled freshly charged battery, checked the plugs (could probably use some new wires but $$$), changed out the antifreeze, new water fuel separator, fresh fuel, hooked the fuel lines back up, and plugged up all the raw water drains anusing the same stuff.d cleaned the filter. While I was doing this I noticed my impeller was in bad shape so I replaced that too. I know a lot of this should have been done at winterization, but what can I say... I got lazy.

So after all this is done I try to start it up and it cranks just fine. After a bit I see some fuel going into the carb (ran it dry for winter) and I think I'm set. After cranking a few more times it seems like its about to start but then I hear an INCREDIBLY loud backfire and the engine dies. This is all it has done since: crank, backfire, and die. I've been working on diagnosing the problem for awhile now and I've just run out of ideas. I ran fresh fuel from an external tank, checked that the distrib was pointed to plug 1 on TDC (can't really adjust timing much without it running), rechecked spark, checked compression (one cylinder is low but acceptable range, same as last year)....

The only other thing I can think of is drive shaft alignment. I didn't mark the shaft's position when I pulled it out and I know it rotated while I was trying to reinstall the gear box. Could this be causing my issue? Any ideas on how to fix? Any of you boat geniuses have other things for me to look at?

Any advice you can contribute would be greatly appreciated.

:welcome: to iboats

Not a Volvo dude but all engines run using the same stuff. Backfire, timing is off either by something moved or broke. Make sure you are starting with number 1, and then check firing order 1-2-4-3. If that is good, have someone crank the engine while you move the distributer slightly one direction then the other.

Edit: change from 8 to 4 cyl, told ya I,m not a Volvo dude

 

[dennis461]

Did you connect a strobe light to the distributer to make sure ignition fires regularly during cranking?


Check the distributer first.
Pull the cap off and see if anything rusted up.
Make sure point open and close with your finger (no need to run engine yet).
Clean the points with some cardboard, like from a cereal box.
Check inside the cap for spider nests.

Next, a little trickier.
Crank the engine for a bit.
Stop cranking, ignition off.
Remove the top of the carb and see if there is fuel in the bowl
If you have the PA44 carb, you can see if the float move freely.

On these motors, it most often is one of these two issues after winter IMHO
Bigger problems are discovered while boating; snapped timing belt, blown head gasket,...

 

[Kris McCuller]

Apologies some unexpected family obligations conspired to keep me away from working on the boat this weekend. Thanks for the advice, I didn't want to leave you guys hanging.

So I've checked and under the distrib cap seems pretty clean, no rust or gunk. I know its pointed to the first spark when the flyweel mark is set on 0. I'll try playing with the positioning. Hopefully it didn't get off so badly that it's the wrong stroke. I'll check out the points next time I'm able to carve out time to work on it. The bowl is definitely getting fuel. I already checked that as part of my earlier diagnostics.

Nobody commented on my concern that I'd rotated the shaft while working on the gear box. Could this cause the issue? I'm worried that I need to take the gear box back apart and try rotating the shaft until I can get it aligned again....

 

[PiratePast40]

Your concern about the drive shaft being rotated, or something like that, is totally unfounded. It's irrelevant. It's just a drive shaft, nothing magic about the position. If the upper gearbox goes on, then the shaft is aligned. It's U-joints on a shaft, not a gimbal bearing, .

You can check the timing while cranking the engine. If you're going to be working on the boat, might as well pick up a timing light and dwell/tach meter now. You'll need them. You have some good advice above. Just remember the basics of, fuel, spark, and timing. The timing light will tell you if you have spark from the distributor to the plugs. You should pull at least one plug to verify that you have a strong blue spark. Start there to see what you have.

When things aren't working it can be frustrating, just stick to the basics and verify one thing at a time.

 

[jerryjerry05]

Timing's off somehow.
just a couple of teeth off and it's an anchor.

 

[Kris McCuller]

Thanks, another buddy of mine recently told me the same yesterday. If the shaft had turned it wasn't an issue since the rest of it (timing, cam, piston, ect) would have advanced with it.
I'll recheck plugs and timing. Thanks guys.

 

[dennis461]

Have you done everything I posted?

 

[gator fan josh]

Double check that you didnt get any of the plug wires crossed while you were checking the plugs. Verify the firing order at distributor and follow each wire to its cylinder.

 

[500dollar744ti]

Make sure to see it the timing belt is turning and check if there are any teeth missing. I don't know about the boats but on the cars we replace these timing belts every 5 years or 50,000 miles.

 

[axisg]

x2 on the timing being off. My bet would be the timing belt jumped a tooth. Check to see if its stretched and that the tensioner it taking up the slack. You can count the teeth and re-set it but for the cost ( like $20 ) I would just replace the belt as it will have all the marks on it. Reasoning is that Backfire occurs when the Intake valve is still open during the compression stroke. If it ran fine before and have not made any changes then I would start there. If you pulled the wires off then make 100% sure you have them back in the correct firing order ( I have seen them run with the 1&2 plug wires crossed ). As mentioned above you may be able to get it to run my moving the distributor but it likely wont make any power. Good luck