99 VP 4.3L back firing over 4000 RPM

[compman723]

I have a 4.3L VP that is back firing over 4000 RPM's. Anything below that it runs great and also idles good. It also seams when i push the throttle down to go a little more it doesn't get anymore power and is back firing. Fuel is good I am running 90 octane which is what the owner before me told me to run.

I haven't done the points and all that becasue I was waiting to make sure I get all the right parts. Does anyone have links to all the right parts for this motor that I should replace.

If anyone has any suggestions for this motor or also what fuel to use I am all open ears.

Thanks for all the help

 

[Don S]

Re: 99 VP 4.3L back firing over 4000 RPM

Volvo has never used points in a 4.3L engine. They have always been electronic ignition.
When was te last time you changed the fuel filters? Sounds like it's running lean at higher rpms. Not good.
Might also want to run the test in the link below.

http://forums.iboats.com/showthread.php?t=167561

 

[180shabah]

Re: 99 VP 4.3L back firing over 4000 RPM

And for parts, you could check out the "Volvo Penta parts" link at the top of this page.....

 

[compman723]

Re: 99 VP 4.3L back firing over 4000 RPM

Okay I will check the filter, well actually i will just replace it. It is also a little boggy getting going kind of like it needs a cleaning. Maybe I will take the carb off and clean it real good.

Does anyone have a picture of the gauge setup they used on a 4.3L VP?

I won't get to it till Friday and want to use it this weekend. Any other ideas that I could be ready for? What should be the correct WOT range?

Thanks for all the help

 

[compman723]

Re: 99 VP 4.3L back firing over 4000 RPM

Well been away for a few weeks and got to play with it again. The problem seams to go in and out, I have changed the distributer cap and the thing that spins inside there along with the fuel filter.

It really pops sometimes when I am under load and it seams if it starts doing it it will keep doing it untill i shut it off.

I have a strong feeling that it is the coil but another part of me thinks it is just a loose wire some where becasue it seams to pop every once in a while when I go over waves.

Anyone got any great ideas

 

[Don S]

Re: 99 VP 4.3L back firing over 4000 RPM

Did you do the fuel system check I posted earler in this thread?

 

[compman723]

Re: 99 VP 4.3L back firing over 4000 RPM

Thanks Don for the fast reply I am going to do that first thing. I forgot all about that. Is there a copy of the wiring diagram for this motor or boat floating around on the internet? The motor model is the 4.3GL PWTR

The only reason I ask is becasue sometimes when I go over bumps it pops or makes the noise it is doing and at the same time the depth finder 0's out and beeps. Also when i do trim the gauges fluctuate for a little bit and also the radio doesn't work.

If the fuel test checks out I think I am going to have to dig in because to me it sounds like a short somewhere.

What do you think

 

[Maclin]

Re: 99 VP 4.3L back firing over 4000 RPM

Instead of a short it sounds more like some ground wires or connections have corroded and need attention.

 

[compman723]

Re: 99 VP 4.3L back firing over 4000 RPM

Yea I could also agree with you on that one. Does anyone have any recommendations on points that could be the main cause or areas that usually have trouble. Or how many grounds there is that deal with the engine running. I know for sure that the neg cable coming off the battery is secure on the motor.

Thanks again

 

[180shabah]

Re: 99 VP 4.3L back firing over 4000 RPM

Start at the battery and clean the connections all the way through the harness(s). Just because a connection is tight, doesn't mean it is making good contact.

 

[compman723]

Re: 99 VP 4.3L back firing over 4000 RPM

working on a different problem but thought about this again, I was trying to look at the wiring diagram but was getting a little confused. If i wanted to cancel out all wires except what the engine is needed to run what wires would i need to put power on and also what ones to ground. I just really want to cancel out the possibility of having a short.

Or is this not the best way to do it?

Thanks

 

[cooter2506]

Re: 99 VP 4.3L back firing over 4000 RPM

Are we still investigating the backfiring issue?

 

[compman723]

Re: 99 VP 4.3L back firing over 4000 RPM

We are replacing a riser manifold gasket this weekend and I was thinking that was the reason it was back firing but a part of me still thinks there is a short or loose ground somewhere becasue I swear going over rough water would cause it to miss for a second.

I also got another thought today, what does the engine do if the knock sensor senses a knock. Does it delay a spark or something or with these engines should i not even know if the knock sensor is sontrolling it.

Another thought is i replaced the distributer cap and rotor. I wonder if they need a little timing done. #1 cylinder should be TDC when the rotor is pointing at cylinder 1 right? And if I am looking at the engine from within the boat #1 cylinder is towards the back and on the right hand side.

Sorry for all the dumb ?'s

Thanks again

 

[cooter2506]

Re: 99 VP 4.3L back firing over 4000 RPM

#1 plug is FRONT on right hand side. Yes at tdc rotor should be facing #1 plug on cap. I really feel you have a ground issue. Riser maifold gasket will not cause this problem. Are you using wing nuts on battery terminals. If you are change them to regular battery clamps. ut check every ground terminal. Follow every black wire you can find remove it and clean the terminal and also where it attaches to the block with a good stiff wire brush. 1-6-5-4-3-2 is also your firing order check that just to be sure. Starting at front of engine 1, 3, 5 on right 2, 4, 6 on left.

 

[compman723]

Re: 99 VP 4.3L back firing over 4000 RPM

Thanks for the great post!!! I will check on these things and get back to you... That is exactly the info I was looking for...

 

[cooter2506]

Re: 99 VP 4.3L back firing over 4000 RPM

Good point Bubba.

 

[compman723]

Re: 99 VP 4.3L back firing over 4000 RPM

I did the fuel system check last night and it was never gettin higher than 3 inches vacuum. There were very little bubbles going through that I could see but it seamed like they were so small that they wouldn't make a difference. Size wise they were about as small as I think they could be. I agree with everyone though that I think I have afuel problem. Maybe it is time to have the carb rebuilt. Is this an easy overhaul with a kit or should it be done by a professional? I am very good with engines just never done anything with boat engines.

 

[compman723]

Re: 99 VP 4.3L back firing over 4000 RPM

I also have the problem where I use the tilt trim at WOT and it will cause the Tach to jump and also the engine to sputter or misfire. The more I write about this seams that there is a bad ground that can't hold the power draw from the tilt trim motor and causes that.

Does anyone have any views on this, I will post my solution once I find it.

Thanks

 

[compman723]

Re: 99 VP 4.3L back firing over 4000 RPM

Well scrounging through forums determined to find the answer I think I did. The wires attached to the tach were completely loose as in the nuts on the studs were unthreaded leaving those wires a inch of play on the shaft. The reason I found this is that there are a few that have had the either bad Tach problem or loose wires on the Tach that cause the coil to be shorted out which in turn causes this at high RPMS when it is bumpier and to work perfectly fine sometimes and others not so well. The reason it hydro locked, which I had another thread about is because I think it cut out and stopped to fast.

Thanks everyone for your help and suggestions, this forum is full of answers. Sometimes you just have to dig. I will confirm this hypothesis and post the results and close up all the forums so someone else can find this use full at some point.