470 3.7L Exhaust flapper question - Engine performance

[nwboater45]

[FONT=&quot]I am curious to know that he effects the exhaust flapper has on the engine timing and performance. [/FONT]​

[FONT=&quot] [/FONT]​

[FONT=&quot]My situation is that I have a 1989 470, 3.7L, 165hp. I purchased the boat about 2 years ago and have been fixing/updating the boat and motor since. I believe the previous owner(s) did not know much about boats or motors and basically abused it. For the engine I have put new electronic ignition, rods & lifters, plugs, wires, etc. So I had finally got the motor to run very well and very responsive on the throttle. So anyways I have always had a slight tick in the motor. So through some threads in these forums I decided to check and replace the exhaust flapper. And not to my surprise the only thing left for a flapper was the bar going across the pipe. So I replace the flapper with the bar side up and ears pointing down like shown in the manual.[/FONT]​

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[FONT=&quot]Now here is the problem. The motor now runs like crap. Idles very rough and barely at all. It also has a loud noise in the back of the motor now which I assume is just the flapper working. So the question I have does the flapper great such a back pressure on the motor that I would cause this? I have checked the timing and it is set at 4 degrees and adjusted the timing to 650 rpms and it still sounds like its missing. I put the timing light on all spark plugs and they all are firing. I reset the idle screws and still no luck. The last time I shut the engine down it coughed and sputtered before quitting. I am at a loss on where to start next. I will check the compression again to make sure everything good there. So any help, thoughts, or ideas would be appreciated. What I really need it to hear another 470 run and compare it to mine.[/FONT]​

 

[Bondo]

[FONT=&quot]I am curious to know that he effects the exhaust flapper has on the engine timing and performance. [/FONT]​

[FONT=&quot] [/FONT]​

[FONT=&quot]My situation is that I have a 1989 470, 3.7L, 165hp. I purchased the boat about 2 years ago and have been fixing/updating the boat and motor since. I believe the previous owner(s) did not know much about boats or motors and basically abused it. For the engine I have put new electronic ignition, rods & lifters, plugs, wires, etc. So I had finally got the motor to run very well and very responsive on the throttle. So anyways I have always had a slight tick in the motor. So through some threads in these forums I decided to check and replace the exhaust flapper. And not to my surprise the only thing left for a flapper was the bar going across the pipe. So I replace the flapper with the bar side up and ears pointing down like shown in the manual.[/FONT]​

[FONT=&quot] [/FONT]​

[FONT=&quot]Now here is the problem. The motor now runs like crap. Idles very rough and barely at all. It also has a loud noise in the back of the motor now which I assume is just the flapper working. So the question I have does the flapper great such a back pressure on the motor that I would cause this? I have checked the timing and it is set at 4 degrees and adjusted the timing to 650 rpms and it still sounds like its missing. I put the timing light on all spark plugs and they all are firing. I reset the idle screws and still no luck. The last time I shut the engine down it coughed and sputtered before quitting. I am at a loss on where to start next. I will check the compression again to make sure everything good there. So any help, thoughts, or ideas would be appreciated. What I really need it to hear another 470 run and compare it to mine.[/FONT]​

Ayuh,.... I don't see it,... Unless ya somehow got the shutters jambed closed installin' 'em,....
Or,...
Maybe the remnants of the failed shutters are blockin' the flow downstream,.....
Pull the drive, 'n look up through the exhaust, ya might see 'em right there starin' at ya,....

 

[nwboater45]

Thanks Bondo......I will do a little exploring tonight. I send a shop-vac hose down the exhaust when I replace the shutter. However I doubt that would have picked up any large pieces. Worst case, can I take off the exhaust pipe without pulling the motor?

 

[stonyloam]

That tic may be a rusted out thermistor plug in the head, that is letting exhaust gasses escape from #4. When it is running (carefully) hold your hand behind the engine to see if you can feel the exhaust gas escaping. If that is it you can get a replacement from your local Ford dealer. 460 Ford thermistor plug.

 

[bfjou812]

Just curious, what is a "thermistor plug". I've never heard of that ,and I've been working on all types of engines for close to 40 years. Just wondering.............

 

[dozerII]

They are a tiny casting plug in the lower rear corners of the heads where the air injection tubes were installed for smog control

 

[stonyloam]

That's it! There is one in the front of the head too.

 

[nwboater45]

Thanks guys. I will have to dig into it a little more this weekend. Won't have any time this week. I did start and run it last night. Before hand I sent a piece of wire up both sides of the exhaust and didn't feel any obstructions. I may buy a mechanics cam and send it down the exhaust pipe if necessary. But I reset the timing back to 4 degrees and the carb to the suggested preset adjustments. Ran it for awhile and then adjusted the carb to run it at 600 +/- rpms. When I went to shut it off is coughed and sputtered real bad. And then on the restarts it was back firing through the carb. Not good. Back to square one. Also while it ran I was getting more and more white smoke (steam?) out of the exhaust. So not sure were to go from here. I did a pressure test last weekend. Pumped it up to 15#'s and it only dropped to 14# over a half hour.

 

[bfjou812]

They are a tiny casting plug in the lower rear corners of the heads where the air injection tubes were installed for smog control

Thanks, That's interesting ,I'll have to check the sets of heads I have here to see what you're talking about. Again thanks!!

 

[mr 88]

You can remove the exhaust elbow off without pulling the engine and check your exhaust flap to see if its jammed.

 

[nwboater45]

Thanks 88....It seems a little tight but I was able to get a visual on 3 of 4 bolts. Tonight I managed to do a compression check and got 160-160-140-140 not bad but a little concerned on 3 & 4. I was getting ready to redo the timing and broke a plug and the local auto shops didn't have them so it looks like I wait until this weekend.

 

[stonyloam]

You don't have to remove the elbow, you can loosen the exhaust elbow bellows and take them off to look inside.

 

[mr 88]

There are two types of exhaust elbows on the 3.7 and if you have the one that is U shaped the only way to see inside is to remove the elbow unless your a contorsionist and have mirrors along with mechanical fingers and or a boroscope.

 

[stonyloam]

Doesn't everyone have that LOL? He has an 89, so should be the same as my 87. I was able to remove the bellows the get to the shutters. On the earlier models, yeah that would be a different matter..

 

[nwboater45]

I don't think there is anything in the pipe. I probed with a wire from the outdrive side and didn't feel anything. I am sure any small items would have been blown out and I would be able to feel any larger items. I just think it would naturally sound different with shutters then without. I put in new spark plugs, reset the timing so now it is running better. But now I have another issue (par for this boat). I am getting a backfire through the carb on shutdown. I will try to research this in the forums and if not I will start a new thread. Thanks.