pcm 351 reverse rotation only running on 7cyl

[v12mac]

I am in the process of waking up a 351 ford inboard in a 1984 ski antique. The boat wasn’t running right then put out to pasture for around a year. <br /><br />I have replaced plugs, coil, cap & rotor and it fires right up but it only seems to be running on 7 cyl. I have pulled the plug and there is spark, compression is around 120 psi on a leaky gauge. I am stumped. Have I been working on 2 strokes too long?<br /><br />Points were removed and a kit with the magnet and sensor was installed years ago.<br /><br />Could I have mixed wires up on the cap? This is a reverse rotation motor and I am having trouble locating a diagram for the wires but I think I have it right since the motor looses rpm when I pull each wire accept the one cylinder.<br /><br />One other thing all the other plugs seem very dirty after only 10 min or so of total run time. <br /><br />Mac

 

[Haut Medoc]

Re: pcm 351 reverse rotation only running on 7cyl

1-8-4-5-6-2-7-3....10* btdc<br />Ya can't have one wire out of place...<br />If ya got one, ya got two!<br />The dist. rotation & wires are still ccw....<br />Spark at all plugs?....<br />When was the last time the ign. wires were changed?...<br />They don't last forever.....JK

 

[v12mac]

Re: pcm 351 reverse rotation only running on 7cyl

Thanks for the reply. I tried swapping a wire from a cyl that is firing with the one that is not firing and it didn’t change how the motor was running.(the cyl that I put the suspect wire on ran fine) So in my head I eliminated the possibility of a bad wire, is that a bad way to approach this?<br /><br />With the pull a wire while the motor is running and see if it runs worse technique I have found only the one cylinder is not firing.<br /><br />I did find a PCM manual on line and it states that the gap should be .038 on the plugs I have them at .045 on the parts shop advise. Could this cause the plugs to fowl out in 10-15 min of run time on the trailer?<br /><br />Why are all my plugs so dirty after such short run time?<br /><br />Mac

 

[DJ]

Re: pcm 351 reverse rotation only running on 7cyl

Switching plug wires around tells you nothing.<br /><br />Do you have a vacuum guage? That will tell you something.<br /><br />A static compression test, is just that. Your reading is a little low. A "leakdown" test will tell you more.<br /><br />I'll bet you have a valve issue or a leaky intake manifold.

 

[Haut Medoc]

Re: pcm 351 reverse rotation only running on 7cyl

Gap should be .030, ta least for AC or Champion....<br />That could contribute to the fouling problem...<br />But I would look at the choke to see if it is operating properly....<br />Have you checked the timing?<br />Have you isolated the dead cylinder?<br />When you say "not firing", you mean that there is no change when you pull that wire? <br />Get a spark gap tester & check every wire or just get a new set of wires....<br />If you are getting spark to the suspected cylinder, then your problem is mechanical.....<br />A compression & leakdown test is in order....JK

 

[paulrfrancisco]

Re: pcm 351 reverse rotation only running on 7cyl

Broken spark plug, or it was dropped and the gap closed up and not noticed maybe?

 

[v12mac]

Re: pcm 351 reverse rotation only running on 7cyl

Dead cyl is #3<br /><br />How can I confirm a leaky manafold? This motor has seen LOTS of salt water time. The exhaust manafolds look like the cannons at fort jefferson! (Very rusty chunks falling off) but this thing has run great for years like this.<br /><br />How can I check for a valve problem? What would be the symptoms?<br /><br />I can't believe how lost I am on a V8 I have been tinkering on outboards too long!<br /><br />Mac

 

[Haut Medoc]

Re: pcm 351 reverse rotation only running on 7cyl

I would do a vacuum test like DJ says....<br />It will tell you alot....<br />You should read 17-21 @ idle....<br />If your exhaust manifolds have chunks falling off of them, the insides can't be to good either....<br />You are on borrowed time with them.....JK

 

[Haut Medoc]

Re: pcm 351 reverse rotation only running on 7cyl

look at this

 

[v12mac]

Re: pcm 351 reverse rotation only running on 7cyl

Cool page! It looks like I am off to the tool store!<br />Mac