View Full Version : Firing order

10-27-2004, 09:54 AM
I started the engine work on my recently purchased '85 S&S with the 351 PCM last night. First on the list was to replace the carb with a remanufactured unit from Skidim. While doing that, I noticed something funny about the firing order - The PCM manual states that for a left hand rotation engine (which is standard, right?), the firing order should be 1-3-7-2-6-5-4-8. Instead, it's 1-8-3-2-7-4-5-6. Now, correct me if I'm wrong, but to check how the previous owner has the firing set up, I look straight down at the distributor while standing over the engine and begin counting at the upper right and continue clockwise, right?

The other thing that was noted during the mechanical check was that the engine was only firing on 4 cylinders. This could obviously be why, but in a way I'm surprised the engine is even running with the firing order off, even though there are probably other configurations which would allow the engine to run (other than the factor firing order).


10-27-2004, 11:42 AM
The #1 cyl is the front LH Cyl. Wherever this wire is, start there and go clockwise. Can't remember if FOMOCO engines are 1-3-5-7 on the left side or 1-2-3-4. Firing order s/b stamped on the intake and plug # indicated on the dist cap (#1 at least). Ford has had several firing orders for their small blocks over the years, so I don't know which one is correct for your motor, but there are alot of guys on here w/ the same era boat as yours. I'm sure you'll get the info.
If you have more than 2 plug wires out of order, it will not run. If you boat is firing on 4 cyl only and actually starts and throttles up at all, I would suspect that the dist cap, wires, plugs, or all 3 are shot and that you have the right order, just a serious need for a tune up.
How do you know that its only sparking on 4 cyl? Did you hook up a timing light to each plug wire? Even if the order is off, you'll get a spark through each wire.
It is possible that if the engine has had a new timing chain, that the cam and distrib are 180deg out and mayber someone compensated for this by changing the firing order at the distrib, not very likely though.
Hope this helps.

10-27-2004, 01:19 PM
The cyliner arraingement is cast intot he intake manifold, on each runner right where it meets the head. The firing order also is cast into the intake.

That's pretty much all the info you need.

You can make any location on the dist. #1. It doesn't matter which one you chose, as long as the rotor is pointed toward that location when the engine is rotated to #1 TDC comprssion/firing. Likewise it doesn't matter if the dist is installed "180* out" as long as you verify the orientation of the rotor whe the engine is at #1 TDC and then make THAT location #1 on the cap. Once you do that, then follow the firing order around the cap in the direction that the rotor turns when the engine is running. You can slap the dist. in the engine in any direction you like. Then you can rotate the house any which way you want. Doesn't matter. All that matters is that you verify the rotor location at #1 TDC, and make the corresponding post on the cap be #1. Now from an appearance stand point there is a better way and a worse way to do it, but you can figure that out for yourself bu tjust looking at your engine/wires, etc.


10-28-2004, 09:43 AM
Thanks for the info guys.......I verified that the Ford distributors turn counterclockwise, but that still means the firing order is not per the factory manual. The cylinders are numbered 1-4 on the right side starting at the front of the boat and working towards the stern. Then 5-8 on the left side. I verified this by the numbers on the exhaust manifold.
When I had the boat checked out, prior to buying, the spark plugs were pulled for a compression test, and 4 of the 8 had liquid gas on them, indicating they weren't firing. Our guess was it's the wires as they look pretty ragged. It has a new distributor cap/rotor, I replace the contacts and condensor last night; plan to replace the plugs/wires too. With all that done, and a new/reman. carb, hopefully it will run like a champ. Since the boat fired up and seemed to run okay (even though it was only on 4 cylinders, we think), I don't plan on changing the firing order back to what the manual says. If I did, could I cause any damage?

Thanks again for the input.

10-28-2004, 09:59 AM
If it runs smoothly, or relatively smooth, the firing order has to be right. Based on the two firing orders you gave, I think they're too far apart for the engine to run if they one that was specified is correct.
Get the serial # off your block and email Indmar. They s/b able to verify what's correct. Or try calling them. I've had good luck talking w/ the tech's there when I had an engine issue. If the order is off and you run it, the engine internals will hold up ok, but you run the risk of backfiring and damaging the carb or mufflers.

10-28-2004, 10:51 AM
If the manifold hasn't been changed, use the firing order cast into the runner. The wires going to the distributor will let you know where to orient it, but you can be off by any multiple of 60 degrees, since the shaft end is hex shaped on a Ford. The #1 cylinder is the one closest to the plane of the crank pulley and Ford uses 1-2-3-4 on that side with 5-6-7-8 on the other. How did the compression test go? If the cylinders are wet, it'll be artificially high. Bad compression would keep the gas from burning completely and cause the plugs to foul. Look for bad compression on adjacent cylinders, especially 2 & 3 and 6 & 7. You can check the rotational direction of the motor by looking at the prop since it sounds like you didn't take it out. If the motor is cranking backward (hey, it's possible, though unlikely and I have heard of this happening), the starter may be wrong if it has been replaced recently. When you replace the wires, use good ones. With all of the moisture under the motor box, you want the wires to be well insulated. Crank it over with no plugs to clear out the gas in the cylinders and make sure to change the oil ASAP. If you sniff the oil, it will probably smell like gas.

10-28-2004, 11:59 AM
So Jim, are you saying I should go ahead and switch the firing order back to factory? I'm worried about doing any damage. I'll check the prop to confirm which way the engine is turning.
The guy I bought it from was the owners son, who isn't a boat guy at all. What I'm worried about is when he changed the cap/rotors (the oil was changed too) just before I bought the boat, he may have put the wires back in the wrong spots. It would be a one in a million if he did that and it still ran okay. When it ran, the guy that checked the engine noticed the slight misfire and slightly odd odor from the exhaust which indicated it wasn't firing on all 8. I was actually surprised since what he noticed was barely noticeable to me (i'm not an expert on engines, but not a beginner either). It seemed to throttle just fine. I was thinking about giving it a nice tune up, and then seeing how it ran before I sort out the firing?

Compression: 1=140, 2=135, 3=140, 4=140, 5=120, 6=125, 7=135, 8=130.


10-28-2004, 12:10 PM
It is really easy to check which cylinders it is firing on. Start it up, and pull off each spark plug wire (off the plug is best to prevent cross fireing) one at a time. If there is no change in idle, something is up with that cylinder. Also, another way to check the direction of the rotation is take of the dist cap and roll it over.

10-28-2004, 02:43 PM
I would verify the firing order before I changed anything. If the wires are old and ratty, change them one-at-a-time and see if it corrects the problem. If it runs well and misses occasionally, it's probably in the right order.

Is it running on 4, as you said in your first post, or just not on all eight? Big difference.

If you do remove the plug wires, while it's running, be sure to use well insulated spark plug wire removal tool, and not just bare-handed. Unless you like being shocked. Do you have a timing light? Verify that you have/have no spark on all cylinders and if you want, attach a spark plug to each plug wire and ground the plug to test for spark. If you have bad wires or wire ends, you won't. You can also buy a spark tester at an auto parts store.

10-29-2004, 09:49 AM
Thanks again for the input guys; I'm going to test each existing wire this weekend. I bought new wires last night and will install them, but I want to check the old ones first to confirm how many are actually firing.

When the plugs were pulled, 4 had liquid gas on them. It was 2 pairs - 2 plugs next to each other on one side, and 2 plugs together on the other side - but I don't remember exactly which ones. The guy thought it could be 1. old wires, 2. automotive carb (which I've already changed), 3. the fact that the boat had been sitting for 3 years.

The contacts were also worn out, so that along with the condensor has been replaced.

Hopefully I'll get it running again in the next week or so.

10-31-2004, 05:53 PM
Well, I've been testing for a spark and can't get one anywhere. I've checked all the wires (to each cylinder) with all combinations of new/old plugs and new/old wires. So I went further back to the coil and couldn't get a spark from the coil wire either. I pulled all wires off the coil, tested resistance, and got 2ohms on the primary and about 10,000 ohms on the secondary; higher than what the manual says, but if it was shot, would it read 0 ohms? I also noticed that I'm only getting 5v at the coil with the ignition switch on - could this mean bad ignition?
This is somewhat stumping me as I haven't done anything electrically to the engine, but I guess anything can go bad at anytime.

Any suggestions?

10-31-2004, 08:36 PM
You said it sat for a few years- you probably have some corroded contacts. I would also check/reset the point gap/dwell and see if you get spark after that. You might want to check the voltage ahead of the ballast resistor. If it's less than the battery voltage, it needs to be fixed. Loosen and retighten each connection in the path from the battery to the dash, then from the dash to the motor. It sounds like a PITA, and it is, but after sitting 3 years, don't expect everything to be clean. Once you have at least 12Vdc before the resistor, assuming the points, condenser, cap and rotor are OK, it should run. Did you replace the coil wire too? I have seen a lot of boats that ran fine one minute and wouldn't start right after shutting it off because of a bad coil wire.

10-31-2004, 10:01 PM
I was thinking along those lines as well; I began testing the voltage of each connection starting at the battery. I found that when I disconnected the resistor, I was getting 12v on the battery/ignition side (wire), but when the 2 wires were hooked back up to the resistor, I would get 10v on the battery side and 5-6v on the coil side. So at this point I'm assuming it's the resistor. Plus, when I pulled the resistor off, the back looked like powdered sugar and was crumbling off - you could see the resistor wires. Becuase of the corrosion on the resistor studs, I was also having a hard time getting continuity. I'm going to order a new resistor and hope that's the problem. I have not replaced or checked the coil wire and won't unless the new resistor doesn't solve the problem.

Thanks a lot for your input, JimN! Once I get it running again, on to cosmetic questions! Carpet and interior is out, swim platform/brackets off for repairs and refimishing, rub rail off, steering cable out, fiberglass repair underway on the bow. Luckily I'm in the putting it all back together phase......

10-31-2004, 11:03 PM
With the cap off, turn the key on and see if the points are closed or open. If they're closed, bump the starter till they're open, or insert a peice of cardboard so they do open. The voltage should go up. Unless the resistor is actually falling apart, you can just check it for resistance, out of circuit. If it's stable and doesn't change when you wiggle the wires, it's OK. If you just want to replace it anyway, you should be able to find it at any auto parts store. Take the old one in and they can match it up for you. Or, if the resistance value is legible, you can get one at Radio Shack, as long as it has the correct wattage rating as well as the resistance.

If you have a multi-meter, you can check the coil wire for resistance. If you can wiggle it and it doesn't vary, it's OK. If it shows open and then continuity, get a new one (there should be one with the new set of spark plug wires, anyway).

11-01-2004, 12:58 AM
Points open or closed, the voltage on either side of the resistor is the same. What confuses me is that I get 12 volts on the wire from the battery/ignition when it's not connected to the resistor. But when I connect it to the resistor, that side registers as 10volts. We had trouble with continuity when we first tested the resistor, but cleaning the studs with a wire brush solved that. So that made me think the resistor was okay - except for the voltage (from 12v disconnected to 10v connected) change on the battery/ignition side.

I checked continuity of the coil wire and it seems fine.

11-01-2004, 05:57 AM
If you have cranked the motor for a long time up to now, disconnect the fuel line to the carb.

Attach the meter to the coil (+) post and turn the key on. You should see at least 12V at that time. If not, there is a problem with the ignition lead(s), possibly the safety switch. You may want to pull the ignition switch and see if the screws are tight and clean. Then, measure the resistance from the ign switch to the coil (+).

When you measure the voltage to the coil (+) while cranking, you should see about 9.5-10.5 volts.

Are you measuring the voltage only at the input side of the resistor with the key ON? You want to measure at the output side. The points only get about 10V when the motor is running. The ignition lead goes through the resistor so the points don't burn. The other lead to the coil (+) is from the crank lead on the ignition switch and this sends voltage directly, which is lower during crank due to the voltage drop caused by the high current draw of the starter.

11-01-2004, 09:54 AM
Thanks again, JimN. I'll try this tonight.

I've been testing both the input and output sides of the resistor - when both wires are connected, I get 10V on the input side and 5V on the output side (as well as 5V at the coil stud). When I disconnect the wires, I get 12V on the wire from the ignition (on the input side), and continuity on the resistor. This makes me wonder if there is a short or bad connection somewhere downstream of the resistor.

I'll pull the ignition switch tonight and test it.

11-02-2004, 09:49 AM
Well I began isolating pieces in between the resistor input and the distributor. It wasn't making sense to me to have a problem with the ignition switch if I was getting 12v on the input side of the resistor (with the wire disconnected from the resistor). I disconnected things one by one until I found that every time I disconnected the main coil wire from the distributor, 12v would show up on the + side of the coil. So I isolated the problem to the distributor. I had put the old points/condensor back in since I knew they were working when I bought the boat. After resetting the point gap 2-3 times, I suddenly had spark again! I wasn't doing anything different, but maybe you were right, JimN; the connections simply needed a little attention/cleaning. So I tested for spark on all plug wires and was successful - changed plugs/wires and tested again for spark. Only think keeping me from running now is pulling it out of the garage and hooking up a water source! Hopefully this weekend so I can get it winterized...........

Thanks again for all your help.

11-02-2004, 09:56 AM
Just for grins, attach the condenser to your meter and see if it's shorted.

11-05-2004, 09:59 AM
Condenser checked out ok.............I talked with PCM yesterday and they couldn't explain any reason why the firing order would be any different than what they specify. So with this firing order: 1-6-5-4-7-2-3-8, new carb, plugs, wires, condenser and points, I attempted a start - to my amazement, it fired right up!! However, it ran so rough the whole boat rocked back and forth. For grins, I changed the firing order to factory spec and couldn't get it to fire. So back the firing order went. Factory says it should be 1-3-7-2-6-5-4-8.

After I let it run for a bit, I pulled the plugs to see if I could tell which cylinders were firing. 1, 2, 7 and 8 had liquid on the plugs and didn't look like they had detonated. Cylinders 5, 6 looked like a fairly clean burn, but 3,4 were black. So I'm wondering if the timing could be so far off, it would only run on 4 cylinders? I guess that's my next step - check the timing, and/or turn the engine to TDC and check the positioning of the rotor vs. #1 wire?

Oh, I also confirmed that there is spark on the #1 wire.

11-05-2004, 11:08 AM
If the timing is too far off, it will try to fire on cylinders where a valve may be open or the piston is in the wrong position. Was the liquid gas or water? If it's water, you may have a bad gasket(either intake or head) and this needs to be checked out.

Did you check for right or left hand rotation? Look at the prop. The motor should rotate in the same direction. Was the starter replaced? Could be the wrong one and it's the opposite rotation to what you need. Again, the bank on one side of the motor is 1-2-3-4 and the other is 5-6-7-8 with the distributor rotating counter-clockwise.

You need to verify timing ASAP. Remember, the crank goes around twice for every rotation of the cam, so when the #1 piston is at TDC, it could be 180 degrees off. You need to make sure #1 is at TDC Just before the intake valve opens and the piston will start going down to suck in the fuel/air misture.

You didn't say anything about backfiring, either from the exhaust or the intake. When you're checking for spark and timing, pull the plugs so you don't have unburned gas getting into the cylinders, flooding it and seeping into the crankcase. This dilutes the oil and it won't provide much lubrication when it finally starts. It's also a lot easier on the starter.

11-05-2004, 12:45 PM
Thanks, JimN.

I'll verify timing this weekend. The liquid actually looked more like oil - not a good sign.
The guy at PCM was worried about rotation too: Based on engine markings, it should be left hand rotation. While looking at the front, it rotates right, or from the prop it rotates left. This all seemed to check out. I ran the engine without water for 10-15 sec. intervals to make sure it wasn't sucking water into places it shouldn't (if it was running backwards).

It was definitely sputtering, with some minor backfiring under the "weird" firing order - only near idle. It would not idle on it's own, I had to give it a little gas to keep it going. When I switched to the factory firing order, it never fired, and did backfire through the intake once. That's when I decided to change it back to the "weird" firing order.

The marks on the crank pulley are "ATC" and "BTC" - where do I set the pulley for top dead center? Then I can check to make sure the rotor lines up with the #1 wire. I just remembered that the previous owner changed the rotor/cap - could he have installed the rotor in a different position?

You mentioned pulling the plugs while checking timing - you mean only the ones not firing? And run the engine? Will this shoot gas out those plug holes? Or will the starter turn the engine fast enough to check timing?

11-05-2004, 03:00 PM
If you think you have oil on the plugs, put some cardboard around the motor so you can crank it over and blow some of whatever is in the cylinders, out. That way it doesn't get all over the boat. Clean the plugs and try it again.

BTDC is before top dead center, and ATDC is after. TDC is the 0 mark. You will need to pull the plugs to turn it over by hand, using a wrench on the crank pulley bolt.

Once the plugs are out, put your finger over the plug hole on #1 and manually turn the crank with your wrench, in the direction the motor is supposed to turn. You'll be turning it so the BTDC side leads the way. When the crank turns, it will have suction on the way down, compression on the way up each time, but what you want to do is find out where the cam is. When it creates pressure on your finger, keep it in the plug hole so that when you rotate the crank to the top, you hear the pressure release through the intake. You can use compressed air for this, blowing in through the spark plug hole (don't use high pressure, it's not necessary), listening for the air to come out of the carb. At this point, the next time you see it at TDC, that's where you'll be referencing the rotor for the spark timing. Now you want to take the cap off and see where the rotor is pointing. It should be at #1. If it's not pointed at the #1 plug, you'll need to rotate the distributor so it is, or if it's too far off, you may need to lift the distributor out and rotate the shaft it so it lines up with #1. You might be able to just move the #1 plug wire on the cap to get it lined up, then reinstall the other wires in the correct firing order.

The shaft has a hex for driving the oil pump, so you may need to turn the oil pump shaft if it doesn't want to go in all the way. Once you get it apart, you can look in the hole and you'll see what I mean.

As I said before, the crank rotates twice for every rotation of the cam. For the future, you may want to mark the cylinder # on each plug wire boot at the distributor for reference.

When I said to pull the plugs, I mean all of them. You don't need them in to crank it over and check timing, the spark will still be there. If it takes a long time to get it timed right, it won't kill your battery or starter as easily. When it starts to slow down when you crank it over, stop for a while so the starter get a chance to cool down. You can also put a charger on it to top off the battery.

11-05-2004, 04:33 PM
Jim's done a good job of explaining how to set the distrib in the correct position, but if you still need help, it would be beneficial to go check out a repair manual from the library and look at the applicable sections, Distributor, timing chain, firing order,timing, etc.
Another idea, the timing sprockets may not be lined up, either jumped a tooth, or timing chain was replaced incorrectly and sprockets not aligned right.
I feel your frustration. I had an 84 Bronco (351) that I replaced the engine in w/ a '78 longblock. There was not a factory firing order for any Ford V8 that worked. Finally found a firing order that worked, by trial and error and then had to slot the distrib clamp bolt to make up the difference in cam timing between the 78 engine and the 84 computerized ignition. PITA!

11-05-2004, 07:10 PM
Wow! Thanks guys!! I'll digest this tonight at the local watering hole and get started tomorrow!

11-05-2004, 07:48 PM
Thanks, Thrall- I forgot to mention the timing chain.

IOKUA- You may be able to find out the valve timing from PCM or Indmar. That way, it you decide to beg, borrow or steal a timing wheel (also known as degree wheel), you can see if the valves open and close when they should. This wheel is like a 360 degree protractor that attaches to the crank pulley and the 0 mark mates with the 0 on the crank pulley.

Another thing I was just thinking about- this boat sat for 3 years, right? It's possible that the gears on the distributor and the cam rusted together and when the motor was run for the first time, the teeth broke off. This will definitely F up any attempts to time it and get it running. You'll need to pull the distributor and look at its gear teeth, then look into the motor where the gear is mounted on the camshaft. Manually turn the crank so you can see the condition of the gear teeth.

If this happened, you'll need to remove the oil pan to get any metal pieces out of the oil. They can mess up the oil pump if they're small enough, then they move on to the rest of the motor and mess up other things. It would be easier to work on if the motor is out at this point and the cam may need to be replaced (or at least the gear on it replaced). If this was my boat and I was done for the year anyway, it would be a great time to consider some power upgrades, too. Cams are cheap, if the heads are coming off, they can be freshened up, maybe some other toys, as well. If you can do a lot of the work, you can have a nice motor with more balls than it would have had otherwise. Plus the added bonus of knowing you did it.

I'm not trying to be all gloom and doom, but I worked on a motor that sat for 3 years and this sounds like the same kind of torture I went through trying to time it.

11-08-2004, 10:04 AM
Well, again JimN, thanks a lot!

I had success over the weekend! Just as you suggested, I rotated the engine to TDC and pulled the dist. cap - lo and behold, the rotor wasn't anywhere near the #1 wire, or 180 degrees out! So I rotated the wire pattern so the #1 wire lined up with the rotor, keeping the "weird" firing order since it was running before. Well then it wouldn't start. So I figured I would try the factory firing order - I about fell out of the boat! Started right away and sounded great! Although I had to tell myself that my reference point (by sound) was when it was only running on 4 cylinders. So without a water source, and the fact that it was too bright outside to accurately see the timing light, I shut it down for now. I'm hoping all it really needs now is some fine tuning (timing, carb). Although your last post has me worrying a little. I'm still going to verify that it's running on all eight by checking the plugs after setting/checking the timing.

Now that I know it's running fairly well, I think I'll set it up for the Winter and work on the cosmetics.

Maybe in the mean time, i'll go ahead and pull the distributor and inspect it as you have suggested.

Thanks again for the help guys, If you're ever on the West Coast, you've got a ride!

This is all I can offer you for now:

11-08-2004, 11:09 AM
If you rotated the distributor 180 and it now sounds great, it may be OK. If you're going to remove the distributor anyway, look at the gear at the bottom for wear and damage. This can be replaced pretty easily. Good to hear that it sounds better.