Rpm's Increase When Plug Wire Is Pulled

[dblanton]

Does anyone have any suggestions as to why when the plug wire on #1 cylinder is pulled while the engine is idling the rpm would increase; pulled on #2 little or no change in rpm, pulled on #3 engines dies?
Each plug wire was placed back on the spark plug before pulling the next one.
I have checked the position of the spark plug wires and they are correct, (the plug wire on #1 coil is connected to #1 cylinder, #2 coil to #2 cylinder and #3 coli to #3 cylinder. I have checked the position of the primary coil wires and all three coils are correct according to the wiring diagram in the manual.

 

[Pony]

Re: Rpm's Increase When Plug Wire Is Pulled

Are you using a tach to determine this rpm increase, or only your ears?

I am just a novice, so others can help you much better than I could, but my first inclination is that the motor is only running on one cylinder, that one being #3. You can idle without all your cylinders firing, and the motor may even sound okay. If it died completely when you pulled #3.....then I think its prolly just running on that one.

 

[dblanton]

Re: Rpm's Increase When Plug Wire Is Pulled

I am using the Tach for the RPM reading

 

[Chris1956]

Re: Rpm's Increase When Plug Wire Is Pulled

Are the plug wires on the correct cylinders? (is the firing order correct)

 

[iwombat]

Re: Rpm's Increase When Plug Wire Is Pulled

Have you hooked a timing light to it to see if it's firing at all? My best guess is that it's either miswired, on the wrong cylinder, the power pack is faulty, or the timing is simply off causing it to fire out of it's proper order or time.

From your other thread I know you checked the cylinders and wiring. I'd go ahead and check to see if _any_ spark is getting through before going on with other theories.

 

[jtexas]

Re: Rpm's Increase When Plug Wire Is Pulled

Tough one...you don't need a mechanic - you need an exorcist! I'm going to hazard a guess........
Logic and reason tell me that #1 is firing at the wrong time, working against #3. Loose flywheel magnets? Sheared flywheel key maybe? Or some wire missing insulation and touching something it shouldn't. Is the timer base still linked to the throttle? Pure speculation on my part.

Take #1 plug out, reattach it to the boot, and using an insulated tool, hold it 1/2" from the engine block while someone turns the engine over. See if there's any spark at all. Same for #2.

Have you done a compression test? No sense throwing time & money at an engine with bad compression.

Oh, and what do the plugs look like after idling? Wet, dry, oily, clean? Any silver flecks? Gap narrower than where you set it? All three the same or different?

 

[dblanton]

Re: Rpm's Increase When Plug Wire Is Pulled

The Plug wires are on the correct coils and spark plugs, primary coil wires are connected to the correct pin on the wiring harness. I have pulled the plugs and checked the spark all plugs have spark, I have removed the flywheel and every thing checks out, looks good. Could this be bad spark plug wires, they look good on the outside no cracks in the boots and no sign of arching but my guess is that are the original plug wires because #2 wire has a sticker on it telling what spark plugs to use. By the way the plugs are new and gaped correctly.

 

[iwombat]

Re: Rpm's Increase When Plug Wire Is Pulled

The only way plug wires would cause that is if spark is leaking across the plug wires - not very likely. Are the plugs wet in the bad cylinders?

Really though, I'd have to say you're chasing a red herring. You really need to find out why those cylinders aren't firing with what appears to be good spark.

Speaking of which, have you done a proper spark check across a 7/16 gap, or just with the plugs grounded? If not, those plugs may not be firing under load at all.

 

[jtexas]

Re: Rpm's Increase When Plug Wire Is Pulled

Did you torque the flywheel bolt to specs? If not, you may have sheared the key. Did you set the timing and link & sync? If not do those before going any further.

If you crank her up at night, you'll be able to visualize crossfiring.

Back to basics: compression, spark, fuel. And timing.

What are the compression numbers?

You have spark on all cylinders, but only one is making power. iwombat's question is a good one, we don't yet know if the spark is adequate. Spark tester set at 7/16, sharp blue spark.

Spark plug condition after running will give us a clue as to what's going on inside the cylinders. Wet, dry, oily, clean, same, or different? What color is the insulator?

Are the carb throats spitting up fuel?

 

[JB]

Re: Rpm's Increase When Plug Wire Is Pulled

Yes, I know that you are sure that the ignition wires for #1 and #2 are correct.

Switch them anyway and see what happens.

 

[dblanton]

Re: Rpm's Increase When Plug Wire Is Pulled

Compression on cylinder #1 - 119, #2 - 120, #3 - 121, I checked the compression twice using a different gauge for each test and got the same reading both times. I have checked the spark but not at the 7/16 gap. I just connected a known good plug to the wire and grounded it against the engine, the spark was not blue, it appeared to be more white. I will test at the 7/16 to see how that looks. By the way WOT runs great no bogging or hesitation when pushing the throttle down and tach shows 5000 rpm at WOT. WOT timing is 19 drgrees BTDC. Fuel consumption seems to be high though. The plugs are clean but a little wet.

 

[CharlieB]

Re: Rpm's Increase When Plug Wire Is Pulled

Time to get your hands on a timing light, verify ignition timing on EACH cylinder.

I supect your have a problem in the ignition module BUT.................
you need to prove the fault before buying parts as the 'NO RETURN ON ELECTRICAL PARTS' can bite pretty hard when your new part doesn't cure your problem.

How long has this problem lasted??

Who worked on it immediately before this problem appeared and what had they done.

Was the trigger removed and possibly installed incorrectly? That would hose the timing, one cylinder would be close to correct and the timing of the other two would appear as if the spark plug leads were reversed.

Pull all plugs and bring each cyl to TDC and chalk a mark on the flywheel for each TDC. Reinstall the plugs and hook up the timing light, crank it or start it and check each cyl timing, remember which mark you made is which, see if 1 and 2 are switched.

If so, verify that the trigger is installed correctly (right side up)

 

[tashasdaddy]

Re: Rpm's Increase When Plug Wire Is Pulled

i think Charlie's idea has merit. use some different colored marker to mark the flywheel, and an induction timing light, clipped to the plug wires. it would atlest eliminate that. your down to elminination to find the cause. which we have to do every day with outboards. rather than throw parts at it.

 

[tmcalavy]

Re: Rpm's Increase When Plug Wire Is Pulled

White/yellow spark = bad
Fat, blue spark = good

 

[dblanton]

Re: Rpm's Increase When Plug Wire Is Pulled

Could the spark plug wires be the culprit here? The reason I'm asking is because in my efforts to isolate the problem I used my multi-meter to check the spark plug wires for continuity. I found the plug wire for the # 3 cylinder as soon as I touched the probes to the connectors inside the boots the meter showed continuity, but on #2 and #1 cylinders I would have to really push and probe hard on the connectors inside the boots to get continuity. I also noticed that with #3 the needle on the meter would swing immediately and fast, on #2 and #1 when the needle would move it would be slow and a lot of the time it would not swing all the way over like it does on #3.

 

[tashasdaddy]

Re: Rpm's Increase When Plug Wire Is Pulled

i'd replace the wires any way, with that reading.

 

[CharlieB]

Re: Rpm's Increase When Plug Wire Is Pulled

Make with the timing light and post back with your results.

What you may see is TWO of your timing marks while your light is on only one cylinder. Proving the ignition module is bad, double firing that cylinder.

 

[steelespike]

Re: Rpm's Increase When Plug Wire Is Pulled

My guess is if you pull the plug wire comepletely and rpm increases that #2 is able to fire thus the increase in rpm. Little or no change on 2 it isn't firing.
If the rpm increases when one is only partially pulled the voltage increases when it is forced to jump to the plug.Plug may be defective or fouled.
But probably is the module as suggested.

 

[dblanton]

Re: Rpm's Increase When Plug Wire Is Pulled

I must have a defective timing light, I can not get a flash from the timing light when cranking the engine. Would the engine have to be running to get the timing light to flash?
By the way I replaced the spark plug wires with new ones from my local marine dealer. I cut the boots off the old wires just to seen how they looked.
The terminals on #3 wire were good, on #2 wire the terminals were rusted very badly, and on #1 wire the terminals were rusted but not as badly as #2.

 

[dblanton]

Re: Rpm's Increase When Plug Wire Is Pulled

Thanks to everyone that has replied to my post. I got my hands on a good timing light and followed the steps suggested by CharlieB, I used a different colored mark for each cylinder when the piston was on TDC, put the plugs back in hooked up the timing light and cranked her over. The timing light flashed at the correct mark for # 1 when attached to #1 plug wire and the same for #2 and #3 so each cylinder seems to be firing at the correct time. I did replace the spark plug wires after discovering that #2 and #1 wires had terminals inside the boots that were very badly rusted. I hooked up the muffs and started her up, seems to be more responsive to the fast idle lever with the new plug wires but the same problem still exist, pull #1 plug wire and rpm's increase, pull #2 no or very little change, pull #3 and she dies. I did switch the wires on #1 and #2 and fired her up but she ran rough and backfired a couple of times. I am leaning towards a bad power pack now. What would happen if I keep running it the way it is?