need assistance troubleshooting v4 crossflow combustion problem using spark plugs

[ryguy1101]

Have a 1986 V4 110HP crossflow not VRO (not new to me) . Currently the engine runs only on the port/left bank (cylinders 2 and 4) b/c there is no change in operation when I remove the boots from the plugs on the starboard/right bank. Verified strong spark and even (but low - 95psi) compression accross all 4 cylinders. Have also traced fuel delivery with no apparent issues from fuel pump through carburetor, and overhauled carburetor twice just to make sure no random blockage anywhere. Installed new plugs and ran the engine for a minute to help with diagnosis. Plugs from cylinders 1-4 each look very different as follows: #1 - very black but dry insulator and electrode, #2 - somewhat dry but normal looking, coffee colored insulator and moderate soot on electrode, #3 - very black and very wet insulator and electrode, #4 - very wet and clean insulator and electrode (as if the cylinder is not igniting regularly). In summary, top plugs appear too dry, right side is black with unburned fuel/oil, and bottom plugs appear too wet. Currently my best guesses are reed valve issues, timing issues, or leaking crankcase/intake manifold gasket. any thoughts or suggestions that can help narrow down the root of the problem?

 

[Faztbullet]

Re: need assistance troubleshooting v4 crossflow combustion problem using spark plugs

Did you test spark with air gap tester, needs to jump a 3/8 gap ? My guess since you have a spark is weak charge coil on stator for that side.

 

[ryguy1101]

Re: need assistance troubleshooting v4 crossflow combustion problem using spark plugs

Fazt-
spark jumps from boot to plug well more than 1/2" when I remove boot...is that enough evidence, or do I need more? Only other wierd observation is that the spark on the one cylinder that seems to combust the best (#2) looks red/orange (cool color), while the two/three cylinders (#1, 3, 4) that are not working seem more white/blue (hotter). Go figure. This thing is giving me fits. I'm on my 5th rebuild of these engines, so I generally have most of the concepts in order, and this is the most baffling problem I've encountered. However, I am an electrical ignoramus so strength of spark, resistance, amps, etc. and all the specific readings that I'm supposed to have are a bit beyond me. I can only really understand continuity and have some concept of resistance... I do have a couple other stators I could switch in if that is a legit reason for the screwy combustion. lemme know your thoughts.

 

[ryguy1101]

Re: need assistance troubleshooting v4 crossflow combustion problem using spark plugs

Bumping this with a bit more info.

Have now replaced every single ignition component on the starboard side with absolutely no change in operation (stator, timer base, power pack, coils, plugs, and plug wires. Therefore, I think it's fairly safe to rule out timing or spark as the cause. Still running on left/port bank only (cylinders 2 & 4). Cylinders 1 & 3 stay cold b/c no combustion whatsoever, yet they still have compression. spraying pre-mix in the stbd carb throats does nothing so I would think a lack of fuel is also not the problem. The research I've done in the past few days now seems to point in the direction of a crankcase or intake manifold seal leak which is completely screwing up the mixture before it gets to the cylinders themselves. Unfortunately, I don't hear or see anything obvious when inspecting the seals from the outside. Any thoughts on this theory before I either pay for professional diagnostics or just tear the thing down again and start from scratch?? Gotta figure it out one way or the other ASAP. btw - the spark plug descriptions in my original post are still accurate after running again last night with new ignition components.

 

[emdsapmgr]

Re: need assistance troubleshooting v4 crossflow combustion problem using spark plugs

You appear to have covered all your bases. The interesting thing is what is going on with the plugs. If the ignition is new, you should now be getting spark on the port and starboard bank. It should fire now, esp if you spray some premix through the carbs while the engine is running. Since that does not work, I'd wonder about a couple of things: 1. are the plugs on the starboard side wet or dry now. If they are dry, that means they are not getting fuel. If they are wet, they may not be getting spark. An inductive timing light will show you the quality of spark on the starboard wires when the engine is running. 2. If the starboard plugs are wet, but not firing, possible you are ingesting water into those cyls, which may be washing or killing spark. An unlikely scenario, but possible if you have a crack or casting porisity in the inner exhaust cover. Usually water leaks affect the lower cyls, but yours could be the exception. Do the plugs have any milky appearance to them?

 

[woody66912]

Re: need assistance troubleshooting v4 crossflow combustion problem using spark plugs

You might want to check your fuel pump diagram. And one of the most over looked is the reticulation hoses, those are the small hoses that come from the intake ports and go to the intake manifold. If they are leaking by the intake It will be( wet & oily) all over the front of the engine. Sorry to say but to check them you will need to remove the carbs again. If the hoses check fine the you need to check the reticulation check valves. They are a one way check valve, air should only pass into the engine.( Note ) just blow and suck DON'T use compressed air.

 

[ryguy1101]

Re: need assistance troubleshooting v4 crossflow combustion problem using spark plugs

EMD-

Appreciate the vote of confidence. This thing is absolutely maddening. I've had "good looking" spark all along but decided to explore a possible spark strength issue based on Fazt's suggestion above...to no avail. Both starboard plugs are wet (bottom moreso than top) but no outward evidence of water intrusion. Have seen water intrusion before so I sorta know what to expect if it's present. I won't rule the water suggestion out entirely, but it's certainly not obvious if it is there. I guess I'm most baffled because the plugs wouldn't be getting fouled with black goo and soot unless they were actually firing with fuel present, but if they are firing with fuel present, then I should be getting some amount of combustion given that I do have compression...I'm literally getting NO substantial combustion. I don't have a timing light, and don't have easy access to one, but I'm seriously considering rolling her out to my local OMC shop (good reputation) and paying them for an hour or two of professional diagnostics.

 

[mekkamaz]

Re: need assistance troubleshooting v4 crossflow combustion problem using spark plugs

Do you check your flywheel key? Just happened to me something like your problem, and found out to be a sheared key...Just in case and to cover all basis....

 

[ryguy1101]

Re: need assistance troubleshooting v4 crossflow combustion problem using spark plugs

woody - I tested the check-valves before I reinstalled the carbs last time and all 4 valves were working properly. I also attached a syringe to the reticulation hoses and they easily transmitted air into and from the ports, but I didn't think to pressure test the hoses themselves to verify they weren't cracked or split anywhere. Can do that later tonight if relevant. No random oily mess anywhere along the path of the reticulation hoses though. Thanks!

mek - Have had the flywheel off and back on about 5 times while replacing ignition components and no change yet, so it's not that but good idea since the problem is behaving as if it could be timing related.

 

[emdsapmgr]

Re: need assistance troubleshooting v4 crossflow combustion problem using spark plugs

You can rent timing lights reasonably at any number of places. Most auto parts retailers rent tools, including timing lights. The inductive type is really good for checking the spark and the wires.

 

[woody66912]

Re: need assistance troubleshooting v4 crossflow combustion problem using spark plugs

Ryguy1101. Hey just another thought about the flywheel. the next time you have it off check the center set of magnets.

 

[ryguy1101]

Re: need assistance troubleshooting v4 crossflow combustion problem using spark plugs

Will do. What exactly should I look for? The more I struggle with this the more it seems like the spark absolutely HAS to be firing on the wrong part of the piston stroke which would explain the black plugs....aka timing. The flywheel is the ONLY part of the entire ignition system that I haven't replaced/examined b/c I just took it for granted that it was pretty inert and hard to ruin. Fingers triple crossed.

 

[emdsapmgr]

Re: need assistance troubleshooting v4 crossflow combustion problem using spark plugs

OMC made two types of flywheels regarding the center timing hub. That hub has magnetic lines which indicate the specific timing degrees to fire each cyl. The early flywheels (1970's) had these magnets embedded in the flywheel casting itself. Some later flywheels have a pressed on ring which has the 4 magnetic marks. I don't know which type you have currently installed on your engine. These later flywheels had a remote possibility that the center timing ring could shift (move location) once the flywheel got some years of age on it. It was almost impossible to correct the timing on that flywheel once that center ring moved. It is likely that the timing would typically be off on all 4 cylinders rather than the possibility of losing timing on just two cyls. The only way to check this is to locate the flywheel on TDC-making sure the timing pointer is dead on. Then check the 1 and 2 cyls for timing based on the factory cast degree marks on the top of the flywheel to see if the timing is significanly off, causing running issues. You really should be working from a factory service manual for this procedure.

 

[ryguy1101]

Re: need assistance troubleshooting v4 crossflow combustion problem using spark plugs

thanks emd - the insight and patience is much appreciated. Actually I do have a factory service manual, but for some reason I still just cannot comprehend how to verify/check/set timing (I've tried over and over and over reading more instructions than I care to admit, but it just escapes me). Pretty sure I just need to watch someone do it once so it "clicks" in my head...or perhaps I can find a good youtube video somewhere.

 

[ryguy1101]

Re: need assistance troubleshooting v4 crossflow combustion problem using spark plugs

Woody - magnets seem good. No obvious missing/loose pieces, and just for grins I swapped in my backup flywheel (same part number but slightly older/uglier condition) with no positive result. Discouraged to say the least. Heading to shop tomorrow AM for some professional diagnostics @ $94.50/hr. Have to assume a concealed electrical issue or a crankcase leak/problem at this point. Hope they can figure it out in short order. Preparing myself mentally for a complete rebuild since I have complete bored/honed spare block and absolutely HAVE to have her running again by next friday.

 

[AlTn]

Re: need assistance troubleshooting v4 crossflow combustion problem using spark plugs

looks to me that the engine wiring harness is the only thing you haven't tried swapping...is that worth trying?

 

[ryguy1101]

Re: need assistance troubleshooting v4 crossflow combustion problem using spark plugs

Hi all-

Back with an update. Ashamed to admit but the ignition problems with the starboard bank were entirely my fault. When replacing a wire with cracked insulation, I accidentally swapped the two orange wires connecting power pack to coils so timing was reversed. Blech. :facepalm:
HOWEVER - I still have a weak/intermittent spark issue on #4 cylinder (bottom port). Cylinder does get some spark but it doesn't jump the recommended gap and doesn't appear to be combusting at all in the chamber b/c no black soot on plug electrode...still just very wet and clean. Also verified its a spark issue by removing plug boot while the engine was runnning. RPM's dropped slightly, but VERY little, while removal of any of the other three boots results in severe loss of power. I have done all the standard diagnostic swaps for every single component betweeen the plug and the power packs, and did resistance tests for all my parts per factory manual - all fell within the specified ranges. Additionally, I have swapped out timer base, several stators, and flywheel as well just in case...but no luck. My best guess right now is that I could possibly have a problem with my stop/kill circuit b/c I had to replace the amphenol pin on the black/yellow wire in my harness and didn't solder the connection, though the crimp was tight. Could this actually cause my #4 cylinder-specific problem?? Completely out of ideas to try other than taking the time to solder the pin, and systematically cleaning every single electrical pin/connection/contact point in the system. AlTn - yes I did replace my wire harness because my old one had several cracks in the insulation down by the red plug, many of the wires were starting to rot after 30 years. New harness is used but in excellent shape per detailed visual inspection, though I can't completely rule out the possiblity of a fault in the harness. Any new thoughts guys??...and thanks again!

 

[dwco5051]

Re: need assistance troubleshooting v4 crossflow combustion problem using spark plugs

No help from me on the ignition problem but 95 psi is a good reading on those crossflows. It is not low.

 

[AlTn]

Re: need assistance troubleshooting v4 crossflow combustion problem using spark plugs

Easy test is to swap known good coil to suspect position and suspect to good position and eliminate one possibility before moving on

 

[will62]

Re: need assistance troubleshooting v4 crossflow combustion problem using spark plugs

I don't think that your spark problem on #4 has anything to do with your ignition kill wire (black/yellow). Grounding the wire would kill the power pack, and you wouldn't have spark on #2 either. Agree with AlTn's recommendation.