2008 3.0L cranks but won't start - long post

[TBarCYa]

I know there are a ton of "cranks but won't start" threads but this one has a story just in case it changes the diagnosis.

This morning when I went to start the engine, I pushed the shift bypass and pushed the throttle to full (like I always do) but it got stuck. I was messing with the carburetor linkage as it seemed like it might have gotten stuck there and my wife was able to get the throttle back to neutral. I didn't actually do anything but wiggle the linkage that I believe is for the accelerator pump.

We made the 20 minute putt from the lift to home (we don't have a lift so we keep it on someone else's) and everything seemed fine. I turned it off and about 40 minutes later tried to start it back up to get on our way for the day. It was a little slow to crank but started and seemed to run fine.

While idling out of the canal, I noticed that the battery gauge was reading about 13v which is low for when it's running. Once we got up on plane, the voltage came up to almost normal but I noticed at times it would drop to 13 then rise back up. I kept an eye on it so I knew that even if it wasn't charging, we'd have enough battery to get it started and back home. The voltage never dropped below 12v.

On the way, there were two instances where the engine sounded like it backfired. That's the first time in 10 years it's ever done that so at this point I knew something was up... Just not sure what. We were down on power but almost to the island where we were spending the day so I anchored and we hung out for the day.

When it was time to leave, the engine was slow to crank and didn't even try to fire. I thought I may have flooded it because I did the usual advance the throttle to full and then back to neutral before starting. I waited a few minutes to try again and it was now completely dead. I had power to the stereo and the VHF, the lights and the GPS... Just nothing to the gauges or the key.

I tried to bypass the key and nothing. I bypassed the tether/kill switch and nothing. We got a tow back home and after reconnecting the kill switch and key and a bunch of poking around with the test light, I found that the 50A breaker on top of the engine is apparently dead and powers the key. I bypassed it to test and now the gauges work and the engine will crank. But not start.

I know the breaker is bad because pushing the reset button didn't connect the terminals, even when tested with a meter and the battery disconnected. I'm guessing that it just died open which I guess is better than dying closed.

I pulled the distributor cap (which along with the wires is original) and it looks brand new inside. There's no corrosion or anything that's burned. The button in the cap springs back smoothly and all of the terminals looks clean. Here's where it gets weird.... When I pulled the coil wire off the distributor to test for spark, there was spark and it acted like it wanted to try to start. It tried more than with the wire connected but I couldn't keep the gap close enough while cranking to see if it would actually start.

So that's where I am. Tomorrow I'm going to try to locate a new breaker and a cap/rotor/wires but because it tries to start with the coil wire not connected but arcing to the terminal I don't know if that points to something that I'm overlooking. Maybe it's timing and the wire being off is delaying the spark just enough to let it try to start? I don't know but the distributor hasn't moved and I tried to turn it and couldn't.

The DVM tells me I have 12.8V at the battery and now the engine cranks normally. I'm going to put the charger on it overnight just in case. One question I have is does the ignition module (under the rotor under the cap) just deal with spark advance since it's a straightforward connection from the coil to the plugs?

Thanks for sticking around this long... Any suggestions for what else to try are immensely appreciated.

 

[alldodge]

I'm currently leaning toward the pickup coil inside the distributor

 

[TurtleTamer]

This is oddly similar to when my riser went bad and leaked water into my cylinders. Slow-cranking that went away after waiting a while (water leaks past rings into crank case), but still a no-start condition once cranking speed returned to normal. Crank it enough times and water gets back in and slows the cranking again. Still no start because of the water in the cylinders, but messing with ignition components would sometimes get a near-hit.

Hopefully it's not that, of course, but it's something I'd have saved a lot of time with if I'd known to look for it. Check for water intrusion to the crank case and see if you're leaking water externally at the riser gasket surface.

FWIW I was also having fuel issues at that time, namely plugged-up jets in the carb. So I had a range of issues. I will save any theories on your throttle getting stuck until you have a repeat problem.

I've had an ignition control module go bad and the fault I got was not going into base mode and, I suspect, not advancing timing. I also had an intermittent miss but I am unsure if the ICM had anything to do with that since I also had a cracked spark plug. The engine still started and ran though. This part, however, was not OEM GM. I do not think your problem is timing related though.

AllDodge may be correct in his assessment, but the range of other symptoms makes me think it's something else. Sounds to me like you are getting good spark.

 

[TBarCYa]

I'm currently leaning toward the pickup coil inside the distributor

I tested the pickup coil, along with the coil, as prescribed in the service manual and everything tested good. I did test for continuity across the rotor, from the center connection to the tip, and it tested open. I also tested a new one and it tested closed. So I'm guessing that the rotor was bad (I don't know for sure that this is a valid test) so I replaced the cap and rotor.

After replacing the cap and rotor, I have the exact same no-start condition. I put the timing light on the coil to distributor wire and get indication of spark. I did the same for the 4 plug wires and didn't get anything on them. Since there's spark at the center terminal but not at the wires, I pulled a wire off and wedged the timing light pickup near the outside of the terminal so it would pick up a signal but not pick up the coil wire and it indicated spark When I bought the cap/rotor I also bought plug wires but they turned out to be the wrong ones but I was able to get one to make enough connection to the terminal that I put the timing light pickup on that wire as far away from the distributor / coil wire as I could and still got spark.

Today I'll be picking up the right plug wires and hoping that the thing starts. One thing I did not test was any of the original (2008) plug wires when not connected to the plug. I don't know if / that this would change anything, but I think it's worth testing just so I know for sure that the wires are in fact bad.

 

[alldodge]

You can ohm the wires but sure is sounding like a bad wire. They should be around 4000 ohms for new and 5000 ohms for old maximum. Coil wire should be less because its shorter, the less ohms the better

 

[TBarCYa]

You can ohm the wires but sure is sounding like a bad wire. They should be around 4000 ohms for new and 5000 ohms for old maximum. Coil wire should be less because its shorter, the less ohms the better

I just replaced the wires and it's still not starting. But at least now it tries in that I can tell I have a cylinder or two that's trying to fire whereas before it would spin without trying. I found that I consistently get spark on #1 and #2 but the rear two are sketchy. If I pull the wire off the plug, I get spark pretty consistently. I can't do it tonight, but tomorrow I'll pull the plugs and take a look but I don't know that bad plugs would cause a lack of energy in the wire.

When I say "get spark" I mean that the timing light is lighting. So there's electricity but not necessarily spark.

 

[alldodge]

If you were getting spark, even with only 2 cylinders, it would run, and run bad. Your getting a pulse the timing light is picking up, but your not getting enough spark to jump the gap on a plug.

Check voltages and test the ignition system, something is not working. May be a bad ground and connection

 

[TBarCYa]

Check voltages and test the ignition system, something is not working. May be a bad ground and connection

First off, I tested the old wires and they were all over 8k ohms... So that was definitely a problem. I tested the new ones and they range from 3600 for the short ones to 5600 for the long ones. A little out of spec for the long ones so I don't know if that's a problem or not.

I tested the system again as specified at http://www.boatfix.com/merc/bullet/90/90_15.pdf and the very first test fails. I'm assuming that when I tested previously the probe on the meter didn't go into the connector on the coil correctly because when I test now with a test pin I don't get infinite resistance from the 12v wire to ground. Next two tests that should read *approximately* 4ohm read .6 and .7 respectively and the last test reads 8k which is in spec. I have 12.6v at the 12v input (b) and 12.6v at the end of the wire from the coil feeding the distributor.

So it sounds like I am buying a new coil next. Ugh....

I did look at the plugs and they all look good except that from front to back they go from grey to reddish. I understand the reddish color is *normal* but I'm wondering if there's a potential cooling issue with the back of the engine. Once it runs I'll mess with the cooling system.

 

[alldodge]

There is such a very wide variety in wires that the norm is 4K ohms. I would not doubt new wires unless they were no name type

 

[TBarCYa]

These are the Mercruiser brand replacement wires so I'm going to assume they're good.

I just did a quick test with the #1 and #4 cylinders where i held the plug wire near a ground and I got a spark from both but I didn't check with a plug because I don't have time. Tomorrow I'll pull plugs and test with a plug in the wire and see how it goes. I may try that before ordering the coil.

 

[TurtleTamer]

...Next two tests that should read *approximately* 4ohm read .6 and .7 respectively and the last test reads 8k which is in spec. I have 12.6v at the 12v input (b) and 12.6v at the end of the wire from the coil feeding the distributor.

So it sounds like I am buying a new coil next. Ugh....

This is normal. The coil is just a long length of wire, so there will be almost no discernible voltage drop until there is a load applied to the coil in a closed circuit. Then, you'd be able to read it in amps. Voltage is simply the potential for difference in polarity, so the coil reads no difference, naturally, since the circuit is still open. One side of the coil will read no different than the other, to ground.

Your coil is reading good; you don't need to buy one.

You're also not using a good test with the timing light. A spark tester or individually removing each wire from the plug and holding it near a ground is the better test. That being said, I sincerely doubt you have a spark problem. At this point, the only electrical fault you seem to have is the slow cranking/bad breaker/shifty voltage gauge at plane.

I suspect you have a fuel problem, and that's where I'd start to look.

 

[Fall Guy]

ok if you have spark its a fuel problem check if your injectors have a pulse. disconnect the injector and check it with an injector noid light. if it lights up good. check if fuel pump is working if its good. now check fuel pressure with gauge you should have over 36 psi, if low pressure is present check your pressure regulator make sure its not stuck open if good replace fuel pump. Also make sure while cranking check battery voltage don't drop below 9.6, if it does battery is bad. What happens here is that logic gate inside the PCM dont know what to do if voltage is below 9.6. Affects spark and fuel.

 

[TBarCYa]

ok if you have spark its a fuel problem check if your injectors have a pulse. disconnect the injector and check it with an injector noid light. if it lights up good. check if fuel pump is working if its good. now check fuel pressure with gauge you should have over 36 psi, if low pressure is present check your pressure regulator make sure its not stuck open if good replace fuel pump. Also make sure while cranking check battery voltage don't drop below 9.6, if it does battery is bad. What happens here is that logic gate inside the PCM dont know what to do if voltage is below 9.6. Affects spark and fuel.

This is a carbureted engine and even with fuel sprayed into the carb, the engine will not start and in fact, it tries more on just the carburetor than with me spraying gasoline into the carb.

Regarding the coil, the first test that checks resistance between the 12v input from the harness and ground failed as it did not test infinite resistance. So better safe than sorry, I ordered a new coil and I'll replace that and the plugs this week.

 

[TurtleTamer]

I see what you were saying now. For some reason I was confused. Out of curiosity, what are you getting for resistance to ground during that test? I would think anything above 1 Meg would still be good, but the manual does state "anything other than infinite."

 

[TBarCYa]

I didn't record the values since it was specified to be infinite. I'll test it tonght and take note.

 

[Fall Guy]

If resistance is not in specs. replace it, It's identifying that the component is bad any technician would replace the coil.

 

[TBarCYa]

Yesterday I replaced the coil and plugs. So now the only part of the ignition system that has not been replaced is the ignition module. I didn't do a spark test but I did try to start it and it tried... And almost started but the battery was weak so I put it on the charger and will try again tonight. Hopefully with a fully charged battery and new ignition system she'll start right up.

One thing that I found very interesting is that all of the documentation and manuals online say that the spark plug gap should be 0.035 and that's what I set the previous set of plugs to but I noticed that the flame arestor cover says 0.045.I gapped these to 0.045 in hopes that it's the right number... At least it was when the sticker was applied in 2008.

 

[alldodge]

3.0 S/N 0L010042 and above - 1998 and higher use MR43LTS plugs gap at .035

 

[TBarCYa]

3.0 S/N 0L010042 and above - 1998 and higher use MR43LTS plugs gap at .035

The plug type is consistent with the sticker on the flame arrestor but the gap isn't. So who / what is right?

 

[alldodge]

Use the sticker, there may have been a change bulletin that I'm unaware of