thunderbolt V problem

[franktrav]

1996 crownline 225 350 mag alpha_ problem is motor starts to misfire erraticly once i reach around 2200 rpm. it continues to misfire in the 2200 to 3600 rpm range unless i smash the throttle wide open then it seems to fire better in the upper rpms. here is what i have tried to correct it.new fuel filter,new spark plugs and wires, new distributer sensor.checked shift innterupt, i have checked the timing and it is correct at 10 deg. btdc.... BUT.. i think the timing advance is not working- here is why....... just out of curiosity trying to find the problem i drove the boat with the timing lead(pur/wht wire grounded,and it runs exactly the same way as when it is not.sooo im thinking it is the ignition module or knock module/sensor. i understand that the knock module sends a 8-10 voltage signal to the ignition module when it does not detect any knocking and this allows the icm to advance timing .it removes this voltage signal to icm when it detects knocking and the loss of voltage dissables the timing advance. so my question is should there be volage on this pur/wht wire(timing lead if the knock module and sensor are functioning correctly?i have also heard that a problem in the alrarm cicuit could shut down the timing advance? i believe that this wire is the only one that is linked between the two modules,so in my mind no voltage reading on that lead points to a bad knock module/sensor that is making the icm disable timing advance.any help appreciated as trying to figure this thing out.dont want to buy an expensive ignition module if i dont need one.the knock module and sensor are far cheaper.

 

[franktrav]

Re: thunderbolt V problem

update: i tested the timing lead for voltage and it has it,so that means the knock module/sensor are working. does this mean my control module is bad or could the alarm warning syystem or tach. be interfering with the timing advance curves from the module?

 

[John_S]

Re: thunderbolt V problem

Welcome to iBoats. I am assuming you have a 4brl weber carb 350 MAG, not injected.

I don't have a knock module on mine, but from the service manual provided info, the knock module defaults to "good" if the sensor is unplugged or purple/wht wire is disconnected. That means it floats at the 8-10V and only when detecting a knock grounds the signal.

I had an advance issue with my ICM last year, and bit the bullet with the replacement icm kit this spring. See: http://forums.iboats.com/showthread.php?t=349441

Your missfire description sounds different. Has the carb been rebuilt in recent history? Given the rpm range, it sounds like the primary rods are not moving into the cruise range. Possibly running way too rich at cruise, and misfiring. Have you looked at plugs right after problem occuring?

 

[franktrav]

Re: thunderbolt V problem

no- carb has never been rebuilt. the boat and motor only has 180 hrs of use. this problem started shortly after the boat was moored at dock after a mild thunderstorm w some lightning. the boat has always ran excellent thru the entire rpm rangebeforethis.if it were to be a carb issue wouldnt the engine still show drastic running differences when i drive it with the timing lead grounded. because it runs totally identical when grounded or ungrounded. she starts and idles fine, once i get thru the erratic misfiring range it runs fairly well at wot with only occasional missing . is the advance working at the upper rpms at wot? or is the ignition in the distributer just spinning so fast at these rpms that it catches and fires the cylinders at a better ratio.some guy at the parts dept. tried to sell me a icm that is for thunderbolt IV system, he said it would work fine but it is questionable to me-although it is half the price of the correct conv.kit-.at first i thought maybe accel. pump, but after inspecting it turned out fine,i am weary of continuing to drive it with this issue afraid of damaging the motor when forcing my way thru this erratic misfiring range,although when idling or running wot you would never know there is a problem

 

[John_S]

Re: thunderbolt V problem

I am not saying that your icm is not the problem, just that your symptoms do not match what my icm was causing with the advance not working. The icm is expensive to replace, and you want to be reasonaby sure other issues are not causing the symptoms. Black plugs after the problem occurs, would indicate too rich.

Be leary of the T4 module. I was under the same impression and ordered one. It had a different number of pins and different size connector. Returned ASAP.

I know some people state that while in base mode, the distributer will not advance. This is not what I have observed with old or new module. It appears to follow the base timing curve but not use any of the T5 enhancements. Outside of the Idle Speed Spark Control, it is hard to determine if the enhancements are working.

Run your engine on the muffs or at dock in normal mode. At idle watch the timing. The T5 will cause the timing to jump back and forth slightly. Rev the engine and watch the advance. You should easily see the advance at 2K rpms. Just rev to that, don't hold it there long. Shut off and put in base mode. Do the same test. At idle, you should not see any jumping timing.

Have you removed module and see if water drained from it? If that is the case, then the probability of the icm being bad goes up significantly.

 

[franktrav]

Re: thunderbolt V problem

i have pulled the plugs-they looked good,then cleaned,chkd gaps and reinstalled- same problem. since then i have replaced them w new plugs with no change in running condition.i will try your suggestion tomorrow about the timing in base and normal mode for comparison of the advance curve. i will say that the miss is not very pronounced when i rev in neutral,but when the motor is under load when accelerating in the water-it is very distinct.i read yer thread on your similar problem,and you stated that you did not attempt wot operation while you had this issue_i wonder if you had tried it if your results would have been like mine. its crazy but i either have to put around under 2K rpm(which dont get me on plane) or go balls to the wall.once i get over the hump of misfiring it runs betr and i can ease bak into this troubled rpm zone but once the engine starts to come under load it goes to crap again.(but only when in the mid rpms) i did take the connectors off of both the icm and knock modules_clean and tottaly dry w no corrosion watsoever. the boat is stored in my garage,never been left in the water except when we had to run for cover from that storm a few weeks ago. i do see 2 black wires near the valve covers that are not hooked to anything, but they came from factory like that,they go back into the harness. i tested them and they go to ground somewhere.

 

[John_S]

Re: thunderbolt V problem

i read yer thread on your similar problem,and you stated that you did not attempt wot operation while you had this issue_i wonder if you had tried it if your results would have been like mine.

While I didn't go to wot, I did put in on plane and to 30mph, which would be in your "missing zone". It certainly had a lack of power and required more throttle to get on plane and maintain that speed.

 

[franktrav]

Re: thunderbolt V problem

results of timing test:
base mode: steady10 btdc @ idle
2000rpm- an additional advance of 24 degrees
operating mode:flickering from tdc to 15 btdc
2000 rpm- an additional advance of 20 to 30 degrees
flickering around a bit
you were right about the timing still advancing while in base mode. far as i can tell t5 is functioning correctly-my problem must lie elsewhere. i will start with the carb. as you suggested, and maybe a cylinder compression test.
any other ideas?
I was playing with the idea of a new replacement edelbrock carb instead of rebuilding the current one as i am not very familiar with carbs. in general
is there a easy way of adjusting the metering rods? any info appreciated

 

[John_S]

Re: thunderbolt V problem

You can access the primary rods very easily on a weber carb. There are two small flaps,one on each side. Under them is a plunger, spring, and rod. You would be able to determine quickly if there was a mechanical, sticking, issue, but most likely the issue will be with some clogged passage.

A new Edelbrock 1409 will go around $340. A carb tear down, cleaning, and reassembly is not that hard. Have a good clean work area, go slow, be maticuless, and take lots of pictures. I'd use the soaking type cleaner as much as you can over the spray type. Your weber carb should be a 750 cfm with the special 3 step rods/jets. Not sure if that takes a special kit or not. Outside of float needle/seat the main part of the rebuild is cleaning.

 

[franktrav]

Re: thunderbolt V problem

thanks for the info.
i did manage to do a cylinder compression test today,and it checked out good with all cylinders in the 150-155 psi range- so at least i know i dont have to rip the top end apart.when i was removing the sparkplugs for the test i did observe that a few of the plugs appeared kind of damp and smelling of gas,but clean,no black fouling.while some of the plugs were very dry with a tannish color @ the electrode. any thoughs on this?
a guy at the dock told me i should replace the coil...but it passed the resistance test, and i thought that the coil would be either good or bad( good if you have spark and bad if no spark).i cant see the coil acting up consistently at the same rpm range every time and no where else in the powerband. my intentions are to focus on the carb for now, unless todays observations give a new idea of the problem

 

[John_S]

Re: thunderbolt V problem

What cylinders were damp, which were just tan? On dual plane intake four cylinders use one side of the carb (2 per side) and four use the other. The weber carb design is such that you can have problems with one side of the carb, but not the other.

Coils can have hot run issues, but never saw one that was rpm dependant. Your indication that it will run fine at wot, would not lead me to the coil.

 

[franktrav]

Re: thunderbolt V problem

thanks for the advice, i will update the thread after the carb cleaning/rebuild.going camping for the week at the lake and intend on having some tinkering time w the boat. according to my notes during compression chek the damp , gas smelling plugs came from cylinders 5,7,6,8(rear half of both sides.other plugs appeared to be tannish in color w no dampness(normal in my mind)