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Use an ohm meter unplug where the pulse gens connect to the cdi box test in pairs eg yellow wire and yellow/white wire is one pulse gen check specs in the manual. If u get a bad reading on 1 rotate the engine a hair and check again. do this 2 or 3 times if u still get a bad number u have a problem. What kind of bike and what are your symptoms? I am pretty knowledgeable about these ignitions. Pulse gens are hard to find on some of the older models, discontinued by Honda.
 

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According to my book both spark units have identical wiring coming out of the spark units but then the wiring coloring changes after it goes through the next connector(s).

Coming out of both of the spark units the wires are the yellow one and the white one that is next to it, after the connectors it changes on one to yellow and yellow/white and the other changes to blue or some kind of purple (the color blend did not work very well when my book was printed).

Either way, unplug the connector put your meter on the lowest OHMs setting connect it to the two wires that are in the connector that is NOT attached to the spark units, this will check the resistance of the coils of the Pulse Generators.

Check the resistance, you should get some kind of reading other than zero (0.00) or nothing (infinity), do this for both connectors I'm not sure what the resistance should be though. If one tests good and one tests bad you should only be firing on one cylinder.

If both appear to be the same set your KILL switch so that the engine will not start, then switch your multimeter to AC Voltage and press the START button to get the engine spinning, the magnets in the alternator should be creating a pulse when they go by the Pulse Generators that looks like AC voltage on your multimeter.

If you don't there may be something wrong in your alternator.
 

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Do you suspect a problem, or do you just want to test them to verify that they are okay?

Most of the pulse generator issues I've run across only crop up when they are heated. They test fine cold, and fail when hot. This is noticeable when the bike starts and runs fine and then seems to drop a cylinder after 20 minutes.

--Justin
 

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tubes_rock said:
Do you suspect a problem, or do you just want to test them to verify that they are okay?

Most of the pulse generator issues I've run across only crop up when they are heated. They test fine cold, and fail when hot. This is noticeable when the bike starts and runs fine and then seems to drop a cylinder after 20 minutes.

--Justin
Don't meant to hi-jack, just a question: Do they typically fail like this: all or none, or do they degrade. I am battling a problem on my '99 ACE 1100 where I pick up a good amount of vibration after the engine gets good and hot. I suspect a coil problem, but wonder about the pickup. I am definately firing on both, but may be missing or out of timing on one. (still haven't ruled out carbs yet).

Thanks.
 

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All of the pulse-generator issues I've come across were all or none. Either it worked or it didn't. However, the work/not work often happens as the temperature changes.

I've never seen one though that works for one revolution, misses the next, work for the next, misses for the next. Either it works 100% and stops working when hot, or it works all the time, or it doesn't work at all. There's pretty much no middle of the road for them, that I've ever seen.

--Justin
 

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Discussion Starter #7
thanks for the help everybody. i checked mine and 1 was ok and 1 was not ok. the one that was bad is running the cylinder that is sparking sometimes and not sometimes. ive got a new one ordered through the local honda dealership for 90 bucks plus 10 bucks for the gasket. thanks again to everybody that replyed.
 

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99 ace has a single pulse generator if it goes south itll stop completely not just on 1 cylinder.
 

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Hey guys.

Thanks for the help you have given me so far. I am pretty sure I have eliminated the carb. It runs great for the first 15 minutes. But when it gets good and hot (15-20 minutes) I pick up the strong vibration. This has to be something in the ignition. When the vibration shows up, I get a lot of vibration in the low RPMs (Its there in the higher RPMs, but not as noticeable) and I get a small performance degradation, but not a lot. It is most noticeable when i give a good twist to the throttle. It just doesn't pull hard.

I put a timing light on some of the plugs to observe the behavior. At idle, it seems normal, with an occassional miss or cut out (light disappears for about a second). As I slowly increase the throttle (about 500 RPM) the flash rate changes and appeass to slow down. It may come back for a bit and at a higher RPM seems to become normal again.

The behavior is similar, front and back, but I am not certain if it is the same. I haven't done enough testing yet.

Based upon your feedback, it seems that I can rule out a bad pulse generator. This leaves me with the coils, wires and module. It does not get hot near the module, so this does not make much sense. I have checked the ground on the coils and also cleaned the connectors (no corrosion).

Any ideas? Does it sound like coils? Seems odd that they would both fail in the same pattern. This one has me stumped.

While riding, I heard a continuous ticking, that sounded as though it could have been a wire grounding. I could not see a spark, but can't see all the way under the tank. However, at idle in the garage it went away and I still had the vibration with spark visibe on all cylinders.

Thanks for any guidance you can provide.

Larry
 

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That ticking could indicate a grounding plug wire. Get out in a pitch black dark shed and look for sparking it should be pretty easy to see even with the tank on. It still could be the pulse gens from what u are saying, they are notorious for breaking down when hot, its easy to test with an ohm meter and the right specs but look for the fireworks show first. Next is the cdi I have found no-one that knows how to test these boogers just rule everything else out first.
I am not an expert at this but I have played around with these ignitions some, and learned enough to be dangerous :twisted: I would be happy to help. I am away during the week but home weekends. You might want to start with new plugs too. Really screwed up plugs could cause something like this.
 

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I was doing the testing last night in the dark. Definately no visible spark on the exposed wires. It is possible that it is arcing up by the coil, as I cannot see the wires under the tank. However, if they are arcing I should not be picking up a firing indication on the magnetic pickup (timing light) connected right near the plug.

Plugs are new with some carbon build up. I'll clean them again to elimianate any possibility of grounding.

What resistance should the pulse generator test at? I figure that I will need to test it hot, once the problem starts.

Thanks for your assistance.
 

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It seems like you're n the right track. The pulse generator is the first thing I thought of.

I think the pulse generator should come in at the 400 ohm range, but anything between 300 and 600 ohms ought to be fine. When they fail, they either open completely (infinite ohms) or ground out. Check the resistance between each lead of the pulse generator and the bike's ground.

And, like you said, test it when it's hot and failing.

--Justin
 

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Well. I can't get a bad reading on the pulse generator. In fact, I learned that I can measure the voltage while it is running and saw that the voltage indicates the RPM to the ICM. I see the voltage exactly follow the RPM. Not a single blip or miss hear; It seems dead accurate.

While I am watching a stable voltage, I can see the RPMs on the tachometer (inductive pickup - external tach) bounce around as much as 500 RPM. It does it more on one coil, but can oberve the behavior on both coils. I can here the engine get rough as spark indicated RPM bounces around. Clearly there is a series of misses happening.

Any ideas. The primary connectors are clean and with a good connection. Seems unlikely that both coils are bad. Any tests I can perform?

Thanks for your assistance here.

EDIT: I tested both coils. 3 ohms on the primary and 35-36K on the secondary.

Larry
 

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Ok, I Tested the two coils. On the primaries, one is 2.9 and the other is 3.0. On the secondaries, I get 35K and 37K with the plug wires attached. The haynes manual (I don't have a Honda manual yet) states the specs as 2.1 - 2.7 and 24 - 32K. I have a 99 VT1100C2 (ACE). These were aken warm, but not hot. I haven't done it hot or cold yet.

That leaves both of my coils out of spec. Are these specs pretty accurate? Could this be causing my intermittant failures when hot? I assume that the coils have a harder time doing their job while hot and if on the outskirts of their tolerance could fail. I have no real experience here. Is this logic sound? Would you suggest replacing the coils?

EDIT: I checked them cold this AM and they are at 2.7 and 32K/34K Should they read the same when hot? Is the drifting in resistance when hot potentially causing the miss or is this normal?

Thanks,

Larry
 

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The fact that both readings are pretty close to each other is usually an indication that the parts are fine.

Try changing the batteries in your test meter and testing them again, some meters read high when their batteries are going dead, if they still read high try a different multimeter if you are still reading high you may be dealing with dying parts.
 

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On the 85-86 vt1100 pulse gens shpuld test at 590-670 ohms at 68 degrees
Your coils are in spec for a 85-86 vt1100.
I think we are down to the mystery (cdi) boxes I have never found anybody that can test these. They do screw up regularly on these earlier bikes.
 

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bananabenda said:
On the 85-86 vt1100 pulse gens shpuld test at 590-670 ohms at 68 degrees
Your coils are in spec for a 85-86 vt1100.
I think we are down to the mystery (cdi) boxes I have never found anybody that can test these. They do screw up regularly on these earlier bikes.
I have a '99 ACE. The manual stated 480 +- 10%. Do the coils fall in spec for this year, based upon your info? If not, will .2 ohms make a difference in a situation like this?
 

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I am still baffled as to why my left front spark plug reads (via inductive pickup tach) 1800 RPM at idle and my right front reads 900. The two sides of the coil read exactly half all the way through the RPM range.

I thought the coils were in series and voltage flowed from one wire to the other and the engine ground completed the circuit between the two plugs. I cannot get an ohm reading between the plug wire and ground, but can get a reading (~34K) between the two plug wires. This leads me to believe it is not a center tapped coil.

This behavior defies all logic for me. I cannot think of a single reason how/why one side fires every other time, but the other side fires every time.

Any ideas? I have verified that I have a good ground. could this be something other than the ignition?

I am trying to narrow this down before I start replacing parts, as 2 coils or and ICM are both pricey.

Thanks for any assistance.
 

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Specs for the 85 - 86 vt1100 coils are quote "approx 2 ohms" so I am assuming its not that critical. Your bike has much the same ignition system. The wild fluctuations (rpm on your inductive tach) leads me to believe you have a faulty cdi. I remember on another thread someone said that the front and rear cdi is interchangeable on these bikes. Try swapping them around and see if the behavior changes cylinders. I cant see the coils causing it as they are basically slaved to the cdi as far as when to fire goes. Another thing you can try is an ohm meter on the wires from coil to cdi while bike is running. see if the fluctuation is duplicated there. This kinda thing makes an ole fashion points ignition pretty attractive doesnt it.
 

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Thanks for the help. After a lot of testing last night, I am not sure that my tach isn't part of the problem on the unequal RPM's. However, I am able to clearly see the timing light slow down it's pulse rate between around 1200-1800 RPM. Same behavior off both coils, so it must be the ICM (only one on my '99). The reduction in spark timing seems to be bracketted by an RPM range. This has to be the ICM, as I see no change in voltage on the Pulse generator leads. I also see a lot of misses. They are really cut-out's, where the light goes dark for almost a second.

I feel sufficiently confident that it is the ICM and will drop the $200 to replace it.

I'll post my results.
 
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