No Spark - Boost Sensor?

[Guest Thainglo]

Been struggling with a no spark condition the last couple of weeks. Bought a TCI off of eBay, didn't fix the problem. I initially had spark on all but cylinder #4, then while working in the area, wrestling the battery around, and swapping the TCIs, nothing. Pulled the ignition and pickup plugs, all resistance reads as it should (114-119 on pickup coils, 3.2-3.5 on ignition coils). The TCI is getting power, bike is in neutral and the kickstand is up.

 

As I was getting ready to unleash some words no child should hear, I decided to check the boost sensor. When getting no reading between the + and - terminals on the TCI, I tracked back to the sensor itself. During my mangling process, the cover of the sensor was broken - enough that there is a hole in the top.

 

I know the boost sensor helps adjust timing, if the circuit is damaged can it shut off spark entirely? If so, any way to fool the TCI into running - even poorly - long enough to shake out any other gremlins?

[Dragonslayer]

Last year I had a no spark problem and could not get any thing to happen. Found GeorgeS who spent a lot of his time emailing me through a total wiring system trouble shoot.

Let me start buy saying that 99 % of the problems thaT HAPPEN WITH THESE BIKES ARE BECAUSE OF RESISTANCE ON ELECTRICAL CIRCUITS MEANING BAD ELECTRICAL CONNECTIONS.

In my case the problem was that between the ignition switch and the kill switch there was enough resistance caused by carbon build up on the switch contacts to decrease the voltage to the the TCI which in turn sent low volts to coils which didn't have enough volts to fire plugs. I took the switches apart, cleaned the contacts and put the switches back together and the bike fired right up . Problem fixed. The fix took about thirty minutes after about two months of tracing and testing and trouble shooting electrical circuits and connections.

 

Boost sensor is part of cruise control system that senses pressure and help adjust pressure in carbs while cruise control system is being used. I don't think it would be causing a no spark issue.

Your close enough to me that I could possible help you work through it if you need help. Just give me a call.

[Squeeze]

I remember a Discussion with GeorgeS about Fuses and rewiring the whole Fuse Panel.

 

I think he mentioned that the Vacuum Sensor is wired and fused with another Circuit than the IGN Fuse Circuit. And if that Circuit would let the Fuse go, you could be stuck in the middle of nowhere because of that.

 

As i type, i remember also a Member, maybe this was Greg_in_London couldn't get his Project Bike started without a Sensor hooked to the Harness. I wasn't a Problem if the Sensor worked on Vacuum or not, it only had to be there.

[GeorgeS]

If you have power to the TCI, then you can assume Ing fuse is OK.

 

------------------------------------------------------------------------------

 

Give the Run-Stop Switch, and the Ignition switch, a Bath , with electrical contact cleaner.

 

-------------------------------------------------------------------------------

 

What you are referring to as a " boost sensor " is actually " pressure sensor " which is the correct term. ( just for clarity )

All it does is sences changes in Intake vaccume, and adjusts Ignition timeing accordingly. It gets, 12V from Ignitioin Fuse Circuit. Thru, the Run Stop Switch!!

 

The bike should run just fine, without the " Pressure Sensor " HOWEVER, Disconnect the Plug from the Sensor ( about 6 inches from sensor ) on the off chance that there is an " INTERNAL ELECTRICAL DEFECT INSIDE THE SENSOR " Which might be causeing a voltage drop down line from the 15 AMP Ing Fuse. You seem to have reason to suspect it, so disconnect it completly. See what happens.

 

NOTE: At this point I am suspecting your RUN- STOP Switch might be the culprit.

 

Also: The 8 pin plug at TCI, has one Black wire, MAKE SURE ITS GETTING A GOOD GROUND. You said you had 12V to the 8 pin plug, so also, check the ground return.

 

Check: Do you have 12V to ALL 4 Ing Coil, Primary Windings ??? The 4 R/W wires to the Ing Coil plugs, All go back to a COMMON " Splice " buried in the wireing harness, so you have to make sure each coil is actually getting power.

 

Also: Just forward, and left, of battery, ( under upper fairing ) is your Main Grounding stud, for almost all " end user electrical devices " there are 4 or 5 black wires grounded at this stud. Access it from under the radio panel. remove bolt, and make sure contacts are all clean.

 

You "" MIGHT "" have a bad, "Side Stand Relay," even if the Switch is Ok on the Stand itself.

 

You "" Might "" have a Bad, Emergency Roll Over Switch, Very unlikley, but possible. Its located " UP " and " behind " the head light assembly.

 

Did you " CLEAN " all the Pins, in both plugs to the TCI ???

 

[Neil86]

The simplest way to check the interlocks is with the connector unhooked at TCI and key on...test for continuity in the black/white wire to ground. If there is no continuity, interlocks are in run state. If there is continuity, the interlocks are shutting down the TCI control.

[pegscraper]

The boost sensor has absolutely nothing to do with the cruise control, and it does not adjust the pressure in the carbs under any circumstances. The V Max has this exact same sensor, and they don't have a cruise control at all.

 

The boost sensor will advance the spark under part throttle conditions, and will retard it under full throttle. If the thing happens to be malfunctioning, it still shouldn't have anything to do with the bike not starting. It should still start and run.

 

This boost sensor - whatever one wants to call it - is badly named. What it actually senses is vacuum, manifold vacuum, which is a measure of engine load. It ought to be called a vacuum sensor. But it's not.

[Guest Thainglo]

The simplest way to check the interlocks is with the connector unhooked at TCI and key on...test for continuity in the black/white wire to ground. If there is no continuity, interlocks are in run state. If there is continuity, the interlocks are shutting down the TCI control.

 

This is an easy way to check, will try this weekend. I could follow the wiring on the schematic but couldn't tell if the circuit on the interlocks should be open or closed for the TCI to spark.

 

Is there a way to confirm the pickup coils are sending a signal to the TCI? Don't have an oscilloscope, wondering if there is another way.

 

Thanks for the tips!

Matt

[pegscraper]

I've been told by a Yamaha dealer's mechanic that if the pickup coil is good, you can measure between 3 and 9 volts on it with a VOM. I didn't think to ask if this works at cranking speed or not, when you have an engine won't run. But I don't know why it wouldn't. That's kind of the assumption anyway, because if the engine were running, you wouldn't need to be checking out the coil.

 

Have you tried measuring the resistance of the pickup coil to make sure it's not open? I'm almost certain the shop manual has a spec for that.

[Guest Thainglo]

Have you tried measuring the resistance of the pickup coil to make sure it's not open? I'm almost certain the shop manual has a spec for that.

 

Did the Ohm test in the service manual for the pickup coils and they tested out within spec. I'm going to track the gound line back and make sure it is making a good connection as well.