Pressure Sensor Testing

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My Gen 1 still has issues. This started last year October. Bike ran normal until it went into Vboost. If felt flat, but still accelerated. Removed spark plugs, found cylinder #4(right front) cylinder to have a black spark plug. All others golden tan. Was told it was a carb issue. Tore into carb, found absolutely nothing. Dealer found nothing as well. They stated it was just out of sync. Seemed to work for about 100 miles. Now the bike is running worse, smells of raw fuel, has a hesitation that can be felt and heard through the exhaust when first starting off. Bike has no power anywhere now. So dealer is looking back at the bike. Call me up and states that the boost pressure sensor is bad. Now, looking back at the download manual(Page 7-30) it shows testing the sensor. But as with ignition coils, it shows a static test. The specified value is 2.0V. I dont know what the value is that was tested. What I want to know is if I apply a vacuum to the sensor, I should see the voltage increase to 5V or more, correct? At least thats what I am gathering from the chart at the bottom of the page.

They are still trying to BS me into saying that the valve adjust after 8000 miles is bad and more than likely the engine is simply worn out. Granted I know nothing of the previous 19,000 miles before I owned it, but from there to 32K, oil changed religiously, mostly highway riding(higher highway speeds of 90+) with some romps here and there. Longest one time ride was around 300 miles.

The bike didnt gradually wind down. It worked on one VBoost event, several miles down the road, it didnt. It was instant. I sent it to the dealer cause I simply dont have time to mess with it and I dont want it to sit while I finish my other projects. Prior to this, the dealer its at was good. The tech who did the work knew his trade. This new crew doesnt seem to know the bike as well at they thought. And New Mexico simply doesnt have a local batch of Vmax riders to tap with knowledge of what to test and diagnose.
 

02GF74

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A compression test is a good indicator of wear and incorrectly adjusted valve clearances. Test is done with WOT and then repeated with a squirt of oil into the pistons to show up piston ring wear.

If I remember correctly, the vboost module only uses rpm, the incorrectly named vboost pressure sensor is wired to the ignition module. Shaun or FM will be along soon to correct me.

Are you able to to swap coils over for the cylinder to see if the problem moves?
Have you fitted new ngk plugs as per manufacturer spec?

Checked the ignition lead? the copper connector tends to corrode, solution is to cut back a couple of mm to reach good wire.

If you pull the plug out, and hold end near earthed part of engine/chassis, is there a healthy spark as the engine is cranked? (remove all plugs to help engine turn over)
 

MaxMidnight

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Call me up and states that the boost pressure sensor is bad. Now, looking back at the download manual(Page 7-30) it shows testing the sensor. But as with ignition coils, it shows a static test. The specified value is 2.0V. I don't know what the value is that was tested. What I want to know is if I apply a vacuum to the sensor, I should see the voltage increase to 5V or more, correct? At least that's what I am gathering from the chart at the bottom of the page.

They are still trying to BS me into saying that the valve adjust after 8000 miles is bad and more than likely the engine is simply worn out. Granted I know nothing of the previous 19,000 miles before I owned it, but from there to 32K, oil changed religiously, mostly highway riding(higher highway speeds of 90+) with some romps here and there. Longest one time ride was around 300 miles.

The bike didn't gradually wind down. It worked on one V Boost event, several miles down the road, it didn't. It was instant. I sent it to the dealer cause I simply don't have time to mess with it and I don't want it to sit while I finish my other projects.


The sensor in question sensor controls ignition advance not V Boost.

The value of 2.0 volts is what would be expected at atmospheric pressure.
The unit operates between 0.5 and 2.0 volts when there is between -600 mm Hg (i.e. negative pressure) and atmospheric pressure and between 2.0 and 4.9 volts between atmospheric and +600 mm Hg (i.e. positive pressure).

On that basis if you apply a vacuum you should see the voltage drop and if you apply positive pressure the voltage should rise.

If they are saying the pressure sensor is bad then I would ask them for their test results. The cynic in me suspects the tumbleweed would roll past before you get them! ☹

Assuming the valves clearances were correct 8K ago then I doubt that would be an issue isn't a worn out motor. Once again I'd ask then to provide data to justify that comment.

From what you say you are between a rock and a hard place; the dealer doesn't inspire any confidence and do you trust their diagnosis? If not then you may well be throwing good money after bad if you let them 'fix' your bike.
On the other hand you say you don't have time to do the work yourself. Only you can decide which way to jump.

As Mr 02GF74 suggests some basic diagnosis needs to be done. You need to get some hard data to back-up any diagnosis rather that opinions which may or may not be right.
A compression test is OK but a cylinder leakage test would be better.
A spark plug tester would let you check if you have sparks to each cylinder and an infra red thermometer would give and indication on exhaust temperature. Any significant discrepancies between the cylinders would indicate where the problem lies.

If #4 is still showing black is it sooty or oily?
 
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Let me answer your last question first....its dry and sooty. Fuel fouled.

I am sorry I didnt clarify properly I know its for the timing advance but more when its under vboost, if I read how the system operated correctly.

"On that basis if you apply a vacuum you should see the voltage drop and if you apply positive pressure the voltage should rise."
Where would positive pressure on a naturally aspirated engine come from? Naturally aspirated engines will always run in a vaccum till the throttle is moved, then pressure goes to 0. At least thats the way every other automobile engine I ever worked on has worked. Unless this system wants to see 2.0-2.3V max as the graph indicated. Then if thats the case, my question is moot.

The last thing I am having them do is swap the coils, replace the one sooty plug and road test. If the problem follows the coil....well, we know then. If the problem stays on 4, then I will do my own compression, leakdown, and valve measurements. Measuring spark will kinda be moot as the problem doesnt feel like it occurs at lower RPMs or when the bike isnt under a moderate load. My gut tells me I think I am in the right direction with the coils. But time will tell if that was correct.
 

02GF74

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Where would positive pressure on a naturally aspirated engine come from? Naturally aspirated engines will always run in a vaccum till the throttle is moved, then pressure goes to 0.
Possibly when a backfire occurs in the carbs, so not under normal conditions.? Or fitted a turbo or super charger? Neither of which applies.

Depending on the sensor design, it may read both negative (vaccuum) and positive pressure so can be tested both ways? I'm sure the service manual will cover testing it so please check before attempting to blow into it.

.... And if it it is a bad coil, time for a COP update?
 

MaxMidnight

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Let me answer your last question first....its dry and sooty. Fuel fouled.

I am sorry I didnt clarify properly I know its for the timing advance but more when its under vboost, if I read how the system operated correctly.

As far as I am aware the control of advance and V Boost are separate entities and don't act in concert.
The only effect V Boost may have on the pressure sensor is how it affects inlet manifold pressure which would change the output voltage of the sensor thus alter advance.

"On that basis if you apply a vacuum you should see the voltage drop and if you apply positive pressure the voltage should rise."
Where would positive pressure on a naturally aspirated engine come from?

As for the +ve pressure, all I'm doing is quoting what is in the service manual which shows how the output voltage alters when +ve pressure is applied.

Pressure sensor output voltage.jpg
 
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As far as I am aware the control of advance and V Boost are separate entities and don't act in concert.
The only effect V Boost may have on the pressure sensor is how it affects inlet manifold pressure which would change the output voltage of the sensor thus alter advance.



As for the +ve pressure, all I'm doing is quoting what is in the service manual which shows how the output voltage alters when +ve pressure is applied.

View attachment 78983
I seen that as well, and thats where the question comes in. Before I do my own testing, I wanted to make sure I was testing right and getting the readings as expected. And your understanding of the Vboost and pressure sensor is my understanding as well, unless I am missing something. The manual doesnt have much in the way of testing beyond that is kinda vague. Based on the search function here where not much is talked about this sensor, I just think it wasnt tested properly for my bike.
 
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Possibly when a backfire occurs in the carbs, so not under normal conditions.? Or fitted a turbo or super charger? Neither of which applies.

Depending on the sensor design, it may read both negative (vaccuum) and positive pressure so can be tested both ways? I'm sure the service manual will cover testing it so please check before attempting to blow into it.

.... And if it it is a bad coil, time for a COP update?

The manual doesnt really indicate how to test different pressures/vacuum to the sensor. It gives a static number of 2.0V-2.3V and if it fails that, replace sensor. And maybe for the coils. Unless I am looking at $1000 to replace a maybe $100 coil, I will fix just the defective part before changing out an entire system just for the sake of changing it all out.
 

02GF74

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I was offering the option of a cheap and more reliable alternative, naturally if you can get new replacement for not excessive cost, then that is the easiest way. (I would do the same even though I have a set of COPs lying around).
 
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So, this is the last I will do with the dealer on the bike. They swapped the coil, still #4(RF cylinder) is fouling the plug after the road test. They said they did a compression test and it was low at 140psi(claims specs are 182psi) on all cylinders. Then they said that the valves are leaking at 60% on cylinder #4. Now, I do this myself on engines with driveability issues. Usually high leakage like that gives alot lower compression readings. Since I havent done any actual testing myself, I am unsure what any of this means at the moment. So, I am gonna take the bike home, fuel stabilize it and see if I can get to it myself soon. Not too many folks up to par on this bike in my neck of the woods.
 

02GF74

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How accurate is their measuring equipment?
A more valid test is to do all four cylinders, if there is more than 10% variation then there are issues.

What does 60% leaking actually mean? And how does that compare to one of the other cylinders?

It may be just be but it sounds like they are trying to baffle you with BS.
 
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When I do leak down tests, 0% means system is leak free. Never have I seen a system at 0%. 10-30% is what they consider low leakage. 40-70% is moderate leakage 80-100% is severe leakage. At least through my gauges from Mac Tools is set up that way. Mine are pressure differential gauges. You put 100psi of air pressure into the system. One gauge shows the psi, the other gauge shows the psi that the engine is unable to keep.


This is the one I have.

So, to answer your question...I have no idea how accurate their methods of measurement actually are. Not really there to see what they are doing. They said the engine was low compression with all cylinders at 140psi when they state spec is 182psi(I know this means beans and in a perfect world would see all operating engines near their peak mark). But I also live 6000 feet in the air. So, pressures are ALWAYS never accurate. Baro pressures, compression figures and so on. When I lived in NY near sea level, you would get result nearing specification. But elevation is something most never take into account. As for the leak down, they told me just on that one cylinder. Since thats the only cylinder fouling spark plugs, it almost makes sense. But I always grab at least one more cylinder for a basis of comparison.

Now can the engine be worn out? Yes. Its possible. Its just not probable since the way it runs now is worse than when they got it. The problem was a fouled cylinder with flat power in the Vboost RPM. Now it has a miss in the 3-4000 RPM with no audible cycle of the Vboost with key on and low power throughout the entire engine RPM range. Your assertion of trying to BS me....is what I also believe. Thats also why I told them to wrap it up and I will pick it up.

Since I still have other projects going, that bike needs to get to the back of the line for the time being. I have a 1978 Hawk I finally sourced a frame for that is next up for work. Then I also need to get the transmission, transfer case, and linkages installed in my truck and I need to gut the interior for holes in the body, installing clutch brackets and pedal with some HVAC actuator work. I wasnt planning on working on the Gen 1 this year. Hence why I had the financial means to send it out.

With the pressure sensor, I was also thinking....it controls timing....but would that affect only one cylinder? 3 cylinders are burning perfect. Only 1 is not. So, I do not think the sensor is really bad. If it is bad, it wouldnt be causing a one cylinder misfire. The low power in Vboost....perhaps....but I think whatever happened started with cylinder #4.

If I can find some time in between, I will do some base tests with pics to show what I come up with. Or worst case, trailer the bike up and take a trip to see Mr. Morely, LOL.
 

one2dmax

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Worst case I can send them an electrical test kit and it would have one of those in it. You can simply unplug it too but they will make them run erratic if they go out. It's more likely a CDI failing which is hard to test and again I can have one in the kit. Best to email me at [email protected]
 

02GF74

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You are correct, the ignition unit reads the sensor signal and treats all cylinders equally.

The carbon build up on the plug is due to rich mixture or weak ignition.

One thing to try is to remove all plugs (lets engine turn over easier), fit lead onto 4 and adjacent leads and hold them against earth.

Turn engine over and compare the sparks and if they are regular.

And another thing worth trying, a bit of a long shot, is let engine warm up, then fit a new plug to no. 4 and immediately hit the road. The reason is that once the plug fouls, it is harder for it to spark causing it to foiul up even more. Some engines are particular to clean plugs and won't run on fouled ones even when plugs have been cleaned hence using new... but as I say, a bit unlikely (this also eliminates the possibility of a faulty plug - presumably you already swapped it out?)

BTW thanks for the info about the leakage test equipment, never knew such stuff existed.
 

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I've written before about this, a KZ1000 I had, ran fine, but I thought it was time for a tune-up. Clean the K&N air filter, oil change, new NGK of the correct heat range & #, but it wasn't running well. I couldn't figure out why and took it to my French-Canadian mechanic friend. He used a water spritz to I.D. which cylinder wasn't up to snuff, and asked me, "what did you do?" I told him, and he said, "change the plug on the cyl not boiling-off the water on the exhaust header like the others." I replaced it w/one of those which I had removed, and it ran fine. It was a bad spark plug.

I'm not saying that's your issue, just that you have to be aware of what's facing you.

"Doctor, I hurt here," patient points to forearm, "here," points to rt. knee, "and here," points to left foot. "What is the matter with me?"

Doctor: "let me see your right hand." Patient winces as doctor examines it. "You have a broken finger!"
 
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The bike is home from the dealer and besides the coil swap, they ate the costs this time around. Riding home, so long as I dont actually use the bike, will move and reach speed. Every stop, I can smell a rich mixture from the bike. Obviously not so much as I am riding it. My buddy said he didnt see any smoke from the exhaust as he traveled behind me but he said as he got close in behind me at stop lights, he could smell it. He was in his car. I didnt get on it cause I didnt want to risk doing any more potential damage.

When I get some time and some of my tools to the house, I will start going over basic checks with pictures so everyone can see what I am seeing. If we are looking at certain electrical components failing, then Mr. Morely will be hearing from me so I can get certain parts tested. But first, I got my frame with title for my little Honda Hawk, so I am gonna start dinking with that. Then next weekend, no bikes get touched as its another camping trip 8200 foot up. After that, we should be getting a smidge cooler and hopefully a lot less humid so I can work longer on these projects.
 

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