Intake Pressure Sensor reading low.

[meosborn]

This is all on my 2003 FJR1300RC. 60k.

So after performing a number of maintenance actions (valve clearance check, TBS, cleaned intake butterflies) I have been having a problem with a nasty hesitation when accelerating from slow speeds.

I have been all over the forum and it seems that there have been a number of people that have had similar problems for what appears to be a variety of reasons. I have checked the battery, cleaned the large electrical connectors under the tank, checked the TPS, swapped the pressure sensor with the atmospheric pressure sensor under the seat, checked the readings using new vacuum hose and I've checked the IPS with a Mityvac.

Someone on the forum mentioned that the ECU has a default map for the IPS so I tried running it with the IPS unplugged. It ran much better although not perfect. To me this points to the intake pressure as the problem.

When I run the diagnostics and use diAG 03 which is supposed to read 10-200 mm Hg I get 7 or 11 and sometimes 15. I suppose technically this is over the minimum value but it seems odd to me. Coupled with how it ran with the IPS unplugged I think this must be low. When I hooked the IPS to one throttle body at a time the reading goes up in the 130s, with two connected it drops to the 50s or 60s, with three it goes to the 20s and 30s.

One thing I notice was that there is a pulse of air that comes out of the throttle body as well when the engine is turned over. This all seems to make sense when I consider that with all four hooked together the pulses of air must cancel out the vacuum.

I cannot rule out something else causing the hesitation in the acceleration but right now I'm focusing on the intake pressure reading since it's the only abnormal indication that I have found and it has me baffled.

So all that boils down to at least two questions at this point. First, if you have a GenI, what reading do you get from the diAG 03 check? Second, is there someone out there that can explain the intake vacuum system to me so that I might be able to figure out what the problem might be?

 

[road runner]

When you're in the diag screen note what it reads with engine off, not cranking (atmosphere). Then note what it reads with engine running at idle (high vacuum). I'm a little rusty on units of measure so I don't know what it should be, but you should see the reading be very different as it should be reading from low or no vac with engine off to high vac at idle or cranking. This should give you readings from one extreme to the other.

Not sure if you can run it while in diag, but you should be able to crank it with throttle closed and get close.

 

[meosborn]

The manual reads "Generate the pressure difference by cranking the engine with the starter, without actually starting the engine."

That's what I've been doing and getting the readings of 7 and 11 (sometimes 15) jumping around.

Also, diAG 03 is "Pressure difference (atmospheric pressure - intake air pressure)". The atmospheric pressure is read using diAG 02. It reads fine.

I don't think the engine will start in the diAG mode. I could be wrong I suppose (it's happened once or twice). Either way, I can't right now as the tank is off the bike.

One of the reason I'm hoping someone might be able to explain the vacuum system to me is to find out if I might have messed something up when I cleaned the intake butterflies. I've looked all over the place for a vacuum diagram or explanation.

 

[ionbeam]

Edit: If you problem is sudden onset then it's not the TPS and ignore the following. The TPS failure is a wear out issue that will subtly develop in the background until one day you notice it.

Your FJR should run fine with the Intake Pressure Sensor unplugged; in fact you shouldn't even notice that it's unplugged. If it still runs bad with the IPS unplugged the problem is someplace else. If you haven't replaced your TPS during the recall I strongly suggest you hook a volt meter to the signal wire, tape/Velcro/tie the meter to the handlebars and go for a ride. Watch the readings on the meter. If the problem is the TPS you will see the problem occur at the same voltage point every time.

If the problem occurs at the same throttle opening, in every gear it's also an indication of a bad TPS. Put a piece of tape on the control pod and the throttle grip then draw a line that aligns up on both, then use this as a throttle position indicator.

 

[wmadoty]

If it ran fine before your maintenance and you did not get rough or obviously damage anything then you are chasing a ghost. Sensors do not go bad while you are doing maintenance. If you had this problem before your maintenance then you might be on to something. I think I would be looking at the reasons the sensor could be reading what it is, and not just assuming that I have a bad sensor.

Any chance you did anything that could have allowed the timing chain to skip a tooth? Did you adjust any shims or slacken the chain? Roll the engine backwards? Your symptoms sound like a classic skipped tooth to me, and the cam timing being off would play hell with that sensor's readings.

If that is not the case, I think I would be looking for a vacuum leak, pinched wire or hose, or something of that nature.

Hope you find your problem and I wish I could be more helpful. The reason I am posting this is simple. I can not count the times I have fixated on a perceived problem and chased it virtually forever when my "problem" had nothing to do with the real problem. Wish someone would have smacked me in the head a few times.

 

[meosborn]

wmadoty, I'm pretty sure that's what I'm looking for. This forum has been very adept at the head smack over the years so I figured I would give it a shot.

As far as a skipped tooth, I did consider that after reading about it in other threads so I checked the timing using a timing light and it checked out just fine. That check along with the fact that it runs just fine at speed leads me to believe that I'm not looking at a skipped tooth issue. I haven't pulled that valve cover again to check the cam marks but I didn't feel I had a good reason to do so. If I did skip a tooth would the timing still be right and could it run well at speed? If the cam did skip a tooth then the valves would be open at the wrong times and that would pretty much explain the vacuum issue. Uggh, I hate pulling that valve cover.

ionbeam, the TPS checks out fine. That was actually the first thing I was looking at since the off idle stumble seems to be the hallmark of a bad TPS. Mine was replaced under the recall but it was a number of years ago. Everything checked out in the diAG mode and using the multimeter. That was got me started checking the other diAG functions which lead me to the IPS.

 

[meosborn]

wmadoty, good call. Looks like I skipped a tooth. Thanks for the head smack.

I'm lucky I didn't destroy it. I haven't been doing so well with my attention to detail lately. A couple of weeks ago I dumped 6 quarts of synthetic oil into the wife's mini-van and remembered just as I finished that I hadn't put the drain plug back in.

I'll post an update when I get the situation corrected and can test it out. Assuming I haven't damaged anything it looks like I might get out of this with only having to buy some more coolant.

 

[Chiefblueman]

Looks like you may have dodged a bullet, Meosborn! I've got my fingers crossed for you.

Are you running the original cam chain tensioner? My '05 has the original in it at 20k and I have a replacement on the bench. Better get off my ass and replace that bad boy.

 

[Donal]

wmadoty, good call. Looks like I skipped a tooth. Thanks for the head smack.

I'm lucky I didn't destroy it. I haven't been doing so well with my attention to detail lately. A couple of weeks ago I dumped 6 quarts of synthetic oil into the wife's mini-van and remembered just as I finished that I hadn't put the drain plug back in.

I'll post an update when I get the situation corrected and can test it out. Assuming I haven't damaged anything it looks like I might get out of this with only having to buy some more coolant.

I haven't done this myself but....................

Do not attempt to 'adjust' the chain at the camshaft sprockets (assuming both camshafts line up - the exhaust is not clear in the picture). Release the chain tensioner and make your 'adjustments' at the crank (bottom). You should be able to remove the timing gizmo so you can see what you are doing. I am sure Fred has written something on this, if I find it I will post a link.

Good info from Radio Howie here just scroll down to post #12

Plenty of good info and good very good pics here as well, scroll down to post # 30 for Fred's words of wisdom.

Some more good info from RadioHowie here

 

[Constant Mesh]

Obviously one should always line up the camshaft pip with the line on the cap and then look down and check the mark on the pickup coil rotor. The pickup rotor turns 2 X the degrees of the camshafts so an error is much easier to detect at the pickup rotor.

You can use a small right triangle to check the alignment of the camshaft pip with the mark on the cap. Put one straight edge against the cap and slide the right angle corner up against the mark on the cap. Now look for the pip along the other straight edge of the triangle. If the pip and the mark are in alignment it should be obvious. You can easily look straight down on the intake camshaft pip and check the alignment -- no problem, right triangle not needed. But, for the exhaust camshaft alignment, the triangle offers an easy verification of proper positioning. All you need to see is the pip's location relative to the edge of the triangle. A side view will offer all the info you need.

 

[meosborn]

Both cams line up with the TDC mark on the rotor off by what appears to be one tooth. I really think I lucked out big time with this but I will give the compression a test before putting it all back together. If that doesn't check out then I just ruined my summer.

Oh, and Chiefblueman, the CCT was replace about 3 years ago. Just as a precaution.

 

[meosborn]

Got the chain corrected. Cranked it through a couple cycles to check and it looks good. It's going to take quite a bit of elbow grease to clean the FIPG off the valve cover. The new stuff sticks quite a bit better than what I used to use.

I only have an hour or so each night to work on the bike right now so this will take a few days. I was hoping to at least test out the IPS tonight but no luck. Thanks for all the help. With any luck I won't be starting a "Where can I get a new engine" thread.

 

[wmadoty]

Glad you found the problem. Hope you get it corrected and it all works out well for you.

 

[Fred W]

That was a good picture of a chain that skipped one tooth on the crankshaft. If it had skipped tooth on the cams it would have been off only half of that amount. That can/will happen any time you slacken the chain tensioner without securing the chain to the 3 sprocket in some way.

 

[meosborn]

Thanks Fred W, it's nice to know I did something good in this process. To add on to your advice, be sure you don't rotate the crank with the CCT slackened. That's what I did to cause my predicament.

I'm having a heck of a time with this FIPG that I used on the valve cover. It's Permatex The Right Stuff. It just plain sticks and doesn't want to let go. I'm torn as to if I should use it again. I'm betting it seals great but I'm not sure i want to deal with it again the next time I check the valve clearances.

I checked my clearances again tonight and everything is just the same as when I checked before I skipped the tooth. My logic tells me that if any of the valves impacted the piston it would have caused interference with the valve closing all the way and the clearance would be out of spec on the high side. So I'm thinking this should mean that I lucked out and didn't damage them. Does anybody want to make me feel good and second that logic?

 

[Fred W]

Lots of people have done exactly what you've done, including factory trained dealership mechanics, because there are no warnings in the factory service manual about restraining the chain at the bottom end when just slackening the CCT. So, there is plenty of empirical evidence to show that having the crank sprocket off by 1 tooth isn't far enough to cause the valves to impact the piston crowns. You are safe. Now. if it had been 2 teeth on the other hand, that may have been enough for a catastrophe.

When I've done valve adjustments, even without moving the crankshaft off of #1 TDC at all, when re-tensioning it the chain wants jump backwards one tooth on the lower sprocket (with the result being the crank is advanced, like yours was). I believe the cause is that the chain has to be perfectly taut and strait to be long enough to reach from the exhaust cam sprocket to the crank sprocket. My "work around" was, with the cams perfectly aligned up top, to turn the crank backwards slightly (a few degrees CCW) to allow the chain to reach easier before tensioning. Then of course check the timing carefully after tensioning.

As for your gasket sealer, best bet is to apply it only to the valve cover and upper surface of the gasket, leaving the lower part of the joint dry. The gasket is rubber (neoprene actually) and can be used and reused over and over and will not leak with the very low oil pressures in the upper head area. It is just splashing oil around a little, no real pressure there. Having it stuck to the cover also makes it easier to get the cover back on in the confined space of the frame, with the gasket properly aligned. The FSM calls for a dab of (3 bond I believe) sealant at the half moon plugs on the ends of the cams, but I have been skipping that and not seeing any weeping oil between checks.

YMMV

 

[meosborn]

My final conclusions for this (self-caused) problem. I got a 200 mile ride in yesterday and the bike is running great.

The problem was entirely caused by me turning the engine over with the CCT retracted. The photos above are not of a cam chain slipped one tooth, they are of a cam chain slipped TWO teeth. Once that was corrected the bike ran perfectly. Can you believe it?

The indications I saw on the IPS were apparently normal or at least weren't the source of the issue I was trying to solve. I can't seem to find any mention of running the diAG 03 while the engine is warm but when the bike is cold the cold idle plunger allows air to bypass the throttle plates and has a significant impact on the intake pressure. I ran the diAG 03 test while manually closing the bypass plunger and the readings rose by about 40 mm. Well into the range specified by the manual.

This was all just another example that a bike will only run as good as the idiot holding the wrench will allow it.

Thanks again to everyone for your help. It's good to be back on the road. Too bad it's so late in the year. Especially with a deployment coming up.