Jump to content

TPS voltage drops when bike starts... normal?


AZBaldur

Recommended Posts

I'm trying to track down an issue with my bike. It idles roughly, stalls occasionally, and vibrates a bit more than usual. When I keep it at a steady throttle, say 2500 rpm, I can hear an occasional misfire.

 

In trying to diagnose the problem, I came across something that struck me as odd. The TPS voltage across pins 1 and 4 measures 385mV when the bike is switched on and not running, but drops down to 350mV with the bike idling. Is that normal? I also noticed that the supply voltage from the Motronic is a steady 4.83V, not 5V like I thought it should be. Could the Motronic be damaged?

 

The other day I took the bike in to have the fault codes read, and that indicated a faulty TPS, so I had it replaced. That did nothing for these running issues, though.

 

Any ideas would be most appreciated.

Link to comment
I'm trying to track down an issue with my bike. It idles roughly, stalls occasionally, and vibrates a bit more than usual. When I keep it at a steady throttle, say 2500 rpm, I can hear an occasional misfire.

 

In trying to diagnose the problem, I came across something that struck me as odd. The TPS voltage across pins 1 and 4 measures 385mV when the bike is switched on and not running, but drops down to 350mV with the bike idling. Is that normal? I also noticed that the supply voltage from the Motronic is a steady 4.83V, not 5V like I thought it should be. Could the Motronic be damaged?

 

The other day I took the bike in to have the fault codes read, and that indicated a faulty TPS, so I had it replaced. That did nothing for these running issues, though.

 

Any ideas would be most appreciated.

 

AZ,

Normal? I really can’t say.. Possible? Sure entirely..

 

Couple of things come to mind..

 

First is; the engine vacuum pulling on the throttle plate moving the throttle shaft slightly (be my best guess here)

 

Or; possibly a 5v return (ground) problem.. Monitor the 5v return between the TPS & battery negative post both before starting & after starting.. Maybe check all ground connections for corrosion & loose connections..

 

In any case shouldn’t be a problem as the Motronic recognizes anything under .4 volts as idle & sprays in fuel based on engine RPM & temperature not throttle position..

 

Were you playing with the TPS before the dealer pulled the codes? If so & you didn’t clear the stored codes that probably left a TPS code in the computer..

 

On you miss problem.. Have you run a compression test? Have you verified no loose valve to valve guide problems? Have you looked for vacuum leaks? Have you looked for loose throttle shafts to TBI shaft bores? Have you replaced the spark plugs? Any chance the R/H spark plug wire is contacting the TBI cam at idle (I have seen a few)?

 

Twisty

 

Link to comment

Thanks for the ideas, Twisty. That TPS behavior might just be normal and the bike seems to track the throttle nicely anyway, so I'm going to assume it's ok, at least for the time being. About that TPS code, well... I might have forgotten to clear the codes after playing with the TPS. Probably not the first perfectly good component I've replaced, most likely it won't be the last.

 

I've been trying to sort these running issues out for a long time and here are some of the things I've checked and tried:

  • Leakdown test: 14% leakage on right cylinder, 17-18% on the left, with 12psi incoming pressure (inexpensive Harbor Freight gauge, don't know if it's accurate enough)
  • Compression: around 190psi both sides
  • No vacuum or exhaust leaks that I can find
  • Heads recently rebuilt by San Jose BMW, on account of a burnt exhaust valve in February
  • Installed a set of low-mileage throttle bodies, which feel much tighter, throttle shaft to shaft bore
  • New coil, spark plug wires, and three or four sets of new spark plugs
  • No interference with throttle body cams
  • Valve adjustment
  • TB sync with both CarbMate and homebuilt manometer
  • Injectors professionally cleaned, within 0.9% of one another
  • New fuel filter
  • SeaFoam

Would low or uneven fuel pressure produce symptoms like the ones I described in the first post? Or perhaps a bad O2 sensor? One thing I forgot to mention: at steady throttle, it hunts/surges quite noticeably, even in sixth gear on the freeway.

 

Ugh... I'm running out of ideas here.

Link to comment

 

AZ,

-Leakdown test: 14% leakage on right cylinder, 17-18% on the left, with 12psi incoming pressure (inexpensive Harbor Freight gauge, don't know if it's accurate enough)….. That is a lot of leakage for 190 psi compression.. Was it done hot or cold? If cold that could explain it..

 

-Compression: around 190psi both sides….. Hot or cold or both? In any case sounds good..

 

-No vacuum or exhaust leaks that I can find….. Well the that pretty well eliminates that as the cause..

 

-Heads recently rebuilt by San Jose BMW, on account of a burnt exhaust valve in February….. That is a place to question then.. Why did the valve burn to begin with? Any chance you have a loose valve stem to guide?. Maybe a cam off one tooth? (difficult to believe with equal compression but worth a quick look)

 

-Installed a set of low-mileage throttle bodies, which feel much tighter, throttle shaft to shaft bore.. Were these installed after or before the problem showed up?.

 

-New coil, spark plug wires, and three or four sets of new spark plugs…. Good,, that more than likely eliminates those as the cause anyhow..

 

-No interference with throttle body cams….. Again at least eliminated..

 

-Valve adjustment…. No chance you have a tight one? Have you checked them when hot just to see if they stay about the same delta valve to valve?

 

-TB sync with both CarbMate and homebuilt manometer…. That is a good place to start.. Probably eliminates that as the cause..

 

-Injectors professionally cleaned, within 0.9% of one another.. Good sign.. Sounds like those are not the problem..

 

-New fuel filter.. Usually the filter shows up first at high engine load or high speed not at idle..

 

-SeaFoam.. Shouldn’t hurt but might give white smoke at start up if a lot used..

 

-Would low or uneven fuel pressure produce symptoms like the ones I described in the first post?… Yes it could but difficult to believe it could be different as they use a common regulator,, a common pump input,, & same high pressure line..

 

Or perhaps a bad O2 sensor? One thing I forgot to mention: at steady throttle, it hunts/surges quite noticeably, even in sixth gear on the freeway… That is a possibility,, just disconnect it at the 02 connector as it (engine) should run good without it.. No 02 signal is better than a erroneous 02 signal so try running with it disconnected..

 

You don’t have a fuel controller on that bike like the Techlusion do you? If so completely disconnect that (completely)..

 

 

Not getting any vacuum I n the fuel tank after a long run are you? If so suspect the evap can being plugged..

 

Any chance of a plugged catalytic converter?.. Usually not an idle issue but could cause the high speed surging.. Pull the 02 & hook a pressure gauge to the 02 bung then ride the bike (inches of water is better than inches of mercury) but a psi gauge can be used as long as it has good resolution in the 1-5 psi range.. Not sure what’s normal on the BMW oil head but would suspect anything over 1-2 psi..

 

Twisty

 

Link to comment

I had a misfiring problem around 3500 RPMs on a R1100RS that turned out to be a bad oil temp sensor.

 

Make sure the rubber intake manifolds are in good shape inside and out. Mine looked fine on the outside but the inside had various groves that had worn into them over time. I'd assume that on a 2003 bike these would be OK but you never know.

Link to comment

AZ,

-Leakdown test: 14% leakage on right cylinder, 17-18% on the left, with 12psi incoming pressure (inexpensive Harbor Freight gauge, don't know if it's accurate enough)….. That is a lot of leakage for 190 psi compression.. Was it done hot or cold? If cold that could explain it.. I did both leakdown and compression tests after warming up the motor with a 15 mile ride. Since that particular gauge only allows such a low incoming pressure, I tried lowering the pistons in the bore a bit from TDC and then wrenching the crankcase bolt against the pressure. That improved the leakage percentage noticeably, by about four percentage points on both sides.

 

-Compression: around 190psi both sides….. Hot or cold or both? In any case sounds good.. The oil coolers were hot to the touch when I came home from the warm-up ride.

 

-No vacuum or exhaust leaks that I can find….. Well the that pretty well eliminates that as the cause..

 

-Heads recently rebuilt by San Jose BMW, on account of a burnt exhaust valve in February….. That is a place to question then.. Why did the valve burn to begin with? Any chance you have a loose valve stem to guide?. Maybe a cam off one tooth? (difficult to believe with equal compression but worth a quick look) Why did it burn, exactly... lean condition, carbon flake, who knows. I assume that SJBMW checked all valves, guides, and such when they rebuilt the heads.

 

-Installed a set of low-mileage throttle bodies, which feel much tighter, throttle shaft to shaft bore.. Were these installed after or before the problem showed up?. After.

 

-New coil, spark plug wires, and three or four sets of new spark plugs…. Good,, that more than likely eliminates those as the cause anyhow..

 

-No interference with throttle body cams….. Again at least eliminated..

 

-Valve adjustment…. No chance you have a tight one? Have you checked them when hot just to see if they stay about the same delta valve to valve?

That's a good idea, I'll check that.

 

-TB sync with both CarbMate and homebuilt manometer…. That is a good place to start.. Probably eliminates that as the cause..

 

-Injectors professionally cleaned, within 0.9% of one another.. Good sign.. Sounds like those are not the problem..

 

-New fuel filter.. Usually the filter shows up first at high engine load or high speed not at idle..

Right... the bike will take full throttle without apparent fuel starvation issues, but it vibrates a lot, though.

 

-SeaFoam.. Shouldn’t hurt but might give white smoke at start up if a lot used.. I put in the recommended SeaFoam-to-gas ratio. The bike doesn't smoke at all, except when I top up the oil past the three-quarters-full mark and give it anything close to full throttle on the road. Then it'll bog down heavily and smoke like a chimney.

 

-Would low or uneven fuel pressure produce symptoms like the ones I described in the first post?… Yes it could but difficult to believe it could be different as they use a common regulator,, a common pump input,, & same high pressure line..

 

Or perhaps a bad O2 sensor? One thing I forgot to mention: at steady throttle, it hunts/surges quite noticeably, even in sixth gear on the freeway… That is a possibility,, just disconnect it at the 02 connector as it (engine) should run good without it.. No 02 signal is better than a erroneous 02 signal so try running with it disconnected.. Another good idea, will try that.

 

You don’t have a fuel controller on that bike like the Techlusion do you? If so completely disconnect that (completely). I did have a Power Commander on it, set to 13.8:1 stoichiometric ratio. That was the setup when it burned the valve. I have since removed the PC completely, in an effort to sort these running issues. The PC comes with its own wide-ratio O2 sensor, and the bike was actually a bit better with the PC installed.

 

 

Not getting any vacuum in the fuel tank after a long run are you? If so suspect the evap can being plugged.. Nope... I've even tried disconnecting the evap can lines from the throttle bodies and plugging the spigots with rubber caps. No change.

 

Any chance of a plugged catalytic converter?.. Usually not an idle issue but could cause the high speed surging.. Pull the 02 & hook a pressure gauge to the 02 bung then ride the bike (inches of water is better than inches of mercury) but a psi gauge can be used as long as it has good resolution in the 1-5 psi range.. Not sure what’s normal on the BMW oil head but would suspect anything over 1-2 psi.. There's an idea... the exhaust puffs seem healthy, although there's this strange whistle or tweet with every one. Could indicate a restriction, a partial collapse perhaps. I wonder if it would hurt it to remove the muffler and cat converter and take a short ride... although it would be loud as hell, of course.

 

Twisty

Link to comment
I had a misfiring problem around 3500 RPMs on a R1100RS that turned out to be a bad oil temp sensor.Interesting... I suppose the Motronic was always in "cold start" mode then, running too rich, lacking the engine temp data.

 

Make sure the rubber intake manifolds are in good shape inside and out. Mine looked fine on the outside but the inside had various groves that had worn into them over time. I'd assume that on a 2003 bike these would be OK but you never know.Yes, these are in very good shape, I verified that when I installed the new throttle bodies.

Thanks for the ideas Mike, I appreciate all input.

Link to comment

 

 

[*]New coil, spark plug wires, and three or four sets of new spark plugs...

.. I'm running out of ideas here.

 

Which coil have you replaced? The secodary plug coil or the primary sticks?

 

Andy

Link to comment

 

 

[*]New coil, spark plug wires, and three or four sets of new spark plugs...

.. I'm running out of ideas here.

 

Which coil have you replaced? The secodary plug coil or the primary sticks?

 

Andy

 

Andy check the bottom of his posts... "Black 2003 R1150R (single spark, non-ABS)"

 

 

Twisty

Link to comment

AZ,, sure you can run it without the muffler/cat but there will be no 02 sensor & no exhaust baffling & real short exit piping so you will get a lot of exhaust reversion at some operating parameters & if that reversion gets back to an open exhaust valve it will run like crap & buck & surge.. Might learn something & might not.. Might be best to clamp on a piece of pipe with a washer welded in the end or the outlet bent over so it doesn’t have a same diameter outlet as the pipe diameter.. Even a big ding in the pipe in a couple of places OD will help kill off some of the reversion..

 

Might be easier to make an adapter & look for excess exhaust back pressure..

 

 

Are you 100% sure your cam timing is spot on?

 

You can always gut your cat (I did both an 1100 & 1150) through a 7/8” holes in the side of the cat then used a stainless plug to close the hole up.. Takes a lot of time & work but can be done with little outside appearance issues & no real noise increase..

 

That “it'll bog down heavily and smoke like a chimney” when full of oil bothers me wonder what you have there.. Is the crankcase breather operating OK? Is the breather tube plugged or kinked? Have you drained the lower air box of accumulated oil?

 

Twisty

 

Link to comment
AZ,, sure you can run it without the muffler/cat but there will be no 02 sensor & no exhaust baffling & real short exit piping so you will get a lot of exhaust reversion at some operating parameters & if that reversion gets back to an open exhaust valve it will run like crap & buck & surge.. Might learn something & might not.. Might be best to clamp on a piece of pipe with a washer welded in the end or the outlet bent over so it doesn’t have a same diameter outlet as the pipe diameter.. Even a big ding in the pipe in a couple of places OD will help kill off some of the reversion..

 

Might be easier to make an adapter & look for excess exhaust back pressure..

 

- Yeah, probably.

 

 

Are you 100% sure your cam timing is spot on?

 

- It should be right on the money. When I reassembled the motor after the heads were rebuilt, I started on the right side (which was pinned at compression TDC), and then did the left side after very carefully rotating the motor a full revolution, holding the left cam sprocket and keeping the chain taut. Now, when I pin the motor at TDC and remove both cam tunnel covers, the arrows on both sprockets are horizontal.

 

You can always gut your cat (I did both an 1100 & 1150) through a 7/8” holes in the side of the cat then used a stainless plug to close the hole up.. Takes a lot of time & work but can be done with little outside appearance issues & no real noise increase..

 

- Cool... I saw an illustrated thread on that very procedure somewhere.

 

That “it'll bog down heavily and smoke like a chimney” when full of oil bothers me wonder what you have there.. Is the crankcase breather operating OK? Is the breather tube plugged or kinked? Have you drained the lower air box of accumulated oil?

 

- It bothers me too, because it doesn't make sense that I can't fill the oil up to the maximum. The breather tube makes a fairly sharp 90 degree turn before it connects to the crankcase, but it's hard to say whether it's kinked shut or not. Couldn't hurt to take things apart there, just to check, or simply install a new one. That plastic elbow that connects to the crankcase, I assume that's the actual breather, much like an automotive PCV valve? If I check or replace those two things, is there anything else that I can do about crankcase ventilation? I've drained the lower air box numerous times, and never get more than a few drops out of there. Both throttle body plastic runners are coated with a thin film of oil though, which I assume is fairly normal.

 

Twisty

Link to comment
Are you 100% sure your cam timing is spot on?

 

- It should be right on the money. When I reassembled the motor after the heads were rebuilt, I started on the right side (which was pinned at compression TDC), and then did the left side after very carefully rotating the motor a full revolution, holding the left cam sprocket and keeping the chain taut. Now, when I pin the motor at TDC and remove both cam tunnel covers, the arrows on both sprockets are horizontal.

 

 

Maybe not,, this was posted by Anton a while ago so maybe a question of arrow vs key notch position..

 

Personally I haven’t seen one that the arrows don’t point out but Anton definitely found one or more that seem to be different..

 

I guess if it were my bike I would pop off both valve covers,, then verify all valves are closed at TDC & the lash is same side to side,, then put a dial indicator on the same valve on both sides & turn the engine in the running direction until the valves are partially open.. They had better be close to the same valve lift side to side or there is a problem in BoxerLand somewhere..

 

 

 

sprockets.jpg

 

Twisty

Link to comment
Maybe not, this was posted by Anton a while ago so maybe a question of arrow vs key notch position.

 

Wow... how does something like that get through quality control? Anyway, I've now verified that both cam sprockets are OK in terms of arrow vs. key notch position.

Link to comment

Andy check the bottom of his posts... "Black 2003 R1150R (single spark, non-ABS)"

 

 

Twisty

 

I consider myself re-briefed.

 

or as they said at school - 'read the whole question'!

Sorry guys.

 

Andy

Link to comment

No worries, Andy, we all jump the gun from time to time. Thanks for chiming in and don't be shy about speaking up if you get some more ideas.

 

I'm going to keep chipping away at Twisty's ideas and I'll post progress notes as they become available.

Link to comment

Ok, progress report. I've now gone back in and adjusted the valves a bit loose (.008/.014) and there was no change, so that rules out tight valves being the culprit.

 

However... we've had some relatively cold mornings here in the Valley for the past few days, so I've been able to start the motor pretty well "chilled". I've now firmly established that the misfire doesn't start until after the motor warms up a bit. For that first minute or two it runs pretty nice and smooth with no misfire. So... what say ye? Oil temp sensor ok? O2 sensor out of spec?

Link to comment
Ok, progress report. I've now gone back in and adjusted the valves a bit loose (.008/.014) and there was no change, so that rules out tight valves being the culprit.

 

However... we've had some relatively cold mornings here in the Valley for the past few days, so I've been able to start the motor pretty well "chilled". I've now firmly established that the misfire doesn't start until after the motor warms up a bit. For that first minute or two it runs pretty nice and smooth with no misfire. So... what say ye? Oil temp sensor ok? O2 sensor out of spec?

 

 

AZ, running worse when the motor warms up some tells us something,, I’m just not sure what..

It could be that the computer controlled cold fuel enrichment just covers up an existing problem,, or a sensor is acting strange as it warms up,, or the problem coincides with the 02 sensor coming on line,, or something simple like a coil or plug wire showing it’s true colors as the system goes leaner as it approaches closed loop..

 

First thing I would try is disconnecting the 02 sensor & if it runs better that would be the place to start..

 

Twisty

 

Link to comment
AZ, running worse when the motor warms up some tells us something,, Im just not sure what.. First thing I would try is disconnecting the 02 sensor & if it runs better that would be the place to start..

 

Twisty

 

Twisty, is the air temp sensor in the air box linked to any of this?

 

Andy

Link to comment
AZ, running worse when the motor warms up some tells us something,, Im just not sure what.. First thing I would try is disconnecting the 02 sensor & if it runs better that would be the place to start..

 

Twisty

 

Twisty, is the air temp sensor in the air box linked to any of this?

 

Andy

 

 

Andy, yes but it isn’t a major player.. More of an attenuator or fine tuner than a major control-to sensor.. In fact in closed loop it is only used for spark table fine tuning & quick throttle changes like snap accel or snap decels.. The oil temp sensor as well as TPS & engine RPM are the major contributors..

 

On most Bosch systems the computer looks for a certain AIT (air intake temperature) range then uses that for fine tuning (more for spark control).. If the AIT is out of range of what the computer thinks it should be it just ignores that & substitutes it’s own value (somewhere in the 70°f range).. If you just simply unplug your AIT sensor I seriously doubt you would even tell the difference in normal riding..

 

 

Twisty

 

 

 

Link to comment

I tried disconnecting the O2 sensor today and went for a 25-30 mile ride. This improved things somewhat, there was less misfiring and less hunting at small throttle openings.

 

In the spirit of trying new things, I then tried fully closing the air bypass screws on the throttle bodies. This improved matters a lot. Almost no misfiring and only minimal hunting, yet it still idles at 1050-1100rpm according to the tach. That seems strange to me, I thought these bikes should barely hold idle with the screws fully closed... is that correct? The throttles are hitting the stops positively and I can see slack forming in both throttle cables when I let go of the grip, so the throttles are not hung up on the cables.

 

Gotta be an air leak somewhere, I thought, so I tried dousing all throttle body joints and O-rings with water for a good while, but the motor never missed a beat. What's more, the bike produces good power and there's no pinging when I give it full throttle, ducking out of the airstream behind the Cee Bailey to listen closely.

 

What the heck am I missing?

Link to comment
I tried disconnecting the O2 sensor today and went for a 25-30 mile ride. This improved things somewhat, there was less misfiring and less hunting at small throttle openings.

 

In the spirit of trying new things, I then tried fully closing the air bypass screws on the throttle bodies. This improved matters a lot. Almost no misfiring and only minimal hunting, yet it still idles at 1050-1100rpm according to the tach. That seems strange to me, I thought these bikes should barely hold idle with the screws fully closed... is that correct? The throttles are hitting the stops positively and I can see slack forming in both throttle cables when I let go of the grip, so the throttles are not hung up on the cables.

 

Gotta be an air leak somewhere, I thought, so I tried dousing all throttle body joints and O-rings with water for a good while, but the motor never missed a beat. What's more, the bike produces good power and there's no pinging when I give it full throttle, ducking out of the airstream behind the Cee Bailey to listen closely.

 

What the heck am I missing?

 

 

 

 

AZ, yes closing the BBS should really slow the idle to be real low or an engine stall..

 

Try using an UN-LIT propane torch to look for vacuum leaks.. You hit a spot that is leaking the RPM’s should pick right up..

 

Maybe look at the TBI shafts for wear & looseness,, TBI inlet “O” rings leaking,, loose TBI throttle plates on the shafts,, maybe loose intake valve guides,, missing vacuum hoses on the bottom of the TBI’s (should be plugged off with vacuum caps or intact hoses to the Evap System)..

 

Sounds like it is getting extra air from somewhere.. Any chance a previous owner or mechanic has messed with the TBI base idle stop screws?

 

Borrowed this picture link from Anton's web site,, check out the throttle shaft wear..

 

shaft.jpg

 

Twisty

 

Link to comment

I removed the throttle bodies a couple of days ago to check everything again, to see if I had missed something the first time. The TBs now installed are a pair of low-mileage ones that I bought used to compare with the original ones which now have over 40K miles on them. These new ones feel quite a bit tighter than the original ones, especially where the butterfly shafts go through the TB bushings. Everything TB-related looked and felt good and tight, and the O-rings were pristine. There was a very light coating of oil in the runners, the TBs themselves were quite clean (being very recently installed), but there was a heavy reddish-brown coating of some sort on the intakes, valve faces and valve stems:

 

Intake.jpg

 

I noticed this coating the other day when I installed the "new" TBs, but it wasn't this heavy at that time. It seems too dark to be motor oil, so I'm guessing it's gas additives? Especially since the TBs themselves are so clean, and this coating is forward of the injectors. Thoughts?

Link to comment

AZ, difficult to tell from the pictures but more than likely varnish or a type of coke from hot fuel condensing on the cooler manifold walls during hot soak..

 

Twisty

 

Link to comment

Archived

This topic is now archived and is closed to further replies.

×
×
  • Create New...