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Ecu Vs Tps: Sick 6Th Gen & I Need Some Help


pres589

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I've got a 2004 VFR800, non-ABS, with about 54k miles on the clock. Nearly a full year ago I took my 6th gen off the street and started to very slowly do some overdue maintenance as well as electrical improvements. Basic things; new thermostatic switch for the radiator fan, manual over-ride switch for the fan in case I have a problem with the switch, a bus bar for accessory grounds. Nothing really earth shattering there. New plugs, new cooling hoses almost everywhere, a new fuel filter.

A couple days ago I had the bike in a state where I could try starting it again. I have the airbox off the bike, the velocity stacks installed, and hoped I would finally do a starter valve sync in the next couple days. All sensors are installed, the PAIR valve is attached electrically, and I've made sure to the best of my abilities that I have all of the vacuum lines attached properly. Gallon of fresh 91 in the tank, hit the starter switch, and it started pretty easily.

It does not respond to throttle well at all. If I really slowly roll in some throttle opening the bike will rev but it's not happy. Quick opening of the throttle usually kills the bike. I let the temp get up to about 135F on the dash display and called it a night, knowing I had more troubleshooting ahead of me. The feeling I had was TPS problems of some sort.

Last night I go out, put the side stand down, and start the bike. Sure enough, 8 blinks of the FI light, which the manual says is a TPS fault. I grab my old digital voltage/ohm meter and some T-pins and start going through the manual's walk-thru for troubleshooting. With the ECU connected I have voltages on the yellow/red and gray (I think? I'm at work, doing this from memory) wires at the TPS with the key & run switch ON. These voltages were nicely in the ranges described by the service manual.

With everything turned off and back probing pins at the TPS I have a change in resistance as the throttle is twisted; I believe the range was about 500 ohms closed, 1.5k ohms wide open, and the change in resistance seems pretty linear and smooth. I have continuity through the wiring harness; with the TPS cable side plug pulled, each conductor rings through from the pin in the connector at the TPS to pins at the ECU connector. So unless a gremlin has done a depin/repin job on the connectors to the ECU, I believe there's good paths from the ECU to the TPS, and I don't see any pushed back pins or damaged terminals anywhere.

My brain says that I have a damaged ECU somehow. My gut says this is nonsense because how would that have happened? I'm not sure how to proceed. I see used ECU's are about $300 on ebay which is an awfully expensive part to purchase not knowing why I'm having to replace it. I have not spoken to my local Honda (and other makes) motorcycle shop about this at all so I'm not sure if they can test the ECU somehow.

What do I do next?

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The 6th Gen .pdf FSM is available from VFRD here: http://www.vfrdiscussion.com/forum/index.php/files/file/220-02-09-honda-vfr-service-manual-optimized-bookmarked/

- I never leave the house for the garage without it. Section 5, page 80 = TPS

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I don't know much about FI error codes (yet), but if it were me, given the explanation above, I would probably review my install of the fuel filter to ensure it is correct and not starving the bike for fuel with a roll-on.

Or it could be totally unrelated, but still the timing is suspect...

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I've already got the FSM and I'm basically to the end of the troubleshooting step list. "Replace ECU and see if it acts the same" is where I've had to stop.

rhoderage: 8 blinks of the FI light means that the ECU isn't happy, electrically, with the TPS circuit. It could be internal to the ECU or it could be external. Fuel starvation isn't related to this.

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Your TPS changing resistance through the throttles' movement would indicate that voltage would also change, if some were applied per the manual, so that is good. I'd want to put the air box back on with the MAP installed and start it up again after clearing the codes. Just to confirm that the ECM is expecting to see a drop in air box pressure as the throttle is opened/TPS output voltage changes and engine speed increases and this may have generated your initial FI light code.

Not that our bikes have electrical issues or anything, but I have always been told to check the grounds and connections. Double check your ECT sensor install - did you use teflon tape or pipe dope to seal the NPT threads? Perhaps try letting the sensor ground to the engine as the schematic shows the sensor going to ground and it's the only point where the G/O (green/orange) wire goes to ground in the manual's wiring schematic.

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The only additional thing I can think of would be to check the output voltage at the ECU and compare to the reference voltage. In other words, key=on, then roll the throttle back and forth to see what voltages are actually making it to the ECU. There can be continuity between the TPS and ECU, but if the resistance in the circuit is high, even if the TPS is doing its job properly, what the ECU ends up seeing could be off.

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VFRpwr: I'll clear codes again, install the airbox and the sensors, and see if anything changes. It seems odd that the bike would be able to calculate this out that well. For fun I pulled the MAP, flapper control solenoid, and TPS connectors off as they all share some common wiring either from the ECU or to ground. Bike acted the same. I did get a MAP sensor fail flash as well as the TPS flash. Plugging it all back in got me back to just TPS fail and it still coughs and wants to stall on roll-on of throttle.

I didn't touch the engine coolant temp sensor in all of this, just the fan switch. The ECT seems to read temps fine so I believe it's functioning properly. Not sure if I want to disturb it now since I haven't yet and I would rather leave the bike as close to as-found as I can. I did run the bike with both the new coolant thermostatic switch as well as my manual fan switch ungrounded in case there was something odd going on with those parts. The coolant switch I added is meant for a Nissan 240sx, which is a two-wire switch that has to be handed a chassis ground to form a complete circuit to control/power the fan. In any case, no change, which actually is what I hoped to see as this really shouldn't have affected the ECU/TPS issue.

Cogswell: Agreed, you suggestion makes sense. Looking at the wiring diagram, what pins should I use for this voltage check? I'm thinking DC voltage between ECU connector A pin 9 and connector B pin 31? I can backprobe those two terminals with T-pins and run the engine to see what this thing does both with Key On Engine Off and Key On Engine On. Thoughts? Anything else to think of?

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Im reading this - what are the test voltages from the 3p connector? The manual has a test harness thing your supposed to use to test from the ecm but you can just probe from the back of the connectors, I dont know anybody who has one of those harnesses, I always just stuck the multimeter probes into the back of the connectors at the right pins.

I see you have some ohm readings but the procedure tests volts from the 3p connector and from both sides of that connector and to ground. Have you done any of these voltage tests? Maybe I missed where you did that?

There are 6 different voltage tests to do, one to check overall voltages since of thats low all sorts of issues can happen. One to rule out a bad ground, its rather comprehensive.

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HispanicSlammer: I've run through a bunch of the voltage checks, all the ones that were easier to do without the factory ECM break-out cable assembly since I don't have one. All were in the limits described by the service manual. I'll do them all again and post results from each when I get home this evening.

Something odd is how they describe a pink wire at the TPS. The wire doesn't go pink until it gets to the 10 pin round engine jumper harness. At the TPS it's red/yellow, which is how the updated schematic from TomG33 drew his clarified version that is downloadable from here. Seems like an error in the FSM. Pretty easy to figure out though but it makes for a more confusing conversation. I also wish the ECU connectors had numbered pins on the connector itself and not just in the service manual.

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Okay, here's what I've done so far. I took pretty comprehensive notes. This is from the 2002 VFR shop manual that's in the downloads section. I started on page 5-19, Step 1.

Step 1 - Start the bike, count the blinks: 8 blinks. No other blinks, just this 8. I inspected the connector and everything looks good and clean. At this point I put the bike on a battery charger to make sure I wouldn't have to worry about a low voltage condition at the battery causing me issues with measurements.

Step 2 - I actually did this two ways, backprobing terminals through the connector with the connector attached to the TPS, and with it disconnected per the manual. It says I should run from the Pink wire at the 3P TPS connector and ground. My bike doesn't have a pink wire here. I checked all three wires in reference to chassis ground. These were done with the key on, run switch on, bike not running.

Connected to TPS:

Lt. Green/Yellow wire to ground - 2.28VDC

Green/Orange wire to ground - 0.03VDC

Red/Yellow wire to ground - 5.04VDC

Disconnected from TPS:

Lt. Green/Yellow wire to ground - 4.92VDC (I think this indicates the TPS is good, or at least is one sign that it is good)

Green/Orange wire to ground - 0.04VDC

Red/Yellow wire to ground - 5.05VDC

Step 3 - Voltage between the AWOL Pink wire and the Green/Orange wire; there's a problem here since, again, no pink wire. So I measure voltage between the following wire pairs with the key & run switch on, bike off.

Lt. Green/Yellow to Red/Yellow - 0.00VDC

Green/Orange to Red/Yellow - 5.00VDC

Green/Orange to Lt. Green/Yellow - 4.89VDC

Step 4 - Pull the ECU connectors off the ECU and check between the Yellow/Red wire at the 3P TPS connector and chassis ground for continuity;

I checked all of them as I don't have a lot of faith in this wire color call-out. Might as well check all of them, right?

Lt. Green/Yellow to ground - No, inf. resistance

Green/Orange to ground - No, inf. resistance

Red/Yellow to ground - No, inf. resistance

The manual states that if I don't have continuity between the Yellow/Red wire at the 3P connector and ground, I have a short circuit in this wire. I think this should be "open" and not "short" but that's besides the point. Which of the three wires at this connector is the ground, really?

For fun I did this next bit where I checked for continuity between the pins at the TPS 3P connector and the ECU plugs to try and figure out where these wires go and if they rang out or not.

The Lt. Green/Yellow wire at the 3P connector rings to a pin on the black ECU connector. I would say it's in the bottom row, fourth position from the left, with the retention tab facing up.

The Green/Orange wire rings to the gray ECU connector, top row, third position from the left.

The Red/Yellow wire rings to the gray ECU connector, top row, farthest right pin.

So I made a couple assumptions at this point. Pink wire at the 3P TPS connector in the manual means light green wire on my motorcycle. I also looked the ECU connectors over; the wiring colors are the same from the TPS connector to the ECU connector. They ring through nice and clear with low resistance. None of them are pushed back or other issues. So I went ahead and did the last couple steps using T-pins at the ECU connector to backprobe the terminals.

Step 5 - Does the Pink meaning Light Green Wire ring through to the TPS Light Green Wire - Yes.

Step 6 - Check voltages from the back of the ECU with the key on, run switch on, engine off.

Lt. Green/Yellow wire on the black ECU connector to the Red/Yellow wire on the gray ECU connector, I have 2.69VDC with the throttle closed and 4.62 with the throttle pinned wide open.

Lt. Green/Yellow wire on the black connector at the ECU to the Green/Orange wire on the gray ECU. 2.31VDC close, 0.40VDC wide open.

I'm really not sure what to make of all of this. Throttle closed has the voltage pretty cleanly divided from the 5V excitation voltage from the ECU, either side of the wiper in the TPS. If the system was built that way, this TPS is working fine, and the ECU is bad. I believe the ground path is through the ECU, so pulling the connectors from the ECU and not having a path to ground is good. A path to ground would drain one side of the TPS as it operates and I don't think the system is build that way. I believe there are some mis-translations in the service manual. But how is it I'm the one finding this now?

Thoughts? If I were to take a wild guess, I have a bad ECU. But that baffles me as well. Help!?

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On page 5-81 of the manual, it mentions output voltages with the throttle open and closed (step 6 in your diagnostic?). If I'm reading it correctly it specs closed output voltage is .1 X input voltage and wide open is .824 X input voltage, which if input is 5V, would be .5 volts and 4.1 volts, both +/- 10%. Am I reading it right that you were getting 2.69 v and 4.62 v? (sorry, I don't have the wires in front of me, so I'm not following exactly). If that's the case, it doesn't look like the ECU is getting what it expects. Maybe re-check against page 5-81 to see if that's what you're getting.

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Cogswell: One thing I find very odd is how we're supposed to do a multiplication step where the input voltage is like a variable. Why is that? If there's supposed to be a 5VDC reference voltage out of the ECU, that should be regulated, so the variability really shouldn't be in there, it should be 5 plus or minus some very small percentage. There's that same sort of math shown in Step 6 of the TPS troubleshooting pages. I can try and check the voltage potential between the Green/Orange and Red/Yellow wires at the ECU connectors to see what they act like through throttle rotation.

I'm not sure why I have these wire color differences on my 2004 vs the 2002 manual. The wiring diagram for 2006's that I have seems more accurate. I may go looking for a later manual.

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I'm not absolutely sure, but I believe the 5 v is or should be constant. The TPS has a base level of resistance, which decreases as the throttle rolls open, but the resistance does not go to zero, hence the math. The throttle closed voltage looks like it might be too high. It appears as though it should be close to zero. Backprobing should give acceptable results, but the mis-match of the manual vs the wires you see makes it difficult to know which is which. My $.02 is that the specified voltage needs to be confirmed coming from the TPS before the ECU be declared bad.

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To do a decent troubleshooting of the TPS the purpose of the three wires really should be known. I'm pretty positive that the Green/Orange wire is the ground path for the TPS. Red/Yellow is the 5V voltage reference conductor into the TPS. That means the Light Green/Yellow wire is the position derived signal from the ECU. Right?

So what's weird is how I have a touch over 5V at the VRef pin at the TPS connector when the connector is pulled, AND I have just under 5V at the signal wire. The next weird thing is that the TPS is acting like a voltage divider and not a pot; Signal wire should have something like .5VDC at that pin in reference to chassis when the connector is attached to the TPS. Not this 2.3V stuff. And then to have the voltage drop with throttle rotating open is contrary to normal TPS sensors.

Anyone have any first hand knowledge of how this circuit works on their early 6th gen VFR? Anyone have a known good TPS lying around they wouldn't mind loaning me?

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You are correct in your assumptions about what each wire does. Green/Orange is Ground, Red/Yellow is 5V into the TPS. Light Green is the wire that varies voltage as you open and close the throttle.

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You are correct in your assumptions about what each wire does. Green/Orange is Ground, Red/Yellow is 5V into the TPS. Light Green is the wire that varies voltage as you open and close the throttle.

Solid, thanks. So it would seem like the TPS itself is not acting in a good way when I have these screwball voltages.

When I get home tonight I'll backprobe the connector at the TPS itself and, with the ECU plugged in and the key on, check the Lt. Green/Yellow to Red/Yellow voltage potential through the full movement of the throttle. Unless something very odd is happening, I believe the readings will match what I saw at the ECU connectors last night, with 2.3V with the throttle closed. I'll also check the resistance through the switch both as a total resistance as well as from the sensor to gnd through the opening range.

If anyone else has things I should check or suggestions, let me know. Thanks for the questions and support.

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Okay, did some more testing this evening. Here we go, with the key on / run switch on, and measuring at the connectors at the ECU;

Lt. Green/Yellow to Red/Yellow wires - 2.72V w/closed throttle, 4.63 w/open throttle. 4780 ohms w/closed throttle, 1340 ohms w/open throttle.

Green/Orange to Red/Yellow wires - 5.01V w/closed and open throttle, 420 ohms w/closed throttle, 687 ohms w/open throttle.

Lt. Green/Yellow to Green/Orange wires - 2.28V w/closed throttle, 0.38V w/open throttle, 4750 ohms w/closed throttle, 750 ohms w/open throttle.

I believe this narrows down the TPS as the culprit. As for the TPS itself, it's marked as a "JT3L 31105". Vehicles using a JT3L seem limited; the Honda Passport from 2003 to 2005 seems to use a similar unit but I don't know if the direction of rotation is the same or not. I'm really not impressed by how Honda makes these units harder than they should be to replace. Anyone replaced a TPS on their VFR800?

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I seem to recall a post on VFR Club (Bikersoracle) that mentioned that the TPS is only sold as part of the entire throttle body assembly. I cannot confirm that though. Strangely however, many of the TB's for sale on ebay have had the TPS removed and yet they're rarely for sale separately. There are good used TB's for sale in the $100 +/- range, so maybe not much more than a TPS would be new if available from Honda. I'd bet that there are either Honda or Acura cars that use the same one if only the part # or compatiblity were known.

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Cogswell: In another example of just how much Honda loves us, the TPS is held in with screws, but at the time of manufacturing the heads are cut off after the TPS is installed. If you look closely you can see that the TPS is held in this way as there are threads existing the back side of the mounting area. You have to rotate them out using tools like a punch and hammer to rotate the screws out until you can grip them with pliers or similar methods.

JT3L is the majority family markings on the TPS on my bike. JT2's are older, JT4's seem to be newer. The next set of numbers, 31105, identifies the exact TPS on my bike. In the Wrist Twisters thread on swapping the TPS off of the Honda 919, it turns out that the TPS meant for late-80's Civics and similar will work interchangeably. The biggest issue is the direction of rotation of the TPS wiper and it matches or not as they can rotate either direction.

I'm about to leave for a short vacation so I can't work on this now. I intend to pick this up on Tuesday. In researching Honda TPS issues I have found complaints of the exact failure to operate that my bike is expressing; 2.5-ish volts out of the TPS with the throttle closed. So this information may come in handy as these bikes age.

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I would send the injectors out to be cleaned and balance while you're at it. They had gas sitting in them for a year, they will be gummed up. $15x4 is way cheaper than $300.

Also I would replace all vacuum lines and insure that the tps is properly mounted and aligned with the throttle shaft and that all the throttle body linkage is properly functioning.

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Cogswell: In another example of just how much Honda loves us, the TPS is held in with screws, but at the time of manufacturing the heads are cut off after the TPS is installed. If you look closely you can see that the TPS is held in this way as there are threads existing the back side of the mounting area. You have to rotate them out using tools like a punch and hammer to rotate the screws out until you can grip them with pliers or similar methods.

JT3L is the majority family markings on the TPS on my bike. JT2's are older, JT4's seem to be newer. The next set of numbers, 31105, identifies the exact TPS on my bike. In the Wrist Twisters thread on swapping the TPS off of the Honda 919, it turns out that the TPS meant for late-80's Civics and similar will work interchangeably. The biggest issue is the direction of rotation of the TPS wiper and it matches or not as they can rotate either direction.

I'm about to leave for a short vacation so I can't work on this now. I intend to pick this up on Tuesday. In researching Honda TPS issues I have found complaints of the exact failure to operate that my bike is expressing; 2.5-ish volts out of the TPS with the throttle closed. So this information may come in handy as these bikes age.

Good info to have. Sorry you're having this issue. :sad: I just don't get the design philosophy behind making the TPS inseparable from the TB when TPS's on most cars are as easy to change as spark plugs. Keep us posted.

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Bringing this thread up from the dead with some potentially useful info and new questions.

So after a lot of research, I saw too much evidence that the 6th gen (and probably every other Honda, car or motorcycle) VFR TPS is screwed onto the throttle body. It's set, "tuned", and the heads are cut off. Here's what mine looked like after I cut slots with my Dremel;

tps_screws_zpsahpklkjk.jpg

I went to the parts store with my existing TPS in hand and returned with a Dorman part meant for a 2004 Honda Pilot. Here it is installed on my bike;

new_tps_zpsjlpxjx4w.jpg

And it acts exactly like the factory unit. What I've discovered is that the TPS work perfectly by the book if I have it loose in my hand and wired to the motorcycle. This is with either the Dorman part or the original OEM part. I also still get 8 flashes of the FI light, but right now the fuel tank is off of the bike in a safe spot, so perhaps that has impact here. I don't know. The PAIR valve is also not installed but reading on vfrdiscussion.com says that this shouldn't drive a flashing FI light. I've also not cleared the ECU memory but the battery was disconnected for the last month plus so I'd think the codes would be cleared by now.

In any case, what I did discover from all of this is that I have to slightly rotate the shaft of the TPS to install it properly on the throttle body. I can almost adjust the TPS to get a proper throttle-closed voltage reading at the ECU. Almost. If I slotted the holes on the TPS (and I'd do that on the Dorman, not the OEM unit) I may be able to get there. But why has this happened?

I took the throttle stop bolt loose on the opposite side of the main shaft, where the cables attach, to make sure that the butterflies were not being impeded from rotating completely shut. This did not fix the situation and the butterflies are closing properly. It's like the tab on the TPS side of the main throttle body shaft is rotated slightly clockwise as seen by the TPS. This is what would be holding the TPS off of its closed stop and why I'm seeing about 2.5VDC at the ECU connectors when I should be seeing 5.0.

So I tried twisting the TPS interface tab around on the throttle body shaft and it seems very well attached to the shaft. No budging it with my bare hands and I wasn't about to put pliers to it.

So to sum up; the TPS sensor itself from the factory seems to be working just fine when I hold it off of the throttle body and attach it electrically to the bike. The TPS interface tab seems to be twisted on the throttle body because of this but it seems solidly attached to the throttle body and doesn't look to be mistreated. 2004 VFR's seem to use the same throttle position sensor as 2004 Honda Pilots and probably some other vehicles. I've got a blinking FI light that may or may not be important.

I wish I had access to a known good throttle body, with or without the TPS sensor. I'm not sure what to do next. Input?

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Wax unit will keep the butterflies opened slightly when cold. That might be the problem with trying to achieve a zero voltage reading.

Never seen the FI light blink because of this. The butterfly plates seem pretty well shut. Will see if I can get it to run and idle up to temp and see if any of this clears itself.

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