Help: I remain fixed position on throttle but RPM"s go down!

Some more information (but please read the post above this). I went to rule out the FPR. I checked the vent line, and there was no gas in it, primed the bike, fired it up, no gas in vent line, so that check passes. I thought maybe the FPR could be a factor. There was no gas in my throttle body/airbox though, and vent line was clean.

Please any ideas, I am at my wits end

 

I couldn't agree more. Return to stock and test. If it's still there, it's something in the bike. If it's ok, it's in the modifications. Put the mods back on, one at a time, and test after installing each. Whichever mod makes it fault is the likely cause. Bear in mind that there could be an interaction, for example, if the O2 eliminator has the wrong resistance and the PC allows the ECU to go into closed loop mode, it will keep leaning out or richening up and quenching combustion. The O2 sensor has a resistance, but puts out a voltage (either 1V or 0.5V at chemically correct air:ruel ratio - I can't recall which voltage). It's the voltage that the ECU reads in closed loop mode, not the resistance. The correct resistance only stops the ECU from turning the check engine light on. If the voltage is out by milli-Volts, it will fool the ECU into doing something stupid.

Good luck!

 

FYI I can tell you syncing the starter valves wont solve the issue. I've done it on mine and while it does make a huge difference in the idle and very low rpm performance of the bike, it wont at speed.

 

Danny,

I pulled the PCV, but still have the issues. Also I think what your saying about the O2 eliminators is a bit incorrect.

Yes its true, that the ECU looks to the O2 Sensor, and its chemically controlled, and will send back a 0-1V to tell the ECU to create a lean/rich mixture in closed loop. But the O2 eliminators are NOT creating that voltage signal for the ECU to lean/rich the mixture. The O2 eliminators are simply letting the heater know that everything is OK, so their is no Fi fault. the other two pins, in the connector, the ones that would actually give the ECU a 0-1V condition to lean/rich, are empty, therefore there is no signal being fed back to the ECU (voltage of 0), therefore there should be no closed loop (no feedback). Ideally I would check the ECU on that wire, to ensure that it really has no voltage, because there could be voltage being picked up in some other way on that lead, and as you say just a few mV and you may have issues. Now as far as whether or not the resistors are correct, well they are, one is 328.2 the other 227.8, well within tolerance. There is no FI fault, which means they are doing their job (heater sees O2 eliminator present). I have pretty much cleared my PCV. I do believe the stock PGM-FI module could be at fault here though.......its one of a few things I am considering, but I don't have a good way to test it.......basically I am just trying to rule everything else out.

 

Just an update, I am still having this issue and its maddening!

I had my valve clearance checked (everything is fine), new plugs, oil change, coolant flush, starter valves synced.

I checked the R/R, stator and loom following all the posts on here, and even put in a VFRness. All electrical checks are fine both hot and cold.

I removed the entire PAIR system, using block off plates.

I snugged up my insulators, cleaned and re-oiled my air filter (K&N).

I looked (visually) for any vacuum leaks, all hoses look like they are fine.

Cleaned my MAP sensor.

I had my throttle cables adjusted (by dealership).

I visually checked my FPR for any gas in the vacuum line.

What could this be? Please give me more ideas. I have the Fuel Filter scheduled to be changed Tuesday, and at the same time I am going to demonstrate to the mechanic my issue. Certainly someone has come across something like this before.

 

Do you have any add-on electrical components that might be draining it? I've got a few extras and mine was fine for a while til last year. Stator burned out, wiring harness was burned so I replaced the stator and, like you, got the VFRness. Once it was all back together it would start and idle but would only go about 100ft before dying. Turns out it was burning out the main VFRness fuse. The shop working on it would replace the fuse, go 100ft and die each time. I talked to the VFRness guy and he said some bikes need a 30amp fuse rather than the 20amp that it comes with. Put in the 30amp fuse and its been fine ever since.

You aren't burning fuses so chances are its not the same issue, but maybe you don't have as much electrical stuff as I do so you'regetting in under that line. Maybe try a 30amp fuse? Its a quick easy thing to test....

Ultimately though it does sound like you may be better off going back to stock, where possible, just to eliminate variables...

 

I have no add-on electrics other than my PCV. I already removed the PCV and have the same issue. My VFRness is not blowing its 20A fuse, so putting in a 30A won't do anything for me right now. I really think my electric is solid, as I spent so much time testing everything, did "The Drill", got solid readings in both hot and cold engine.

 

So this problem still plaugues me. I replaced the fuel filter, more as just a maintenance item, and I get the same problem.

I brought my bike into Honda today. They say it could be 1-3 days before they can even look at my bike. The mechanic that will be working on it rides a VFR, so thats a plus. I worry about Honda harassing me because I have a VFRness installed, etc.

I wish I had more input as to what the likely suspects would be for this issue.

I thought "fuel pump". But if a fuel pump is problematic, wouldn't it be problematic under acceleration as well? My problem is only during steady throttle.

Fuel Pressure Regulator makes more sense for a possible suspect, but the vacuum line was bone dry. Could their still be a problem with the FPR? How is this checked?

Then of course there is always the issue of potential air leak. What are the usual suspect places of air leaks on VFRs? I am guessing the insulator boots have to be one of the common places. I checked all the "regular" vacuum hoses attached to the airbox, my pair system is removed and plugged.

Also another symptom is that even at idle, the needle seems to float around, just +/- 100 rpm's or so not sure if this is normal or if it should be rock steady.

Really sucks having bike in the shop, 1-3 days before they can see it, then if they need parts maybe 5 days.......ugh. I would be so happy if they can slay this problem though, makes you really not like your bike when your having a problem like this and not getting anywhere.

 

I think I read it correct that you removed the PC V but left the 02's disconnected??? You need to put those back in or get new ones if you cut the wires, etc. I would all but bet that is your issue....

 

CRFan, I simply removed the PC V, to make sure I saw the same problem, which I did. I connected the PC V back. same problem. I do not have O2 sensors anymore. But if I have no O2 sensors, then there should be no information sent back to the ECU to lean/rich the mix, and therefore it should follow the ECU map correct?

My bike did this before removing the O2 sensors, before installing the PC V, etc.

 

With the stock set up you need to have the 02 sensors or it will not run right. Also, I would check your TPS sensor to make sure that is operating correctly.

 

TPS is operating as far as I can tell correctly. I checked it on my PC V software, shows like its going 0% to 100% at appropriate spots. I also re-calibrated it in PCV just to be sure. I don't have my O2's anymore. But as I stated, the bike was reducing throttle with O2's installed and stock ECU.

 

Here is some more information:

I pulled my fuel injectors and had them checked. I was going to have them cleaned, but the shop said they are perfect. They also leak tested them, and no problems. I replaced all the o-rings and cushions, and at the same time replaced the seals in the fuel rail (since they come in the gasket kit for the injector seats).

I am back to thinking possibly something electrical or sensor related which is effecting this problem.

It seems to me, like when I go on bumpy roads, I see the problem happen more prevalant. Now at first I thought, it was all in my head, and that a bumpy road was just translating to throttle change........but i don't think so, I think something bouncing around is causing this to drop off RPM's.

I have checked the grounds and connectors in the past, sprayed them with electrical contact cleaner. There were some I missed however. I did not do the main ECM connectors, and I did not do anything under the front like the Fuel Cut Relay.

I am only aware of these grounds on our bike: The starter cables next to the battery, the "main ground" right by the rear cylinder head, there is also a radial looking ground with a bunch of stuff connected to it on the left rear. What other grounds exist?

What types of sensors would cause this? Something like an IAT or ECT etc doesn't seem it would give these results of fuel being cut off/power loss.

One such sensor that DOES, is the CKP. I actualy read a thread on line which i can no longer find, where someone traced a similar problem to mine to his CKP. It was totally lose and actually had become damaged, so he had to replace it.

Anyone have a thought on that? CKP seem like a logical thing to check? The manual explains how to check it using peak voltage, but I am wondering if anyone has any other ideas on how I can rule it out or see if its acting up. I was going to start by wiggling the cable and see if I can get it to act up. of course, the cable may be fine, but the actual sensor is seated inside the case cover and so trying to figure out what I may be able to do outside of that, like check for some sort of spark or other thing somewhere which would confirm CKP is acting up?

At idle things seem fine, I notice it at steady throttle.........RPM's just start to dive, event though my throttle is held constant.

 

It's good to know that they're heated O2 sensors. Having a '99, and a '98 before that, I haven't had a VFR with O2 sensors to know what type they are. The bit of info you provided about the O2 sensors is the missing link in the puzzle.

You've disconnected the sensors and put resistors into the heater lines to trick the ECU into thinking that they're still there. However, instead of setting a diagnostic trouble code (DTC) and not going into closed loop mode, it goes into closed loop mode, but doesn't find the correct output from the O2 sensor's output. Because of this, it changes the mixture to try to get the right output, and the engine dies because the mixture is wrong.

As I said, you need to return it to stock. This means plugging in the O2 sensors, putting the PAIR system back on (the ECU expects to see its effect when it enables it), etc. stock with O2 sensor eliminators still isn't stock! You're throwing good money away because you didn't use a good diagnostic approach, like I told you. I've been an automotive engineer for nearly 13 years, including 6.5 years fixing other engineers' stuff-ups in an OEM. I do know a thing or two about diagnosis and fault finding. ;-)

Once you see it working correctly again (which I bet it will when it's stock), then you can start modifying it, one thing at a time. The modification that sends it haywire is the thing that caused the problem. Once you can turn the problem on/off at will, you know you've found it.

Now... My educated guess is that you need to fool the ECU into thinking it has the air:fuel ratio it's looking for, and you're never going to get that with one resistor in the O2 sensor heater circuit. You need a circuit that gives the ECU the signal it's expecting to see.

Good luck!

 

PS: I just read your post about the crank position sensor. I had troubles with the ECU wiring terminals for the crank and cam position sensors in my '98, and it simply wouldn't start. It would crank, but not run. I could be wrong, but I don't think you have a problem with either of these sensors.

 

Danny,

I am confused by your post. It would seem to me, that most people on this forum running aftermarket exhausts are running a power commander, and that most of those people are using O2 eliminators.

Yes the resistors are just there to trick the ECU so no code is thrown. So there is no input from the O2 sensors. But that is the whole point of a fuel map isn't it? The bike should be following the fuel map. Which I can make lean or rich at any given RPM and throttle position.

I suppose its possible my fuel map is bad, but I have tried many, the same ones that so many on here have no problems with. I have also seen this problem happen at various RPM's so its not just one small segment of the map.

Dynojet recommends removal of the O2 sensors if your using a PCV. If you want to use a O2 sensor you are suppose to use their wideband sensor. But if the bike were tuned there shouldn't be a need for this is my thinkng, but please correct me if I am wrong here.

You mention "it doesn't find the correct output from the O2 sensors, because of this it changes the mixture". This is contrary to the way I thought the system works. I thought the bike follows a fuel map. It only deviates from this map (which is based on RPM and throttle position), if there is an O2 sensor to tell it to make a change. With no O2 sensor, there should not be any change going on. I realize this is an oversimplification, as there are sensors like the MAP sensor which are giving inputs as well. But what you are saying is that despite my fuel map, and the lack of O2 sensor, this actually causes the ECU to go "searching" for something? That doesn't make sense to me.

 

You've told it that there IS an O2 sensor there by putting the resistor in (no check engine light, and no DTC when in diagnostic mode, presumably?)... The heater circuit only heats the sensor to make sure it's hot enough. Seemingly the DTC only detects the heater's presence. When it has something there telling it that the O2 sensor is there (ie:the resistor), it still goes into closed loop mode, and detects whatever floating voltage is on the signal line. Yep, I still think it's the O2 sensor eliminator...

 

Just remembered... When my research team built a hydrogen powered car, we had an intermittent problem of it going lean when we were running it on the stock petrol ECU (switchable petrol/hydrogen). When we turned the computer on in the back, it was all ok. When it was off, the separate wide-band lambda meter (with its own separate wide-band sensor) told us that the engine was going WAY lean. We figured out that the data acquistion card in the computer shunted the sensors to ground when it was switched off. One of these was the OEM O2 sensor. Actually, stuffed if I know why we didn't have more troubles.

Moral of the story: wrong voltage on the O2 sensor signal wire = wrong A:F ratio.

Good luck!

 

danny_tb, yes it should use whatever voltage is on the signal line. And since the voltage is 0, there should be no correction. The signal line has a voltage of 0, since the signal line is open, since there is no O2 sensor connected. Correct me if I am wrong, but if there is no O2 sensor, there is no signal, and if there is no signal, the ECM should be following the fuel map. I realize the conditions may be present for closed loop (i.e. Throttle position, temperature, presence of O2 according to "heater" line, etc). But there should be no corrections since the O2 signal line is open. I don't believe I am doing anything different/weird here, I am running a PCV without O2 sensors. Wouldn't everyone on this forum running a PCV without O2's experience the same issue as me? I don't think they do, which is why I am trying to understand what's wrong.

 

In theory, if you have a voltage of less than 0.2V or more than 0.8V, the ECU could be made to go into open loop mode (ie: fuel map). OTOH, that functionality costs money to put into the ECU/software, so there's a possibility that that functionality may not be there. Even if it is there, it might not work. I'll use the example of my '98 when it died and wouldn't start: There were no DTC's, but when I checked the resistance across the ECU pins at the crank and cam sensor plugs (through the wiring harness), my multimeter said it was an open circuit (checking the resistance across the pins directly on the ECU showed a resistance). When I pulled out the cam/crank angle sensor plugs, the DTC's instantly set, yet when they were plugged in, no DTC's set. I pre-loaded the wired into the ECU in one direction, and the resistance across the ECU pins through the wiring harness showed the same as across the pins directly. I plugged the sensors back in, hit he button and it fired up. The cause was that there was enough of a circuit to fool the ECU into not setting the DTC, but not enough to actually receive a signal from the crank/cam sensors.

With your situation, there might be something just that little bit weird going on (as with my cam/crank sensor signal issue) that means it goes into closed loop mode when there's no signal applied to the O2 sensor signal line (that's if this potential functionality is used).

On the other hand, perhaps everyone who has O2 sensors eliminated (at least the same model as yours) does have the issue, but most people ride around it, or are never steady enough on the throttle to go into closed loop mode. Perhaps there was a limited run of ECUs which didn't have an "outside of range signal" function (supplier quality spills happen), and Honda may have decided to replace the ECU's on complaint, instead of doing a recall - most people wouldn't see the issue because most people don't have that ECU with the O2 sensors eliminated. OTOH, perhaps there are different O2 sensor eliminators, and some work (ie: put 0.45V onto the signal line), while others don't - a very likely explanation, and I vaguely recall hearing of people having this issue before. The list of possibilities could be nearly endless.

If I'm correct, your bike didn't have the issue, then you made some modifications, then it did have the issue. Something that you've changed has caused the issue. OK, so you put it back to nearly stock (ie: O2 sensor eliminators still in place, but otherwise stock), and it still had the issue. It's a very interesting clue pointing toward the O2 sensor eliminators - especially when the conditions where it happens seem to indicate that it's happening when a completely stock bike will go into closed loop mode (this is another piece of evidence pointing at the O2 sensor eliminators). The issue is that it progressively loses power - in closed loop mode, if the ECU isn't seeing the right air:fuel ratio, it will put in more or less fuel (according to the rules in its algorithm), and either one will result in a progressive loss of power (yet another piece of evidence pointing toward the O2 sensor eliminators).

Here's a really easy test that you can do, even if you've thrown your O2 sensors away. Unplug the O2 sensor eliminators and go for a ride. You'll get the engine light because the ECU realises that you've unplugged the O2 sensors - put up with it for the test ride. It won't go into closed loop mode because it knows that there are no O2 sensors, so it should stay in open loop mode (unless it goes into limp home mode, which I doubt - you'll soon know if this happens, because it will ride like a pig). If the problem disappears, then it absolutely must be that the ECU is going into closed loop mode with the O2 sensor eliminators in place. If nothing else, it doesn't hurt to try it to see if I'm right/wrong.

As always, good luck!