Engine Surging 2500-3000 rpm - SV1000 Portal
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post #1 of 14 (permalink) Old 11th July 2018, 01:29 PM Thread Starter
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Engine Surging 2500-3000 rpm

I'm trying to figure out the cause of my engine surging that occurs between 2500 - 3000 rpm. It happens in neutral and in all gears, clutch lever in and out. It's fine below that RPM and above that RPM but anywhere in that range the RPMs raise and drop by 250 - 500 rpm. It's been going on for a while but didn't really bother me at first since I rarely spent time in that range. However, that RPM range happens to be where I'm at in stop-and-go traffic and parking lots and is very frustrating as the bike bucks like a bronco at those speeds.

27500 miles:
* Valves adjusted at 20000 miles. Didn't notice anything then.
* Rear coil pack replaced - no change
* Both plug caps replaced - no change
* Spark plugs in great shape and fairly new (NGK iridium) - no change
* TPS adjusted, then replaced/adjusted, put back to stock/adjusted - no change
* Vacuum leak found in loose front throttle boot. Tightened boot and no more leaks detected with spray downs with electronic parts cleaner - bike ran smoother overall but no change to surging
* CPS replaced - no change
* Simple resistor TRE installed (was hoping maybe different timing would show a change in rpm) - no change
* Throttle bodies sync'd - no change

* Charging system is strong, supplemental ground wire installed, and green connector eliminated

The strange thing is that it's exactly in that 2500 - 3000 rpm range, nowhere else. Idles great and runs up to redline great. 2400 rpm and below is absolutely fine as is 3100 rpm and above.
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post #2 of 14 (permalink) Old 11th July 2018, 02:22 PM
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Is this a CA E-33? Please check and don't go by living in MD that it's not. I'm here in PA and got an E-33 new so it could be and they try to purge the carbon can right about at that throttle opening which is why I ask. Also....have you synched the throttles? The sequence is valve adjust, synch then set TPS.
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post #3 of 14 (permalink) Old 11th July 2018, 03:52 PM Thread Starter
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Quote:
Originally Posted by RecoilRob View Post
Is this a CA E-33? Please check and don't go by living in MD that it's not. I'm here in PA and got an E-33 new so it could be and they try to purge the carbon can right about at that throttle opening which is why I ask. Also....have you synched the throttles? The sequence is valve adjust, synch then set TPS.
Forgot to mention the throttle body synch, it has been checked or done several times with no change. Added to original post.

I'll have to look up how to check VIN to determine if this is an E-33. If a carbon canister was present then it was removed by one of the previous owners but very well could have been there previously.
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post #4 of 14 (permalink) Old 12th July 2018, 08:22 AM
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One way to easily tell is the throttle bodies will have stacked vacuum nipples which were used for the purge canister which the 49 State bike lacked.

The ECU operates in dual-modes: at light throttle below about 11% it runs in Speed Density where the airflow is inferred by MAP (Boost sensors according to Suzuki) sensor readings, rpm, and throttle application. After 11% the ECU reverts to Alpha/N where the TPS and rpm are the prime motivators to fueling. If the surging is happening within the Speed Density range...which it sounds like it is, then the MAP sensors or their signals are suspects. They need to see manifold vacuum....while the throttle bodies also have ported vacuum nipples that deliver when the throttles are cracked. If the MAP sensors were hooked to the ported nipples it wouldn't like that very much. Would be good to verify all vacuum hose connections just to be sure everything is correct.
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post #5 of 14 (permalink) Old 12th July 2018, 02:51 PM Thread Starter
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RecoilRob, thanks for the explanation of the fuel mapping vs sensor input - that's very helpful with diagnostics.

I looked up the E33 vacuum fittings (tees) on a parts fiche and I'm not seeing any signs of an EVAP system. My TB auxiliary ports are plugged with OEM appearing vacuum caps that seem to be in decent shape. I know they're usually suspect but the MAP hoses seem to be in surprisingly good condition although maybe I'll replace them this weekend out of an abundance of caution. MAP hoses are going straight into the throttle body ports. By mentioning the ported nipples, are you saying that one of the ports (of two each) on the throttle bodies is larger/or routed differently than the other? I had originally assumed that the second set of throttle body ports was for auxiliary (such as EVAP) or diagnostic purposes and otherwise identical.

The MAP signal or fuel injection programming do seem suspect since this issue occurs in such a precise and repeatable RPM range with no deviation. Exactly at X rpm to X rpm at Y range of throttle input.

It seems to me that quick way to diagnose might simply be to unplug the MAP sensors and force it into Alpha/N and see if the problem is still present.
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post #6 of 14 (permalink) Old 12th July 2018, 06:13 PM
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I just double-checked my spare TB's and there are three vacuum nipples, two stacked on one side and a single one on the other side of the centerline and under the injector. Both lower nipples (closest to the engine) are manifold vacuum while the upper one of the stacked side is ported vacuum. It must be plugged while either lower nipple can be used for the MAP sensor or for synching the throttles. Watch that there is not a hose linking the cylinders together as I found this did affect how it ran.

You cannot and should not disconnect the MAP sensors!! What year engine is your bike? The K3-4 has a single MAP sensor along with a cam sensor on the back valve cover so the ECU can determine where in the engine cycle it is, while the K5+ uses dual MAP sensors which the ECU watches for the vacuum pulses to determine the proper phasing.

How sophisticated is your available testing equipment? If you could hook a scope to the MAP outputs it would clearly show if one or both were giving flaky info to the ECU. You might also be able to do a bench test on them with a Mighty Vac by slowly applying vacuum and watching their outputs. There have been a few bad MAP sensors reported here and there which could very well be your culprit. As long as the sensor isn't shorted or open and still reporting a voltage within the min/max the ECU isn't going to show a trouble code. This kind of failure can be a fun thing to find.
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post #7 of 14 (permalink) Old 12th July 2018, 07:03 PM Thread Starter
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Quote:
Originally Posted by RecoilRob View Post
I just double-checked my spare TB's and there are three vacuum nipples, two stacked on one side and a single one on the other side of the centerline and under the injector. Both lower nipples (closest to the engine) are manifold vacuum while the upper one of the stacked side is ported vacuum. It must be plugged while either lower nipple can be used for the MAP sensor or for synching the throttles. Watch that there is not a hose linking the cylinders together as I found this did affect how it ran.

You cannot and should not disconnect the MAP sensors!! What year engine is your bike? The K3-4 has a single MAP sensor along with a cam sensor on the back valve cover so the ECU can determine where in the engine cycle it is, while the K5+ uses dual MAP sensors which the ECU watches for the vacuum pulses to determine the proper phasing.

How sophisticated is your available testing equipment? If you could hook a scope to the MAP outputs it would clearly show if one or both were giving flaky info to the ECU. You might also be able to do a bench test on them with a Mighty Vac by slowly applying vacuum and watching their outputs. There have been a few bad MAP sensors reported here and there which could very well be your culprit. As long as the sensor isn't shorted or open and still reporting a voltage within the min/max the ECU isn't going to show a trouble code. This kind of failure can be a fun thing to find.
It's a K5 with dual MAP and no crank sensor. No trace any of the EVAP vacuum connections, just a separate MAP plugged into each TB and a second, unused port that's capped on each TB. I've disconnected the MAP sensors in the past by accident and then a few months ago disconnected them while diagnosing another issue and the bike runs without them connected - just throws the code for lack of MAP signal but runs OK otherwise. I think I've read before that it will default to Alpha N in the absence of the MAP and it appears that's what mine has done in the past.

No scope unfortunately.
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post #8 of 14 (permalink) Old 12th July 2018, 11:49 PM Thread Starter
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Just ran it with both MAP sensors disconnected and the problem goes away. Tried twice with the same result.

Engine runs fine with the MAP disconnected (as it did before) but a little on the rich side which makes sense for a backup fueling mode. So I think I've narrowed it down to MAP, either electrical or vacuum, but could also be a fuel map if that changes when the ECU defaults to Alpha N at that low of a load site.

I guess at the very least I can replace MAP vacuum hoses and vacuum caps (2nd ports) to see if that does anything. The bike is old enough to warrant replacement vacuum lines although they do look in excellent shape (surprisingly so).

Then on to the MAP sensors themselves I guess but that will be a fun one to diagnose.
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post #9 of 14 (permalink) Old 13th July 2018, 06:52 AM
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Quote:
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Then on to the MAP sensors themselves I guess but that will be a fun one to diagnose.
Try service manual. If I remember well, there is vacuum vs output voltage table. With proper equipment, you can test them.

But another thing comes to my mind...try to get osciloscope and measure the output signal on two positions andirectly...sensor connector (sensor) and the ECU pin (can be removed - sensor + wiring). There may be a good signal out of the sensor and some bad connection of the signal wire itself.
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post #10 of 14 (permalink) Old 13th July 2018, 04:30 PM
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You got me to wondering how it runs without knowing the phasing. Two options: it could just guess according to the crank sensor and if it starts...then it knows it guessed correctly. Or...it could be firing on both possible cycles which will run but not ideally. Wasting a spark on the exhaust isn't a big deal but in such a limp mode it might also be firing the injector...but I don't know for sure. I believe the manual says the map reading defaults to something like 760mb which would explain some of the richness, but the phasing part I'm stumped.
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post #11 of 14 (permalink) Old 16th July 2018, 06:22 AM
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Originally Posted by RecoilRob View Post
You got me to wondering how it runs without knowing the phasing. Two options: it could just guess according to the crank sensor and if it starts...then it knows it guessed correctly. Or...it could be firing on both possible cycles which will run but not ideally. Wasting a spark on the exhaust isn't a big deal but in such a limp mode it might also be firing the injector...but I don't know for sure. I believe the manual says the map reading defaults to something like 760mb which would explain some of the richness, but the phasing part I'm stumped.
I've read somewhere, the K5+ models are using those dual MAPs for phasing. Basically the engine always runs by crank position sensor, the ECU just need to sync when cranking - detect, which crank revolution is induction+compression and combustion+exhaust -> using MAPs to detect pressure drops -> induction stroke.

Quite easy to check it...disconnect both MAP hoses from sensors or TBs and crank the engine...it shouldn't be able to start.
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post #12 of 14 (permalink) Old 16th July 2018, 12:51 PM Thread Starter
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Throttle Body Boots. I'm pretty sure now. I was able to get it to stumble and eventually stall by thoroughly hosing down the throttle body boots at precise locations. Needed a lot of spray from the QD electronic parts cleaner pointed exactly at the trouble spots but I was able to see that the throttle body boots were sucking in air/solvent from the bottoms and from the top of the front throttle body. Targeted sprays showed no cracks in the middle, MAP hoses and vacuum nipples were fine, but when thoroughly soaked the boots are leaking from top and bottom. Didn't pick this up before because the leaks appear to be really small, which is why I think they're only affecting a certain RPM range, and didn't show until I really had at it with the spray can at precise locations (I used about 1/2 large can in the entire process).

My bike (K5) uses the MAP sensors for phasing as discussed. If both MAP sensors are disconnected before starting then it appears to run off of wasted spark AND fuel as a limp mode. It also appears to remember the phase if you disconnect one or both MAP sensors while it is running (didn't detect any increased/wasted fuel) but I didn't run it for long that way so I'm not positive.
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post #13 of 14 (permalink) Old 26th November 2019, 12:24 AM Thread Starter
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Finally got around to fixing this a few weeks ago as it had gotten pretty bad.

The base gasket had failed on the front intake manifold. It looked like either the gasket had flattened enough and lost elasticity or the base of the manifold had warped a little over time - I think it was a combo of the two. I had some leaks around the hose clamps as well but fixed those last year by using a thin layer of Threebond so it was just the base gasket leaking on the front.

I replaced both manifolds with excellent condition used ones off eBay and resealed them at the base with Yamabond and a thin coating of lanolin on the bases of the manifolds. I let the Yamabond cure until it was thick and tacky before installing so that it made a nice cushy gasket without permanently attaching the manifolds.
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post #14 of 14 (permalink) Old 26th November 2019, 06:44 AM
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Ummm....this must have been a long term project, or you wintered that bugger for a long time... ha ha

You posted today and your previous post was July 2018.... HA HA

Glad you seem to have found the problem.....it is SO satisfying when it gets sorted.....

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