Vespa gts 250 fuel tuning
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Enthusiast
2008 GTS 250
Joined: 14 May 2019
Posts: 58
Location: Rancho Palos Verdes, CA
Fri Jun 21, 2019 7:17 am quote
Going to add a dobech ejk, looks like it will fit the bill since I don't want to up the redline, and the malossi is $100 more.

Thoughts?

Will update on tuning, just need to weld a o2 bung on.
Enthusiast
2008 GTS 250
Joined: 14 May 2019
Posts: 58
Location: Rancho Palos Verdes, CA
Mon Jul 29, 2019 7:26 pm quote
Unfortunately, my wideband controller wasn't working, but using a combo of acceleration runs and feel I was able to dial in some settings that improved the initial throttle dead spot and made the bike quicker.

The mods are the arrow exhaust and some airbox trimming with some uni push in filter hole inserts
Hooked
2008 GTS250, 2009 S150, 2017 GTS300Super, 2006 GT200
Joined: 18 Oct 2014
Posts: 134
Location: Houston
Sun Aug 11, 2019 5:43 pm quote
Are you saying you bought the Dobech controller but it didnít work? I went to their website after reading your post and it reads like itís a great product. Sucks it didnít work for you.
Enthusiast
2008 GTS 250
Joined: 14 May 2019
Posts: 58
Location: Rancho Palos Verdes, CA
Sun Aug 11, 2019 8:04 pm quote
rob g wrote:
Are you saying you bought the Dobech controller but it didnít work? I went to their website after reading your post and it reads like itís a great product. Sucks it didnít work for you.
Controller works great, I was talking about my standalone wideband controller. The power was way too noisy for the controller. Once I connected it to a separate battery it worked fine. I did a run where I pulled the ejk, and the stock map was afr of 15. With the ejk reinstalled, it's 13.4, which isn't great, but one can only do so much. Throttle response is better off idle and much less lean popping. This is with some UNI push in filters and a arrow exhaust
Enthusiast
2008 GTS 250
Joined: 14 May 2019
Posts: 58
Location: Rancho Palos Verdes, CA
Fri Aug 23, 2019 2:46 pm quote
I ended going up a size on the injector to the IWP158.

That brought AFR to ~12.5. and to the lower range of adjustment on the ejk.

So even if you just did the injector, it would still be a bit lean.
Hooked
GTS 250
Joined: 26 Apr 2008
Posts: 224
Location: California
Tue Aug 27, 2019 5:05 pm quote
I just finished installing a PLX wideband lambda sensor & Forcemaster 2 on my 250. The PLX sensor came with a narrow-band output, that is supposed to satisfy the ECU, but I am getting a CEL a few seconds after starting. I suspect that I need to plug in the some/all of the remaining sensor wires (Right now I just have the PLX o2 output fed directly into the OEM lambda pigtail). I haven't ridden the bike yet, still trying to get the AFR to a point that I am comfortable with.

Here is a video of the gauge in action: https://youtu.be/lpKk48jFukA

Current motor spefications:
- Malossi V4 head (with mild polish, port matched intake & exhaust) cylinder & piston
- Malossi Forcemaster 2 on preset 3
- Polini camshaft
- PM-80 without baffle
- UNI filter on OEM intake tube
- OEM fuel injector



Sort of related: My motor has always sounded like the intake is "gasping" for air during warm up. I can now see that it runs pretty lean during this period also (around 17:1). Occasionally the motor will stall when it reaches operating temperature, but will start back up just fine and without the gasping sound. The video above is already at operating temperature, which is the only way I have been able to attempt to tune the AFR.

Does anyone know anything about this?

IMG_20190827_172636.jpg

Enthusiast
2008 GTS 250
Joined: 14 May 2019
Posts: 58
Location: Rancho Palos Verdes, CA
Tue Aug 27, 2019 6:07 pm quote
17 afr is extremely lean especially at cold start where it should be richer than normal idle. I still have my narrow band as it is needed for closed loop.

With all that work I would bet a bigger injector is for sure needed. Just look at the sparkplug. It's probably white not medium brown.

Not sure how the narrow band output on your unit needs to be configured.

Idle should be in the 15/16 or so.
Wot should be 12.3-12.7
Cruise should be 14.5-15

There are charts online that show good AFR targets.

Another thing to consider is the cone filler, the runner length is tuned to resonate at the power band RPM. Going shorter means a higher resonant rpm. A little restriction helps sometimes
Hooked
GTS 250
Joined: 26 Apr 2008
Posts: 224
Location: California
Tue Aug 27, 2019 8:57 pm quote
raceratb wrote:
17 afr is extremely lean especially at cold start where it should be richer than normal idle. I still have my narrow band as it is needed for closed loop.

With all that work I would bet a bigger injector is for sure needed. Just look at the sparkplug. It's probably white not medium brown.

Not sure how the narrow band output on your unit needs to be configured.

Idle should be in the 15/16 or so.
Wot should be 12.3-12.7
Cruise should be 14.5-15

There are charts online that show good AFR targets.

Another thing to consider is the cone filler, the runner length is tuned to resonate at the power band RPM. Going shorter means a higher resonant rpm. A little restriction helps sometimes
That's what I think is odd, it has always made the gasping noise during warm-up, which I can now assume correlates with running lean. I suspect it might be programmed to do this to get the catalytic converter up to temperature. Right now "cold" start is roughly 100įF where I live, so I'm not sure if it really has to warm up for very long.

The cone filter is directly on the OEM runner. I was running a pod filter directly off the throttle body, but I decided to give this a try for better intake temperatures & correct runner length.

[/img]
Enthusiast
2008 GTS 250
Joined: 14 May 2019
Posts: 58
Location: Rancho Palos Verdes, CA
Tue Aug 27, 2019 9:34 pm quote
If you look at the MIU just to the right of the screw holding the fuel line, you see that cone shape in the casting. That's a idle air control valve. The wheezing your are hearing is likely that valve opening up to raise the idle to keep the bike from stalling. Op temp is ~180 so even though 100 is a good start, it's still going to put the ECM in it's warm up sequence. It was happening with the airbox, only you couldn't hear it.
Enthusiast
2008 GTS 250
Joined: 14 May 2019
Posts: 58
Location: Rancho Palos Verdes, CA
Tue Aug 27, 2019 9:41 pm quote
I'd suggest welding on another bung for your wideband, especially since there is a heater circuit on the narrow band you will need to emulate
Hooked
GTS 250
Joined: 26 Apr 2008
Posts: 224
Location: California
Fri Aug 30, 2019 4:45 pm quote
I temporarily wired up the OEM lambda sensor, with the PLX wideband controlling the 0-1V signal (black wire), and got the CEL to turn off. The ECU must do a check that involves the lambda ground (gray) and two heater wires (white).

I don't really want to install a second sensor bung in PM80 exhaust, and I also don't think that there is enough physical room for two sensors anyway. I'm going to look into lambda sensor simulators or a place to physically mount the OEM sensor in the engine bay. Most of the simulators I can find are for tricking the rear sensor (post-catalytic converter), which obviously is not present on this motor.

The lean AFR during warm-up is still present, and the CEL had nothing to do with it. I have also noticed that if I restart the motor with two bars (out of 11) on the temperature gauge, the warm-up cycle resumes as expected (without the noise, and with proper AFR).
Enthusiast
2008 GTS 250
Joined: 14 May 2019
Posts: 58
Location: Rancho Palos Verdes, CA
Fri Aug 30, 2019 4:56 pm quote
You are correct, the ECM will be looking for a open circuit (both sensor and heater). If you figure out the proper resistance, that will give you a wattage for the resistor. You for sure want the sensor input for the closed loop cycle. 2 bars likely puts you out of the cold cycle sequence, so no high idle.
Hooked
2008 GTS250, 2009 S150, 2017 GTS300Super, 2006 GT200
Joined: 18 Oct 2014
Posts: 134
Location: Houston
Fri Aug 30, 2019 7:52 pm quote
Where do yíall read to learn about this stuff? Extra bungs, widebands, narrow bands, what checks what and the things you do to trick it? Fascinating to me and I want to be able to participate in the conversation but I donít know shit.

I just picked up an 08 250 with the intent to mod it and it looks like to do it right Iím gonna have to do a lot more than just slap on a new 4v head and cylinder kit. Iím gonna need some electronics.
Enthusiast
2008 GTS 250
Joined: 14 May 2019
Posts: 58
Location: Rancho Palos Verdes, CA
Sat Aug 31, 2019 7:12 am quote
There are some books out there on fuel injection. But without a logging wideband sensor like the innovate LM series, any changes you make will just be a best guess. The AFR targets are somewhat generic which makes things easier. Direct tuning the MIU would be best, but that doesn't seem to be a easy option. There is some software for the MIU3 but mine is MIU1
Hooked
GTS 250
Joined: 26 Apr 2008
Posts: 224
Location: California
Tue Sep 03, 2019 1:34 pm quote
rob g wrote:
Where do yíall read to learn about this stuff? Extra bungs, widebands, narrow bands, what checks what and the things you do to trick it? Fascinating to me and I want to be able to participate in the conversation but I donít know shit.
Google mostly. These topics come up more frequently on other forums where the motors get modified. Most people interested in wideband sensors are also running boost, where the AFR is even more important since things can go wrong much faster.

I was lucky enough that my car (Honda S2000) came with a wideband lambda sensor from the factory, and that there were many options for e-tuning. This has helped me understand the terms/concepts and how they transfer to a Vespa.
Hooked
GTS 250
Joined: 26 Apr 2008
Posts: 224
Location: California
Tue Sep 03, 2019 2:02 pm quote
raceratb wrote:
You are correct, the ECM will be looking for a open circuit (both sensor and heater). If you figure out the proper resistance, that will give you a wattage for the resistor. You for sure want the sensor input for the closed loop cycle. 2 bars likely puts you out of the cold cycle sequence, so no high idle.
I did measure the resistance of the lambda sensor out of curiosity, and it was around 11 ohms if I remember correctly.

I need to read-up on resistors, and see if I can come up with the correct way to wire this in.
Enthusiast
2008 GTS 250
Joined: 14 May 2019
Posts: 58
Location: Rancho Palos Verdes, CA
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