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Old 08-28-2009, 11:44 PM   #1
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Default Strange fueling problem i think

My injectors are less than a year old 750cc RC. I am running MS-II 2.0.1, Walbro 255 (brand new), M-tuned dual feed fuel rail.

LC-1 wideband, dyno tuned.

The problem is that cylinders 1 and 2 are running "hotter" than 3 and 4. I see a visible difference in the header and an IR gauge shows them to be 50 to 60 degrees cooler. I am thinking this is a bad thing. How do I get more fuel to 1 and 2?

It can't be spark as they don't share a coil. Are the injectors banked differently than the coils? If so, is there a way with Megasquirt to add fuel to just one bank?

--Chris
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Old 08-29-2009, 11:34 AM   #2
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In the usual configuration, the injectors are banked as 1-3 and 2-4, although this is of course entirely a matter of how the harness is built. If you're still running the one I made for you, this is how your injectors are paired.
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Old 08-29-2009, 09:11 PM   #3
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Joe,
Thanks for the response. I am still running the harness you built. It looks like it need to get my injectors cleaned and tested. The problem is, I am supposed to leave for nationals in four and a half days. If I can't find someone local to do it, it looks like I will have to buy another set, and either keep the originals as a spare after cleaning or try to sell them.

RC SH4-750D 750cc injectors
Flow Rate - CC's:
750 CC's / MIN @ 43.5 PSI

Flow Rate - LB's:
71 LBS / HR @ 43.5 PSI

Resistance:
12.5 Ohms @ 68 F

Voltage:
8-15 Volts, nominal 13.5 Volts

Amperage:
1.0 Amps

Pressure:
Min 30 PSIG / Max 70 PSIG

and only $98.75 each from RC Engineering.
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Old 08-29-2009, 09:32 PM   #4
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That's what you get for trying to pump corn syrup through the fuel system...
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Old 08-29-2009, 09:38 PM   #5
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These injectors have never run e-85.


Any Megasquirt hardware changes needed if I go Peak and Hold instead of Saturated?

Any preference for one over the other?
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Old 08-29-2009, 10:26 PM   #6
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Hmmm....

I had to search back through my old posts, but I found a picture of your board here, and judging by that, yes, you are configured to run lo-z injectors.

As to preference? Well, the P&H units will give you finer mixture control at low load, so your idle will be a tad smoother. I'm sure you couldn't care less. OTOH, they are noisier (electrically) but if you did a decent job hooking up those extra ground wires I provided to the head, this shouldn't be a major problem.

Amusingly, I stlll have a can of the Old Chub left in my fridge. I just can't bring myself to drink the last one.
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Old 08-31-2009, 12:03 PM   #7
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I know where there is more old chub, we just have to work out the logistics as they relate to geography.

I have a new "concern" on my fueling issue.

The rail pressure is 43.5 on the money with just the fuel pump running. I haven't verified it under load yet, but I am assuming that the brand new Walbro 255 pump can maintain that pressure under load.

I have logs from the dyno, both a step test and just a baseline pull that show me in the 95% duty cycle range, but autocross logs show a more reasonable 70% duty cycle. The autocross logs are showing about 500 rpm and 10 kpa less than the dyno runs, but I wouldn't think that would account for the difference.

With the cylinder temp differential I may have to order new injectors today and am trying to decide whether to stick with the Saturated 750ccs I have now, or order 1000cc peak and hold. Same price, and the peak and hold should be easy enough to idle. I just don't know if I want to risk that much change 4 days before nationals. But I also don't want to risk the investment I have in the motor.

Any thoughts? Do I just raise the pressure from 43.5 to 60, and make the injectors flow 880 cc?
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Old 08-31-2009, 02:05 PM   #8
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Do you already have an adjustable FPR? Sounds like an easy one to me. I wouldn't be surprised if the stock FPR starts to become nonlinear and peter out at higher manifold pressures. Never measured it, just a guess.
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Old 08-31-2009, 02:16 PM   #9
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I actually have a RRFPR, but if you don't connect the vacuum line it becomes a FPR

I can up the pressure, and then just recalc the required fuel and all should be well with the world. I don't know that I really believe that my cylinder temp differentials are a result of running out of injector but it is an easy enough fix to give it a try.
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Old 08-31-2009, 02:17 PM   #10
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I have to wonder if you're not putting the dyno owner's kid through college at this point...
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Old 08-31-2009, 02:25 PM   #11
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There certainly is that possibility. But dyno time is still cheaper than building another motor.

Ever hear this one: How do you make a small fortune tuning cars?

Answer: Start with a large one.
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Old 08-31-2009, 02:31 PM   #12
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At some point, you might just look into purchasing a damn dyno...
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Old 08-31-2009, 02:33 PM   #13
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Chris what are your plugs telling you while 50 degrees isnt a **** ton i would think that you would notice something alil off on the plugs if this where fueling, where as a timing or coil strenght issue could very well account for the change in temp. Just something free you can look at while you troubleshoot gl man.
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Old 08-31-2009, 02:50 PM   #14
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Thanks for the ideas. The plugs all look consistently good. I was having thermal issues with my COP setup so I reverted to the 1.6 coil packs. So .... if i suspected a coil I would expect 1 and 4 or 2 and 3 to be off. Likewise my question on the injector banks. 1,3 or 2,4. Nothing "easy" seems to point to 1,2.

I hooked up the pressure regulator a little bit ago and dialed in 60 PSI. I just have to find the time to validate that it helped. Hopefully just adjusting the required fuel from 4.4 to 3.6 will take care of the fuel map and all will be right with the world.

Do you guys think my "running out of injector" theory will really account for two cylinders running leaner? Keep in mind the injectors were new 16 months ago and I have a dual feed rail. No evidence of any leakage. Just the different colorations on the header primaries and laser pyrometer readings to indicate a problem.

The dyno was saying 270 rwhp. All the injector calcs seem to indicate that my 750cc injectors should support at least 350 CRANK HP at standard fuel pressure.
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