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agrump |
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Member ![]() ![]() Group: Members Posts: 141 Joined: 13-November 04 From: Atlanta, GA Member No.: 3,103 ![]() |
Yes, it started!
I finally got all of the parts I needed to convert from carbs to MS. My car has 96mm pistons and performance cam (Fat FC442 280 dur.) so going with a stock system would not work. I bought a box of FI parts from Ebay, I thought they were all from a 2.0 liter Porsche but it ended up being a mix of just about everything. The throttle body and plenum are 914 2.0 parts, the injectors are 1.7l Porsche, the runners are 2.0l VW bus and the fuel pressure regulator was from someones trash can. It was quite a mix but it all seems to work for the most part. The megasquirt computer I’m using is on a version 2.2 board using the MS-I chip (soon to be upgraded to a ver 3 board and MS-II) with an LC-1 WB O2 sensor. I’m running the extra code to get 12x12 tables. I have not hooked my ignition into MS at this time since I thought it would be too much to figure out at one time. I’m also using the MS relay board. I modify the stock throttle body for a TPS. I was able to install the TPS inside of the stock throttle switch assembly and wire it to the original connector. It looks like a factory job. I rebuilt a stock wiring harness to include the extra wires that I need and am using the original relay board to run the auxiliary air valve and to supply the MS board with the switched positive. I’m using a fuel pump from CB performance. I had a problem with the fuel pressure being too low. It turned out that the fuel pressure regulator was not adjusting properly. I had to cut it open to loosen the internal nut so the adjuster would work. It works now but looks terrible, I will probably replace it. I also found that the PVC had a hole drilled through it. I glued the hole shut but will probably need to find a new one. Once I fixed the regulator and the PVC the car started just fine. The idle was ok but it would skip every now and then. I checked the logs and saw that the processor was resetting. The problem was that the tach signal circuit was being grounded internally in the MS box. I brought the ground out of the box (XG1 mod) and it cured the problem. I had the wide band correction turned on and let it determine what the proper values for the VE table should be at idle using MSTweak. Judging from my idle values I think my VE table is going to be very different then what others have posted. I’ll post them once I get it tuned. The only major problem I have left is with the CHT sensor. I’m using that for the MS Coolant sensor and it is just maxing out way to fast. I need to artificially scale it to typical coolant values. MS will only read the sensor up to 215 degrees which is too low. I think that if MS “saw” the value of the sensor as being 180 degrees when fully warmed up instead of the actual reading of 215+ it would work better and give a more appropriate warm up curve. Anyway, now that the car idles it time to road tune. Wish me luck! Dean |
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lapuwali |
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Not another one! ![]() ![]() ![]() ![]() Group: Benefactors Posts: 4,526 Joined: 1-March 04 From: San Mateo, CA Member No.: 1,743 ![]() ![]() |
It's been done, quite a few times. One way is to make a small plenum (a large fuel filter works for this), and plumb all four runners into this plenum, then read the other side. It works, as long as the cam you use isn't too wild. Sometimes it's difficult to get a good MAP reading near idle, as the intake pulses are the strongest and spaced out the most at low engine speeds. Reading only one manifold increases the intake pulsing problems. Plumbing in all of them tends to smooth the signal a bit. Commonly, when using an IRTB (individual runners throttle bodies) setup like this, you'll see people use Alpha-N (throttle angle and engine speed only), not speed-density (manifold pressure, air temp, and engine speed). This eliminates the intake pulsing problems, and allows you to use really wild cams. However, it's very fiddley in terms of tuning, and generally isn't the best setup in terms of efficiency (fuel mileage tends to suck). An alternative is to to both, and blend the results together. Do Alpha-N at low engine speeds were you have a hard time getting a good MAP signal, and then use the MAP signal once it stabilizes. The current code for MS does not do this (it will do one or the other), but it's expected that code to do this will appear eventually, probably as part of the MS-II project. As far as the O2 sensor goes, you can just read one cylinder if you like. When using a wide-band sensor (which, IMHO, everyone setting up a new system should be doing, now that the hardware is so cheap), you can place the sensor in the muffler, or even in the tailpipe. You only have to ensure it's far enough from the open end of the tailpipe that you're not diluting the exhaust gases with fresh air. Unlike most narrow-band sensors, wide-band sensors are accurately heated on their own, and so aren't dependent on using the heat of the exhaust itself to get up to operating temperature. |
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