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pbanders |
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#1
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Senior Member ![]() ![]() ![]() Group: Members Posts: 939 Joined: 11-June 03 From: Phoenix, AZ Member No.: 805 ![]() |
Here are my thoughts on a systematic approach to optimizing D-Jetronic for a specific stock or near-stock engine - just putting this down and looking for comments:
Comments? If the intake system has been significantly modified (e.g. different cam, big valves, etc.), then to do the dyno procedure correctly, an assessment of the VE changes would need to be made, and the ECU daughter-card SC circuit would need mods - but this is beyond a reasonable approach for most people. |
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pbanders |
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#2
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Senior Member ![]() ![]() ![]() Group: Members Posts: 939 Joined: 11-June 03 From: Phoenix, AZ Member No.: 805 ![]() |
If adding a lot of ballast resistance makes your 914 run better, then do it! Be aware, however, that adding too much may make the mixture vary once the engine is fully warmed up, possibly causing drivability problems.
This chart is from my ECU web page: (IMG:http://members.rennlist.com/pbanders/CTCVoutBallast.gif) It shows the relationship between the Cylinder Temperature Compensation (CTC) circuit output voltage and the resistance of the TS2 (also called the CHT sensor) plus any ballast resistance. Higher values of CTC Vout translate to richer mixtures. The blue trace is for an 037 ECU with an 012 TS2 and no ballast, the other traces show the effect of increasing ballast, up to 500 ohms. The temperature ranges on the chart were deduced from calibrating the resistance values of the TS2 to actual temperatures. What you see is that if you add between 50 and 270 ohms of ballast, you richen the mixture only through cold start and warm-up. If you add 500 ohms, now the mixture varies once the engine is fully warmed up. The ECU circuit is designed to linearize the TS2 characteristic and to cut off its effect once the engine is fully warmed up. |
computers4kids |
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#3
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Love these little cars! ![]() ![]() ![]() ![]() Group: Members Posts: 2,443 Joined: 11-June 05 From: Port Townsend, WA Member No.: 4,253 Region Association: None ![]() |
If adding a lot of ballast resistance makes your 914 run better, then do it! Be aware, however, that adding too much may make the mixture vary once the engine is fully warmed up, possibly causing drivability problems. What you see is that if you add between 50 and 270 ohms of ballast, you richen the mixture only through cold start and warm-up. If you add 500 ohms, now the mixture varies once the engine is fully warmed up. The ECU circuit is designed to linearize the TS2 characteristic and to cut off its effect once the engine is fully warmed up. The chart was very helpful understanding what the resistance does...especially after warm-up. Since I currently have 270 ohms...I'm only seeing the effects during warm-up...it will be interesting when I crank up the pot between 270-500+ how that will effect warm running. Do you suspect the 043 MPS responds simarily to the 037 MPS? Thanks |
pbanders |
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#4
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Senior Member ![]() ![]() ![]() Group: Members Posts: 939 Joined: 11-June 03 From: Phoenix, AZ Member No.: 805 ![]() |
The chart was very helpful understanding what the resistance does...especially after warm-up. Since I currently have 270 ohms...I'm only seeing the effects during warm-up...it will be interesting when I crank up the pot between 270-500+ how that will effect warm running. It'll be richer, and as the head temps vary within the normal range of operation, the mixture will vary instead of remaining constant. Why do you want a richer mixture once the motor is warmed up? From what I've seen, there are more problems with 914's due to rich mixture than due to lean mixture. The only systemic lean condition problem I've seen is on warm-up, where Porsche had to meet tough standards from the EPA for the technology of the time. |
computers4kids |
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#5
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Love these little cars! ![]() ![]() ![]() ![]() Group: Members Posts: 2,443 Joined: 11-June 05 From: Port Townsend, WA Member No.: 4,253 Region Association: None ![]() |
The chart was very helpful understanding what the resistance does...especially after warm-up. Since I currently have 270 ohms...I'm only seeing the effects during warm-up...it will be interesting when I crank up the pot between 270-500+ how that will effect warm running. It'll be richer, and as the head temps vary within the normal range of operation, the mixture will vary instead of remaining constant. Why do you want a richer mixture once the motor is warmed up? From what I've seen, there are more problems with 914's due to rich mixture than due to lean mixture. The only systemic lean condition problem I've seen is on warm-up, where Porsche had to meet tough standards from the EPA for the technology of the time. I have a desmogged 76 motor with stainless exhaust--which leans the mixture as compared to the restrictive stock 75-76 exhaust. Now removing the air injection and the recyclyed gasses????who knows....I really need to get this thing on analyzer or wideband meter to truly see what's happening...other than just driving. I not going to monkey with the mps...period. |
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