Optimizing D-Jetronic, Brainstorming.... |
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Optimizing D-Jetronic, Brainstorming.... |
pbanders |
Apr 18 2007, 04:28 PM
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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. |
r_towle |
Apr 18 2007, 05:02 PM
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#2
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Custom Member Group: Members Posts: 24,585 Joined: 9-January 03 From: Taxachusetts Member No.: 124 Region Association: North East States |
You know what would be nice here.
I detailed drive and tune section to replace step number 2. A Dyno is not always within reach, and can make it cost prohibitive to do. Rich |
jasons |
Apr 18 2007, 05:25 PM
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#3
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Jackstand Extraordinaire Group: Members Posts: 2,002 Joined: 19-August 04 From: Scottsdale, AZ Member No.: 2,573 Region Association: None |
Thats basically what I did when I had my idle hunt problem. I never touched my MPS, but I basically refurbed the rest of the system. The only parts I didn't touch were the MPS and the ECU. Otherwise, everything else was new or refurbed.
I had the idle hunt, so I put in a variable resistor and dialed it up to about 380 ohms (where the idle stabilized). Now it runs great, idles stable when hot, and passed AZ Emissions no problem. (other than the monkey that worked there couldn't shift my car!) My FI is 73 and obviously requires at least the factory spec'd 280 ohm resistor. Oh and my car has MSD, Pertronix, and Euro-race header. |
computers4kids |
Apr 18 2007, 07:44 PM
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#4
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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 |
I put in a variable resistor and dialed it up to about 380 ohms (where the idle stabilized). Now it runs great, idles stable when hot, and passed AZ Emissions no problem. (other than the monkey that worked there couldn't shift my car!) I would be real intrested in what size of resistance did other 914 owners place in series with thier TS2. I know I added a 270 ohm resistor in series and it made a huge difference in stabalizing my system (76 2.0, early exhaust, petronix). This weekend I plan on playing with a pot to find the ideal size. |
jk76.914 |
Apr 18 2007, 07:53 PM
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#5
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Senior Member Group: Members Posts: 809 Joined: 12-April 05 From: Massachusetts Member No.: 3,925 Region Association: North East States |
I'd try a 1000 ohm pot. I've heard about people taking old pots from radios and using them, but I think the resistance is too high. After a half degree or so of turn, it would probably do a rich shutdown.
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computers4kids |
Apr 18 2007, 07:59 PM
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#6
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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 |
I'd try a 1000 ohm pot. I've heard about people taking old pots from radios and using them, but I think the resistance is too high. After a half degree or so of turn, it would probably do a rich shutdown. I picked-up a 2000 ohm variable pot (0-2,000) at Radio Shack for $2...I should be able to dial in pretty good. |
jasons |
Apr 18 2007, 08:28 PM
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#7
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Jackstand Extraordinaire Group: Members Posts: 2,002 Joined: 19-August 04 From: Scottsdale, AZ Member No.: 2,573 Region Association: None |
I think my pot is 1k and I got it at the Shack too.
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pbanders |
Apr 19 2007, 10:46 AM
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#8
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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 |
Apr 19 2007, 05:53 PM
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#9
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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 |
r_towle |
Apr 19 2007, 06:01 PM
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#10
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Custom Member Group: Members Posts: 24,585 Joined: 9-January 03 From: Taxachusetts Member No.: 124 Region Association: North East States |
So, from what I see there, if I want the motor to be a tad richer over the entire heat range, I have to start at 500 ohms.
Anything less seems to only affect the warm up time period, which may only last a few minutes. Now, back to the MPS. What is a simple and effective way to set up the MPS on a bench, like it was done at the factory, BUT...big BUT...with normal tools, normal guages...I will consider normal a hand vacuum pump. I would love to find a way to do this without buying the two (one time use) tools to set up the car. Without an O2 sensor, and without the special meter (cant remember the name) These two tools seem to be one time use only..once the car is set, its set...no need to futz with it iny more, at least the FI settings..they are not dynamic, so no need to watch them with a meter/guage...who cares. Rich |
Bleyseng |
Apr 19 2007, 08:38 PM
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#11
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Aircooled Baby! Group: Members Posts: 13,035 Joined: 27-December 02 From: Seattle, Washington (for now) Member No.: 24 Region Association: Pacific Northwest |
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 of course as they are the same unit other than different calibrations. For bench set up the Wavetek works with setting a MPS to known working specs ie Stock... For a engine with different then stock parts you must tune it yourself or find a motor build thats very close to yours . |
pbanders |
Apr 20 2007, 11:00 AM
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#12
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Senior Member Group: Members Posts: 939 Joined: 11-June 03 From: Phoenix, AZ Member No.: 805 |
So, from what I see there, if I want the motor to be a tad richer over the entire heat range, I have to start at 500 ohms. You can try it, but again, the issue is you'll never have a stable mixture when warmed-up. QUOTE Anything less seems to only affect the warm up time period, which may only last a few minutes. It only affects warm-up if it's 200 ohms or so. Warm up lasts a lot longer than a few minutes, even in warm areas (I live in Phoenix) it takes a minimum of 10 minutes in the summer and up to 20 minutes from what I've seen. QUOTE Now, back to the MPS. What is a simple and effective way to set up the MPS on a bench, like it was done at the factory, BUT...big BUT...with normal tools, normal guages...I will consider normal a hand vacuum pump. There is no simple way to properly set up the MPS using "normal" (i.e. found in nearly every garage) tools ang guages. See my web pages for details. The only way I've found that you can accurately set an MPS to factory spec is to have a setup that simulates the FI system running at a set engine speed, and to measure the injection pulse duration over a full range of load conditions. This requires a specialized D-Jetronic tester or a homebuilt setup that simulates the contact trigger points operation at a set engine speed. You also need a reference characteristic for the MPS you're calibrating to. I've gone and done this for the 043, 037, and 049 MPS's. My web page describes a procedure using a Wavetek LCR meter, but I do not consider this to be an accurate procedure. It's OK for getting an MPS to a workable state, but has too much variation to be a calibration method. |
pbanders |
Apr 20 2007, 11:21 AM
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#13
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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. |
brp914 |
Apr 20 2007, 01:57 PM
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#14
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Unregistered |
Does the adjustment on the ecu only affect idle mixture or is it across rpm range, or what? I added a 500 ohm on my '76 and then dialed down the ecu as low as possible to maintain stable idle after aar closes, but not really warm. But if the ecu knob is idle only I may be running lean at speed. I never monkey with mps's.
QUOTE 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. lean running will lead to higher temps and possibly valve seat problems (as in falling out). |
computers4kids |
Apr 20 2007, 05:52 PM
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#15
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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. |
pbanders |
Apr 20 2007, 06:03 PM
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#16
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Senior Member Group: Members Posts: 939 Joined: 11-June 03 From: Phoenix, AZ Member No.: 805 |
Does the adjustment on the ecu only affect idle mixture or is it across rpm range, or what? I added a 500 ohm on my '76 and then dialed down the ecu as low as possible to maintain stable idle after aar closes, but not really warm. But if the ecu knob is idle only I may be running lean at speed. I never monkey with mps's. QUOTE 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. lean running will lead to higher temps and possibly valve seat problems (as in falling out). The knob on the ECU affects the mixture only at idle and depending on the ECU, during overrun (throttle closed, clutch released, coasting). Rich running also has problems. High fuel consumption, engine wear, oil contamination, high emissions. Too many 914's I've seen are running extremely rich. 5% is common, I've even seen one that was at 8%! |
computers4kids |
Apr 20 2007, 10:40 PM
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#17
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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 |
I added a 500 ohm on my '76 and then dialed down the ecu as low as possible to maintain stable idle after aar closes, but not really warm. Well, I added 470 ohms today, and the car runs pretty darn good. The idle is a little high (1200 at full warm-up, and the warm-up works well with the AAR functioning well) rpm but I should be able to fix that with the ECU knob (lean it out some)..if not I'll drop 100 ohms and run with 370--I built the resistors with quick connects so its easy to add and subtrack a resistor ( 270 +100 +100=470). The idle screw on the throttle body is screwed all the way in. |
DNHunt |
Apr 21 2007, 09:02 AM
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#18
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914 Wizard? No way. I got too much to learn. Group: Members Posts: 4,099 Joined: 21-April 03 From: Gig Harbor, WA Member No.: 598 |
For what it is worth. Here are the measured resistances and temps for sensor 0 280 130 017
32 degress = 3455 ohms 66 degress = 1627 ohms 212 degrees = 120 ohms. Unfortunately this is not a linear curve. The points on the curve can be calculated by using the Steinhart-Hart equation. The math is too much work for me but if someone wants the values these represent I'll post them. Or I'll wait for one of the kids to wakeup and solve it on their graphing calculators. Dave |
JoeSharp |
Apr 21 2007, 09:12 AM
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#19
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In Irvine, Ca. May 15-18 Group: Members Posts: 3,947 Joined: 9-July 03 From: DeLand, Florida Member No.: 898 Region Association: South East States |
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computers4kids |
Apr 21 2007, 09:17 AM
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#20
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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 |
For what it is worth. Here are the measured resistances and temps for sensor 0 280 130 017 32 degress = 3455 ohms 66 degress = 1627 ohms 212 degrees = 120 ohms. Unfortunately this is not a linear curve. The points on the curve can be calculated by using the Steinhart-Hart equation. The math is too much work for me but if someone wants the values these represent I'll post them. Or I'll wait for one of the kids to wakeup and solve it on their graphing calculators. Dave At one time, I could have use my trusty graphing calculator to plot the progression...been tooooo long, I would be lucky to figure how to turn the thing on now. I would like to follow this one up...a lot of good info here to be found...if anything for my own understanding of what's going on. One of the problems that complicates my car, is the TS2 is on the wrong head (PO switched heads when motor was gone through and I didn't catch it until the motor was in). The car is running really good now...just got to address the higher idle...perhaps I'll play with the ECU knob today and then open up the throttle bypass screw some. Any info you come across would be appreciated. Mark |
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