DTA ECU to replace Bosch K-Jet for economy.
Discussion
I have a 1987 Saab 900i (no turbo) with the 8v engine running with Bosch K-jet and conventional ignition with hall effect disi, it also has an auto gearbox and this doesn't help with fuel economy either, the box will be replaced with a manual one. I have the option to continue with the 8v or replace it with the saab 16v engine, but i also have the inclination to run everything from an ECU, i have a DTA ECU i can use, i do not intend to carry out any major tuning mods by way of jenveys/cams etc, my dilema is...how much more fuel efficient will the ECU be over the K-jet and will it be worth the hassle?
Edited by sonett on Saturday 12th January 17:04
Assuming you know what you are doing, then you could make pretty significant economy gains imo!
1) Map it "lean on cruise" as you don't need to fit a Catalyst
2) optimise the ignition timing more aggressively (especially perhaps in conjunction with a small CR increase)
3) Push the cold start fuelling much closer to LBT (the original mapping will be very rich for a long time due to the crudeness of the control system
Will you make you money back? Probably not, unless you do mega miles.
1) Map it "lean on cruise" as you don't need to fit a Catalyst
2) optimise the ignition timing more aggressively (especially perhaps in conjunction with a small CR increase)
3) Push the cold start fuelling much closer to LBT (the original mapping will be very rich for a long time due to the crudeness of the control system
Will you make you money back? Probably not, unless you do mega miles.
Steve_D said:
Unless you know the original setup is not running right then I doubt you will notice any improvement.
You will spend plenty on the aftermarket ECU and having it tuned.
Steve
The original set up is in excellent working order, i already have the ECU and getting it mapped will be around £100-150. You will spend plenty on the aftermarket ECU and having it tuned.
Steve
I was hoping someone would post with first hand experience of such a conversion and maybe offer some real life comparisons, but i am still grateful for any comments.
Max_Torque said:
Assuming you know what you are doing, then you could make pretty significant economy gains imo!
1) Map it "lean on cruise" as you don't need to fit a Catalyst
2) optimise the ignition timing more aggressively (especially perhaps in conjunction with a small CR increase)
3) Push the cold start fuelling much closer to LBT (the original mapping will be very rich for a long time due to the crudeness of the control system
Will you make you money back? Probably not, unless you do mega miles.
Thanks for the reply. I already have access to a free 16v 900i engine and box, apart from some service items and maybe a headgasket change as a matter of course and some odds n sods, the main outlay will be my time and the mapping.1) Map it "lean on cruise" as you don't need to fit a Catalyst
2) optimise the ignition timing more aggressively (especially perhaps in conjunction with a small CR increase)
3) Push the cold start fuelling much closer to LBT (the original mapping will be very rich for a long time due to the crudeness of the control system
Will you make you money back? Probably not, unless you do mega miles.
Is there anyway of nailing down any ball park figures?
DVandrews said:
Is K jet a mechanical system? If so you will need a lot more than just the ECU......
Dave
Yes dave, you are correct, the 36/1 toothed wheel and associated sensors are all catered for, plus loom. I have never posted on here, but i do lurk and read the technical forum quite often. I have carried out a similar conversion before but the engine was not standard and it was on a similar car, a Saab 99. Dave
I want to use the car more often and as a daily/family car, its a 5 door and very practicle, extra mpg would be a real bonus.
In my experience of K Jet in good state of tune, it's both reliabile and economical. It's generally only when the metering head has lot it's adjustment that things go bad on the economy front.
The only way to gain more mpg with the DTA is to run it leaner than Saab intended. It's safer to do this on part throttle, but your combustion chambers might not give a smooth running leaner than lambda 1. With modern fuels such as V power, you could experiment with leaning off the WOT fuelling a bit, but it's risky without knock sensors to back you up, and DTA doesn't support knock.
What model of DTA is it?
And as already mentioned, you will need a crank trigger wheel and sensor and if you want to run sequential injection, you'll also need a cam trigger and sensor. You may as well get a coilpack too so that you can get the ECU to control the ignition advance as well.
You know how K Jet engines fire immediately like an old A series? You'll lose that with the DTA.
The only way to gain more mpg with the DTA is to run it leaner than Saab intended. It's safer to do this on part throttle, but your combustion chambers might not give a smooth running leaner than lambda 1. With modern fuels such as V power, you could experiment with leaning off the WOT fuelling a bit, but it's risky without knock sensors to back you up, and DTA doesn't support knock.
What model of DTA is it?
And as already mentioned, you will need a crank trigger wheel and sensor and if you want to run sequential injection, you'll also need a cam trigger and sensor. You may as well get a coilpack too so that you can get the ECU to control the ignition advance as well.
You know how K Jet engines fire immediately like an old A series? You'll lose that with the DTA.
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