Jetronic 'Flapper' Fuel map extracted
Discussion
Thought this may be of use to any of you looking to tweak your fueling with AFM spring tensioning mods and the like.
I've extracted it from an NCK marked (& possibly modified) ECU, but i don't think it is even possible to modify the base map, so it's likely to be the same for all 4cu ECUs.
Points to note;
-Increasing airflow = Decreased voltage at the AFM wiper pin, 3.7v is no airflow, 1.6 is max airflow.
-A very small decrease in voltage at high airflow equals a very large change in Pulsewidth i.e @ 5k rpm 0.03v = 2ms less fuel (which is significant). If your car is running lean at full load & high revs, check your flap is fully opening.
-At low load small changes of voltage have very small effects on PW & thus AFR's
-The voltage of the AFM does not directly indicate load, one of the big IC's takes the AFM voltage & rpm and calculated load from this.
e.g. at 1000 rpm max load is at ~1.9v ish & further opening the flap doesn't give any more fuel. (you can see this as plateaus on the graph)
I've extracted it from an NCK marked (& possibly modified) ECU, but i don't think it is even possible to modify the base map, so it's likely to be the same for all 4cu ECUs.
Points to note;
-Increasing airflow = Decreased voltage at the AFM wiper pin, 3.7v is no airflow, 1.6 is max airflow.
-A very small decrease in voltage at high airflow equals a very large change in Pulsewidth i.e @ 5k rpm 0.03v = 2ms less fuel (which is significant). If your car is running lean at full load & high revs, check your flap is fully opening.
-At low load small changes of voltage have very small effects on PW & thus AFR's
-The voltage of the AFM does not directly indicate load, one of the big IC's takes the AFM voltage & rpm and calculated load from this.
e.g. at 1000 rpm max load is at ~1.9v ish & further opening the flap doesn't give any more fuel. (you can see this as plateaus on the graph)
A run at 1k and 4k rpm would be useful so we can compare idle, and peak power.
THanks.
This looks like the sort of thing I could set up with a microcomputer driving the inputs, as a diagnostic test for the 4CU. With an aim to automating the whole run. Maybe one day...
It would be interesting to see what Martin's megasquirt setup does in comparison.
THanks.
This looks like the sort of thing I could set up with a microcomputer driving the inputs, as a diagnostic test for the 4CU. With an aim to automating the whole run. Maybe one day...
It would be interesting to see what Martin's megasquirt setup does in comparison.
adam quantrill said:
This looks like the sort of thing I could set up with a microcomputer driving the inputs, as a diagnostic test for the 4CU. With an aim to automating the whole run. Maybe one day...
It would be interesting to see what Martin's megasquirt setup does in comparison.
You don't really need to go that advanced for fault finding, a duff ecu is pretty easy to diagnose on the o-scope now i've got a good idea of how most of it works. It's more like a guitar amp with a bunch of FX pedals than a modern ECU though, a 1950's ham radio enthusiast would be right at home, i guess the 80's are a lot further back in time than i remember It would be interesting to see what Martin's megasquirt setup does in comparison.
What would really help me is if anyone could give me their AFM pin 7 (the wiper pin) voltage at idle as my car's off the road while i chase a fuel tank leak. Voltages at cruise rpms would be nice as well.
I'll run that test for you at some point, i can tell you that there is absolutely no enrichment beyond around 40c to 45c clt temp tho'.
If I ever get my 400SE back on the road, I plan on hooking up my racecar data logger to the ECU, this way I capture all the inputs and outputs to a memory card, this can also be viewed live on a simulated dash you can design, so could be handy for diagnostics, the plan is to use a Male and female connector with jump lead so it can be connected onto any ECU.
Yeah that's right, grounding of the throttle pot wires would have caused grounding of Vref which would mean loss of signal from the airflow meter and loss of power to some circuits in the ecu.
On 4cu the TPS does;
-PW adder on transient throttle increase. (which is why high power RV8's with 4cu run better when progressively feeding the throttle in rather than stamping on the gas)
-Pump shot
-PW trim on transient throttle decrease.
-Enrichment at WOT
It doesn't know or care what the idle throttle position is.
Range Rover ECU's don't have some or all of the above enrichments (though they can be added) so careful when buying a replacement ECU off the ebay or the like.
On 4cu the TPS does;
-PW adder on transient throttle increase. (which is why high power RV8's with 4cu run better when progressively feeding the throttle in rather than stamping on the gas)
-Pump shot
-PW trim on transient throttle decrease.
-Enrichment at WOT
It doesn't know or care what the idle throttle position is.
Range Rover ECU's don't have some or all of the above enrichments (though they can be added) so careful when buying a replacement ECU off the ebay or the like.
Edited by SuperApeInGoodShape on Thursday 28th June 21:06
Gassing Station | Wedges | Top of Page | What's New | My Stuff