Tune resistors and ecu shenanigens
Discussion
Eh up fellas.
I've got my ecu in bits here, as I'm less than sure of its heritage. For a start it lacks the official looking Lucas sticker, and instead has a paper piece of crap on the front that says "parts for Landrover". Errgh.
Secondly, its got a number scrawled into the casing and written on both boards inside. it reads: "11572 RR".
Thirdly, its date stamped March 1986 on the connector housing. 1988 car, so plausible that its the original, but in the light of the above facts, i smell a big s
tty rat.
So I look through the bumf about differences between different ecu applications and am wondering about these fabled tune resistors.
Does anyone know which components are the tune resistors (i.e. R### numbers on the component side of the PCBs)??
Bonus question for beer: does anyone know the sorts of values they should be for a 390SE engine. So it'll need a bit more top end fuel than a Strangerover cos its got a slightly hotter cam in it (and the chaps at the rolling road told me it was going lean at high revs and losing power). Still, 256lbft at about 4500 RPM is pretty good midrange, but above 5k it wouldn't pull a greasy stick out of a pigs arse.
Mechanically then engine is in fine fettle.
Any clues??
I may just hoy it in the bin and buy a Megasquirt 2 from www.extraefi.co.uk cos I can get one with direct drive 8cyl wasted spark and other shiny goodness.
Thankyou!
I've got my ecu in bits here, as I'm less than sure of its heritage. For a start it lacks the official looking Lucas sticker, and instead has a paper piece of crap on the front that says "parts for Landrover". Errgh.
Secondly, its got a number scrawled into the casing and written on both boards inside. it reads: "11572 RR".
Thirdly, its date stamped March 1986 on the connector housing. 1988 car, so plausible that its the original, but in the light of the above facts, i smell a big s
tty rat.So I look through the bumf about differences between different ecu applications and am wondering about these fabled tune resistors.
Does anyone know which components are the tune resistors (i.e. R### numbers on the component side of the PCBs)??
Bonus question for beer: does anyone know the sorts of values they should be for a 390SE engine. So it'll need a bit more top end fuel than a Strangerover cos its got a slightly hotter cam in it (and the chaps at the rolling road told me it was going lean at high revs and losing power). Still, 256lbft at about 4500 RPM is pretty good midrange, but above 5k it wouldn't pull a greasy stick out of a pigs arse.
Mechanically then engine is in fine fettle.
Any clues??
I may just hoy it in the bin and buy a Megasquirt 2 from www.extraefi.co.uk cos I can get one with direct drive 8cyl wasted spark and other shiny goodness.
Thankyou!
I'm pretty sure the tune resistor is in the fuse board..
There were differences in the 4CU ECU - mainly to do with model varient ..
Wedgies website .. don't think he mentions tune resistor
http://www.wedgeneering.co.uk/Lucas%20Diagnostics....
RPI mention a tune resistor on 14cux cars only.. think it was used as a speed limiter device of sorts for Range Rovers..correction it's just used to tell ECU that it's a cat equiped car !
http://www.v8engines.com/carbs-2.htm#Tune-resistor
Down load this useful 4CU manual .. although it leans towards the US cars and some of these have the 1volt lambda probe.
http://www.vintagemodelairplane.com/pages/Rover_Te...
There were differences in the 4CU ECU - mainly to do with model varient ..
Wedgies website .. don't think he mentions tune resistor
http://www.wedgeneering.co.uk/Lucas%20Diagnostics....
RPI mention a tune resistor on 14cux cars only.. think it was used as a speed limiter device of sorts for Range Rovers..correction it's just used to tell ECU that it's a cat equiped car !
http://www.v8engines.com/carbs-2.htm#Tune-resistor
Down load this useful 4CU manual .. although it leans towards the US cars and some of these have the 1volt lambda probe.
http://www.vintagemodelairplane.com/pages/Rover_Te...
Edited by rev-erend on Wednesday 23 September 21:51
[shuffles papers]
[coughs]
The tune resistor is, as stated by Alan, usually installed remotely from the ECU... and needn't concern us here - in fact I've never actually seen one on a Wedge
Ed, you're correct, there are a number of resistors on both boards of the ECU that, in the parlance, are 'SOT' or Select On Test.
Apparently, any given ECU was matched to a specific airflow meter. The pair were then set-up to suit the particular epplication, whether a torquey but low-revving Range Rover or a screaming banshee of an SD1 Vitesse twin-plen... er, yeah, right.
Anyway, several of us nosy Parkers have in recent years had the opportunity to ransack a multitude of ECUs of varying provenance and it is fair to say that certain resistors have a prominence, whereas some of them hardly seem to alter at all irrespective of application - and the 390SE does indeed have one or two notable differences.
The problem is, of course, that unless you have the original ECU and AFM then you have no way of knowing what to alter just to match them, even before you start trying to 'tune' for your :cough: 275bhp monster.
That said, it's not too much work to take a boggo Rangey ECU and swap in the values for a 350i or 390SE, just to see what happens
Adam: I'd be interested in finding out which resistor your variable pot replaces; I have a Sprintex modified ECU that has two external pots, one of which replaces one of the fixed resistors and the other connected to an ancillary circuit board that does some wizardry related to ignition pulses - presumably a frequency-to-voltage converter that pokes current in where it can do some good
Ed: let me know what value resistors you have, I may be able to give you some pointers. Read them in daylight though, some of the colours can fool you under electric light! They're 5-band as well, so you can have daft values like 35K8...
[coughs]
The tune resistor is, as stated by Alan, usually installed remotely from the ECU... and needn't concern us here - in fact I've never actually seen one on a Wedge
Ed, you're correct, there are a number of resistors on both boards of the ECU that, in the parlance, are 'SOT' or Select On Test.
Apparently, any given ECU was matched to a specific airflow meter. The pair were then set-up to suit the particular epplication, whether a torquey but low-revving Range Rover or a screaming banshee of an SD1 Vitesse twin-plen... er, yeah, right.
Anyway, several of us nosy Parkers have in recent years had the opportunity to ransack a multitude of ECUs of varying provenance and it is fair to say that certain resistors have a prominence, whereas some of them hardly seem to alter at all irrespective of application - and the 390SE does indeed have one or two notable differences.
The problem is, of course, that unless you have the original ECU and AFM then you have no way of knowing what to alter just to match them, even before you start trying to 'tune' for your :cough: 275bhp monster.
That said, it's not too much work to take a boggo Rangey ECU and swap in the values for a 350i or 390SE, just to see what happens
Adam: I'd be interested in finding out which resistor your variable pot replaces; I have a Sprintex modified ECU that has two external pots, one of which replaces one of the fixed resistors and the other connected to an ancillary circuit board that does some wizardry related to ignition pulses - presumably a frequency-to-voltage converter that pokes current in where it can do some good
Ed: let me know what value resistors you have, I may be able to give you some pointers. Read them in daylight though, some of the colours can fool you under electric light! They're 5-band as well, so you can have daft values like 35K8...
Righty ho, theres 19 of them:
Lambda board:
R925, 6k8, blue grey red
R335, absent althoug the mounting tags are there
R614, 1k5, brown green red
R617, 39k, orange white orange
Logic board:
R337, 5k6, green blue red
R404, 24k, red yellow orange
R401, 1k8, brown grey(I think) red
R124, 56k, green blue orange
R118, 1k6, brown blue red
R509, 43k, yellow orange orange
R111, 47k, yellow purple orange
R110, 15k, brown green orange
R106, 20k, red black orange
R107, 1k3, brown orange red
R320, 1k3, brown orange red
R321 is absent, no tags either
R322, 1k8, brown grey(I think) red
R309, 13k, brown orange orange
R116, 1k8, brown grey red
Hopefully a few of these are wrong, and I'll get some FREE POWER!!
Well, you never know...
Ed.
Lambda board:
R925, 6k8, blue grey red
R335, absent althoug the mounting tags are there
R614, 1k5, brown green red
R617, 39k, orange white orange
Logic board:
R337, 5k6, green blue red
R404, 24k, red yellow orange
R401, 1k8, brown grey(I think) red
R124, 56k, green blue orange
R118, 1k6, brown blue red
R509, 43k, yellow orange orange
R111, 47k, yellow purple orange
R110, 15k, brown green orange
R106, 20k, red black orange
R107, 1k3, brown orange red
R320, 1k3, brown orange red
R321 is absent, no tags either
R322, 1k8, brown grey(I think) red
R309, 13k, brown orange orange
R116, 1k8, brown grey red
Hopefully a few of these are wrong, and I'll get some FREE POWER!!
Well, you never know...
Ed.
Right, your values are ballpark for a Range Rover. The notable differences between yours and a random 350i from my records (not far from Pilo-Wedgbits actually!) are...
:drumroll:
Lambda board: fit R335 as 5K6
Logic board: change
R404 to 13K
R107 to 1K0
R111 to 62K
R124 to 20K
R322 to 4K7
I can't see R408 on your list, it'll probably be about 2K...?
Watch some of those red bands, they can actually be orange (and vice-versa). Best way to be sure is (of course) to lift one end of the resistor and hang a multimeter across it.
The fuel pressure is set by the fuel pressure regulator, not the ECU...
:drumroll:
Lambda board: fit R335 as 5K6
Logic board: change
R404 to 13K
R107 to 1K0
R111 to 62K
R124 to 20K
R322 to 4K7
I can't see R408 on your list, it'll probably be about 2K...?
Watch some of those red bands, they can actually be orange (and vice-versa). Best way to be sure is (of course) to lift one end of the resistor and hang a multimeter across it.
The fuel pressure is set by the fuel pressure regulator, not the ECU...
Yeh, 'swot I meant. resistors change the fuelling characteristics as does the fuel rail pressure. Fuel rail pressure is set by the spring loaded spill valve (regulator), which is normally adjustable if its got a grubscrew in the back.
Thankyou VERY much for those resistor values. I reckon I need to get the soldering iron out and change them resistors. Of course, the car has been rolling roaded with the strangerover ecu, so it might need some more diddling when the ecu is set up right... But that'll just be adjusting the position of the fuel curve rather than changing its shape.
Thankyou VERY much for those resistor values. I reckon I need to get the soldering iron out and change them resistors. Of course, the car has been rolling roaded with the strangerover ecu, so it might need some more diddling when the ecu is set up right... But that'll just be adjusting the position of the fuel curve rather than changing its shape.
From what little I've read of the 4Cu..
It's quite primative in that it does not adjust for altiture (via MAF) or for temperature ..
So it was a step on from the TR6 mechanical system where fuel was just mechanically metered..
The American versions of 4CU did have Lambda but very crude.
So in essence it's probably a 2 dimensional map rather that a 3 dimensional map..
BUT no other ECU comes close for pops and bangs.
Game on
It's quite primative in that it does not adjust for altiture (via MAF) or for temperature ..
So it was a step on from the TR6 mechanical system where fuel was just mechanically metered..
The American versions of 4CU did have Lambda but very crude.
So in essence it's probably a 2 dimensional map rather that a 3 dimensional map..
BUT no other ECU comes close for pops and bangs.
Game on
So if fiddling with the resistors adjusts the fuelling, a gizmo that could be programmed to adjust the resistor value based on engine RPM could be a useful as by the sound of it this is exactly what the board in the sprintex ECU does, or doest it take boost into the equation as well ?
Maybe I should get the megajolt & EDIS, bigger injectors, 72mm plenum & AFM fitted before I start buggering about with the ECU
For what it's worth I think that having separate digital control systems for fuel and ignition would be a mistake. For one thing they need to share the throttle pot signal (and possibly others) and that is not as simple as connecting another set of wires. For another you have twice as many places to look for problems. If you're going to the trouble of installing an aftermarket ignition system, for relatively little additional effort and money you can fit a complete EFI system. That gives you full access to find out exactly what your engine management system is doing and why. It may not be as good at managing the fuel as the original ECU, but in my book being able to get inside the system and find what's wrong for yourself (and then fix it) outweighs any slight advantage the OEM system might have over your aftermarket one.
Right. I've modified the ecu, and all is good! Starts better, behaves better in traffic, and the engine is definitely more crisp. It's a bit stally when hot in traffic, but then I've just buggered about with the fuelling, so I guess the idle air bypass needs tweaking and it probably wants a session on the rollers or an AFR meter fitting to get it just so.
Still, I have changed the resistors, so a big thankyou to Wedg1e and all for their help.
Ed.
Still, I have changed the resistors, so a big thankyou to Wedg1e and all for their help.
Ed.
Ed: Sounds good! May be able to suggest a few other changes when I find my full spreadsheet of ECUs, I think it's on a hard disk in my safe.
Alan: the title of 'lambda board' was given by the US guy who put the full PCB layouts on the 'net. The US versions of the SD1 and TR8 did have lambda sensors but the 'rest of world' versions didn't, hence the large open spaces where Lucas didn't fit the components. There is a bit of other circuitry on there not connected with the closed-loop side of things.
Peter: the 4CU is an analogue computer. Effectively it sums and differences voltages and currents (hence some of the very odd bits of circuit design)... nothing has ever been officially published; one or two people have had an educated guess at what's going on inside the two big ICs but those who REALLY know, keep schtum.
Some of the resistors are fairly obvious in their contribution and from memory, most of them are selected from a very narrow range of values so I guess you could (as I once intended to) have a rack of switches to select the various values for each location... but the setup time could be horrendous! Some of the old radiation monitors we get in at work are calibrated in the same manner and it can literally take all day to get one range reading correctly.
The best clue is probably those ECUs with one or two external pots. fitted: if so few variables can have so much effect it would point to quite a few of the resistors serving to match the EFI components, rather than being to fine-tune particular areas of the fuel 'map'.
Perhaps it'd be fair to say the 4CU is the first step on the ladder up from a carburettor?
Alan: the title of 'lambda board' was given by the US guy who put the full PCB layouts on the 'net. The US versions of the SD1 and TR8 did have lambda sensors but the 'rest of world' versions didn't, hence the large open spaces where Lucas didn't fit the components. There is a bit of other circuitry on there not connected with the closed-loop side of things.
Peter: the 4CU is an analogue computer. Effectively it sums and differences voltages and currents (hence some of the very odd bits of circuit design)... nothing has ever been officially published; one or two people have had an educated guess at what's going on inside the two big ICs but those who REALLY know, keep schtum.
Some of the resistors are fairly obvious in their contribution and from memory, most of them are selected from a very narrow range of values so I guess you could (as I once intended to) have a rack of switches to select the various values for each location... but the setup time could be horrendous! Some of the old radiation monitors we get in at work are calibrated in the same manner and it can literally take all day to get one range reading correctly.
The best clue is probably those ECUs with one or two external pots. fitted: if so few variables can have so much effect it would point to quite a few of the resistors serving to match the EFI components, rather than being to fine-tune particular areas of the fuel 'map'.
Perhaps it'd be fair to say the 4CU is the first step on the ladder up from a carburettor?
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