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14CUX Tube Fuel Map Characteristics?


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If you assume I have a pre-school level of knowledge in this subject (and many others), you won't be far off.

I have a 3.5 block (1982 Range Rover) with a U.S. NAS Defender 3.9 top end and 14CUX EFI fitted with the yellow " Saudi - no Cat" tune resistor in my Series III. 

I am trying to find out the basic characteristics of the four (or five with the U.S. no-resistor) tune resistor selected fuel maps in the 14 CUX ECU. To clarify, I would like to understand the relative profile of each tune's fuel map.

My engine runs quite rich. How much of this is about a fuel map for a 3.9 running in a 3.5 vs the fueling selected in the "no Cats/no O2 sensors Saudi" tune, I don't know. I know the "with Cats" tune fuel maps are said to run rich to help keep the Cats  from frying. 

I'm in Colorado, living at 5,000 feet and most of our trails are in the 8,000 to 12,000 feet range. While I understand that the Hotwire system adjusts for air-fuel mixture as Oxygen diminishes, mine runs extremely rich and I wonder whether another of the non-Cat tunes would be better in this respect.

So, does anyone know the differences between the non-Cat, non lamda sensors tunes and whether one might tend to be a bit leaner than others? I have tried to read up on the subject in some of the TVR fora, but they are all on about re-chipping and mapping. Pointing me in the right direction would be helpful. 

 

Thanks very much.

 

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Is it running lambda sensors? Without those it can't run closed-loop and self-tune.

Also not sure how the hotwire would adjust to altitude other than by the AFM seeing the lower mass of air passing through, not sure it "knows" anything about altitude.

Had a quick search through my library;

 

You probably know this stuff:

Quote

Tune Resistor
A Tune Resistor was originally specified in the wire harness so that one ECU part number could serve multiple vehicle markets.
(Multiple computer programs could be stored within the ECU, and the ECU could "decide" which one to use based on what
resistance it sensed.) One leg of the Tune Resister was wired to terminal 5 of the ECU, and the other leg was spliced to ground.

At some point during 14CUX production, Rover apparently decided to eliminate the Tune Resistor. (According to Rover service
literature, this started with VIN number LA451517.) It isn't clear from the literature whether any US-market 14CUX systems would
be effected by having an incorrect or damaged tune resister. The example system we photographed and described for this article
NEVER HAD A TUNE RESISTOR!


The following information on Tune Resistors is based on Rover service literature.

Visual inspection of wire color codes will allow you to quickly differentiate between resistors.

  • White 3900 Ohms USA and European vehicles with catalytic converters
  • Green 470 Ohms UK and European vehicles without catalytic converters
  • Yellow 910 Ohms Saudi vehicles (without catalytic converters.)
  • Red 180 Ohms Australia and "the rest of the world.

Note: all four types of Rover Tune Resistors were rated for 0.5 Watts.
When fitted, the Tune Resistor was connected to the ECU through terminal position 5, and it was also connected to terminal
position 27 through a splice. If you wish to check the resistor, first disconnect power to the system, second disconnect the EFI
Cable Harness Assembly from the ECU, and finally simply measure resistance (using an Ohmmeter) from pin 5 to pin 27 on the
main ECU connector. (Resistance isn't polarity dependent.)

 

Perhaps more useful, a factory technical bulletin refers to some of them as open-loop (no lambda sensors):

Quote

AFFECTED RANGE:
Discovery - Australian and Gulf Specification vehicles only, with 14CUX Open Loop Engine Management System prior to VIN WA 784607.
Classic - Australian and Gulf Specification vehicles only, with 14CUX Open Loop Engine Management System.

Which means it won't correct the richness or "learn" your engine (if 14CUX ever did?)

It's possible you've got a dodgy coolant sensor, worth checking that as it's a simple and cheap fix.

 

Can't find any info on actual tune, although the WITH cats one should be richer as you say, being open-loop is going to run blind and I guess erring on the side of too rich (and assuming it's attached to a 3.9) so it might be worth the experiment for 50p's worth of resistors.

 

 

...or, y'know, megasquirt it :D

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As fridge said: check the coolant temp. If everything checks out and you get no joy playing with the resistors, fit an adjustable fuel pressure regulator and knock a few psi off until its about right. Even with lambda sensors working, it'll only fuel trim at idle or light cruise anyway. 

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1 hour ago, lo-fi said:

As fridge said: check the coolant temp. If everything checks out and you get no joy playing with the resistors, fit an adjustable fuel pressure regulator and knock a few psi off until its about right. Even with lambda sensors working, it'll only fuel trim at idle or light cruise anyway. 

Knocking the FP down does risk going too lean at certain spots in the map, which is worse than being too rich.

If it's just idling rich, well, they all do that sir :D

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Indeed, it does depend on how rich! But... To be bad enough to be noticeable without a sensor of some kind, it's ~9.5:1 or worse. Which is horrific. Knocking it down a bit with a regulator ought to mirror the change in air density relatively uniformly. If in doubt, pop a volt meter on the lambda output - it's easy on a narrow band sensor. 

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Thanks. May not be the answer that I want, but it's a clear answer. I'm on the Gulf Spec open loop, no lambda sensors. It's stinky rich at 5,000 feet. At above 10,000 I think it's choking the bloody engine. I have the Rovergauge and there's no fault code for coolant sensor.

Is there such a thing as a manually adjustable fuel pressure regulator? Again,.my apologies for my ignorance, but ideally it would have a second lower pressure setting for high altitude and when I hit 10k or so, I hit a switch and it drops a few psi. Probably not, right?

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You're risking stacking bodges on bodges here - you've got an ECU that's not right for that engine, with no feedback loop, and you're trying to fudge variables to pull it back into spec - even if you get it closer to right you've effectively put a blindfold on the ECU and lied to it so you won't be running anywhere near as well as you might.

You can to some extent fudge it with adding a resistor (or two) into the coolant temp sensor circuit via a simple little switch which is slightly less nasty than tweaking the fuel pressure IMHO, make the ECU think it's hotter than it is. It's a lot cheaper than an adjustable FPR too.

 

Ultimately though, you need to fuel it right - naturally I recommend going Megasquirt, MS1 is more than good enough for the RV8 and you can convert from 14CUX with minimal wiring tweaks if you're retaining the dizzy.

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Does it actually work like that, though? I mean does the ECU continue leaning the mixture beyond normal operating temp. Most after start enrichment systems are pretty much done once ~60C is reached, so that doesn't seem quite right. 

Not often anyone is looking to make an engine leaner! 

Agreed that you're going to get the best result from a Megasquirt setup. It's probably well worth the investment. And for what it's worth, I put a carb setup from a 3.5 on a 3.9. I had to machine custom needles as I couldn't get enough fuel into it with the needles available. The 3.9 heads and manifolds are cast far more precisely than the old 3.5, so it's not just that lost half litre of displacement you're compensating for - they flow better too. 

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Well after it drops out of "warmup" past ~60deg or so it won't be doing nearly as much leaning off but we're into the weeds of bodgery here anyway :SVAgoaway: you could do the same with the air temperature sensor in the AFM or indeed try to tweak the AFM bypass (if it has one?) or hang a resistor divider on the AFM output but it's all pretty nasty.

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There seems to be some confusion. The Gulf Spec tune resistor was used for engines without Cats or lambda sensors. So,while my 0.4 litre smaller block is not right for the 3.9 too end, there were lots of Land Rivers sold with 14CUX EFI and no Cats or Lambda sensors and that is one of the maps in the EPROM.

Do I want to add complexity to the Tonka? No. Do I care about mpg or efficiency? No. Are there some benefits to running rich? Yes. So what I will probably do, based on past experience, is cogitate and waffle on an adjustable fuel pressure regulator for a couple of years while doing nothing. That has saved me a lot of time and money in the past

But thanks for your patience and good advice. I understand that Megasquirt has an established track record of succes, but what I want is simplicity. If I could get good off-road performance with one, I might well go back to a carb...

Edited by RPR
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You could also try playing with the AFM adjustment?

There's a bunch in a round boss that prides out, underneath is the adjuster, if you do it with a CO meter to hand it may help even more, if you have a wideband lambda handy, also better.

Are you sure the AFM is still working? They are pretty old to be honest.... And may not be. If you unplug it and the drive changes, it is probably unplugged.

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RPR - I believe the ECU's for different engines/tunes had different part numbers not just different tune resistors, they don't hold the 3.5 AND 3.9 map in the same ECU.

I agree with Bowie about looking at the AFM adjustment, I couldn't remember if there was any on the hotwire but as Bowie confirms there is, that will make the single biggest difference I would think.

BTW, Megsquirt would reduce complexity - you can throw the AFM away and you don't need lambda sensor(s) if you don't want them - and it would give you a system you can tune, diagnose, and fix more easily.

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First thing I thought when reading: "Runs way to rich" =>> How did you measure? With your nose or with a AFR-meter?

 

I used to run a 4.2 LSE engine with 3.9 14CUX and tubular exhaust manifolds.

I found out that there where no Lambda sensors and no tune-resitor in the loom. Also the AFM was broken. It ran quite well... and a bit better when I replaced the AFM. Not really a change when I placed a tune resistor telling the ECU that there where no lambda sensors.

 

Also: MS1 is about to be fased out. MS2 is the way to go nowadays which not really more complex than a MS1. I have a MS2 waiting to bi-fuel my RV8.. 😎

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4 hours ago, Carloz said:

Also: MS1 is about to be fased out. MS2 is the way to go nowadays which not really more complex than a MS1. I have a MS2 waiting to bi-fuel my RV8.. 😎

MS2 is only a plug-in on the MS1 board replacing the CPU with a slightly faster / more modern one, MS1 isn't going to stop working or being supported, there's tens of thousands of them out there. Mine have been running for years, the one in the 109's been on it for over a decade and never missed a beat.

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So, in the Spring cleaning motif, I opened up the battery box under the driver's seat and to my utter amazement, one of the batteries was a minimum of 10 years old and the other possibly 15. It's absolutely amazing that they were still running at all. The 15 year old deep cycle battery was still alive, barely, but the other was kaput, unsurprisingly. As I understand it the 14CUX system is unhappy with voltage irregularities. I have had issues with an uneven idle hunting between 800 and 900 rpm and had turned down the IAV to near choking to keep idle under 1000 rpm. Why it never dawned on me to check the batteries is beyond me, but there you go. Quite ridiculous. 

Replaced the batteries, opened up the idle air valve a fair bit and I've got steady idle at @775rpm. Seems much happier. Still socked in with heavy snow above 8,000 feet, so it will be a while before I can get up high and see if that makes any difference. But seems a happier little V8 down here at a mile high.

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  • 2 weeks later...
On 4/18/2020 at 3:37 PM, FridgeFreezer said:

MS2 is only a plug-in on the MS1 board replacing the CPU with a slightly faster / more modern one, MS1 isn't going to stop working or being supported, there's tens of thousands of them out there. Mine have been running for years, the one in the 109's been on it for over a decade and never missed a beat.

Yes, I know that. There is a lot of MS1 on the net but it is all about MS2 nowadays and MS3 is out already for maybe 10 years with even more features. Of course, you can ask yourself: do I need (all) those features? For me I am happy with MS2 able to run a V8 semi sequential, just that bit more sophisticated than simple bank injection with the MS1.

Now starting with MS1 is not the way to go. They are stopping (or already stopped?) to sell it. When you have it there is no problem at all, it is just fine.

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I guess I look at it from a software perspective - the more features / complexity you add, the more stuff there is to go wrong. The MS1 is so basic it's easily diagnosed and fixed by any idiot with a soldering iron, the MS2 and MS3 are less DIY friendly.

Semi-sequential may not make that much difference - the only downfall of the default MS1 code is its time resolution due to the addition of PWM injector current limiting, but as most Rover V8's don't need that you can run the high-resolution code and achieve similar resolution to the MS2. I think a lot of people forget the HR code exists.

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The later MS version are decidedly less DIY friendly and expensive for what you get. The torch for genuine, affordable DIY EFI has been picked up by Speeduino. It even does sequential injection, if you must. 

MS is in a no-mans land these days: Expensive enough that you're almost in the territory of proper commercial offerings, but commercial enough in itself that it's edging out of DIY hands. Having used Speeduino, MS of all versions, Emerald (briefly) and Link, I'd not choose MS for any new project these days. Sounds like Speeduino will do all you want for a very reasonable price. If you have a bit of budget, you want all the toys and a reliable, well supported ECU, look no further than Link. 

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