Fuel economy D1 cux versus gems

[joeblack5]

Hi folks , what is the general consensus between fuel economy from cux injection system versus gems management. ..3.9 vs 4.0
Is there a practical advantage for either of them?
It seems the cux is easier to understand and trouble shoot.
Please let me know your thoughts.

Johan

 

[p m]

Fuel economy - same.
Easier to troubleshoot: 14CUX.
By far more reliable: GEMS.

 

[joeblack5]

What part makes it more or less reliable?

 

[p m]

What part makes it more or less reliable?

All of 14CUX parts make it less reliable. Coil pickup in the distributor, distributor itself, cap, rotor, ignition amplifier, coil / ignition amplifier wiring, throttle position sensor...
Basically, GEMS extremely rarely works poorly - it is mostly all or nothing. My old D1 refused to start ONCE in 24 years and 290kmi - when the reluctor ring fell off the flywheel altogether (after dangling around on two rivets for years before that). If you watch what GEMS does live in Torque Pro or some other app - all of it makes sense.
14CUX can run half-assed for years, and you can be chasing bizarre gremlins based on anecdotal information and baseless advice. Watching what 14CUX does live is like watching Pulp Fiction for the first time.

 

[Tugela]

My experience is similar to what Peter describes. I've owned a GEMS D1 for 16 years and a pair of 14CUX Range Rovers for a total of about five years.

In all that time my GEMS D1 has had zero engine issues - at least around engine management. The Range Rovers were a merry-go-round wild goose chase to hunt down electrical problems. They seemed particularly sensitive to parts specifications. Like misfiring with a Pertronix ignition coil but running fine with a Lucas. Same with rotors and distributors. Don't even get me started on the fuses and wiring - there's a reason why the Lucas slogan is "Prince of Darkness." When the Range Rovers were in tune, they were a joy to drive, but I lived in constant apprehension of the spell breaking, which happened a few times.

Given the opportunity I'd own a RRC again, they are such magnificent vehicles. But when I go on a multiday trip into the wilderness, it's the D1 keys I reach for.

There is no good fuel economy from any engine of this vintage of Rover. The least worst is the 200/300 TDI, but that comes with tradeoffs that make it, let us say, an acquired taste.

 

[joeblack5]

PM, haha, ok ,yes, I forgot the cux has a distributor and indeed it gave me a small unreliable start issue that went away after I adjusted the gap between the toothed wheel and sensor.

Thanks Tugela, just bought my second disco 1 1998 with a gems ( not running yet) , the first a 3.9 manual with cux.


Johan

 

[best4x4]

With a 14CUX the first thing I'd do is ditch the old Lucas Dizzy and Amp for a newer style dizzy. That will delete a lot of issues right there! GEMS is just a basic yet durable setup. CPS wiring is usually what will drive them nuts as the insulation is old and will literally just fall off. Besides that very dependable!

 

[Blueboy]

Given the opportunity I'd own a RRC again, they are such magnificent vehicles. But when I go on a multiday trip into the wilderness, it's the D1 keys I reach for.

Reminds me of a show:

Due to the Suzuki's hard ride and the Toyota failing to reach their final destination, Jeremy declared that although the Range Rover was the most unreliable car in the world, it had proven itself to be the most reliable car in the world and with agreement from his colleagues, Clarkson declared that the winning car was the Range Rover.

 

[robertf]

14cux problems are almost always ignition related.

iac will fail sometimes the tps fails. sometimes water leaks down the kickpanel and ruins a relay

Ive never seen a bad fuel temp sensor, but thats usually the first thing brought up on forums.


common gems problems ive had are cps wiring and o2 sensors. I dont think Ive had a bad coilpack in several hundred thousand miles in several discos.

 

[4Runner]

Same mileage for me as well. The only GEMs problems I’ve had were both butt kickers for me. I has water intrusion into the ECM which caused all kinds of random issues that kept changing. And the crank trigger ring came loose and knocked the end of the crank trigger off. I’d unplug the crank trigger and the motor would die so I didn’t give it another thought. Someone who knew what the Rover crank trigger looks like obviously said I was missing a part. I was able to repair the ring with everything but the oil pan in place. I wouldn’t think twice about having a Gems motor again. I also have a 14CUX that’s been very reliable. Not flawless but certainly not bad.

 

[p m]

14cux problems are almost always ignition related.

Correct. But it has a vast variety of ways for "graceful degradation" - meaning running like shit without obvious signs.
It was my third 95 Classic that made me carry a two-channel scope in the vehicle.

 

[jymmiejamz]

14cux problems are almost always ignition related.

iac will fail sometimes the tps fails. sometimes water leaks down the kickpanel and ruins a relay

Ive never seen a bad fuel temp sensor, but thats usually the first thing brought up on forums.


common gems problems ive had are cps wiring and o2 sensors. I dont think Ive had a bad coilpack in several hundred thousand miles in several discos.

I’ve never seen a bad fuel temp sensor, but definitely have seen a bunch of coolant temp sensors fail causing poor running and stalling.

 

[best4x4]

I've had 1 bad fuel temp sensor. Once warmed up truck then would stall and not restart. You can simply unplug the fuel temp sensor if it cranks right up = it's bad. I grab em every time I see em at a salvage yard, but so far have only had 1 fail in all my years.

 

[DiscoClay]

Fuel economy:

14cux = 1.34 semi-truck equivalents (STE)
GEMS = 1.186 Semi-truck equivalents

Options:
- with flat-roof-rack then +0.43 STE
- with Safety Device's Highlander roof rack then +0.118 STE

:-D

 

[DiscoClay]

In all seriousness,

Mine is a 1995 NAS R380 (5-speed manual transmission) 3.9L 14CUX Disco1 has a wilderness rack (so... +0.43 STE ;-).

With SUV snow tires (basically SUV highway tires with soft-ish compound) and finally "dialed in", I got as high as 17.8 US miles per gallon on the freeway at about 55-60mph (2350-2450rpm-ish in 5th gear, I don't recall precisely). This wagon has 220K miles on it and the camshaft is flatter than the Bonneville salt... flats. This means there is a serious degradation of "rated horsepower". TLDR: Getting almost 18mpg out of this 125hp rolling barn on a mixed-level stretch of highway (400ft altitude +/- 100ft) is....amazing.

That said, when I put the LT235/85/16 mud tires on it (taking the tire diameter from ~29 inches to 32 inches) was like adding a tall overdrive; with a serious drop in gas mileage. In this configuration, I am seeing about 14-14.5mph on the freeway at about 60mph (now at 2000rpm) on the same ~flat stretch of freeway.

 

[DiscoClay]

The single biggest problem with the 14CUX, IMO, is: idle control. That screw servo has a ridiculously slow slew rate. I keep thinking it would be interesting to modify the system to use a BMW style rotary idle control valve (the old small & big sixes of the 80's and early 90's). That valve was MUCH more responsive than the screw-servo style.

That said, the simplicity of the CUX is hard to hate. Sure, it requires a distributor (with it's own amplifier issues) but all in all, the 14CUX is a reliable and simple unit.

I hear the Tornado chip helps with the other 14CUX problem: the 2500rpm flat spot. The muddy torque that occurs in the mid 2k's is allegedly fixed with the Tornado, for the most part.

re: https://thewedgeshopstore.com/14cux-nas-spec-chip-upgrade-3-9/

 

[DiscoClay]

TWS recommends the GEMS injectors and the GEMS 2AM MAF... I wonder if these would help with a stock CUX? Have any of you swapped out the GEMS 2AF mass airflow meter? I am wondering if the wiring/connector is identical.

Just to have the reference for my Tornado comments, here is what their site (TWS Motors) says:
-----------
What do we recommend?

• For best results the fuel pressure should be set to the standard 2.5 Bar (36psi)
• We recommend upgrading your fuel injectors
• Upgrading your MAF to the GEMS 2AM unit is recommended

What are the benefits?

• 10-15 BHP power increases with
• Improvements in fuel economy of 10-15%
• Better response above 4500RPM and removal of the "flat spot" on full load between 1750 and 3250RPM
• Improved idle speed, idle stability, shift patterns, cold starting, crank fuelling, rev limit (6500rpm), etc.
• Improved engine acceleration via the ECU configuration, to make it more responsive
• Service and fault diagnosis procedures are unaltered, and the upgrade is undetectable to Land Rover TestBook, Autologic, Rovacom or Lucas/Sun PDL test equipment
• Removal of speed limiters if applicable (except TVR)
• “Check Engine” (or MIL) lamp is disabled in the software for all territories except North American Specification (NAS) vehicles.

Important Notes There are two families of Lucas 14CUX ECUs. Before you place your order we need to check which type you have, so please contact us first. All original TVR supplied ECUs have “plug-in” chips, with the appropriate socket fitted. If the ECU is not original (e.g. replaced by a Land Rover standard version to fix a fault) then it may not have a socket, so in this case it will be necessary to have a socket fitted to receive the new chip. We can arrange this for you at a small cost, but again it is essential that you contact us first.
------------

 

[DiscoClay]

I've had 1 bad fuel temp sensor. Once warmed up truck then would stall and not restart. You can simply unplug the fuel temp sensor if it cranks right up = it's bad. I grab em every time I see em at a salvage yard, but so far have only had 1 fail in all my years.

I have found the problem to be "vapor lock" in the rails. I supposed it's just "vapor" rather than ye olden carbureted vapor lock.

When I spray cold water on the fully "warmed up" fuel rails... the problem goes away instantly. I suppose this could be the fuel temp sensor being out of calibration, but I figure if it's actually failed then the cold water should not cause a difference.

Because of all this, I think a higher pressure regulator could solve it (near the top of the range but not far past it... say around 45-50psi max), as would fully recirculating (pressurized, of course) fuel system.

 

[best4x4]

I have found the problem to be "vapor lock" in the rails. I supposed it's just "vapor" rather than ye olden carbureted vapor lock.

When I spray cold water on the fully "warmed up" fuel rails... the problem goes away instantly. I suppose this could be the fuel temp sensor being out of calibration, but I figure if it's actually failed then the cold water should not cause a difference.

Because of all this, I think a higher pressure regulator could solve it (near the top of the range but not far past it... say around 45-50psi max), as would fully recirculating (pressurized, of course) fuel system.

Yeah in my case the D1 would crank, run fine then once up to temp, and you shut it off, and immediately went to start it = nothing. I messed around with other stuff and yep even thought of vapor in the rail (had an 05 TJ Rubicon back in the day with the I6 4.0L and it would do that due to injector #3 being more exposed to heat) although when I hit the schrader valve cold fuel shot out. I was just going thru the list of things to check finally & got to fuel temp sensor, unplugged it & it fired up and ran fine. I removed the sensor from the fuel rail and plugged it in (reading air temp basically vs fuel rail temp) and once again a no start condition. Opened my trail spare box, grabbed a fuel temp sensor, plugged it in and it fired right up. Installed it, and that D1 never acted up again after it was warm.

Had a guy out in CO have the same situation out on the trail. Stopped for a scenic view, and the D90 refused to start. He messaged the FB Group I'm in and I said for giggles unplug the fuel temp sensor. Fired right up. He bought a replacement sensor and no more issues after that. Only two times I've had it be the issue, but it certainly was.

Fuel injector wise I've ran the 4 hole on a 14CUX & GEMS. On the 14CUX it would toss fuel injector codes eventually for flow issues with the stock fuel pressure regulator. I upped the fuel pressure regulator to one from a VW/BMW with a higher PSI and the issue went away. Never really noticed any increase or decrease in MPG, but it did idle smoother, with a more crisp acceleration. On the GEMS setup (non AEL) I did the exact same thing as the 14CUX with the same results.

Never tried to swap out MAF's as the plugs are different and I went with the old saying if it isn't broken don't fix it lol.

 

[DiscoClay]

I upped the fuel pressure regulator to one from a VW/BMW with a higher PSI and the issue went away. Never really noticed any increase or decrease in MPG, but it did idle smoother, with a more crisp acceleration.

I've been toying with this idea. Do you recall which application had the correct orientation/configuration of the connections? Most are pointing the return line the wrong way.

When I worked at Dinan (a LONG time ago, for the original guy, Steve) we built a regulator "can crusher" that would let us precisely increase the bypass pressure (crushing the can correctly will squeeze the spring that's pushing against the diaphragm) for our turbo builds.

Another thing to note, on your fuel temp sensor fix: DO NOT OVERTIGHTEN it! It will spin/rotate and you will tear the internal wires loose and it will cease functioning (don't ask me how I found this out).

Regarding cold fuel coming out of the Schrader valve, the vapor comes out really fast with liquid fuel quickly following. If I had to guess, I'd say it's about 1/10 of a second to about a half a second (depending on how long it sits after a full hot soak). Fun fact: the RRC 14cux rig does NOT have that convenient little schrader valve!

I have the 4-hole injectors... I don't see how that would drop the pressure in the rail (well, meaningfully, anyways). Do you recall by how much? I figured the 14cux would eventually shorten the pulse if "more" fuel per shot occurred due to Lamda (O2 sensor) feedback. That said, I thought the actual orifice area was essentially the same as the single hole version (4 little holes vs. 1 large one)? Do tell!