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Discussion Starter #22
LR Max, thanks for sticking with me. I have some work to do this weekend thanks to everyone at Defender Source. I hope by Sunday night I'll be telling everyone what the problem was.
 

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Discussion Starter #23
Check fuel pressure. Should be 30-35PSI with the regulator still connected. I have seen the "sock" hooked to the bottom the fuel pump inside the assembly start to come apart and gets sucked into the pump itself and cause these same symptoms.
Hello Roverchef, I have been working to resolve this problem for over three months. A lot of individuals have looked at it but can't figure it out. Even professional Land Rover shops gave up and it was never about the lack of me paying them. So far I think your suggestion makes the most sense of anyone. And credit to you; no one else even thought of it. This weekend I'll drop the tank and remove the pump with the special tool. I hope by Sunday night I'll be telling everyone what the problem was. Thanks for your time!
 

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Discussion Starter #24
Diesel Jim raises a good point. I would look at that first. Going back to the main issue of the ECU cutting power to the ignition indicates that the ECU is receiving some sort of fault that causes it to go into a "safe" mode. So either the ECU is bad (VERY VERY UNCOMMON).

See below document for information regarding sensor voltage ranges. Might be worth while to get out the ye olde volt meter and see what you are getting.


Also if you can trace it, I'd check the wires between the speed sensor and ECU plug. A bad connection could also do it. Make sure to wiggle the connector and wires while testing to see if you've got a bad pin connection. Run a ohm test and a voltage drop test.

If voltage differentiation is more than 0.02v, then you've got a bad connection.

Yes checking for voltage drop on wires super sucks and is time consuming. But it does indicate if the wiring is good or not. Common testing in construction equipment diagnosing but uncommon in automotive (guess automotive wiring is better?).

I'd do this before dropping the tank and messing with that.
Thank you for the helpful information. Like a lot of you; I have a large Land Rover technical library. I am mostly dedicated to NAS Defenders. The information on the 14CUX will be added to my notebook. The Land Rover shop has tested every sensor thoroughly along with the ECU. They also say the input / output signal and values are good. This weekend I'll drop the tank and if that doesn't reveal anything; I will start testing in this direction myself. Thanks!
 

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it is very difficult to find experienced technicians whom are old enough to have worked on vintage vehicles when those were new and know how to work on them, many have retired or moved on. I have come across techs whom have never seen a timing light or what it does and how to use it, same with distributors or carburetors, hence your difficulty.
Gems equipped Land Rovers did have an issue with speed sensor, if you can scan for codes after a road test and find misfire codes for one bank and not the other and or multiple misfire codes do suspect and replace the speed sensor.
 

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One more for ya...Remove the serpentine belt but leave everything else connected. Obviously the battery light will be on and the steering will be stiff and the H2O pump won't be driven but it won't hurt anything for a quick trip. Go for a short ride up the street and see if the stumble is gone. I've seen the alternators cause this issue too but they have to be connected and have no rotational movement. in case you are wondering this alternator issue won't show up on a voltage or amp test.
 

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Gems equipped Land Rovers did have an issue with speed sensor, if you can scan for codes after a road test and find misfire codes for one bank and not the other and or multiple misfire codes do suspect and replace the speed sensor.
IIRC, the GEMS engine senses misfires from the CPS
 

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Discussion Starter #29
Does it rev OK about 1500 rpm while in neutral? Just throwing out things.
Welcome and thanks for jumping in! As the description; it starts and idles perfect then above idle it stumbles badly. Tonight I checked the fuel pressure. Not running 38, at idle 28, above 1,300 rpm when is starts to miss-fire 32. Tomorrow I'll check the regulator that should go up to 38-40. It is frustrating to me as this is so predictable. Sooner or later we will figure it out.
 

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Discussion Starter #30
One more for ya...Remove the serpentine belt but leave everything else connected. Obviously the battery light will be on and the steering will be stiff and the H2O pump won't be driven but it won't hurt anything for a quick trip. Go for a short ride up the street and see if the stumble is gone. I've seen the alternators cause this issue too but they have to be connected and have no rotational movement. in case you are wondering this alternator issue won't show up on a voltage or amp test.
Thanks, I'll try this tomorrow.
 

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Discussion Starter #31
There is a sensor off of the transfer box (in the line that feeds the speedo) that makes the 19CUX increase it's idle (tickover) speed, but I think that kicks in more or less over walking pace, but it would be worth maybe unplugging that "just in case" and see if it still happens.
Thanks diesel jim. This on my list for the weekend tests the VSS.
 

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IIRC, the GEMS engine senses misfires from the CPS
there is more to GEMS than the CPS, land rover limits speed and performance by cutting cylinders based on VSS and not throtle as other manufacturers. this was done to ensure the driver maintains control when off road in granny gear.
the VSS is a piezo crystal sensor when it fails it looses "frequency" and cuts half the engine bank of cylinders, the engine management system does not know what to process so it logs it as misfire.
 
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If it idles fine the cps is working. Will it rev freely when stationary ?
Have you tried unplugging the speed sensor (VSS) on the transfercase and taking a spin ?

Edit-what my friend Carlos said....
 

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My 1997 NAS Defender 90 has a unique problem that I’ve never seen before or able to locate a similar issue through a detailed search.

It will start and idle as normal. However once it goes beyond about 1500 rpm and driven up to 8 mph it stumbles badly.

This all began after I installed a new motor from a reputable Land Rover supplier. Before installing I carefully inspected the long block. Hoping to avoid some simple questions; yes it was for a GEMS motor with the correct cam sprocket, the prior motor ran without any problems other than a slipped cylinder liner, the motor does have a solid ground strap; nothing other than the motor on the Defender was changed.

Pulling codes and further diagnosing shows the ignition coils are being cut out. I feel this is the source of the problem.

I have followed the electrical schematics back from the coils and tested everything.

I have tested everything electrical / mechanical and even exchanged the ECU (ERR6937/ 80742A) with no changes.

I gave up and had a local Land Rover shop try to fix it. After three weeks it was disappointing to me they could not find the problem either. I’m at a dead end.

I’m at a loss and greatly appreciate your time for any insight.
I have had so many issues with my 94 NAS that I am forgetting which symptoms match with the many fixes. But I had the same problem myself. I do not know if this applies to the 97s as it did to my 94, but you might wish to look into an Ignition Amplifier Module Relocation Kit . It took at least three LR specialists to tell me about this, but finally a former LR master tech from South Africa pointed it out to me and many problems disappeared since. Rovers North sells them.
 

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Hi Lar, sorry hear the problem your having wither then 90. Sounds/reads like you checked a lot of boxes off of what it isn't. Your fuel pressures seamed ok. A couple things...1.did you stay with the Lucas injectors or did you bump up to the Bosch style 2. Did you test your vacuum regulator(a hand operated vac pump works great, if it holds pressure it's most likely just fine.3. Did you change the air in the tires? You've done everything else.
 

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Pull the plastic cover off the wires going to the crank sensor. The insulation on the wires going to the crank sensor near the crank sensor often deteriorate. Between the oil dripping on them and the heat from the exhaust tends to break off. I have seen this a bunch on gems discovery. Sometimes it gives symptoms like you described.
 

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Pull the plastic cover off the wires going to the crank sensor. The insulation on the wires going to the crank sensor near the crank sensor often deteriorate. Between the oil dripping on them and the heat from the exhaust tends to break off. I have seen this a bunch on gems discovery. Sometimes it gives symptoms like you described.
M.A.R.S. is Drew Swoboda, LR Richmond's Master Tech for decades. He's now working with Jimmy Kelly- another former Master Tech. Drew worked on the GEM's trucks when they were new and knows them like a savant.

Once took him a $300 craigslist find non running 5 spd d1 that had been sitting with the hood propped open in Coastal NC for 6 mos, it was a rusty heap that I wanted it to build a 90 from, had to get it running to see if the engine was any good. He ran a few jumper wires etc and had the thing purring in 20 mins. This after I had spent a day swapping the ecu and every other major component with know good parts trying to get it running.

When Drew speaks..... well

 

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Discussion Starter #38
MY UPDATE AND REVIEW / October 9, 2020

PERSONAL NOTES
So far it has been very frustrating and I’m at a loss of what to do next. A lot of individuals have looked at the Defender but no one can figure it out. This also includes being at a well-known established independent Land Rover shop that after several weeks could not find the problem. To be clear, this is not because I told them to stop, ran out of money or we had a personality conflict. No. I work on the railroad and consider myself a competent DIY mechanic. Sorry if I can’t respond every day. I’m open to any constructive criticism or humor. I am very appreciative of everyone along the way with me on Defender Source.

CONDITION / SITUATION
1.) 1997 NAS Defender 90.
2.) Will start and run as normal then stumbles above idle. When running in park; it will rev to about 1300-1500rpm but then the coil packs are being cut out after that what I call mis-firing. Putting it into drive about the same rpm range and/or about 8mph causes the same miss-firing. Inducing the “mis-firing” is very predictable and easy to demonstrate.

WHAT HAS BEEN DONE THIS WEEK / Suggestions and thanks from you at Defender Source
1.) Tested fuel pressure; 35 psi at key on/engine off, 30 psi running, 32psi when “mis-firing” occurs. 42 psi when removed vacuum line from fuel regulator. This looks good and don’t feel I need to drop the tank to inspect if the fuel pump sock is damaged. Thanks Roverchef.
2.) Remove the serpentine belt; it has a new Bosch alternator, no charging issues, I did remove the belt with no change. Thanks for the idea Roverchef.
3.) Tested the VSS; the Land Rover shop looked at this and the ECU through “testbook” they found no problems. I have also checked the wiring and the sensor itself. I have unplugged and able to drive up to 8mph then mis-firing. Thanks carlosz and Uncle Douglas.
4.) Tested the voltage on or to the injectors; really on every sensor. With about 60k on the Defender the injectors are original. Thanks cascade90.
5.) I have unplugged and driven up to 8mph with same mis-fire condition; all (4) O2 sensors, CPS, VSS, both knock sensors, MAS, ATS, off. I’m actually surprised it still ran. Basically only the TPS (tested okay on VOM) and crank sensor connected.

WHAT I AM WORKING ON FOR NEXT WEEK
1.) Test the crankshaft sensor, wiring and carefully inspect the flex plate again. Thanks M.A.R.S.
2.) Re-focus on what I do know; the coil packs are being cut out. They have been changed and tested by a Land Rover shop but something is obviously wrong.
 

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sorry for any typos, i'm dealing w recent elbow surgery here...

if you feel this is ignition-related, please check the distributor. i'm not sure if this applies to GEMS ignitions, but this was also a mysterious issue in my 95 nas d90 because....

the rotor sticks onto the distributor shaft. when one removes the rotor by pulling up, and it sticks, it damages the clip on the bottom of the distributor shaft. hence, at about 1200 or 1500 or 1800 rpm, the timing is changing as the distributor shaft now moves inapprpriately up and down as it should not be allowed to move.

if this is the case, the fix is to replace the dist shaft clip (on bottom) or dist shaft as well. you will see too much up and down play on the distributor shaft. check this by temporarily installing a known good distributor

i now use channel locks to fracture and break apart the rotor before i take it off the shaft vs pulling on the vulnerable dist shaft and clip via the rotor

use anti-seize on the female mount of the new rotor also


My 1997 NAS Defender 90 has a unique problem that I’ve never seen before or able to locate a similar issue through a detailed search.

It will start and idle as normal. However once it goes beyond about 1500 rpm and driven up to 8 mph it stumbles badly.

This all began after I installed a new motor from a reputable Land Rover supplier. Before installing I carefully inspected the long block. Hoping to avoid some simple questions; yes it was for a GEMS motor with the correct cam sprocket, the prior motor ran without any problems other than a slipped cylinder liner, the motor does have a solid ground strap; nothing other than the motor on the Defender was changed.

Pulling codes and further diagnosing shows the ignition coils are being cut out. I feel this is the source of the problem.

I have followed the electrical schematics back from the coils and tested everything.

I have tested everything electrical / mechanical and even exchanged the ECU (ERR6937/ 80742A) with no changes.

I gave up and had a local Land Rover shop try to fix it. After three weeks it was disappointing to me they could not find the problem either. I’m at a dead end.

I’m at a loss and greatly appreciate your time for any insight.
 
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