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Discussion Starter #1
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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Discussion Starter #3
Barry, thank you for responding. It has been about two years since I have changed the fuel filter. It's the only thing I have not recently changed. I will post my results in a few days after installing a new one.

Yes, I have a few codes that mostly focus on the coil pack. The other code/alarm is from my wife to sell it and buy a Jeep.
 

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When this happens, is the engine cold or hot? Under load? Not under load? (aka when driving or can create while parked and just revving the engine??) Need specifics!!

If cold, this sounds like some sort of ignition/timing issue. So I'd be looking at the coil packs or wires. If you are down a cylinder, it is a bit noticeable but it sounds like you are down 2 or more cylinders. So that would be one or more coil packs.

I'd almost say, find someone breaking a later D1/P38 and get the coil packs off of it to work with.

Another test:
At night (AKA DARK) open the hood and fire up the engine. Then rev the engine. If the spark plug wires look like fire works, then focus there.

How are your spark plugs? Gapped?

If engine hot, check for vacuum leaks. Get a can of compressed air (like what you use on your computer and keyboard) and with the engine running, start blowing around the intake. See if you get a change in engine tone.

Or change your shop. I had a Hyundai (!!) at the dealer for 4 months and they couldn't figure out why it was pulling to the right under braking. They gave it back to me. Took it to an alignment shop. Took them 30 minutes (I think the car sat for 15 minutes before the guy could get to it) to find a bad suspension bushing that was causing the whole problem.

If you looking to check your fuel system (I doubt its the problem but I have had trash in the fuel tank which is a bad time), look into renting a fuel testing kit. Autozone has them. If memory serves, there is a schrader valve on the fuel rail to connect it to. Hook up the tester and re-create the problem. See what your fuel pressure does. I think for a NAS v8, fuel pressure is in the 70-90 psi range?? I think? I haven't rented this tool from them, but I've rented all kinda other randomness from them. Love their tool rental program.


If your code reader can, data log the failure. It'll probably poop out a big ole excel file, but this will help.
 

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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.
 

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To be fair if a Land Rover specialist could not figure it out in person after three weeks there is no chance it will be solved over the internet.
 
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Discussion Starter #7
Barry, thank you for responding. It has been about two years since I have changed the fuel filter. It's the only thing I have not recently changed. I will post my results in a few days after installing a new one.

Yes, I have a few codes that mostly focus on the coil pack. The other code/alarm is from my wife to sell it and buy a Jeep.
Any codes?

Changed the fuel filter recently?
Hello again Barry, I'm so desperate for anything I appreciate your suggestion. I just changed out the fuel filter and no change.
 

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Discussion Starter #8
To be fair if a Land Rover specialist could not figure it out in person after three weeks there is no chance it will be solved over the internet.
Hello Red90, I wish that I had the opportunity to tell you just how many professional Land Rover mechanics have looked at this. Along with as many Land Rover owners and friends. I never thought that I would ever be in this situation; after 3 months and virtually unlimited finances, no one knows what's wrong or can fix it. Crazy. I remain steadfast and look forward to posting this solution to help others.
 

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It is a pretty simple system. You check each sensor by itself and that the information is getting to the ECU. It is beyond me how multiple experts could not check every item out in a few hours.

How about you let us know where you are located and what shop(s) have looked at it. Maybe there is a better option nearby. Some people are better at troubleshooting than others.

I can’t imagine how you will get a magic answer here that is missed first hand.
 

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Discussion Starter #10
When this happens, is the engine cold or hot? Under load? Not under load? (aka when driving or can create while parked and just revving the engine??) Need specifics!!

If cold, this sounds like some sort of ignition/timing issue. So I'd be looking at the coil packs or wires. If you are down a cylinder, it is a bit noticeable but it sounds like you are down 2 or more cylinders. So that would be one or more coil packs.

I'd almost say, find someone breaking a later D1/P38 and get the coil packs off of it to work with.

Another test:
At night (AKA DARK) open the hood and fire up the engine. Then rev the engine. If the spark plug wires look like fire works, then focus there.

How are your spark plugs? Gapped?

If engine hot, check for vacuum leaks. Get a can of compressed air (like what you use on your computer and keyboard) and with the engine running, start blowing around the intake. See if you get a change in engine tone.

Or change your shop. I had a Hyundai (!!) at the dealer for 4 months and they couldn't figure out why it was pulling to the right under braking. They gave it back to me. Took it to an alignment shop. Took them 30 minutes (I think the car sat for 15 minutes before the guy could get to it) to find a bad suspension bushing that was causing the whole problem.

If you looking to check your fuel system (I doubt its the problem but I have had trash in the fuel tank which is a bad time), look into renting a fuel testing kit. Autozone has them. If memory serves, there is a schrader valve on the fuel rail to connect it to. Hook up the tester and re-create the problem. See what your fuel pressure does. I think for a NAS v8, fuel pressure is in the 70-90 psi range?? I think? I haven't rented this tool from them, but I've rented all kinda other randomness from them. Love their tool rental program.


If your code reader can, data log the failure. It'll probably poop out a big ole excel file, but this will help.
Hello LR MAX, Thank you for responding.

The issue; "It will start and idle as normal. However once it goes beyond about 1500 rpm and driven up to 8 mph it stumbles badly" happens all the time under all conditions. Because the condition is so predictable it only adds to the frustration that no one can find or fix.

Virtually everything has been changed in an attempt to solve this problem. The short list to answer your questions are that the coil pack, spark plug wires, plugs are all new. I do subscribe to your advice about trying different shops. Two different Land Rover shops with Land Rover proprietary software (textbook?) and others have given up. I don't want to complain, I'm just hoping to find something on this forum to look at that others might have missed. I'm not giving up.
 

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is there a crank trigger wheel that might be off a tooth? it sounds from what you describe like the timing is too advanced and its starting to ping, can you put a timing light on it and check where the timing is? from the pictures I can see online it doesn't have a pin that holds it in place and could be off depending on which tooth its on. I would start there
 

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Discussion Starter #12
It is a pretty simple system. You check each sensor by itself and that the information is getting to the ECU. It is beyond me how multiple experts could not check every item out in a few hours.

How about you let us know where you are located and what shop(s) have looked at it. Maybe there is a better option nearby. Some people are better at troubleshooting than others.

I can’t imagine how you will get a magic answer here that is missed first hand.
Hello again Red90,

Perhaps you can sense my frustration. I am grateful for everyone and their time. I've been a member of the Pacific Coast Rover Club (PCRC) for about 20 years. I would be happy to share with you in a positive private conversation about the shops in Washington and Oregon states that are aware of the "Unfixable Defender." I'm not comfortable naming the shops over the forum. Because I'm not here to bad mouth anyone. I believe they did their best and have a good relationship with everyone despite the inability to fix it. It is a challenge when you are presented with a repair bill for diagnostic time and the shop tells you: "we are at a dead end and don't know what is wrong or how to fix it." So I brought the Defender home and just don't know what else to do.
 

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Discussion Starter #13
is there a crank trigger wheel that might be off a tooth? it sounds from what you describe like the timing is too advanced and its starting to ping, can you put a timing light on it and check where the timing is? from the pictures I can see online it doesn't have a pin that holds it in place and could be off depending on which tooth its on. I would start there
Thanks for this! I did remove the rear cover plate to inspect the alignment of the crank trigger and all the elevated square metal pickups on both sides of the flex plate. They all look in place with none missing or making weird contact. It was also just at a Land Rover shop two weeks ago trying to diagnose this problem and they confirm the correct signal from the crank sensor.

You have given me something to follow up on; checking the timing if possible. This is a 97' and might be a challenge. The timing chain cover was removed by a Land Rover shop to inspect cam / sprocket / crankshaft. All were correctly aligned and they verify the timing is correct. Odd because it starts and runs great up to 8 mph. I keep wanting to come back to a bad ECU but the shop says no.

Appreciate your time!
 

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Discussion Starter #14
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.
Thanks, I'll check this tomorrow.
 

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Hello LR MAX, Thank you for responding.

The issue; "It will start and idle as normal. However once it goes beyond about 1500 rpm and driven up to 8 mph it stumbles badly" happens all the time under all conditions. Because the condition is so predictable it only adds to the frustration that no one can find or fix.

Virtually everything has been changed in an attempt to solve this problem. The short list to answer your questions are that the coil pack, spark plug wires, plugs are all new. I do subscribe to your advice about trying different shops. Two different Land Rover shops with Land Rover proprietary software (textbook?) and others have given up. I don't want to complain, I'm just hoping to find something on this forum to look at that others might have missed. I'm not giving up.
Yeah I'm going to say look at the fuel tank. Either the fuel pump assembly/sock is all messed up or there is trash in there causing issues. I've had similar issues when...magically chunks of RTV ended up in my fuel tank. That was a fun one to diagnose.

As mentioned before, get that fuel pressure gauge and see what you are getting. Try to recreate under load and see what the pressure is doing. If its low, I'd drop the tank.
 

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Discussion Starter #16
Yeah I'm going to say look at the fuel tank. Either the fuel pump assembly/sock is all messed up or there is trash in there causing issues. I've had similar issues when...magically chunks of RTV ended up in my fuel tank. That was a fun one to diagnose.

As mentioned before, get that fuel pressure gauge and see what you are getting. Try to recreate under load and see what the pressure is doing. If its low, I'd drop the tank.
Thanks for being a helpful friend. I’ll check the fuel pressure tonight, drop the tank this weekend and get back to you.
 

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Is that stumble happening at the same time as a gear change?

Want to check the fuel pressure as well?
 

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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.
 

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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.
 

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This is GEMS, not 14CUX.
 
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