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  #1  
Old April 15th, 2016, 11:22 AM
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Ryan Noonan
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NAS 5th gear/3000rpm surging

Anyone have any ideas?
1994 NAS D90, stock V8, recent tune-up with new plugs/cables/rotor/oil. R380 trans with LT230. GBR 4.43 front and rear diffs. Brand new air intake hose. New air filter. Throttle body recently cleaned.

Pulls like a train and accelerates smoothly up to 3500 and 3800 rpm in 3rd and 4th but starts to surge at 3000rpm in 5th gear at about 65 mph. Feels like a rev limiter is cutting in.

Defender gurus please enlighten me.
Gracias.
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  #2  
Old April 15th, 2016, 11:56 AM
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Split in the MAF hose to the plenum.
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  #3  
Old April 15th, 2016, 12:04 PM
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Mike Doligalski
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65 mph as measured by your speedo or actual mph? Is this a new phenomenon?

There is a governor set ~80 (okay i'm not sure exactly where it's set but it's somewhere around there) and once the ecu thinks it's hit that mark, it starts cutting off fuel.
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  #4  
Old April 15th, 2016, 12:08 PM
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Quote:
Originally Posted by down_shift View Post
Split in the MAF hose to the plenum.
I'll check but it is a brand new hose. The old one was held together by tape for a while. Thanks.

------ Follow up post added April 15th, 2016 12:10 PM ------

Quote:
Originally Posted by JSBriggs View Post
How old is the clutch? -Jeff
Clutch was replaced last year when the bellhousing was off to swap-in the R380

------ Follow up post added April 15th, 2016 12:12 PM ------

Quote:
Originally Posted by sherpamike View Post
65 mph as measured by your speedo or actual mph? Is this a new phenomenon? There is a governor set ~80 (okay i'm not sure exactly where it's set but it's somewhere around there) and once the ecu thinks it's hit that mark, it starts cutting off fuel.
65 mph as measured by GPS. The speedo is showing close to 90. Haven't adjusted that.

New phenomenon. Just swapped out the diffs last fall. She has been hangared all winter to hide from the salt. First real highway stretch since then.

------ Follow up post added April 15th, 2016 12:15 PM ------

Quote:
Originally Posted by sherpamike View Post
65 mph as measured by your speedo or actual mph? Is this a new phenomenon? There is a governor set ~80 (okay i'm not sure exactly where it's set but it's somewhere around there) and once the ecu thinks it's hit that mark, it starts cutting off fuel.
The ECU gets its speed info from the LT230 right? Maybe that's it? The LT230 is grinding away as fast at 65 as it would at 90 with stock diffs.
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  #5  
Old April 15th, 2016, 12:18 PM
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Quote:
Originally Posted by Nooner View Post
I'll check but it is a brand new hose. The old one was held together by tape for a while. Thanks. ------ Follow up post added April 15th, 2016 12:10 PM ------ Clutch was replaced last year when the bellhousing was off to swap-in the R380 ------ Follow up post added April 15th, 2016 12:12 PM ------ 65 mph as measured by GPS. The speedo is showing close to 90. Haven't adjusted that. New phenomenon. Just swapped out the diffs last fall. She has been hangared all winter to hide from the salt. First real highway stretch since then. ------ Follow up post added April 15th, 2016 12:15 PM ------ The ECU gets its speed info from the LT230 right? Maybe that's it? The LT230 is grinding away as fast at 65 as it would at 90 with stock diffs.
you are hitting the limiter if the speedo is saying 90.
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  #6  
Old April 15th, 2016, 12:20 PM
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Mike Doligalski
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Quote:
Originally Posted by Nooner View Post


The ECU gets its speed info from the LT230 right? Maybe that's it? The LT230 is grinding away as fast at 65 as it would at 90 with stock diffs.
Exactly. Truck thinks you're driving too fast.
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  #7  
Old April 15th, 2016, 12:23 PM
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Quote:
Originally Posted by Nooner View Post
65 mph as measured by GPS. The speedo is showing close to 90. Haven't adjusted that.
There's the issue
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  #8  
Old April 15th, 2016, 12:34 PM
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I'd start with refreshing the fuel filter.
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  #9  
Old April 15th, 2016, 12:36 PM
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Thanks Tyler and Mike. That makes sense to me.
Not a huge deal, I'm never in a hurry. Just wanted to make sure there wasn't something larger looming.

However, this revelation sparks an additional question(s):

1) is the limiter designed to protect the transfer case from overheating? Or to protect the world from someone driving a D90 at 100mph?

2) if I wanted to achieve 70mph, I see my options as removing the limiter, bigger tires, or a 1.003 high range transfer case swap. TC being most extreme/expensive, tires may not be desirable due to garage door limits, what are the dangers/drawbacks to disengaging the limiter?

3) could anyone who had disengaged their rev limiter explain why they did it? And how?

I don't necessarily need to go faster than 65 but at the same time it is kind of annoying to bounce off the limiter while keeping pace with traffic. 70-75 would give me more than enough leeway, I would think.

------ Follow up post added April 15th, 2016 12:37 PM ------

Or is there a way to adjust the output from the TC to the ECU?
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  #10  
Old April 15th, 2016, 12:49 PM
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Edit: below is for a NAS 110

The limiter is installed because it came with S rated tires which are speced for 89mph. If you have the original ECU, I believe and I need to check mine, that the chip is soldered in. If it is not, you can easily swap the chip for one in a disco I or RRC. However, if it is soldered in, you can replace the ECU with one from a disco I 94/95 or RRC 92 and up -- need to check year when they went to 14CU) to eliminate the rev limiter. The catch is the mounting is different as they are under seat mounted. So you can either swap the case from the 110 ECU or, in an ideal world, get an ECU out of a 94 D90 (which has the same mounting) and put in a chip from a Disco I or RRC. None of this fixes your speedo and you have to be running at some crazy RPM so you may wish to go about resolving that issue directly. A swap to a 1.2 LT230 (by far the most common ratio in the US) would get you your 75 mph or so.

Every D90 I had I swapped in a chip out of a disco I or RRC. The "new" chips were the same between the 3.9 and 4.2 V8s so I bought some of them. Keep in mind this was 10 to 15 years ago. I have a spare 94 D90 ECU that has been chipped I am going to run in my 110.

Why? Well, when I was younger I liked to go 90mph+ in a defender. Now, I don't but I still have the stuff so it stays in.
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  #11  
Old April 15th, 2016, 12:59 PM
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Quote:
Originally Posted by evilfij View Post
The limiter is installed because it came with S rated tires which are speced for 89mph. If you have the original ECU, I believe and I need to check mine, that the chip is soldered in. If it is not, you can easily swap the chip for one in a disco I or RRC. However, if it is soldered in, you can replace the ECU with one from a disco I 94/95 or RRC 92 and up -- need to check year when they went to 14CU) to eliminate the rev limiter. The catch is the mounting is different as they are under seat mounted. So you can either swap the case from the 110 ECU or, in an ideal world, get an ECU out of a 94 D90 (which has the same mounting) and put in a chip from a Disco I or RRC. None of this fixes your speedo and you have to be running at some crazy RPM so you may wish to go about resolving that issue directly. A swap to a 1.2 LT230 (by far the most common ratio in the US) would get you your 75 mph or so.
Great info. Thanks.
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  #12  
Old April 15th, 2016, 01:22 PM
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Ryan Noonan
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My shop put in a rebuilt LT230 when they swapped in the R380 since the old transfer case was pretty much on its way out (thank you previous owner). I guess I always assumed I already had a 1.2 LT230 but maybe I didn't?

Bummer. I would have put in a 1.2 back then if I had known.

Hindsight and 20/20 and all that.

(Insert super sad "wah waaah" trombone sound here")
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  #13  
Old April 15th, 2016, 01:32 PM
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I am an idiot. For some reason I thought you has an NAS 110 which come with 1.4 LT230s stock and a different ECU.

You have a 1.2 case if it is stock NAS D90.

I would just swap the chip for a Disco I chip as the 94 NAS computer the chip is not soldered in. 4.43 gears are really steep, but still doable. If the chips are still available, they are $50 or so new. It is an easy job, a bit fiddly if you have AC, but still easy. You need a torx bit to open the ECU.

------ Follow up post added April 15th, 2016 01:37 PM ------

Call roversnorth and see if this is the right part. You want a 94/95 disco I or up to 95 RRC ECU cold start prom.

PROM COLD, PRM3654 - Rovers North - Classic Land Rover Parts
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  #14  
Old April 15th, 2016, 01:50 PM
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Quote:
Originally Posted by evilfij View Post
I am an idiot. For some reason I thought you has an NAS 110 which come with 1.4 LT230s stock and a different ECU. You have a 1.2 case if it is stock NAS D90. I would just swap the chip for a Disco I chip as the 94 NAS computer the chip is not soldered in. 4.43 gears are really steep, but still doable. If the chips are still available, they are $50 or so new. It is an easy job, a bit fiddly if you have AC, but still easy. You need a torx bit to open the ECU. ------ Follow up post added April 15th, 2016 01:37 PM ------ Call roversnorth and see if this is the right part. You want a 94/95 disco I or up to 95 RRC ECU cold start prom. PROM COLD, PRM3654 - Rovers North - Classic Land Rover Parts
You're not an idiot. You rock.

I'll do just that. Thanks again!
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  #15  
Old April 15th, 2016, 02:04 PM
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Rover 14CUX Hot Wire Mass Flow EFI: Service and Troubleshooting

This shows the ECU and the PROM chip. Just remove the ECU, take the top off (make sure to ground yourself by touching metal before you do) and swap chips, then put the cover back on and reinstall in the truck.
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  #16  
Old April 15th, 2016, 02:20 PM
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Quote:
Originally Posted by evilfij View Post
Rover 14CUX Hot Wire Mass Flow EFI: Service and Troubleshooting This shows the ECU and the PROM chip. Just remove the ECU, take the top off (make sure to ground yourself by touching metal before you do) and swap chips, then put the cover back on and reinstall in the truck.
Super informative website. Sounds easy enough. Thanks again.
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  #17  
Old April 17th, 2016, 11:42 PM
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So... I was fairly confused when I was troubleshooting this whole rpm/speed enigma.
The Ashcroft gear ratio calculator was too confusing so I made my own and at first I thought i had the math wrong or something because by my math, my speedo should have been showing 85mph at 66mph actual (when I was hitting the limiter)

Instead... I was bouncing off of 90 So I double check the spreadsheet...

Nope the math was all solid.

Well...shit, I thought...and then I was worried that maybe the shop put a 1.4 LT230 instead of a 1.2 when they rebuilt it two years ago and maybe I didn't notice?

But that didn't make sense (for many reasons) and besides, the math didn't line up.
If I had a 1.4 LT230, my RPMs at 66MPH would have been 3200...not 3000... So that wasn't it.

Then I had an epiphany: WHAT IF... when the shop ordered my R380 to swap in for my busted ass LT77 two years ago... WHAT IF they put in a R380 with TDI ratios instead of V8 ratios?

So I switched the ratios on my spreadsheet...and whaddaya know?

66mph at 3000 rpm

Sonofamuffin

So it appears I have a TDI ratio'd R380 in my NAS V8 D90. Which loses me about 4 mph on the top end and gives me a 1% slower crawl on the bottom end (in high ratio).

Kind of disappointed to say the least that the shop didn't know the difference/or didn't care/or didn't think I'd notice. Just sloppy, in my book.

I probably wouldn't have noticed except for the limiter issue with the 4.43 R/Ps (which I love by the way...thanks Bill at GBR).

Sigh.

Well.. Driving up to Westford tomorrow first thing to get the ECU chip I need from RN (thank you evilfj) and a new gas cap (thanks dad for leaving the old one on the spare after filling up).

Other than that, this was a fairly pointless rant. Except I was excited that I actually got to the root of the quandary, and my wife could care less, and I wanted to share the news with someone.

Cheers to you if you actually read all that.
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  #18  
Old April 18th, 2016, 12:35 AM
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Success. Well done Watson! You will at least now sleep at night, although you will get home to bed slower! Sorry ;-)

And you're all set for that 300 swap someday!

But I did learn something, so thanks for posting.
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  #19  
Old April 18th, 2016, 02:27 AM
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There is very limited differences between the gear ratios of a 300tdi and a V8 R380 (so it does not matter much) and, if I had to guess, your speedo and tach are off slightly and you have a V8 r380 ratio trans. Oh and the input shafts are different (pretty sure need to check to be 100%) so that also makes me doubt it. Anyway, read the number on the side of the box and you will know what you have. In any event, get the chip (make sure it is the right one), report back.
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  #20  
Old April 18th, 2016, 09:05 AM
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I ran into this when I put my 4.10's in as well. Freaked me out the first time it happened as I was passing someone and the engine cut right out. Took me a bit to realize what was going on. I've just left it as is for now as I really shouldn't do 75-80 in my truck anyway. But 4.43's and a top speed of 65mph would be tough
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