Infuriatingly Mysterious Lack of Oomph (Power) - Land Rover Forums : Land Rover and Range Rover Forum
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post #1 of 29 (permalink) Old 11-22-2018, 09:08 AM Thread Starter
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Infuriatingly Mysterious Lack of Oomph (Power)

Gentlemen and Ladies, I beseech you, help a poor fool with your collective centuries of Land Rover knowledge. I bought my first Range Rover Classic 3 years ago and love it to death, but I have been trying to sort out an infuriating lack of power from day one and have come up with nothing! She was stock and a bit tired when I got her, but I have methodically replaced thing after thing to no avail. I understand RRC's are absolutely not speed demons, but my father's '94 3.9 disco (bone stock) would run circles around her, so there HAS to be something hinky. Below is a list of the facts, and hopefully my frustration will come to light.

1989 RRC 3.9 (low compression), 136K miles at purchase, 155k currently

Compression test averaged between 148 and 154 for all but one cylinder, which was at 142

Starts easy, idles smoothly and revs nicely, no hiccups or bobbles underway, no smoke out the exhaust, no blow-by out the oil filler cap, doesn't burn a drop of oil, passes smog with flying colors.

Replaced all plugs and wires (magnacors) - 3 years ago

Replaced all fuel injectors with upgraded bosch 4-nozzle ones -1.5 years ago

Replaced distributor (old one had a leaking vacuum advance) and ignition amplifier with new factory one - 1 year ago

Replaced air filter and cleaned MAF with MAF cleaner - multiple times

Checked for dragging brakes (all fine)

Replaced timing gears and chain with Cloyes double roller set - 1 month ago

Replaced cam with custom grind high torque cam from "The Wedge Shop" which specializes in rover v8's, original cam had some lobes worn down almost flat, tremendous lift difference between the old and new - 1 month ago

Timing adjusted per Wedge Shop recommendations for new cam, 8 degrees BTDC at idle, 36 degrees BTDC at 3500rpm.

Verified correct fuel pressure with test kit at pump and at regulator, all good

Replaced original 14CU fuel injection computer with newer 14CUX module from a 1993 3.9 RRC - 2 weeks ago


All this and (much more) has been done, to absolutely no difference (per the butt dyno) whatsoever. She still struggles to climb hills on the freeway, takes absolutely forever to reach freeway speed (merging is a bit tense). I did a 0-60 test, wound her up pretty good, and ended up with the painfully disappointing figure of 19 seconds. I am at a complete loss, and other than dropping in a fresh 4.6 (which I know many will suggest, but I don't have 6-10K to drop on a new motor). The engineer in me is dying to solve this, and at this point I feel like it's got to be something electrical, like a sensor sending bad values that's causing the fuel computer to cut fuel or something of that nature, but I welcome any and all ideas. Please, men and women of the Land Rover community, share your knowledge!!!
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post #2 of 29 (permalink) Old 11-22-2018, 06:31 PM
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As you have already spent a lot on it, I would spend a bit more and get a wide band O2 gauge. It is very helpful is sorting out tuning problems and will tell you whether it is fuel related.
Have you taken off the plenum and cleaned the throttle body, etc.
Could be a lot of crap around the intake and exhaust valves. So large does of injector cleaner or other cleaner could help remove this stuff.
A good high output ignition coil can also help with power.
You should also check that your mechanical advance on your distributor is working properly. The distributor has a fragile bit of plastic holding the 2 sections of the shaft together. When you remove the rotor button it can break and the shaft comes up. When it does it pulls the springs off the mechanics advance.

You also might want to check that the timing marks on the crank pulley are in the correct position. That is, is TDC actually TDC.

Last edited by p76rangie; 11-23-2018 at 12:19 AM.
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post #3 of 29 (permalink) Old 11-23-2018, 07:32 AM Thread Starter
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Thanks for the response, I hadn't considered a wide band O2 gauge. Since the EFI computer controls everything air/fuel related, is there much in the way of tuning I could do if the ratio is off? Or would it be more of an indicator that a particular sensor is wonky and is feeding bad data to the computer?

When replacing the cam and timing chain/gears, we pulled the upper and lower plenum apart and cleaned them all up along with the throttle body. It was all surprisingly clean actually, as was the area under the valve covers, no big bits of gunk. We tried to be very careful making sure the timing gears and harmonic balancer were all aligned correctly with TDC when we reassembled, so I'm pretty sure it's all correct. I did check the timing with a timing light after reassembly, and it looks like it's getting the full 35- 36 degrees of advance at around 3500-3800 rpm. We added some extra marks to the harmonic balancer when it was out to make it easier to check.

I forgot to mention I replaced the coil with an MSD Blaster II when the new distributor went in, so I think it should still be good (unless I got a lemon). Is there a good way to verify spark intensity/coil output? Make sure I'm getting a good white hot spark and not a weak yellow one? I assume it should be fine considering the parts are all pretty new, you but never know.
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post #4 of 29 (permalink) Old 11-23-2018, 07:46 AM
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You should put in a new MAF to be ruled out cos if it's "dead" cleaning it won't help

My friends call me Fery

2000 Discovery Td5 ES manual

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if you think my english is peculiar it means you didnt hear my japanese

ALL MY ADVICES ARE BASED ON MY OWN KNOWLEDGE AND MY WAY OF UNDERSTANDING THE DESCRIPTION AND OPERATION OF SYSTEMS... I'M NOT A LAND ROVER TRAINED SPECIALIST JUST AN ADDICTED ENTHUSIAST.
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post #5 of 29 (permalink) Old 11-23-2018, 08:13 AM Thread Starter
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You should put in a new MAF to be ruled out cos if it's "dead" cleaning it won't help
Is there a good way to tell if the MAF has bitten the dust? I assume it's doing something, because if I unplug the MAF connector with the engine running, it dies almost immediately.

Side note, yesterday while running up a long steep freeway hill I don't usually travel, I had it under so pretty heavy load to maintain speed (80-90% pedal in 3rd gear at 3500-35800RPM to keep up with the slow traffic in the right lane, started the hill at 65mph, had dropped to 55 by the top...) and at the top of the hill, the EFI light came on. Coolant temp and oil pressure were fine (I have auxiliary gauges installed for both) nothing changed in terms of how it ran, but it has stayed on. No indication of anything being any different, sounds the same, drives the same, but the light is now on.
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post #6 of 29 (permalink) Old 11-23-2018, 08:32 AM
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Then read the fault code maybe it points you to the right direction and the management part which was guilty from the beginning but not completely failed gave up the gost for good... for the MAF you need to watch it's live readings under load but i dont know what are the good figures for your kind of management

My friends call me Fery

2000 Discovery Td5 ES manual

Hawkeye v.6, Nanocom EVO,
VDM UCANDAS, oscilloscope


if you think my english is peculiar it means you didnt hear my japanese

ALL MY ADVICES ARE BASED ON MY OWN KNOWLEDGE AND MY WAY OF UNDERSTANDING THE DESCRIPTION AND OPERATION OF SYSTEMS... I'M NOT A LAND ROVER TRAINED SPECIALIST JUST AN ADDICTED ENTHUSIAST.
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post #7 of 29 (permalink) Old 11-23-2018, 10:34 AM Thread Starter
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Then read the fault code maybe it points you to the right direction
Do you have a particular pre-OBDII diagnostic tool/method you recommend? I was under the impression (could certainly be very wrong) that only the fancy Land Rover service machines at shops or dealerships could read the codes from the pre-OBDII computers. Also, my rover being an '89 originally had the 14CU computer, which has no diagnostic capability. I replaced the computer with a 14CUX from a '93, however I don't think there is a breakout connector in the harness for diagnostic tool to be connected to, unless I'm wrong about how to pull diagnostic data from these computers?
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post #8 of 29 (permalink) Old 11-23-2018, 10:57 AM
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Read carefully the dscription https://www.ebay.ie/itm/V8-Range-Rov...item41f3f5647f and maybe you need this too: https://www.ebay.ie/itm/RANGE-ROVER-...item41f38e1d75 to rewire the socket to the ECU if it's missing, more info here http://ecumate.com/docs/Ecumate%20inst.pdf , i didnt do it myself but i have a friend who did it some time ago also here's the software https://github.com/colinbourassa/rovergauge , find somebody who knows what's what with these kind of things

some more info https://www.pistonheads.com/gassing/...f=66&t=1132719

My friends call me Fery

2000 Discovery Td5 ES manual

Hawkeye v.6, Nanocom EVO,
VDM UCANDAS, oscilloscope


if you think my english is peculiar it means you didnt hear my japanese

ALL MY ADVICES ARE BASED ON MY OWN KNOWLEDGE AND MY WAY OF UNDERSTANDING THE DESCRIPTION AND OPERATION OF SYSTEMS... I'M NOT A LAND ROVER TRAINED SPECIALIST JUST AN ADDICTED ENTHUSIAST.
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post #9 of 29 (permalink) Old 11-23-2018, 10:57 AM
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Read carefully the dscription https://www.ebay.ie/itm/V8-Range-Rov...item41f3f5647f and maybe you need this too: https://www.ebay.ie/itm/RANGE-ROVER-...item41f38e1d75 to rewire the socket to the ECU if it's missing, more info here http://ecumate.com/docs/Ecumate%20inst.pdf , i didnt do it myself but i have a friend who did it some time ago also here's the software https://github.com/colinbourassa/rovergauge , find somebody who knows what's what with these kind of things

My friends call me Fery

2000 Discovery Td5 ES manual

Hawkeye v.6, Nanocom EVO,
VDM UCANDAS, oscilloscope


if you think my english is peculiar it means you didnt hear my japanese

ALL MY ADVICES ARE BASED ON MY OWN KNOWLEDGE AND MY WAY OF UNDERSTANDING THE DESCRIPTION AND OPERATION OF SYSTEMS... I'M NOT A LAND ROVER TRAINED SPECIALIST JUST AN ADDICTED ENTHUSIAST.
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post #10 of 29 (permalink) Old 11-23-2018, 02:28 PM
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Quote:
Originally Posted by LanceL View Post
I hadn't considered a wide band O2 gauge. Since the EFI computer controls everything air/fuel related, is there much in the way of tuning I could do if the ratio is off? Or would it be more of an indicator that a particular sensor is wonky and is feeding bad data to the computer?
The O2 sensor is a narrow band and basically only used at cruise. It is not used when under power.
The timing mark I was talking about is for the ignition timing. Rarely the marks stamped on the pulley can be in the wrong spot so any timing set using those marks is wrong.

Do you have standard size tyres or have you fitted larger ones?

Last edited by p76rangie; 11-23-2018 at 04:42 PM.
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post #11 of 29 (permalink) Old 11-23-2018, 05:32 PM Thread Starter
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Do you have standard size tyres or have you fitted larger ones?
The tires are slightly larger than stock, but not much. My father's disco had the same size tires so the comparison was fair.
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post #12 of 29 (permalink) Old 11-23-2018, 05:34 PM Thread Starter
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Thanks for all the info on the diagnostics, I'll order one of the FTDI cables and pull the code down from github, it's great to know someone has taken the time to write some open source software for reading data from these things. Hopefully that will narrow down the mystery.
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post #13 of 29 (permalink) Old 11-23-2018, 09:20 PM
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Good luck with it, let us know how you get on

My friends call me Fery

2000 Discovery Td5 ES manual

Hawkeye v.6, Nanocom EVO,
VDM UCANDAS, oscilloscope


if you think my english is peculiar it means you didnt hear my japanese

ALL MY ADVICES ARE BASED ON MY OWN KNOWLEDGE AND MY WAY OF UNDERSTANDING THE DESCRIPTION AND OPERATION OF SYSTEMS... I'M NOT A LAND ROVER TRAINED SPECIALIST JUST AN ADDICTED ENTHUSIAST.
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post #14 of 29 (permalink) Old 11-28-2018, 03:00 PM
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May be as simple as o2 sensors, they can do a number on performance. sometimes they don't throw a code but still interfere with mixture. worth a try, simple fix!
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post #15 of 29 (permalink) Old 12-03-2018, 02:30 PM
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It is interesting to read your post as I have had similarly frustrating issues with my 3.9 (1995). I have replaced a fair bit under the bonnet (all ignition, O2 sensors, air filer, earth points.....). I have just started to get the same lack of power and hesitations (only slight at speed, hills are a killer) and i got the Check Engine light. The fault was fuel supply and i am leaning towards ordering a new fuel pump.

This is frustrating as i only put a new fuel pump on 2-3,000 miles ago but it was a Britpart pump and I wish that I had put a better quality unit on! I thought that i would mention the fuel pump as I didn't see it listed and they tend to go over time.
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