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1970-1995 Range Rover Classic
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Discussion Starter #1
Background, for about a year I have been trying to improve driveability in my truck. It simulatenously suffered misfires, bucking and jerking under load, rough shifting, erratic idling/revving. I have mostly tamed it to a point it drives very well, but still one more hurdle. Here is a shortened history:

(1) I had hot stall issues so I took out the land rover dizzy /ignition amp and installed a pertronix dizzy /msd ignition system - problem solved
(2) Had really bad misses at high RPM, truck never revved beyond 3,000 RPM, new plugs, magnecor wires - shifts are now at 3500 - 4000. BUT revs were still an issue here and there. So I changed one at a time brand new TPS sensor, brand new MAF sensor, brand new IACV, reset base idle - problem seems to be solved
(3) Every time I encountered even the slightest incline - it bogged down, no power. Ignition timing was correct, fuel pressure perfect. So I got new passenger side cat as old was found to be clogged. Problem somewhat improved. Eventually changed fuel pump - problem seems solved - hills not an issue any more - fuel pump was original (26 y.o.!!!).

All these problems were happening together, it wasn't one problem at a time. The parts were swapped in over time. Tried one solution and then next if no success.

The truck runs fine and has never left me stranded - I have driven at least 5,000 miles this year and as my DD now, am looking at 10K+ next year. Except there is one problem I cannot solve. When tackling a hill the truck kicks down as expected and holds revs a 3000 RPM for a while and then it starts bucking as though it's about to stop - I can tell it's searching for the next gear but can't find it so it violently jerks till I let go of the gas pedal momentarily and then it shifts up.

Q1 My mechanic says it should rev much higher than 3000 RPM, what gives?
Q2 Could this be an ignition timing issue given the pertronix dizzy, though my mechanic swears the timing is dead on
Q3 Transmission issue? Although I notice with the engine "tune" and new fuel pump the bucking has significantly reduced - so much so that on a hill on which it used to buck all the way up, it now bucks maybe once and sometimes never.

Any solutions to fixing the limited RPM range? The highest I have reached is 4000 RPM then shift, I know they should shift much higher. Am I looking at transmission issues? I just did a full transmission service with new filter and new transmission oil (at Land Rover indie shop). Also flushed the transfer case, flushed CVs and flushed both axle pumpkins - filled up with 85W 140 gear oil.

Thanks in advance for any help/advice.
 

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1995-2002 Range Rover P38A
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If you put it in first does it rev out? I mean is it a kickdown problem or won't the motor rev out? If it won't rev out I would think it is a fuel flow problem, although it could be something electrical failing at higher loads. Some things you could look at is cleaning the MAF and the distributor cap.
 

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1970-1995 Range Rover Classic
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Discussion Starter #3
Thanks Johnno, but forgive my ignorance here - I have an auto, does "first" mean put it in "D" or "1" on the (PRND321)

About revving, when I fire it - jumps to 1000 rpms, for maybe 5 seconds then incrementally drops till its idling at 650 rpm. Then when cold and in drive, if I stop it will idle at about 550 and this will increase to idling at 650 when warmed up and in drive.

When cold in park it idles at 650 dead on, when warmed it will idle slightly over 650 in park but after a long run, say 50 miles, it idles at 735 - 800 and sounds to be racing (not a resting idle) - and if I am running a 13cux computer nothing spectacular happens, but when using a 14cux it will throw an EFI light, except not each time.

All 8 of my spark plugs look good so it's burning fuel well. I did upgrade to Bosch gen III injectors over OEM and that greatly increased the smoothness of the engine. I changed both oxygen sensors a year ago to date, so I am a little flummoxed by the weird gear shifting and wondering if it has anything to do with the unpredictable RPMs or if there is no relation at all.
 

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1995-2002 Range Rover P38A
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The idle rpm sounds like the AIV doing its job. Nothing odd there. By first I mean 1, If you put it in 1 and plant it, can you get it to rev out to 4,000 or so. I am just trying to understand if the problem is the motor or the gearbox as it wasn't so clear to me from your post.
 

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1970-1995 Range Rover Classic
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Discussion Starter #5
Nope. If I plant it, the most I get is 3500 rpm, once in a while like almost never, I have got it to 4000 rpm.

Pedal to the metal it will surge and choke and then shift at 3500 rpm max.

Normal acceleration it shifts smoothly at 3000 rpm max.

Going uphill it shifts down, revs to 3000 and starts choking - so imagine the motion you'd create if you hit the gas then brakes then gas then brakes continously and as it does this, speed falls dramatically and rpms drop till 2000 where it revs up again and repeats till hill is cleared and then runs as though nothing is wrong. That there is what I am trying to figure out.
 

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1995-2002 Range Rover P38A
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So the problem has nothing to do with the gear shifting, it's due to the engine not running right. With the selector in 1 it should only use first gear and planting the throttle to the floor should result in it shooting up to at least 4,500 rpm and sitting there, in 1 it won't even try to change up. Sounds like a fuel problem to me.
 

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I would have said fuel as well, but sometimes you can get electric problems at high revs. A way to check it is to set up the timing light and see if you are still getting a spark once it gets to 3500. Can you get it to 4-5000 without a load i.e. rev it up in neutral or park? If you can then it is probably fuel, but if you can't then it is probably electrical.
 

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1970-1995 Range Rover Classic
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Discussion Starter #8
Am gonna say fuel pump too, truck just died on me this evening with no ceremony, was just driving then engine shut down mid travel. Won't start, all ground and connections are fine. All uses fine too. Can't hear the fuel pump prime with key in on position, if I try crank it then turn off, I hear immediately following a screeching like noise from underneath the passenger seat where the fuel relay sits. Odd thing is this is a brand new fuel pump that is 48 hours old. Well, there goes my weekend!
 

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1970-1995 Range Rover Classic
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Discussion Starter #10
PROBLEM SOLVED - it was the distributor rotor arm all along. I never thought to check it since the distributor is brand new installed in June, but as soon as I swapped in a rotor arm from a spare I had, the truck fired to life and idles like a champ. Go figure.
 

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1970-1995 Range Rover Classic
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Discussion Starter #12
Yes, shifting at 3500 RPM, revs up to 4000 rpm very reluctantly, but it's more consistent now. So I am not out of the woods completely yet, but headed in the right direction I suppose. And now my EFI light is on permanently!
 

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What can you rev it out to when its in neutral? The reason is that it doesn't need much fuel flow and so if the problem is fuel it should rev all the way.
 

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1970-1995 Range Rover Classic
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Discussion Starter #14
Problem is elsewhere. I exploded a second viscous fan at around 4200 RPM (the first was less than 3 mos ago, the newly exploded one was brand spanking new both clutch and fan from AB). The fan was completely destroyed, and somehow the rotor arm in the dizzy was split in half in that kerfuffle. Plugged in new rotor arm and the truck is running again, but he's grounded for now while I contemplate taking out the engine and stripping it down for a complete engine rebuild this summer with an e-fan setup. In the meantime, I just acquired a new daily driver that is not a Land Rover while I get to the bottom of my exploding fans and limited revs woes.
 

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4000 rpm. Is really high my engine has never gone to 4000 , maybe 3200 at kickdown ( flooring throttle to accelerate onto freeway or to pass ) your kickdown linkage may be out of adjustment , disconnect to see if this eliminates problem
 

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1995-2002 Range Rover P38A
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There's something wrong with yours too then. Maximum power on the 3.9 engine is produced at 4,850 rpm (4,750 rpm on the 4.2) and in neutral it should rev to the red line at 5,000 rpm. If it only gets up to 3,200 rpm on kickdown at full throttle, it isn't right.

Here's what the shift speeds and revs should be.

REVS.jpg
 

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1970-1995 Range Rover Classic
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Greetings. New to the RRnet forums. I have an '88 Classic that had a similar problem. Drove really well but had a bad stumble at 2500 rpm. Took me a while but I eventually narrowed down the exact RPM range and also realized that it was not only under load. A friend has the rovergauge setup on his laptop and we tested it out using a 14cux ECU. At 2500 rpm the tach signal to the ECU jumped to 4000rpm. The tach on the dashboard is buffered or something so the fault didn't show up there, only on the ECU side. Tach signal comes from the alternator so we swapped out the one that was bouncing around in the boot when I bought the truck. Problem solved instantly, driveability was completely restored (on all 7 cylinders haha) and it charges better now too. If you aren't getting 14.5 volts or if you're seeing "ripple" in the interior lights or other lighting then you have a diode problem. If its the one that feeds the tach signal to the ECU, then guess what :)
Good parts shop can tell you if you have a flaky diode too.
 

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1995-2002 Range Rover P38A
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Yeah I was going to suggest doing an independent check of the tacho also, as it runs off the alternator and they can be a bit flakey. The ECU gets its signal off the coil.
 
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