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HUGE difference in power 4.0 vs 4.2

10K views 88 replies 7 participants last post by  Gerk 
#1 ·
I currently have an 89 SWB with 4.0 and I have a 92 LWB with the 4.2
Nearly the same amount of miles (approx 200,000)
The 4.2 drives 10 times better. So much more power.
I have some steep hills in my area. The 89 almost does not make it up where the 4.2, I need to take my foot off the gas sometimes to slow down around corners.

The 89 passed California smog with flying colors.
I do have slightly bigger tires but I can't imagine that is the problem.


What could be the problem?
Where should I look next?

Thanks all
 
#2 ·
Tell me if you think I am on the right track.
I cant get up a hill easily, because I think it is shifting into 2nd too early.

I went out testing today and found the 4.2 shifts into all gears at around 3000 RPMs when I put my foot into it.
When I do that on the 4.0, from 1st to 2nd, it shifts at 2000 RPMs and it takes a while to catch up and then shifts OK in other gears

I think when I go up hills (they are usually starting in 1st) The 4.0 shifts into 2nd too early and then I never really get a good start at it

Could it be kickdown cable? Shift cable? Bad transmission?

What do you all think?
 
#3 ·
IMHO, shifting 1-2 at 2000 RPM with your foot in it is way too early. Think you might be on to something. As far as kickdown, I don't know anything about older RRs (mine's a DII), but you should follow that line and see if it gets you where you want to be. Could be a simple fix.
 
#4 ·
Shifting the transmission by hand up hill is what I think you should do
The kick down cable is More for jumping into traffic and passing
Also replacing that cable isn’t exactly an easy fix
Look at its connection to the throttle body
And see if it needs adjusting
 
#5 ·
So here are a couple things I have found/learned.
I feel like a bit of an idiot, but when I was checking the kickdown cable and throttle cable, I saw that the hose clamp that I have on the hose directly in front of the throttle was facing stright up. In other words, when the car was given full throttle, it was stopped by the head of the clamp. I just needed to loosen it and turn it and then I have 15% more throttle.
Something else that I learned is that going to a 265/75/16 tire can lose anywhere from 13% of power without changing gear ratios. I am not sure how that was calculated.
My 92 have stock wheels and tires. I may swap them just to see the difference there.
With those 2 factors, I believe I have my answer.
Going up long steep hills, I just have to manually shift it
 
#7 ·
The tyres will make a hell of a difference with power and fuel economy. I have standard tyres and the same diameter tyres as yours. The difference in power is very noticeable.
On the classics the kick down cable is easily adjustable. Just adjust it to suit what you want. As I mainly use my range for towing a car trailer, I have the kick down set to change down a bit earlier than standard.
 
#8 ·
I am hoping someone can help me with this now.

Since I have 265/75/16 tires and they rob me of quite a bit of power, what would be a good tire size for a rover 4.0 with approx 3" lift.
I have a set of 235/70/16s that I put on just to see the difference in power.
It is noticeable but not by a lot. Pretty much just when I climb hills.
I will not be keeping the 235s on there. They look ridiculous with my lift.

Here is where I need the most help.
Is the problem with the weight of the tire, the diameter of the tire, width of the tire, or.......?
I was looking at some smaller tires that I liked and they were actually heavier than what I have now. Must be the tread type.

What I have now are 31.7 diameter 10.6 width and weigh 43.9 lbs.
What I am possibly looking into are 30.5 diameter 9.8 Width and 38.6 lbs.

Will I notice a difference at all with the new setup?
Will be bummed with the stance being smaller?
Will the new setup be better overall for my rig. Meaning transmission not working as hard, less weight to have to roll, etc....

Interested in your thoughts

Thanks all
 
#10 ·
A little update here and in need of some advice.

I just did a compression test and I think my lack of power is due to tired engine with low compression.
The test went as follows.
Just going from back to front looking toward the rover

P D
95 90
91 94
100 99
115 98

Where do I go from here?
The Rover runs perfect with no real problems other than it is very slow and I am not sure if I could hit 70MPH
 
#20 ·
I had a long fight with my '89 over a lack of power, trying everything from better plugs and wires, better exhaust and intake, better newer fuel injectors, even a high performance cam and new timing set, but all of it did absolute diddly squat. My compression numbers were very similar to yours, and despite it running perfectly smoothly, not burning oil, and passing CA smog like a champ, it was just beyond gutless. It really is about the compression, and a drop like that from stock (about 150-160psi for the 8.3:1) results in a huge loss of power, and cannot be overcome by anything short of a rebuild. 85-90psi is actually the lower limit at which the engine will actually properly combust fuel and run, so despite not showing the obvious signs, what you have is an extremely tired motor. Buying one with 120K may not be a good idea either, as it entirely depends on how it was cared for. Yours lasted 250K which is fantastic. Mine, which I bought with 140K, was nearly as tired (despite being in very nice shape), so your 120K engine might not have all that much life left in it. Despite the high expense, a fresh motor is really the way to go if you want to keep the truck.
 
#13 ·
A very nubbie question here. Sorry. One thing I have learned about having a Rover is to have lots of tools and know how to use them
I have a vacuum tester.
Can you give me basic instructions on where I should connect it so I can get you some accurate results?
 
#14 ·
Heres my test results.
Let me know if I installed the vacuum tester in a good place.
That picture is with the engine running. The needle stayed right where it is. When I blip the throttle, it jumps to 0 and then right back to what you see in pic.
91463
 
#17 ·
I can tell you this.
When cold it just sits at 12
I just took it for a drive and warmed it up. Sits between 12 and 14. Not fast moving. Pretty steady
Gauge says 17-22 =normal motor
Mine reads average 13. Almost to red ignition timing area on the gauge.

This motor is a bit old at approx 250,000 miles
 
#21 ·
I agree. There’s too much guessing and hoping involved with a used swap. If you plan to love the truck forever I would also suggest a new engine. I went that route and it’s awesome to have the new-car confidence.
May not be worth it to you tho
 
#23 ·
I appreciate the reply.
I ended up buying that engine.
I am going to try to clean it up and do everything I can to it with it out. Also do a compression test with it out before I waste all that time and energy.

I almost purposely drove it off the cliff yesterday (if I could have gotten it there).
I have an EFI light on recently. Now when I start her up she has very very low idle for the first 4-5 seconds and then seems to be fine.
Went to the store and then tried to leave and had an extremely hard time starting and then put into gear, it would die. Took me about 30 minutes to get 1 mile but I did not need to go get my hauler.
Seems like a lack of fuel, but I don't think that is what will trigger an EFI light
 
#25 ·
Think you were right not to buy a used engine. Hopefully I am wrong, but stuck in a predicament. I got it home and put on a stand.
Removed plugs and tried to look in each hole. Couldn't see much.
Didn't want to try to turn a motor by hand if it had been sitting a while, so I oiled the cylinders. Put in a decent amount, but not crazy.
Few days later, went to turn engine by hand and it was easy and smooth. Then heard a big splash. It was in cylinder #s 1 and 3 or 3 and 5. To be honest, it was a few days ago.
Seems like fluid (water or coolant mixed with oil) was getting into the cylinder and shooting out the spark plug hole. Was this old water in the heads?
The oil in other cylinders had already moved down and was no issue.
Predicament is what to do now.
How can I tell if liners are slipped "IF" I remove heads and go that route?
Could it just be head gasket?
Did I purchase a really cool anchor for my boat?
 
#27 ·
Its my fault for trusting what someone says and not getting proof that it is was he said it was.
Now I have 3 rover V8s in my shop haha
1 4.0 in the Rover, and 2 3.9s in the shop. (all poor condition)
Ive got time. Money is a different story. I have money to do the job, however is it worth putting in?
 
#29 ·
OK I think i just need to vent a minute and hopefully I just need to stop and think. (kinda doubt it)

I tore down that 3.9 that I bought off of Craigslist that was supposedly "GOOD" with low miles.

The engine looks like new now - yee haw.
Spent 3 days pulling out my 4.0 in there and installed the 3.9.
Replaced freeze plugs, head gasket, head bolts, cleaned up the heads and valves

Tried to finally fire it up today at end of the day. Nothing, just spins. Maybe my timing is off. I ran out of time. I swear I put the rotor at #1 at TDC
Was running out of time and decided to check a couple cylinders compression.
Cylinder #1 was 70 and cylinder 2 down toward firewall was 100

Now I did not replace cam, rings, bearings while it was out.
It has not run in years. While heads were off. I let the rings soak in the cylinder with Marvel mystery.

Am I over reacting? Do I need to get it running before I make assumptions?

I have had this rover for 2 years and have yet to have a good strong runner.
I think I have aged 15 years due to this thing.
 
#31 ·
Agreed. Get to where you can properly assess the situation before making rash decisions or assumptions.

besides after you master this you’ll finally have your solid running rover
 
#32 ·
I was off by 1 tooth on the timing. Eventually got her to fire up and run.
Got her nice and warm (actually it seems to want to overheat)
Compression is up to an average of 90 and have a slight tick.
Vacuum gauge reads steady around 11
If thats the case, it says late valve timing.
Does that mean-
1. My cam is worn?
2. Rings are shot?
3. all of the above?
 
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