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Discussion Starter · #1 ·
My TJ manual 5 6 speed seems to be lagging some torque at low to mid rpm. I am running 32" tyres with 4.10 R&P on the diffs. Exhaust is magnaflow, straight pipe from pacesetter headers no cats. Replaced the AFE CAI, as I don't like them and went back to stock intake filter and housing.

I have looked at the forum, and tried to address some of the issues, so cleaned the throttle body, replaced spark plugs, tested the TPS (has a smooth curve as observed on Torque App).

I drive mostly in the dunes, the trick is to have enough momentum to clear the area ahead, may it be soft sand in a bowl, or steep climb. At times we don't have the space to gather that momentum, and hence need the throttle to respond when flooring the accelerator.

My TJ from idle to around 2000-2500rpm is a little lagging in delivering the torque that this engine can produce, but after 2500rpm it is great, but that immediate power availability is not there. Perhaps it's just me expecting too much from this older designed engine and need to change my expectations.

Any ideas on what to check for faults would be good.
 

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It seems to me like you covered most of the basics. I'd check for codes, and vacuum leaks, next and see if that yields anything. Then I'd swap the wheels with stock, if you still have the old ones and see if that makes a difference. You might be expecting too much, and that will rule it out.
 

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In sand yeah I'd say the problem is your gear selection... keep the rpm's closer to 2800... that's the 4.0's sweet spot
 

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Discussion Starter · #4 ·
No codes, other than missing O2 sensors after CAT. What should vacuum be on this engine at idle as torque app shows just below 17 which seems low. And any normal culprits for vacuum leaks. Engine is fairly simple which makes me happy. I bought the TJ with these tyres and rims so it will be difficult to go back.

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My 4.0's vacuum at idle in neutral is over 20 inches, maybe 22 or so if I remember correctly, as reported by an actual vacuum gauge.

All the factory equipment is still in place on mine, including the O2 sensors and cats.
 

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Discussion Starter · #7 ·
My 4.0's vacuum at idle in neutral is over 20 inches, maybe 22 or so if I remember correctly, as reported by an actual vacuum gauge.

All the factory equipment is still in place on mine, including the O2 sensors and cats.
It is a 6 cylinder 2006 with coil packs. My vacuum with external gauge and torque app show 17.8 to 18.1, I am at sea level. I sprayed carb cleaner around intake and throttle body but no change.

I can hear hiss sound around the throttle body large spring and the pin that connects to the butterfly internally to throttle body, but when sprayed with the carb cleaner, there is no change. If I push in the opposite direction of the butterfly valve opening, that is close it further the vacuum climbs to 20, but so do the idle rpm to 1000, and engine is not able to return to 690 to 750 rpm unless I rev it a little with my hand on the throttle. I assume ignition on these coil pack engines can not be adjusted. Engine is around 60,000miles only from what previous owner told me, he replaced the engine as he blew the original engine with a an engine from a rally jeep. Am I going to need to do a compression test for warn piston rings. Note issue is that the engine is a little lazy from idle to below 2000-2500rpm. Once going it seems to have enough power and driving in 2nd gear 4h is all that is needed to climb dunes and chase Fj cruisers or manual 3.6 jks, but if I let off the throttle I can't get the immediate power delivery until I am above 2500rpm.

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Discussion Starter · #8 ·
Also note I have had another tj manual owner drive my tj and a mechanic that specialises in jeeps , although just on the street both of them for a few minutes. Both reported that engine pulls well. Maybe I just to used to daily drive which similar to a landcruiser 4500 petrol engine. Double overhead cams, variable valve timing and variable intake length.

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Discussion Starter · #9 ·
Hi just did a compression test. Borrowed a tester via my local Auto sky forum. Unfortunately the the threads were not enough to screw into the spark plug mounts. So removed the o-ring and tried. Somehow 2 threads grabbed on. I assumed that the compression would be too low as there is a possible leak. But I got the following...some threads were not as tight I assume as the pipe was a pita to turn and only 1-2 threads caught on. WOT and cranked 3-4 cycles. Had to do this on my own so could not see initial reading of crank. Battery also drained just before last cylinder, which was cylinder 1. Battery on a smart charger now. But I am happy...maybe a little higher than factory spec???

1 150psi
2 170psi
3 150psi
4 169psi
5 160psi
6 150psi

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Is this your first vehicle with a manual transmission? Are you trying to climb those dunes in too high of a gear? If you're in 3rd, drop back to 2nd, etc.
 

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Discussion Starter · #11 ·
No this is my second manual tranny. I am using 2nd currently as you rightly advise. But the initial throttle response is lethargic, once over 2000 it has the dune climbing ability. Maybe I am too used to the DOHC variable valve timing valve train as last 3 vehicles have been.

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You are asking the engine for torque where it has very little.... again, keep the rpm over @2600 at all times when you want power the sand
 

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Discussion Starter · #13 ·
Okay understood. But sometimes we need to crawl over a lip or small bowl and climb a dune after.

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Discussion Starter · #15 ·
I am going to get out with a buddy that drives a TJ in the dunes and have him drive car and ask him for tips.

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Your 'crawling' should be in 1st gear and slipping the clutch a little if needed....
You can't use 1 gear for everything....
 

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Once going it seems to have enough power and driving in 2nd gear 4h is all that is needed to climb dunes and chase Fj cruisers or manual 3.6 jks, but if I let off the throttle I can't get the immediate power delivery until I am above 2500rpm.
4lo and 10psi will keep the power in the powerband when climbing dunes. Save 2-4hi for the flat dunes.
 

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Discussion Starter · #18 ·
Gents have been driving in dunes for the last 12 years. That's all we have here and a few mountain trails...but most of my off-roading is dune driving. If it were mud I would not have a clue. Don't use the first much. Also as mentioned before my vacuum as per torque app and a vacuum gauge is 17.8 to 18.1 at idle so was that led me to compression due to work piston rings.

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like "Gofast" said, these engines do not produce torque under 2000 rpm. you just need to match your gear selection to the rpms. If you need to crawl, that's what low range is for. If you need more HP and torque to spin the wheels and sling sand, you gona have to get a bigger engine.
 

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No this is my second manual tranny. I am using 2nd currently as you rightly advise. But the initial throttle response is lethargic, once over 2000 it has the dune climbing ability. Maybe I am too used to the DOHC variable valve timing valve train as last 3 vehicles have been.

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you have answered your own question.
"once over 2000 it has the dune climbing ability"
 
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