Improving the TJ's 2.5L gas engine's efficiency -
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Unread 05-12-2013, 06:54 AM   #1
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Improving the TJ's 2.5L gas engine's efficiency

Some time back, someone told me that power and torque gains are available from TJ 2.5L engines by fitting the YJ's 2.5L fuel injectors. My informant advised that efficiency would be improved due to the YJ injectors having a slightly bigger internal diameter to those fitted as standard on the TJ 2.5L engine.

Is this the case and, if so, is it a simply a matter of swopping out the injectors and resetting the ECU? Any subsequent increase in air flow/volume that may be required should not be a problem, as my TJ is fitted with a larger bore non-restrictive air induction/intake system. Please note that the current intake system already benefits from the fitment of a Helix Power Tower Plus throttle body spacer (highly recommended) which is further complimented by a couple of other proprietary "swirl" type devices, located within the induction pipework, between its truck air filter and the throttle body.

Oh, now why do I choose to drive a 2.5L? Because my TJ (plus driver's experience) can go off-tarmac wherever the 4.0L boys go but with better gas mileage. We are currently paying close to $1 PER LITRE for unleaded petrol in the UK and there are 4.55 litres in our Imperial (British) gallon!

Keep on Jeeping.


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Unread 05-12-2013, 07:13 AM   #2
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They are different injectors both at the connector and the psi output. I would think that they would not work...

Here is a good thread to help you out with the 2.5 injectors for the TJ:
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Unread 05-12-2013, 07:13 AM   #3
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There are tons of posts on this-short version: you will not improve fuel efficiency with modified injectors. The ECU regulates HOW MUCH fuel the injector delivers, so an injector that can deliver larger amounts of fuel will be restricted by the ECU itself. Some folks have derived benefit from 4 port injectors from vehicles like certain Dodge Neon models-the theory behind this is that, even though the fuel delivered is the same amount, the improved distribution pattern from the injectors provides a better burn. The benefits are mainly around response and smoothness. Mileage improvements, from a general consensus, are negligible.

As for the rest of the widgets that you have, I really hate to say it, but they really aren't doing anything. These engines really don't react to such gadgets. In fact, the stock intake is not restrictive at all...most mods in this case are aesthetic, such as better sound of a CAI, or location specific (moving to protect against water).

TB spacers on these engines, in my direct experience, are non-effective. Mine has one from the PO, and i have run it with and without-have never noticed a difference. I have it in there because the PO also modified the intake to accommodate the TB spacer, and I have not gotten around to my cowl intake relocation project.

Proprietary Swirl devices- This is my logic on these....if you are looking to eliminate restriction in an intake, why would you put something into said intake that increases overall drag to the innards of said intake. The interference these devices introduce merely disrupt airflow, and in fact, provide restriction. I would love to be proven wrong here, but that is my reasoning.
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Unread 05-12-2013, 10:58 AM   #4
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The only way to get better fuel efficiency is to drive slower. On a cross-country drive last year in my Daughter's jeep we would get 20 mpg or better at 55 mph, at 70 mph we would get less than 16. At 70 mph we actually got worse mileage than my younger daughters jeep with the 4.o engine.
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Unread 05-12-2013, 11:13 AM   #5
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Just by installing larger injectors will do nothing UNLESS you do something with the valves, i.e. head work, cam size, ECU settings and so on. Also TB spacers do nothing as well as the air sucked into the engine is determined by what? The VALVES and CAM SHAFT. An engine is nothing more than a fancy air pump.
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Unread 05-12-2013, 11:15 AM   #6
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The only improvement in 2.5L fuel consumption I got was because of regearing. I used to get 18 mpg on highway cruising around 60 mph with 31 tires and 4.1 gears, now I get 19.5 mpg with 33 tires and 4.88 gears. But regearing is a rather expensive way to save some money
2002 TJ 2.5L
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Unread 05-12-2013, 11:56 AM   #7
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Originally Posted by eurojeeper View Post
We are currently paying close to $1 PER LITRE
I paid $28 US dollars for a litre the other day.It was Grey Goose though.
When I had 3.07s I would draft behind birds as an attempt to do the speed limit.
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Unread 05-12-2013, 02:32 PM   #8
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Having owned the TJ 2.5L and later two other 4.0Ls, I can tell you that there really is no cost-effective way to squeeze worthwhile power out of that engine. It is what it is and in stock or near-stock form, it does very well. TB spacers, air intakes, all that $100 crap does nothing.

As far as torque goes, look into the inertia ring go to on the flywheel if you really want to. This is help build torque without looking for it at higher RPMs. But you'll need to drop the whole trans to install...

And as mentioned, keep axle gearing proportional to tire size. You'll do far worse on gas mileage if you are lugging.

Yes, there are a few superchargers out there- but that costs roughly what it would to swap an engine and you'll be running higher-octane fuel.

No replacement for displacement. If the lack of power in the 2.5L bugs you to the point of contemplating multi-thousand dollar power mods, just trade it in and get a 4.0L or a Pentastar JK.
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Unread 05-12-2013, 04:23 PM   #9
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Hpa makes a tdi diesel swap but with motor and install unless you are a boss and can do it yourself you are looking at 7k

I have a friend that did a 5.0 mustang v8 swap for under 3k

Stroking or supercharging the 2.5 is cool factor points but will cost 2k plus to do it right...

Roller rockers are 400, efan 10-250, an with intake exhaust headers and programmer you are already in the 1000 dollar range and that is without synthetic fluids, gears or additional cooling upgrades. If I knew what I know now, as much as I like the 2.5, I would keep my magnaflow muffler, keep my drop in aem dryflow filter and keep it bone stock with gears. Or, swap over a 4.0 or srt turbo. If I was feeling uber cool, swap in a tdi diesel.

Cliff notes: keep as close to stock or switch with a larger displacement motor.
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Unread 05-12-2013, 04:25 PM   #10
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prius engine swap
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Unread 05-12-2013, 07:33 PM   #11
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So funny.

Originally Posted by ItsJustD View Post
prius engine swap
2000 Sport.
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Unread 05-12-2013, 07:35 PM   #12
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Best way to improve fuel efficiency of the 2.5 is to take it out. I get same if not better milage with my 4.0 after the swap. V8 guys get even better.
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