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General Forums => The Mess Hall => Topic started by: 95yjester on March 12, 2010, 06:57:22 PM
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Okay, heres the deal '95 2.5l with 4.0l tb w/2.5l sensors, air tube restrictor removed from air box, ford 19lb injectors. Operating temps are normal now engine codes. When the ambient temperature is cool 40 or below jeep runs great even at highway speed (5 speed with 4.10's & 32's and i can get 65 in fifth gear) last couple days temps have been in the 60's and on my way home on the highway could barely make 55 after jeep got up to normal operating temp guage spikes @ 210 drops to like around 190 at cruising speed. My question is why such a loss of power with such a minor ambient temp change and is there any thing I can do to change that.
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Okay, heres the deal '95 2.5l with 4.0l tb w/2.5l sensors, air tube restrictor removed from air box, ford 19lb injectors. Operating temps are normal now engine codes. When the ambient temperature is cool 40 or below jeep runs great even at highway speed (5 speed with 4.10's & 32's and i can get 65 in fifth gear) last couple days temps have been in the 60's and on my way home on the highway could barely make 55 after jeep got up to normal operating temp guage spikes (at) 210 drops to like around 190 at cruising speed. My question is why such a loss of power with such a minor ambient temp change and is there any thing I can do to change that.
can you maintain 65 in 4th gear?
you lose about 5HP between 40F and 60F
if you want to calculate the difference yourself go here http://www.msdfuelinjection.com/MSDInjectorV1/main.html
use these variables
displacement: 150
max rpm: 5250
inlet air temp: 70 (normal operating conditions), 60 and 40 for your example
#of injectors: 4
estimated VE: 76
air/fuel ratio: 13.5
BSFC (brake specific): 0.47
comes to 120HP at 70F, 121 at 60 and 126 at 40F
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it takes a while to get there but it does get there. 65 is screaming in 4th gear
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it takes a while to get there but it does get there. 65 is screaming in 4th gear
what you describe is relatively normal, with 4.10 and 32s the 5th becomes more or less useless. If you want it back you need to regear.
also, make sure you're not getting hot air from under the hood in the intake
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it takes a while to get there but it does get there. 65 is screaming in 4th gear
What do you consider 'screaming'?
I drove with 4.10's and 32's for 5 years. BTDT, regear and revel in your new found power.
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One thing to consider is how much the temp of the air actually going into the intake changes with outside temp. Has anybody done any testing to see how much difference the outside temp actually makes? I don't notice much difference myself and it get to over 100 F here every summer.
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One thing to consider is how much the temp of the air actually going into the intake changes with outside temp.
if the outside temp is 60 that's what the intake air temp should be at wot (ok, maybe a few deg higher due to the intake being hot). if it's 100 outside, then should be 100 for the air entering the cylinders at wot. If you're drawing air from the engine bay will be higher than the ambient so that's why is better to make sure you get air from outside.
for his example there is a 5HP difference at top power rpm, of course would be less at 3000rpm for example but proportionally (percentage wise) about the same.
not talking when the throttle is not fully open since that creates a vacuum and the temp will be lower than the ambient due to the drop in pressure.
this is all relevant for wot since in between you'll compensate by pressing more or less on the accelerator pedal.
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I understand that it is 4 banger on 4.10s with 32's 5th gear on the thruway is fine. My point is the same drive on the freeway at 35-40 degrees jeep feels as though it still has power @ 60 degrees it has no power I was looking for tips or things that i me be able to check. Just looking for ideas I have had the jeep for 2 couple years now and am aware of its capacity for shear unadulterated power.
And it is so sexy that ......... :hitit:
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Are you driving it at the same speed/gear/RPM? Again, what do you consider 'screaming' to be? There are many variables that you might not notice like wind as well.
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it's kind of funny because today was nice here high in the afternoon was like 50 on the same stretch of road that I could barely keep 55 mph the other day when it was 60 degrees today i swear i could of hit 70 with no problem if it wasn't for othercars on the road.
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it's kind of funny because today was nice here high in the afternoon was like 50 on the same stretch of road that I could barely keep 55 mph the other day when it was 60 degrees today i swear i could of hit 70 with no problem if it wasn't for othercars on the road.
head and tail wind make a big difference on a Jeep since it is shaped like 2 bricks on top of each-other.
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it's kind of funny because today was nice here high in the afternoon was like 50 on the same stretch of road that I could barely keep 55 mph the other day when it was 60 degrees today i swear i could of hit 70 with no problem if it wasn't for othercars on the road.
What RPM are you running and what do you consider 'screaming'? This makes a big difference in known if you're in the powerband or not.
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iirc at like 60 mph's on tghe speedo in fifth gear I am 2500 rpm and in fourth gear same speed is like 3000 rpm. also one thing i noticed today was that in fifth gear at cruising speed the jeep responds better to light throttle than to floor board approach.
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iirc at like 60 mph's on tghe speedo in fifth gear I am 2500 rpm and in fourth gear same speed is like 3000 rpm. also one thing i noticed today was that in fifth gear at cruising speed the jeep responds better to light throttle than to floor board approach.
is 60mph what the speedo is showing or the corrected speed (did you change the speedo gear in the t-case to correct for the 32'' tires)? if it's what the speedo is showing you're in fact traveling at about 68mph
since you have not regeared the 5th is completely out of the power band, your engine does not produce enough power at the new rpm to sustain the speed and overcome the air resistance, even if you floor it, and in fact it will continue to decrease the speed until the consumed power would be equal to the power produced at the corresponding rpm (so forget about gaining speed in 5th).
if you still think that something is wrong with it you can try changing the air filter, o2 sensor and also verify the fuel pressure to make sure it has enough gas. I would also have a look at the ignition but it doesn't sound like there's a problem there (you didn't mention anything).
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Sounds like he's either lugging it or running WOT in which case it's running lean.
2500-3000 RPM isn't considered screaming.
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I don't know about the speedo gear the 32's and lift were on it when i bought it as i stated it isn't a dog all the time in 5th gear only seems to have a lack of power when the ambient temperature warms up O2 sensor is new with exhaust last year (less than 500 miles) plugs were changed last year can't remember if I did the cap rotor and wires though I have to look. Today ambient temp in the afternoon was high 40's and it ran great it does accelerate in 5th gear even up mild hills. I was thinking it could be lean but then I thought with the 19lb injectors and the 4.0tb maybe the ignition isn't hot enough to handle the increased fuel mixture. Maybe a better set of plugs and wires and a performance coil? I can live with the way it is but would like to try to make it better. Also mpg seems to be between 10-12 again I have no idea about speedo gear if it was still stock gear on 32's how would that effect mileage.
I really appreciate the help here. Thanks alot
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I don't know about the speedo gear the 32's and lift were on it when i bought it as i stated it isn't a dog all the time in 5th gear only seems to have a lack of power when the ambient temperature warms up O2 sensor is new with exhaust last year (less than 500 miles) plugs were changed last year can't remember if I did the cap rotor and wires though I have to look. Today ambient temp in the afternoon was high 40's and it ran great it does accelerate in 5th gear even up mild hills. I was thinking it could be lean but then I thought with the 19lb injectors and the 4.0tb maybe the ignition isn't hot enough to handle the increased fuel mixture. Maybe a better set of plugs and wires and a performance coil? I can live with the way it is but would like to try to make it better. Also mpg seems to be between 10-12 again I have no idea about speedo gear if it was still stock gear on 32's how would that effect mileage.
I really appreciate the help here. Thanks alot
5th gear is OD and you're not making enough RPM's to keep it in the power band, which is what I keep asking you what you consider screaming is but you still haven't answered.
Your mileage sucks because your speedometer is off as so is your odometer. Your actual mileage is probably 10-12% better.
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Jeffy I thought I answered that 4th gear screaming to me is 3000 rpm and climbing.
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5th gear is OD and you're not making enough RPM's to keep it in the power band, which is what I keep asking you what you consider screaming is but you still haven't answered.
Your mileage sucks because your speedometer is off as so is your odometer. Your actual mileage is probably 10-12% better.
even more than that
32/28=1.1428
so more like 14.3%
(if my memory serves me well and the stock tires were 28'')
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Jeffy I thought I answered that 4th gear screaming to me is 3000 rpm and climbing.
3000 isn't really screaming. It's actually right about where you want to be. Your powerband will usually start around 2700 RPM and peak around 4300 RPM. You can wind it up more but you won't get any more power. Although this does help keep you in the powerband as you climb a hill and your RPM's start to drop quickly.
5th gear is a cruising gear. It's for when you're not passing anyone and you want to conserve gas.
Also, if you haven't swapped out the speedometer gear your speed and mileage are going to be around 7-10% off. So when you think you're doing 60MPH, you're actually probably pushing 67-70MPH.
First thing I would recommend is to calibrate your speedometer (it's in the FAQ). This will not only help you gauge your problems but also help the computer as it uses the speed to set the air/fuel. I would also consider a gear swap. 4.56's would be good for 32's but you might as well go with 4.88's as you will probably swap to 33's eventually. This will make a huge difference in power. Other mods are good but not earth shaking.
Overall, your findings are normal for a stock Jeep with 32's. You're going to have to learn to rev it up more if you're going to stick with those stock gears.
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even more than that
32/28=1.1428
so more like 14.3%
(if my memory serves me well and the stock tires were 28'')
Stock should be 205.75R15's which are 26-27" I think. (I'm going from memory since I don't like math. :lol:) You're probably right though.
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That does make sense, so based on the chart the correct gear would be 36 teeth. best price I found online was like $40.00 I'll call the local dealer and see what they have to offer.
Thanks for the tips.
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That does make sense, so based on the chart the correct gear would be 36 teeth. best price I found online was like $40.00 I'll call the local dealer and see what they have to offer.
Thanks for the tips.
Dealer should be $12-19, IIRC.
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I thought the peak TQ on the 2.5L was 3200RPM. I run between 2800-3300 or so. On the steep hills I'll do 4th gear and stop the RPM's at 4000.
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I thought the peak TQ on the 2.5L was 3200RPM. I run between 2800-3300 or so. On the steep hills I'll do 4th gear and stop the RPM's at 4000.
But keep in mind peak HP is at 5250 RPM.