4.0 with no power

ok everybody says the 4.0 is powerfull but mine will not make power till 4500
its a 87 with new plugs, wires, cap/rotor, tps, crank position sensor(on bell housing)
as a matter of fact it will idle fine but when you give it gas it revs up with a little go but not enough to keep up with a loaded 18 wheeler leaving a stop sign

the 2 4.0 that I had were power. Even with miles of 203,000

are you loosing your tranny?

Have you checked your CAT. If it's going or gone it could be your problem, especially with acceleration. Give it a few light punches, shake it around (when cool) and see if it rattles. If you can hear it rattling it's gone.

it has 217000 on it and last week i gutted the cat (shhhh) i am having tranny problems, got new filter today but its raining and no garage so work will have to wait till later

thanks for your input

Is it just me or does 4500 seem very high? My 4.0L sounds like it's screaming at 3000! I rarely push it past 2300 or 2400 and the one time I pushed it to 3100 kinda scared the crap out of me (we are talking rpm right?). Is the 4.0L really capable of such high rpms without shrapnel? I know the tach goes much higher than I push mine, but damn! How much does higher milage figure into it? (mine approx 200,000 km).

Not tryin to dispute ya bro, I'm just kind of amazed. Mine would explode at that rpm!

Cheers.

My Jeep can rev up to the limiter (5300 rpm) if I hold the shifter in the 1-2 position till about 80 mph.

lornius said:

Is it just me or does 4500 seem very high? My 4.0L sounds like it's screaming at 3000! I rarely push it past 2300 or 2400 and the one time I pushed it to 3100 kinda scared the crap out of me (we are talking rpm right?). Is the 4.0L really capable of such high rpms without shrapnel? I know the tach goes much higher than I push mine, but damn! How much does higher milage figure into it? (mine approx 200,000 km).

Not tryin to dispute ya bro, I'm just kind of amazed. Mine would explode at that rpm!

Cheers.

Click to expand...

Considering that peak hp is @ 4750rpm and peak torque is at 4000rpm depending on year 4500rpm isn't too bad. I almost never get above 2500 either but on occasion you need a little more.

I had low power problems with mine since I bought it over 2 years ago. Replacing the dead cat got me more power to maybe 20% of factory spec. Tune up, fixing the ground problems, replacing the O2 sensor (and actually attaching it), new muffler, setting the transmision throttle cable properly, etc. got me to about 50% of rated power. Replacing the TPS sensor which was lying to my transmission computer while it was telling my ECU mostly the truth about the actual throttle position got my TCU computer working and got my power up to 100%.

For 2 years I wondered if I had internal engine and transmission pronblems, but I continued to search for what I was convinced were control demons and finally discovered a few days ago it was the TCU side of the TPS that was not working properly at WOT. At WOT my TPS was only signaling my Engine to go to 70% of WOT and my Transmission to go to 35% of WOT, while acting normal from idle to about 40% of WOT. No wonder it acted like a 70 hp 4 banger :banghead:

Have you checked the compression? I used to have a "90 XJ w/4.0 and I had the same issues. Idled fine but when you went to go, it was like driving a Mini towing a 20ft. trailer.

I had my compression checked and found out I had a couple of dead cylinders due to bad valves.

There was an easy fix to it though; I just bought a new XJ. :smoker:

thanks alot for input, i seem to have plenty of rpm ( by the way it has seen 7000 rpms can't belive it stayed together) my be a dumb question but could it be my tourqe converter

welter5370 said:

thanks alot for input, i seem to have plenty of rpm ( by the way it has seen 7000 rpms can't belive it stayed together) my be a dumb question but could it be my tourqe converter

Click to expand...

From that description It sounds like it is either the torque converter or the hydraulic pump or the valve body that is shot.

do you know any way to test the tourqe converter without haveing to pull it first? i was also told today that if my iac is not opening it would make it run lean and not have enough fuel to make power, could this be true? how do you test the iac? the haynes book says how to replace it but not to test. it is my second one ive put on.


i know, i know,
alot of questions but i really do apprreciate all ya'lls input

thanks again, jason:anon:

I wouldn't think the iac would have anything to do with lack of power....

What does it do from a dead stop if you shift it into the 1-2 position (first gear) and floor it. Does it have any power then. If you have not tried that, then try it. If the torque converter is gone or going, it should be obvious running this test. The power response should be obvious. If the engine revs to 3000 rpm and the Jeep just crawls then it is a transmission problem, if the jeep takes off with power, then your problem may be the TPS sensor like mine was. Mine had power in first (1-2 position), but in drive it kept shifting up to the next gear at like 1800 rpm even at WOT so it never showed any real power (which is at 2500 to 4000 rpm apx) and then it wimped out at like 60 mph even at WOT which was also a TPS problem.

Once again the torque converter only works if the transmission fluid hydraulic pump is working right, and if the valve body valves are moving into the right positions to get the fluid to the torque converter.

I assume you have checked the transmission fluid level? If it is low, the torque converter will not work properly, no power.

You might try draining it and then make sure you put in the right tranny fluid for that year model. Sometimes the shops put the wrong fluid in these transmissions, and the tannys don't like it. There are several posts here by 5-90 on the proper fluid for these trannys. Also, if you are absolutely convinced it is the transmision, you might try a can of transmission additive like Trans-X as a flush first to free up any stuck valves in the valve body, before draining and refilling the transmission. You drain some fluid (up to a quart), add the quart of trans X, drive it for 10 to 20 minutes, then drain the transmission and change the fluid and filter.

Beyond that I would try and find a reliable shop that is willing to hook up some gauges and maybe dyno test it and pressure test the pump, etc. to see if is the transmision, and the better equiped shops should be able to verify if it is the transmission and if so which part is definately bad. If it is the pump or valve body, they will not be able to verify the torque converter, but you will know where to start.

Forget the IAC, It has nothing whatsoever to do with your power problem.

thanks ecomike, it's going it the shop next weekthey say this guy it THE 4.0 wiz so were going to put him to the test.I just noticed you are from houston so you mite know of them:: gulf coast crawl shop ( Javiers Autos Unlimited )
thanks

I know you replaced your wires, but are all your injectors squirting? (are 2 wires backwards?)
When I replaced my motor on my XJ it had sat for 3 years & the gas had clogged 3 of the injectors - it ran on 3 cylinders, but ran like poo like you describe. I swapped out the tank & ran it (with some injector cleaner) till all the injectors opened up. It has mucho power now.

lornius said:

Is it just me or does 4500 seem very high? My 4.0L sounds like it's screaming at 3000! I rarely push it past 2300 or 2400 and the one time I pushed it to 3100 kinda scared the crap out of me (we are talking rpm right?). Is the 4.0L really capable of such high rpms without shrapnel? I know the tach goes much higher than I push mine, but damn! How much does higher milage figure into it? (mine approx 200,000 km).

Not tryin to dispute ya bro, I'm just kind of amazed. Mine would explode at that rpm!

Cheers.

Click to expand...

My 89 4.0L will hit 4000+ RPM if I go WOT at 45-60 MPH. Unfortunately, WOT is the only way I can get it out of OD, and then it kicks all the way down to 2nd. This is with ~ 216,000 miles and *no* engine work (knock on wood....)

PROBLEM FOUNDarty:arty:arty::roflmaoarty1:


IT WAS A TEMP SENSOR ON THE SIDE OF THE BLOCK, NOT THE ONE FOR THE GAUGE $15.99 FOR 1YR OF CHASING AND CHANGING HIGH DOLLAR PARTS TO FIND THIS LITTLE JEWELL IT ALSO FIXED THE NO POWER & SHIFTING ISSUES I HAD COME TO FIND OUT IT GIVES THE COMPUTER INFO. AND IT CHANGES TIMING WHICH CHANGES SHIFT PATTERNS

Cool, good news I have a question for ya? Did you notice if your running temp was always at the first mark? Mine is always at the first mark but I seem to still have pretty good power. I get terrible mileage though. Thanks. [email protected] if you have time

no the temp read around 190-200, this sensor has nothing to do with the gauge it is for the computer only