midtiger

Hi Jeep Goers
i have 2000 jeep cherokee with 4.0 automatic
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4.5 inch lift on 33s

I am facing an issue while driving.
When i am going about 40 mph consistently my rpms surge up and down by over 400 Rpms
I do have a cold air intake on my Jeep that is very cheap and not connected very well. I was thinking this could be a vacuum leak but im unsure

my jeep idols alright
ive changed
spark plugs
coil rail
injectors
Tps sensor

any ideas? It makes driving difficult.

Jeepin'_Aint_EZ

Have you checked for vacuum leaks?

midtiger

I never checked for vacuum leak. You think that could be it?

Jeepin'_Aint_EZ

It's pretty easy to check for, so you tell me if it's that or something else. Report back after you've checked. Let's do some actual diag work.

Also, put your stock airbox back on.

midtiger

Ok ill check later and report. Thanks and ill put stock one back

BlueRidgeMark

At least until you have solved this problem!

Cold air intakes are highly overrated, by the way. In a race, where even 1 horsepower can make the difference between winning and losing, they make sense.

On a street or fun vehicle? Nah.

midtiger

I have not solved this problem yet.. the problem continues and i checked for vacuum leaks and there are none.

tjwalker

1. Any check engine light? If so, must retrieve codes.

2. Do you ONLY have the surging at this speed/rpm? Or do you see it in other parts of the power band? You mentioned that it idles okay. Does it surge at 50 mph, 60 mph, or just 40 mph? This is a very important distinction to understand.

If it is only in that very narrow rpm where it happens, it maybe a torque converter issue as when that can be responsible for about that amount of rpm change when it locks/unlocks.

midtiger

No check engine and no surge does happen in 40s and 50s

tjwalker

If it happens on AND always above a certain RPM, then fuel pressure needs to be tested. Not saying that is what it is, but it needs to be ruled in or out. The fuel pressure spec. for yours is 49 psi, plus or minus 5 psi.

Hooking up an engine analyzer or a scan tool to look at all input data real time would also be a good idea. How many miles on your oxygen sensors?

midtiger

Fuel pressure is running at 52 psi
o2 sensors have not been replaced yet cause check engine has not appeared saying i need to them.
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fb97xj1

Have you checked the TPS for dead spots, clean the throttle body or the IAC lately?

Also, using the CEL to gauge an o2 sensor is not always the best way. They wear out gradually, so gradual that most never notice it. But it is happening. The CEL will come on when the sensor ceases to produce a signal, or falls out of range (too high or too low). A CEL pertaining to the o2 sensors could also be the wiring to it and not the sensor itself, should such a code pop up. Some say you should replace them every 60k miles, some say 100k. Even without a CEL. Just throwing that out there.

midtiger

I checked Tsps for dead spots.. Nothing.
I checked for vacuum leak... nothing
This surging is so irregular I am at a loss

midtiger

I may go about changing o2 sensors .... cause im lost....