Sluggish Acceleration

Duner

Doonigan
Supporting Member
Joined
May 6, 2020
Messages
249
Location
Buffalo, New York
Hey all,

I’ve gotten to the point where I think I’ve exhausted testing all the causes for why my Jeeps acceleration is slow as balls in anything other than 1st gear. I’ve read as many forum threads as I could but I’m truly stumped. Here are the details:

Vehicle specs:

2003 2.4L SE

Initial symptoms:

Last fall I noticed on rare occasion there was this “popping” noise coming from the exhaust manifold side of the engine when I would accelerate, as if there was a backfire. This slowly became more frequent until I began to experience rough idle accompanied by bogged acceleration.

After testing the spark to each spark plug and changing nothing the backfiring/rough idle went away on its own but the poor acceleration remained.

No codes/CEL

It starts and idles fine! No high or low RPM. Bogs down when under heavier load, I.e. accelerating in 2nd,3rd,etc.

It’s not my 33” tires either. I drove it 6 months straight without any issues.

It was put away for the winter and here is what I’ve done this spring so far with no success:

Part Replacement:
  1. Spark Plugs - Champion 7570
  2. TPS sensor
  3. MAP sensor
  4. IAT Sensor
  5. Bank 1 upstream O2 - NTK 23138
  6. Crankshaft position sensor (CKP) - standard motor PC386
  7. Fuel pump and filters - Bosch 69316

Testing Done:
  1. Plugged cat testing - I’ve test driven the Jeep with the O2 sensors unplugged and separately test drove it with the lower half the exhaust disconnected at the intake manifold.
  2. Plugged cat inspection - just to double check I fed a wire cam to look at both cats, they look fine to me.

    065CD682-09CB-459F-AE24-6839CC8D7019.png


    29894BFC-BD0E-4386-A637-A6519176734D.png
  3. Cleaned throttle body
  4. Cleaned battery terminals
  5. Measured battery voltage - 12.5 V
  6. Measured alternator voltage - 14.5 V when running
  7. Unplugged battery to reset computer.
  8. Swapped ignition block from my dads running 2.4
  9. Inspected spark plugs for fouling
  10. Test drove with air filter removed.
At this point I don’t know what it could be. Maybe my PCM is failing? I’ll take any suggestions.
 
Last edited:
Pull each spark plugs and test cylinder pressures.
The cylinder pressure shouldn't be less than 120 psi, but preferably more...
The sound you are hearing could be a valve no seating properly which lowers cylinder pressure during engine operation.
The 2.4L doesn't create much power as it is; so IF the cylinder pressure is low so is the power the engine creates.
 
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Pull each spark plugs and test cylinder pressures.
The cylinder pressure shouldn't be less than 120 psi, but preferably more...
The sound you are hearing could be a valve no seating properly which lowers cylinder pressure during engine operation.
The 2.4L doesn't create much power as it is; so IF the cylinder pressure is low so is the power the engine creates.

I’ll have to snag a kit for this. Have any recommendations?
 
How many miles on the Jeep? Has the timing belt ever been replaced?

Edit, This might show up on a compression test...
 
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How many miles on the Jeep? Has the timing belt ever been replaced?

Edit, This might show up on a compression test...

200k, but to my knowledge it was replaced when the engine was rebuilt by the PO, but at this point I shouldn’t assume anything.

I’ll see if there’s a way to test the chain condition without doing compression since I don’t have a gauge on hand.
 
Update:

- Replaced crankshaft position sensor with standard motors sensor

- Swapped MAP and camshaft position sensor. Engine seems to start up quicker, previous cam sensor gap may not have been set correctly.

- new diehard gold battery. I don’t run any winches so I didn’t bother getting the platinum. Old battery wasn’t holding charge so I swapped it.

Only thing I haven’t had a chance to do is a compression/leak down test.

@CharlesHS do you think a valve might be stuck open? The “popping” sound I originally heard no longer happens.

Might snag this.



5B7710DA-6EB5-4736-A864-4FA1EF014D33.png


Only symptom is dog water acceleration.

Man this is getting dumb…
 
There may be an intermittent problem with a valve generally heard thru the exhaust as a popping sound.
I would still perform a compression and leak down test using the test manifold you posted above.
That will either rule out or verify there is a problem with the valves or rings.
 
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Update:

- Replaced crankshaft position sensor with standard motors sensor

- Swapped MAP and camshaft position sensor. Engine seems to start up quicker, previous cam sensor gap may not have been set correctly.

- new diehard gold battery. I don’t run any winches so I didn’t bother getting the platinum. Old battery wasn’t holding charge so I swapped it.

Only thing I haven’t had a chance to do is a compression/leak down test.

@CharlesHS do you think a valve might be stuck open? The “popping” sound I originally heard no longer happens.

Might snag this.



View attachment 518227

Only symptom is dog water acceleration.

Man this is getting dumb…

Most auto parts stores will loan you the compression test kit for free. You just have to pay for it up front and then they refund your money when you bring it back.
 
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Does the 2.4l have a timing belt? I had an isuzu 4cyl hop one tooth during some spirited thrashing and it was low on power. Took a vacuum gauge hooked to the intake and learning how to read it for me to diagnose. I was totally stumped
 
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Does the 2.4l have a timing belt? I had an isuzu 4cyl hop one tooth during some spirited thrashing and it was low on power. Took a vacuum gauge hooked to the intake and learning how to read it for me to diagnose. I was totally stumped

yes it does. From what I could tell both cams seems to be aligned, but the crankshaft timing is impossible to see without taking off the crank pulley
 
So I went to put the Jeep in the garage for the night at cold start, and the intake was making this weird wheezing sound…


Maybe I have a vacuum leak somewhere. It did seem like the RPMs ever so slightly increased when the wheeze occurred.

Ive been starting to think I have a perfect size vacuum leak that isn’t present during idle or throttling at idle, but when I actually drive there is enough vacuum pressure that it becomes an issue.
 
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Update:

Swapped the PCV valve, no change.

Decided to pull the intake manifold off while I wait for my compression tester. Looks like my head gasket is leaking on both sides of the block…
21D52D20-0A5D-4BE0-8A32-D3D1631877B9.jpeg


7BEFC27A-06C2-4AFE-97DB-197799EE1782.jpeg
 
Well with the intake off you're only a couple of hours away from swapping out the head gasket...I used a Felpro set (on a 4.0) and checked flatness with a good straight edge. I used copper gasket spray for extra insurance in lieu of quick and available machine shop work.

Good find!

Might want to do a compression test and leakdown test. If you pull the head and you miss needing valve work or rings you'll be kicking yourself later.

None of this is terrible to do.

-Mac
 
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Well with the intake off you're only a couple of hours away from swapping out the head gasket...I used a Felpro set (on a 4.0) and checked flatness with a good straight edge. I used copper gasket spray for extra insurance in lieu of quick and available machine shop work.

Good find!

Might want to do a compression test and leakdown test. If you pull the head and you miss needing valve work or rings you'll be kicking yourself later.

None of this is terrible to do.

-Mac

Thanks for the advice! At that point I wonder if it’s even worth doing it all or just upgrading to a 4.0 or doing an LS swap…

My dad had a 2.4L as well so maybe I could donate him the engine. Not opposed to fixing things but this thing does have damn near 200k miles with a rebuild.
 
You're maybe two to three hours...hell, call it a day of work...or even a weekend. Let's say you do rings, pistons, roll in new main bearings, new valves and lapping compound, studs and a new head gasket...tops $500-$600.

If you're lucky you can find a donor 4.0 TJ complete with PCM and harness for maybe $2k to $3k depending on your market and availability. I got lucky and found a frame and tub at the right time for fixing my accident damage. It was a 2.4 frame so I had to cut and swap moter mounts.

LS is $10k without even thinking about it and weeks if not months of work.

Get your Jeep running and start saving up for that LS or watch out for that wrecked 4.0.

-Mac
 
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You are definitely right. Technically I have a whole complete 99 but it’s an auto and I honestly like having a stick…

I’ll have to look into it and see what’s going on. Compression and leak down test first then I can go from there!
 
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You are definitely right. Technically I have a whole complete 99 but it’s an auto and I honestly like having a stick…

A brand new AX-15 from Novak or Advanced Adapters is just under $2k. You'd probably need to find another 231J or research the shaft lengths.

I essentially did a 2.4 swap when I rebuilt my 97 in eight days.

It's an option...

-Mac
 
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