Low Compression
Thread Starter
Newbie
Joined: Feb 2017
Posts: 2
Likes: 0
Model: Cherokee
Low Compression
To Start - I am a novas
I picked up a 1998 Jeep Cherokee to work on for my sons first car.
The jeep sat in a yard for 3 years - I picked up a battery and flushed out all of the fluids. Dropped the tranny pan and it looked good - replaced tranny filter.
Had to get 100 miles on it to get the computer data for a smog - that is when the fuel pump went out - replaced fuel pump and got it back on the road
then the check engine light went on - codes were
P0300 Cylinder Misfire Fault Detected Random Cylinders
P0320 Ignition/Distributor Engine Speed Input Circuit
P0303 Cylinder Misfire #3
P0304 Cylinder Misfire #4
P1282 Fuel Pump Relay Control Circuit Condition
Spoke to the guys at NAPA Auto Parts - they suggested I start with a compression test.
Compression Test Results -
#1 = 120 psi
#2 = 100 psi
#3 = 005 psi
#4 = 030 psi
#5 = 120 psi
#6 = 120 psi
I assumed there was a crack between #3 and #4 - I spoke with the local mechanic - he suggested we do a complete diagnostic on it for 75 bucks to see what he finds - he said that low compression does not always mean a bad cylinder head....
Any comments? Next steps??
I picked up a 1998 Jeep Cherokee to work on for my sons first car.
The jeep sat in a yard for 3 years - I picked up a battery and flushed out all of the fluids. Dropped the tranny pan and it looked good - replaced tranny filter.
Had to get 100 miles on it to get the computer data for a smog - that is when the fuel pump went out - replaced fuel pump and got it back on the road
then the check engine light went on - codes were
P0300 Cylinder Misfire Fault Detected Random Cylinders
P0320 Ignition/Distributor Engine Speed Input Circuit
P0303 Cylinder Misfire #3
P0304 Cylinder Misfire #4
P1282 Fuel Pump Relay Control Circuit Condition
Spoke to the guys at NAPA Auto Parts - they suggested I start with a compression test.
Compression Test Results -
#1 = 120 psi
#2 = 100 psi
#3 = 005 psi
#4 = 030 psi
#5 = 120 psi
#6 = 120 psi
I assumed there was a crack between #3 and #4 - I spoke with the local mechanic - he suggested we do a complete diagnostic on it for 75 bucks to see what he finds - he said that low compression does not always mean a bad cylinder head....
Any comments? Next steps??
Thread Starter
Newbie
Joined: Feb 2017
Posts: 2
Likes: 0
Model: Cherokee
Low Compression
To Start - I am a novas
I picked up a 1998 Jeep Cherokee to work on for my sons first car.
The jeep sat in a yard for 3 years - I picked up a battery and flushed out all of the fluids. Dropped the tranny pan and it looked good - replaced tranny filter.
Had to get 100 miles on it to get the computer data for a smog - that is when the fuel pump went out - replaced fuel pump and got it back on the road
then the check engine light went on - codes were
P0300 Cylinder Misfire Fault Detected Random Cylinders
P0320 Ignition/Distributor Engine Speed Input Circuit
P0303 Cylinder Misfire #3
P0304 Cylinder Misfire #4
P1282 Fuel Pump Relay Control Circuit Condition
Spoke to the guys at NAPA Auto Parts - they suggested I start with a compression test.
Compression Test Results -
#1 = 120 psi
#2 = 100 psi
#3 = 005 psi
#4 = 030 psi
#5 = 120 psi
#6 = 120 psi
I assumed there was a crack between #3 and #4 - I spoke with the local mechanic - he suggested we do a complete diagnostic on it for 75 bucks to see what he finds - he said that low compression does not always mean a bad cylinder head....
Any comments? Next steps??
I picked up a 1998 Jeep Cherokee to work on for my sons first car.
The jeep sat in a yard for 3 years - I picked up a battery and flushed out all of the fluids. Dropped the tranny pan and it looked good - replaced tranny filter.
Had to get 100 miles on it to get the computer data for a smog - that is when the fuel pump went out - replaced fuel pump and got it back on the road
then the check engine light went on - codes were
P0300 Cylinder Misfire Fault Detected Random Cylinders
P0320 Ignition/Distributor Engine Speed Input Circuit
P0303 Cylinder Misfire #3
P0304 Cylinder Misfire #4
P1282 Fuel Pump Relay Control Circuit Condition
Spoke to the guys at NAPA Auto Parts - they suggested I start with a compression test.
Compression Test Results -
#1 = 120 psi
#2 = 100 psi
#3 = 005 psi
#4 = 030 psi
#5 = 120 psi
#6 = 120 psi
I assumed there was a crack between #3 and #4 - I spoke with the local mechanic - he suggested we do a complete diagnostic on it for 75 bucks to see what he finds - he said that low compression does not always mean a bad cylinder head....
Any comments? Next steps??
CF Veteran
Joined: May 2012
Posts: 7,965
Likes: 964
From: Lost in the wilds of Virginia
Year: 1998 Classic (I'll get it running soon....) and 02 Grand
Model: Cherokee (XJ)
Engine: 4.0
If you really think he can give you a definitive answer for $75, I'd go for it.
Could just be the gasket, but really, none of those numbers are cause for joy.
Could just be the gasket, but really, none of those numbers are cause for joy.
CF Veteran
Joined: Nov 2010
Posts: 5,839
Likes: 116
From: In the middle of Minnesota!
Year: 1999
Model: Cherokee
Engine: 4.0
Low compression on two adjacent cylinders is often a blown head gasket.
No matter what, this cylinder head is coming off. Save the $75 and get wrenching. Your compression test is enough diagnosis for now. The rest will come when the head is off.
Once the head is off, take it to a reputable machine shop where they can completely go through the head and also check for any cracks.
If you're lucky and the head is okay, slap on a new head gasket, new head bolts and rock and roll.
Good luck and keep us updated!
No matter what, this cylinder head is coming off. Save the $75 and get wrenching. Your compression test is enough diagnosis for now. The rest will come when the head is off.
Once the head is off, take it to a reputable machine shop where they can completely go through the head and also check for any cracks.
If you're lucky and the head is okay, slap on a new head gasket, new head bolts and rock and roll.
Good luck and keep us updated!
Last edited by tjwalker; Feb 15, 2017 at 07:00 PM.
::CF Moderator::
Joined: Dec 2016
Posts: 3,538
Likes: 416
From: SoCal
Year: 1987
Model: Cherokee (XJ)
Engine: 4.0
Do a leak down test on #3 and 4. That will tell you where it is leaking from. You will be able to hear the air coming out of the intake, exhaust or valve cover.
CF Veteran
Joined: May 2012
Posts: 7,965
Likes: 964
From: Lost in the wilds of Virginia
Year: 1998 Classic (I'll get it running soon....) and 02 Grand
Model: Cherokee (XJ)
Engine: 4.0
CF Veteran
Joined: May 2012
Posts: 7,965
Likes: 964
From: Lost in the wilds of Virginia
Year: 1998 Classic (I'll get it running soon....) and 02 Grand
Model: Cherokee (XJ)
Engine: 4.0
Yeah, he's right (as usual). Once you have spent the $75 and he's told you what he thinks it is, the head still has to come off to be 100% sure, so you might as well get the head off and be 100% sure. My two inexperienced boys did it on mine recently in a few hours. It's not that bad.