Thinking about testing my 97' XJ w/130k for

Compression
Fuel Pressure
Vacuum Test
Injection

Just fixed a weird electrical gremlin, thought i was going to need all the extra check ups, in short - dielectric grease is the $#!% an night vision is key

If you say you want to see it - I will more likely get it tested soon then

Other then that -

I've got to flush my anti-freeze soon too (or more like feel I should, looks clean but neglected to do so with a new water pump, whats done is done... )

And have any of you lubricated or cleaned up the steering linkage before? I have not, and its starting to sound stuffed up

Thanks for the thread and info everyone

 

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did i miss something? thought this was a thread on Botas compression test, not your weekend maintnance?

 

So, what's your fuel mileage been through all this troubleshooting? And are you burning any oil? Are you running synthetic oil (cleans internals and valve train efficiently)? How is power using 87 octane?

To me, those parameters are the most accurate indicators of engine performance for a DIYer. If you're in the range of normal MPGs you've got a good engine still.

 

MPG, burning oil, power =....not driven yet

Manual says 6qt of oil but i only put 5.25qt (Mobil1 10w30) in and oil level (cold engine) says "safe"......
would this be the cause of low compression and low oil pressure?

Care to elaborate more on "clean internal and valve train efficiently"?

 

I would agree that evaluation of all these parameters is required to get an accurate picture of what's going on in the motor. For what it's worth, my Haynes manual says that compression tests should be done with the motor warm and cranked at least 7 compressions (is overkill in my book), as was previously mentioned. This ensures that all parts have reached operational temperature and are performing as they do when running.

Secondly, your numbers seem very, very low to me. If, in fact, they are actually that low, you will experience a very weak motor (trouble getting up to normal speeds, bogging down going up a hill, etc). As stated earlier, factory specs for the 4.0 are 120-150psi with no more than 30psi difference between high and low cylinders.

There are several potential causes for your numbers. The first and most likely is that the gauge is not calibrated correctly (that's the fault of whoever you rented it from). If that's the case, the %difference between cylinders will give you as good of an idea as you'll get from the measurement. Another less likely cause could be that you didn't assemble/tighten the tester correctly and you have a pressure leak during the test.

But, if everything's set up correctly, then you could have a very worn engine. Look for lack of performance to be your biggest indicator there.

As far as low oil pressure, low compression could be a cause - bad rings and/or valve seals would let oil into the chamber and not maintain system pressure, but you'd notice a loss of oil and/or smoke out the tail pipe. Low oil pressure can also be due to low volume of oil (but 3/4 quart shouldn't cause that big of a difference - especially if you're still in the "safe" area on the dipstick as you've mentioned), failing oil pump, worn bearings/seals.

Just my $.02

For what it's worth, as a comparison, my '87 Wagoneer with 194k miles put up these dry numbers last weekend (engine warm):
Cyl PSI
1 135
2 145
3 150
4 141
5 138
6 150

 

Thx for the detailed explanation.

I just bought the Jeep and have not driven yet, so i can say much about the mpg as well as the performance, but it does fine.

I'm gonna replace the valve cover gasket as well as the rear main seal....will take a thorough look then.

 

So I Search....SO I SHALL FIND!!!!
Thanx Guys great thread, found it 1st, and its recent.
Doin it ASAP

 

This the result after the timing chain replaced = replace motor

...Dry
#1 67
#2 72
#3 69
#4 77
#5 75
#6 80

Gave up! didn't bother to do the wet test.

FM
WTB motor!

 

Did you ever rebuild? Did you ever find a new engine? Did you have the throttle plate completely open and the intake not restricted while cranking?

 

I'm looking at an engine from a junkyard. They only gave me one number and it was 162. Is this too high? I'm going to try and get the other numbers from them too. Just wondering if 162 is a little too high thanks.

 

If they are all around that number then the engine has good compression.

 

It's likely they haven't followed the FSM method of measuring compression if that's the case.

- Remove ASD, fuel pump relay, etc
- Remove all spark plugs
- Block throttle WIDE OPEN
- Record compression measuring on THIRD revolution

A lot of guides say run it until the pressure stops going up, or 5 cycles, or whatever, however "The Official Method" is 3 strokes and that's what the specifications are based on. (In 1999 this was 120-150 PSI, max 30 PSI variation between cylinders)

 

Thanks guys! Going to pick it up on sat.

 

I don't know what all these guys were talking about calling an engine with a compression of ~70psi OK or saying only the difference between the numbers count. That's pure BS.
A healthy 4.0 should have a compression between 120-150 or higher, may be with a slight variation if done cold vs. hot. I know the thread is old but it bugs the heck out of me when people give bogus information to someone with a genuine interest in the correct answer.