A Compression Test...

Ok, I've established that I have zero oil pressure at idle while at normal operating tempature. Before I replace the oil pump, I'm going to get a compression test to see if an entire rebuild is in order. Do I need to get this done at Jeep, or can any shop do this and how much would this run... ball-park. Thanks.

You can do it yourself for around 20 bucks, or you can pay around 80 at Jeep. Go to you local auto parts store and buy a cheap compression tester. They may have a loaner you could borrow with a deposit. Here are instructions. It's very simple. Your readings should be 120-150.

1. Make sure that the proper amount and viscosity of engine oil is in the crankcase, then ensure the battery is fully charged.
2. Warm-up the engine to normal operating temperature, then shut the engine OFF.
3. Disable the ignition system.
4. Label and disconnect all of the spark plug wires from the plugs.
5. Thoroughly clean the cylinder head area around the spark plug ports, then remove the spark plugs.
6. Set the throttle plate to the fully open (wide-open throttle) position. You can block the accelerator linkage open for this, or you can have an assistant fully depress the accelerator pedal

1. Install a screw-in type compression gauge into the No. 1 spark plug hole until the fitting is snug.
2. Repeat the test on each cylinder, cranking the engine approximately the same number of compression strokes and/or time as the first.
3. Compare the highest readings from each cylinder to that of the others. The indicated compression pressures are considered within specifications if the lowest reading cylinder is within 75 percent of the pressure recorded for the highest reading cylinder. For example, if your highest reading cylinder pressure was 150 psi (1034 kPa), then 75 percent of that would be 113 psi (779 kPa). So the lowest reading cylinder should be no less than 113 psi (779 kPa).
4. If a cylinder exhibits an unusually low compression reading, pour a tablespoon of clean engine oil into the cylinder through the spark plug hole and repeat the compression test. If the compression rises after adding oil, it means that the cylinder piston rings and/or cylinder bore are damaged or worn. If the pressure remains low, the valves may not be seating properly (a valve job is needed), or the head gasket may be blown near that cylinder. If compression in any two adjacent cylinders is low, and if the addition of oil doesn't help raise compression, there is leakage past the head gasket. Oil and coolant in the combustion chamber, combined with blue or constant white smoke from the tailpipe, are symptoms of this problem. However, don't be alarmed by the normal white smoke emitted from the tailpipe during engine warm-up or from cold weather driving. There may be evidence of water droplets on the engine dipstick and/or oil droplets in the cooling system if a head gasket is blown.

imthehink basically summed it up

Compression Test *Results*...

Alright... I did the compression test myself. The result is 170psi on all cylinders, except one. The 1st cylinder closest to the radiator is running at 149psi.

So, given my oil pressure problem... I'm assuming if I get some head work done I can fix this problem and maybe get a few extra HP out of the deal. Am I kind of in the ball-park?

Re: Compression Test *Results*...

ODXJ97 said:

Alright... I did the compression test myself. The result is 170psi on all cylinders, except one. The 1st cylinder closest to the radiator is running at 149psi.

So, given my oil pressure problem... I'm assuming if I get some head work done I can fix this problem and maybe get a few extra HP out of the deal. Am I kind of in the ball-park?

Click to expand...

I'm going to go with the following suggestions....

1. No oil pressure ? Replace the Oil Pump first.

2. Still a problem, then work your way around. There is NO guarentee that doing head work will solve your oil pressure issue.

Start with the basics and work your way to the harder stuff.

Re: Compression Test *Results*...

ODXJ97 said:

Alright... I did the compression test myself. The result is 170psi on all cylinders, except one. The 1st cylinder closest to the radiator is running at 149psi.

So, given my oil pressure problem... I'm assuming if I get some head work done I can fix this problem and maybe get a few extra HP out of the deal. Am I kind of in the ball-park?

Click to expand...

You're not in the same park, you're not even in the same sport. WIth all cylinders at 170 and one at 149, there really is no problem there. There may be a bit of excess wear in the #1 cylinder, but at 149psi it's nothing to worry about. Head work will not fix an oil pressure problem, oil gets up into the head through the pushrods.

Lack of oil pressure also may not be the pump, it may be a problem with main bearing clearances. I've seen 4.0 engines before that have no oil pressure because of main bearing problems, but make no clanking noise or anything. Replacing the pump may not fix your problem...you can try, but chances are it won't work. Either a complete rebuild (with at least the block and crank going to a machine shop) or junkyard motor swap is probably in order.

This may sound dumb, but did you remove the oil pressure sending unit and replace it with a cheap mechanical guage (available at any AutoZone) to verify that it's indeed a real pressure problem and not a sensor/guage/electrical problem?

"This may sound dumb, but did you remove the oil pressure sending unit and replace it with a cheap mechanical guage (available at any AutoZone) to verify that it's indeed a real pressure problem and not a sensor/guage/electrical problem?"

Yes I did. The mechanical gauge was identical to the electrical one. I only have zero oil pressure at normal operating temp, at idle.

Bottom line... with all of this in mind... will a 4.5L stroker kit rebuild fix my problems, and how much am I looking at in labor costs to install the basic Stroker kit? Thak you for the help.

ODXJ97 said:

"This may sound dumb, but did you remove the oil pressure sending unit and replace it with a cheap mechanical guage (available at any AutoZone) to verify that it's indeed a real pressure problem and not a sensor/guage/electrical problem?"

Yes I did. The mechanical gauge was identical to the electrical one. I only have zero oil pressure at normal operating temp, at idle.

Bottom line... with all of this in mind... will a 4.5L stroker kit rebuild fix my problems, and how much am I looking at in labor costs to install the basic Stroker kit? Thak you for the help.

Click to expand...

You'll have to call around to local machine shops if you want to have them build the engine for you. The block is probably salvagable, and you'll get a new crank with the stroker kit anyway. So, if you've got the coin, the stroker kit should indeed fix all your problems.

I'd throw an oil pump at it first anyway just for kicks, worst case scenario is that your problem remains and the new pump goes on the stroker motor. Might as well use a new pump with the new rebuild anyway.

In another thread, I've already suggested that the problem is excessive bearing clearances. The reason why it's not the oil pump is that the oil pressure is still 45-50psi at cold idle and that's with a lightweight 10W-30 synthetic. Unfortunately the oil pressure drops very quickly as the engine warms up, and that's a classic sign of excessive bearing clearances especially if the oil pressure is very low at hot idle but rises to 40+psi when you rev it up.
Replacing rod/main bearings and the oil pump should fix the problem, and it's a good idea to replace the rear main seal as well while you've got the no.7 main cap off.