1998 Buick LeSabre

[JLKINSER1970]

Hi All

I am new to this forum and so glad I have found it.

I have a 1998 Buick LeSabre that is giving me fits. I have only had it for about a month. The car has a little over 200,000 miles on it. The mechanics I bought it off of had recently placed an lower mileage (70K) short block in it but put the 200K head back on it. They replaced the lifters but used the same push rods.

The check engine light came on the code scanner read a P301 misfire on #1 cylinder. The car makes no jump or anything when it misfires. The only way I knew if misfired was the engine light came on.

I am no mechanic so I am learning as I go. I replaced the plugs with the correct AC plugs, new wires, and new ignition module, replaced all three coils, replaced the number one fuel injector, checked the injector pulse with a node light and it was perfect. Still, misfire on #1 cylinder. It also gets LOUSY gas mileage. I filled it up on Monday, drove it 130 miles on Monday, and it sucked a half a tank of gas.

So tonight, I did a compression check. The results are as follows:

Cylinder PSI
#1 115
#2 160
#3 175
#4 185
#5 190
#6 185

I put 3 squirts of oil in the #1 spark plug hole and got a PSI of 135.

I am at a loss now. I know how to do the compression test but the manual I have doesn’t have a compression spec to go by. The spark plugs ends were dry but the threads were wet. When I did the compression check, the threads on my tester got wet as well. Also, it sounds like the #1 and #2 lifters are chattering.

Here is what I was told. Since it is misfiring, the head is most likely the issue which would give me bad gas mileage as well. But, I was also told the cam and/or rings could be bad which would cause a misfire and bad gas mileage. I was told if I did a compression test it would tell me if it was the head, cam, or rings. But this is where I am lost because I don't know how to diagnosis it from here.

From the readings, can any one tell me what your opinion is. Am I dealing with a bad head or a bad cam? I would think the rings are fine since I don't get any blow by but since the PSI moved up when I put 3 squirts of oil in the spark plug hole, the manual tells me it is the rings.

Thanks in advance!

John

[maxwedge]

The right way to do this is a leak down test, this will determine what valve if any is bad or if the rings are not sealing . I doubt this a cam issue here. I would also check idle vacuum readings for a steady reading at say 18-91 in.

[auto trainy]

Max, did you mean 18-19 in. of vacuum? 18-91 if were possible would pull nuts off a brass monkey.

[maxwedge]

LOL, my typing skills are the worst!! Yes of course 18-19. Thanks.

[JLKINSER1970]

Originally Posted by maxwedge

LOL, my typing skills are the worst!! Yes of course 18-19. Thanks.

Thanks for the info MAx. I bought a Leak Down Gauge tonight and plan to do the test this week end. Could you tell me the correct way to do this test? Since I am only planning on testing the #1 cylinder, do I remove all the spark plugs? Also, how do I do the idle test?

Thanks!

John

[maxwedge]

bring the engine to tdc #1, find a way to stop the engine from turning as it will do as you put pressure in the cyl., leave the rest of the plugs in. You will need 100 psi line pressure.

[HotZ28]

I have a 1998 Buick LeSabre that is giving me fits. I have only had it for about a month. The car has a little over 200,000 miles on it. The mechanics I bought it off of had recently placed an lower mileage (70K) short block in it but put the 200K head back on it. They replaced the lifters but used the same push rods.

Also, it sounds like the #1 and #2 lifters are chattering.

Almost anything can affect lifter preload. If you do a valve job, surface the block or heads, change the head gasket thickness, or buy a new camshaft, the amount of preload can be affected. Sometimes these changes cancel one another out and your preload stays the same; this is more by luck than design. This is why you must always inspect the amount of preload the lifter has when reassembling the engine and be sure that it is correct.

Just to elaborate a little more on the leak down test, be sure to begin testing the cylinder with the piston @ TDC on the compression stroke (both valves closed) before applying pressure. If not in the right position the piston will try to move (as mentioned). Once you have regulated air pressure set @ 100 psi (just an easy setting for reference) you will read the leak-down on the other gage. Example: If the regulated gage is reading 100 psi & the other gage is reading 90 psi -- you have a 10% leak-down. In addition, while testing, you can here where the leak is, it may be going through the intake, or exhaust valve, or past the rings into the crankcase. You can check with lower air pressure if you like, just remember all things are relative concerning percentages. Example: Using 90 psi regulated pressure, 10% leak-down would be 81 psi on your other gage. 50 psi regulated pressure and 45 psi on the other gage would still be 10%! BTW, the acceptable leak-down range for a street engine would be 4 - 12%. I hope this helps, let us know what you find.

[JLKINSER1970]

Originally Posted by HotZ28

Almost anything can affect lifter preload. If you do a valve job, surface the block or heads, change the head gasket thickness, or buy a new camshaft, the amount of preload can be affected. Sometimes these changes cancel one another out and your preload stays the same; this is more by luck than design. This is why you must always inspect the amount of preload the lifter has when reassembling the engine and be sure that it is correct.

Just to elaborate a little more on the leak down test, be sure to begin testing the cylinder with the piston @ TDC on the compression stroke (both valves closed) before applying pressure. If not in the right position the piston will try to move (as mentioned). Once you have regulated air pressure set @ 100 psi (just an easy setting for reference) you will read the leak-down on the other gage. Example: If the regulated gage is reading 100 psi & the other gage is reading 90 psi -- you have a 10% leak-down. In addition, while testing, you can here where the leak is, it may be going through the intake, or exhaust valve, or past the rings into the crankcase. You can check with lower air pressure if you like, just remember all things are relative concerning percentages. Example: Using 90 psi regulated pressure, 10% leak-down would be 81 psi on your other gage. 50 psi regulated pressure and 45 psi on the other gage would still be 10%! BTW, the acceptable leak-down range for a street engine would be 4 - 12%. I hope this helps, let us know what you find.

Thanks for all the advice guys.

I have been looking at leak down test on Youtube and after reading what you guys have written, and watching some videos, I think I can do this!

Two questions I have though because all of the videos on Youtube seemed to have ring issues. When I apply pressure, should I hear any air coming through the oil cap or the dipstick IF the rings are good? One fellow on Youtube said you always hear air escape through these openings. If this is correct, how do I figure out if it is bad rings or not?

And my next question is if it is an exhaust valve, I will hear pressure escaping through the tail pipe and if it is an intake valve, I will hear pressure escpaing around the throttle body: am I correct here?

Thank for all of your helpful advice!

[maxwedge]

Pretty close, a leak down percentage of over about 12% on a modern engine usually indicates weak rings, if the exhaust valve is leaking yes you hear it in the tailpipe, and the leak would be a much higher percent, same with the intake, thru the throttle body, rings you hear pressure escaping into the crankcase, remove the oil filler cap for a better listen to, make sure you can hold the crank at tdc compression or none of this will work.

[JLKINSER1970]

Okay, hit a stopping point. The fellow that was going to help me do the leak down test had an accident and is laid up for a few months. I was going to turn the crank and he was going to let me know when we were on the compression stroke. Is there a way I can do this all by myself? If so could some one give me the steps on how to do it? I know how to tell when I am on the compression stroke because the air pressure that will come out of the spark plug hole. But how do I tell when I am at TDC? the way the engine is positioned in the car, I ca't get my head in to see down the spark plug hole so I can't see the piston. How can I find TDC? If any one knows if you would please let me know a step by step procedure if possible.
Thanks all!
John

[maxwedge]

Stick a skinny rod piece of coat hanger in the plug hole so it hits the piston, when it reachs to top you can tell by the movement of the rod, try and get someone to at least turn the crank or watch the movement of the indicator you use.