1988 Jeep Wrangler 2.5L TBI: Blow-by, High Idle and Oil Leak

[Nathanteig]

My 1988 YJ with TBI has given me hell over the past few years. She's never failed on me but causes me headaches everyday trying to make it run perfectly. My issues include high idle (1100 rpm) for the past few years, recently have noticed a good amount of blow-by and oil leaks. It gets 120psi on all cylinders during a compression test. I will list all work I have done to it to try and fix these problems. Please let me know if im missing anything. I have followed the diagnostic tree on the FSM to the tee and nothing has really fixed it.

- Metal valve cover from newer jeep YJ

- New Head gasket, Head valves reseated, new rockers and push rods

-New valve cover, PCV and CCV cleaned,

-New exhaust/intake manifold gasket

-New Injector

-New ISA

-Full rebuild on intake manifold (all gaskets replaced, and all sensors are within what the FSM states they should be, Cleaned inside and out)

-New EGR valve

-Timing checked (was off by 2 degrees but made no difference when corrected)

-TPS and ISA readjusted

-New cat

-New Exhaust manifold

-New Cap, Plugs, and wires

 

 

Oil is now coming out of where the distributor meets the block - I just replaced the gasket and am still experiencing the leak. Please note I am a novice mechanic, I know I have fired the parts cannon a few times but it was all for good reasons. Please let me know what you think my issue may be or If I am missing a part of the diagnostic process.\

 

BTW - I love this thing, the diagnostic process is half the fun...

[Moses Ludel]

Nathantieg...You've been thorough, and I like your use of the FSM.  Of the things you've done, the rpm issue pointed toward the ISA motor.  You replaced it with a new one.  Was there any improvement with the new ISA?  Did ISA tests turn up any related troubles?

What's the mileage on this engine?  Are the spark plugs oil fouling?  The blow-by is a wear indicator and not something you can fix with tuning.  The oxygen sensor is likely having a difficult time with oil burning, which could contribute to the tuning and idle speed challenges. The gasket blowing out at the distributor base could be from too much crankcase pressure.  One cause would be piston ring wear and compression blow-by.  A bad PCV valve or incorrect vacuum hose routing is always a consideration.

I'm not a fan of cranking compression tests.  Years ago, this was the popular quick check, but a cylinder leakdown test is far more insightful.  A cranking engine can squeeze enough air volume into a compression gauge to give the impression of "normal" compression.  A leakdown test with a piston at TDC and valves closed is far more reliable for several reasons.

At a static TDC, the rings and cylinder walls are at their most vulnerable position. Cylinder taper and wear are greatest at the top of the piston stroke.  Compressing air into a cylinder with the piston in this position will reveal wear and the percentage of air getting past the rings and valves plus casting and gasket leaks.  If you can, invest in a cylinder leakdown tester, new or used.  For the tests, remove the coil wire and carefully bring each cylinder to exact TDC with its valves closed.  Remove all spark plugs and use a socket and ratchet to rotate the crankshaft.

When an engine drops to 120 cranking psi, there is wear.  Uniform compression is always important, and you're getting those results.  I never want to see more than 10% psi difference between the highest and lowest compression results. 

There is one thing you can do with your compression gauge. Squirt a small, uniform amount of clean oil into each cylinder right before the cranking test.  If compression jumps up significantly at a cylinder(s), you definitely have ring wear and likely cylinder taper.

Moses