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86 L98 TPI - Is this bad valve seal, or stuck injector?
Gents,
I've been on the forum for over a decade over in the C3 section, but recently I acquired a red on red 86 convertible at a great price so I'm going to be frequenting this area as well.
The L98 in my car has three wiped cam lobes so I'm working on getting that straight. During my troubleshooting I noticed that the #6 plug was fouled with a liquid. I assumed it was fuel as it seemed to happen very quickly to a replacement plug as well. As a result, I made the assumption that I had a stuck injector on #6.
In the process of doing the 'While I'm at it' portion of the job of replacing the injectors, I performed a leak-down test of all the cylinders and measured the cam lobe travel. Well, the leak down was fine, so I don't think any of the valves themselves are leaking. The cam lobe measurements were another story. I found three worn lobes and started disassembling the motor to get the cam out.
So tonight I removed the Intake manifold and the condition of the #6 intake port on the head was noticeably different from the other cylinders. The pic below shows the #6 and #8 intake ports. Notice all of the buildup on #6.
I took a paper towel and wiped some of it out in the hopes of telling what it was. Pic below shows the crud...
So this looks like oil to me, but how did it get all the way up into the port like that if it is oil and not fuel? Would a stuck injector cause this kind of buildup in the port? Would a bad valve seal do it? I think I should have been able to detect a bad valve seal during the leak-down test.
Looking to some of the L98 gurus for some help on this one.
Valve seals keep the oil from entering the combustion chamber via the valvestem. They have nothing to do with compression or leakdown. If you have 3 wiped out cam lobes, I would recommend pulling the motor and rebuilding or freshening it up. The cam material circulates throughout the motor and can wipe out cranks and bearings. Oil can get into the intake area through leaky valveguides/seals or the pvc valve or from reversion if you have oil in the combustion chambers.
I agree with 383. All that metal went al through your engine. Valve stem seals are of course a well known problem, also the EGR sits right on top of there and could have been stuck open or not closing completely. That mixed with some oil and gas (if you had a stuck injector) will give you a bunch of gunk.
Valve seals keep the oil from entering the combustion chamber via the valvestem. They have nothing to do with compression or leakdown. If you have 3 wiped out cam lobes, I would recommend pulling the motor and rebuilding or freshening it up. The cam material circulates throughout the motor and can wipe out cranks and bearings. Oil can get into the intake area through leaky valveguides/seals or the pvc valve or from reversion if you have oil in the combustion chambers.
Your absolutely right on the leak-down test and valve seals. Brain fart on my end.
But would a leaky valve seal cause this kind of build-up in the intake port runner?
With respect to rebuilding the whole motor, I'm still assesing what I want to do. Probably pull a main bearing cap or two and see what the main bearings look like.
Your absolutely right on the leak-down test and valve seals. Brain fart on my end.
But would a leaky valve seal cause this kind of build-up in the intake port runner?
With respect to rebuilding the whole motor, I'm still assesing what I want to do. Probably pull a main bearing cap or two and see what the main bearings look like.
A bad valve guide or seal will cause oil to enter the intake port.
08-21-2017, 10:50 PM
86 L98 TPI - Is this bad valve seal, or stuck injector?
