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This one is getting me confused and irritated... engine diagnosis

Fellro

Moderator
Staff member
So we have a 98 Buick Century beater car. Daughter runs it but doesn't pay attention to gauges, as well as doesn't apparently realize that H is not a good place for the needle to be...

Anyway, as a result, the heads warped badly, so I replaced them. Had a parts car sitting, motor was locked up but had coolant in it. These motors are notorious for broken cams, and all that. Took the heads off, seemed fine. Nope, one had a bent exhaust valve, #5. Pulled it back apart (foolishly assembled it...) and bought another head to put on. Ran good for a while, then it developed a shudder and now it trips cylinder #4 misfire. Took it apart, found oil in the intake runner, so though maybe just intake gasket troubles... New high end Felpro gaskets which have never been an issue before, still has #4 misfire. Compression test shows good, all cylinders are at about 150. I can hear a little bit of a ticking in the exhaust manifold which has the offending misfire, but if you take the oil cap off, which is directly over the offending cylinder, quiet there. Is there something funky going on with the exhaust valve?

Never really had one work me over like this, just about ready to swap the whole damn motor since I have a few available to me, down side is they are nearly twice the mileage on them as the one in the car now.
 
i remember this engines having some rocker arm issues, bolts coming loose or just plain pulling out of the head.

might be time for a 3400 upgrade ;)
 

Fellro

Moderator
Staff member
I haven't had troubles with the rocker bolts coming loose, and I had tightened them literally an hour before... Also I am told the 3400 has cam breaking issues as well.

Another little tidbit, it seems to run slightly better when I have the plug wire disconnected... and the exhaust sound is a little "puffy", kind of like when the valve was bent.
 

dustybumpers

don't play well w others
How much difference is there in the length of the head?
Not sure if I said that right
Did you Mill the new head for true flat?
Could be the head is shorter and bending the valves on the pistons
I would bore scope through the plug hole
 

blacksnapon

Moderator
Staff member
Do a cylinder bleed- down test.Its more precise than just a compression test.
 

Fellro

Moderator
Staff member
Charlie, the had in question was a used take off. It was checked for flat but that was it.

I will have to try the leakdown and see what it shows me. Also may try the injector first as I have plenty of those around...

The engine ran fine for a week or so, then this code and obvious misfire came up.
 
Last edited:

Sparky83

Virginia Chapter member
5,564
217
Norlina NC
i use to have a 92 lesabre (pretty much the same vehicle different name).. thing was nothing but an electrical nightmare...

i almost wonder if your problem isnt a short pushrod causing the tick.. or maybe a bad hydraulic lifter.. buick liked them finicky things..
 

polarbear

just growing older not up
12,878
607
Boring, Oregon
I haven't had troubles with the rocker bolts coming loose, and I had tightened them literally an hour before... Also I am told the 3400 has cam breaking issues as well.

Another little tidbit, it seems to run slightly better when I have the plug wire disconnected... and the exhaust sound is a little "puffy", kind of like when the valve was bent.

You sure that's a 3400? Thought Century's had 3100's. Worst case scenerio- motor should be dirt cheap in a wrecking yard.
 

Fellro

Moderator
Staff member
Yes, all 98 Centurys have the 3100. The 3400 will plug into the same hole with minor harness adjustments... that was in response to Lorddurock.

Sparky, the Lesabre would have a 3800 typically. The 3100 does have varying length pushrods, and I was very careful about keeping them in order. I made that mistake once... only once. That was on the first version of the 3100, the 3.1, which replaced the 2.8. The 3100 has an inherent intake gasket problem, so I have gotten very skilled at swapping them. Much of the time that someone thinks a head gasket is the source of the coolant in the oil, it is actually only the intake gasket.
 

Sparky83

Virginia Chapter member
5,564
217
Norlina NC
for the year i had they were either the 3800 or the 2800... but mine was the 3800...

did the 3100 still run the hydraulic lifter too?? im just trying to give ideas as to the ticking your hearing in the exhaust with the rough idle and the code...
 

CowboyBilly9Mile

Charter Member
7,118
442
USA
Any updates? I'm curious to hear what becomes of this. :)
 

Fellro

Moderator
Staff member
I don't get a lot of time during the week, so weekends only.

The 3100 does have hydraulic lifters, but the sound isn't metallic like slack. Getting ready for the leak down test, see what that shows me. Be bummed if both pull off heads were no good... The heads are ok, just need valve jobs if that is the case. The old heads were so far gone there would be way too much material taken off.
 

CowboyBilly9Mile

Charter Member
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442
USA
The old heads were so far gone there would be way too much material taken off.

What did the head surfaces on the block look like?
 

Fellro

Moderator
Staff member
Block was fine, cast iron. Heads, aluminum, and only held by a total of 8 stretch torque bolts. Not too hard to warp them.

So did the leak test, and it seems a bit past the rings, which static isn't a huge surprise, but nothing else really. I did swap the injector just to verify, and no change. There apparently is something up with the head somehow. Might as well pull it. I can have a low miles used head for $65 shipped. I want to pull it off before ordering though. Seems the parts motor had way more issues than I realized. But, when DOA, hard to know for sure.
 

Fellro

Moderator
Staff member
So I went ahead and pulled the head off again. The #4 cylinder is quite clean, and oily...
Since I had seen something kind of like this before, I though maybe I should check warpage on the intake... Seems a little bit, but perhaps gets worse with warming? I would have thought it would seal but perhaps she got the darn thing so hot that the intake also got hot and warped? They don't have it held down well at all...
 

CowboyBilly9Mile

Charter Member
7,118
442
USA
I've heard of intakes warping (SBC long ago, and aftermarket ones) but not on that engine.
 
So I went ahead and pulled the head off again. The #4 cylinder is quite clean, and oily...
Since I had seen something kind of like this before, I though maybe I should check warpage on the intake... Seems a little bit, but perhaps gets worse with warming? I would have thought it would seal but perhaps she got the darn thing so hot that the intake also got hot and warped? They don't have it held down well at all...

Can you have it shaved or re-surfaced?...:scratch:
 

Fellro

Moderator
Staff member
I have spares...
 

dustybumpers

don't play well w others
You have to torque the intake in with the heads
1's step heds, then intake
2nd torque heads, then intake,
3rd torke heads then intake

If you don't it will leak SOMEWHERE
been there done that
 

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