Buick T-Type ignition timing BTDC Issues

[Black Six]

1987 Buick Regal T-Type
3.8L Turbo
New engine and transmission


Symptoms

After the rebuild, drove the car for 3-4 hrs then started to run like crap. Hesitant then a pre-detonation knocking coming from the exhaust headers when warm.

​

Figuring it was ignition cause it was running BTDC (Was like an inch off the scale), I replaced the crank position sensor and knock sensor. Reset the cam position sensor as well. Its not so retard now but still on the edge of the scale. Still knocking lightly when warm. Runs and drives. No engine light.

History

I bought this car from a friend after sitting for 8 yrs. He pulled it apart cause the trans blew. The engine ran fine. It was in bags and boxes when I got it. He had all the machine work done to the block (Honed and washed) and rebuilt heads.

Rebuild

I rebuilt the entire engine stock and new trans. New water pump, alternator, cam, lifters, head work, rings, wrist pins, crank polished, gaskets, all bearings, cam tensioner, timing set, oil pump, seals, cleaned everything out, etc.

What to do?

Keep in mind this car was running and rolling for 3-4 hrs before this problem occurred. Still running retard (BTDC on edge of scale). I am thinking ignition module? Coil packs?

We are developing a love hate relationship. Any feedback would be greatly appreciated. If you are in the Maryland area, the beer of your choice is waiting for you if you can take a look!

 

[earlbrown]

Put a dial indicator on each of the pushrods and see if you have 12 cam lobes that are the same height.


Fresh rebuilds have an established track record of taking a dump.


as far as the ignition, a good running donor car to loan a coilpack/ign module is invaluable. Also, check the crank bolt to make sure the hub isn't dancing around.

 

[Black Six]

Put a dial indicator on each of the pushrods and see if you have 12 cam lobes that are the same height.


Fresh rebuilds have an established track record of taking a dump.


as far as the ignition, a good running donor car to loan a coilpack/ign module is invaluable. Also, check the crank bolt to make sure the hub isn't dancing around.

earlbrown,

Thanks for the reply. I just checked the crank bolt and its tight. I also checked the pulley.

I bypassed the turbo (Just ran airbox hose to throttle) and it ran like crap but no knock. Its reading ~25 BTDC.

Pushrods.... like if they were bent?

 

[earlbrown]

No, like the cam lobes are flat on the new build. It pretty common for flat cams on fresh builds if all the voodoo and sacrifices aren't made.

Are you reading 25* BTDC at idle and that's what you're concerned about?

 

[Black Six]

Wouldnt you see chips in the pan and filter? I changed the oil and cut open the filter. Looked clean.

What would cause the retard timing? You are saying its the valve train?

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[earlbrown]

When a cam is going flat it's the very small debris that works as liquid sandpaper. You don't really see chips until after things go from bad to catastrophic.

25 BTDC is 'before' top dead center. What ign point are you looking for?

 

[captndave737]

I have a dumb question.. How does a cam going flat affect ignition timing?

 

[earlbrown]

it doesn't. But I can't get a straight answers from the OP so I really have no idea what's going on.

 

[captndave737]

Thanks,

I didn't think it did, I've been working on engines for 48 years (hobby) but I learn tons on this site. I bought my car new, have the service manual and only recently found out how to check the timing on these with a timing light. LOL I've always just set the cam sensor by the book.

 

[Heisenberg]

it doesn't. But I can't get a straight answers from the OP so I really have no idea what's going on.

LOL
It's ok Earl.
In another month, I'll be starting up my new motor, and I'll have plenty of issues, and maybe even a straight answer or two for you!

 

[Black Six]

I believe its supposed to be self setting at 14 BTDC.

The severe BTDC is concerning to me. Why would it do this?

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[earlbrown]

So you were calling it retarded but you're actually worried about how advanced it is.

What chip do you have?

 

[Black Six]

Its to the left of the 0 mark. It would make it around 20 deg or so.

Sorry for all the questions, I know little about this car....

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[Black Six]

Stock chip as far as I know....

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[earlbrown]

That stock chip needs to be tossed. It's far too outdated for todays fuels and usage.

 

[Black Six]

So you contribute the knock noise and 20 deg advanced timing to a chip (pending and valve train measurement) ?

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[87-WE2]

You betcha! Spark timing is controlled by the chip. If you have stock chip, it's generally the consensus that the timing settings within are far too advanced for today's pump fuels (even 93 octane). BTDC means your timing is advanced (spark happens prior to top dead center); ATDC means your timing is retarded (spark happens after top dead center).


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[Eric Stage I]

25-28 degrees at idle is normal for timing.

 

[Black Six]

Would u agree about the chip?

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