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GrandPrixMaster

1993 Grand Prix cold engine tapping sound

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As the title suggests, the 3.1l LH0 v6 "vin T" in my car makes a noise that sounds like a knock (tap tap tap tap tap) on a cold startup. It sounds like it's coming from the middle of the engine. If I rev it past 2k rpm or so, the noise is no longer audible. I've also noticed that if I get rambunctious with it and floor it when cold (as much as I hate doing that), the noise disappears quickly, suggesting to me that maybe it's a lifter that is not properly pumping up. 

It's also worth mentioning that the engine is super quiet after warming up besides a little rocker arm noise. The rapping "tap tap tap" goes away after the temp gauge raises up above it's lowest reading. 

 

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I’m going to assume that it’s just your lifters sticking a little bit until the oil gets all the way through them. The LQ1 engines are pretty bad for that, I’ve never had one that didn’t sound like that that start up.

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Might be lifter noise.  Might be rocker arm noise.  Both have a history on the 3.1 engines.

Potentially piston slap.   As soon as the pistons expand a little, they quit knocking.  (at least to start.  As time goes by, they may knock even when warm.)

GM has had problems with piston slap for years if not decades.  The "Lifter tick" on my 1992 and 1993 3.4L Luminas is actually piston slap--because the official "fix" for the lifter problems did nothing at all for the knocking noise, and there are no rocker arms.

A web search on "Piston Slap" will yield lots of different web sites.  My favorite has disappeared--I guess they quit paying the web hosting.  It used to be www.pistonslap.com

GM knows all about it.  They've been sued over it.  They cannot acknowledge the existence of piston slap without getting sued again, so they'll deny, deny, deny.  Lying bastages.  For awhile, they promised customers a "fix" that they never implemented because they'd have had to recall everything they ever made.  GM claims the noise is harmless.  It more-or-less is, except that it can trigger the knock sensor, and then your timing is retarded and the fuel economy and power tanks.  If it's only knocking when cold, that doesn't matter.  My Luminas knock all the time.  I've lost about 3 mpg.

 

For the record, the engine I built for my '68 El Camino has very mild piston slap--a known problem with KB Hypereutectic pistons.  Fifteen seconds of run time and the noise--which was never all that loud--is gone.  By contrast, my Luminas knock so loud I don't need a horn, and they knock pretty much all-the-time at idle where they used to knock only when cold.

Edited by Schurkey

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4 hours ago, Schurkey said:

Might be lifter noise.  Might be rocker arm noise.  Both have a history on the 3.1 engines.

Potentially piston slap.   As soon as the pistons expand a little, they quit knocking.  (at least to start.  As time goes by, they may knock even when warm.)

GM has had problems with piston slap for years if not decades.  The "Lifter tick" on my 1992 and 1993 3.4L Luminas is actually piston slap--because the official "fix" for the lifter problems did nothing at all for the knocking noise, and there are no rocker arms.

A web search on "Piston Slap" will yield lots of different web sites.  My favorite has disappeared--I guess they quit paying the web hosting.  It used to be www.pistonslap.com

GM knows all about it.  They've been sued over it.  They cannot acknowledge the existence of piston slap without getting sued again, so they'll deny, deny, deny.  Lying bastages.  For awhile, they promised customers a "fix" that they never implemented because they'd have had to recall everything they ever made.  GM claims the noise is harmless.  It more-or-less is, except that it can trigger the knock sensor, and then your timing is retarded and the fuel economy and power tanks.  If it's only knocking when cold, that doesn't matter.  My Luminas knock all the time.  I've lost about 3 mpg.

 

For the record, the engine I built for my '68 El Camino has very mild piston slap--a known problem with KB Hypereutectic pistons.  Fifteen seconds of run time and the noise--which was never all that loud--is gone.  By contrast, my Luminas knock so loud I don't need a horn, and they knock pretty much all-the-time at idle where they used to knock only when cold.

I have an official GM letter about this issue for my parts car, an 89 CS International coupe with the 3.1.  I bought it from the original owner and he kept every record and receipt for it.  I'll try to find it.  In the meantime, concerning the issue with the LQ1's, what years apply?  I have a 91 and a 93 LQ1 car.

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1 hour ago, jiggity76 said:

 concerning the issue with the LQ1's, what years apply?  I have a 91 and a 93 LQ1 car.

I have no info about piston slap on LQ1.  There may be a bulletin--but I don't have it and I've never seen one.  When I went to the stealership to bitch about the knocking noise, they wanted me to pay for the "Lifter tick" bulletin procedure since my vehicle was out-of-warranty at the time.

 

The info I do have is for early-95 and prior LQ1 "lifter tick".  The web site that hosted the actual bulletin has been gone for years.

http://www.60degreev6.com/vb5/articles/-1991-1997-dohc-aa/424720-lq1-service-bulletin-57-61-09-lifter-tick-cold

Edited by Schurkey

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17 hours ago, Schurkey said:

Might be lifter noise.  Might be rocker arm noise.  Both have a history on the 3.1 engines.

Potentially piston slap.   As soon as the pistons expand a little, they quit knocking.  (at least to start.  As time goes by, they may knock even when warm.)

GM has had problems with piston slap for years if not decades.  The "Lifter tick" on my 1992 and 1993 3.4L Luminas is actually piston slap--because the official "fix" for the lifter problems did nothing at all for the knocking noise, and there are no rocker arms.

A web search on "Piston Slap" will yield lots of different web sites.  My favorite has disappeared--I guess they quit paying the web hosting.  It used to be www.pistonslap.com

GM knows all about it.  They've been sued over it.  They cannot acknowledge the existence of piston slap without getting sued again, so they'll deny, deny, deny.  Lying bastages.  For awhile, they promised customers a "fix" that they never implemented because they'd have had to recall everything they ever made.  GM claims the noise is harmless.  It more-or-less is, except that it can trigger the knock sensor, and then your timing is retarded and the fuel economy and power tanks.  If it's only knocking when cold, that doesn't matter.  My Luminas knock all the time.  I've lost about 3 mpg.

 

For the record, the engine I built for my '68 El Camino has very mild piston slap--a known problem with KB Hypereutectic pistons.  Fifteen seconds of run time and the noise--which was never all that loud--is gone.  By contrast, my Luminas knock so loud I don't need a horn, and they knock pretty much all-the-time at idle where they used to knock only when cold.

So piston slap is a known issue with the LH0 3.1 mpfi as well? I can't say I'm particularly surprised. I know the 3100 SFI's are known to have the issue, along with it's cousin the 3400. Honestly I'm not too worried about the noise, as it's completely gone after driving the car for a while to let everything get up to temperature. Driving hard also alleviates the sound quickly. The sudden increase in oil pressure incurred by the engine upon flooring it and allowing it to rev to 5500 must either forcefully pump up my lifters or the temperature increase allows the pistons to expand and fully fill the bore. It wouldn't surprise me even slightly if I have a lifter that is sludgy. Either one sounds plausible.

 

It also doesn't help that my thermostat seems to now be stuck open. The temp gauge is able to move itself off its peg fairly quickly, but the temp will not manage to make its way higher than a quarter of the way up while driving, unless I'm cruising at around ~60mph (2k rpm) for a long period of time, in which case it'll traverse to about one mark above a quarter of the way up and stay there. The engine will also maintain operating temperature (195-200) if I allow it to idle long enough, and at that point the engine is as quiet as a Cadillac. Anyways, I digress. Because of this, the engine sometimes gets itself stuck in this "in between" state where the tapping is greatly reduced, but still very sightly audible. This only happens if I drive at low speeds and use the throttle very judiciously.

 

So yeah. The sound is definitely one that only occurs when the engine is cold, and seems to be related to the oil pressure conditions to a point as well.

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14 hours ago, jiggity76 said:

I have an official GM letter about this issue for my parts car, an 89 CS International coupe with the 3.1.  I bought it from the original owner and he kept every record and receipt for it.  I'll try to find it.  In the meantime, concerning the issue with the LQ1's, what years apply?  I have a 91 and a 93 LQ1 car.

No piston slap issues with the DOHC's,  the skirt area of the slugs is fuller bodied than the pushrod slugs, so no slap is encountered, the only other issue that was never TSB published is the timing chain tensioner, in early engines it was known to cause issues by partially failing allowing the timing chain to slap against the inside of the cover when the throttle is in the overrun position (one is off the throttle, the tension alters from the frontside to the backside).   

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