93 lt1 ignition knock on start
Thread Starter
3rd Gear
Joined: May 2005
Posts: 3
Likes: 0
93 lt1 ignition knock on start
hi fellow c4 owners.finally got one! being a bmw tech i'm still learning aboutmy c4.ok,it's a 93 c4 6 speed.70,000 miles.new optispark,plugs,wires,water pump,all filters.all oe parts, running 94 octane sunoco.no codes. most of the time it knocks as soon as it fires up for a split second,like the timing is way advanced.otherwise is perfect.any thoughts would be appreciated.thanks,andy
Le Mans Master
Joined: Feb 2002
Posts: 7,858
Likes: 2
Hmm... some piston slap is not uncommon for LT1's to exhibit on cold start, usually in winter weather though, and this doesn't sound like what you describe anyhow. The timing is not adjustable on the LT1's, it is fixed at the opti and all advance and retard is handled by the PCM.
Intermediate
Joined: Apr 2005
Posts: 31
Likes: 0
From: Ormond Beach (North of Daytona Beach) Florida
Originally Posted by ascauto
hi fellow c4 owners.finally got one! being a bmw tech i'm still learning aboutmy c4.ok,it's a 93 c4 6 speed.70,000 miles.new optispark,plugs,wires,water pump,all filters.all oe parts, running 94 octane sunoco.no codes. most of the time it knocks as soon as it fires up for a split second,like the timing is way advanced.otherwise is perfect.any thoughts would be appreciated.thanks,andy
I have the same problem. I cant diagnose it either.
Melting Slicks
Joined: Apr 1999
Posts: 2,521
Likes: 4
From: Windham, NH
Originally Posted by MaxLean
It's totally normal. The ECM induces knock on startup to verify the knock sensor is reporting something. Almost all GM cars do this as well as most other manufactures. Nothing to worry about. 
Both of my 93s do the same thing.
Safety Car
Joined: Dec 2002
Posts: 3,655
Likes: 24
From: Charleston SC
Originally Posted by MaxLean
It's totally normal. The ECM induces knock on startup to verify the knock sensor is reporting something. Almost all GM cars do this as well as most other manufactures. Nothing to worry about.
Yep its normal
Le Mans Master
Joined: Feb 2002
Posts: 7,858
Likes: 2
Originally Posted by MaxLean
It's totally normal. The ECM induces knock on startup to verify the knock sensor is reporting something. Almost all GM cars do this as well as most other manufactures. Nothing to worry about.
AH HA! That explains the flurry of knock counts that show up in a Datamaster log if you're logging when you crank the engine over and start it up. I usually see knock counts go from zero to a couple thousand or more if I start it up with Datamaster actively logging a recording. I thought it was all from the extra noise of crank up, but apparently some of it is not.
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