Severe LT1 spark knock
Thread Starter
Safety Car
Joined: Jul 2001
Posts: 4,871
Likes: 15
From: Detroit's West Side MI
Severe LT1 spark knock
After rebuilding the top end I have some serious spark knock on my 93 LT1. I was on a few other threads so decided to move to my own instead of hijacking other people's...
I ordered a data cable to get some downloads to send to Alvin, but until it comes I'd like to consider every other option and see what makes sense.
Symptoms:
Severe spark knock above ~3000 rpm (more noticeable under load)
Possible causes:
Bad knock sensor (possibly damaged when removing from old block)
False knock from new headers or RR
ECM changing timing due to removal of AIR and EGR
Fuel pressure drop at higher RPM
Wrong temp spark plugs with EGR removed
What was done to the motor:
1993 LT1 6 speed (track only car)
Bottom end replaced with late model B-body shortblock
Heads from PP (285 cfm flow)
Aggressive cam (236*, 0.574/0.571 lift, 112 LSA)
1.6 RR, stiffer valve springs, titanium retainers
EM Headers
30# FMS injectors
New PROM from Alvin to tune for changes listed above
So...suggestions for other causes?
I ordered a data cable to get some downloads to send to Alvin, but until it comes I'd like to consider every other option and see what makes sense.
Symptoms:
Severe spark knock above ~3000 rpm (more noticeable under load)
Possible causes:
Bad knock sensor (possibly damaged when removing from old block)
False knock from new headers or RR
ECM changing timing due to removal of AIR and EGR
Fuel pressure drop at higher RPM
Wrong temp spark plugs with EGR removed
What was done to the motor:
1993 LT1 6 speed (track only car)
Bottom end replaced with late model B-body shortblock
Heads from PP (285 cfm flow)
Aggressive cam (236*, 0.574/0.571 lift, 112 LSA)
1.6 RR, stiffer valve springs, titanium retainers
EM Headers
30# FMS injectors
New PROM from Alvin to tune for changes listed above
So...suggestions for other causes?
Melting Slicks
Joined: May 2002
Posts: 2,670
Likes: 4
From: Severna Park MD
Originally Posted by ScaryFast
After rebuilding the top end I have some serious spark knock on my 93 LT1. I was on a few other threads so decided to move to my own instead of hijacking other people's...
I ordered a data cable to get some downloads to send to Alvin, but until it comes I'd like to consider every other option and see what makes sense.
Symptoms:
Severe spark knock above ~3000 rpm (more noticeable under load)
Possible causes:
Bad knock sensor (possibly damaged when removing from old block)
False knock from new headers or RR
ECM changing timing due to removal of AIR and EGR
Fuel pressure drop at higher RPM
Wrong temp spark plugs with EGR removed
What was done to the motor:
1993 LT1 6 speed (track only car)
Bottom end replaced with late model B-body shortblock
Heads from PP (285 cfm flow)
Aggressive cam (236*, 0.574/0.571 lift, 112 LSA)
1.6 RR, stiffer valve springs, titanium retainers
EM Headers
30# FMS injectors
New PROM from Alvin to tune for changes listed above
So...suggestions for other causes?
I ordered a data cable to get some downloads to send to Alvin, but until it comes I'd like to consider every other option and see what makes sense.
Symptoms:
Severe spark knock above ~3000 rpm (more noticeable under load)
Possible causes:
Bad knock sensor (possibly damaged when removing from old block)
False knock from new headers or RR
ECM changing timing due to removal of AIR and EGR
Fuel pressure drop at higher RPM
Wrong temp spark plugs with EGR removed
What was done to the motor:
1993 LT1 6 speed (track only car)
Bottom end replaced with late model B-body shortblock
Heads from PP (285 cfm flow)
Aggressive cam (236*, 0.574/0.571 lift, 112 LSA)
1.6 RR, stiffer valve springs, titanium retainers
EM Headers
30# FMS injectors
New PROM from Alvin to tune for changes listed above
So...suggestions for other causes?
Race Director
Joined: May 2001
Posts: 14,165
Likes: 9
Are you getting any audible knock or is it just showing up as timing retard on a scan?
Obviously if it's audible you can rule out the bad knock sensor and false knock.
Removal of AIR and EGR shouldn't hurt anything so long as the ECM has been told about it.
EGR can be used to control detonation but it would typically be at cruise, EGR should never function at WOT.
Fuel pressure could be a problem, suggest you temporarily tape a gauge to the windshield and go for a short spin and watch it.
Spark plugs, just pull one and see what it looks like. Most of us who are modded are still running the stock heat range plug unless we're working with nitrous or forced induction.
Obviously if it's audible you can rule out the bad knock sensor and false knock.
Removal of AIR and EGR shouldn't hurt anything so long as the ECM has been told about it.
EGR can be used to control detonation but it would typically be at cruise, EGR should never function at WOT.
Fuel pressure could be a problem, suggest you temporarily tape a gauge to the windshield and go for a short spin and watch it.
Spark plugs, just pull one and see what it looks like. Most of us who are modded are still running the stock heat range plug unless we're working with nitrous or forced induction.
Thread Starter
Safety Car
Joined: Jul 2001
Posts: 4,871
Likes: 15
From: Detroit's West Side MI
Originally Posted by Nathan Plemons
Are you getting any audible knock or is it just showing up as timing retard on a scan?
Obviously if it's audible you can rule out the bad knock sensor and false knock.
Removal of AIR and EGR shouldn't hurt anything so long as the ECM has been told about it.
EGR can be used to control detonation but it would typically be at cruise, EGR should never function at WOT.
Fuel pressure could be a problem, suggest you temporarily tape a gauge to the windshield and go for a short spin and watch it.
Spark plugs, just pull one and see what it looks like. Most of us who are modded are still running the stock heat range plug unless we're working with nitrous or forced induction.
Obviously if it's audible you can rule out the bad knock sensor and false knock.
Removal of AIR and EGR shouldn't hurt anything so long as the ECM has been told about it.
EGR can be used to control detonation but it would typically be at cruise, EGR should never function at WOT.
Fuel pressure could be a problem, suggest you temporarily tape a gauge to the windshield and go for a short spin and watch it.
Spark plugs, just pull one and see what it looks like. Most of us who are modded are still running the stock heat range plug unless we're working with nitrous or forced induction.
No power adders or NO2, so standard plugs should be fine?
What about EGR giving the O2 sensors false reads?
Thread Starter
Safety Car
Joined: Jul 2001
Posts: 4,871
Likes: 15
From: Detroit's West Side MI
Oh, one more thing. Could hose routing from EGR / air removal cause an issue? I left most hoses in place except the obvious ones that went to the pump and headers.
Slalom - I'll have to get a compression tester and check.
Slalom - I'll have to get a compression tester and check.
Le Mans Master
Joined: Jan 2002
Posts: 9,036
Likes: 13
From: Edmonton AB
Actually, I wondered about the compression ratio, not
the results of a compression test.
With the blending of parts on the new build and now a
knock, I was curious whether the root cause might be
more C/R than the fuel will support.
Another thought - until your cable arrives, what about
using JoBy's Tech Tip and building yourself a knock-light.
IIUC, his light should display when/if the knock sensor
signals to the ECM. If you don't see the light flashing,
wouldn't this point a finger at the sensor?
(Of course, it might be simpler to hook up with someone
nearby who already has a scanner or the cable/software)
.
the results of a compression test.
With the blending of parts on the new build and now a
knock, I was curious whether the root cause might be
more C/R than the fuel will support.
Another thought - until your cable arrives, what about
using JoBy's Tech Tip and building yourself a knock-light.
IIUC, his light should display when/if the knock sensor
signals to the ECM. If you don't see the light flashing,
wouldn't this point a finger at the sensor?
(Of course, it might be simpler to hook up with someone
nearby who already has a scanner or the cable/software)
.
Race Director
Joined: May 2001
Posts: 14,165
Likes: 9
If there's audible knock you would hope to hell that the sensor would pick up on it. If the sensor isn't picking up on it that is certainly a problem that needs to be resolved, but there's still a problem. Say the sensor picks up on it and retards the timing, you're still losing performance. Ideally the sensor is just there as a safety feature, not to make it run.
I would have to say that if it's audible knock you can pretty much rule out the sensors as the problem. They may not be working, but it shouldn't be knocking in the first place.
I would have to say that if it's audible knock you can pretty much rule out the sensors as the problem. They may not be working, but it shouldn't be knocking in the first place.
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Drifting
Joined: May 2003
Posts: 1,730
Likes: 1
From: Charlotte NC
St. Jude Donor '05
Originally Posted by Nathan Plemons
If there's audible knock you would hope to hell that the sensor would pick up on it. If the sensor isn't picking up on it that is certainly a problem that needs to be resolved, but there's still a problem. Say the sensor picks up on it and retards the timing, you're still losing performance. Ideally the sensor is just there as a safety feature, not to make it run.
I would have to say that if it's audible knock you can pretty much rule out the sensors as the problem. They may not be working, but it shouldn't be knocking in the first place.
I would have to say that if it's audible knock you can pretty much rule out the sensors as the problem. They may not be working, but it shouldn't be knocking in the first place.
Thats what I told him on the phoen yesterday. When he called me I was more worred about him audibly knocking than anything else.. THe Lt1 system is pretty on top of things to where it will never get to the point where you hear it.
I'm thinking that he may be loosing fuel pressure as that will set the car off into pinging.
The timing table I used for him is definately not aggressive by any means and even without knock sensor it should never get anyhwere near close to knocking.
I tell you it would really help if he had a SES light or means of gettnig a datalog.. hes taken his dash completely out to make a race car.
Safety Car
Joined: Sep 2002
Posts: 4,030
Likes: 6
From: Maryland
Originally Posted by ScaryFast
After rebuilding the top end I have some serious spark knock on my 93 LT1. I was on a few other threads so decided to move to my own instead of hijacking other people's...
I ordered a data cable to get some downloads to send to Alvin, but until it comes I'd like to consider every other option and see what makes sense.
Symptoms:
Severe spark knock above ~3000 rpm (more noticeable under load)
Possible causes:
Bad knock sensor (possibly damaged when removing from old block)
False knock from new headers or RR
ECM changing timing due to removal of AIR and EGR
Fuel pressure drop at higher RPM
Wrong temp spark plugs with EGR removed
What was done to the motor:
1993 LT1 6 speed (track only car)
Bottom end replaced with late model B-body shortblock
Heads from PP (285 cfm flow)
Aggressive cam (236*, 0.574/0.571 lift, 112 LSA)
1.6 RR, stiffer valve springs, titanium retainers
EM Headers
30# FMS injectors
New PROM from Alvin to tune for changes listed above
So...suggestions for other causes?
I ordered a data cable to get some downloads to send to Alvin, but until it comes I'd like to consider every other option and see what makes sense.
Symptoms:
Severe spark knock above ~3000 rpm (more noticeable under load)
Possible causes:
Bad knock sensor (possibly damaged when removing from old block)
False knock from new headers or RR
ECM changing timing due to removal of AIR and EGR
Fuel pressure drop at higher RPM
Wrong temp spark plugs with EGR removed
What was done to the motor:
1993 LT1 6 speed (track only car)
Bottom end replaced with late model B-body shortblock
Heads from PP (285 cfm flow)
Aggressive cam (236*, 0.574/0.571 lift, 112 LSA)
1.6 RR, stiffer valve springs, titanium retainers
EM Headers
30# FMS injectors
New PROM from Alvin to tune for changes listed above
So...suggestions for other causes?
Thread Starter
Safety Car
Joined: Jul 2001
Posts: 4,871
Likes: 15
From: Detroit's West Side MI
Originally Posted by Alvin
Thats what I told him on the phoen yesterday. When he called me I was more worred about him audibly knocking than anything else.. THe Lt1 system is pretty on top of things to where it will never get to the point where you hear it.
I'm thinking that he may be loosing fuel pressure as that will set the car off into pinging.
The timing table I used for him is definately not aggressive by any means and even without knock sensor it should never get anyhwere near close to knocking.
I tell you it would really help if he had a SES light or means of gettnig a datalog.. hes taken his dash completely out to make a race car.
I'm thinking that he may be loosing fuel pressure as that will set the car off into pinging.
The timing table I used for him is definately not aggressive by any means and even without knock sensor it should never get anyhwere near close to knocking.
I tell you it would really help if he had a SES light or means of gettnig a datalog.. hes taken his dash completely out to make a race car.
It will be a few days until I get the data logging cable, They're making one with clips instead of a cig lighter for power...
Thread Starter
Safety Car
Joined: Jul 2001
Posts: 4,871
Likes: 15
From: Detroit's West Side MI
Originally Posted by sothpaw2
Sorry to hear it. Is this on 93 octane at least? Was the block decked and are you sure it was a stock block? I have my stock pistons out so if you describe your reliefs I can maybe say if you are looking at stock pistons (of course you are not looking at them now but you did when you bought the block).
Block was bone stock, no machine work at all. I tore it down and the pistons / rods were the same as the ones in my original block.
I'd assume the compression has changed from stock, though.
Race Director
Joined: May 2001
Posts: 14,165
Likes: 9
I can't imagine the compression ratio being so high as to cause a problem though. If the bottom end is stock the only things that affect your compression are the head gaskets and the heads. Most port work shoots for approximately the same compression ratio as stock. Even if it was a little higher and you ran a thinner head gasket you should fall in the 11:1 range. With reverse flow cooling I've seen LT1's run 12.5:1 with no problem, the larger cam only helps in that regard.
Safety Car
Joined: Feb 1999
Posts: 3,504
Likes: 4
From: Mexico Beach FL
When my Opti-Spark carbon tracked, I had "gobs" of knock retard at about a 20% throttle opening after the engine was warmed up, but it wasn't consistent.
I triggered a data capture (snapshot) of the data with my Tech-1A when the problem happened.
I could see that, at a small throttle opening, I would get massive knock retard for a few seconds.
I guessed it was the Opti-Spark, and I was right.
The tracking inside the cap was firing the next cylinder in the firing sequence early -- 90 degrees early.
Tom Piper
I triggered a data capture (snapshot) of the data with my Tech-1A when the problem happened.
I could see that, at a small throttle opening, I would get massive knock retard for a few seconds.
I guessed it was the Opti-Spark, and I was right.
The tracking inside the cap was firing the next cylinder in the firing sequence early -- 90 degrees early.
Tom Piper
Thread Starter
Safety Car
Joined: Jul 2001
Posts: 4,871
Likes: 15
From: Detroit's West Side MI
Allright, here's another theory -
The current block (and therefore the crank) are from a newer car. My car is a '93. My timing set has the splined hole in the center of the crank timing gear for the optispark dowel pin, which is much shorter than the pin on the newer cars (which I think go all the way into the crank itself?)
I put an older style timing gear on the newer crankshaft and used my '93 dowel pin. So who can tell me this:
Is there a possibility that the timing could be slightly off and I need to purchase the longer style dowel pin and go directly from the optispark to the crank? This of course requires using a newer crank timing gear with the bigger hole...
It really sounds like a timing issue, upon startup it really struggles with the compression of a few cylinders, you know, fast turn over then slow.
The current block (and therefore the crank) are from a newer car. My car is a '93. My timing set has the splined hole in the center of the crank timing gear for the optispark dowel pin, which is much shorter than the pin on the newer cars (which I think go all the way into the crank itself?)
I put an older style timing gear on the newer crankshaft and used my '93 dowel pin. So who can tell me this:
Is there a possibility that the timing could be slightly off and I need to purchase the longer style dowel pin and go directly from the optispark to the crank? This of course requires using a newer crank timing gear with the bigger hole...
It really sounds like a timing issue, upon startup it really struggles with the compression of a few cylinders, you know, fast turn over then slow.
Thread Starter
Safety Car
Joined: Jul 2001
Posts: 4,871
Likes: 15
From: Detroit's West Side MI
Oh, and I wasn't able to mess with anything last night.
I'm hoping to get the data cable today and get a log to send to Alvin.
If it does turn out that my crank is a hair off my timing gear, can we adjust that in the PROM?
blur - the car won't run with the OEM PROM. Tried already.
I'm hoping to get the data cable today and get a log to send to Alvin.
If it does turn out that my crank is a hair off my timing gear, can we adjust that in the PROM?
blur - the car won't run with the OEM PROM. Tried already.
Race Director
Joined: May 2001
Posts: 14,165
Likes: 9
Even though there was a length diference in the dowel pins they are located in the same spot so that in itself would not cause the timing to be off. Now if you are using the '93 style timing chain you must also be driving a '93 style opti. It uses the little splined shaft to drive the distributor, which can be installed incorrectly if enough force is used. Furthermore if it was installed only one tooth off the car could actually still run as opposed to the newer style drive pin that is keyed in such a way that it would be so far off the car probably won't even start if installed correctly.
It is a possibility, but as with all things opti related I would certainly suggest covering all other possibilites first before you tear it apart to look at that.
It is a possibility, but as with all things opti related I would certainly suggest covering all other possibilites first before you tear it apart to look at that.
Drifting
Joined: May 2003
Posts: 1,730
Likes: 1
From: Charlotte NC
St. Jude Donor '05
Originally Posted by Nathan Plemons
Even though there was a length diference in the dowel pins they are located in the same spot so that in itself would not cause the timing to be off. Now if you are using the '93 style timing chain you must also be driving a '93 style opti. It uses the little splined shaft to drive the distributor, which can be installed incorrectly if enough force is used. Furthermore if it was installed only one tooth off the car could actually still run as opposed to the newer style drive pin that is keyed in such a way that it would be so far off the car probably won't even start if installed correctly.
It is a possibility, but as with all things opti related I would certainly suggest covering all other possibilites first before you tear it apart to look at that.
It is a possibility, but as with all things opti related I would certainly suggest covering all other possibilites first before you tear it apart to look at that.
I agree..
I really think it could be a fuel related issue. I recently had a car go low on fuel (gas tank) while on the dyno and it just started pinging . We where confused as it was going well up to that point.. A few minutes later I noticed the reserve tank was lit up.