Pinging Problems since head recon
Thread Starter
Burning Brakes
Joined: Dec 2002
Posts: 1,199
Likes: 4
From: Cairns Australia
Pinging Problems since head recon
I've had my 88 nearly 3 years. I always run it on the higher octane fuel.
I recently had the heads reconditioned, and the injectors cleaned and tested.
Since then I am getting serious pinging under load, once the engine temps are higher than 205F. The pinging is still there at lower temps but not as loud and the engine needs to be under more load, like going up hill.
When I first noticed the pinging I suspected a bad tank of fuel. I drained the tank and replaced the fuel with another brand but still have the pinging. It got so bad yesterday that I was having to shift the auto down a gear to avoid pinging.
I have checked the timing - 6 degrees BTDC.
There are no codes showing. Car runs fine although starts up and runs fast - 10,000 - 12000 RPM for 20-30 seconds - that's a bit more than it used to do. I have checked base idle and TPS voltage is 5.4v.
Are there any experts here who can give me some ideas what could be wrong? -
is this a typical scenario?
is the spark module or ECM failing ?
Is this related to the head recon or injector clean?
S'nut
I recently had the heads reconditioned, and the injectors cleaned and tested.
Since then I am getting serious pinging under load, once the engine temps are higher than 205F. The pinging is still there at lower temps but not as loud and the engine needs to be under more load, like going up hill.
When I first noticed the pinging I suspected a bad tank of fuel. I drained the tank and replaced the fuel with another brand but still have the pinging. It got so bad yesterday that I was having to shift the auto down a gear to avoid pinging.
I have checked the timing - 6 degrees BTDC.
There are no codes showing. Car runs fine although starts up and runs fast - 10,000 - 12000 RPM for 20-30 seconds - that's a bit more than it used to do. I have checked base idle and TPS voltage is 5.4v.
Are there any experts here who can give me some ideas what could be wrong? -
is this a typical scenario?
is the spark module or ECM failing ?
Is this related to the head recon or injector clean?
S'nut
Racer
Joined: Nov 2005
Posts: 456
Likes: 3
From: Sumner Texas
First of all do you know if the machine shop milled any surface from the heads to straighten them? If it was very much then this is aggravating your problem.
Secondly you need to check the knock sensor by connecting test light to the connected sensor and watch the test light will striking the exhaust manifold with a hammer. I can't remember if the light will flash on when the knock sensor senses knock or flash off. Regardless the test light should flash when the manifold is struck. If it does not, check the connector and trace it back, or at least use an ohmmeter to satisfy yourself that it is connected back up the line. If it is, then the knock sensor is bad and should be replaced. If the knock sensor works properly then the computer is not retarding timing for some reason. You will need to check the distributor connections.
Best of luck,
Secondly you need to check the knock sensor by connecting test light to the connected sensor and watch the test light will striking the exhaust manifold with a hammer. I can't remember if the light will flash on when the knock sensor senses knock or flash off. Regardless the test light should flash when the manifold is struck. If it does not, check the connector and trace it back, or at least use an ohmmeter to satisfy yourself that it is connected back up the line. If it is, then the knock sensor is bad and should be replaced. If the knock sensor works properly then the computer is not retarding timing for some reason. You will need to check the distributor connections.
Best of luck,
Thread Starter
Burning Brakes
Joined: Dec 2002
Posts: 1,199
Likes: 4
From: Cairns Australia
Hi MBDiagMan, I've jacked the car up and have a wire on the sensor and one on the frame - connected to a DMM. I've verified both are good contacts .
There is continuity between the wire 'E' on the ESC and the sensor.
With the ESC disconnected and the DMM set on 20k Ohms, there is up to .05 showing with a hard knock on the sensor body.
With all leads connected and ignition on - No volts showing.
No signs of movement on the DMM (set at 20volts) when banging exhaust hard. Put a tyre lever on the sensor base and hit it with a hammer - no movement.
Connected 12v globe to leads and no light showing during banging or not banging.
If the sensor is supposed to recieve enough volts to light a globe , then it's not recieving any electricity? But there is continuity.
Does that mean the ESC is faulty?
When I checked the timing last week, I revved the engine to 1500rpm in nuetral, the timing moved a lot - I'd guess 20-40degrees BTDC this proves the timing is being advanced but thats doen by the ECM (I think).
S'nut
There is continuity between the wire 'E' on the ESC and the sensor.
With the ESC disconnected and the DMM set on 20k Ohms, there is up to .05 showing with a hard knock on the sensor body.
With all leads connected and ignition on - No volts showing.
No signs of movement on the DMM (set at 20volts) when banging exhaust hard. Put a tyre lever on the sensor base and hit it with a hammer - no movement.
Connected 12v globe to leads and no light showing during banging or not banging.
If the sensor is supposed to recieve enough volts to light a globe , then it's not recieving any electricity? But there is continuity.
Does that mean the ESC is faulty?
When I checked the timing last week, I revved the engine to 1500rpm in nuetral, the timing moved a lot - I'd guess 20-40degrees BTDC this proves the timing is being advanced but thats doen by the ECM (I think).
S'nut
Racer
Joined: Nov 2005
Posts: 456
Likes: 3
From: Sumner Texas
S'nut,
Have you checked to see if there are any codes set? If the ESC module is bad or has bad connection to the ECM I believe you will get a 43.
Meanwhile I will try to remember to bring my factory manual in from the shop so we can get deeper.
Good luck,
Have you checked to see if there are any codes set? If the ESC module is bad or has bad connection to the ECM I believe you will get a 43.
Meanwhile I will try to remember to bring my factory manual in from the shop so we can get deeper.
Good luck,
Team Owner
Joined: Jan 2003
Posts: 20,316
Likes: 246
From: Summerland B.C. Canada
Cruising
Joined: Nov 2005
Posts: 14
Likes: 0
Knock sensor or lean mixture. I would be proned to think mixture since that is the area that you were working.( injectors.)
Knock sensor would malfunction no matter the engine temp I think. Lean mixture problems would be more temperature specific. Hotter cylinder temps and lean mixture equal pinging under load.
Knock sensor would malfunction no matter the engine temp I think. Lean mixture problems would be more temperature specific. Hotter cylinder temps and lean mixture equal pinging under load.
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Thread Starter
Burning Brakes
Joined: Dec 2002
Posts: 1,199
Likes: 4
From: Cairns Australia
Thanks everyone, especially AGENT 86 for the PDF files - I have the GM Manual for my 88, and spent a while yesterday looking for those pages -but somehow yours explain things clearer than anything I found.
No Codes are being set.
Thanks to Ben73 I now have a test procedure for the ESC using an LED
There's vid of it being done here - http://jobyteknik.homeip.net/corvett...r/MOV08144.MPG
But he also says that the engine SHOULD NOT knock - which makes sense to me, the knock sensor should be saving the occasional knock, not the constant knock that I'm getting.
He suggests that maybe the timing marks are out and that I should reduce the timing by 2 degree increments until the knock is removed.
I've discovered there's a possibility that when I changed the bad fuel, I got exactly the same fuel from a different company -so I will change the fuel again next week and use the highest quality I can find.
If it's a lean fuel situation, could having the injectors cleaned have any bearing on this?
Thanks again for everyone's input.
S'nut
No Codes are being set.
Thanks to Ben73 I now have a test procedure for the ESC using an LED
get an LED, the clear 'superbright' type is best, and put a 560-1000 ohm resistor in series with it. At the esc module, connect the longest leg of the LED (+) to the pink/black wire (+12v) and the short one to the black wire (knock signal to ecm).. doesn't matter which side the resistor is on.. turn on the key, turn off the garage lights and tap lightly on the exhaust manifold..
note that the test works on the output (ECM) side of the ESC, not the input (knock sensor/dk blue wire) side as you tried before
note that the test works on the output (ECM) side of the ESC, not the input (knock sensor/dk blue wire) side as you tried before
But he also says that the engine SHOULD NOT knock - which makes sense to me, the knock sensor should be saving the occasional knock, not the constant knock that I'm getting.
He suggests that maybe the timing marks are out and that I should reduce the timing by 2 degree increments until the knock is removed.
I've discovered there's a possibility that when I changed the bad fuel, I got exactly the same fuel from a different company -so I will change the fuel again next week and use the highest quality I can find.
If it's a lean fuel situation, could having the injectors cleaned have any bearing on this?
Thanks again for everyone's input.
S'nut
Burning Brakes
Joined: Jul 2003
Posts: 922
Likes: 1
From: Brisbane Queensland, Australia
Originally Posted by CorvAdel
Sorry for jumpin' in here, but I'm curious..what relationship does manifold air temperature have to ignition timing...?
I was under the impression that the MAT sensor controlled EGR functions...?
I was under the impression that the MAT sensor controlled EGR functions...?