Topic: Problems with DTC's
in Forum: C4 Electrical
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Orange Park, FL - USA
Joined: 12/4/2009
Posts: 56
Vette(s): 1996 LT4 Blk/Blk coupe all origional
I need to have help with diognostics. When I bought my '96 LT4 I bought the factory manuals and an Innova Scan Tool thinking that if I had a problem these tools would tell me what's wrong and where to go to fix it.
Last night the car quit running and based on past problems it felt like the timing had changed suddenly and radically. This morning I plugged in the Scan Tool and got a P0372 general code telling me the timing reference high resolution signal A too few pulses. Great..but I can't find a list of DTC which tells me what what this means. Is it the Optispark or is a coil failing. How do I understand what these things mean. Anyone want to take time to try to help me understand? Contact me direct if you want to keep it simple.
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Orange Park, FL - USA
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Vette(s): 1996 LT4 Blk/Blk coupe all origional
OK, I'm still on it. Sec6 of vol 2 engine manual says with A0672 only replace distributer. As it left me stranded halfway across the Chesapeke Bay bridge with a 21/2hr wait for a flatbed to take me 5mi home I think that solution is prudent.
So now I as you for input on what to replace it with. Do I go with origional GM, MSD, or Acell which seem to be the choices? Same with the water pump; new or rebuild. I have 56,700mi on the car and it's my driver. Come on guys voice your opinions!
PS plan to clean engine while torn down too. Dave
Original GM....lot's of opinions , good and bad, about MSD and Acell. And a new water pump. It's a lot of work tearing it down to replace opti and pump, not that bad, just a PITA. Unless you want to do it again if the rebuild fails, IMO go new. I did a opti, wp replacement on a friends car and spent the whole time cursing out the GM engineers. And about to do it again on mine for a cam swap.
We'll all be here to lend you moral support as you do yours buddy 
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lanoka harbor, NJ - USA
Joined: 3/22/2009
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Vette(s): 1990 L-98 white/ red/black leather interior targa top auto
1975 L48 blue/black leather interior t tops auto
just a quick question dave. in your first post you said the code was PO372 and in the second you said A0672, what changed to change the code? does the scanner you bought come with any troubleshooting programs?
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Orange Park, FL - USA
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Vette(s): 1996 LT4 Blk/Blk coupe all origional
Thanks guy's. I appreciate your help and interest. I called a few shops today and got the same advice..go GM. The local dealer has all the parts in stock. When I bought the car I promised myself to do all my own work so I'm digging in. I replaced all the water hoses last spring when I got the car with 45,000mi and I changed all the fluids. I'm labeling all the wires and taking before and after pics.
What really has me scared is having to remove the crank pully. There is only an inch between it and the steering rack. Wish I was like the guy in the hamburger commercial with the really small hands.
When I took off the right side injector cover I found a small plastic piece with two tubes coming out of a harness from the back of the motor and fitting into an L into the side of the intake. Looks like a vacume device of some kind. All the connections were broken. Any idea what this thing is??
I'll need all the support I can get as I moved here a year ago and still don't know anyone. Being retired I don't go out much and wife has been on 7 month deployment to Middle East and 5 weeks after returning she left for Haiti. I'll be going it alone as I want to have it done before she gets back we hope by April.
Tomorrow I'll get the car on stands and drain the cooling system. Will see how far I can get from there. Thanks again, Dave
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Orange Park, FL - USA
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Vette(s): 1996 LT4 Blk/Blk coupe all origional
BTW, code was P0372..Dave
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Duncanville, TX - USA
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Vette(s): 1985 Coupe-L98/Auto,Bright Red/Carmine.
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Why are you removing the "crank pulley" to remove/replace the Opti and water pump?
It's been a while since I've worked on anything with an Optispark, but I don't remember having to remove the balancer to get to the distributor up there...perhaps my memory really IS gone!
By all means, go with GM AC/Delco parts for this.
The code for the reference signal too low usually indicates that the opti is not reading the signal thru the tiny windows of the shutter wheel. This could be because of dirt/funk/moisture on the wheel itself, or the opti sensor. Since it's not really possible to clean the wheel, or the opti lens & sensor, replacement is about your only course of action.
It's been a while since I've worked on anything with an Optispark, but I don't remember having to remove the balancer to get to the distributor up there...perhaps my memory really IS gone!By all means, go with GM AC/Delco parts for this.
The code for the reference signal too low usually indicates that the opti is not reading the signal thru the tiny windows of the shutter wheel. This could be because of dirt/funk/moisture on the wheel itself, or the opti sensor. Since it's not really possible to clean the wheel, or the opti lens & sensor, replacement is about your only course of action.
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[QUOTE=bagpipedave] Thanks guy's. I appreciate your help and interest. I called a few shops today and got the same advice..go GM. The local dealer has all the parts in stock. When I bought the car I promised myself to do all my own work so I'm digging in. I replaced all the water hoses last spring when I got the car with 45,000mi and I changed all the fluids. I'm labeling all the wires and taking before and after pics.
What really has me scared is having to remove the crank pully. There is only an inch between it and the steering rack. Wish I was like the guy in the hamburger commercial with the really small hands.
When I took off the right side injector cover I found a small plastic piece with two tubes coming out of a harness from the back of the motor and fitting into an L into the side of the intake. Looks like a vacume device of some kind. All the connections were broken. Any idea what this thing is??
I'll need all the support I can get as I moved here a year ago and still don't know anyone. Being retired I don't go out much and wife has been on 7 month deployment to Middle East and 5 weeks after returning she left for Haiti. I'll be going it alone as I want to have it done before she gets back we hope by April.
Tomorrow I'll get the car on stands and drain the cooling system. Will see how far I can get from there. Thanks again, Dave
[/QUOTE]
You will have to remove the balancer from the hub (which I believe is what you're calling the crank pulley) in order to remove the "opti". The balancer is attached to the hub by 3 bolts. In most cases the balancer will be frozen/stuck on the hub. At this point it's a good idea to soak the area where the balancer and hub contact each other with penetrating oil ( i like "PB Blaster") and let it sit for a while soaking in the oil. I've seen some that i let sit over night in order for the penetrating oil to do it's job.
From underneath the car use a short piece of wood ( 2x4) against the balancer and smack the wood w/hammer...you'll likely have rotate the crankshaft 180 degrees and smack w/hammer and then rotate again and smack etc. some can be VERY difficult...but it will come. Remember the penetrating oil is "your friend".....I say the above but hopefully yours will come off easily (they usually don't)
You MAY have to rotate the crank hub a little in order for the opti to clear and be able to remove it.
Your opti is "vented" so along with the plug wires and the opti electrical connector you'll have 2 vacuum lines connected to the opti dist cap. pay VERY close attention to the opti electrical connector be sure the terminals are in good shape and not corroded (they are known for this) It's not a bad idea IMO to replace the "opti harness" at this time...your choice. Plugs and plug wires are easier at this time....also your choice.
Finally the new opti will only go on CORRECTLY..one way there is a dowel pin which seats into the back of the opti...look for this when you remove the old opti--then look at the back of the opti to "see" where the pin goes. Lastly when installing the new opti it MUST seat against the timing cover using your hand only!! DO NOT use the bolts to pull the opti into place it's easy to ruin a new opti this way so use care when installing. All in all it's not a bad job---the above are just some things to be aware of. 
Vaughn
Dave: look in forum topics under Engines.....LT1*C4 posted a excellent writeup with pictures on replacing the opti. Really will make your job easier.
jimmymack 2010-02-26 04:55:34
And Vaughn is spot on with his advice.
in Forum: C4 Electrical
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