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Discussion Starter · #1 ·
Last week my 84 corvette would not start. I had a friend come over and verify that it did not jump timing. So I changed the ignition module and the coil. Turned out to be the coil, so I left bot brand new parts in the car. Then I drove it about 100 miles. Ran better than it ever ran. The car only has 13k miles and the engine was rebuilt at 10k because it sat for 30 years. Having fully enjoyed the 100 mile cruise my wife decided she wanted to drive it also. She claims it was running amazing when she pulled out directly in front of someone. Not wanting to die she gunned it in first gear and when she shifted into second the car died. I tried to start it, she wants to start but sputters. Eventually she shot flames out of the TB. It now sounds to me that it has jumped timing, but is that even likely with such few miles? Could a bent rod or a rod that came off of a rocker cause a no start?
 

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to go farther.. you can disconnect the injectors connector.. careful replacement connectors are not cheep.. disconnect the big red wire into the cap. with no spark and no fuel .. crank the motor for a few seconds. does it sound like it has even compression or does it crank really fast indicating timing sprocket jumped..

you can since you know how to get the cap off.. use a 15/16 socket on the alternator pulley nut and bring the timing mark to the top... with the cap off.. you might want to see if the rotor is pointing toward the #1 spark plug wire or #6 spark plug wire.. either will usually be OK.. timing marks on that are straight down from the top behind the water pump usually.

is this a straight 4 speed crossfire car.. or a doug nash 4+3, 4 speed car.. or just an automatic that she held in low gear.

lack of fuel pressure or low fuel pressure will cause the engine to backfire thru the throttle body.. as will other ignition system damage .. like fractured magnets in the pickup coil inside the distributor.. usually easily seen with the rotor off when viewed from the side.

did you use silicone dielectric grease under the module...

when you replaced the coil.. the carbon button goes in the bare cap first.. then the silicone gasket. then the coil.

there is also a flat folded ground strap that fits in under the coil.. if that did not get transferred or installed.. it will blow the coil and the module out..

while the cap is off.. take off the rotor and flip it over.. make sure there are no burn marks. where the high voltage has burned thru.
 

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Floated the valves and kissed the pistons? Valves would be bent and not closing.
FORGET jumping cam timing... didn't happen with 100 miles or 10,100 miles on the timing chain set... she did what Greg says... bent one or more valves... a compression test of all 8 cylinders will quickly and easily tell how many cylinders are involved... A bent, leaking intake valve allows combustion fire to surge back into the intake manifold which explodes any fuel in the intake manifold as a 'backfire'... The backfiring confuses the engine computer...

Teach your wife how to watch the tach out of the corner of her eye and shift in time by the yellow line - drag race style... Have her practice it until it becomes second nature and she can do it in an emergency.. Most 1980's engines pump up the lifters and/or begin to float the valves by only 5,000 RPMs... if you don't let off the instant that happens, the valves can reach the pistons... some Z28 spec valve springs (90 - 100 lbs. seat/closed pressure, 250 - 280 lbs. open pressure) can increase that to 6,500 RPMs...

https://www.summitracing.com/parts/hrs-98214/applications
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Discussion Starter · #8 ·
I will get a hold of a compression kit and find out. Yes I will also try to get a better look at the timing and/or the distributor.
 

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Check to make sure the distributor is tight and in time. If it is tight you can pull the cap and bring up the timing mark on the crank to TDC to see if the chain jumped or broke or you stripped the cam gear. If you bring up #1 on compression the rotor should be pointing to the #1 plug wire tower. If none of this nets any results a compression test would be my next test.
I have seen many distributors left loose after initial tuning or one of the junk aftermarket hold downs that don't hold even when tight.
 

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How do you know it over revved?

Can't blame everything on the wife.

Bet one of your new components died or bad wiring to one of them.
 

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I have seen many distributors left loose after initial tuning or one of the junk aftermarket hold downs that don't hold even when tight.
That was the first thing that went through my mind when I read the intro....Go ahead and do the compression test, you need to know that info anyway, but I'd put my money on the dizzy twisting some. The only hold-down that is worth having on the dizzy is the stock GM piece with stock bolt.

When doing the compression test, run the motor first to bring it up to operating temperature, then wire the primary throttle blades wide open so the motor can breathe and remove all spark plugs to make the starter's life easier.
 

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When doing the compression test, run the motor first to bring it up to operating temperature, then wire the primary throttle blades wide open so the motor can breathe and remove all spark plugs to make the starter's life easier.
It doesn't run. tough to warm it up :D
 

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I doubt it over revved. They would be lucky to rev past 5k with a brick on the gas and in neutral,,,,Do standard diagnostic testing, ignition(on time), fuel management working(84s have a querkie twin tbi ), cr.
 

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Discussion Starter · #15 ·
Thanks to all for the inputs. I agree that it seems very unlikely to jump timing and I highly doubt there is any valve-piston clash, whereas I do not hear anything as it turns over. I will start checking the distributor first and then the fuel system. As I remember correctly the TB's did not seem to be flowing quite as strong as they did before this instance. I suppose that it is possible the fuel line got clogged. Would that prevent a no start as opposed to just running bad? Could the coil be shot again? I am hoping to God that the power source to the distributor came unplugged and life can go on happy and peaceful
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If the cross fire is a problem? Edelbrock has an intake with 8 injector bongs and you convert the TBIs to dry.Add a little power too. Dont chase large power gains with that engine though
 

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Thanks to all for the inputs. I agree that it seems very unlikely to jump timing and I highly doubt there is any valve-piston clash, whereas I do not hear anything as it turns over. I will start checking the distributor first and then the fuel system. As I remember correctly the TB's did not seem to be flowing quite as strong as they did before this instance. I suppose that it is possible the fuel line got clogged. Would that prevent a no start as opposed to just running bad? Could the coil be shot again? I am hoping to God that the power source to the distributor came unplugged and life can go on happy and peaceful
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I doubt if it came unplugged. You have spark if it is back firing, just not at the right time. Plugged fuel injectors on that setup would have to be pretty bad to keep it from starting at all and i doubt you would plug both at once. Those cross fire setups were troublesome but about 75-80% of the problems were due to vacuum leaks
 

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Discussion Starter · #18 ·
I see your point. good thinking. I will check all of the vacuum hoses also. Do you think it could be fuel pressure? I just installed a brand new injector before the mishap. The other one was atomizing fine so I just changed the one that was pouring fuel into the TB.
 

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Anything is possible but the thing that makes the most sense is the distributor turned. You need to check the timing first. If you just start tinkering with everything you may introduce new issues. Check the timing, if it does not net any results, do a compression check to be sure you didn't hurt anything. And then get back with results
 

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I highly doubt there is any valve-piston clash, whereas I do not hear anything as it turns over. I am hoping to God that the power source to the distributor came unplugged and life can go on happy and peaceful.
I highly doubt it is anything but a bent valve... you have the precipitating event: a panic'd overrev... and the symptoms: backfiring into the intake... and you likely won't hear anything turning the engine over...

I know you don't want this to be an internal engine problem, but 99+% it is... if you can do the repair yourself, it's about $5 - $50 in parts/gaskets...

Long ago, a friend (now deceased) was irritated because the Chevy 250" straight 6 in my boat (definitely a slow revving engine) was stalling and he gave it a good throttle blip in neutral... it bent a valve... was backfiring through the intake, but being carbureted, it did start, but just wouldn't make any power with fire in the intake... he felt bad and helped me pull the head and put a new valve in... I discovered later I could have run the boat with reduced power but still at planing speeds just by pulling the one sparkplug wire on the effected cylinder and putting it on an unused plug outside the engine and running on 5 cylinders... since that would have stopped the backfiring into the intake...

Please don't let this become another thread that goes on for 3 - 20 pages before the real problem is diagnosed... just do the compression test... or try starting it with each spark plug wire alternately on a separate spare plug... until you find the (hopefully only one) bad cylinder/valve...

In another vein, a common problem with CrossFires is the hood design allowed water through to get on the injection system and cause various kinds of water damage to components...
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