Help! Timing Problems

[Ron59]

1993 Base Vette.. was running a little rough after taking out of storage .. After a few days it got worse and quit. When I was able to get it going it was barely running ... timing appears to be way advanced .. hard start and bad spark knock once it is running. I suspect a problem with the optispark , but don't really know where to start. Any suggestions .. Car has 120,000 miles on it .. no major work yet.

Forgot to mention also ... no codes .. Fuel wasen't a problem .. was stored over winter with a full tank and was on second tank (Had a 350 mile trip on the second day out)

 

[John Robinson]

First the timing is controlled by the ECM. The ecm adjust the timing based on information from sensors all over the engine. As you say car was in storage but you don't say how long. If it was stored with a partial tank of gas the following could happen. Water condensed in the tank. ( Like a small rain forest). Gas has a gone bad. (It really does have a shelf life) In running the engine you have sucked all the contaminated junk in the fuel tank into the fuel filter. ( Starving for fuel). And the list goes on and on. So if the fuel is bad and the sensors for knock tell the ecm it is knocking the ecm will retard the spark. I would suggest you pull the fuel pump and look at the condition of the tank and the fuel pick up filter. If there is rust in the tank and on the fuel pump bracket clean it up. suck out all the gas you can from the tank put in fresh and replace the in line fuel filter. While the in line filter is off put a rubber hose on the fuel line from the tank and run it to a gallon jug. do a quick on off cycle of the key to flush out the fuel line before putting the new filter on. Once that is done run the engine and if it still is running bad you need to look at the injectors (replace them) because they could be clogged with the same crud that was in the fuel tank. Let us know how it turns out.

 

[vetteoz]

I suspect a problem with the optispark , but don't really know where to start.

Lt1 No Start Diagnostic - Automotive - Forum

 

[Ron59]

Fuel

No problems with the fuel system .. pressure is ok .. checked connectors on ECM and coil .. looks ok .. no codes and now it won't start at all. Going to remove the opti and check it out a little closer... car has fuel and spark but not at the right time ..

 

[John Robinson]

When the car was brought out of storage did you clean it up inside? Like use a spray to detail the dash etc. If you did you may have gotten some spray inside the ignition opening and it is not reading the chip on the key. That will shut down the car. Been there done that. You still may have an opti problem but there are so many small things that can cause the same problem. If you have a spare key you might try it.

 

[vetteoz]

you may have gotten some spray inside the ignition opening and it is not reading the chip on the key. That will shut down the car. .

VATS only comes into effect when trying to start the engine ; takes out the injectors and the starter
Once the engine has started VATS plays no part in ECM or engine operation

 

[John Robinson]

VATS only comes into effect when trying to start the engine ; takes out the injectors and the starter
Once the engine has started VATS plays no part in ECM or engine operation

That is interesting. But I believe it can also shut down the engine. The reason I say that is I was cruising along on the interstate and my car shut down and would not restart. Had it towed to a dealer and they spent all day working on it and finally replaced the vats and the keys and it started. So it appears that once the engine has started the vats can affect the engine operation and the ECM will shut it down. If what you say is true then I paid nearly a $1000.00 that day to get back on the road and the dealer just stumbled into a fix while replacing the vats. AS for the op problem the article you provided is just what we both are saying. He needs to methodically go through the diagnostic procedure. This is a process that will lead the op to his problem regardless of what each system does. Vettoz you and I are using our experience to guide the op to learning about their car just as others have showed us. I sometimes wish I could go and stick my head under the hood of the problem car. But all I can do is stand by and wait to find out how the problems are solved.

 

[John Robinson]

I just remembered I also have had the TPS go bad and not allow the car to start. Did not find that one until after replacing the ECM. Oddly in that case I did not get any codes. In the last two weeks I had the engine get hydro locked with fuel in the crank from a bad fuel pressure regulator. But oh the thrill when I hit the starter and drive it out of the garage is priceless.

 

[Ron59]

Not a key problem .. I actually managed to get the car to limp home the day the problem happened. It started to run really bad and stalled several times but I was able to get it running and spark knock all the way. If there had been any hills to climb I doubt it would have made it. It was running like the spark was advanced way too much .. That is why I suspected a problem in the opti spark but I know very little about the ignition system on this engine so it will be a learning experience to say the least.

 

[John Robinson]

That's interesting. I was reading a book written by a Chuck Probst on the engine control fundamentals of the corvette. My printer scanner is down so I am going to type a small section of what he says. about Limp Home When the computer, itself is not operating normally engine management changes to Fuel Backup, or "limp home" mode. This could be under any of the following circumstances: A computer voltage less than 9 volts A cranking voltage less than 9 volts Missing or nonfunctioning Programmable Read -Only Memory (Prom) If the computer fails to issue Computer Operation Pulses (COP) When one of these situations occurs, the computer runs on something called the Cal-Pak chip, operating the engine only on inputs from a few sensors: Manifold Absolute Pressure, Throttle Position, Engine Coolant Temperature, and rpm . In another section he talks about battery voltage If the battery voltage falls too low, slower fuel pump speeds may reduce the fuel delivery to the injectors. The computer increases the injector pulse time to compensate, and can raise the idle rpm to increase generator output. Electric ignition in the LS! and ZR! can increase dwell time, So it may be that you have bad grounds land am losing voltage to the ECM Cleaning all the grounds may solve your problem.

 

[Ron59]

Thanks for the diagram .. Gives me something else to check. I'll keep you posted,,

 

[Ron59]

Grounds all look good. Actually for the mileage and age this car is very clean under the hood. Problems point to trouble with the optispark so I will be changing it out as soon as I get a replacement. Should be here by Thursday I'll update after it is installed. Thanks for the replies...

 

[Schrade]

You should get a log scan and post it up here, before spending cash on a new opti unit.

 

[Ron59]

Problem Solved ****

Trouble was with the Optispark unit. As soon as I got it off the car I could tell it was worn out. It was so tight I almost couldn't turn it. The berring was toast and it finally failed to the point where debris caused problems with the optical sensor. Changed out the unit and it fired right up ... Running perfect .. Glad I was able to fix it myself . Makes me appricate a good running motor.. Love the feeling .. The older small block chevy's are easy to work on but I was a little overwhelmed by the LT1 .. Turns out to be just as easy to work with .. just needed a little information to get started.. Thanks everyone..