I'll preface this by saying that the car is no long in my possession. I sold it to a friend and then it started acting up. The mechanic is stumped and so am I.

1994 Z28, 98k miles with just bolt ons, still N/A.

Last summer I took it to the track and just before I got to run the car it started missing on at least two cylinders. Needless to say, drag racing was out of the question. The unfortunate thing, I had to drive it home like this. Probably a good 80-90 mile trip.

So, I went ahead and replaced the water pump and opti and it ran good again. Not great, it needed a plug change. Sold it to my "friend" and he changed the plugs in my garage. It ran 100% better.

Two weeks go by and the motor hydro-locks. It took over two months for my "friend" to figure this out though. We knew the starter died and replaced it and the car still would not start. Well my "friend" finally got it towed to a local mechanic and he found approximately 5 gallons of gas mixed in with the oil!

So, the mechanic changes the plugs, puts in fresh oil and the motor runs rough and smokes like a bastard. No knocking though. A week or so later, the car fires right up but then starts loading up. Mechanic gets it in the shop and there is another gallon of gas mixed in with the oil.

Now, the mechanic figures all this gas didn't get in the oil from when I drove it back from the track. He says it would have locked up on me then. So, what is causing this? None of the injectors are stuck open according to the mechanic, but he is getting codes 16, 18, and 43.

I believe 16 is something about the opti, 18 is something with an injector circuit, and 43 is the knock sensor. Which, I have no doubt the knock sensor is going nuts from the motor loading up.

Did I get a faulty optispark or what? What else could be causing the motor to load up so badly? Bad FPR?

Help me out CZ28, I'm trying to help get it running so my friend stops hassling me.


Edit: If anyone needs to know anything, please ask. I owned the car for almost 6 years and can pretty much tell you the car inside and out.

 

Make sure your injector circuits are not shorted to ground, if they are they may opening 100% of the time as soon as you turn on the ignition. Injectors should have 5 volts all the time, and fired when the PCM grounds them (quick pulses of varying time length). Got to an autoparts store and purchase a injector test light. Maybe $5. Test each injector, you should have a steady flicker in idle. If the light bulb remains solid, you have a problem.

Joe
Good Luck!

 

Check your fuel pressure regulator. I had this problem until I went back to the stock regulator.

 

I'll tell him.

978Racing- Has the stock FPR now. Never been touched or changed.

 

The problem seem severe.

Check if you dont have leak FPR, check the vaccumm hose that feeds into the intake plenum. It can suck major fuel through there.

Is it stock cammed? Ask them to check vacumm at idle, should pull about 20 inches if stock. Reference back to the map sensor, and see if it matches your readout with the mechanical gauge. Not sure if it will matter much given this car is non speed-density. If it does not match, it will throw off your VE table fueling by a lot causing these type of problems.

 

FPR and injectors are fine.

Code 16 is what has the mechanics eye at the moment. He says it's not reading the cam position somehow. It's a brand new GM opti. Is it possible that it's a lemon unit?

96ZRDR - Yes, stock cam still.

Unfortunately, I do not have access to the car. It's not even my problem truthfully, but there's a deeper motive for me to try and get the car running. The mechanic that has it is very good. But as we all know, LT1s can be tricky.

I'll definitely let him know about the vacuum line. It's very possible that it got bumped or whatever.

 

Reality check... is your mechanic seriously suggesting that 5 gallons (20 quarts) of gasoline will fit into your oil pan?

16 is loss of low res pulse signal from the Opti. If the engine is running, its not an active code, only a stored code. If DTC 16 is active, the engine won't run because the PCM shuts down the fuel system.

18 means one of your injector circuits is open or shorted (see next quoted post re injector shorted to ground). Check for +12V at each pink wire with the key on, engine not running. Then with the connector off the injector, check the resistance across the two pins of the injector - should read in the range of 12-15 ohms. 43 means the wire is off the knock sensor or the knock sensor is defective. This code will give you continuous knock retard.

The injectors are supplied with 12 volts on the pink wire at each connector, not 5V. The injector test light is called a 'noid light.

Not according to DTC 18.

As noted above, loss of low res pulse signal from the Opti, and that it the output of the optical sensor, which is the cam position sensor. But it is not unusual to see DTC stored. As noted above, if it was an active code, it would not be running at all. Pull the "PCM BAT" fuse for 30 seconds to clear the code (or have the mechanic clear it with his scanner) and see how soon it comes back. If it keeps coming back right away, first check the two connectors in the Opti harness for corrosion or pin damage. If the harness is OK, the Opti is suspect. Is it an AC/Delco (Delphi) Opti, or some "off" brand?

 

It's an AC Delco Opti straight from a GM dealer.

Maybe not 5 gallons, but quite a bit. He said the dipstick was wet until about the top two inches of it. I didn't ask him for an exact measurement, it's a moot point anyway. There shouldn't be any gas in it at all. Thank you for replying Injuneer, I was hoping this would catch your eye.

 

When my buddies car was fuel dumping it was an injector stuck open.

Put a FP gauge on the car, set it to on, see if it holds pressure steady.