On the '95 TA, wife had been driving it all day fine...yesterday evening I go out to move it, it fires right up and runs for about 1-2 seconds then sputters and dies.
I crank it again and it sounds like 1 cylinder fires and it will run for 2-3 seconds and that 1 cylinder will fire 4-6 times then die.
So I thought maybe I flooded it...sat for a few hours, tried to start it same thing.

Today I pulled all the plugs, they didn't look to bad, several were black the others looked ok, a few wet with oil/gas.
I check the spark on every wire, they all have spark, would only jump about 1 inch on the spark tester gadget, seems like they should jump a little farther, but should idle fine.
While testing spark, I had all plugs in finger tight...pulled them all back out, had gas on all of them, so each cylinder is getting gas, doesn't seem to be an injector issue.
Fuel pressure is at 43 psi when key is on and holds there for over an hour with key off.

Also was able to run the Datamaster on the PCM with the key on, looked fine. Also read the computer flash memory with TunerCat, so it appears the PCM is fine...No codes were stored either.

I just put brand new plugs in it, checked all the wires, hooked it all back up and cranked it and it backfired through the exhaust very very loud, filled the entire garage with soot so decided to call it night before the neighbors called the police thinking it was a gunshot at midnight...
But I did double check all the wires to make sure they were all connected correctly and they are...checked routing all the way to opti.
Backfire could have been all the excess gas in the exhaust from cranking it checking the spark on each cylinder too.

So my next guesses would be..optispark bit the dust somehow, but would it still have spark to each piston and still be bad?? Like the position sensor part is whacked?

Other thought would be timing chain jumped, but on startup?? The chain is a LT4 ED, has maybe 45k miles on it.

 

Do you have any problems when the car sits over night and then you start it? Whenever my opti failed, the car would be fine til it warmed up. car would awlays leave me sit and then would run fine after sitting for like 15 minutes. car would backfire louder then you could believe....

 

It's ran and started flawlessly for the last few years, driven daily.

So it sounds like when the opti fails, its still gets spark to the plugs, just not at the correct time...so replacing the opti fixed your issue?

I did try starting it this morning, no backfire, but same as before, just one cylinder half firing it sounds like. I have a spare Delco Opti so I guess I'll be slapping that on in the next week or so, I can also tell if the chain slipped when the opti is off if I can find a pic of where the dowl should be a TDC, my hub is on correct and I have the flywheel marked also.
BTW, this opti has about 50k miles on, it was a Delco also.
Thanks

 

Does the fuel pressure stay high when the engine starts?

A problem with the optical cam position sensor in the Opti will set codes, neither of which turn on the SES light.

If the rotor came loose, it's conceivable the plugs would continue to fire, but at the wrong time.

I hear about "timing chain jumped a tooth" all the time but I've never seen it actually happen on an LT1.

 

Injuneer, is the opti even used at first startup? or once the car warms up? not sure exactly how it works, but i have had it fail a lot.

I just rebuilt my lt1 and i cant remeber where the dots on the gears were but i know the cam dowel was at 9 oclock. I dont see that chain being able to jump a tooth but im no expert...lol

Has your opti gotten wet at all? Mine had never given a code so I always just went by my gut and that was always the opti, i have never had any other problem with any ignition components.

 

The "opti" has two functions.

1 - It's a conventional ignition distributor - the coil sends the voltage to the Opti, and the Opti sends it to the right spark plug. That happens any time the engine it running.

2 - The second function is to tell the PCM where the engine rotation is with respect to TDC on the compression stroke for each cylinder. The PCM needs that info (cam position) to fire the sequential injectors and the plugs at the right instant.

So the Opti is used to start the engine, and to keep it running AT ALL TIMES.

 

Yes fp remains above 40 psi when it sounds like the one cylinder is firing. I scanned it with DataMaster and it showed no DTC codes.
This all happened just all of a sudden with no issues before hand, so I'm leaning towards thinking the rotor or something within the opti came apart.
I still have my 90k opti that worked ok with a little extra noise sitting on the workbench, I really need to find the right tool to take it apart and compare to the one on the car now....may be a few days before I actually take it off due to holidays and some really cold weather moving in on Christmas and some other projects I was in the middle of.

 

If you mean you need the E4 Torx socket for the screws on the Opti cover, you can make your own socket out of a T15 Torx bolt.... like the ones in your throttle body cover.

 

Damn, never thought of that...I just had some of those torx bolts too, they were in the glove box of my truck when I sold it..now if I can figure out what I did with them.. Thanks for the tip!

 

Take one of the throttle body cover bolts out, wrap the threads in tape, and grab the tape with vise grips

 

I found a couple of the torx bolts in my misc bolt/screw draws, they were very short, the tip didn't stick up enough out of the recessed holes to get the vicegrips on it, so I took a small hex head bolt and spot welded the ends together, so now I have a good tool and a regular 1/4" socket will remove the torn bolts on the opti.
I got the 90k good one apart, and it seemed very clean inside...what I don't understand is how the spark timing could get off??
The rotor is solidly attached to the part that is spun by the cam snout so it will always hit the spark caps at the same time. I also see the optical disk with the windows in it, but don't understand how the spark could get mis-timed...something I'm not getting with it.

When I get the one off the car I'll shoot a pic with both side by side and apart.
Going to work on it some now but probably won't get far, only got a couple of hours.

 

The screws that hold the rotor on fall out.

 

Ok, well I got a little more time than expected, got it out and you are CORRECT Fred! Problem solved, although it will probably be next weekend before I get it back together... Both screws rattling around in there.
So I took the brand new opti I have, a Delco, same as what was in there, and took it apart and put some red high strength loc-tite on the tiny screws...looks like they may have had some type of thread locker on them, but they came out as easily as the ones on the 90k opti I took apart earlier.

Here is a pic of the bad opti all apart, it had all kinds of oil and sticky crud in it, and a pic of the reluctor wheel, it had some bad wear spots on it too..again this is only about 50k miles old.



And the new one with one of the screws out with the stuff on the threads that was already on it.

 

The shutter wheel appears to have been forced forward, to rub against the emitter/receptor housing. Could be due to a worn Opti bearing. Or it could be a problem with the cam dowel pin being a bit too long. I'd check the dowel length.

 

Yes, it did rub for a short time, or at least made a grinding/rubbing noise...goes back to that discussion a while back about shimming the opti out by placing some thin washers between it and the timing cover rather than trying to hammer the dowl in with the cam in the car... Will check the depth on the new one before I start putting back together.