Before I tear the front of the engine apart and replace the optispark unit, help me diagnose a no start LT1 in a 1994 z28.
what is known:
car ran one day, would not start 3 days later
It has gas and the gas is not old
battery full and good, cranks at a normal sbc rpm
there is 42psi fuel pressure at rails
as a check of “is it fuel or spark related” the car didn’t fire on starting fluid
pulled a plug from each bank and they read good, very clean, are almost new and there is verified spark at both tested cylinders. It isn’t blue though. Delco rapidfire plugs gapped properly.
It attempted to chug once, and basically gave one poof every couple seconds for about 10 seconds, this was not with ether. It sounded like one cylinder may have been firing very late.
Generally the LT1 diagnosis is “replace optispark” but I’d like to actually prove that before I tear stuff apart though at the same time i really just want the car running or gone or possibly both
Coil? Ground and/or wire plug that goes into coil. Often this is the source of problems. Not the Opti.
It’s an msd coil. I may see if someone has a stock one with module i can borrow.
I shouldn’t have bought it when i got there and it wouldn’t start. I’m upset with myself that i still took it and now i just hate the car. He offered to give back my deposit and about half my diesel and hotel costs, and i should have agreed. But i was dumb and loaded it anyway.
I felt like i would be going home empty handed, but sometimes that’s the right thing to do.
It isn't very common, but I've had a couple optisparks snap the rotor off. It sometimes gives you a warning with a couple high-rpm backfires and then one day - wham. Mine would barely idle and wouldn't accept any throttle so I limped it home. Sure enough, rotor had mostly sheared off and was crooked.
Get yourself a set of E-sockets. They're like reverse torx. That's what is holding the cap on the Opti.
The opti is an amazing piece. It gets a bad rap because of the early ones not being vented. The optical pickup is probably still the most accurate on the planet in a production car, but they are a cap and rotor configuration so they will eventually fail. Mine finally died at 130k, which is more than I can claim for the coils on a Triton V8, or the cap and rotor on anything old-school, or the injectors on a Duramax LB7.
Opti is one of the best out there. LT1 is a great engine. Don't beat yourself up. E36 M3 happens.
+1 on replacing the MSD piece with a stock one, I've seen many threads in the Mustang world with problems traced back to an MSD ignition component.
94 corvette.
Ignition module died first. Drive into the show fine, wouldnt run 4 hours later.
The next failure was cap and rotor. Same scenario. Fine on the way, dead after. I could find no actual failure with the cap and rotor, but regardless, swapping fixed it.
If you decide to punt, ill give you a hundred bucks and a grilled cheese sandwich for it......
An lt1 in the stepside would be awesome.
Dusterbd13 said:
94 corvette.
Ignition module died first. Drive into the show fine, wouldnt run 4 hours later.
The next failure was cap and rotor. Same scenario. Fine on the way, dead after. I could find no actual failure with the cap and rotor, but regardless, swapping fixed it.
If you decide to punt, ill give you a hundred bucks and a grilled cheese sandwich for it......
An lt1 in the stepside would be awesome.
There’s a whole aluminum head lt1 in the back of my truck.
Dead_Sled has both styles of lt1 coil/module on known working engines and has graciously offered that i can borrow whichever kind it needs for testing. Andrew and Calvin gave me a new optispark unit when I stopped at their place on the way home.
i don’t want to punt on it right now but I’m also upset about the whole thing(not the seller, he had run it a few days prior to going to pick it up to make sure we were good to go) because the whole reason for buying it was it was a running driving car that we could massage into a low 12 second car on the cheap so Carli would have something easier to drive to learn how to go progressively faster.
Spark, Gas, Compression, Timing. Which one are you missing?
Vigo
UltimaDork
9/22/18 9:12 p.m.
If it has spark and won't start even with starting fluid it's a timing issue. Since the distributor cap isn't easy to get off, hook a timing light to it and see if it's got correct 'base timing' while cranking. If not, you're diving in for some kind of failure with the distributor, or the timing chain jumped. I would guess if it's a timing issue it would probably come down to the tiny rotor screws or the pin that indexes the whole thing to the cam. I've actually never touched an optispark so this is my educated guess based on looking at some pictures.
Unfortunately it doesn’t have traditional timing marks on the balancer to watch with a timing light.
In reply to Patrick :
Can you do one of the various find-TDC-through-a-plug-hole and make a mark just to see whether there's something happening in the right ballpark? Seems like if it's timing it'll be far enough out that precision shouldn't be needed to spot it.
Vigo
UltimaDork
9/22/18 11:13 p.m.
Yeah, that's what i'd do. Just put #1 at TDC somehow or other and make an arbitrary mark in some place that it's easy to shine the timing light on. It will try to start within a pretty big window like 40 degrees (say 30btdc to 10atdc, for example) so if it's outside of that it'll be plainly visible to the human eye.
Rained out part of work day so I’m going down the list beginning with what i have on hand. I have a known working coil and swapped that on with no change. So cross coil off list.
Hoping i can borrow a known good module from dead sled this evening and swap that in. Then if that fails(these are obviously the two easiest things to check) will pull valve cover to make timing marks. Then it would come down to the opti itself. I won’t be surprised if it’s the module because if it is anything like tbi ones they like to die, but also because i want this done yesterday it’ll probably be the most involved piece(opti)
if it goes beyond that i have zero issues parting it out
Dead sled is awesome, he disabled his hearse so I could use known good coil and module to test. No go. Just got done pulling the water pump so I can swap the opti unit next free chance i get. It looks pretty crusty. If that works, we’ll pick up water pump gaskets at summit racing Saturday and slap it back together. If it doesn’t work, well I don’t want to think about that right now.
I used one of the ebay China replacements Opti sparks on a 94 LT1, it was only $73 (back in 2007). Way cheaper than the Delco ones, which were being made in China as well. Ran quite well and was still going 4 years later. It was cheap enough to take the risk on.
In reply to Patrick :
Remember to reinstall the splined drive coupling for the water pump during reassembly. Or else you'll chase an overheating problem for days.
Ask me how I know 
Check the MAF. I had one go bad on my old 9C1. Did a whole bunch of goofy things. Also had a brain box go bad and do weird things as well.
You can replace just the sensor in your existing optispark, if everything inside looks OK. https://www.amazon.com/Ignition-1992-1994-Generation-Optispark-Distributor/dp/B00FSC65P4/ref=sr_1_3?ie=UTF8&qid=1537930525&sr=8-3&keywords=AIP+Electronics+optispark#customerReviews
I took my 93 apart and it was rusted so I replaced the whole thing. I would recommend changing to the vented style cap and rotor, then you can seal the holes in the bottom of the optispark and keep the water out.
I have used the slip the seal over the correct size socket ( you have to go through your box and find the best candidate) for the water pump oil seal, it is a very easy seal to fold over and create an oil leak right over the new opti you are installing. Don't ask how I know this, but lets say that I am very good at taking the front of this motor apart by now. Mine is installed in a 34 Ford Roadster so the radiator and grill have to come out as well.
I did have an ecu problem as well by it still ran just in limp mode, you are looking at the most common spark not at the right time problem section of this engine. Good Luck
Just tossed on the new $0 optispark unit and it fired and ran immediately. So like all the internet armchair mechanics say, if LT1 replace opti.
have to put it all back together and the battery is low from the previous diagnostic cranking so i’ll have to bring it across the street to charge. There are a few things i found to correct while putting back together but it’s alive and it came with a new belt so hooray because the old one was missing a rib and frayed.
If everything else then tests ok, watch out.
Really interested to hear if you take it apart. My money is on a busted rotor.
I will definitely do an autopsy, it’s just not a priority as much as getting the front of the motor back together and getting it out of my trailer so the Datsun can stop sitting outside.
Heading to summit racing for water pump gaskets because they have them in stock(and clearance shelves, yo)
