Hi my mother and I are trying to fix my late fathers 1996 C4 Corvette, automatic. We just had a new distributor and crank shaft put in a few months ago and now $1500 later, she is running rough again! I am getting codes 372 and 1371. From what I can find that is distributor and cam sensor. Is that right? Any suggestions? Any tips/tricks?

 

need more info like year, 6sp or automatic, etc....

 

you said new crank shaft, do you mean crank sensor? to me it sounds like it might be a cam/crank retard coalition problem, but that is from my experience on a 98 vortec engine, not a 96 lt1. i went through all of that when i did my heads on vortec truck, ended up spending 2500 bucks for a snap on ethos edge to fix it myself cause i am too bull headed to pay anyone else to work on my stuff, my brother laughed at me.. him "so you payed 2500 bucks for a tool to fix it yourself instead of paying a shop 200??? " me ... "yup" he wasn't laughing when i used that same tool to fix his 03 mustang though LOL

 

Your codes do come back to the Optispark distributor. I would contact installer if there's is any warranty with the distributor installed. Do you know brand that was installed? Leaking water pump will cause distributor concerns.

 

On 96, the opti is vented; it's not uncommon for the hoses in the vent harness to get cut by the serpentine belt or otherwise become deteriorated from oil and heat; price wise the hoses aren't expensive, but labor wise it means paying twice to have something replaced that should have been done when the new distributor was installed. good luck.

 

when you change a cam or crank sensor you need to let/ make it re-learn, there is a procedure to do that, i think...

 

If you spent 1500 dollars a month or two ago and the parts failed.. I'd be inquiring about the quality and the warranty on those parts.

 

I'm wondering if they installed new spark plug wires while in there??

 

No you don't.

 

He might be thinking about the Vortec stuff, in which there is an insane procedure to re-learn the base advance. I have not touched one in ten years but remember it being quite silly.

The optispark is keyed, you'd have to go out of your way to screw up the timing.

-- Joe

 

I thought about the L31 Vortec too. Still, no "learn" required; the key there is that the distributor needs to be properly synchronized with the crank (pick up). The Crank provides the "now, now, now..." and the distributor provides the 180* info -which cylinder is firing, 1 or 6, so to speak. So if the ECM sees that dist signal out of time w/the crank, it throws a code. If it's off enough, the spark can jump to the wrong post in the cap when fully advanced (cruising hwy w/EGR) and cause some pretty violent bucking.

Anyway, you're right. You can't screw up an opti install unless you REALLY try...and even if you did...the ECM ain't never gonna "re-learn" what you screwed up.


OP or her mechanic need to take a closer look at the OPTI. If I were diagnosing that car, I'd hook up a scan tool, run the car, and when the symptom occurs, I'd be looking at the low res, high res and tach signals,very closely.

OP, does the tach needle jump all around spastic-ly when the engine is missing and acting up? If so....that's your Opti.

 

I just re-read the procedure on the L31. After aligning the marks you start it and then you look at the retard offset value in the scanner and adjust the distributor body until you get it as close to zero as possible.

But yeah, they need to diagnose it properly in a shop. My '94 was doing something similar last spring, and it was a faulty wire to the ICM.

-- Joe

 

Im going to guess you had a crappy china optispark installed.

Yes I know the original optispark’s arent made anymore but if you get lucky on ebay - sometimes you can find an old man selling an NOS spare he may have in a tattered box. You have to know the right questions to ask the seller of it.. expect to pay $350 plus to get an NOS unit. Price alone is not a guarantee of a good quality optispark - for example the expensive MSD optispark (non-OEM replacement) also has an optical sensor known to fail.

you need an optispark with the original mitsubishi optical sensor. The cheap copies dont hold up under the heat / ozone of an engine environment.

Questions to ask: does he have 1 or 10 he is selling? If its 10, then its probably not NOS unless theres a good story behind (ie. Take offs off of old crate motors)


Is the cap the tan one or the opaque/charcoal green one that you can see the wire traces through? The NOS OEM caps were the tan ones that you cant see the spark plug wire traces through

You can post you are looking for an OEM one in the for sale section here or other f body or b body websites.

Other options are there is a guy in ohio - optidoc, that takes a msd optispark / installs a genuine mitsubishi sensor in it. He also tests to make sure it works.

remanufactured by GM is not preferred as they do a great job replacing seals , bearings, but ‘recycle’ the old optical sensor. But Id rather have a GM remanufactured - as long as it has the original working mitsubishi optical sensor vs a brand new china optispark with a cheap repro optical sensor.

id rather have a used known to be working oem optispark (with a mitsubishi optical sensor) vs a chinese repro optispark.

you can take the opti spark apart and look for mitsubishi symbol on optical sensor before install if in doubt.

finding a reproduction optispark ‘with a good warranty’ is not a good option bc your warranty does nothing for you when you break down due to an optical sensor failure from a non mitsubishi optical sensor failure - let alone the inconvenience/cost of spending hours replacing that hard to get to part.

The optispark gets a bad rap for no reason. The gen 2 optisparks usually dont fail unless the vent system clogs. The gen 1 92-94 optisparks need a vent added to make them reliable like gen 2

if you had the oem part on this 96, im surprised it went bad.ive heard of some beating failures, but thats it. Many people here make mistake of proactively replacing a good oem optispark with a chinese unit thinking they are doing preventative maintenance.


Really the only preventative maintenance it needs (on the 95-96 gen2) is a new cap/rotor eventually

good luck !

 

no offense tom but yes.. on a vortec there is a procedure to follow after you change a cam or crank sensor, my 2500 dollar ethos edge walks you through it and i did it several times while repairing c/k trucks with a vortec..
i know it may not pertain to the 96 lt1 but i was telling her what it sounded like was going on to me.. they did have a 96 vortec engine also, when i get home from work i can punch in all the info on my ethos for a 96 lt1 and see if it gives me any "usual" known fixes for the problem

 

Right....on a '96-'99 VORTEC engine (which the OP does not have), there is a procedure for properly installing the distributor. That is not the same as "you need to let/ make it re-learn". The ECM isn't "learning" anything...you just have to install the part correctly. Anesthes and I just discussed all of that, in the posts immediately above yours.

The LT1 has no such set up procedure. You can only install the distributor one way (unless you berak something) and what the OP needs to do now, is observe the performance of the distributor, while the car is acting up.

Ethos is a good tool. I have one too.

 

yeah without it being connected to the car it is very limited info also, i just looked. like i said, i do not have much experience with an lt1 . so the lt1 engines do not have a cam sensor in the distributor that needs to be lined up a certain way like the vortecs? gm got all goofey in those years, why would they even make so many different set ups. then a couple years later scarpped it all for the ls base

 

They did what they had to do to meet criteria; they were still working w/the old architecture, but needed to meet criteria.

The early LT1's have the crank sensor and the cam sensor on the same "wheel", inside the distributor. All the info came from the dist. Later LTx's added a crank wheel for mis-fire detection. Still, those could only go together one way, so you still can't screw up the dist. installation. No special "lining up" needed.

The truck? IDK...I guess they had realized by that point that the optical wheel/sensor in the LTx was too susceptible to contamination and used a different system. It was probably cheaper too, since it used standard SBC items like that dist mount in the intake, standard timing chain/cover, block, cooling etc.

 

I'm still struggling with this. Other optical sensors in GM's last 30+ years. I've spoken with Matt Cramer about other applications (i.e nissan) that use optical sensors and never have problems. Yet people have optispark issues.

I'm kind of on board with the whole water pump leak issue - if the bearing fails (and they do) it will puke coolant out the hole and onto the optispark, but I'm confused as to how coolant is getting inside the unit. I've submurged these things as a test, then took them apart. They are sealed.

Then other people say "high voltage inside the unit takes out the optical sensor".. wtf ?

Then there are the theory's that only hitachi can make a good optical sensor. That's horse doodle. These are not complex devices.

I wonder if anyone has actually dissected a 'bad opti' with a scope and seen what exactly isn't working. What I have found to be suspect in these cars is the factory wiring. I've fixed more wiring problems on 4th gen fbody's and C4's than I can cound on all my fingers and toes. The grounds are always suspect as a start, but more than that wire corrosion within a few inches of the connectors. Strip back the wire on the IAC, TPS, ICM, etc and you'll find the conductors are corroded. Do a ohm test and they fail.

-- Joe

 

The two codes the OP is getting indicate problems on both the low-res and hi-res outputs from the Optispark sensor. The signals that go back to the PCM from the opti. Typically what seems to happen in these cases is that the car goes into a limp-home mode where it runs, but not as well as it should (I assume it has to at least be getting one of the two signals to run at any given time). I just went through this with a friend's 95. His original opti died outright, and he (his mechanic - he's not local to me) two replacement optis from Autozone, and both had faulty hi-res signals right out of the box. He sent his original dead opti to Optidoc who confirmed no signals coming out of the sensor at all. Meantime, the two Autobone units would allow the car to run, but as soon as the car went into open-loop it ran kind of badly - like the timing was soft...which is exactly what the computer was doing to keep it in a fail-safe, limp-home mode. In his case, the tach didn't bounce around, but keep in mind that he still had a good low-res signal and that's surely all the tach uses.

So in the OP's case, it sounds like the newer opti installed in her car does indeed have a failing sensor. Anesthes, the original sensors were Mitsubishi. I'm sure it's true that they aren't the only company that can make a decent optical sensor, but it does seem to be the case that most China-made replacements don't have good sensors for whatever reason. Supposedly the Petris and AIP replacement optis have better sensors in them. And Optidoc uses NOS or refurbished Mitsubishi sensors.

To the OP, if your car is running rough and missing, especially when it's still warming up, you're probably getting intermittent low-res signal. Whereas if it ran fine until warmed up and then just felt kind of low on power and "soggy," I would assume that hi-res signal is the main issue (note that you got codes for both signals). The fact that it's running at all tells me you must have at least one of the two signals at any given time. I would expect the tach to be acting crazy, like Tom mentioned, if the low-res signal is faulty. I'm afraid you're going to need to replace that opti again. If it were me, I'd insist on an AIP, Petris, or Optidoc unit. It seems like all the normal parts-store optis are just garbage.

 

where is the O.P.? No reply 3 days later and 1 post.......