Hey C4-ers, I have an 81 corvette with a 96 LT1 installed. Its smog legal and all engine wiring are connected. I completed the transplant last year and she's been running fine. Last Thursday I took it out in the rain for the first time. No problem while driving in the rain. About two hours of driving with no rain, she died. She would start again and die after a minute. I let it sit for about an hour, tried it again and it ran 3 minutes and died. I let the car sit three days. On the third day she wouldn't start at all. I flatbedded her home and she sat four more days and now the battery is dead. Put a full charge on the battery and she is running again. I let it run over 30 minutes and no problem. Prior to the problem, I received an O2 sensor code (sensor 2, Bank one) followed by a P0507 code (Idle problem) which I attributed to the bad O2 sensor. Does this sound like an Opti going bad? The Opti was brand new (AC Delco) when I installed and the car has less than 3000 miles on the transplant. If not opti, have any of you guys experience this? Appreciate the advise

 

Lots of C4 owners drive on the rain and dont have that problem. I wonder where you LT1 sits. Does the front of engine receives water splash from the tires? I would check all wiring connections to ensure they are dry before you start removing parts for a Opti inspection.

A bad O2 sensor code doesn't necessary means you have a bad O2 sensor.

Start with the coil and spark plugs connections at the opti.

I would not hurt to check the alternator, auto zone would test yours for free.

Do a search, there are thousands of Opti Threads in here.

 

Because it didn't fail in the rain while I was in it (for about 3hrs) but long after, i'm thinking it may be something else. But you bring up a good point about the location of my engine. A C3 was not designed to be opti safe when it comes to tires throwing up water from the rain. I will go thru the various checks but isn't it true that if the problem is Opti, its not going to get better? Its only a matter of time before I get a complete failure?

 

You didn't say anything about the car running badly when it does run, so I'll presume you don't have cross-firing in the high-voltage section of the distributor. You also said nothing about the ECM reporting Opti failure codes. For these reasons, I seriously doubt there's anything wrong with your Opti.

Employ standard troubleshooting procedures. First, determine whether the fuel supply is failing, or whether the ignition is malfunctioning. Then take it from there.

I'd start by putting a fuel pressure gauge on it, and watching what happens the next time it stalls.

Good luck with it.

Live well,

SJW

 

Wierdly enough my opti died the same way. On the way back from school the highways flooded about 4 inches of water which is a ton, and my opti surely got soaked, however the car didn't even stutter or die. 2 days later (the next time I drove it) it died after 30 minutes of driving. It would crank immediately but no fire, 2 hours later it started up but dies after 10 minutes.

How bad do you think the rain was? A lot of us drive in rain all the time, its just a matter of how many inches of water is piled on the ground. You mentioned a 96 LT4 which should have the vented optispark so moisture and light rain should be no issue.

 

SJW - your assumption is correct; she runs fine now that she is running - no misfire or rough idle. And I had no idea that there was a code for Opti failure. If there is, then I do not have an opti failure because I only have two codes P0137 and P0507. Thanks, that's good to know! I will start my troubleshooting after Christmas. It would have been easier if she was still dead.

Rinosaur - the rain wasn't bad at all. I didn't drive thru any puddles, just constant rain. But as I told PLRX, just driving my C3 could be spitting up more water on the opti than a 96 corvette does. and yes my opti is vented!

Thanks all for the expeditious replies. I will keep you posted.

 

Don’t go off on a tangent with the O2s, deal with the obvious issue of engine dying and no start. Clear the codes with your scanner (or software) and see if they get stored again. The O2 should not kill the engine.

In the mean time it sounds like the ICM could be causing your engine running problem. It's got the classic symptoms of it going bad. But testing the ICM this for this kind of condition will probably yield no positive results with an intermittent condition. I would consider replacing the ICM since it is not to pricy and an easy job to do. Of course the coil could cause similar effect but the probability much less.

At this time I would consider the battery issue a separate one. A light cold have been left on, who knows. If it persists, make sure all lights are going out and make a current measurement for battery when everything is off. Should be 50 ma or less. If you get 30-35 ma, it would be in the ball park.

Also as indicated already, make a fuel pressure check to make sure the pump is not dying on you.

 

There are two codes that indicate failures of the Opti. One for a failure of the high-resolution sensor, and one for a failure of the low-resolution sensor.

If only the high-res sensor fails, the ECM can still run the engine (albeit not quite optimally), as it will still receive the low-resolution camshaft position signals.

If the low-res sensor fails, the ECM will not even attempt to run the engine, because it has no idea whatsoever about camshaft position. Spark timing can't even be approximated without camshaft position information.

The absence of Opti codes pretty much exonerates the sensor side of the unit. The absence of cross-firing or misfiring pretty much exonerates the distributor side of the unit. Look elsewhere.

If the engine just dies, without any stumbling or misfiring, look for a loss of fuel pressure, a complete absence of spark at the plugs, or in rare instances, a massive vacuum leak (this is highly unlikely given the intermittent nature of your problem). Once you've isolated the fault to one of these areas, troubleshoot from there to isolate the fault to the specific failed component.

Live well,

SJW

 

I started it up again today and let it run 20 minutes, shut it down and when I went back to start up, it was difficult to start and when it did start it ran like crap, very rough. I shut it down and began to inspect and I found a vacuum line to the intake manifold disconnected. I connected the line and she started and runs smooth. However, I know have a P1371 code (high resolution sensor) as proffered by SJW and a P0372 (misfire) which I would expect since she ran rough. I cleared the codes and let it run for 20 minutes and it runs fine and no code.

My question (SJW) could the vacuum trigger the P1371 and now that the vacuum is connected, i'm good? Or did I only solve one problem with the vacuum and still have an opti problem?

By the way, I think I had this vacuum problem for over two months. Around the 1st of November, I went to turn my A/C on and air would not come out of the dash registries, only the floor. Whenever that happens, I know I have a vacuum leak somewhere. But I didn't worry about it because the cold season was approaching and i wouldn't be using the a/c. After connecting the vacuum line that I discovered today, the a/c regiters are working again. I bring all this up to say why would a vacuum leak take so long to affect the engine performance.

Whats making this difficult is that the problem won't stay around long enough to diagnose.

 

Congrats on finding the vacuum leak. One problem solved.

However...

You won't want to hear this, but DTC P1371 is the Opti low-res fault code. This means that either the low-resolution sensor in the Opti is failing, or that the signals it's generating aren't getting to the ECM. In short, this likely means either a wiring harness problem (check the condition of the connectors that are in-circuit with the Opti), or you need a new Opti. The odds tilt toward the Opti itself, but it could be a corroded or loose connection on the low-res signal line.

Good luck with it.

Live well,

SJW

 

OK, i'm ok with replacing the Opti if that the problem but why would it be so intermittent. Should I anticipate an Opti DTC code coming back soon if Optis is failing? And i know i'm reaching here but the could the vauum leak have caused the lack of low resolution circuit? I checked connections and they are all good.
.

 

is the opti hard to get to in the c3 chassis?

 

Solid-state electronic components often go intermittent as they start to fail, and their failure modes often have a thermal element to them. It's not uncommon for them to exhibit problems first at elevated temperatures. Vibration can also be a contributor to intermittent faults.

It most likely will.

No.

That's good to know, but it means that you almost surely will need to replace the Opti to make this problem disappear.

Live well,

SJW

 

Thanks SJW, I already went thru the analysis in my mind and came to the same conclusion. I was just looking to lie to myself and have you swear to it! :-).

I guess I need to get busy. I would hate to be somewhere far when the opti has a complete failure. There is a silver lining in this as I always wanted to add red spark plug wires to match the under hood theme of red and black.

Deepa - it doesn't appear to be that hard to get to. Remove CAI, water pump and there she is! Obviously, that was easy to type; hopefully just as easy to remove.

I'm going to build a type of under-panning to minimize water splashes. I have a 2003 Lexus LS430 and the bottom of the car is completely hid by panels.

Merry Christmas to you guys and thanks for the help!

 

You'll also need to remove the harmonic damper and pulley (but not the hub) from the crankshaft to get the Opti off. There's no better time to replace the plug wires than while you're doing the Opti.

Be sure the pan you're planning to install doesn't obstruct the airflow downward from the cooling stack, or the car will run hot.

Live well,

SJW

 

I didn't know the balancer and the pulley had to come off. Wow! I have the shop manuals for the 96; I will read up on it. I also have a friend who has a auto shop. If it looks to laborious, I guess I will help him with his kids thru college. Thanks again.

 

SJW - I went driving the car this morning, seven miles north on the freeway and then 14 miles south, (trying to stay within AAA 7 miles free towing if she dies). Anyway after 30 minutes, she died but here is the interesting part that I failed to mention when I first made the post here. It dies completely, no lights, no fasten seat belt, no check engine.

Anyway, I cruised over to the side of the road and waited for it to come to a complete stop. Tried to start it again and she starts, runs about 15 seconds and dies. I call AAA. While i'm on hold with AAA, I start it again and she's running fine while i'm on hold with AAA. I'm four miles from the house so I hang up and drive home with no problem. While the engine is running, I pull power to the fuel relay and she dies, but my check engine light and fasten seat belt light comes on. I connect the fuel relay back up and pull the distributor wire, and she dies, but my check engine light and fasten seat belt light comes on. Where i'm going with this is my failure is due to a complete loss of electrical power; not a loss of fuel (only) or ignition (only) indicative of no fasten seat belt or check engine light.

The way we wired my car when we installed the LT1 was my ignition switch in my car powers relays to drive the 96 system. The 81 system in the car is not FULLY integrated to the 96 wiring under the hood. By turning the key to "ON", I'm power relays to run the 96 system. (sounds complicated but we did it that way to make it easy to trouble shoot) Anyway, there is a main relay that i had trouble with when we first completed the transplant. We used too small of a relay. When that relay would get hot, I loss all power to the engine, no lights (no fasten seat belt, no check engine). I think that's my problem. Another fact that supports this assumption is I still have no DTC codes after she dies.

However, I don't believe this explains my subsequent P1371 I got last week (or does it?)

 

This is definitely getting a bit more interesting now. What you've described above might be explained by a loss of power or ground to the ECM.

If the ECM is intermittently losing its +12vdc power, or its chassis ground, I can imagine that it might also trigger bogus, phantom DTCs, so it's possible that your only problem is that you're losing power or ground to the ECM.

Definitely, check (and/or temporarily bypass) the relay you have in series with the battery feed to the ECM before you go any further, and also make sure all of the electronics that should be grounded are in fact well-grounded. Only after you know that all's well with these items should you begin looking elsewhere for any gremlins that might remain, if all's still not well.

If I were chasing this problem, I'd hang a temporary test lead on the switched side of the power relay, and monitor it with a volt meter while the car is running to see if the 12vdc at that location disappears when the engine dies. If it does, I think you've found your problem.

Live well,

SJW

 

After constant prayer and pain in my back, I found the problem. My power distribution was fine so i proceeded with the tear down of the components to get to the Opti. After removing the waterpump, I found the vacuum line for the Opti vent was pinched between the water pump and the block. (I didn't install it). It had a hole in it. (I wish I knew how to post pictures; I would show you guys the hole). I guess that day of driving in the rain I was sucking nothing but rain into the Opti. Although that's a bummer, i'm relieved to have found the problem and so gald it was an installation error rather than poor reliability of the LT1. I was starting to regret installing that engine. I haven't put the car back together yet as I decided to take care of an oil leak while I was in there. I can't tell you guys how much I appreciate the support of this forum. It is truly awesome to get this kind of support when chasing down unknowns! I will post again when she is running.

 

Congrats on finding the pinched hose. Here's hoping the new Opti will solve your problems.

LT1 engines are not inherently unreliable. Quite the contrary, in fact. They tend to be very durable engines. The Opti is the only questionable component in terms of reliability and durability, but even those can last quite a long time if they're kept dry. The later, actively-vented Opti such as your LT1 has, is a significant improvement over the first-generation, passively-vented unit.

Good luck with the project. Let us know how you're doing with it.

Live well,

SJW