LT4 O2 Sensors?
Thread Starter
Instructor
Joined: Sep 2009
Posts: 114
Likes: 16
From: NE Ohio
LT4 O2 Sensors? NOT!!!
I just got a lower mile (53k) LT4 running after 8 years of sitting dormant in a garage. I had all of the fluids, filters, and plugs changed before having it started. After an uneventful 100 mile drive home I parked it in my garage in order to make an appointment for new rubber this week. On the way to the tire shop today it started shuddering and running poorly. The check engine light came on. I was near my local parts store and headed right there for a diagnostic scan. When I got there the car had a "hot metallic smell" to it even know the engine temp was normal. The code reader showed that there was (1) an intermittent miss and (2) the O2 #1 sensors on banks #1 and #2 had extremely erratic readings. The other sensor read normally.
At pretty much the same time, it sounds like the inside of one of the resonators came apart inside and started rattling very loudly. Possibly, it's a cat, but it's hard to tell.
My guess is that bad O2's might have caused a rich enough mixture to blow out a resonator or cat. Does this seem reasonable?
.
I plan on changing both O2 sensors with the bad readings. Should I just go ahead and change the third as a precaution? Could bad sensors cause an intermittent miss code or should I go looking for ignition issues?
Thanks
At pretty much the same time, it sounds like the inside of one of the resonators came apart inside and started rattling very loudly. Possibly, it's a cat, but it's hard to tell.
My guess is that bad O2's might have caused a rich enough mixture to blow out a resonator or cat. Does this seem reasonable?
.
I plan on changing both O2 sensors with the bad readings. Should I just go ahead and change the third as a precaution? Could bad sensors cause an intermittent miss code or should I go looking for ignition issues?
Thanks
Last edited by meh92; Aug 15, 2020 at 05:09 PM.
Le Mans Master
Joined: Aug 2015
Posts: 6,118
Likes: 1,994
From: St. Charles MO
It is certainly possible that one or both upstream (before the cats) sensors was bad, caused rich running, and that caused one or both cats to come apart inside. The sensors after the cats have no effect on the way the car runs - they are only there so the PCM can detect a malfunctioning upstream sensor or AIR system. I'd change the two upstream sensors and then very carefully check both cats for internal failures.
Le Mans Master
Joined: Aug 2015
Posts: 6,118
Likes: 1,994
From: St. Charles MO
My guess is that you'll find that the car runs fine on cold startup because the PCM is in open-loop mode and ignores the O2 sensors. But once the coolant warms up enough for the PCM to go into closed-loop mode, it start relying on the sensors to meter fuel properly and the mixtures goes haywire based on bad data from the sensors.
Thread Starter
Instructor
Joined: Sep 2009
Posts: 114
Likes: 16
From: NE Ohio
My guess is that you'll find that the car runs fine on cold startup because the PCM is in open-loop mode and ignores the O2 sensors. But once the coolant warms up enough for the PCM to go into closed-loop mode, it start relying on the sensors to meter fuel properly and the mixtures goes haywire based on bad data from the sensors.
Thread Starter
Instructor
Joined: Sep 2009
Posts: 114
Likes: 16
From: NE Ohio
I went digging through a box of parts and tools that wen along with the car looking for any spare O2 sensors and came across a Snap On MT2500 scanner. It has the correct cartridges, key, and ODB-IIB connector so over the weekend I'll hook it up and see what it says. That was a nice find.
Corvette Stories
The Best of Corvette for Corvette Enthusiasts
Top 10 Most Expensive Corvettes Ever Sold on Bring A Trailer
Brett Foote
10 Things Every Corvette Owner Needs (2026 Edition)
Michael S. Palmer
8 Most "Only Corvette Owners Understand" Quirks and Problems
Pouria Savadkouei
10 Reasons the C6 Z06 is Still A Performance Benchmark After 20 Years
Joe Kucinski
How Much Horsepower Every Corvette Engine "LOST" in 1972
Joe Kucinski
Top 10 DOs and DON'Ts for Protecting Your Convertible Top!
Michael S. Palmer
Top 10 Most Explosive Corvettes Ever Made: Power-to-Weight Ratio Ranked!
Joe Kucinski
150 hp to 1,250 hp: Every Corvette Generation Compared by the Specs That Matter
Joe Kucinski
8 Coolest Corvette Pace Cars (and Replicas) of All Time
Verdad Gallardo
Race Director
Joined: Sep 2001
Posts: 14,680
Likes: 752
From: NEwhere Ohio
I just got a lower mile (53k) LT4 running after 8 years of sitting dormant in a garage. I had all of the fluids, filters, and plugs changed before having it started. After an uneventful 100 mile drive home I parked it in my garage in order to make an appointment for new rubber this week. On the way to the tire shop today it started shuddering and running poorly. The check engine light came on. I was near my local parts store and headed right there for a diagnostic scan. When I got there the car had a "hot metallic smell" to it even know the engine temp was normal. The code reader showed that there was (1) an intermittent miss and (2) the O2 #1 sensors on banks #1 and #2 had extremely erratic readings. The other sensor read normally.
At pretty much the same time, it sounds like the inside of one of the resonators came apart inside and started rattling very loudly. Possibly, it's a cat, but it's hard to tell.
My guess is that bad O2's might have caused a rich enough mixture to blow out a resonator or cat. Does this seem reasonable?
.
I plan on changing both O2 sensors with the bad readings. Should I just go ahead and change the third as a precaution? Could bad sensors cause an intermittent miss code or should I go looking for ignition issues?
Thanks
At pretty much the same time, it sounds like the inside of one of the resonators came apart inside and started rattling very loudly. Possibly, it's a cat, but it's hard to tell.
My guess is that bad O2's might have caused a rich enough mixture to blow out a resonator or cat. Does this seem reasonable?
.
I plan on changing both O2 sensors with the bad readings. Should I just go ahead and change the third as a precaution? Could bad sensors cause an intermittent miss code or should I go looking for ignition issues?
Thanks
the spark plugs were those ngk iridium types with tiny Easy to foul up electrodes
so i dont run any ‘platinum’, ‘iridium’ or the gimmick plugs anymore
Le Mans Master
Joined: Mar 2006
Posts: 5,775
Likes: 585
From: Texas
On a car that hadn't been started for 8 years, you might also check around the intake manifold for cracked vacuum lines. The rubber elbow on the passenger side of the throttle body has a bad habit of cracking on the inside of the elbow where you can't see it.
Safety Car
Joined: May 2001
Posts: 4,759
Likes: 1,647
From: Fairfax Virginia
Being a big believer in the virtues of a "Functional Oxygen Sensor" I would seriously think about replacing all four at one time. If one side has failed you should replace all of the Oxygen sensors at one time. These little buggers are critical to the proper running of your LT4. They get expensive when you buy four at a time but that is a small tax on the fun you have with your LT4! The OBD1 Oxygen sensors were designed for a 24 months or 50k miles. OBD2 goes to 48 months and 100k miles.
I like going to someplace that sells a lot of parts and has a constantly changing inventory and buy the O2's from them. I gave ordering online after paying for 4 brand new Bosch Oxygen sensors and getting 3 that worked. Be sure to buy them from somebody who will take back defective units and replace them.
Those Iridium Spark Plugs work well for me on my daily drivers but when I tried them in my 1968 C3 427 they quickly started getting fouled out. The newer engine burn less oil than they did in the old days. The C3 had just been started recently and had about one ounce of thin motor oil added to each cylinder prior to starting. I cranked the engine with oil in the cylinders with the spark plugs out to clear it out. Fortunately it is easy to get to all eight plugs from above. And they are cheap...
I like going to someplace that sells a lot of parts and has a constantly changing inventory and buy the O2's from them. I gave ordering online after paying for 4 brand new Bosch Oxygen sensors and getting 3 that worked. Be sure to buy them from somebody who will take back defective units and replace them.
Those Iridium Spark Plugs work well for me on my daily drivers but when I tried them in my 1968 C3 427 they quickly started getting fouled out. The newer engine burn less oil than they did in the old days. The C3 had just been started recently and had about one ounce of thin motor oil added to each cylinder prior to starting. I cranked the engine with oil in the cylinders with the spark plugs out to clear it out. Fortunately it is easy to get to all eight plugs from above. And they are cheap...
Thread Starter
Instructor
Joined: Sep 2009
Posts: 114
Likes: 16
From: NE Ohio
That makes sense and I suppose I don't mind the extra expense. It's a project car so it will give me and the boy something extra to do together. First things's first though, I want to throw the scanner on the car and see what it says.
What sensor manufacturer is recommended? It's an unmodified weekend and track day toy. Of course, if I blew out a resonator (hopefully not a cat), I suppose I'll need to upgrade the exhaust with a nice new system.
What sensor manufacturer is recommended? It's an unmodified weekend and track day toy. Of course, if I blew out a resonator (hopefully not a cat), I suppose I'll need to upgrade the exhaust with a nice new system.
Last edited by meh92; Aug 13, 2020 at 02:10 PM.
Le Mans Master
Joined: Aug 2015
Posts: 6,118
Likes: 1,994
From: St. Charles MO
Being a big believer in the virtues of a "Functional Oxygen Sensor" I would seriously think about replacing all four at one time. If one side has failed you should replace all of the Oxygen sensors at one time. These little buggers are critical to the proper running of your LT4.
That said, there's no reason not keep them maintained as well as the fronts. They aren't really that expensive, and avoiding a DTC is a worthy goal - especially if you have to pass a scanned emissions test. The alternative is to purchase expensive tuning software (Jet DST) to turn off the relevant diagnostic tests and tell the PCM not to report on them. But that's far more costly than just replacing the sensors.
Originally Posted by meh92
What sensor manufacturer is recommended? It's an unmodified weekend and track day toy. Of course, if I blew out a resonator (hopefully not a cat), I suppose I'll need to upgrade the exhaust with a nice new system.
I've had NGK recommended to me by a friend who does a ton of automotive electrical work. I believe Denso are pretty good too. I would stay away from Bosch - their electrical parts seem to have high failure rates.
Last edited by MatthewMiller; Aug 17, 2020 at 01:11 PM.
Thread Starter
Instructor
Joined: Sep 2009
Posts: 114
Likes: 16
From: NE Ohio
Problem found!
Well, the O2 sensors might still be good and they might not be, but it's not going to matter with the #6 wire melted onto the exhaust manifold!!! The wires have the cylinder # on them so I suppose they could be original. That explains why it didn't have to warm up to run poorly. It's a shame it took some of the exhaust with it, though.
Le Mans Master
Joined: Aug 2015
Posts: 6,118
Likes: 1,994
From: St. Charles MO
Thread Starter
Instructor
Joined: Sep 2009
Posts: 114
Likes: 16
From: NE Ohio
Le Mans Master
Joined: Aug 2015
Posts: 6,118
Likes: 1,994
From: St. Charles MO
Last edited by MatthewMiller; Aug 17, 2020 at 01:31 PM.
Thread Starter
Instructor
Joined: Sep 2009
Posts: 114
Likes: 16
From: NE Ohio
Thanks, I'll give them a try. I planned on just doing the two upstream but also saw this kit.
They look like two different types for upstream and downstream. Can you help with clarity?
They look like two different types for upstream and downstream. Can you help with clarity?
Last edited by meh92; Aug 17, 2020 at 01:35 PM.
Le Mans Master
Joined: Aug 2015
Posts: 6,118
Likes: 1,994
From: St. Charles MO
Thanks, I'll give them a try. I planned on just doing the two upstream but also saw this kit.
https://www.amazon.com/234-4012-asce...7685477&sr=8-3
They look like two different types for upstream and downstream. Can you help with clarity?
https://www.amazon.com/234-4012-asce...7685477&sr=8-3
They look like two different types for upstream and downstream. Can you help with clarity?
