My 93 LT1 with 154,000 miles has started to idle rough with some sort of ticking noise going on. The car cruises just fine with no exhaust smoke. After a while, the SES light goes on. But it resets after I shut the car off. Does this sound like a prtially clogged fuel injector?

 

While a clogged injector MIGHT be a possibility, I have my doubts. If you're getting a SES light, you'll definitely want to find out what code is being thrown. Are you familiar with using the "paper clip" method of getting the codes from your car's computer? If not, read this: http://www.corvettepics.net/misc/ccm-codepull.pdf. Write down any codes that you have stored and post them back here.

Ron

 

I have had this vette for 9 years, so this is embarassing- where is the module located that I put the paper clip in?
Thanks

 

OK- I spotted it under the dash- I will give it a shot this weekend and report the numbers back

 

OK- I did the paperclip thing on my ecm- here are the codes: 74, 32,44
It looks like the 44 is the issue "left oxygen sensor lean". Does that mean I need to replace the sensor? I think that might be the case, I suspect that the sensor might have broken, because I have some excess exhaust noise going on. Please advise- Thanks

 

The code 44 doesn't necessarily mean that the 02 sensor needs replacement, although if you are at 150k on the clock and if your 02 sensors are original, you might want to consider doing that just the same. That code just means that the sensor is picking up a higher level of oxygen in the exhaust on the left side indicating a lean condition. This could be caused by any number of things. A vacuum leak, an exhaust leak BEFORE the 02 sensor, or low fuel pressure can all cause a lean condition. The strange exhaust noise is likely just the result of the lean condition. The code 32 that you are also seeing could actually be very key to your problem. This code indicates a problem with your EGR system, in specific, a potential problem with your EGR solenoid. The EGR solenoid uses vacuum from the intake manifold to operate the EGR valve based on directions it receives from the ECM. When the ECM wants the EGR valve to activate, it will energize the solenoid, which then opens and allows vacuum from the intake manifold to flow through the solenoid to the EGR valve, thus activating it. The EGR solenoid is located under the driver's side fuel rail cover, along side the intake manifold near the firewall. There is a vacuum line that comes out of the intake manifold in a "T". One side of the T runs back toward the firewall, makes a sharp bend, and attaches to a small vacuum block that in turn is attached to the EGR solenoid. The other side of the block has a short vacuum line that runs to the EGR valve, right behind the intake manifold. I'd start there, checking to make sure that that vacuum line isn't broken or disconnected.

I'm also dealing with the same code on my car. I've done extensive troubleshooting and about the only thing that I haven't verified is the ground connection for the ECM on my engine block, which I'm planning on doing next week when I can get the car up in the air. This is a large bolt just above the oil filter. The negative battery cable, as well as the ground for the 02 sensors and a couple of other ECM grounds connect there. If those connections get corroded, it can cause strange things to happen with your 02 sensors, including a lean code (44). That's something else you might want to check, however, I'd initially focus on the EGR system.

Do you have the factory service manuals for your year of Corvette? If not, I'd highly recommend getting them. I know they aren't exactly cheap, but being 17 years old and with 150k on the odometer, your car is likely going to be needing some mechanical TLC over the coming years, and if you're planning to hang on to her, the FSM and a few basic troubleshooting tools (i.e., fuel pressure gauge, vacuum gauge, hand vacuum pump, digital volt/ohm meter) would be a wise investment.

 

OK- I checked out all vaccuum line under the drivers side fuel rail area. _ I had replaced the PCV and line to that a couple of years ago. Every thing else is intact and healthy- I pulled and inspected them all. So- exactly where is the left O2 sensor located? I guess I will try that next.

 

The 02 sensors are installed in the exhaust system on either side of the car. You'll need to get underneath the car to see them. If you follow the pipe coming down from the exhaust manifold, just after where it makes the bend toward the back of the car, you will find your 02 sensors, one on each side. Each sensor will have an electrical connector, and the wire will run back up to your ECM. Unfortunately, removing an 02 sensor, especially if it happens to be original, can sometimes be a bit of a challenge. I farmed that job out to my mechanic, and I'm glad I did. He ended up having to drop the exhaust system from the manifold back to the catalytic converter and heating up the sensor with a torch in order to get one of my sensors out. There is also, supposedly, a proprietary wrench that is used to install/remove them, but I have no experience as such. Just wanted to give you a heads up on that. Who knows; yours might pop right out with no problems.

In that same document that showed you how to pull the codes with a paperclip, there are instructions for clearing the codes. You might want to try clearing those codes and drive the car around for a bit and see if your SES light comes back on. I'm still a little leary of the EGR solenoid. You no doubt saw it when you were checkout out the vacuum lines. Double-check the electrical connector that goes to it and make sure it is properly clipped on. Since your problem is only happening at idle, and since you did get a code 32, you could be looking at a situation where you are getting EGR flow at idle. There should be no EGR flowing to the intake manifold at idle, but if your solenoid and/or valve is malfunctioning and somehow sticking open, that'll definitely cause the symptoms you are having. Do you know if the EGR valve is original? The EGR valves can get gummed up with carbon deposits and start getting stuck. If yours is 150k miles old, it might be in need of cleaning or replacing.

 

OK- instead of resetting the codes, I just disconnected the battery and reconnected. When I started in up aggain- 90% of the rough idle was gone! I will drive it around a little and see if I get the SES light. Maybe the computer was feeding bad information?

 

The computers on our cars have a "learn" function, that keeps track of various things, primarily air/fuel ratio adjustments that it has made. By disconnecting the battery, you erased all of that, which is okay. The computer will start fresh and as you drive the car, it will re-learn everything it needs to. However, I'd be surprised if just disconnecting the battery for a while clears your issue permanently. BUT, there's always that chance!

Let us know how it goes.

 

Although the car continues now to idle ok- the SES light came on- the only code being thrown (aside from C12) is C44- Left O2 sensor lean.
any comments? Thanks

 

Glad to hear that you at least have a good idle again!. I would say that at this point, the only way you're going to be able to completely diagnose the lean condition will be to get the car hooked up to an OBD-1 scan tool and look at things such as block learn modifiers (BLM), integrators (short term fuel trim), MAP sensor voltage and 02 sensor activity. A lot of people on this forum, myself included, prefer to diagnose the root cause of a problem by testing various components, rather than to just begin replacing parts blindly in hopes that you happen to replace one that corrects the issue. For doing this, you'll either need a scan tool and the various tools I mentioned earlier, or you'll need to take the car to a reputable mechanic. In this case, you shouldn't necessarily need a Corvette "specialist" since the LT1 was installed in a number of cars other than the 'Vette.

The FSM for my '92 (pretty much the same as your '93), lists the fuel filter, MAP sensor, and potentially, the 02 sensor as a cause for a code 44. Since you've had the car for nine years, and if you've never replaced the 02 sensors or fuel filter and would like to try doing some basic maintenance first and perhaps solve your lean condition at the same time, I'd start by replacing those components.

 

It turns out that I have an exhaust leak! That is why I am getting a lean reading! Now going to a muffler shop!

 

EXCELLENT!!

In fact, that was one of the other things that the FSM mentions as a cause for a lean condition.

Now, if you wouldn't mind answering a question for me, how did you come to find the exhaust leak? I have a suspicion that I also have an exhaust leak, but I haven't the faintest clue as to how to locate it!

 

Well, I took the car to my mechanic with the intention of having the O2 sensor replaced. When they got it up on the lift, they discovered a large leak, although not being exhaust specialists, they could not repair it. So, on to the muffler shop! Here is the good news, The bracket had loosened where the exhaust manifold hooks to the left cat, all it took was a new bracket and nut!

 

How many miles on the car? Those O.E.M. stainless steel exhausts aren't leak prone are they? I've got more than 120,000 miles on my car and the stock exhaust is leak free.

 

154,000 miles- you are correct- as I mentioned, there was no real leak, just a loose fitting.