My 95 lt1 been running rich ever since i purchased it about 4 months ago. My avg mpg in city goes from around 11-13 mpg if given the info is still accurate after 24 years. I had just changed the pcv and plugs and was wondering if maybe a pcmforless tune or if i buy an aldl cable to edit pcm files etc would help the car run a bit better. Any help is appreciated thanks!

 

I would start by giving it a tune up, including O2 sensors. I'd also put an OBD 1 scan tool on it to look at sensors and see if the "jibe" with what they should be showing.

I can't fathom why you'd need an ECM tune.

 

Thanks for the info!

 

I agree with Tom on that - you need to work a good diagnostic regimen rather than try to tune the PCM. Just FYI though, if you ever do want to fiddle with the calibrations in the PCM, you can get a package from Tunercat that includes the cable and software required to do that. It works very well, and your PCM is very tunable.

 

I also agree with Tom and Matthew! Your oxygen sensors have a limited life and when they fail they start to lag time wise and that really screw around with your fuel system. I would either test your or just replace all of them with good quality replacements. There are ways of testing them but you need a scanner to see it work properly. I use a multi meter and watch for a fast oscillating between .1 and .9 volts DC.

Does the LT1 have Coolant temperature sensor similar to the one on the L98 engines? Sometimes it is possible that the car thinks it is colder outside and will add fuel to compensate. I am NO EXPERT on the LT engines but that happens frequently enough on the older L98 cars.

Good Luck and Welcome to The Corvette Forum!!

Best regards,
Chris

 

Yes it does. It has one in the water pump to talk to the PCM. There's one in the passenger-side head too, but it's only for the analog gauge and doesn't affect the way the car runs. But the one in the pump will sure affect things. It also gives the digital coolant temp readout its info. I would think that it could be diagnosed easily by comparing the digital temp readout with the analog, or just what one would expect for a warmed up coolant temp, but I'm not sure of that.

 

Thanks for the help everyone! I got around to scanning the car and found these codes:

It is a 95 vin p car.

DTC 13 – Bank 1Left Front) Heated Oxygen} Oxygen Sensor (H02S) #1 Circuit (Open Circuit)

DTC 23 – Intake Air Temperature (IAT) Sensor Circuit (Signal Voltage High,

DTC 29 – Secondary Air Injection (AIR) Pump Circuit

DTC 44 – Bank 1 (Left Front) Heated Oxygen Sensor (HO2S) #1 Circuit (Lean Exhaust Indicated)

DTC 78 – Fan Control PCM Terminal “Al0”

Im not sure why i thought a tune would help with it running rich or lean. Looks like we found the culprit haha. But i do think ill buy a cable and use tunercat/eehack to change my fan temp settings my auto trans does tend to get high up there hitting 230 on a hot day. Also being in socal with it being 100+ doesn't help much lol.

 

The ones in bold are the ones that have the most influence over your symptoms.

 

O2 sensors

Dont use bosch auto store garbage

try to find NOS acdelco’s (not the new made in china ones)

 

I'll add to the above with getting those O2 sensors replaced. There are some people that say they are lifetime parts but they will degrade over time and if yours are the originals they are 24 years old. Physical age has a large impact even if there are low miles.

Some clarification on this one, Bosch sensors claim they are OEM spec but they are not always calibrated right. You can get good ones but the vast majority will be worthless trash. the NOS/ACDelco are much better at getting factory specs right. The Chinese ones work okay for a short time but they seem to burn out and fail quickly so you would be back in the same predicament. If you can find the American ones somewhere they will last a long ways.

 

I have never heard of a Lifetime Oxygen sensor!!

I was taught that they HAD to be replaced at 50 k miles or 2 years. Oxygen sensors DO wear out and the time it takes may vary but the result will be the same. I use a wide band on my 1968 C3 BB and as long as I am careful with my fuel additives the O2 will work okay for me. If I put tetra-ethyl lead into the fuel the sensor would not survive the tank of fuel. Always check that your fuel additives are okay to be used with O2 sensors.

The newer cars all use the heated O2's farther downstream in the exhaust flow where it is not so hot. End result is they last longer and work better and are so reliable that people forget about them and assume they last forever.

If the O2 was new and installed 5 years ago it is a 5 year old O2. If the 02 was installed yesterday and it was made in 2014 it is still a five year old O2 sensor. I do not stock O2's in my garage as I want the freshest newest ones I can get on my cars. I have also seen way too many defective "New O2 sensors" for my lifetime. They are expensive and cars today use a lot of them.

On all the C4's it seems the O2's are critical to good clean performance and when they start to go bad it takes people a while to replace them. I suggest people test them or replace them as one of the first items when they have issues with the fuel system. I read that you can test them by adding different fuels into the intake air (like Propane) to make the O2 react and you can watch it work. I am not an expert on these tests so I recommend those interested read in you FSM about the O2's and testing them.

I also suggest people leave the little plastic cover over the O2 sensor's tip while working with the O2 sensor. That cover is there to minimize corrosion on the sensor and will protect it and make it last longer. I only remove the cover right before I install the new O2 sensor.

Most O2's come with their own anti-seize, don't wipe it off as it is critical if you ever plan on removing that O2.

best regards,
Chris

 

I've had my '93 for about the same length of time you've had yours and the the guys that have been helping you have helped me as well. Lots of good advice here.

If you haven't done so yet get a manual, either paper ($$$) or on CD ($) and start reading about your engine control system. I read here about a phone based app called ALDLDroid to gather real time data from the ECM. I bought a blue tooth dongle to plug into the under dash connector, got it off eBay. I've been pestering these guys with my log files and they've been making suggestions about what I should test based on the logs.

 

Or maybe they just want to assume it lasts forever like the brake fluids so they don't have to spend money till it breaks. Of course, before it breaks, it will nickle and dime them literally, simply because the fuel mixture is less controlled. $200 out today is more painful than $1 every day for a few years.

I'm honestly interested how we can do that? Is there a way we can buy it off the factory floor that you can do as a shop?

IF you graph a newly installed sensor under certain conditions, would that work as a baseline? So say 70 degrees ambient, engine coolant at 180 and you log the O2 response and save it. 3 years later, repeat experiment and if the graph shows significant difference, say it switches 20 times more than when it is 3 years old, you condemn the sensor?

 

I wish there was a way to verify a O2 "easily". I would probably need an oscilloscope to see the differences between a new one and an old one. It has to do with how fast it goes from lean to rich and how much time it takes it to do it.

As the sensor ages the upper and lower numbers are not read as fast and there lies the problem. The only solution is a faster reading new O2. With all the technology changes in O2 sensors it might be smart to update our Corvettes to a newer Heated O2 that is farther sway from the extreme heat.

You are so right about the brake fluid! I remember an idiot trying to sell me a 1990 Pontiac Grand Am at a dealership when new. I could not see the spark plugs and wondered where they hid them. The dealer walked up and told me to my face that "they don't use spark plugs any more in the Pontiac engines". I laughed and asked him when they went to diesel engines as I was heading out the door as quickly as I could. I guess this is why people are buying all the maintenance on their car at the initial purchase today more and more. My wife has her VW maintenance all paid for up to 125,000 miles as part of the purchase price. By the way, it does not include brake fluid flushes when I read the paperwork. Another useless warranty as far as I am concerned.

Unfortunately I think that a lot of the problems we see here on the forum regarding the fuel system are related to O2 sensors being "not quite new".

As per buying good fresh O2's I shop at the central warehouse for my local NAPA chain, the turnover they have on parts is pretty impressive. You must have a better connection someplace higher on the food chain for auto parts.

I am grateful nobody did a baseline on me when I was younger, I certainly have more lag... and a few misses every now and then.

 

IF you have the software, IIRC DIACOM did allow you graph a value (TPS, CTS, etc) over time so you can do a 30 second snapshot and see what it is at idle and look at the peaks and troughs? Probably right that the effort isn't worth it. Just dump the sensor.

I suppose you can do a heated O2 sensor AND also move it away from it's current location. IIRC, I put a switched positive from one of my emissions leads as a power source. My sensor is further down but that is because I have LT headers and that is where TPIS puts it but if desired, I suppose welding a bung further down is an option. Makes it easier to get to for changes.

Refresh my memory. Was there a Pontiac engine anymore at that time? I thought the last one was on an 81? I bought my own flusher and do it on all 5 vehicles every even year. Takes me a day to do all 5 plus a couple of ATVs and a trike. I'm surprised at VW though. I would have thought that would be in their service spec? I know it is in MB spec.

The exact term IMO is "Not broke". If it ain't broke, it's good and we don't need to replace.

Good to know. I see a lot of O2 sensors with dusty boxes at the local parts stores so I'm kinda wondering how long it has sat when you mentioned it.

Statute of Limitations as far as I am concerned.

 

Hello again Aklim!
You might be right about the Pontiac making their own engines as the one I bought was a Quad Four rated at 180 hp made by and for Oldsmobile if I recollect properly. It was a dual overhead cam with the spark plugs down several inches into the cylinder head. It was a great design but executed poorly. I had one of the darn plugs break off at the threads which was a real nightmare. It was the original plug from the factory and I am not sure what they put on them but #4 would not come out until it broke off.

Using an oscilloscope would also give you a great picture of how the O2 is working. I have been reading more about O2 failure modes. It seems that they also don't get to the peak voltages after getting older so they don't measure the entire waveform after starting to fail. Then they also start to lag as they age which is the major problem for most people. What is DIACOM? The machine that replaced the Snap on MT 2500 had the ability to graph things on the screen from what I have read. I am stuck using an oscilloscope for the time being.

There are people who wait for things to break and replace them and then there are people like me who will replace a working part to prevent a breakdown. Probably has something to do with my being a Pilot and spending a lot of hours with my mechanic working on my Cessna. Nothing worse than having something break at the worst possible time.

Brake fluid is very important to keep fresh. I too have a tool that allows me to flush the fluids out in a hurry. I do mine every five years no matter what. I was surprised as the Germans are usually pretty complete on their service visits. They replaced my rotors with every brake change but never flushed the fluid on a 2004 Passat my son drives. I had to ask to have it done and I paid the price ~ $100 for the flush. It is cheaper to flush the anti-freeze....

The O2 sensors that have been made the past few years all have the protective cap on them which had a grease seal keeping air from entering the tip area. This is supposed to prevent any corrosion from forming before it is put into use.

How often do people replace their radiator caps? Such a simple action can save your engine from a bad boil over. Radiator caps age and loose their ability to hold 16 lbs pressure and then you are in danger. The anti-freeze is not what gives you the 260* of protection, it is the 16 lbs of pressure inside your cooling system. A bad $10 radiator cap can cost you a pair of cylinder heads, is it worth changing?

Anti-freeze is another item that wears out and is frequently not replaced until there are problems. How about the rubber lines that connects the caliper to the brake system? DOT said they have a life span of 10 years, maybe 15. How many people are driving on hoses that should have been replaced? I have the SS braided D.O.T. Approved hoses on both of my Corvettes. If they are not D.O.T. approved you might not get any insurance money after an accident. Kind of important I would say.

Owners of todays vehicles have become lazy and most have no idea how the vehicle works. I would like to help inform our fellow Forum members about these pieces and when to change them.

I just had my RV with it's Ford V-10 serviced, I replaced all the O2 sensors on the vehicle as I don't want to have one drop out on my while on the road. I also replace my perfectly good (looking) tires on my RV at 6 years Just to protect my family. Why take risks? When I raced motorcycles I used to remove entire top ends and replace them between races. I threw away a lot of serviceable parts back then but only so they would not fail in the midst of a race.

When I built my BB 427 up for my C3 I replaced my crankshaft due to small (invisible to the naked eye) cracks that showed up when magnafluxing the parts. I purchased and returned 9 crankshafts before finding one with no cracks at all. I won't compromise on some things. Maybe this is why I did 99% of all the maintenance on my own aircraft, because my mechanic "knew" how I was. She would sign off that she did the work herself after checking my work. My mechanic "Trusted Me" and that was very important to me. While working I had the manufacturer of small diesel Engines in England call me to ask me questions about diesel engines, it impressed the hell out of my boss.

My philosophy in life is still "Keep It Simple Stupid", I just don't like surprises.

Nice chatting with you and the rest of the folks on the Forum!

Best regards,
Chris

 

https://www.rinda.com/acro/dcmstd.pdf

I'm not a pilot but I'm pretty sure that in the air, you can't pull over and pop the hood and see what is going on.

https://www.motiveproducts.com/colle...r-bleeder-kits with adapters as needed

It's cheap enough that before the car is road worthy, after a flush, a new cap goes on. I do this ever 3 years. MB is ever 3. Didn't know VW was 5.

Getting money after the accident is good. NOT getting into the accident, way better. Besides, you got to be alive to collect.

I think they want to go for the least maintenance and the Domestic dealerships also use it as a selling point. MB doesn't talk too much about it but they do suggest it at service time and the customers, more often than with Domestics, or at least, that is what friends who worked in both places tell me, agree to it.

IIRC, Paul walker with a Porsche and 9 year old tires might agree that newer tires might have mitigated some of the accident.

That many bad ones? Shocking. 1 or 2, sure. 9 in a row?