3D-Aircrew

I searched the topic and the racers swear by it. I hear 105-110 octane. I'm pretty sure my engine knocks even on 93 Octane so I was thinking of putting a 1/4 tank of E85 on top of 3/4 tank of 93 octane. I'm thinking I have carbon buildup on my pistons and valves which causes knockand hope the higher % alcohol fuel would clean that up. Who here is currently running any % of E85 in their early C4 and what challenges would I have to deal with?

BLUE1972

Two friends are running E85 but using carbs.

Just be aware any rubber parts. "O" rings etc that were not designed for E85 will not last long.

You would have to do the research as to what may fail.

bjankuski

The real problem you will run into is the tune. E85 uses about 33% more fuel to run at the proper AFR and your stock tune was not designed for that additional fuel volume so it could set a check engine light. I am running E85 in my 1986 and have been doing so for 5 years and have had no issues with any of the fuel system components failing, but create my own tunes and have added extra fuel to accomidate the richer running AFR required for E85.

FYI, My 1986 with cats iron heads would ping on 93 octane fuel, the only way it would not ping was by keeping the operating temperature at 190 degrees or less. The car was maintained properly it just had a tendancy to ping. I have owned the car for years and it is no longer anywhere near stock but i still run E85 for the extra power it can provide. (I assume you know that E85 will reduce your gas mileage by about 33% in an otherwise stock engine designed for gasoline)

aklim

If you have multec injectors, it will accelerate the dying process. If you think you have pinging, maybe you need to ask yourself how you know this. The ECM will retard the timing so if you aren't scanning, how do you know it pings? If you can hear the ping, something is drastically wrong. Also, if you think there is carbon, maybe a boroscope will help instead of just assuming what it is and tossing something that may or may not fix the issue?

3D-Aircrew

I'm pretty sure I don't have multecs. I know it pings because I hear it when i get on it but I need to run some data logs with tunerpro and see if it is pinging otherwise. I'm a grandpa now and I drive like one unfortunately.

3D-Aircrew

So my plan was to mix it and run something that would be like a tank of E30 to clean things up.

aklim

I hope not since it might mean that the system is so far out, there is no way the ECM can compensate for it which makes me wonder. Last time I had that issue, we dumped the thickest oil in it and either Motor Honey or STP or something and it worked. Problem is, that mean the engine was making so much noise, it was toast.

3D-Aircrew

I just changed my plugs last weekend and from what I could see with my mirror the top of the one piston I could see was blackened. I'm pretty sure my heads are like that too. Pulling the heads and freshening it up is not in cards right now and I don't like that seafoam stuff so I thought I try a stronger mix of alcohol in my fuel to clean it up. I think starting from a 1/4 tank of E85 on top of a 3/4 tank of 93 I think is a good compromise. That's why I was looking for input from guys who ran E85. I have about a week to think about it until my tank is down 3/4.

vader86

If you want to run higher than E10 you need to go through the whole fuel system and see what rubber needs replacing.

If you tune to E85, then put in E10 in a pinch, your tune will be all whacked up. I think you manually putting in 3/4 tank of E10 and then E85 to fill is begging for problems with how the car runs normally. Tweak the tune for one fuel or the other, not both. You don't have the E85 sensor in the car.

Bad Karma

If the whole point of this is to clean up the fuel system, I would go with fuel system cleaners instead. Techron, seafoam, Red Line, etc, plenty to choose from.

3D-Aircrew

I read somewhere from one of the racers that the E85 kept the heads and pistons really clean ... your probably right.

aklim

Every piston top will be black so look for hot spots

JackDidley

All of the above is true. I ran E85 in 87 for 3 years, no problems. If you do this, put a couple gallons in a fill up and datalog. It will tell you how lean it is. You can probably adjust fuel pressure to compensate. Also get a % tester so you know exactly what you have. Around here in the winter its only 75%. I did it and probably got to near 40% before I had to tweak the tune. I really liked the E85 but is just too hard to find around here.

3D-Aircrew

I don't have an adjustable FPR but I do think some data logging is in order. This weekend I plan on doing some testing and I will post what I find especially knock counts, IAC steps and O2 sensor.

Red 91

If it was mine I would check the knock sensor and egr system. Good Luck!

KyleF

Racers swear by E85 because the added octane allows for more aggressive timing curves and boost. It also requires more fuel as mentioned above. At first, I thought a lot were just using E85 as a crutch in place of good tuning, but discussions with a few know tuners showed me otherwise.

Also, unless you drive your car frequently and use a lot of gas, you should know alcohol fuels are hygroscopic, it will absorb moisture from the air. It will eat O-rings and any other seals more aggressively than conventional fuel. A lot of good points made in this thread.

Instead of running fuel you weren't designed to use, changing fuel pressure, and possibly getting a tune... and a host of other problems that may occur, I suggest you spend more time getting to the root cause of the ping.

Start with the basic health. Base timing, IAC settings and cleaning the passages, TPS Voltage, Fuel Pressure (Under load not just idle), what are your BLMs and cross counts? You may be pinging because you don't have enough fuel in upper RPMs that doesn't show up.

Depening on your mileage, your timing chain could have slack and may not be keeping the timing accurate... could be a host of things.

Also, as far as the carbon build up, keep in mind that most fuels have detergents built in and deposit controls built in. Every engine with any miles on it will have some. I would not go down the path you are on unless I was 100% confident all the systems were functioning properly and I knew my build should require higher than 93 Octane. Have you tried bumping the timing back just 1*?

84 4+3

Yea, the cleaning effects of e85 are blown way out of proportion... it won't build up anything if fresh but it won't really clean up much either. We use 195 proof ethanol in the lab and it works eh with burnt pavement, similar to the carbon build ups you'll get in an engine. A chemical based top end cleaner, the real deal ones that you have to change the oil when you dump it in the chamber, do work however. You could also dump some bromopropane in the plug holes. Just look out for the cancer but that will quite literally clean anything. If you want a more safe alternative then use D-Limonene. Again just spray it in the plug hole, it'll break it down. I would change the oil after that as well. And your car will smell citrus fresh.

aklim

Generally, I "hear" things through the sensors so I'm probably terrible at feeling, hearing, etc when it comes to engines. Still, I wonder if at higher RPM with all the engine noise that is LOUDER than idle, would you be able to hear it with your ear? Also considering that the ECM will retard timing to compensate for the knocking, it makes me think that if you can hear it, it is out of adjustment range of the ECM and very loud. So what would be happening, I THINK, is that the pinging is so abundant that the ECM cannot retard timing anymore (and it should suck, power wise) and it is loud enough to hear over the engine roaring. Makes me wonder if it is really pinging or just something else rattling and resonating into the cabin.

ctmccloskey

Hello again rharker,

Over the decades of working on gasoline and diesel vehicles I have become familiar with some products that might help you reduce the need for premium fuel in your Corvette. You probably have carbon deposits in your cylinder head and on the crowns of the pistons and this can cause pre-ignition which sounds a lot like detonation. In the old days on air cooled VW's we used to pour a little cool water down the throat of the carburetor and the carbon would start blasting out the exhaust system in size-able chunks. With today's cars we have a different way of cleaning out the inside of the cylinder much more effectively. BG 44K Fuel System Cleaner is the product I would run through your Corvette fuel system. There are naysayers who claim it is a "snake oil" and you shouldn't use it, the choice is yours and yours alone. BG products are Extremely effective at cleaning up the fuel system, including the fuel injectors and the specifically the cylinder and piston crown. I have been using this stuff for decades and have never been unhappy with it. As a matter of fact I have some in one of my cars right now that was not idling as smooth as I like it. This stuff will clean up the injector spray pattern and bring my idle back to smooth as glass.

I truly believe that a can or two of the BG 44K would make your car run better and not ping anymore. air cooled VW's used a low compression and they frequently had issues with pinging from the hot carbon stuck to the piston crown or the odd piece on the cylinder head that glows red hot and pre-maturely ignites the fuel mixture. I use a can of 44K every 2-4 thousand miles in my cars or when they start idling funny.

Have you tested the EGR vacuum solenoid to ensure it is working properly? I would probably also check your O2 sensors as I found this recently in a book called Corvette Fuel Injection & Electronic Engine Management by Charles Probst. It mentions the following:
"As a (02) sensor ages, voltage changes get smaller and slower---"Lazy Sensor" voltage changes may lag behind changes in the exhaust gas oxygen."
If your air fuel ratio determining sensor is not giving you instant accurate data it might make the car run lean and possibly ping. How old is your 02 sensor? Have you tested it?

I did learn something interesting about our L98 fuel system. It seems that when the Corvette is running in open loop right after starting the "Corvettes Engine Computer applies a reference voltage (bias voltage), usually of 450 mV (0.45V). This reference signal takes the place of the Oxygen Sensor output, during open loop operation. In Closed Loop, the computer compares the reference voltage to the actual voltage, generated by the Oxygen sensor. Voltage below 450 mV is considered lean; above 450 mV is considered rich". It seems that the MAF and the TPS are the primaries in open loop control until the 02 warms up.

I hope that this might help a bit. Good Luck!

KyleF

A lack of ability to maintain pressure and deliver a correct volume of fuel and spray pattern may create a condition beyond what the ECM can compensate for. Or a general lack of fuel could be caused by the MAF, 02 sensor, weak pump, low voltage, dirty filter, or even a vacuum leak that can be compensated for at lower volumetric requirements.

I have only had pinging issues in an old carb'ed Ford 302. Was just giving it too much timing. I could definitely "hear" it. Soundeds like a dull mechanical rattle to me. I simply took 2* timing out of it and it went away. It happened because I was giving the old Bronco a tune up and wanted to see how much timing she would take. This could also be a factor if there is stretch in the chain or wear at the Cam/Distributor gear interface. Could cause timing to jump around and setting it at the right base timing difficult, or at least fool you. It's a simple check It's not a visual inspection, but will show you if you have slack between the movements.