Question: Excessive carbon build-up removal ?

[killain]

I have huge carbon build-up in the heads from the previous owner of my l-98 using nothing but cheap regular 87 and now I have an engine that won't start if the outside temps are below 50 degrees. The problem is the desist of the air/fuel mixture and it can't get around the carbon buildup and into the cylinder before the intake valve closes, the piston come up and the spark plug fires, but there's not enough fuel in the air/fuel mixture to start.

Is there anyway to decarbonize a cylinder heads intake ports without removing the cylinder heads or is the only remedy taking off the heads and sending them out to be cleaned and rebuilt ? I've run it on only ExxonMobil supreme 93 octane and I've added about 12 to 15 bottles of Chevron/Techron cleaner to a tank of fresh gas but it hasn't reduced the build-ups ? :ugh

 

[YumaZ06]

I don't know if this would help considering the amount of Techron you have added, but twice a year I add a bottle of "Seafoam" to the tank. Seems to help. They have a procedure to add to the intake system to help clean internal engine parts.

 

[hcbph]

Carbon

Is there anyway to decarbonize a cylinder heads intake ports without removing the cylinder heads or is the only remedy taking off the heads and sending them out to be cleaned and rebuilt ? I've run it on only ExxonMobil supreme 93 octane and I've added about 12 to 15 bottles of Chevron/Techron cleaner to a tank of fresh gas but it hasn't reduced the build-ups ? :ugh

If you added that much to 1 tank of fuel, I'd hate to see your fuel system and engine and how much it's been eaten up.

As far as I'm concerned, it didn't happen in a day and won't go away in a day. If it was me, I'd think about doing a tank with Techron (per their mix ratio), then a tank of just fuel and then Seafoam in a tank (again at their mix ratio) then a tank of just fuel and continue the cycle. I would look at the brand of fuel rather than the grade in this case. I've read about additives, some use many while some brands use next to none.

Getting back to the basic statements made regarding regular fuel, mine says to run unleaded fuel with an octane rating of at least 87, though you can use as low as 85 octane in high altitude areas. That's for a L98 engine.

 

[killain]

Carbon Build-up ?

If you added that much to 1 tank of fuel, I'd hate to see your fuel system and engine and how much it's been eaten up.

As far as I'm concerned, it didn't happen in a day and won't go away in a day. If it was me, I'd think about doing a tank with Techron (per their mix ratio), then a tank of just fuel and then Seafoam in a tank (again at their mix ratio) then a tank of just fuel and continue the cycle. I would look at the brand of fuel rather than the grade in this case. I've read about additives, some use many while some brands use next to none.

Getting back to the basic statements made regarding regular fuel, mine says to run unleaded fuel with an octane rating of at least 87, though you can use as low as 85 octane in high altitude areas. That's for a L98 engine.

Ah No. I've added the Chevron Techron over a two year course of time, in conjunction with the use of clean 93 octane fuel. And all of last winter it seemed fine. but about a week ago the temps dipped at night into the low 50's, and when I came out to start it in the morning it did the "No Start" routine. If you let it sit till noontime, and the temperature gets above 58 degrees, it fires right up ? It's a perplexing problem. The previous owners must of found the "fountain of filthy gasoline of all time". I bought it during the summer in New Jersey. In jersey just about all the gas station are owned by Pakistani's or Hindu's, and I'm not kidding.

And I know that a recent local TV report, the grades of gasoline sold by these guys is crazy. The state sent out a team to check 19 gas stations not for the price, but the quality of gasoline. Of the 19, 8 were selling 89 as 93 octane, and 9 were selling 85 as 89 octane, and the last two were selling something that didn't even register as an octane fuel slightly above 83. But I'm getting tired of this. The only REAL way to fix this is just pull the heads and send them out to a machine for a complete cleaning and a rebuild. I getting tired of taking things apart.

 

[Vettehead Mikey]

Jim-

Octane rating is not directly connected to the 'quality' of gasoline or the amount of cleaning additives it has. There's no reason to believe that all 93 octane has more additives than 87. From what Carbon says, your engine was built to run on 87 anyway.

Sounds like your engine has a bigger/different problem than carbon build up due to cr*p gas. Have you actually seen these deposits?

 

[hcbph]

Jim-

Octane rating is not directly connected to the 'quality' of gasoline or the amount of cleaning additives it has. There's no reason to believe that all 93 octane has more additives than 87. From what Carbon says, your engine was built to run on 87 anyway

Actually in the day of carburetors, distributors etc, running over octane fuel was as bad as under, just in a different way. Over octane fuel will not burn as clean as the proper octane fuel required by an engine, all other things being equal. Remember octane retards burning of fuel, which then is compensated by higher compressing ratio etc. If you don't compensate for the higher octane, you have a incomplete burn: carbon buildup.

There is a procedure to ingest Seafoam directly into an engine to help knock out carbon buildup. I've never tried it so I'm not going to say either way but Seafoam listed how to do it. In the days of carbs, there was a similar method of ingesting a small amount of water to help break out carbon buildup in a running engine but I don't know how to do it to a FI engine.

 

[c4c5specialist]

HI there,

Lets start from the beginning, ok ???

#1, octane has never been a quality of gas, but as noted above, a rating of resistance to burning. The higher octane you use, the MORE carbon will build up in the cylinders on cooler running engines.

#2, TOP TIER FUELS will help alleviate alot of carbon buildup on the backs of intake valves. Lower quality of gasolines can ALWAYS contribute to this condition. ALL EPA guideline specifications will clean the backs of intake valves regardless of make. TOP TIER FUELS CLEAN MUCH BETTER.

#3, exhaust gas recirculation or EGR also plays a part here. Remember, when hot exhaust gases flow past the cold intake valves, carbon will condense on the colder parts.

#4, I would very much ask WHAT type of carbon buildup is there. If it is WET, then I am thinking differently than gas or EGR, I am thinking leaking valve stem seals as part of the issue.


As far as decarbonization, in the dealership, we use 88861802 and we FOG 2 bottles into the vehicle engine while it is running at 2000 rpm. The spray is directly into the throttle body. This will soften any carbon buildup and then add a can of BG 44 K to the fuel tank and filling it will probably take care of your issue after driving your car through the tank.


However, I would really wonder about THAT MUCH carbon buildup on the intake valves that it absorbs all the fuel being sprayed. I might be checking other things as well.

Allthebest, Paul

 

[Vettehead Mikey]

HI there,

Lets start from the beginning, ok ???

#1, octane has never been a quality of gas, but as noted above, a rating of resistance to burning. The higher octane you use, the MORE carbon will build up in the cylinders on cooler running engines.

Sorry all, but this is an old myth. Absolutely false. Octane rating is NOT a measure of resistance to burning. It is a measure of resistance to detonation. Apples and oranges.

Too high an octane rating will waste money but nothing else.

Regarding the top tier fuels. This is a marketing scheme only. There's nothing to say that non-top tier gas does not have the same type and volume of additives.

 

[Kevo]

Top Tier is not a scheme. It's intended to burn cleaner and reduce emissions...epa thing. Way back when the car was new, fuel quality was really bad people were told to run premium mostly because it was likely to have detergent in it. Fuel got better so drivers advised to run MFR recommended grades. It seems carbon isn't necessarily your problem. Carbon build up is more common in cars that just putt around. Fuel quality could be,but you should run 87 while you try to fix this condition. What is fuel pressure when you turn key on and does it hold. You could try to disconnect fuel pressure regulator and see it it helps. You will need a scanner to check son things. Does coolant sensor and air temp sensors read approx the same prior to attempting to start car? Engine timing? At 50-60 degrees its not really cold enough for ecm to add extra fuel (Choke) so a lean condition can occur. There was a revised chip for manual transmission....stated may help.

On the engine repair side of this does engine use or lose oil. Execessive carbon build up on valve is normally tied to worn valve guides or seals. Oily spark plugs?

 

[Hib Halverson]

You may have a high level of carbon build up on your pistons and on chamber walls but that's likely not why the engine will not fire when the temperature is below 50°

If it were really true that your carbon build up is blocking the flow of air/fuel mix into the cylinder, it would happen regardless of the temperature. Also, if it were really true that enough carbon deposits could exist to block airflow into the cylinders there is no way you could remove it without rebuilding the engine.

The first thing to do is find out why the engine will not start when cold.

Then address the carbon issue.

You can try the decarbonizing suggestions made by c4c5Specialist and if they don't work, you need to tear down the engine and repair the problem.

Also, carbon deposits are not always caused by "cheap gas." They can be cause by poor quality fuel, but they also can be caused by an engine controls system that's not operating properly–say it's running rich. They can be caused by poor oil control–bad rings, bad guides, messed-up PCV and, etc. They can be caused by frequent short trips or starts-without-warm ups. They can be caused by an engine that misfires a lot.

As for "top tier" gasoline...that's some BS mixed with some facts and a lot of great marketing by the car companies (GM and six offshore mfgs) which got together and decided you need more detergent in your fuel. For the real story on "top tier" gasoline, read the CAC's technical article about gasoline. In that article most of the third page covers the facts of "top tier" gasoline. Corvette Action Center | Tech Center | Corvette Action Center Deep Dive Series: Gasoline for your Corvette - Page 1 of 8

In a practical sense, if that L98 were my car, here's what I'd do. First I'd make sure the ignition and cold start valve (if so equipped) are working properly. Then I'd go buy three bottles of Red Line Complete Fuel System Cleaner. Run that, one bottle per tankful of gas, for three fill-ups in a row. Then, if you still feel you have a problem with carbon, I'd pull the intake and look down the ports with a bright light. If you see sludged-up intake valves, try the decarbonizing ideas suggested above by c4c5Specialist.

If you still have a problem, overhaul the engine.

 

[Tuna]

Back in the days of carburetors, my dad used to drizzel Marvel Mystery Oil into the carb with the engine at 1500 to 2000 RPM and that cleaned out the carbon build up.

c4c5specialist's way of cleaning up the carbon sounds just like what my dad used to do but for injected engines.

Trying to clean carbon off the tops of the values too fast can result in a "too large" chunk getting into the cylinder and that can cause problems with the pistons. Try not to rush the removal process.

I'm a fan of BG 44K for cleaning the fuel system also. Works good.

 

[BigJimZ16]

Sorry all, but this is an old myth. Absolutely false. Octane rating is NOT a measure of resistance to burning. It is a measure of resistance to detonation. Apples and oranges.

Too high an octane rating will waste money but nothing else.

Regarding the top tier fuels. This is a marketing scheme only. There's nothing to say that non-top tier gas does not have the same type and volume of additives.

Actually, two ways of saying the same thing... Detonation is the pre-mature ignition of the fuel in the cylinder; it's the "resistance to burning" quality that prevents pre-mature ignition... the higher octane level raises the ignition temperature required.
Also, as a side note... the higher octane fuel is also less efficient due to a lower BTU value as a measure of volume.

 

[Vettehead Mikey]

Actually, two ways of saying the same thing... Detonation is the pre-mature ignition of the fuel in the cylinder; it's the "resistance to burning" quality that prevents pre-mature ignition... the higher octane level raises the ignition temperature required.
Also, as a side note... the higher octane fuel is also less efficient due to a lower BTU value as a measure of volume.

Nope.

Detonation is not burning, it is much closer to 'exploding'.

Here's a short explanation:

Engine knocking - Wikipedia, the free encyclopedia

"Knocking (also called knock, detonation, spark knock, pinging or pinking) in spark-ignition internal combustion engines occurs when combustion of the air/fuel mixture in the cylinder starts off correctly in response to ignition by the spark plug, but one or more pockets of air/fuel mixture explode outside the envelope of the normal combustion front.

The fuel-air charge is meant to be ignited by the spark plug only, and at a precise point in the piston's stroke. Knock occurs when the peak of the combustion process no longer occurs at the optimum moment for the four-stroke cycle. The shock wave creates the characteristic metallic "pinging" sound, and cylinder pressure increases dramatically. Effects of engine knocking range from inconsequential to completely destructive.

Knocking should not be confused with pre-ignition."

We're getting off topic. but the difference in BTU/vol is insignificant. There's greater potential for variation between one brand to another than 87 vs. 93.

 

[killain]

Cold temperture woes ?

Ok and a big THANK YOU to you Hib, Mikey and Paul. In the beginning, when I bought the car, I started to do some of the light style of work, Compression test (All Cylinders were real close @ 140 PSI) I had a complete tune-up done, there wasn't any work other than that as all other items seemed fine so why change something for the sake of change. It ran good and we enjoyed it until September 27th 2011 when the morning temperatures were in the low fifties. I went out and the car turnover fast and on occasion did a burp, but wouldn't ignite or start. I let it sit and tried to start it around 12:45 PM and it fired right up like nothing was ever wrong. I used the car that day and parked it in the driveway and the next morning it had stayed warm and the car ran fine and the following morning it dropped to 49 degrees and I went out to go to work and of course, The L-98 decided it wasn't going to work with me as it just wouldn't fire up. I had the car flat bedded to the Chevy dealership and of course it fired right up as the tow truck dropped it off in a warmer ambient air temperature. This happened five more times before the dealership decided it needed something else. and the ran the cleaning process Paul spoke of and for the last two years it has been OK , but I assume it has now gotten dirty again.That was the history of the car.

Now for me, I'm not the sharpest pencil in the box, but I always thought the say ExxonMobil supreme 93 was a good quality fuel that had a good additives package with detergents and cleaners designed to keep the fuel system clean. ( We don't have any 'Top-Tier fuels sold anywhere close by.And I use ExxonMobil 93 in my C5 LS-1, the only 91 octane fuel around here is Sunoco and the GM master tech at the Dealership, Steve Spencer has advised me from using Sunoco as it has too high a sulfur content. (He only does work on the complicated Corvette and Cadillac work, but he dedicates his skills on Corvettes but he lent a hand as I a longtime client, so he and the shop foramen did the clean-up work described by Paul. It seemed to do the trick as the last two years have been trouble free. but the problem is back. What has me in a bind, is the engine when it runs, runs so smooth even a cup of coffee won't have ripples on it's surface while sitting on the console, which is why I'd hate to have to tear the top half of the engine off so the heads can go out for a complete cleaning and rebuild. But Hib, Your experience & advice is legendary, and Mickey and Paul you are all extremely well versed in the corvette and Paul you make your living from your knowledge of the many forms of Corvette and their engine. I suppose in the end, The engine will need to have it's upper end rebuilt. Thank you all.

 

[Vettehead Mikey]

Now for me, I'm not the sharpest pencil in the box, but I always thought the say ExxonMobil supreme 93 was a good quality fuel that had a good additives package with detergents and cleaners designed to keep the fuel system clean.

It is an excellent fuel, but their 87 octane also has more than enough additives to keep any engine in good condition clean.

, the only 91 octane fuel around here is Sunoco and the GM master tech at the Dealership, Steve Spencer has advised me from using Sunoco as it has too high a sulfur content.

Contrary to popular belief, fuel retailers don't have their own unique, dedicated refineries. Pretty well all fuel comes from the same refinery or pipeline and only as it's being loaded onto the delivery truck are the propriety additives blended in. That's the only real difference from one brand to another. The days of ANY fuel having high sulphur content are long gone. For all their other failings, the EPA fixed this in 2004.

What has me in a bind, is the engine when it runs, runs so smooth even a cup of coffee won't have ripples on it's surface while sitting on the console, which is why I'd hate to have to tear the top half of the engine off so the heads can go out for a complete cleaning and rebuild.

This points away from intake tract contamination. You've got a cold start issue, I suppose there's no choke lever on these new-fangled cars is there?

 

[killain]

Cold choke ?

It is an excellent fuel, but their 87 octane also has more than enough additives to keep any engine in good condition clean.



Contrary to popular belief, fuel retailers don't have their own unique, dedicated refineries. Pretty well all fuel comes from the same refinery or pipeline and only as it's being loaded onto the delivery truck are the propriety additives blended in. That's the only real difference from one brand to another. The days of ANY fuel having high sulphur content are long gone. For all their other failings, the EPA fixed this in 2004.



This points away from intake tract contamination. You've got a cold start issue, I suppose there's no choke lever on these new-fangled cars is there?

Ah No ! The techs at the dealership explained to me that this problem has to do with air temperature, The ambient air temperature @ 40 degrees doesn't flow as well and hot air as in summer. They told me the the size of the carbon or dirt build-up was so big that the engine couldn't draw enough air/fuel mixture into the cylinder fast enough before the intake valve closed, once that happened you got compression and then the spark plug fired, but there wasn't enough air /fuel mixture to have ignition. And of course as the piston came back up the exhaust valve opens and whatever air/fuel mixture get pushed out into the exhaust manifold. truly frustrating.

 

[Vettehead Mikey]

Ah No ! The techs at the dealership explained to me that this problem has to do with air temperature, The ambient air temperature @ 40 degrees doesn't flow as well and hot air as in summer. They told me the the size of the carbon or dirt build-up was so big that the engine couldn't draw enough air/fuel mixture into the cylinder fast enough before the intake valve closed, once that happened you got compression and then the spark plug fired, but there wasn't enough air /fuel mixture to have ignition. And of course as the piston came back up the exhaust valve opens and whatever air/fuel mixture get pushed out into the exhaust manifold. truly frustrating.

Ouch. I'm calling BS on that explanation. If anything, air is denser as temperature decreases so the problem would NOT be present when cold and only when hot. The difference in air density between 40F and 58F is insignificant in any case. To be precise, assuming sea level altitude and 50% relative humidity, at 58F the air is 0.0761 lbm/ft3 vs. 0.0788 lbm/ft3 at 40F.

If the carbon build up is so bad that the engine can't breathe enough during start- how could it breath enough at red line or WOT?

 

[killain]

Climatic troubles !

Yeah, I thought so when they told me too ! Thank you !

 

[Ol'Scratch]

Howdy Folks...
A side question if I may... I have the opposite problem. I have an "88" Vette, and she starts instantly when cold... But you have to crank for a bit to start her warm. She also idles rough. Idle is around 600 rpm but if you gently raise it to 700 she smooths right out. I know I have to replace the Fuel Regulator Valve, and I've purchased the valve and assorted gaskets. The valve in there has been jimmyed up where some one has stuck a bolt through the top of the valve to somehow get some adjustment. Now as far as I can tell... 88's did not have the adjustable valve, and you can tell the bolt doesn't belong there. It's so long it hits the bottom of the plenum overhead. Could this be part of my problem?...;help

Thank you for your time

Fast Freddie...

 

[roger longman]

Hi Freddie, My '88 has similar characteristics. Instant start when cold and, cranks for about 3 seconds, before 'catching' when hot. Slightly uneven idle, that irons out when given some throttle. I put this down to the 'leaner burn' mixture, on closed loop and a 'hotter' cam. I'm sure someone with better knowledge, will put me straight, if wrong......Roger.