Intake Manifold Carbon Build Up?

[olddog]

5.0 / 347 stroker engine.

Cam (from memory) is 236 / 242 duration @ 0.050" and 106 or 108 LSA

Mass Flow Injection system, which is a Edel Vic Jr single plane intake for a carb, with injector bungs welded at each intake port. A throttle body, designed to look like a carb, sits on top of the intake.

I had the intake off and polished it about 3-4K miles ago. I pulled the throttle body, over the week end (another story), and I was surprised to see the amount of carbon build up in the intake manifold. It pretty much looks like the inside of an exhaust manifold. I realize that with the valve overlap exhaust gasses get sucked up into the intake, however I wonder if this is typical.

With a carb there is fuel and air traveling in the intake at all times. Perhaps it washes itself out. In this case, the fuel is injected after the intake runners, so the intake runs dry, except for reversion flow at idle. It doesn't get much natural washing with fuel.

Do you see this with a carb or is this normal?

Also I was trying to decide what is the best way to clean it up. I'm not real big on washing a bunch of gritty carbon down on the intake valves. Advise is welcome please?

[bobcowan]

A certain amount of that is pretty normal. Standard tune up procedures for modern cars include cleaning the carbon out of the throttle body.

[FWB]

do you have a pcv plumbed into the intake plenum?

[olddog]

Originally Posted by FWB

do you have a pcv plumbed into the intake plenum?

Yes at the base of the throttle body, pretty much like a carb would be.

[FWB]

that is where your oil residue is coming from. is there a baffle where you pull the pcv from the crankcase? if it's from the valve cover you might be sucking raw oil into the plenum.

there isn't a trick to cleaning it, because if its that way in the runners the backs of the valves prolly look worse. when the oil mist hits the hot valve , it immediately crystallizes on the back of the valve. i would pull off the intake to clean it, and then it will give you the ability to see what the intake valve looks like

[Mr Jody]

I ran into a similar situation recently, and have one trick you may want to try before pulling the manifold. I am in the process of replacing fuel injectors on an old Nissan Maxima and saw the same oily, gritty residue inside the manifold, which I attributed to the flow of oil vapors through the PCV, but at 160k miles this should not have been a surprise. I knew I wouldn’t be able to get it squeaky clean without taking it off of the engine, but I did want to clean the bunghole area for each injector and any other places I could get to that appeared to have excessive buildup. I could see the back side of the intake valves through the bungholes and they actually were surprisingly clean.

To avoid having any residue I scraped off end up on the valves and subsequently into the cylinders, I took my shop vac, attached the crevice tool to the suction hose, and then stuck a piece of clear rubber hose (about a foot long and small enough to fit into the bungholes) into the crevice tool and wrapped tape around it at the crevice tool to hold it in place and close up gaps in the crevice tool opening around the hose.

After scraping inside each bunghole I would then suction out the residue either through the bunghole or the intake runner. The intake manifold on this car is made in three sections stacked on top of each other. To gain access to the injectors you have to remove the top two sections. This actually opens up each intake runner and helps in being able to gain access to other areas of the manifold, which may be more difficult in the one piece manifold of your engine. But the suction of the shop vac did remove residue that I was scraping off that ended up on the backside of the valves.

In your case, you may not be pulling the injectors, but maybe you can use the suction trick to remove what residue you can get to through the top of the manifold.

I would NOT recommend this method in conjunction with use of a volatile cleaner for fear of the vapors passing through the electric motor of the vacuum and potential sparks in the motor not playing well together.

[wrogers55]

While you are at it, have a close look at the mass-flow meter on your system. If the manifold is that bad, you have another bigger problem. Three little, really little, wires across the air inlet of your mass flow meter. If they are coated with "anything", the meter will report bad information to the computer. The result is usually very poor fuel milage and poor throttle response, at the least. Clean them without touching them if at all possible and only with something made for the purpose. Brake clean or carb cleaners will likely leave a residue on the wires and cause the same problem. In the worst case use a stream of isopropyl alcohol, better case is a spray can of cleaner made specifically for the purpose from the auto parts store. Don't break the wires cleaning them....$350 or more to replace that little jewel.

I'm not that smart, just lived through total frustration with this exact problem once upon a time........

[olddog]

I do not believe it is oil. It is dry carbon, just like you find in an exhaust manifold. A hair oily right by the PCV port, as you would expect, but the rest is dry.

I do understand the MAF cleaning.

[FWB]

if no fuel is running thru there......if an air cleaner is on the throttle body

if your neighbors cat isn't defecating into there

what else would it be?

you would have to have one hell of a cam overlap to push oil up from the bottom, coupled with a crappy ring seal


when the oil hits a hot surface it cooks and gets hard.

[olddog]

Shined a light down ports 2, 3, 6, & 7 and I can see the intake valves (Single plane intake). They are clean and dry. From where the injector sprays on is clean and directly under the injector still looks as polished as the day I installed the intake.

I rubbed my finger all around the intake. On the floor of the intake under where the PCV valve port is there is a hint of an oily film. The rest is a very thin layer of dry powdery carbon just like you would find in an exhaust manifold. I could rub it off.

I sprayed some carb cleaner on a rag and it wiped off. So I wiped the entire intake down until I had it clean. Then sprayed the cleaner directly on it and wiped it off with clean rags a couple times and it is just like the day I installed it again.

This intake has an air gap between the lifter gallery and the manifold. I don't think it gets hot enough to carbonize oil. Do you still think it is oil? I'm still thinking exhaust gasses sucking into the intake from the valve overlap, but it is everywhere. Even on the bottoms of the throttle plates. I wouldn't think reversion would go that far.

I'm interested in more opinions, as I'm not sure what it is.

[Gaz64]

Olddog,

If it is only a dry film of "fuel carbon", I wouldn't be too concerned.

The reason you're getting it is because you don't have carbs to keep the runners clean AND you have reversion from a higher overlap cam.

Technically your system would be sequential, but as to when the injector fires in relation to the valve opening period is something to discuss with the injection manufacturer.

Even if the injector truly fires only during inlet open period, you will get some air/fuel mixture blown back into the manifold at low to medium engine speed.

[olddog]

ECU is a Ford A9L EEC-4, so it is sequential, and I have verified the cam is the correct firing order for the ECU. I believe Ford puts the fuel in before the intake valve opens, so the fuel has time to vaporize sitting on top of the valve.

So you think the carbon is coming from gasoline, correct?

When I originally saw it and started this thread, I thought is was a much thicker layer than it turned out to be.

[Gaz64]

There's your reason, fuel injected prior to opening will vaporise earlier but it leaves a trace of carbon dust.
It also gets blown back up the runner at low engine speeds during the valve overlap period.
The small amount of oil from your pcv is the other contributing factor.

Injection should really occur after the exhaust valve shuts, say 40 ATDC or later at low engine speed, then bring them on earlier as the engine speeds up.

[FWB]

Originally Posted by olddog

ECU is a Ford A9L EEC-4, so it is sequential, and I have verified the cam is the correct firing order for the ECU. I believe Ford puts the fuel in before the intake valve opens, so the fuel has time to vaporize sitting on top of the valve.

So you think the carbon is coming from gasoline, correct?

When I originally saw it and started this thread, I thought is was a much thicker layer than it turned out to be.

ditto on gary's post.......


yes in the beginning of the thread i got the impression there were globs of crap in there, if it is just a dust, so to speak, Gary seems to have nailed it.

one thing though, this is assuming you have an air filter actually doing its job, dirt isn't getting drawn in there is it?

[olddog]

Originally Posted by FWB

This is assuming you have an air filter actually doing its job, dirt isn't getting drawn in there is it?

It has a good air filter and seals up nicely. The MAF sensor sits inside the air filter. It is clean, and the throttle body is clean above the plates.

I was tuning up my Grand Marque, 120K miles, so I opened the throttle body on it to see what was inside. I has carbon on it too but less sooty. More miles but less overlap on the valve timing. I have to believe the overlap is playing a key roll.

Thanks for the replies to all who responded.

[olddog]

Originally Posted by Gaz64

Injection should really occur after the exhaust valve shuts, say 40 ATDC or later at low engine speed, then bring them on earlier as the engine speeds up.

It does what ever Ford programmed it to do; no modifications. I have read the injectors fire prior to the valve opening, but you know what they say. Only believe half of what you read and nothing you hear. I'm not sure what it does.

[Gaz64]

Yes that's correct, and works fine with low overlap cams, becomes more of an issue with longer overlap cams.

Can you post some pics of your manifold? (carb flange and down to the heads).

[olddog]

Gaz64 - I have already cleaned everything up. Here is one picture of the intake before it was installed.