Intake Manifold Carbon Build Up?

[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.

[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).

[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.