View Full Version : Carbon Build Up on EFI - Normal?
On my 427(351w), from Blueprint, with a Holley sniper has run into an issue of not going into idle. To elaborate, once you take your foot off the throttle the engine stays at the highest RPM. Only way to unlock it is to blip the throttle. After calling blueprint they sent me a new sniper unit. Question - when I took off the old sniper I found a lot of carbon build up. Engine has about 1,300 miles on it. Is this normal? Photo attached for reference.
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Just noticed the PCV valve at the bottom of the air filter is oily. The other PCV tube that goes into the lower section of the intake manifold has a catch can. Perhaps it’s engine oil?
Norm B
10-08-2022, 11:37 PM
No, that’s not normal. The normal flow pattern for a closed PCV system is shown in the attached screenshot. Unless the engine is severely worn or is run at WOT, there should be no airflow out of the breather line attached to the air cleaner in a properly installed PCV system.
The sticking at high rpm is most likely not related to the carbon build up. The IAC valves have been known to stick at their park position of 20 percent instead of dropping to the 5 to 10 percent you should have setup during the initial tuning procedure when the throttle goes to idle.
Good luck
Norm
narly1
10-09-2022, 08:46 AM
The normal flow pattern for a closed PCV system is shown in the attached screenshot.
Great diagram although it could be a bit clearer in depicting that the air going into the crankcase breather originates from the "clean air" side of the filter.
Earl
Geoff H
10-09-2022, 08:48 AM
Just noticed the PCV valve at the bottom of the air filter is oily. The other PCV tube that goes into the lower section of the intake manifold has a catch can. Perhaps it’s engine oil?
Does the pcv hose from the catch can go to a fitting on the intake or a fitting on the bottom of the sniper?
narly1
10-09-2022, 08:49 AM
MVTV, have you gutted out the inside of your breather cap? Many of them house a PCV valve inside of them. You may inadvertently have two PCV valves in your system, which would not be good.
Earl
BradCraig
10-09-2022, 09:41 AM
Agree with previous poster, IAC hanging can cause high idle. MOST of the time it's the rear secondaries hanging a bit and you can determine by trying to close by hand when the high idle condition exists. Simple fix by putting another round of spring tension on the shaft spring. If the new one does the same, give that a try.
I thought the IAC sticking would be an easy fix but blueprint sent a new unit. So I’m not complaining.
Regarding the PCV system … the passenger side has a PCV valve and air flows freely through it. Goes to a catch can (which has a few drops) then to the lower portion of the sniper. Driver side has a breather tube which also lets air flow freely. I took a picture of the inside of the air filter where the breather tube connects and you can clearly see oil. No idea what to do besides call blueprint on Monday. Thoughts?
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Geoff H
10-09-2022, 10:46 AM
Seems your pcv is set up right if you are only getting a small amount of oil in the catch can. For the air cleaner side of the system - do you have a baffle in the valve cover? Is there a foam filter of sorts in the breather?
Nope, breather cap is empty. Suppose to have one? If so, that’s something to ask BluePrint about.
Geoff H
10-09-2022, 11:35 AM
I am no expert but I have a foam insert in mine. 347 (not blueprint) with the same pcv set up. I have no oil in the air cleaner or sniper. Would be worth asking, but also easy to change it out with a breather cap with foam and see if it helps.
Good luck with it!
Hoooper
10-10-2022, 11:05 AM
Under heavy throttle where the engine doesnt make much or any vacuum, blowby will go into the intake through both of those paths unless you have a check valve in the one going to the top of the intake. Most engines make more blowby under throttle than those little 3/8" hoses support so you will be getting vapor from the engine going into the intake through both lines. Whether the amount you have is normal depends on how much "heavy" throttle youve been at. If it was all idle time, that would be a lot. If it was all track time, that would be very little.
Norm B
10-10-2022, 04:35 PM
It is also possible that your PCV valve is not compatible with your camshaft or, more specifically, the intake manifold vacuum that results from your cam profile. This usually manifests as poor idle characteristics. The Sniper could be fighting a large vacuum leak because the PCV valve is not being sucked to the airflow restricting idle position due to low manifold vacuum.
Norm