C4 TPI Inlet Manifold mysteries.

[Vettech]

Here is a question for you rev heads out there.

Once upon a time as a small boy I ran an 1800cc with 2x 1&3/4" SU carbies on a Warnerford inlet manifold.
Naturally I tinkered with them all the time, but one thing I noticed, from the butterfly's to head, the inlet was always bright and clean.

Yesterday I ripped the Throttle Body off the 87, from outside it looked grungy up to the butterflies, but when removed, the inside of the butterflies and thru up into the manifold was as black and sooty as the proverbial.

With consideration to the fact that this part of the fuel system should only have clean filtered air - there should be no fuel, oils or any other combustible flowing thru this part of the intake plenum. SO WHERE DOES ALL THE CARBON BLACK COME FROM ?.

Dont forget on 85 thru 90 (I think) the engine injected left bank thence right bank - all 4 at once, the runners gave the air sequence to get there at the right time for valve timing, hence it arrives, valves open, fuels injected, mixed and the rest is power.

Can some one explain why this area of the inlet manfold is so carboned up..........

[Vettech]

Well after a think - this car has for a long time had a slight stumble in its idle. I've just cleaned or at least tried to clean the IAC valve, i can now see most of the pintel, umm bad, and with the crud in the housing, its easy to now understand the uneasy idle. Also upon removal I found NO gasket seal.

Also, for quite a while it had a hot starting issue caused by an RS nose bushing in the original GM starter motor, once engine was hot the starters shaft shifted and bound up in the bushing, the result was very slow cranking, which sounded like a flat battery, current draw went thru the roof and the batteries terminal voltage drops drastically. Quickly turning from crank to run let the engine fire and start, but occasionally it backfired and sometimes fired up with a horrible metalic clinking sound - like a valve getting hit !?!?.

Anyway a new HiTorque reduction gear starter resolved the start issues. (After a long chase)

These have a module to electronically  shift the spark timing, if the engine is struggling to start, battery voltage is low, then the EST module is getting the wrong operational voltage - then it may give an incorrect spark command - firing at the wrong time ergo a horrible metalic clinking sound.

But maybe also backfire - this would maybe account for black soot in the intake -

[sirfixalot]

Mine looks exactly the same runners are black

[Vettech]

A little more of Google.

Whilst the EGR Valve has no overall effect on performance,  it does however feed back into the intake manifold burnt exhaust gases, this may then explain the black soot etc found in the inlet manifold.

If the EGR valve is stuck open - this will effect Idle, stalling, hesitation etc.

[Vettech]

Good to catch up Sirfixalot.

I found out what the extra port on the EGR Solenoid switch is for.

We know one is Vac in and the other Vac out to the EGR valve itself.

The third port, which mine has a rubber stub on, but feels like it has a hole in the end (cant see in there) is supposed to he a moulded rubber filter / muffler - this stops dust entry, muffles sound, and allowes the vac to dissapate to atmosphere, when the egr is unenergised.

[peterw]

Mine was black also and my car is low mileage and runs sweet.  EGR is a good guess.

I feel sorry for you asking questions and having to answer them yourself but your knowledge of the C4 seems to be way greater than mine.  I am still learning.

[Vettech]

Yes - life is a leaning curve.
 My Father used to say "you need to learn something new each day - else you've wasted a day of your life".

And its amazing how much info is out there on the net, you just need to filter some of it.

Yes - I think you are on the money, I  cant see any other way for sooting up other than via the EGR Valve.