Carbon shooting from tailpipes

TT350chevelle · Post by **TT350chevelle** » Mon Aug 14, 2006 10:23 pm

Did you swap the suspect injector with a cylinder that is working well? This will tell you if the injector is bad.
It wouldn't hurt to swap a spark plug and/or plug wire too.

Brad J.

rs2000 · Post by **rs2000** » Tue Aug 15, 2006 12:03 am

How is your charcoal cannister (if you have one)? Could it have expired and released its carbon into the engine or something? The granuals look very grey, the soot that usually comes with running rich is black i thought.

TPI 85 Blazer · Post by **TPI 85 Blazer** » Thu Aug 17, 2006 5:39 pm

rs2000 wrote:How is your charcoal cannister (if you have one)? Could it have expired and released its carbon into the engine or something? The granuals look very grey, the soot that usually comes with running rich is black i thought.

This was my theory because I couldn't believe that the engine could have made so much carbon.

I will actually be putting in a new set of injectors soon. The suspect injector is ticking, but if I have one or more that is slower than the others, my idle mixture would be all wrong on that one.

TPI 85 Blazer · Post by **TPI 85 Blazer** » Sat Aug 19, 2006 8:03 am

Here's what I found on disassembly of the intake.

-Carbon everywhere - there is dust in the plenum and runners. Just below the injectors there is the crusty stuff.
-The EGR passages for the right bank are dirtier than those for the left. This is the side with the O2 sensor and the side that had more junk in the exhaust.
-Intake manifold may have been a bit loose
-FPR was broken! The nut on top that adjusts the pressure broke off. This probably happened during dissasembly because I did have 30-some PSI at idle before tear down and it would have been 44 with that big vacuum leak in the regulator.
-Passages in from the charcoal canister look clean.
-Carbon inside the FPR! -just near the vacuum nipple. I guess when the throttle opens, the cavity inside the FPR sucks a little air back in from the intake.

I only have two injectors off so far (#5, #7), but they appear to be fine. 12.2 Ohms and I can blow fuel from them with a rubber hose when I energize them.

What if the right bank has a bad injector and I was tuning everything else too rich to try and compensate?

Is it possible that the crusty black "sand" is carbon dust mixed with fuel?

PSIG · Post by **PSIG** » Sat Aug 19, 2006 9:11 am

Are the granules attracted to a magnet by any chance?

David

TPI 85 Blazer · Post by **TPI 85 Blazer** » Sun Aug 20, 2006 8:36 am

PSIG wrote:Are the granules attracted to a magnet by any chance?

Some of it does show some interaction with a magnet. What does this mean?

I tested the injectors as I took them off by blowing into a rubber tube and spraying out the gas that was still in them. Most of them showed 5 clear streams, but #4 only had 2 or 3.

TPI 85 Blazer · Post by **TPI 85 Blazer** » Sun Aug 20, 2006 6:47 pm

I installed new injectors and did a compression test today. Here are the numbers (1,3,5,7,2,4,6,8):
150
154
153
154
150
151
145
150

This looks fine to me. Spec is 150 with rebuild at 20psi difference between any two. I started it up and got a good idle with 21" of vacuum.

A little tweaking of the fuel table and it looked so good I drove it. It pulled hard and no signs of pinging like before. This is really the best it has run since the carb came off.

Were all of my problems due to bad injectors? Where did all of the junk come from? Is my engine doomed or are all of my problems behind me?

PSIG · Post by **PSIG** » Sun Aug 20, 2006 9:15 pm

TPI 85 Blazer wrote:
PSIG wrote:Are the granules attracted to a magnet by any chance?
Some of it does show some interaction with a magnet. What does this mean?

That can mean inter-granular corrosion in (usually) the exhaust and egr passages of the manifolds. The particles can be dislodged by extreme duty or the gross variances in exhaust heat such as in base tuning. I am not convinced this is the case as I would not have expected it up in the FPR and such.

David

TPI 85 Blazer · Post by **TPI 85 Blazer** » Mon Aug 21, 2006 4:57 am

PSIG wrote:That can mean inter-granular corrosion in (usually) the exhaust and egr passages of the manifolds. The particles can be dislodged by extreme duty or the gross variances in exhaust heat such as in base tuning. I am not convinced this is the case as I would not have expected it up in the FPR and such.

David

It must be formed in the combustion chamber and then carried up to the intake via the EGR passages. On the side that had more junk, the EGR passage is clearly dirtier. The only other possibility would be sticky intake valve(s) that let stuff go backwards, but no other evidence suggests this. On TPI, the EGR opens into the intake right behind the throttle blades and everything downstream from this is black. The EGR is not crusty at all, just powdery. I'm wondering if a little fuel weeps through the diaphragm of the FPR and mixes with the powder to get crusty. Other than the exhaust tubes, it's only crusty right around the injector slots, which is why I'm thinking that it has to do with fuel.