Carbon in Intake

I recently had my 96 blazer in the shop, they told me my Intake was carboned up pretty bad. They wanted to remove the intake and clean it all out to the tune of $400. They also said my egr was bad. I ran down to the local auto parts store and asked about seafoam. I followed instructions on how to use the stuff by running it through the brake booster. Once I started the truck back up, I got some black stuff coming out of the tailpipe, but not as much as I expected. I dont know if it just wasent as bad as they said it was or whether it is so bad seafoam wont take care of it. I was wondering if I can use seafoam a second time right away, or if this might damage something. I bought the new egr but I dont want to install it if it is just going to get all carboned up again. Thanks for any help you can give.

Truck has 204,000 miles, 4X4, 4.3

Is the carbon giving any problems?
Is the egr valve actually bad or?
Does the egr valve have a carbon ball stuck in it.
Is the truck tuned up good?

I am not to sure how to tell if the egr is actually bad or not. I just took thier word for it. As far as a carbon ball, I dont think so. The shop I took the truck to said that their was enough carbon build up to have to worry about the possibility of blowing a head gasket if I drove it much longer. The car is tuned up well. About 15,000 miles ago I put new AC plugs, wires, and a new distributer cap and button. The truck runs well. At the top end of first gear I will get a slight hesitation, feels like its missing, but then it shifts to second and I dont notice any problems. They had also mentioned that the O2 sensors rear of the cat are bad. (Forgot to mention in first post) I picked those up today, but again dont want to put them in if they are going to go bad again from the carbon problem. Thanks for any assistance.

I can not see anything about carbon build up that would blow a head gasket.
Carbon in the intake part of the intake does usually not give you any problems.
Heavy Carbon build up on valve steams may give a little running good problem.
But with the mileage on it I would just sea foam it again and just drive it.
Carbon build up in the exhaust gas port to the egr valve would give you more problems than anything.
Like stopped up egr valve port or putting carbon balls in the egr valve.
Check out the egr valve for why it is not working or they aid it was bad.
And if it needs the 02 sensor replace it.
You need the engine running good to keep it from building up more carbon.

Thank you, that makes me feel a bit better. I wont be afraid to drive it. I will try and figure out why the egr is bad and add it to a post later. I appreciate your help.

If it has a egr valve or a 02 sensor problem there should be a code set.
Have it checked for codes and post back code no if it has any.
But remember a code does not say replace the part .
It only says there is a problem that needs to checked it out.
MT

I dont have my own scanner, so I ran up to autozone and they read the codes for me. They said the only code they were getting was a P0420. As far as I can tell this means "catylist system efficiency below threshold (bank 1). From what I have found online this could be caused by a number of problems, from o2 sensors to the cat, egr, maf, pcv, and a few other things. Do you have any suggestions on how I might narrow this list down.
Thanks for the responses.

the 4.3 engine is a carbon generating monster. go back to the balzer forum and do a search on key word "carbon" and you'll get over 30 threads on the subject including some with p04xx codes.

I dont have my own scanner, so I ran up to autozone and they read the codes for me. They said the only code they were getting was a P0420. As far as I can tell this means "catylist system efficiency below threshold (bank 1). From what I have found online this could be caused by a number of problems, from o2 sensors to the cat, egr, maf, pcv, and a few other things. Do you have any suggestions on how I might narrow this list down.
Thanks for the responses.

Yes the code 420 is a hard code to figure out.
It is usually caused by a engine not running right.
Engine miss fire or running rich.
A good scanner and knowing how to read out the sensor readings is the first step.

If the repair shop said the egr valve and o2 sensors was bad I would ask them how they figured that out or what they found in that area.

To give you a idea of how to deal with it.
Here is a little info on it that may take a little time to go threw but should explain how to fix it or deal with it.
Good luck and let us know how it goes.
MT

http://www.troublecodes.net/articles/catfailure/

DTC P0420, P0421, and P0430 & P0431: Check Possible Cause Of Misfire DTC P0420 and P0421 indicate bank one catalyst system efficiency is minimum requirement. DTC P0430 and P0430 indicate bank 2-catalyst system efficiency is minimum requirement. Possible causes are as follows: Use of leaded fuel. Oil contamination. Cylinder misfire. Fuel pressure too high. HO2S sensor improperly connected. Damaged exhaust system component. Faulty ECT sensor. Faulty HO2S. Ensure ignition timing is correct. Retrieve all Continuous Memory DTCs. If misfire code is not present, go to next step. If misfire code is present, isolate cylinder and repair as necessary. Check HO2S Monitor DTCs If DTCs P0136, P0138, P0140, P0141, P0156, P0158, P0160, or P0161 were present in step 1), service as necessary before continuing. If none of these codes are present in step 1), go to next step. Check ECT Sensor DTCs If DTCs P0117, P0118, P0125 or P1117 were present in step 1), service as necessary before continuing. If none of these codes are present in step 1), go to next step. If any codes except P0420, P0421, P0430 and/or P0430 were present in step 1), service as necessary before continuing. If no codes except P0420 and/or P0430 were present in step 1), go to next step. Check Rear HO2S Wiring Harness Turn ignition off. Ensure HO2S wiring harness is correctly routed and connectors are tight. Repair or replace as necessary. If wiring harness and connectors are okay, go to next step. Check Fuel Pressure Turn ignition off. Release fuel pressure. Install fuel pressure gauge. Start engine and allow to idle. Note fuel pressure gauge reading. Increase engine speed to 2500 RPM and maintain for one minute. For fuel pressure specifications, see FUEL PRESSURE SPECIFICATIONS article. If fuel pressure is as specified, go to next step. If fuel pressure is not as specified, go to CIRCUIT TEST HC. Check For Exhaust System Leaks If exhaust system leaks, it may cause catalyst monitor efficiency test to fail. Inspect exhaust system for cracks, loose connections or punctures. Repair or replace as necessary. If exhaust system is okay, go to next step. Check For Exhaust System Restrictions Inspect exhaust system for collapsed areas, dents or excessive bending. Repair or replace as necessary. If exhaust system is okay, go to next step. Check Manifold Vacuum Install tachometer. Connect vacuum gauge to intake manifold vacuum source. Start engine and raise engine speed to 2000 RPM. Manifold vacuum should rise to more than 16 in. Hg. If manifold vacuum is okay, go to next step. If manifold vacuum is low, go to step 11). Leave tachometer and vacuum gauge connected. Start engine and raise engine speed to 2000 RPM. On a non- restricted system, manifold vacuum should quickly rise to normal range as increased RPM is maintained. On a restricted system, manifold vacuum will slowly rise to normal range as increased RPM is maintained. If manifold vacuum is okay, no indication of exhaust leak or restriction has been detected and testing is complete. If manifold vacuum is low or slow to respond, go to next step. Leave tachometer and vacuum gauge connected. Remove exhaust pipe from exhaust manifold. Start engine and raise engine speed to 2000 RPM. If manifold vacuum is now okay, fault is downstream from exhaust manifold. Reconnect exhaust pipe to exhaust manifold and go to next step. If manifold vacuum is still low or slow to respond, fault is in exhaust manifold or intake manifold gasket. Repair or replace as necessary and repeat QUICK TEST. Leave tachometer and vacuum gauge connected. Disconnect muffler/tailpipe assembly from rear of catalytic converter. Start engine and raise engine speed to 2000 RPM. If manifold vacuum is now okay, fault is in muffler/tailpipe assembly. Repair or replace as necessary and test-drive vehicle to verify elimination of symptom. If manifold vacuum is still not okay, fault is in catalytic converter. Repair or replace as necessary. Check tailpipe/muffler assembly for debris from catalytic converter. Test drive vehicle to verify elimination of symptom.

A quart of tranny fluid ran through the brake booster vacuum line will clean it right out. I've also had people tell me to use water, on a cold engine, and its easiar on the O2 sensor and catalytic converter. Using tranny fluid will smoke like crazy as well and dont let the engine die while running it through...