Not sure if you've read through these diagnostic pages:
P0171 - Fuel Trim System Lean Bank 1
P0174 - Fuel Trim System Lean Bank 2
P030x - Random/Multiple Cylinder Misfire Detected
P0420 - Catalyst System Efficiency Below Threshold (Bank 1)

If not, read through them and any links provided in there. You can also search for the codes either separately or together (ex. "P0171+P0174" without the quotes which will result in threads where other members have come across concerning these two codes).

I am inclined to think that your P0420 code is a result of the aftermarket catalytic converter not quite meeting the standards that your PCM is looking for out of the rear O2 sensor.

 

So I checked for a vacuum leak and found the hose feeding into the ORB was completely dry rotted and broken off. I replaced the 6 inch piece of vacuum hose. I idle went from almost 900 to below 600(should be around 600),the load on the motor went from 28% down to 19%. Everything seems to be running so much better. Weird how the $500 computer only got one code and the more expensive one got four which lead me to believe it was a vacuum leak.

 

Glad you found your problem. If you are dissatisfied with the quality/quantity of the advice, feel free to look elsewhere...

 

I always look more then one place for advice or help, compare results and proceed with what I feel the problem could be. I try not limiting myself to one set of theories. It's funny how one group tends to have a certain way of thinking when compared to another. I'm thankful for any suggestions I get and I know I can go elsewhere. We'll just see if this vacuum leak really does fix everything.

 

UPDATE:

The vacuum leak I fixed helped everything run way better. But now it is still cutting out on me. I am assuming I will get the misfire P0300 and the P0171 & P0174 and the P0420. I don't get it. It's very frustrating and I only have 12 days before I am supposed to drive this to CA from PA. My CAT is a Magnaflow 23455. Direct fit. I have until the 10th before my one year replacement is up on the CAT if it is faulty. It looks fine. Is there another way to check it?

I have gone through dozens of pages now. Searching for anyone who has had an issue that really matched mine.I found two that seems mirror to mine.

V8S10.ORG • View topic - Solved - '97 4.3 Blazer hesitation, P0300 - random misfire

https://blazerforum.com/forum/2nd-ge...g-59088/page2/

What is you take on it?

 

Have the codes come back or are you just theorizing...

Describe the circumstances behind when it cuts out.

Have you run through all of the checks described in the associated trouble code links provided above?

Are you assessing the health of the catalytic converter by looking at it from the outside? There really isn't any way other than looking through the inlet side of the cat at the catalyst inside to visually assess the health of the cat... I highly doubt that a catalytic converter problem is causing a random hesitation.

 

Thanks for the quick reply.

No codes yet(I am sure it wont be long now).So I guess I have to do research and guess work on symptoms until codes come back.

If I'm at a stop and start accelerating it will cut out a few times. Then while keeping a steady speed(40-60mph) it cuts in and out(I am sure it is the misfire I am feeling).

I completely unbolted the CAT and looked inside it. Everything looks fine.

Swartlkk,
I just got done reading this 9 page topic. The person was having a very similar issue. You posted a lot in this one and is seems like the dielectric grease helped him on his ICM. So I was thinking I could take my new cap and rotor off and look to see if the slots or holes(screens) were plugged or anything out of the ordinary and dry some of the dielectric grease. I really do not have any more money to spend on it but if I don't get this solved ASAP then I wont be able to drive it home to CA anyway. Also posted in his thread was about the coil and MAP sensor. Are there ways to clean these? I'm going nuts over here and reading everything. I called the dealer and they tell me what they always say"bring it in we need to see it". But being mechanically minded it doesn't take any effort to help rule some things out or make a suggestion. I have read through the links that were posted.I printed everything off for my mechanic friend across the street. He brought tools from work and used the list. He is stumped but said maybe he is missing something because he works at a Ford dealer. Thanks again

 

You could try the screens & making sure that the ICM is properly installed with thermal paste between it and the heat sink. Typically though, once an ICM overheats to the point of a fault, it just stops functioning.

Does the hiccup change if you turn off the A/C?

 

It doesn't at all with the A/C. I does feel like it "hits" harder in D instead of OD.

I just went out to check my MAP sensor. I unplugged it and carefully pulled it out. When I did there was a small piece of the rubber that came off. I quickly grabbed it before it fell back into the hole. The sensor itself was filthy and loosely sitting in the hole and smelled of gas. Either way I will have to buy a new one. There is carbon build up all the way past the rubber boot. So maybe this was another vacuum leak?

 

Looks fine from the outside to me. The rubber seal does tend to tear like that when removing it after it's been in service for awhile. I think the damage occurred during the removal and it likely wasn't leaking as installed. I always test the MAP to see if the ambient atmospheric pressure is resulting in the proper voltage readout prior to removal.