Hello everyone,
This is my first post, but I really need your guy's help. Here are the basics = 86 K5 Blazer, 350 sbc (from an 88or newer). It previously had the stock TBI system that is on 88+ I removed all that and put on an Edelbrock performer intake with EGR, and an Edelbrock 1406 carb. I replaced the high flow fuel pump with an electric pump (4-7psi ) or so. I have a Holley fuel pressure regulator and the fuel pressure is at 5-5.25 psi. It runs like a champ in idle, and under CERTAIN driving situations. The main issue now is ***when I am driving around and there is a slight load, Perhaps up a small hill or when I was on a dyno with load, the gas pedal is constant and there should be a constant RPM but the engine seems to be intermittently slowing or speeding up in 3-4 second intervals. The smog test computer showed that the engine was "accelerating" and this pulsing caused my test to fail. I cannot seem to hold the vehicles rpm steady under a load. No other issues. Emissions are fine, no smoke, no misfiring, backfires, overheating, stumbling on acceleration or anything else.
Things I have tried already or parts are new or been replaced twice.
new carb
new intake
new fuel pump twice
new rotor - cap - distributor twice - ignition module - and coil twice.
changed new copper autolite plugs to platinum autolites, re-gapped and even color was fine on old ones.
new fuel pressure regulator and indicator. twice
new EGR valve, and new Cat conv.
I have adjusted the timing from about 4-6degrees, well past 12degrees and none of the ranges help.

There may be more that I have done. I basically have replaced everything I could besides the long block itself. Please, if there are any ideas, let me know. I am not an expert but I have built several motors that have passed California smog etc... I have tried many things but am open for suggestions. I am lost at this point.

 

Also replaced wires twice :/ no shorting out or burns.

 

A/C cycling, or any high idle switch on the carb?

 

The A/C has long been disconnected and is not involved. Yesterday I sprayed around with carb cleaner and didn't find any new leaks. I checked the fuel pressure while the engine stumbled (during power braking) and the fuel pressure remains constant. There are no switches on my carb. Only fuel air mix for idle, and the idle itself. I am beginning to think there must be a certain range of RPM that the carb is not performing well. Like 1000-1800RPM it stumbles under load, but any RPM after, it is perfect. So perhaps there are certain jets or something for that range and I need to rebuild it??? I am debating on heading to the carb shop. I cannot think of anything else.

 

So, I installed new pickup springs, metering rods, and jets for my edelbrock carb. Problem remains. Seems like it is not a fuel issue X check...
I am going outside to try and block off the EGR valve to see if anything changes. Some people had luck doing this.

** checked EGR, it works and is not problematic. Connected or disconnected/blocked, it does the same stumble.

 

Did it run that way since you changed to the carb, or did that develop at a later time?

 

It was running pretty funky and with a possible miss at random times, the tbi setup that was on there was not done well and had issues. However, I think this issue started more recently. I wish I could be sure. The very last think I have to try is replacing the ignition control module. It is brand new, MSD ignition model and was 43dollars. I have an old one from my monte carlo, I am just going to swap it to see if anything hAppens. it is a low percent chance but yeah,.