Chevy Silverado and GMC Sierra Forum banner
Status
Not open for further replies.

5.7 light throttle stumble

9K views 5 replies 2 participants last post by  Mascobe 
#1 ·
1995 Silverado, 2wd, 5.7L Auto & AC.
-New: Plugs, wires, cap, rotor, air filter, EGR control valve, IAC (x2), TPS (x2), PCV, all rubber parts replaced, Brake booster, installed Witch hunter match flowed injectors (old injectors were dripping at idle, fuel pressure regulator diaghram.

Idle is normal. WOT seems normal ( pull a heavy trailer 4000lbs no problem). Interstate driving is fine (better milage at 70 mph than at 35 mph). Open loop it does not have the problem. Closed loop it will start hesitating (not every time) from idle to moving. It runs rough with light throttle on the flat and level at 35 mph. I pullled the EGR valve, looks clean and tested with hand vac pump and holds pressure for long time and also seems to close ok. Is this still and EGR issue (seems like the cause to me)? It also takes more time to start the longer the truck has been sitting. Any ideas or advice?

Mascobe
 
#3 ·
I have run it with the EGR unplugged at highway speeds and did rack up the code for no EGR/knock. Wouldn't the EGR sticking open cause poor idle? It is like a switch, as soon as the throttle comes off idle (slowly, in closed loop operation) the fluttering and surging starts. Surging is consistent in lower RPM ranges but has never surged at idle (IAC should be good then right?). No noticeable surging at speeds above 50 mph. Reducing throttle from 45 mph can cause bucking sometimes (all at closed loop operation). Open loop and it runs fine... Before starting the tail pipe had a thick coating of soot, mileage was poor and it cranked a long time before firing along with the same issues listed above. All other problems are fixed but the surging and bucking. Any other things I can do to test the system in closed loop operation? Also, what is the open connector for near the dizzy? Factory test port?
 
#6 ·
Well, I replaced the EGR (picked it on a whim while also picking up the power steering lines to replace them) and all of the issues went away. Everything that is on the net about the EGR start with "poor idle" or "rough idle". This EGR never caused a problem with idle. Also open loop operation was pretty good as well other than a long crank to get the engine going (the new EGR fixed the long crank time thing too). All I can figure is that it must have started to stay open once it had warmed up a little. Funny thing is that once warmed up the cranking time was also greatly reduced... I thank you for your help in this problem. Maybe this post will help someone else with the same issue. :D
 
Status
Not open for further replies.
You have insufficient privileges to reply here.
Top