jQuery not supported.



5.7 light throttle stumble

EGR issue

5.7 light throttle stumble

Postby Mascobe [OP] » Mar 18 2011, 7:43pm

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
Original Poster
Mascobe
Newbie
Newbie
Posts: 5
Topics: 2
Joined: Mar 18 2011, 7:14pm
Years of membership: 3 years of membership3 years of membership3 years of membership
Location: Madison
Year: 1995
Make/Model: Chevrolet Silverado
Extra Info: 5.7L auto 2wd
Group Membership:
Registered users

Re: 5.7 light throttle stumble

Postby lzn197 » Mar 18 2011, 8:19pm

So if you unplug the EGR it runs ok? If it does run better, it should spark knock with it unplugged. Does it ?
Gordon
2004 Chevrolet Silverado Extended Cab Z71
Semi-retired Master Mechanic
User avatar
lzn197
ASE Certified
ASE Certified
4x4 High Mode [L3]
4x4 High Mode [L3]
Posts: 1810
Topics: 6
Images: 22
Joined: Apr 01 2010, 3:45pm
Years of membership: 4 years of membership4 years of membership4 years of membership4 years of membership
Location: Central Michigan
Year: 2004
Make/Model: Chevrolet Silverado
Extra Info: K1500 5.3L Z71 EX
Group Membership:
Automotive Technicians
Registered users

Re: 5.7 light throttle stumble

Postby Mascobe [OP] » Mar 21 2011, 6:07am

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?
Original Poster
Mascobe
Newbie
Newbie
Posts: 5
Topics: 2
Joined: Mar 18 2011, 7:14pm
Years of membership: 3 years of membership3 years of membership3 years of membership
Location: Madison
Year: 1995
Make/Model: Chevrolet Silverado
Extra Info: 5.7L auto 2wd
Group Membership:
Registered users

Re: 5.7 light throttle stumble

Postby Mascobe [OP] » Mar 22 2011, 5:57pm

Bump, anyone have a clue on this problem? Could a weak fuel pump still cause this issue?
Original Poster
Mascobe
Newbie
Newbie
Posts: 5
Topics: 2
Joined: Mar 18 2011, 7:14pm
Years of membership: 3 years of membership3 years of membership3 years of membership
Location: Madison
Year: 1995
Make/Model: Chevrolet Silverado
Extra Info: 5.7L auto 2wd
Group Membership:
Registered users

Re: 5.7 light throttle stumble

Postby lzn197 » Mar 22 2011, 6:34pm

Yes a weak fuel pump could cause the issue but you said you have a black tailpipe and that indicates a rich running engine. Check your fuel pressure and flow.
Gordon
2004 Chevrolet Silverado Extended Cab Z71
Semi-retired Master Mechanic
User avatar
lzn197
ASE Certified
ASE Certified
4x4 High Mode [L3]
4x4 High Mode [L3]
Posts: 1810
Topics: 6
Images: 22
Joined: Apr 01 2010, 3:45pm
Years of membership: 4 years of membership4 years of membership4 years of membership4 years of membership
Location: Central Michigan
Year: 2004
Make/Model: Chevrolet Silverado
Extra Info: K1500 5.3L Z71 EX
Group Membership:
Automotive Technicians
Registered users

Re: 5.7 light throttle stumble

Postby Mascobe [OP] » Mar 25 2011, 5:26pm

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
Original Poster
Mascobe
Newbie
Newbie
Posts: 5
Topics: 2
Joined: Mar 18 2011, 7:14pm
Years of membership: 3 years of membership3 years of membership3 years of membership
Location: Madison
Year: 1995
Make/Model: Chevrolet Silverado
Extra Info: 5.7L auto 2wd
Group Membership:
Registered users

Return to Engine

 

  • Similar topics
    Replies
    Views
    Last post

Common search terms

light problem still engine same stumble throttle check post thing black right help looks anyone installed

It is currently Oct 26 2014, 8:39am

  • Sponsor
Login  •  Register
SHOP TALK (Live Chat)
Engine Forum
EngineThis is where all of our engine discussion and conversation takes place. Talk about engine diagnostics, adjustments, modifications, performance and care. Motor tuning and repair to gain horsepower and fuel efficiency.
To create a new topic in Engine, click this button:
Previous topic Next topic
Sitewide News Sitemaps & Feeds

Who is online

Users browsing this forum: No registered users and 1 guest