1999 4.3 only runs only with maf disconnected - GM Forum - Buick, Cadillac, Olds, GMC & Pontiac chat

Chevrolet When starting new posts, please specify YEAR, MAKE, MODEL, ENGINE type, and whatever modifications you have made.

1999 4.3 only runs only with maf disconnected

Old 02-14-2013, 09:33 AM
  #1  
Junior Member
Thread Starter
 
Join Date: Feb 2013
Posts: 5
Thanks: 0
Thanked 0 Times in 0 Posts
200VEGAS is on a distinguished road
Question 1999 4.3 only runs only with maf disconnected

my sons truck will barely accelerate and wont get on the freeway at all with the maf plugged in. it shows low volt at all 4 o2 sensors we pulled the o2'* ahead of cat and didnt help. he accidently unplugged maf and it runs ok.not perfect, but preety goog. so he is driving it like that. we replaced the maf and it didnt change anything so we returned it and put the old one back on, but it is not plugged in. any ideas... fuel rail is at 35lbs and fuel filter is new
200VEGAS is offline  
Old 02-14-2013, 10:31 AM
  #2  
Senior Member
True Car Nut
 
jwfirebird's Avatar
 
Join Date: Dec 2009
Location: western,ny state
Posts: 9,616
Thanked 563 Times in 481 Posts
jwfirebird has a reputation beyond reputejwfirebird has a reputation beyond reputejwfirebird has a reputation beyond reputejwfirebird has a reputation beyond reputejwfirebird has a reputation beyond reputejwfirebird has a reputation beyond reputejwfirebird has a reputation beyond reputejwfirebird has a reputation beyond reputejwfirebird has a reputation beyond reputejwfirebird has a reputation beyond reputejwfirebird has a reputation beyond repute
Default

i think you should have 50+ psi for poppets, maybe pump going out

shouldnt even run. you try a different gauge?
jwfirebird is offline  
Old 02-14-2013, 11:13 AM
  #3  
Junior Member
Thread Starter
 
Join Date: Feb 2013
Posts: 5
Thanks: 0
Thanked 0 Times in 0 Posts
200VEGAS is on a distinguished road
Default he converted it to the newer style

spyder upgrade injector style and we think its regulator is set at like 35
200VEGAS is offline  
Old 02-14-2013, 11:14 AM
  #4  
Junior Member
Thread Starter
 
Join Date: Feb 2013
Posts: 5
Thanks: 0
Thanked 0 Times in 0 Posts
200VEGAS is on a distinguished road
Default

we tried several gauges, yes
200VEGAS is offline  
Old 02-14-2013, 11:36 AM
  #5  
Senior Member
True Car Nut
 
jwfirebird's Avatar
 
Join Date: Dec 2009
Location: western,ny state
Posts: 9,616
Thanked 563 Times in 481 Posts
jwfirebird has a reputation beyond reputejwfirebird has a reputation beyond reputejwfirebird has a reputation beyond reputejwfirebird has a reputation beyond reputejwfirebird has a reputation beyond reputejwfirebird has a reputation beyond reputejwfirebird has a reputation beyond reputejwfirebird has a reputation beyond reputejwfirebird has a reputation beyond reputejwfirebird has a reputation beyond reputejwfirebird has a reputation beyond repute
Default

wont run on 35, 50 to 55 will run 58+ will make it run properly.
jwfirebird is offline  
Old 02-14-2013, 01:58 PM
  #6  
Junior Member
Thread Starter
 
Join Date: Feb 2013
Posts: 5
Thanks: 0
Thanked 0 Times in 0 Posts
200VEGAS is on a distinguished road
Default

even though it is mpfi and not cpfi. i thought i read somewhere the pressure regulator runs at 35 on the mpfi conversion.
200VEGAS is offline  
Old 02-14-2013, 02:46 PM
  #7  
Senior Member
True Car Nut
 
jwfirebird's Avatar
 
Join Date: Dec 2009
Location: western,ny state
Posts: 9,616
Thanked 563 Times in 481 Posts
jwfirebird has a reputation beyond reputejwfirebird has a reputation beyond reputejwfirebird has a reputation beyond reputejwfirebird has a reputation beyond reputejwfirebird has a reputation beyond reputejwfirebird has a reputation beyond reputejwfirebird has a reputation beyond reputejwfirebird has a reputation beyond reputejwfirebird has a reputation beyond reputejwfirebird has a reputation beyond reputejwfirebird has a reputation beyond repute
Default

no ive done the conversion, its exactly the same. is this a full size? shouldnt matter 35 is way to low. but ive got new delphi pump, filter, and the new delphi mpfi and mine is 58psi engine off and runs at mid 60'* engine on
jwfirebird is offline  
Old 02-14-2013, 04:16 PM
  #8  
Junior Member
Thread Starter
 
Join Date: Feb 2013
Posts: 5
Thanks: 0
Thanked 0 Times in 0 Posts
200VEGAS is on a distinguished road
Default

ok, we will replace pump. thank you very much. i also called delphi and they said 60-68
200VEGAS is offline  
Old 02-14-2013, 05:02 PM
  #9  
Senior Member
True Car Nut
 
jwfirebird's Avatar
 
Join Date: Dec 2009
Location: western,ny state
Posts: 9,616
Thanked 563 Times in 481 Posts
jwfirebird has a reputation beyond reputejwfirebird has a reputation beyond reputejwfirebird has a reputation beyond reputejwfirebird has a reputation beyond reputejwfirebird has a reputation beyond reputejwfirebird has a reputation beyond reputejwfirebird has a reputation beyond reputejwfirebird has a reputation beyond reputejwfirebird has a reputation beyond reputejwfirebird has a reputation beyond reputejwfirebird has a reputation beyond repute
Default

vortec engine is really pressure critical. when i did my pump a month or tow later it started acting weird again, the pressure was going down to 53. it ended up being the filter i had on it must have gotten trash in it when i dropped the tank, so something to watch out for
jwfirebird is offline  
Related Topics
Thread
Thread Starter
Forum
Replies
Last Post
nick52405
Buick
10
05-12-2011 11:45 PM
racer42
General GM Chat
3
03-04-2011 01:13 AM
trixster68
1992-1999
5
08-03-2009 10:57 AM
HurstGN
2000-2005
3
11-07-2007 04:23 PM


Thread Tools
Search this Thread
Quick Reply: 1999 4.3 only runs only with maf disconnected


Contact Us Archive Advertising Cookie Policy Privacy Statement Terms of Service

© 2018 MH Sub I, LLC dba Internet Brands

We are a participant in the Amazon Services LLC Associates Program, an affiliate advertising program designed to provide a means for us to earn fees by linking to Amazon.com and affiliated sites.