1. This site uses cookies. By continuing to use this site, you are agreeing to our use of cookies. Learn More.

1994 Z-71 Cold start Runs bad 30 seconds??

Discussion in 'Engine & Performance' started by Durfman77, May 12, 2020.

  1. Durfman77

    Durfman77 Junior Member

    Posts:
    12
    Likes Received:
    7
    Joined:
    Jan 12, 2020
    Location:
    Michigan
    First Name:
    Charles
    Truck Year:
    1994 /2001
    Truck Model:
    GMC
    Engine Size:
    5.7/5.3
    This truck has been fine for me and runs perfect all day long----But when first started when cold it starts right up fine,,idles fine for about 20 seconds then starts acting like its being flooded with gas for another 20 to 30 seconds then clears right up and runs fine all day???
    Just cant put my finger on whats going on?

    P3211216 (1024x768).jpg

    P3211218 (1024x768).jpg

    P3211228 (1024x768).jpg
     
  2. Catbox

    Catbox Full Access Member

    Posts:
    698
    Likes Received:
    1,367
    Joined:
    Jul 12, 2018
    Location:
    Portland Oregon
    First Name:
    Peter
    Truck Year:
    1979
    Truck Model:
    C20 Silverado Camper Special
    Engine Size:
    461
    My 1995 Suburban will occasionally give me fits when it first starts up.
    It will idle like it has a huge cam in it for 45 seconds to 90 seconds and then it evens right out.
    I have put Seafoam in the tank and it helps clean that issue up.

    But I haven't bothered to actually figure out what is causing it.
     
  3. Frankenchevy

    Frankenchevy Supporting Member Supporting Member

    Posts:
    3,723
    Likes Received:
    3,316
    Joined:
    Jan 3, 2018
    Location:
    USA
    First Name:
    Guy
    Truck Year:
    Square
    Truck Model:
    CUCV
    Engine Size:
    Small
    I’d start by checking the fuel pump and filter.

    Maybe a problem with CTS enrichment or after start enrichment. Not sure how those two items are controlled by the factory ecu.
     
    Catbox and bucket like this.
  4. bucket

    bucket Super Moderator Staff Member

    Age:
    38
    Posts:
    21,267
    Likes Received:
    6,725
    Joined:
    Aug 3, 2010
    Location:
    Usually not in Ohio
    First Name:
    Andy
    Truck Year:
    '77, '78, '79, '84, '88
    Truck Model:
    K5 thru K30
    Engine Size:
    350-454
    A faulty CTS can 100% cause a cold start issue like described.
     
    Catbox likes this.
  5. AuroraGirl

    AuroraGirl Supporting Member Supporting Member

    Posts:
    1,192
    Likes Received:
    627
    Joined:
    Sep 8, 2019
    Location:
    Northern Wisconsin
    First Name:
    Taylor
    Truck Year:
    1980
    Truck Model:
    K2500
    Engine Size:
    5.7
    i mean, not a square body. but definitely digging the truck, looks real nice. Any check engine lights?
     
  6. Durfman77

    Durfman77 Junior Member

    Posts:
    12
    Likes Received:
    7
    Joined:
    Jan 12, 2020
    Location:
    Michigan
    First Name:
    Charles
    Truck Year:
    1994 /2001
    Truck Model:
    GMC
    Engine Size:
    5.7/5.3
    No engine codes at all am going to try the CTS change today and see?
     
    Catbox likes this.
  7. scwaters

    scwaters Supporting Member Supporting Member

    Posts:
    58
    Likes Received:
    31
    Joined:
    May 26, 2017
    Location:
    Chester Springs, PA
    First Name:
    Sunny
    Truck Year:
    1976
    Truck Model:
    K10 Shortbed 4x4
    Engine Size:
    350
    Alright, what is a CTS? My K10 behaves the same way
     
  8. Durfman77

    Durfman77 Junior Member

    Posts:
    12
    Likes Received:
    7
    Joined:
    Jan 12, 2020
    Location:
    Michigan
    First Name:
    Charles
    Truck Year:
    1994 /2001
    Truck Model:
    GMC
    Engine Size:
    5.7/5.3
    Well I tried the CTS today and No change?? So am getting an oxy. sensor next day or so and see if thats it???
     
  9. SirRobyn0

    SirRobyn0 Full Access Member

    Posts:
    349
    Likes Received:
    308
    Joined:
    Dec 6, 2019
    Location:
    In the woods in Western Washington
    First Name:
    Rob
    Truck Year:
    1984
    Truck Model:
    C20
    Engine Size:
    350
    CTS = Coolant Temperature Sensor. @Durfman77 someone else said fuel pump possible issue and they are right. O2 sensors are not in play until closed loop so that won't effect the cold run at all. I would hook a fuel pressure gauge up to it and see if the pressure drops off when it acts up. Hooking up a scanner and monitoring the sensors when it is happening would sure be helpful. You might find an issue that way.
     
    Cuba likes this.
  10. Bextreme04

    Bextreme04 Full Access Member

    Posts:
    164
    Likes Received:
    146
    Joined:
    May 13, 2019
    Location:
    Salem, OR
    First Name:
    Eric
    Truck Year:
    1980
    Truck Model:
    K25
    Engine Size:
    350-4bbl
    Just throwing parts at it will get expensive. Try and hook up to see what the various sensors are showing the ECU. If you don't know how to do that, at least test the sensors before trying to change them out.
     
    Cuba and Catbox like this.
  11. Durfman77

    Durfman77 Junior Member

    Posts:
    12
    Likes Received:
    7
    Joined:
    Jan 12, 2020
    Location:
    Michigan
    First Name:
    Charles
    Truck Year:
    1994 /2001
    Truck Model:
    GMC
    Engine Size:
    5.7/5.3
    Thanks--I had a good CTS so just tried it,, I dont see how fuel pump would be problem when all day it runs fine and I pull a trailer with about 3600 on it about 3 times a week and runs good? NOT trying to argue or doubt you but just not understanding the fuel pump issue?

    Just started this couple months ago I bought the truck 1 1/2 years ago and it never did this? 95 year old lady had it bought it new and had all service records.

    I know about parts ,,just throwing parts at it goes against everything I ever did --just getting lazy I guess and looking for easy fix??

    I put ele, fan on it last winter did all wiring myself dont think that could have any affect on this????
    I can check pressure on it next couple days,,
     
  12. Durfman77

    Durfman77 Junior Member

    Posts:
    12
    Likes Received:
    7
    Joined:
    Jan 12, 2020
    Location:
    Michigan
    First Name:
    Charles
    Truck Year:
    1994 /2001
    Truck Model:
    GMC
    Engine Size:
    5.7/5.3
    OH--I also put new exhaust on it last fall and knocked the cat out of it but dont think this started then if I remember right?
     
  13. SirRobyn0

    SirRobyn0 Full Access Member

    Posts:
    349
    Likes Received:
    308
    Joined:
    Dec 6, 2019
    Location:
    In the woods in Western Washington
    First Name:
    Rob
    Truck Year:
    1984
    Truck Model:
    C20
    Engine Size:
    350
    So the fuel pump issue would be this. It bleeds down over night and the fuel is replaced with air in the lines, you turn the key on and it pressures up, there is still fuel in the fuel rail, but there is now air in the lines, so it starts on the fuel in the fuel rail and then when it gets to the air it runs bad and once that is clear it is good all day. This is a problem I've seen on that generation chev truck before, testing the fuel pressure should help you identify that. BUT there's other sensors, that if monitored on a scan tool you might find one out of whack. Bottomline is tests need to be run, or you may end up spending a lot of time on money on unneeded repairs.
     
  14. Durfman77

    Durfman77 Junior Member

    Posts:
    12
    Likes Received:
    7
    Joined:
    Jan 12, 2020
    Location:
    Michigan
    First Name:
    Charles
    Truck Year:
    1994 /2001
    Truck Model:
    GMC
    Engine Size:
    5.7/5.3
    Thank you!!! Now that makes sense to me for sure. Will be checking into that.
     
  15. SirRobyn0

    SirRobyn0 Full Access Member

    Posts:
    349
    Likes Received:
    308
    Joined:
    Dec 6, 2019
    Location:
    In the woods in Western Washington
    First Name:
    Rob
    Truck Year:
    1984
    Truck Model:
    C20
    Engine Size:
    350
    Let us know what you find out.
     

Share This Page