Page 1 of 3 1 2 3 LastLast
Results 1 to 10 of 21

Thread: 4age Blacktop swap, bogging / hesitating badly

  1. #1
    Senior Member
    Join Date
    Aug 2013
    Name
    Graham
    State
    VIC
    Location
    Melbourne
    Country
    Australia
    Posts
    111

    Default 4age Blacktop swap, bogging / hesitating badly

    Car: KE70
    Engine: 4age blacktop 20V, bought as a complete runner from an importer
    ECU: Standard (Auto)
    Ignition: SQ Engineering Distributor relocation kit
    Fuel pump: Lift pump, surge tank, Bosch EFI pump, new lines and filter

    Problem: Engine starts and idles fine but bogs badly when the throttle is applied. Will rev OK if throttle is applied slowly.

    Already checked: Cam timing OK, ignition timing OK (10 degrees BTDC), no fault codes on ECU. Pulled plug off TPS and the idle jumped up slightly but otherwise not much difference. Pulled plug off MAP sensor and engine wanted to die. After doing this I got fault codes for both sensors, as expected.

    Any suggestions?

  2. #2
    Member
    Join Date
    Jan 2015
    Name
    Dave
    State
    Michigan
    Location
    South Lyon
    Country
    USA
    Posts
    65

    Default

    Borrow a VOM then check the TPS per manual. I would also verify the wiring from the TPS to the ECU and check fuel pressure.
    Dave

  3. #3
    Member
    Join Date
    Mar 2011
    Name
    Ced
    State
    VIC
    Location
    Rowville
    Country
    Australia
    Posts
    80

    Default

    I had a similar issue. Faulty / incorrect knock sensor installed. Swapped it for a new one and the bogging dissapeared. Another thing that can cause hesitation is the VVT pulley.

  4. #4
    Noooob
    Join Date
    Jun 2010
    Name
    Matt
    State
    NSW
    Location
    Campbelltown
    Country
    Australia
    Posts
    5,246

    Default

    There are a number of things as the guys have said. I have experienced the knock sensor myself on a couple of occasions. Leaky capacitors in the ecu is another common one.

    Have you given the car a chance to warm up? My daily has a faulty temp sensor which causes it to big down until I've driven about a km. It's worse in winter than summer.

    02 sensor or missing sta signal from the ecu won't cause it. Speed sensor input missing from the ecu also retards the timing a lil and will drop the rev limit but won't cause it to bog down.
    Ae86 Drivingclub - Toyota AE86 Car Club where AE86 | KE70 | Toyota 86 / GT86 | Subaru BRZ | Scion FRS owners

  5. #5
    Moderator Sam-Q's Avatar
    Join Date
    Dec 2008
    Name
    Sam
    State
    VIC
    Location
    Endeavour Hills
    Country
    Australia
    Posts
    4,242

    Default

    Make sure that there isn't any vacuum leaks, spraying soe engine start spray around the throttles would help determine that. If the revs go up then it's sucking it in somewhere.

    The MAP and TPS sensors can both cause these issues. The TPS sensors however are much more known to wear out and need replacing. But make sure that the MAP sensor rubber line doesn't have any cracks or similar.

    I have TPS sensors in stock but no knock sensors, but by memory I added some to my last order and they should be here in about a week. I should also start to stock MAP sensors seeing this isn't the first time that someone may of needed one.
    My website: SQ Engineering - 4AGE and 3SGE upgrade/replacement parts

    - SQ Engineering on facebook -

    Please e-mail to contact me instead of sending a private message on here.

  6. #6
    Senior Member
    Join Date
    Feb 2009
    Name
    Tan
    State
    VIC
    Location
    West
    Country
    Australia
    Posts
    102

    Default

    Could also be clogged injectors not opening which would explain idle and rev slowly. Typical problem if the engine has been sitting around for a long time...just have to check bit by bit until you find it...

  7. #7
    Senior Member Futo_gt86's Avatar
    Join Date
    Mar 2011
    Name
    Ali
    State
    QLD
    Location
    4300
    Country
    Australia
    Posts
    728

    Default

    I had a Silvertop do the same kind of thing to me.
    Does the Blacktop have same Idle Speed Control Valve as Silvertop?
    If yes, might want to check out how ISCV is plumbed.
    I deleted mine altogether which made the symptoms disappear, opened up the top end and wide open throttle.
    I had aftermarket ECU so I could tinker with the idle to get it right, not sure how Stock ECU would react.
    Good luck with it and let us know how you get on with this issue.

  8. #8
    Noooob
    Join Date
    Jun 2010
    Name
    Matt
    State
    NSW
    Location
    Campbelltown
    Country
    Australia
    Posts
    5,246

    Default

    It will throw a check engine light if it is unplugged , I had a high idle issue years ago which turned out to be a stuck valve.

    Carby cleaner usually un-sticks these.
    Ae86 Drivingclub - Toyota AE86 Car Club where AE86 | KE70 | Toyota 86 / GT86 | Subaru BRZ | Scion FRS owners

  9. #9
    Senior Member
    Join Date
    Aug 2013
    Name
    Graham
    State
    VIC
    Location
    Melbourne
    Country
    Australia
    Posts
    111

    Default

    Finally got around to looking at the car again today:

    TPS resistance is in spec and wiring to ECU is all intact
    Sprayed ether all around intake and no obvious vacuum leaks. All vacuum lines are new.
    Knock sensor is connected but have no way of testing it.
    Pulled ECU apart and all looks fine (no leaky capacitors)
    Unable to check fuel pressure as I don't have a gauge but both fuel pumps and lines are brand new, wired and plumbed correctly. FPR is factory and untouched. What would be potential causes of fuel pressure issues?
    Car idles really high with ISCV disconnected, much better with it on.
    When I was messing around with the dizzy it definitely seemed more responsive when the timing was advanced.
    Also noticed there is a lot of carbon buildup in the intake manifold behind the throttle plate. Car has backfired out the intake on previous starts. Is this anything to be worried about?

  10. #10
    Noooob
    Join Date
    Jun 2010
    Name
    Matt
    State
    NSW
    Location
    Campbelltown
    Country
    Australia
    Posts
    5,246

    Default

    Check the condition of the dizzy cap, the carbon pile can wear out over time.
    Ae86 Drivingclub - Toyota AE86 Car Club where AE86 | KE70 | Toyota 86 / GT86 | Subaru BRZ | Scion FRS owners

Page 1 of 3 1 2 3 LastLast

Similar Threads

  1. ..20v bogging/spitting
    By Tore in forum Technical - Questions
    Replies: 17
    Last Post: 10th September 2014, 08:05 AM
  2. 4AGE ST20V with BT A/T ECU and COP bogging/no power AE86 JDM
    By 4.5AG in forum Technical - Questions
    Replies: 8
    Last Post: 10th May 2014, 07:05 PM
  3. 4age slightly down on power and hesitating in lower rpm
    By Sprinter Freak in forum Technical - Questions
    Replies: 28
    Last Post: 26th December 2012, 05:11 PM
  4. badly need iac or iscv for 4age 20v
    By ae8620v in forum Cars or Parts Wanted
    Replies: 1
    Last Post: 24th August 2011, 04:39 PM
  5. Need help badly....
    By jinjaninja in forum General Topics (No Technical Questions)
    Replies: 15
    Last Post: 9th February 2007, 02:32 AM

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •