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420A unknown issue with my 96 420a

Posted by RonSolo33, Sep 13, 2018

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  1. RonSolo33

    RonSolo33 Probationary Member

    6
    1
    Joined Sep 13, 2018
    Dallas, Georgia
    Ive been stuck on this problem for 2 weeks now.
    Manual
    Egr delete
    Cat delete
    Actual cold air intake
    Full exhaust
    Full rebuild
    4g63 ignition coils and wires
    .020 oversized 9 . 1 pistons
    BC 264 (i believe, cant remember) cams and valvesprings
    Ported throttle body
    Ac delete
    Powersteering delete
    Thermostat delete
    Charcole canister relocate
    Powersteering resivior relocate
    Battery relocate
    Ecu relocate
    Mishimoto radiator
    Radiator fans to toggle switch
    Daily 18 mile drive to work and 18 miles home
    All modds done by me and me alone a minimum of 1 year ago and max of 6 years ago with no issues untill 2 weeks ago
    Bought in 2012 full stock.
    Now stuck at work.
    First thing in the morning i can crank right up no problems idle fine no issue can rev up no issue no odd sounds no odd anything, have had plenty of tests over 2 weeks and can even handle 7k rev. Anyway after about 2 minutes of idle/with or without revs, engine shuts off and will turn over with starter but will not crank up to run. After 6 to 12 hours of sitting, cranks up just fine and repeats.
    Story and what Ive replaced (in order and trys between each part replacement)
    Shut off on way to work, got a ride from very kind retired man, that night cranked up and drove home sputtered just before naborhood entrance and shutoff in driveway would not start again untill morning 12 hours later. Took rides to work for next 2 days testing each each morning and night same repetition.
    -Fuel pump
    -Crank sensor
    Work good for 2 days and started repeating same issues shut off on way to work and was towed to work.
    -A 2nd crank sensor
    -Cam sensor
    -Map sensor
    -Ecu
    -Knock sensor
    -Sparkplugs
    -Fuelpump relay
    -Automatic shutdown relay
    Still no change. Still cranks up runs for few minutes with or without revs suddenly shuts off wont start again for 6 to 12 hours.
     

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  2. dustyboner

    dustyboner Proven Member

    596
    181
    Joined Mar 13, 2016
    abq, New Mexico
    so are you getting fuel and no spark when it won't start?
    or spark but no fuel?
    or neither spark or fuel?

    if you are running 4g63 coils on a 420a ecu, how exactly do you have it wired up?
     
    RonSolo33 likes this.
  3. RonSolo33

    RonSolo33 Probationary Member

    6
    1
    Joined Sep 13, 2018
    Dallas, Georgia
    No spark or fuel. And theres 1 power wire that splits for both coils on the 4g63 and 420a stock coils and theres 1 signal wire for each coil (a) and (b) on both 4g63 and 420a. So i wired in the connectors for the 4g63 coils useing the same wires from the 420a coils. Pretty easy and i dont have to replace both coils if one goes bad and have potential for other brands than msd or whatever oreillys has.
     
  4. dustyboner

    dustyboner Proven Member

    596
    181
    Joined Mar 13, 2016
    abq, New Mexico
    when it won't start, check to see if your getting power to the ECU. also check ECU grounds.

    im pretty sure that 4g63 coils need to be run with the power transistor, just because of the sticker.

    [​IMG]
     
  5. dustyboner

    dustyboner Proven Member

    596
    181
    Joined Mar 13, 2016
    abq, New Mexico
    upload_2018-9-13_18-24-33.png
     
    RonSolo33 likes this.
  6. silvreclips

    silvreclips Proven Member

    786
    41
    Joined Jul 19, 2005
    Greenville, South Carolina
    The 420a ecu has the ignitors built into the ecu where as the 4g63 uses a transistor pack to fire the coils. IDK how the coils compare output wise but I would expect he could run it no problem.

    I have seen bad ECUs cause a similar issue. But since you switched that already I would be checking into the wiring. I had a bad speed sensor once that cause the car to randomly die on me.
     
    RonSolo33 likes this.
  7. dustyboner

    dustyboner Proven Member

    596
    181
    Joined Mar 13, 2016
    abq, New Mexico
    where did you source the replacement cam sensor from? i have seen alot of non-OEM cam sensors that didn't work out of the box or they only lasted a short time. the ones from autozone are the worst. I had one car that i tried 3 new cam sensors from autozone, after the 3rd one, i threw on a used mopar one i had laying around. problem solved.
     
  8. RonSolo33

    RonSolo33 Probationary Member

    6
    1
    Joined Sep 13, 2018
    Dallas, Georgia
    I have been running the 4g63 coils for a year with no issues till now but i dont think the issue is the coils. Ill check the speed sensor tomorrow, although i thoight that only went to the odometer? Probably the ecu too, since you can see the speed with certain obd2 scaners.
     
  9. RonSolo33

    RonSolo33 Probationary Member

    6
    1
    Joined Sep 13, 2018
    Dallas, Georgia
    The cam sensor was taken off my wifes 98 420a that runs fine with it, and if it was the cam sensor, it wouldnt crank up and run fine every 6 to 12 hours would it? Or would the cam sensors values not affect anything for a few minutes? Same with the crank sensor? And thank you all for helping me.
     
  10. RonSolo33

    RonSolo33 Probationary Member

    6
    1
    Joined Sep 13, 2018
    Dallas, Georgia
    Would the ignition switch be doing this? i didnt check that yet, if its shorting out and thinking ive turned the key off it would tell the mfi/asd relay to turn everything off and with it shorted out it not register that im trying to crank back up? Or starter relay messed up? Is the starter relay connected to the ignition switch?
     
  11. dustyboner

    dustyboner Proven Member

    596
    181
    Joined Mar 13, 2016
    abq, New Mexico
    here is the starting circuit for MT without theft
    DSC04333_cr.jpg

    starting circuit: MT with theft
    DSC04334_cr.jpg

    this is the ignition circuit, it shows which ECU pins to check for (+)power and (-)grounds.
    page 1
    DSC04335_cr.jpg

    page2
    DSC04336_cr.jpg

    i would also check for corroded wires and terminals. ground wires are more likely to be corroded (and the end where it connects to the chassis). a corroded wire will have a high resistance and it will get worse when it gets hot.
    When i have dealt with similar problems, its usually a relay that is bad. It heats up and stops working until it has cooled down.
     
    Last edited: Sep 14, 2018
    silvreclips likes this.
  12. dustyboner

    dustyboner Proven Member

    596
    181
    Joined Mar 13, 2016
    abq, New Mexico
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    Attached Files:

  13. RonSolo33

    RonSolo33 Probationary Member

    6
    1
    Joined Sep 13, 2018
    Dallas, Georgia
    Thank you for all your help! I didnt know that the ignition switch was connected to the automatic shutdown relay. So i got a new ignition switch and before i installed it, i found a very very poorly sliced and i guess an attempt to be fixed by the previous owner so i fixed that and havent had a problem since. Its been a week now but i wanted to make sure the problem wouldnt randomly come back again. It was the black with red stripe wire on the ignition switch connector.
     
    tametalon92 likes this.

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