1990 Suburban starting issue...

Discussion in 'GM Powertrain' started by bigjunk93yj, Jan 20, 2009.

  1. bigjunk93yj

    bigjunk93yj New Member

    Hi all, I own a used 1990 Chevy Suburban 2500. It has the TBI 350, a little over 300K on the chassis but the motor has about 100K and is out of a 93, at least that is what the previous owner said. The motor is stock except for a Holley TBI and Accell cap and rotor. It has an issue starting though. Here is the routine:

    • motor cranks for 10-30 seconds
    • check engine light comes on as oil pressure drops and comes back up again
    • truck will start (rarely will require a little throttle once it starts to fire) and c/e will clear

    I had my wife Sarah start the truck while I watched the injectors. They didn't start firing until the o/p dropped and the c/e light came on. Now here is the list of parts I have replaced so far (including parts replaced in a very recent tune-up):

    • plugs
    • wires
    • cap/rotor
    • coil
    • ignition module
    • fuel pump relay (brought the start time down to about 10 sec instead of almost 1 min!)
    • fuel filter
    • O2 sensor
    • Cat/Magnaflow cat-back (should have got the Flowmaster :grrrrrr: )
    • PCV valve
    • coolant temp sensor
    • MAP sensor

    The fuel pump is also supposed to be new, the previous owner said he replaced it right before I bought it less than a year ago.

    I have also tried SeaFoam with some results: Oil pressure has come down slightly(now about 25 from at least 35) and changes more with RPM. She seems to idle smoother but that could also be from the plethora of parts that has been thrown at her.

    I haven't checked the fuel pressure yet but I'm not really thinking that's the problem. From what I understand: the Injectors are activated by the ECM which receives a signal from the Ignition Module in the distributor as the motor cranks. If the ECM doesn't receive that signal, Oil Pressure is used as a backup: once the pressure reaches 4psi, the ECM activates the injectors.

    So with a new Ignition Module, am I to assume my ECM may be bad? I have tried the jumper technique for retrieving codes with no luck: the C/E light never comes on. And when my buddy used his scan tool he wasn't able to connect. I would think those would be some strong signs.

    Well, sorry to ramble but I wanted to try to give every bit of info I could up front. Thanks in advance for any and all replies.
  2. mrfixdit

    mrfixdit Rockstar 100 Posts

    starting issue

    Have you checked the timming?
  3. bigjunk93yj

    bigjunk93yj New Member

    i have not, but can tomorrow. i'll let you know what i find.

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