355 5.2 No Start Issue | FerrariChat
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355 5.2 No Start Issue

Discussion in '348/355' started by USAF - 1, Aug 31, 2025 at 9:42 PM.

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  1. USAF - 1

    USAF - 1 Karting
    Silver Subscribed

    Mar 27, 2021
    94
    San Jose CA
    Full Name:
    Todd
    #1 USAF - 1, Aug 31, 2025 at 9:42 PM
    After 9 months of resealing/restoring the engine/engine bay, replacing the clutch, etc., I have a no start issue. Here's some important background. I was having intermittent, slight misfires when hot, and a CEL related to low voltage on an O2 sensor. It turns out that a previous owner had messed with ECU wiring harness and connectors. Initially I only discovered the bad O2 connector crimps, but was still having issues and reviewed the service records, finding that a PO had attempted to install the gold connector kit. I then pulled off the boots on the ECU harness and found 50% or more of the crimps were done so poorly, the wire pulled out of the connector easily by hand. I then looked at the main connector to the ECU, and it was done just as poorly, but the PO had used "liquid electrical tape" to try to prevent any shorts from occurring as he had left bare wire exposed at the end of the connectors. I couldn't remove the wiring from the ECU connector, and so I ordered a new harness, as this thing was such a mess at this point, it wasn't worth dealing with. Image Unavailable, Please Login
    With everything reinstalled again, the car will not fire, but will crank. It will not give an indication that it will or start quickly then suddenly and die. Here's what I have done so far in trouble shooting after reading no start issues. When key is in position 2, proper lights appear, CEL, brake, slow, down, etc. Immobilizer turns the LED off upon hitting the button, but upon cranking it is solid red.

    1. Fuel pump seems to be okay, I measured the draw upon crank and there is a short amp spike which appears to be consistent with the pump priming. There appears to be pressure at the fuel filter in checking the relief valve, although I have not checked the actual pressure.

    2. I measured 12v at the injector connectors, but using a noid light, it does not blink when cranking.

    3. Swapped crank sensor just in case with a new one I already had. No difference.

    4. I double-checked the ECU wiring diagram with the connectors on the new harness for continuity, and there does not seem to be a problem; I get continuity.

    5. Checked ECU ground to battery, chassis ground to battery. Seems ok.

    6. Camshaft sensor and knock sensors are brand new.

    Am I missing something? This seems like an ECU issue rather than a fuel issue, but I defer to the experts here.

    Todd
     
  2. Qavion

    Qavion F1 World Champ
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    Feb 20, 2015
    14,446
    Sydney
    Full Name:
    Ian Riddell
    #2 Qavion, Sep 1, 2025 at 12:14 AM
    Weird.
    On my gated 5.2, I don't get cranking if the immobiliser has not disarmed. Do you have a starter relay? If you do, then yours may be the same as mine, suggesting the immobiliser is (partly) ok. The immo disable signal still has to go to the Motronic ECU.
    I know when I put a new engine harness in mine, it was wired incorrectly from the factory. I was working with my local indy and he let me do some wiring checks while he worked on another customer's car. I found some brown wires swapped over, but even after I swapped them back, he still had to reset something in the Immo ECU with his SD1 tool.


    With cranking, the current should be constant. There is a 2 second prime (even with the Immobiliser active), but it only happens once, then the car has to be started before the priming circuit resets (Not even a battery reset will reset it).

    Just make sure you didn't swap over the plugs for these. That will stop firing. The cam plug is usually blue, but I'm not sure if you can rely on plug colour.
     

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