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General 1990 ECU Test

Posted by sacrileger, Oct 31, 2016

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  1. sacrileger

    sacrileger Proven Member

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    Would any one here know how to perform a fuel pump test on a 1990 ECU (n/t) in a similar fashion as was done on various other components at this link: https://tinyurl.com/jummda7 ?

    Alternatively, how do i get on OK code that, at bare minimum, would indicate that the ECU is in good health; meaning, for example, the circuit for proper fuel pump functioning is not fried?
     
  2. AllanL

    AllanL Proven Member

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  3. sacrileger

    sacrileger Proven Member

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    thanks for taking me back to this link which showed up in my search and i just didnt appreciate its significance when i glanced at it. this is exactly what will help me diagnose the problem.

    quote from the link:

    my interpretation is that as soon as the red engine light goes off, the ECU self-diagnostics test is completed and the ECU is healthy, all circuits functioning. Is that safe to say?

    Furthermore, the malfunctioning of the MPI relay could, hypothetically speaking, lead one the believe that the fuel pump is the problem. Would that be also a reasonable assumption? In other words, intermittent problems with the MPI relay could be interpreted as malfunctioning fuel pump and instead of jumping to a conclusion that the pump needs to be replaced, the MPI has to be investigated first?
     
  4. Vegas Smith

    Vegas Smith Previously Vegas smith

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    First off, what problems are you having? I'm not aware of a test of the fuel pump except for just getting proper voltage. Check your mpi relay as it's pretty easy to do. If that checks out fine, you should probably check your ecu for ic driver damage.
    http://www.ecmtuning.com/wiki/driver01

    See at the bottom where they talk about ic drivers controlling fuel components. I'm currently dealing with this.
     

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  5. sacrileger

    sacrileger Proven Member

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    thanks for the input. I didnt even realize this could get this complicated.

    My problems are intermittent. When the car is cold, it starts and runs fine. However, when some components reach certain temperature, at least that's how it appears to me, the car stops. Just shuts off. Stalls. For example, hot summer, i cannot drive anywhere during the day. It just stalls for no particular reason. Then I come back to it at night, it starts and gets me home no problem. Now it's fall and winter. I know for a fact I can get through fall and winter w/o any problems. Needless to say, I just cannot get a good handle on the problem. I can only say, that after the car stalls, I take the key out, and then turn it back on, I dont hear the fuel pump come on and prime the fuel rail. The pump doesnt start. It's quiet. Many hours later, i do the same thing w/ key in the ignition, the pump starts whirling and the engine starts after that and runs fine.
     
  6. Vegas Smith

    Vegas Smith Previously Vegas smith

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    I would just read that whole link on the second post and check everything on that circuit. It could be some type of weird vacuum issue as well but I'm not sure.
     

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  7. steve

    steve DSM Wiseman

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    I know this is almost a year old but I just saw it.

    There isn't really any sort of ECU self-diagnostics done at startup. All the Check Engine light getting turned on and then later turned off is doing is verifying that the light bulb works and that the ECU stayed running long enough to accomplish this. Most serious issues with the ECU hardware would keep it from running that long or at all.

    Over the years many have chased no start issues and replaced all sorts of parts before they checked the ECU. Since nothing interesting will happen on a modern car without the ECU it should be the first thing verified and on a DSM making sure that the Check Engine Light and boost gauge work and normal is a good indication that the ECU is functional enough to turn on the MPI relay, CEL, and PWM the boost gauge output. Knowing that doesn't eliminate other ECU problems but help eliminate tearing into ignition and fuel systems when the problem is a dead ECU.
     

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  8. 1990TSIAWDTALON

    1990TSIAWDTALON Moderator

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    Water temperature sender? My 90 was brittle as hell so I replaced it and the connector to it. I don't know if it has a dam thing to do with the cars problem but you brought up temperature effects it. Just at least look at it and its wires. It is the 2 prong L shaped plug on the thermostat housing. I will keep watching and give any 90 advice I can.
     

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  9. sacrileger

    sacrileger Proven Member

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    Turns out the intermittent fuel pump problems were not at the 1990 ECU or MPI relay level. It was the '90 fuel pump itself malfunctioning. I ended up swapping the '90 4g37 for a '92 4g63 n/t and ran into the same problems, except worse. The engine would sometimes start, other times start after cranking it for a long time or just die for no reason. I traced it down to the fuel pump, replaced the '90 pump with the '92 fuel pump that came with the 4g63 and problem was solved.
     
    AllanL and steve like this.

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