Fuel 91 Mustang 5.0 Lx, Injectors Not Pulsing But Have 12v At Red

Discussion in 'Fox 5.0 Mustang Tech' started by Lain, Nov 29, 2013.


  1. Lain

    Lain New Member

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    i have abit of a strange problem i cannot figure out what is happening. i have a 1991 ford mustang lx 5.0
    ive replaced the fuelpump, put the Relay back under the seat ( it was missing ) checked the inertia switch
    all good. pump runs alittle weakly but that isnt the full issue.

    The issue is my fuel injectors are not pulsing. i checked the Red wire on the fuel injectors and i get
    12v so i know its getting power, But making a quick makeshift Noid light and connecting it to red and
    the other wire on my injector connector and it doesnt even turn on at all, not pulsing, double checked my noid light and it lights up with 12v red and chassis ground. Its that secondary wire.

    Has anyone ran in to this problem and know a fix or where to search.. i checked the connectors {Salt and pepper} and they seem to be ok..... so im abit stumped dont know what else to check other then the EEC and its relay ( relay works cause i hear the fuelpump relay turning on)

    parts that are new in the vehicle, Entire Ignition system. from colum switch all the way to pip on distributor and new starter and solenoid, new Fuel pump relay ( one under the seat, I heard there was 2 of them and one sits under the Mass Air box? i see it but.. is it a fuel pump relay for my 91 lx 5.0 foxbody?) There is a new Caps and rotor and a new ignition module ( one connecting to the side of the distributor) i got the timing right again (reason car is having problems is because of another person fiddling with it) And the vehicle starts right up when i dump Carb/injector cleaner (o2safe) in the throttle body, fires up and runs then dies because the injectors arent opening....
     
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  2. mikestang63

    mikestang63 Mustang Master

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    search PIP sensor....run the codes first
     
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  3. Lain

    Lain New Member

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    first i need to learn how to get the codes, am searching pip sensor lots of stuff comes up. reading thru it all.
     
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  4. liljoe07

    liljoe07 Active Member

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    Pip sensor wont be the issue. If it was, it wouldn't run with when gas is poured into the intake.

    Check the TPS voltage and make sure its not maxed out. That will keep the injectors from pulsing. Otherwise, and because it runs with gas poured into the intake. I'm thinking your computer as took a crap, and the injector drivers aren't working.
     
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  5. motherhd

    motherhd New Member

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    My injectors stop pulsing only after the car has been running. It fires right up, runs great, but wont restart until it has been sitting for at least ten to fifteen minutes. Previous owner installed new fuel pump and it has a new relay and TFI. I am at the PIP and TPS also.....keep us posted please!
     
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  6. Lain

    Lain New Member

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    OK it seems my computer might be bad, because i purchased a Diagnostic code tool from Ford for this car... its not getting any codes from the computer, And after taking the computer out
    and opening it up 2 47uf capacitors were blown, unfortunatly replacing the capacitors with exacts allows the Tool to Atleast attempt to start reading... but i believe the computer is too far blown
    to give me back any codes at all even on KOEO and other things the book asked me to do.. nothing but all 000's it tried getting odes blinking square.. left it go for 5 hours.. nothing it stoped blinking and sat there XD. time to find a new computer... not goign to be easy for a 91 mustang 5.0 lx convertable
     
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  7. jrichker

    jrichker StangNet's favorite TOOL SN Certified Technician Founding Member

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    Wrong answer.@liljoe07

    PIP problems & diagnostic info
    Spark with the SPOUT out, but not with the SPOUT in suggests a PIP problem. The PIP signal level needs to be above 6.5 volts to trigger the computer, but only needs to be 5.75 volts to trigger the TFI module. Hence with a weak PIP signal, you could get spark but no injector pulse. You will need an oscilloscope or graphing DVM to measure the output voltage since it is not a straight DC voltage.

    See http://www.wellsmfgcorp.com/pdf/counterp_v8_i2_2004.pdf and http://www.wellsmfgcorp.com/pdf/counterp_v8_i3_2004.pdf for verification of this little detail from Wells, a manufacturer of TFI modules and ignition system products.
     
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  8. liljoe07

    liljoe07 Active Member

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    Or a computer problem. Or a TFI problem. Ive never seen the PIP behave in that manner. And Ive worked on a ton of ignition issues over the years.

    Ive read that plenty of times. It doesnt prove much really, but it is nice information to have. There is nothing concrete in the article that suggest thats the way the system is designed to work. It could simply be a voltage figure isolated to the test case at hand. Its also said the TFI is able to produce its own PIP in the event of a PIP failure. Ive never seen that either. And I own a pretty good arsenal of electrical testing equipment. Oscope is one of those. I wouldnt take that article as Fact until it was confirmed another way. Like hands on, or from Ford. It would seem more plausible to me if the voltage spread was wider between the ECM and ICM. .75v is a little strict when youre talking about the engine shutting down.
     
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  9. jrichker

    jrichker StangNet's favorite TOOL SN Certified Technician Founding Member

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    @liljoe07

    What I am going to say is based on the computer/ electronics background I have. I have a 2 year electronics degree and spent the next 10 years after I got my electronics degree fixing minicomputers at the component level. That included countless hours spent chasing 1's & 0’'s around circuit boards with an oscilloscope. I am well familiar with how digital circuits are supposed to operate.

    Every digital circuit has a signal range where it is designed to operate correctly. As an example, the TTL logic found most computer circuitry uses a 5 volt supply, and 0-.8 volts = 0 and 2- 5 volts = 1. That leaves the range.9 volts to 1.9 volts as a no man's land where circuits cannot distinguish between a 1 or a 0. Trying to get a TTL circuit to operate reliably in the .9-1.9 volts signal out just isn’t possible.

    The PIP input to the computer is going to be faced with a similar problem: how to tell a 1 from a 0. Since the PIP signal voltage level is obliviously higher than 2-5 volts, we can know that it isn't TTL logic. So we have some different voltage figures to match the circuit in question. We still need a certain minimum voltage to represent a 0 and a voltage higher than that to represent a 1. The more difference between the voltage for a 0 and a 1, the better the noise immunity and the less false triggering of the circuit. I will tell you that the electrical environment under a car’s hood is electrically very noisy. Spark plug wires, solenoids like the injectors create a whole world of EMI (electro-magnetic interference) that circuits must be designed to either ignore of filter out.

    So, our PIP signal seems to need a voltage greater than 6.4 volts to be seen as a 1 due to the EMI or electrical noise. That is not unreasonable considering that all the voltage spikes that are radiating out from much of the rest of the electrical system. Remember that the greater difference between a 1 and a 0, the more immune an electrical circuit is to stray EMI.

    You are going to say “Why is 5.75 signal volts good enough for the PIP to work when the computer needs 6.5 signal volts?” The TFI lives in a much more electrically shielded environment. It has an aluminum housing and an aluminum cover over the Thick Film Integrated circuit. That shielding combined with a filter network on the DC power input makes a nice clean electrical environment. Very little of the EMI dancing around out the outside of its’ aluminum house has any effect on it. So it can get away with a lower signal voltage and still function correctly.
     
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  10. Lain

    Lain New Member

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    it Was the computer, i had to replace it though this new one that came in is a E9ZF-12A650-C2A where my old one was a E9ZF-12A650-CA i suppose the 2 between the CA is a revision? Now the injectors are firing, Still alot of Work i need to aquire t he correct Firing order of the 5.0 HO with the 302
     
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  11. liljoe07

    liljoe07 Active Member

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    Good deal! And yes, the 2 is just a hardware revision number.
     
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  12. jrichker

    jrichker StangNet's favorite TOOL SN Certified Technician Founding Member

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    It's early in the morning for me, and I think I read that you need the HO firing order. If so see below...

    The HO firing order is 1-3-7-2-6-5-4-8.
    Non HO firing order is 1-5-4-2-6-3-7-8
    [​IMG]
     
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