Announcement

Collapse
No announcement yet.

Need help from car audio guys about car alarms

Collapse
X
 
  • Filter
  • Time
  • Show
Clear All
new posts

  • Need help from car audio guys about car alarms

    I have a 30 year old car that I bought used from a dealer. I've owned it over 20 years. The first owner was into car audio, and had some kind of alarm. I've never used, or had issue with it, but I think it's still installed. My question is...Do these alarms disable the vehicle? I have been trying to fix a no start condition, and wondered if an old failing anti-theft system could be the problem.

  • #2
    Spark, Fuel & Air.

    Check all of the above.

    Comment


    • #3
      Originally posted by Steve Lee View Post
      Spark, Fuel & Air.

      Check all of the above.
      You forgot compression.

      It seems like my ecu is dead, but that's not confirmed yet. If a car alarm does more than make noise, ie shuts off something critical, then the car might not start, or run due to the defective alarm.

      This car ran mostly normally until a few months ago. After my initial testing, it appeared that the fuel pump was weak, and needed replacement. That's done now, and pressure at the rails is normal at 40psi. Still no start.

      The ecu has caps that go bad just like the caps in old audio equipment. The ecu is 30 years old. The symptoms matched others who had caps failing in the ecu. A few days ago, I replaced the caps. The old ones were leaking, and I'm pretty sure they were not doing their job. That didn't fix the car. There appears to be no spark, and no fuel. The fuel pump is running, but it seems the injectors do not open. I tested spark with a timing light, and it seems that there's no spark. No flashing. I tried starting fluid, and that didn't produce even a hint of doing anything, so no spark either.

      I would hate to chase these symptoms down, and find that an old car alarm was causing the problem. They likely have caps that are failing too, and who knows if it's cutting a signal wire, or something in an attempt to prevent a non existent cat theft. I could dig around under the dash, and look for the unit, but I'm big, and old for that sort of thing.

      Comment


      • #4
        Actually I didn't mention compression for the same reason you didn't check it - unlikely to be the cause - it should at least run, maybe not well but . . . .

        Man - I had an '85 BMW 325e that did this to me and after replacing the ECU twice, the idle controller module, idle injector and timing position sensor I finally sold the vehicle as is.

        That buyer had a mechanic friend who worked on BMW's for a living and the tools/lifts to actually work on it where I did not.

        Turned out to be a $0.50 part.

        The TDC lobe/pin on the flywheel had fallen out and the ECU could not find TDC so it just sputtered sometimes, ran others and mostly left me where I last turned the ignition-off.

        Check the simple stuff 1st.

        Good luck, Sir.


        Comment


        • #5
          What kind of car? Does it have an integrated ECU or separates for fuel and ignition? Does the ECU have good power and ground? Battery fully charged? Does the voltage when cranking stay above the factory spec?

          Comment


          • #6
            Originally posted by devnull View Post
            What kind of car? Does it have an integrated ECU or separates for fuel and ignition? Does the ECU have good power and ground? Battery fully charged? Does the voltage when cranking stay above the factory spec?
            It's a 91LX 5.0 Mustang. Mostly stock with a few little bolt ons. One computer controls everything. I need to check power and ground on the wiring harness, and maybe a relay, or fuse for the ecu. The fuel pump does come on, which I don't think can happen without the ecu being powered up. Not sure though.The system reference voltage is supposed to be 5v. Currently, I measure zero volts at the tps. (Throttle position sensor) Battery is fine. I have a second Mustang that I can compare with, and swap parts to test. I've ruled out quite a bit this way.

            Comment


            • #7
              It's been a while since I've worked on a ford that old. If I remember correctly it doesn't have OBD2 but you should be able to pull the codes with a jumper wire and count flashes on the check engine light. That might help narrow down the search. Good luck.....

              Comment


              • #8
                Originally posted by devnull View Post
                It's been a while since I've worked on a ford that old. If I remember correctly it doesn't have OBD2 but you should be able to pull the codes with a jumper wire and count flashes on the check engine light. That might help narrow down the search. Good luck.....
                Tried that yesterday, but it did nothing. I don't even see the check engine light! That might be a clue, I don't know.

                Comment


                • #9
                  I'm really glad I read this thread. I'm looking at an early 90's porsche that has an aftermarket alarm apparently installed just after purchase. I had no idea the alarm could be so intrusive to the internal components of a car. I can't imagine letting an aftermarket car audio/alarm shop work on a new porsche. I may stay clear of this one.

                  Comment


                  • #10
                    Originally posted by rpb View Post
                    I have a 30 year old car that I bought used from a dealer. I've owned it over 20 years. The first owner was into car audio, and had some kind of alarm. I've never used, or had issue with it, but I think it's still installed. My question is...Do these alarms disable the vehicle? I have been trying to fix a no start condition, and wondered if an old failing anti-theft system could be the problem.
                    To answer your original question, yes old alarms had the ability to disable the vehicle, but iirc it was a starter kill, either by onboard or remote relay. The onboard relays were usually too small and burned up. Sounds like cranking us not your issue though. I suppose though the installer could however route any number of functions in place of or addition to starter kill on this circuit.

                    You could look to see if the alarm has a valet mode switch or button under the dash to help bypass as many alarm functions as possible. I uninstall the alarm though to not only help your current diagnosis, but also eliminate future issues.

                    Comment


                    • #11
                      Originally posted by dwigle View Post
                      I'm really glad I read this thread. I'm looking at an early 90's porsche that has an aftermarket alarm apparently installed just after purchase. I had no idea the alarm could be so intrusive to the internal components of a car. I can't imagine letting an aftermarket car audio/alarm shop work on a new porsche. I may stay clear of this one.
                      I don't know that it's the problem. I'm just trying to find out if I need to dig it out from under the dash. I did see mention in my Ford EEC-IV book that this kind of thing can happen.

                      Comment


                      • #12
                        Originally posted by dynamo View Post

                        To answer your original question, yes old alarms had the ability to disable the vehicle, but iirc it was a starter kill, either by onboard or remote relay. The onboard relays were usually too small and burned up. Sounds like cranking us not your issue though. I suppose though the installer could however route any number of functions in place of or addition to starter kill on this circuit.

                        You could look to see if the alarm has a valet mode switch or button under the dash to help bypass as many alarm functions as possible. I uninstall the alarm though to not only help your current diagnosis, but also eliminate future issues.
                        That makes sense. All they would have to do is interrupt the signal wire to the starter relay.

                        Comment


                        • #13
                          I can’t recall if those are MAF or not, but if it has a MAF, try unplugging it and see if it runs.

                          Comment


                          • #14
                            Originally posted by dynamo View Post
                            I can’t recall if those are MAF or not, but if it has a MAF, try unplugging it and see if it runs.
                            Will do. I may unplug the spout connector and try as well.

                            Comment


                            • #15
                              No check engine light when key on and not running is probably ECU or power.

                              Comment

                              Working...
                              X