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Thread: '87 Shelby Z Daytona died, won't start

  1. #1
    Mitsu booster
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    '87 Shelby Z Daytona died, won't start

    I'll try to keept this short...



    Engine hiccupped and died while car was running on the last few millilitres of fuel. Figuring it ran dry, I did a roadside refueling... but the car wouldn't start anymore! Not even a little bang or sputter. Seeing as how it completely died instantly and unable to restart at all (not a "loss of performance" or "rough running" or something intermittent), I can't imagine running it dry could have caused this fault. (I accidentally ran the car dry once before about a year ago; had no problems refueling and restarting after that incident.)



    So I can only conclude this recent possibly-tank-ran-empty incident must be unrelated, and the actual fault having manifested itself at this same time must have been purely coincidental.



    I've been trying to diagnose the mysterious fault now for days, to no success. Any help would be much appreciated.



    So far, I've determined:

    -ASD relay is fine, fuel pump is fine, fuel rail is at pressure.

    -Ignition coil is receiving +12V when ASD relay engages.

    -Harness line from ign coil (-) to power module is fine.

    -Harness line (for ignition pulse signal) from logic module to power module is fine.

    -Analog multimeter needle jumps a little when probing logic module ignition pulse signal (suggesting to me that logic module is fine).

    -Onboard diagnostics flashes code 12 (batt. disconn. within last 50 starts) and code 55 (end of reporting) -- No real faults are reported!



    Perplexing things, shown by an LED test rig I made (single LED w. 1k resistor):

    -Connecting the test LED across the ign coil does not show any light pulses. From this, I was pretty sure (at first) that the power module's ignition transistor had failed open-circuit. But then...

    -Upon disconnecting the power module's ign coil drive / pull-down line from the ign coil (-), and connecting it only to the test LED (-) (keeping the test LED (+) on ign coil (+) / ASD relay output), the LED shows light pulses when cranking the engine! (Suggesting to me that the power module's ign coil transistor is actually doing something!)



    So is the transistor OK? Or is the transistor "partially-bad" (having failed with super-high impedance) and unable to pull the low-impedance ign coil (-) down to GND? (But can sink a tiny 12 mA to GND to light an LED?)



    I read somewhere else the ECU is supposed to throw a code 43 if the ignition coil driver circuit fails ...But no fault codes are being reported!


    Any help diagnosing this matter would be much appreciated.

  2. #2
    Hybrid booster
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    Re: '87 Shelby Z Daytona died, won't start

    are you hearing prime at key-on? didn't see in your post if you did. stock pump run dry a few times in its life for sure not going to do well with that, I always make sure that I run closer to full just to keep the pump cool.

  3. #3
    Hybrid booster
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    Re: '87 Shelby Z Daytona died, won't start

    if you look behind the battery along the frame rail, you'll find a 6-pin terminal. I forget exactly which circuits run thru there...sensors & 5v to LM for sure. anyhow, the location to the battery but lower in the bay makes it susceptible to moisture & acid fumes from the battery. pull the terminal apart, clean as much as possible & re-grease it. that terminal going dry has confounded me twice over the decades by drying out like that, but it makes sense (no power/sensor signals to LM, so no prime at key-on). I tested every inch of harness from fuel pump forward before I realized it the first time.

  4. #4
    Mitsu booster
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    Re: '87 Shelby Z Daytona died, won't start

    x.Gen,
    I forgot to mention, the fuel pump is indeed working ok. It does do it's priming on key-on.

    I'll check that harness connector you mentioned... thanks for the tip.
    Though I'm still baffled as to how no fault codes are being tripped by this, and really baffled as to what's going on with the ignition coil driver.

  5. #5

    Re: '87 Shelby Z Daytona died, won't start

    Someone had a coil die and still provide some spark. I'd check another known good coil, could have just died.
    [SIZE="3"] [B]Jon Trotter[/B][/SIZE] [B]1985[/B] Dodge Shelby Charger, Currently decommissioned [B]1987[/B] Shelby GLHS, #937 [B]1987[/B] Shelby Lancer, #628 [QUOTE=Reeves;587010]I can be ready. Please send pics of wife. _____DodgeZ add comments here______[/QUOTE]

  6. #6
    Hybrid booster
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    Re: '87 Shelby Z Daytona died, won't start

    I've had LED test lights lead me in the wrong direction before, to the point where I don't really trust them. Do you have spark? What is the fuel pressure? The pump can run and still have no fuel pressure... gotta stick with the basics. You need spark fuel and air/compression to run.

  7. #7
    Hybrid booster
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    Re: '87 Shelby Z Daytona died, won't start

    you should also check your HEP and the terminals on its harnesses.

  8. #8
    turbo addict looneytuner's Avatar
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    Re: '87 Shelby Z Daytona died, won't start

    Quote Originally Posted by RattFink View Post
    I've had LED test lights lead me in the wrong direction before, to the point where I don't really trust them. Do you have spark? What is the fuel pressure? The pump can run and still have no fuel pressure... gotta stick with the basics. You need spark fuel and air/compression to run.
    You are +2 correct. You need a test light that puts a load on the circuit. I'm guessing the pump sock and filter are clogged from sucking up the stuff at the bottom of the tank.

  9. #9
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    Re: '87 Shelby Z Daytona died, won't start

    The pump may prime but are you getting any fuel at the rail? If so, is there adiquate pressure? Fuel filter may be blocked.
    Are you getting spark at the plugs?

    Stick with the basics.

  10. #10
    Mitsu booster
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    Re: '87 Shelby Z Daytona died, won't start

    Further updates:
    The ignition coil primary was 1.4 ohms DC resistance.

    I tried another test rig: Connecting coil (+) to battery, and coil (-) in series with a normally-open SPST switch and an incandescent light bulb. (The idea was to manually actuate the switch, similar to mechanical "contact points", and see if the coil produces high voltage. The light bulb was a crude "PTC thermistor and heater", so I don't blow the coil by inadvertently having too much dwell with my "manual triggering", but with rapid triggering the filament stays fairly cold, hence the resistance stays low, and so the coil current can then be decently high.)

    The result: The coil seems good, as far as I can tell from this! It produced a spark that jumped a gap of about 4 mm.

    Unless anyone has a better suggestion, I'm thinking next stop is to build a crude coil driver from an NPN transistor, resistor (limit its base current), and diode (to prevent damage from coil's back-EMF), and see if I can make the engine run. (If that works, then the power module is indeed faulty. Cutting away the urethane rubber potting to repair a power module circuit board is my "last resort", as I have no way of re-potting it... at least not nicely.)

    - - - Updated - - -

    Quote Originally Posted by RattFink View Post
    I've had LED test lights lead me in the wrong direction before, to the point where I don't really trust them. Do you have spark? What is the fuel pressure? The pump can run and still have no fuel pressure... gotta stick with the basics. You need spark fuel and air/compression to run.
    I don't have a pressure gauge (that I want to foul with fuel) to read the rail, but pressing on the relief valve sprays out a high-pressure mess of gasoline. So the rail is pressurized... and pressurized with liquid fuel.

  11. #11
    Mitsu booster
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    Re: '87 Shelby Z Daytona died, won't start

    Quote Originally Posted by looneytuner View Post
    You are +2 correct. You need a test light that puts a load on the circuit. I'm guessing the pump sock and filter are clogged from sucking up the stuff at the bottom of the tank.
    If the sock and filter were clogged, I'd think the rail wouldn't have pressure. (Or at least not adequate pressure). But if the rail pressure is too low, wouldn't the engine at least caugh and sputter a little on trying to start!??

    In my situation, I'm not getting even a single bang. That seems far too unlikely, when just before the car stalled on the side of the road, engine was purring like a kitten (or growling like a lion, WOT). I can't see how little bit of junk being sucked up suddenly goes from running perfect to not even a single bang, especially when I've had the pump prime the system several times before attempting to start, and fuel does spray out the fuel rail's relief valve when pressed.

  12. #12
    turbo addict blk86trbo's Avatar
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    Re: '87 Shelby Z Daytona died, won't start

    How old is the timing belt...may have jumped time or stripped a few teeth from the belt.
    [FONT="Arial Black"]Paul[/FONT] [B][SIZE="1"]US ARMY INFANTRY VETERAN[/B] 1995 Dodge Stealth R/T White DOHC 5 speed 1994 Dodge Stealth R/T Red DOHC 5 speed 1992 Dodge Daytona IROC, Blue TI 5 speed (2) 1992 Dodge Daytona IROC, Red TI auto 1991 Dodge Spirit R/T, Red (project) 1989 Shelby CSX-VNT #382 1989 Dodge Shadow ES, White TI auto 1987 Daytona Shelby Z, White TII 1987 Chrysler T&C wagon, Tan TII auto 1985 Dodge Lancer ES, Bronze TI auto 1982 Wife, White[/SIZE] [SIGPIC][/SIGPIC]

  13. #13
    Garrett booster
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    Re: '87 Shelby Z Daytona died, won't start

    sorry if I missed this, but after one of the failed start attempts did you pull a sparkplug and see if it had any wetness from fuel?
    That would be an indicator that you are getting enough fuel delivery to cough and sputter.

  14. #14
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    Re: '87 Shelby Z Daytona died, won't start

    Update / Closure: The problem has been solved -- it was a defective power module.

    I borrowed an oscilloscope, and with that I determined the logic module was sending a good ignition pulse signal. Then I found a surplus power module I had forgotten about, which I think came from a Laser XE (turbo) I cannibalized many years ago -- because when I swapped it into my '87 Shelby Z Daytona, the car started up like it was a perfect drop-in replacement.

    If anyone's curious, the LM ignition pulse is not a 5V TTL pulse train, but rather appears like a 2V DC-biased pulse train where the "dwell" half-cycles (of fixed duration) have a slight "voltage ramp-up".

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