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No spark 90 W150...ASD, PCM, Hall-sensor, other ?

Discussion in 'Pre-1994 trucks, commercial vehicles' started by Nickle, Dec 17, 2017.

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  1. Nickle

    Nickle New Member

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    Sorry for jumping in here as a new member, but I have a no-start on my 90 W150 plow truck and 'winter is coming'.

    My 90 W150 plow truck cranks, but won't start.

    I have no spark at the coil output when cranking.
    I have no voltage at the coil B+ with ignition on or cranking.
    I have no check-engine light when ignition is turned on, so no 'key diagnostics' available.

    From there, the FSM points to the ASD relay or the PCM. However it has no troubleshooting procedure without a DRBIII tool.

    I tried a few things from other postings, but am still looking for a way to figure this out.

    With the ASD relay removed, the ASD's Red wire has 12V all the time, the Dk Blue wire has 12V with key-on.

    The ASD Dark Green/Black wire does NOT have any voltage with the engine cranking … this seems wrong. I am cranking the car by removing and jumpering the start-relay if it matters.

    I tried jumping the battery to coil B+. I got a solid 12V on both sides of the coil when cranking. No spark.

    When I jump the battery to coil B+ I can hear fuel pumping at the throttle body for a few seconds before it gets up to pressure and shuts off.

    I will really appreciate any suggestions for next steps … and thanks for listening. J
     
  2. Bob Lincoln

    Bob Lincoln "CHECK FAULT CODES"
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    Check all fuses, both under dash and underhood. Sounds like the PCM is not getting power.
     
  3. Nickle

    Nickle New Member

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    There are no fuses underhood as far as I know, and none of the dash fuses indicates that it is ignition-related. I think the PCM is only protected by a fusible link in the wiring harness. I'll check all the fuses anyway, then try to probe for power at or near the PCM.
     
  4. pt006

    pt006 Active Member

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    Start with a fully charged battery. Disconnect the negative battery terminal. Step on the brake pedal for 10 seconds. Turn the key to run [not start]. You should hear the fuel pump run for 1 or 2 seconds and then stop. This tells you that the ASD relay is working. When the ASD relay contacts close, it takes the 12v battery current [# 14 red wire] and sends it to the fuel pump AND to the Negative side of the coil thru the #14 dk blue/black wire. The other 2 smaller wires go to the computer. They energize the relay to close the contacts.
    Always start the truck using key!
     
    Shane Estabrooks likes this.
  5. Nickle

    Nickle New Member

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    That all makes sense....tnx. I will confirm that I am only getting fuel pump when jumpering 12V to the coil...not when key is turned on. FSM schematic shows the ASD’s #14 DarkBlue/Black going to the + side of the coil. Negative side of coil goes to the PCM. So when I jumped 12V to the + side of the coil, I think that would have been equivalent to jumpering the ASD. No spark or start with 12V on the coil has me thinking that the PCM or the distributor pickup isn’t working, but I may be getting ahead of myself. I’ll take another run at it and post back.
     
  6. Bob Lincoln

    Bob Lincoln "CHECK FAULT CODES"
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    When the ignition is turned to ON without cranking, the ASD relay and therefore the fuel relay will close for 1-2 seconds, until no signal is detected from the crankshaft position sensor. The relays then open. When the key is turned to ON, the + side of the relay coils are energized to 12V, and the PCM pulls the - side of the relay coils low, for those first 1-2 seconds. Then the PCM output switches high, back to 12V, so that there is 12V at both sides of the relay coils, and the relay coils open.

    So, if you turn the key ON, you should hear the fuel pump hum for 1-2 seconds, then silent, and at that point, you should be able to measure 12V from both the + and - sides of the relay coil (and the ignition coil) to ground. If you get zero volts everywhere, the PCM is not supplying any voltage at all. This means it has either failed, or is getting no power from the battery, or through the ignition switch. So you could have a failed PCM, or an open fuse, or a bad ignition switch. Failed PCM is the least likely.
     
    AllanC and valiant67 like this.
  7. AllanC

    AllanC Well-Known Member

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    Bob L is on the right track with his analysis. The only additional comment I would add is that on 1990 model engines, a crankshaft position sensor was NOT used. The distributor pulsing signal to the PCM was generated by the Hall Effect device in the distributor.

    This is bothersome. You should have a CHECK ENGINE lamp. Is the bulb burned out? If NO then part of the PCM might not have electrical power ????

    See the attached schematic for the distributor pickup device. There is a 8 volt constant power source wire from the PCM. There is a ground wire. There is a signal wire. Color conventions are from a 1991 service manual but I would expect the same for a 1990 model. Back probe each wire in turn at the distributor connector. With someone operating the starter and ignition switch in the RUN position, you should have a pulsing voltage of 0 - 8 volts on the signal wire. If no pulsing voltage then this is the cause of your no start. The PCM must see a pulsing voltage from the distributor. When it does it grounds the ASD relay control circuit and provides power to the electric fuel pump, coil, etc. on the load side of the ASD relay circuit.

    Distributor Hall Effect Wiring.gif
     
  8. Bob Lincoln

    Bob Lincoln "CHECK FAULT CODES"
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    It's possible that the check engine light has burned out, or that a previous owner removed the bulb to avoid a problem showing at an inspection, or because an unresolved problem presented the light continuously.
     
  9. Nickle

    Nickle New Member

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    Great input all. I was hoping for just a failed ignition pickup, but it’s not looking that way.
    Sorry for the long post. I tested a lot and need you guys to keep me honest on conclusions.

    1. All fuses are good … shouldn’t matter though.
    2. CEL does not illuminate with ignition. The Message center CEL bulb is good.
    3. Fuel pump does not run when key is turned on.
    4. ASD relay tests good on bench. Clicks and shows 5ohms with 12V applied.
    5. With key on (and ASD relay reinserted), backprobing shows that the ASD is not closing.
    6. With key on, jumpering ASD Dark Blue/Yellow to ground, fuel pump runs for its few seconds.
    ** So the PCM is not activating the ASD relay. **
    1. Dark Blue/Yellow wire from ASD relay to PCM has continuity and is good.
    ** So the PCM is not activating because it is has no power, is dead, or has no input from the distributor ignition pickup. **
    1. PCM has good power and ground (12V on pin 3, power ground on pins 11 and 12, and signal ground on pin 5).
    2. Power on the three-wire ignition pickup is out of whack.
    3. Key-on, the orange power wire from PCM to pickup shows 0.7V at the PCM when it should be 8V.
    4. The grey signal wire from pickup to PCM shows 0.8V (key on and not cranking).
    5. I get the same readings at the pickup connector with the pickup disconnected, so the orange and grey wires seem good.
    6. I measure good ground at the pickup connector.
    7. Wiring between PCM, pickup, and ground seem good.
    *** So what do you guys think … am I looking at a dead PCM ? No CEL with key-on points that way as well. :-(
     
  10. Bob Lincoln

    Bob Lincoln "CHECK FAULT CODES"
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    Surely this is a mistake. You don't measure resistance with voltage applied, and a typical relay coil resistance would not be 5 ohms, as that would pull 2 1/2 amps through the coil.
     
  11. Nickle

    Nickle New Member

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    You are correct Bob. Line 4 above should have read 0.5 ohms.
    The 12V is across the relay coil. The 0.5 ohms is across the relay contacts.
    The voltage gets applied to two of the terminals. Resistance gets measured across the other two.

    I could have measured the coil resistance with no voltage applied, or the current with voltage applied. I just didn't bother when I saw that the contact-side was opening and closing normally.

    As far as I can tell the ASD relay is working ...it just isn't getting signaled (grounded) by the PCM.
     
    Bob Lincoln likes this.
  12. Nickle

    Nickle New Member

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    BTW...great diagram AllanC. It really shows that critical PCM to pickup piece.
    Rockaut* has a Cardon* rebuilt PCM for 127+core.

    Does anyone have experience with rebuilt PCMs from Cardon* or others ?
     
  13. AllanC

    AllanC Well-Known Member

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    The orange wire at the distributor hall effect should indicate 8 volts with the ignition switch in the RUN position. Lack of voltage on that wire indicates the PCM is not supplying the necessary voltage.

    Before condemning the PCM as bad, I would remove the 60 way connector at the PCM. It is located on the inner fender, right front area of engine compartment. Check and make sure all pins are tight and clean and not loose. Check mating receptacles in the electrical connector for no corrosion.

    Reattach 60 way connector at the PCM. See attached schematic for location of fusible links in power feed wires to ignition switch and PCM.

    Fusible Links Positive Battery Cable.gif

    Turn ignition switch to RUN position. Check for battery voltage on pin 9 at 60 way connector at PCM.

    Switched Power Feed to PCM.gif
     
  14. Nickle

    Nickle New Member

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    Ah, I did miss checking the ignition feed (pin 9) to the PCM. That would explain a LOT if not right !

    I did unbolt the PCM so I could get to the back of the 60 pin connector with it still connected. I fully disconnected and reconnected it one time. It was tightened securely originally. It had dielectric grease, and the pins and sockets looked good...no moisture or dirt.

    Your have a very good point ... it IS well worth disconnecting and reconnecting it a few times to see if anything changes. It would be great to find that it is just a connection issue.

    And I will be sure to push in on the 8V pin and the CEL pins. Thanks for the suggestions. I'll post back results.
     
  15. Nickle

    Nickle New Member

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    No joy ... ignition voltage is good at the PCM. I connected and disconnected the 60 pin connector 3 times. No change. The connector sockets all look good on the connector mate side. They all the same height ... none are backed out and not connecting. I double-checked grounds while at it. The most I could read body to battery with ignition on was 2-3 mV. I think it is time to order a PCM.
     
  16. AllanC

    AllanC Well-Known Member

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    You indicated there is dielectric grease on the terminals. I would use cleaner and remove that grease from all the pins and receptacles. Then I would spray a solvent on the receptacles and the blow dry with compressed air. On each pin on the PCM is would take fine sandpaper and clean each and every pin.

    Turn ignition switch to RUN position. Back probe the terminal in the PCM connector pin #7. This provides 8 volt power to the distributor hall effect device. It should have 8 volts????

    I would try and bend pin 9 on the PCM slightly sideways to make a better, tighter fit in its receptacle. Reattach and see if anything changes. I have seen gold plated pins and receptacles on a PCM look clean but still not make proper electrical contact. I do not think the pins and receptacles are gold plated on your vehicle so slight corrosion that is not apparent can cause issues.
     
    #16 AllanC, Dec 18, 2017
    Last edited: Dec 18, 2017
    Bob Lincoln likes this.
  17. pt006

    pt006 Active Member

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    My diagram from an 88 truck manual is different than Allan's diagram. I don't know if it applies to your truck, but I'll add it anyways.
    60 pin conn. ----- pin # 41 ---- red wire --- 12v battery feed
    ------ pin # 10 ---- d green/blk wire ----12v from ASD when on [lasts 1 or 2 seconds]

    14 pin conn. ----- pin # 1 ----- orange wire ------ 8v output to the distributor
    ----- pin # 4 ----- dark blue wire ------- 12v from ignition run

    There is a ground screw on the firewall near the distributor. The terminal and screw must be clean and greased. This is an important ground!
     
  18. AllanC

    AllanC Well-Known Member

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    As fuel injection advanced from its infancy in the early 1980s, Chrysler has changed the location, configuration and architecture of electronic software engine control. In 1988 the former logic and power modules (used through 1987) were combined into one module but still retained 2 separate circuit boards. Starting in 1990 the logic and power module circuit boards were combined into a single circuit board. So the 1988 wiring diagram as it pertains to the engine controller pin outs would not be correct for a 1990 model. A detailed discussion can be found through this link.

    Understanding The Chrysler ECU (at http://minimopar.net/ecu/index.html )
     
  19. Nickle

    Nickle New Member

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    This thread should now read SOLVED. This 90 W150 sprang to life immediately with a reman PCM.

    AllanC, pt006, and Bob L ... you guys really saved me here. Thank you. I hope I can pay it back or forward somehow.

    Summarizing, my key symptoms for dead PCM were:
    • no check engine light with ignition on and engine not running.
    • no check engine light codes by toggling ignition switch on-off-on-off-on within 5 sec.
    • no +8V at the hall-effect sensor (ignition pickup)
    YMMV, but my troubleshooting from no-spark went ASD --> Ignition Coil --> PCM:
    1. Confirmed no spark by holding coil output wire near ground while cranking.
    2. Confirmed no voltage at coil +.
    3. Confirmed no fuel pumping by listening to tank when turning key on.
    4. Disconnected coil + and confirmed no short across terminals.
    5. Confirmed fuel pump OK by jumpering 12V to coil + and listening to tank or throttle body.
    6. Following up on no-spark, confirmed ASD functional by grounding its PCM side. (PCM activates the ASD by providing a path to ground).
    7. Checked 3-wire ignition pickup connector for supply voltage and found it only 0.7V versus normal +8.
    8. Confirmed all ignition wires good from pickup to PCM and ground. *** PCM is bad ***
    9. Unlikely, but the ignition pickup could also have been bad. On vehicle test would require an external 8V supply, but I didn't have power nearby.
    I had the service manual (and good guidance above) for this. At a minimum you need the connector pinouts for the ASD, PCM, and ignition pickup.

    Finally, reman on these 90s vintage mopar PCMs is apparently not very extensive ... 3 electrolytic caps and possibly a diode or two. DIY is possible in a pinch with decent electronics skills....should reman or a yard PCM be unavailable.
     
    Bob Lincoln, Devildodge and NYBo like this.

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