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.
Check-engine light does not come on when ignition is turned on ( so no PCM 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.

How about Hall-effect sensor...could that cause these symptoms ?
No ignition diagnostics and symptoms have me thinking PCM, but I'd like to know for sure before dropping $.

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

 

Is the PCM triggering the ASD relay? If you just use the ignition switch, does the pump prime when you first turn the key on? Fuse for the PCM good?

 

the pcm/asd is triggered by the by the key which sounds like it is working properly. do you here the fuel pump cycle and throttle body do its stuff with when you turn the key on with the relay hooked up?

 

Thanks for the quick responses guys. I don't think that there is a plug-in fuse to the PCM...at least I haven't found one on the truck or FSM schematic. I guess the PCM is only protected by a fusable link in the wiring harness.

From inside the cab, the key seems to be working. When I turn it on I get the normal relay clicks, a brief buzzer, and the oil pressure light.

• I do not hear the fuel pump cycle when I turn the ignition on.
• I can definitely hear the fuel pump and fuel flow at the TB with ignition on AND 12V jumper to the + side of the coil.

I suspect that the PCM is not triggering the ASD. I'm not sure how to confirm it.

• Should I be probing the back of the ASD connector with relay plugged in, ignition on, and cranking ?
• And should I be seeing something near 12V under those conditions ?

I suppose that I should test the ASD relay itself by putting 12V across it and checking its resistance.

Is this on the right track ?

 

where are you checking for spark from? did you try starting the truck with the 12v wire to the coil when you heard the fuel pump cycle? if it cycled the fuel pump and shut it off then it sounds like the pcm might be working. do you hear the throttle actuator moving when you turn the key on/off? it is normally pretty noticeable. if you think the relay is bad you can generally borrow 1 from a newer vehicle. any bosch style relay that is used in quite a few newer vehicles should work or swap with the starter relay if you know it works properly

 

Well, I gave it a good going-over and all roads seem to point to bad PCM. See if you guys agree please.

1. CEL does not illuminate with ignition. The Message center CEL bulb is good.
2. Fuel pump does not run when key is turned on.
3. ASD relay tests good on bench. Clicks and shows 5ohms with 12V applied.
4. With key on (and ASD relay reinserted), backprobing shows that the ASD is not closing.
5. 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 the ASD 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. :-(

 

That's what I am thinkin'. If the PCM was doing it's job, the fuel pump should prime, regardless of if the PCM sees the engine turning or not. That, and no cel under any circumstances just ain't a good sign.

Take a paperclip, and short the two upper right pins on the ALDL together. That *should* force the PCM to display any codes. (it should also tell you at the very least, end of message. (55))

 

Help me out here pls ...I am not familiar with ALDL (just OBDII).
I see in the service manual that there is an EFI diagnostic connector on this 90 W150.
Is that what you are suggesting I jumper ?
I did try the key on-off-on-off-on within 5 seconds method...nothing.

 

Your 2010 post is clear on the DLC connector location...on harness on firewall near brake booster.

I'm just not following the jumper part. Upper 2 (of the six) as shown in manual are D-3 SCI trans and D-5 J-2 Ignition.

.........D-6 D-5
TAB [ D-4 D-3
.........D-2 D-1

The top four are horizontal slots and the bottom 2 are vertical slots when the tab is on the left.

D-1 Ground
D-2 NC
D-3 SCI Trans
D-4 SCI Recieve
D-5 J-2 Ignition
D-6 ASD Relay

I like the idea of forcing codes ... I'm just am not seeing how it might work.

 

the key dance should work if the pcm is working but definitely sounds like you really might have a dead pcm. if you know someone with a dodge obd1 code reader you could try getting them to pull the codes but a lot of people don't have one that will work on obd1 and just do the key dance just like SEAL has posted in the DIY info thread. i don't think there is really much else you can look at