1997 SOHC 4.0 No Spark after Timing Chain R/R

[Gokussj5okazu]

Hello everyone! I've got an issue I'm hoping someone may be able to help with.

I have a 1997 Explorer, 4.0 SOHC that I bought a month or so ago. I got it for a steal because it had the death rattle, but it was running, so I knew nothing had gone FUBAR yet.

Got it all torn down and apart, replaced all of the chains, gears, etc, and I made sure I had the timing 100% perfect. Well today I got the engine back in, all wired up, fresh oil, the works. But I'm not getting any spark.

I'm getting fuel, the injectors are ticking, and the plugs are wet, but there's no spark. I checked the coil pack, it has a good ground, and 12V ignition. The CPS is 1.6V across the wires, and the CMP has the correct resistance.

Any other ideas where I should start checking? I'm 100% all of the plugs are plugged in where they go.

Thanks in advance!

 

[2000StreetRod]

no spark verification?

How did you determine that there is no spark? Did you use a timing light or an inline indicator? Or did you assume there is no spark because everything else seems OK?

If you're certain there is no spark:
1. Make sure the PCM connector is on good. Snugly held in position with the bolt.
2. Make sure PCM pins 26 (BLU/GRN), 52 (RED/LT BLU) and 78 (PNK/WHT) are not pushed back in the connector and not making contact.
3. Check the ground strap that goes from the PCM to chassis.

 

[Gokussj5okazu]

How did you determine that there is no spark? Did you use a timing light or an inline indicator? Or did you assume there is no spark because everything else seems OK?

Initially while cranking, I smelt fuel, and confirmed by smelling near the exhaust. Then I pulled several spark plugs, and they were wet with fuel. Also, there was no soot, or marks of any sort that indicated any sort of spark. I then tested with a powered timing light. There is definitely no spark at all.

If you're certain there is no spark:
1. Make sure the PCM connector is on good. Snugly held in position with the bolt.
2. Make sure PCM pins 26 (BLU/GRN), 52 (RED/LT BLU) and 78 (PNK/WHT) are not pushed back in the connector and not making contact.
3. Check the ground strap that goes from the PCM to chassis.

I double checked the PCM harness, bolt, and ground. Everything with the PCM seems to be functioning perfectly, hence the injectors firing.

I will check 26, 52, and 78 just to make sure.

 

[boominXplorer]

Check and make sure the knock sensor and crank sensor are plugged in.

 

[Gokussj5okazu]

That was one of the first things I double checked. Both are plugged in, getting correct voltage, and have correct resistances.

 

[Gokussj5okazu]

Ok here's what I found out today.

The PCM connector is fine, as is the ground from the PCM. I measured it to about 5 ohms to the battery.

The CPS and CMP sensors are plugged in, and are getting correct readings across the wires. While I doubt it, I suppose it may be possibly that one went bad.

Is there an adjustment guide for the CPS? I noticed the bolt holes are slotted for adjustment.

Also, I tested all of the coil wires. With the key on, it's getting 12V ignition on one wire, and the other three are grounded. Is this correct?

 

[Gokussj5okazu]

Another thing I've noticed:

When I crank on it, the starter only runs for about 2 seconds at once. It will start cranking, then shut off after about 2 seconds, and all of the dash lights light up.

Any relation? It certainly didn't do this before.

 

[2000StreetRod]

CPS adjustment

Ok here's what I found out today.

The PCM connector is fine, as is the ground from the PCM. I measured it to about 5 ohms to the battery.

Seems high but probably not enough to disable the ignition.

The CPS and CMP sensors are plugged in, and are getting correct readings across the wires. While I doubt it, I suppose it may be possibly that one went bad.

Is there an adjustment guide for the CPS? I noticed the bolt holes are slotted for adjustment.

The crankshaft position sensor should be aligned so the pointer points to the TDC mark (line next to 0) when #1 piston is at TDC on the compression stroke. The sensor should be close to the teeth on the harmonic balancer but not rubbing against them. If you didn't take it off then it still should be in the correct position.

Also, I tested all of the coil wires. With the key on, it's getting 12V ignition on one wire, and the other three are grounded. Is this correct?

Yes. The PCM grounds the trigger wires to build an electromagnetic field in the coil section. It "opens" the circuit to fire the plug. The Explorer uses a waste spark ignition system - paired cylinder plugs fire at the same time. That's why there are only three coil sections. I suggest that you disconnect the coil pack electrical connector and measure the resistance from the supply line (Red/LtGrn) thru the coil pack to chassis ground. There is no ground wire for the coil pack. It is grounded thru the mounting hardware. If the resistance is large, clean the area unde the heads of the mounting bolts to get a good electrical connection. Also, make sure the engine to chassis ground strap is properly connected.

 

[Gokussj5okazu]

In casre anyone's wondering, it was the classic ground issue. I ran a new wire from one of the coil pack screws straight to the battery, and viola! It fired right up. Thanks fellas!