1991 Ranger No Spark

[ylidk]

Not quite stable, it jumped to 12V for just a moment, before dropping again, even as I crank the engine more. The Red/green wire at the harness at the plug still reads okay, I think there's just a loose connection later in the harness that caused it to not get the full 12V or something.

Also, when I managed to get the harness to sit still, and it actually read 12V at the ignition module, connecting the CKP did make it drop to 6V, I don't really know if this is caused by the CKP sensor itself, or the red/green wire that goes to it might be messed up too, and connecting it just connects the rest of the red/green wire to that issue.

Vehicle wiring has to be the worst part, I always hate chasing these ghosts down

 

[RonD]

Crank sensor is not a big amp draw, it is basically an on/off switch, so something is wrong but..................

Voltage is one thing AMPS are another.

i.e. if a battery shows 12v and if you activate the starter motor that 60amp draw will make battery read 10volts while starter is active

So the 12v on the red/green wire may only have .5amps available, so crank sensor hooked up, or anything else, causes the drop to 6volts, or 2volts

That is almost always caused by a corroded connection or wire, wires can corrode on the inside, battery cables are notorious for that, just FYI.
So you may be chasing a splice or connector corrosion issue on the main red/green feed

 

[ylidk]

That was in fact the problem! (Well, most of the problem)

I took the engine harness out and tore all the tape off to trace all the wires, the previous owner spliced 6 points of the red/green wire together at one splice, so I decided to remove that splice and replace it with soldered joints. Taped the thing up, attached the wiring harness back on the truck, and measured the red/green wire to have 12V at every point, every connecter attached.

Problem is, while the wire now has proper voltage, the truck still won't get spark. Back to square one, any suggestions? Anything that would have gone bad due to the wire or anything?

 

[RonD]

That was a Factory splice, just FYI

It only sparks on the exhaust side, the coil pack with tan/red and tan/orange ground wires

Crank sensor test again to make sure you get the 12v-0v when crank is turned manually

Crank sensor starts the ball rolling for spark, its pulse tells the ICM when to ground and then unground a coil in the coil pack to make it spark

Retest to make sure you are getting the 12v when key is in START position, as seen, RUN 12v and START 12v have different paths, only one will provide the 12v in each position

 

[ylidk]

Tested Crank sensor, it is getting the 12V-0V now.

Test light shows that it is getting 12V in start as well.

Ignition coil?

Update: following the ICM and CKP test, and wire #2 on the ICM gets the 12V - 0V changes, but wire #4 stayed at battery voltage. Will retest each to double check.

Update #2: After retesting, neither signal was changing, just battery voltage. After checking the connection found the wires were loose in the connector. Fixed them and she fired up!

 

[ylidk]

So it's running, but rough. Sounds like it's misfiring. Checked the timing on engine while it's running, read 20 deg btc without the spout. With the spout it's correcting to 30deg btc. Going to have to start checking into the misfire, any guidance on that?

 

[RonD]

Good work

Yes, there is no way to adjust spark timing on these, so 20deg BTDC without SPOUT will have to be fine


Check coil packs spark plug wires

Each coil pack has 2 coils inside NOT 4

Cylinders #1 and #4 share the same coil, cylinders #2 and #3 share the other coil, and thats on each coil pack

Picture here of a 2 coil pack: https://www.route66hotrodhigh.com/images/Ignition/CoilPack2.jpg

2 and 3 are to the right of the wire connector, 1 and 4 to the left, slightly in this picture, lol.

1<>4 doesn't matter, as long as both are on that same coil
2<>3 doesn't matter either, you can swap them around

With the 1991 after engine starts you can unplug the wires on either coil pack and the engine should continue to run on ONE coil pack
This is a good way to test if all 4 spark plugs on the working coil pack are OK.
Or if a coil is working, lol

Dual spark plugs give better performance and MPG, but this engine ran fine from 1974 to 1988 on just 4

 

[ylidk]

Disconnecting the wires on the exhaust side, #4 seemed to make no change - will take out the spark plug to see if its electrical, or maybe the injectors.

Thanks for all the help with this, I really appreciate it!

Edit: Tach is not reading anything while running, but will when cranking. Also, when I give it gas it will stall after the rpms go back down. I don't know if these are common symptoms of something, but I figure they'd be good to include!

Doesn't seem to want to start when turning the key like usual, but will start when I also hold the gas pedal down (keeps fuel injectors from spraying, right?), and then will idle after that. Found out that the major misfire on #4 was caused by somebody forgetting to plug the #4 fuel injector in, but it's still running rough after plugging that in.

 

[RonD]

There should be a Black/yellow stripe wire on the ICM, thats the IDM or Tach wire

Computer needs that wire hooked up, it is also splice to a Tan/yellow wire for the tach signal on the dash and to computer pin 4

 

[ylidk]

Well the wire has continuity to the computer. Idle seems smoother now (still dies after revving it abruptly), and I could even drive it around the neighborhood. Nearly no throttle response, and the tach still isn't working. Pulled codes, KOER, the truck did not do the usual procedure (no, engine ID blinks, no blink to indicate when to give it throttle, etc) but it just started to read out codes 98, 48, 98, 48, etc, without stopping. 98 - Hard fault, 48 - Loss of IDM Left side//Coil 3 failure OR High flow unmetered air (different sources provide different explanations). Code 98 - Hard fault, would explain the lack of throttle response if it has put the truck into limp mode, correct? Possibly failing ECM? Bad ECM would cause the tach to stop responding as well, right?

 

[RonD]

98 is a test code, key on/engine off test, ignore it


Code 48 can be used for loss of Ignition Diagnostic Monitor(IDM) LH side which is either wiring issue, i.e. No Tach signal, or ICM issue
Your ICM could be damaged and the new one didn't help at THAT TIME, because there was no voltage then.

This is a new wrinkle, most parts stores can test ICMs but not sure IDM signal is part of that test

 

[ylidk]

I did take the ICM to Autozone and it tested good, but if that doesn't test the IDM signal that could still be the problem. I may go ahead and re-purchase a new ICM to verify whether it is that or not. I will double check the black/yellow wire at every point as well, to make sure it doesn't have a break somewhere.

Any idea why the truck skipped the typical code reading process, and just began to immediately spit out those codes?

 

[RonD]

The IDM is the RPM of the engine(tach signal) and computer needs that for timing but also where to set idle using IAC Valve


Not sure why computer didn't set code right off the bat but................engine does need to get to operating temp before it will set codes usually

 

[ylidk]

Been busy this past week with school stuff, finally had a chance to work on the truck today. Swapped the ICM and the tach is back and she accelerates smoothly again! Codes were able to be pulled again with the swap, got codes 21, 31, and 52. My truck still will flood when stalled and will start only when I hold the gas pedal and crank it, which may be caused by the ECT out of range. Code 52 probably pulled because I must not have turned the steering wheel fast enough during the test.

In each gear it accelerates smoothly, as long as the rpm's don't dip too low for the given gear. If I lug it in second it reaaaallly doesn't like it, surges violently and sounds like it's clunking.

 

[RonD]

Good work