93 rough run and pop 4.0 no check engine light

[FEandGoingBroke]

93 4.0 no check engine light….

thinking the ECU was hammered I put new capacitors in it today, one diode had an iffy solder arm that I touched up, (the rest of the three layer board was perfect) thinking that the hesitations and popping that happened on occasion while hard acceleration but are more normal now we’re coming from the bad PCM.
this occurred after replacing the plugs, properly gapped to .052, crank sensor the coolant temp sensor the throttle position sensor and the thermostat, while pulling the motor apart and fixing the lower intake leak and the timing cover leak….

So either the ECM is bad still, or the whole skip fire and pop chug on mild to hard acceleration is due to a bad MAF sensor….

But there’s no codes detected by the ECM.

loan me your thought friends!

 

[franklin2]

Do you still have the old sensors? If so, I would plug them back in. The new parts you get now do not have a very good reputation. Even though you do not have any codes.

 

[RonD]

Yes +1 ^^^

If no codes then its not a sensor issue

Misfire causes "popping" noise when its unburned air/fuel mix is ignited in exhaust manifold

And of course "rough running" means misfires, so.............

Recheck coil pack spark plug wires
3 4
2 6
1 5
front

5 6 4 side always gets mixed up
Follow each wire to driver's side cylinder

1993 4.0l uses a separate spark module, EDIS-6, they never break, bulletproof
Coil packs can crack, usually easy to see the cracks, causes random misfires

1993 4.0l uses Batch Fire fuel injection, so 3 injectors open on each 1 RPM, and they alternate, so a bad injector shouldn't cause a misfire, might set lean code

"Bad gas", if problems arose the day after filling up..............water in the gas causes rough running and popping, "bad gas" is gasoline with too much water in it, all gas has some water, but too much causes issues

So if Spark is OK, and fuel is OK that only leaves Compression
You will need to test all 6 cylinders with all 6 spark plugs out, write down result of each cylinder

1993 4.0l should be 150 to 160psi
125psi or lower is misfire territory, usually burnt exhaust valve, on any engine, not a 4.0l or even a Ford thing, its a valve thing, lol

 

[FEandGoingBroke]

Your overview is impeccable thank you.

new coil pack produced same results, new wires last year, power is excellent and the misfire doesn’t show in free reving the engine. Belden plug wires arent arcing out nd are in the correct holes.

I just don’t understand the misfire. It has to be electrical. Even while maintaining speed it has this un timed random misfire. Still no check engine light.

I replaced the bad capacitors in the ECM yesterday, no change sadly.

 

[FEandGoingBroke]

A compression test is not necessary at this point because the compression isn’t the culprit. Maybe it’s that dang old bullet proof ignition box.
Is there a test for them?

 

[RonD]

No, no test for the EDIS-6 but because they never break, so there should be quite a few around, but the Hotrod/custom car guys do scoop them up as they are a "stand alone" spark system, so easy to go distributorless on any V6

 

[2011Supercab]

this occurred after replacing the plugs, properly gapped to .052

I know what I would be checking or replacing.

 

[FEandGoingBroke]

Beside the driver, what would you be replacing or testing?

 

[RonD]

Yes, I would be with 2011Supercab, I missed the "this occurred after replacing the plugs,..........."

If you still think "new" means "it works", then its been a long time since you bought new parts, 40 years
"New" means "YOU TEST IT" and "we will replace it if it doesn't work"
Even applies to "new" cars now

Quality control went out the window when minimum wage got above $5/hour, lol

 

[FEandGoingBroke]

I feel your frustration. But what the hell is there to test that causes intermittent spark loss in this system besides the coil pack or the ignition control box?

 

[RonD]

The new spark plugs.........................

 

[2011Supercab]

But what the hell is there to test that causes intermittent spark loss

The defective spark plugs

Or you bought Bosch, Denso, or NGK's, they don't work very well in Fords.

You need Autolite or Motorcraft

 

[SenorNoob]

I've seen 4 new plugs in a box all be open circuit. No spark under any conditions. So test everything.

And agreed leave the NGK's to the four wheeler. They work great there.

 

[FEandGoingBroke]

The defective spark plugs

Or you bought Bosch, Denso, or NGK's, they don't work very well in Fords.

You need Autolite or Motorcraft

Autolite double platinum, gapped per spec. Problem was there before the new plugs.

 

[2011Supercab]

First you tell us

this occurred after replacing the plugs, properly gapped to .052

Now you tell us

Problem was there before the new plugs.

Then I think it's time for a compression test and to have the injectors flow tested.

Or at least run a couple cans of injector cleaner through it.