4.0 SOHC Popping/Bucking Under Load

[Gokussj5okazu]

Ok, I had posted about this once before, thinking it was a transmission issue, but it isn't.


I just redid the SOHC in this 97' I bought. It had the infamous timing chain noise, so I immediately yanked it out, and did a refresh. Didn't pull the pistons, or do any of the bearings, but I inspected them and they were fine.

Anyhow, it's all together now.



The first issue I have is that when it's cold, the idle is erratic for about a minute, and stays very low, around 600RPM. I have adjusted the throttle so that when warm it idles at 500RPM without the IAC, set the TPS at 0.97V, and then confirmed that with the IAC plugged in it increases to about 900RPM. So that system is working as intended.


The second issue is a bit more severe. When any load is placed on the engine, it occasionally bucks and makes a loud pop. It does it when in gear, or with the AC on. I initially thought it was the transmission doing it, but it is most definitely the engine. Also, the hotter the engine gets, the more frequently it does it.

Here are two videos of it. Ignore the higher pitched clattering noise, it's not from the engine, my phone just picked it for some reason. Towards the end of the first one I brake torque it to show how bad the sound gets.

 

[TestPoint]

I chased a 'bucking and popping' problem under load but good at idle through spark plugs, wires, replacement of injectors, frogging injector operation, timing, and coils without resolution. Turned out to be swapped plug wires.

 

[Gokussj5okazu]

You sir are a scholar and a saint. Thank you! My coil pack was hooked up 123456 instead of 123564

 

[TestPoint]

Glad I could help!

My problem defined all logic and not even the big Ford manual specified the spark plug wiring layout. The only reference was to 'mark the positions . . . '

Everything OK now?

 

[Gokussj5okazu]

Yeah, it's running great. I had my #4 plug going to 5 on the coil, #5 going to 6, and #6 going to 4. I still don't understand how it actually ran reasonably well, but I'm sure not complaining. I had to readjust my idle and TPS, but it's all great now, tons of power and smooth as can be. Thanks again!