Big block juddering at lower revs

[D4NS]

Interestingly, I think there are 2 narrow band sensors wired into a toggle switch under the dash. My guess is it can swap from left to right for tuning purposes. The sensors do look a tad rusty and a pain to get out so will try one and see what happens first. 

It's a pro-flo so only handles the single narrow band sensor, so still none the wiser of the 3rd sensor.

Many thanks. Fingers crossed

[JON1D]

Strangely there seem to be 3... I haven't figured out what / why as yet.

1 in the left and right side pipe at the correct angles after the pipes merge and another seemingly to air, next to the right pipe. I doubt the EFI can handle 2 with it being older.

Thank you. It may be beneficial to just upgrade the EFI, just didn't want it to tune itself to handle say sticky injectors.

All you need is one faulty sensor to give you incorrect meter readings. A lot of the after market ones fail after time so a good Bosch one. Some systems just use the one wideband. You really need live monitoring on the system to know what is going on. If you have two and both operational then one side failure will be obverse with different mixture and colour of the exhaust pipe. Also pull some sparkplugs to see there colour. Your system might be perfectly ok to run and just needs some investigation.

You say Edelbrock EFI unit. Is it E-street or Proflow as I think either only uses one Wideband or narrow band sensor.

[Happy Jim]

I'd guess that you have 2 narrow band O2's that feed the ECU and then a Wideband O2 dangling ready to be put in place on one of the narrow band ones for when you are tuning it - wild arsed guess!

[D4NS]

Strangely there seem to be 3... I haven't figured out what / why as yet.

1 in the left and right side pipe at the correct angles after the pipes merge and another seemingly to air, next to the right pipe. I doubt the EFI can handle 2 with it being older.

Thank you. It may be beneficial to just upgrade the EFI, just didn't want it to tune itself to handle say sticky injectors.

[JON1D]

You do need to look at your AFR at idle. Do you have a O2 sensor as these can go faulty and cause issues. Its usually the angle of the sensor 15 deg down but difficult on a cobra side pipe.

[D4NS]

Hey all,

Looking for some tips in a logical order to fault find...

502 engine starts easy every time, but seems to struggle at lower revs to the point where I end up dropping a gear as it feels it will kangaroo. When I say low revs I mean under 2k. Keeping above this is fine in any gear. It has a Edelbrock EFI unit so a few more variables.

First check was the plugs which were sooty and fuely so replaced them. No difference.

All manifold branches seem to heat up evenly.

It's an old EFi unit so no mapping software to check AFR but think it would just show me it's rich. So where would you begin?

Temp sensor?
Oxygen sensor?
Map sensor?
Injectors sticking open?
Vacuum leak?

I am likely to replace the EFi with a Holley Sniper for piece of mind it's running perfect, but want to solve this issue first.

Any tips in where to begin before I throw money at the wrong things?

Many thanks