7747 on a Ford 400 - what knock sensor to buy

[Dr_Grip]

Hi guys,
several of you have advised me to fit a knock sensor to my Ford 400 (M-Block/Cleveland) TBI conversion. The thing is - I have no idea which knock sensor to fit and where. Is it possible to fit the knock sensor from the TBI donor K-series? If not, what's the alternative? What do other TBI coverters do in a case like that?

Any help is appreciated...

[dave w]

If possible try getting a 7747 knock sensor from an engine with a nearly identical cylinder bore diameter as the Ford 400 (M-Block / Cleveland).

dave w

[Dr_Grip]

Hi Dave! Thank you! :)

It seems like GM used the same knock sensor over all V8 engines, so I ordered one of them. The mounting thread is the same between Ford and GM, so it'll just screw into the coolant drain hole?

[dave w]

Ok, same knock sensor for the V8's. Maybe it would be a good plan to figure out which electronic spark control module / knock filter module to use? I think the part numbers will be different for the knock filter module (305 vs. 350 vs. 454)?

dave w

[Dr_Grip]

Ok, same knock sensor for the V8's. Maybe it would be a good plan to figure out which electronic spark control module / knock filter module to use? I think the part numbers will be different for the knock filter module (305 vs. 350 vs. 454)?

dave w

Makes sense, thank you for pointing that out. The 400 (4.00/4.00) slots in right between the 350 (4.0/3.48) and 454 (4.25x4) when it comes to bore and stroke. As the 400 is a small block like the 350, I think going with the 350's filter module makes more sense.

What do you think?

[dave w]

I think the 350 filter makes the most sense also. Post back when you have an update on how the 350 filter works.

dave w

[1project2many]

I've read that the bore diameter is much more important than the stroke. It has to do with the resonant frequency of the sensor. I remember reading some test results which demonstrated that aftermarket sensors may not be tuned so closely to a specific bore as the original parts. That fits with the parts store listings which often show the same part number sensor for both 350 and 305 engines. The external amplifiers likely help ensure the sensor works best with a particular engine and years ago I know folks who would try as many knock modules as they could in the pursuit of maximum performance.

[Dr_Grip]

So, I fitted a brand-new knock sensor and a 350 filter module I found in my parts box.

Knock sensor in:


Filter module in:



Sadly, I made a stupid wiring error (patching the filter module ground to C14) which I just figured out while writing this post. Seems like I got to re-wire that before the sensor will work :)

[dave w]

Thanks for posting back.

dave w

[Dr_Grip]

Thanks for posting back.

dave w

You are very welcome! Now I fixed the wiring:
-Red wire goes to ignition-switched power
-Black wire goes to B7
-Red/Black goes to ground
-Purple goes to the sensor

Engine runs flawless now, no weird sensor readings any more. BUT I did not see a single knock yet in TunerPro. No code has been thrown, either, though. Does that simply mean my engine does not knock (yet) and I should throw some timing at her? Or does that mean that the junkyard ESC module is toast?

[dave w]

I think if you tap on the block with a small hammer, you should be able to produce a "Knock" that should be detected by the ECM?

dave w

[Dr_Grip]

Looking at the picture again and comparing with a pic of the stock wiring harness I found online I realized I had the ESC module wired up backwards. Just rearranged the wires. A test will tell whether I fried the module by hitting the ground connection with +12V or not.

[Dr_Grip]

Soooo, that didn't go well! Knock counts go through the roof while timing gets dialed back to a point that makes her misfire under acceleration. Log (ends apruptly after 30 minutes as the laptop went to sleep, please ignore that) and bin attached.
Sooooo, questions arise:
1. Did I mess up the wiring again?
2. Is the ESC module broken and thus behaving like an open wire (the log files makes this most likely)?
3. Is the ESC module broken and thus hyper-senstiive/not filtering enough?
4. Is the valvetrain of a stock Ford 400 so noisy it totally throws the knock sensor off?

If none of you sees a fault in my wiring (see below) or has any other pointers, I'll order a new ESC module, I think.

Current wiring:
-Red wire goes to ignition-switched power
-Black wire goes to B7
-Red/Black goes to ground
-Purple goes to the sensor

[ony]

there is a thread on this web site called 1217747 to a 7427 conversion that has a wiring diagram I think.

[Dr_Grip]

there is a thread on this web site called 1217747 to a 7427 conversion that has a wiring diagram I think.

This is the wiring diagram for the donor truck I am working off:
Attachment 10322