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 (http://www.rockauto.com/en/moreinfo.php?pk=40271&cc=1050882&jsn=425)? 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 wMakes 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:
http://pic.armedcats.net/d/dr/dr_grip/2016/03/05/IMG_20160305_160232.jpg (http://www.armedcats.net/image/view/UJtXixqAGcWvvCjN)

Filter module in:
http://pic.armedcats.net/d/dr/dr_grip/2016/03/05/IMG_20160305_181810.jpg (http://www.armedcats.net/image/view/3VwnM7NPFsu3UGjx)


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 wYou 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 (http://s226.photobucket.com/user/RFmaster89/media/TBI%20Photos/Picture025.jpg.html) 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

http://pic.armedcats.net/d/dr/dr_grip/2016/03/13/IMG_20160312_180952.jpg (http://www.armedcats.net/image/view/xTXrumSnrS3Upd3w)

[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:
10322

[ony]

when it gets day light I will look at my truck I think its wired right.

[dave w]

As pictured, the ESC Module is wired correctly.

dave w

[Dr_Grip]

As pictured, the ESC Module is wired correctly.

dave wHi dave, hi ony,
thank you for confirming!

In that case, it's toast. I'll order a new one tomorrow morning.

[Dr_Grip]

Reporting back - new module installed. Works like a charm. I wonder if it works too good, i.e., if it takes off more timing than it should. Here's the new prelim SA table I distilled from the logged data:
http://pic.armedcats.net/d/dr/dr_grip/2016/03/20/Bildschirmfoto_von___2016-03-20_12-26-56__.png (http://www.armedcats.net/image/view/tVqRwAk8zuofsK5W)

And the diff:
http://pic.armedcats.net/d/dr/dr_grip/2016/03/20/Bildschirmfoto_von___2016-03-20_12-26-48__.png (http://www.armedcats.net/image/view/iSuadEfGkVIlgD75)

Log attached. Looking forward to your opinions.

[Dr_Grip]

Any ideas? Anyone? ;(

The best thing I can come up with to find out what's going on is this: If my original timing table was that far off (up to 5° at WOT, up to 10° elsewhere) this should have had a huge negative impact on performance. Thus, a couple of 1/8 mile sprints should theoretically tell me which timing table works better and thus, whether the knock sensor is to be trusted.

Or is this totally stupid?

[jim_in_dorris]

Start your car. Look at the knock count. then tap your block with a hammer. Did the knock count increase? if so your knock counter is working. Being sensitive to knock on a ford block is another question. I would try an experiment (very carefully) where I advanced the timing until it pinged and monitor the knock count to see if it detects knock. Again, I would do this at idle and approach the timing carefully, but that is an empirical approach to determine if the knock sensor is detecting knock on your ford. Good luck

[Dr_Grip]

Hi Jim,
thank you for your reply! The question is not whether it is working (it is, I am seeing knock counts) but whether it detects non-knock engine noise as knock...

[jim_in_dorris]

False knock is tough to diagnose. Do your knock counts increase rapidly when driving? I would try as a test, turn key on, start TP, record knock counts, start engine and check knock counts again. It most likely will go up as this is normal. Rev motor while in park. Do knock counts increase? If they do, try the test while listening under the hood for a rattle like a loose exhaust. If you don't get any knock counts reving in park, but you do driving, it quite probably is something loose somewhere rattling. If everything is tight, and you still get knock counts increasing, you are in for a long hard stuggle trying to figure out what is causing it. On cheverolet small blocks, it can be double roller timing chains (noisy) or certain roller rockers among other things including noisy lifters. Good luck in your hunt.

[Dr_Grip]

Yep, as far as I know Fords generally have noisier timing chains than Chevys, so maybe what the sensor is hearing really is the timing chain. For my upcoming weekend trip, I'll disconnect the sensor as further testing is required....

[Terminal_Crazy]

Hiya Dr_Grip

I've been following your thread recently. I had a 1974 Ford Torino with 351 Cleveland in 20 years ago.
I've just rebuilt my 95 Z28 LT1 into a High compression 383. I've been struggling with the knock sensor counts going up fairly continuously. Followed all the usual advice/ replacement without any success. Nothing is hitting or banging anywhere.
General concensus on the interweb is to either ignore it or tune it out. Neither of which i'm really happy with.

I came across a circuit called the "Knock Knocker" desensitizer by Mike Chaney. Lots of references & It takes some finding but is out there.
Basically it is 2 resistors to lose some signal between the knock sensor & PCM.
I think results vary from what i read.

Anyway. I made the circuit using a 1K resistor & 50k Linear adjustable Pot instead of a fixed resistor going to ground & could vary the amount of signal from the knock sensor.
By tapping the Alternator with a hammer ( 5 taps @ 1 per second) I seem to be getting approx 500 knock counts for each tap.
By varying the voltage from 2.5 - 0 I could reduce the counts from 500/tap down to around 70 at 0.5V.
While this seems to be consistant & repeatable i found when I checked the data log it appears i was missing taps and the associated knock counts.
Figures are for show...
ie on full sensitity i got 5 taps showing 2500 counts
but at 0.5V I only saw 1 tap of 500 counts so averaging 100 per tap.
at say 1.0V i saw 2 taps and 1000 counts per 5 taps.

OK I know that's inconclusive but this was as far as i got and it was suggested that i just reduce the Knock tables for the PCM which is where I am at the moment.

Food for thought if anyone is interested.

HTH

Mitch

[Dr_Grip]

Thank you for the input ;) I tried the timing table as sensed by the ESC and it's rubbish. Down on power, driveability sucks, she's running noticeably less smooth... I think I'll play it by ear/stopwatch for now and figure out a way to use a knock sensor manually (using speakers/headphones and an equalizer) for fine tuning when I find the time....

[Dr_Grip]

Soooo.... by-ear update: Not being satisfied with how she feels at higher rpm, I decided to give up on the self-imposed 48° advance limit and just see what happens when I let the timing curve move on uncapped:
http://pic.armedcats.net/d/dr/dr_grip/2016/03/28/current.png (http://www.armedcats.net/image/view/sozjhpa3gdjUgMMl)
The results are surprisingly fine, the engine feels noticeably smoother above 2200 rpm (where the cap started to affect timing).

So, this old iron block really loves itself some timing. So I wonder what happens if I put the full 25° the stock dizzy's vacuum would add in there, like this:
http://pic.armedcats.net/d/dr/dr_grip/2016/03/28/new.png (http://www.armedcats.net/image/view/RdlGL0oZLztIxNmx)
Will try that later this week. The biggest fear I have is that even with the dizzy being phased correctly, I might run into arching problems at higher engine speeds... Apart from that, I should be fine. The combination of the more precise fuel mixture provided by the injectors and the HEI ignition's stronger spark should mean I can run more timing than stock...