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Discussion Starter #1
I've read quite a few posts here and in other forums concerning the lack of availability of the knock sensors for our trucks. I've read some comments, but was wondering if anyone knows, for sure, how the computer acts when the knock sensor is unplugged. Will it lock down the timing if it isn't getting a signal back from the knock sensor, or will it move the timing around? If it doesn't do anything other than throw up the engine light, I can live with it and just set the timing in a good place. I just want to be sure it won't push the computer into some "safe mode" map or something and not run as good as it could. Obviously I realize it will no longer adjust the timing in the event of detonation.

Much appreciated! ;)
 

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yo,
As Seattle asked, is this for the 87 5.0/AOD or the other vehicle you were driving during the 87 rebuild?

Overview & Ford Part numbers, Bronco & Ford;
"...Detect cylinder block vibrations caused by engine knock and send a signal to the computer to retard ignition timing.
FAILURE SYMPTOMS, Engine knock, loss of power, MIL light.
Check connection and signal from sensor when complaints of engine knock are present; 1996-1986 5.0L (N)/ 302 Bronco, E150, 250, F150, 250 E3AF-12A699AA,E3AZ-A Tomco PN 29021,

$66.64 as of 10 JUN 2010..."
Source: by tomco-inc.com

Wiring Diagram in 87-89 5.0 Bronco & F series (Mitchell)

Source: by equivalent (Beetlejuice) at SuperMotors.net
See B-9

Location pic in an 89 5.0; "...After you have unplugged all the injectors, temp sensors, AC, oil sender, distributor and whatever else you can see, including this knock sensor at the rear pas side of the motor,..."
Source: by Waltman at FSB


Waltman wrote; "After you have unplugged all the injectors, temp sensors, AC, oil sender, distributor and whatever else you can see, including this knock sensor at the rear pas side of the motor..."


Location pic in 84-86 5.0 (& ECT & Temperature Gauge Sending Unit)
Source: by Ryan M (Fireguy50) at http://www.fordfuelinjection.com/public/302truck_1986_lower-intake.gif

Location in Engine Bay Diagram in an 87-88 4.9L; #1
Source: by Ford via Chilton


Ford Part Number in Vehicle Emission Control Information (VECI) Decal; Contains Vacuum Diagram & Calibration Parts List for 88 & UP. On-Line for Free at Ford. Click "Quick Guides" in left panel; Scroll to & CLICK VECI Labels "Provides Vehicle Emission Control Information (VECI) and a related calibration parts list." Enter applicable info (need to know your Calibration number from your B-pillar sticker). Vacuum Diagram is the same as the one on the core support or hood or air filter cover. Suggest Right Clicking this Hot Link & Open in New Window
Source: by Ford @ http://www.motorcraftservice.com

Overview & Depiction; "...1996 7.5L, 5.0L and 5.8L do not require a knock sensor;

During engine operation the knock sensor (KS) (12A699) will generate a signal to the powertrain control module (PCM) (12A650) to retard timing if the engine knocks..." from 1996 F-150, F-250, F-350, F-Super Duty Series and Bronco Vehicles Workshop Manual
Source: by Ford

Late night reading version;
Overview; "...A knock sensor monitors vibration in the engine and reports this information to the PCM. The PCM is calibrated to react to a range of vibration that is associated with the frequency and intensity of the ringing in the engine assembly associated with audible detonation. The physical location of a knock sensor on the engine should be chosen to allow, as nearly as possible, equal sensitivity to knock in all cylinders. The PCM calibration is carefully adjusted to insure detection of detonation while ignoring other background engine noise. Inclusion of a knock sensor and its calibration strategy helps to insure that the timing will be optimized despite variations in fuel octane, changes in ambient temperature and humidity, formation of combustion chamber deposits and compression changes caused by high mileage engine wear. In late model Ford engines, the knock sensor is allowed a range of influence, both above and below the corrected base timing value. A typical number for this range is plus or minus 6 degrees for a total range of 12 degrees. The base timing table is calibrated using 87-octane fuel. When the engine begins running above idle, the ignition timing is initialized at a number equal to the current 87-octane base table value plus any spark adders from associated scalars or tables (positive or negative). An example of a spark adder would be a table of values that adds spark at different speed/load cells while the EGR is active. Other adjustments to spark timing are available in the calibration for corrections based on intake air temperature, coolant temperature, barometric pressure, etc. As in the case of the IAT sensor on late model engines, these tables or adders may be 'zeroed out' and not used, at the discretion of the calibrator. (Note: Spark tables are defined in terms of RPM and 'load'. Although load is a composite number based on several parameters, it can be thought of as proportional to throttle opening for purposes of this discussion.) If knock is detected while running above idle at the corrected base value, the timing jumps back immediately by a calibratable amount, typically -3 degrees. If knock continues to be present at this new advance value, the timing will jump back 3 more degrees in the negative direction. The total negative deviation from the "correct" laboratory value is usually limited to 6 degrees. If, on the other hand, the engine at its current base spark value shows no knock, the timing is steadily advanced at a calibratable rate (typically 1 degree/second) until knock is detected. Then the immediate 3-degree jumpback occurs as many times as necessary to eliminate the knock, again limited to -6 degrees from base. The ignition advance remains in this continuous tug-o'-war between this slow 1 degree advancing and immediate 3 degree jumpback. The goal is to provide an engine free of audible knock while maintaining the highest possible spark advance to provide maximized power and fuel economy. Use of a fuel with octane higher than 87 can provide a small but noticeable increase in power and fuel mileage. There are certain RPM vs. load points in the table where the full 12 degrees of ignition adjustment by the knock sensor strategy is not available. At high load and/or high RPMs, gasoline engines typically have maximum spark advance values that are detonation-limited requiring that they run a base value that is below optimum. In these table cells, there is an advantage to allowing the spark to advance when possible. At lower RPM-load points, the base value provides the optimum spark advance and any additional advance would reduce power rather than add it. Therefore, there is a clipping table which overrides the other calculations to define the maximum spark advance allowable at any given RPM vs. load point. So, at lower RPMs and engine loads, the range of influence for the knock sensor may be limited by the clip to as few as 6 degrees, all negative. Side note: The above strategy applies to conditions above idle. When the engine is idling and there is normally no possibility of spark knock, the ignition timing goes into a different mode that does not involve the knock sensor. At idle, the timing advance is used to help control the idle speed. The Idle Air Controller (IAC) provides the slow, coarse adjustment and the ignition timing is the fine adjuster, reacting quickly to correct small RPM errors from the desired idle speed..."
Source: by rwenzing
 

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My 86 BKO has a "knock sensor" on the drivers side of the lower intake manifold towards the back maybe just below the FPR area.......in 08 when I had swapped in a new 302/5.0 EFI long block I inadvertantly over tightened the "pipe threaded" temp guage sending unit and cracked the manifold badly though I found a local JY 92 pickup 5.0 manifold I had to have a hole drilled for the knock sensor.....a $125.00 mistake....:rofl:......PITA

You wonder why companies stop manufacturing important emissions componenets where you're required to smog.....it makes no sense.......?


Good Luck ~ :thumbup
 

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The later models had the knock sensor threaded into the block in the back topside behind the intake on the passengers side. But its the same thing really. I snagged up the last one I could find off of rock auto. By current EEC V does not use one and that one is still in the box, so I may end up letting someone who needs one use it. Some of the 80s model cars used the same knock sensor, and those are still available. Whenever you cannot find a part for a bronco, look for the same part for an F-150, then a van and then a 5.0 car. Chances are someone makes it for something and it will work.
 

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i guess i stand corrected. never saw anything bout it in auto parts store and didnt see it on my 88 5.0. thats too much readding for me tho
yo,
:haha

I have a solution... don't read it, unless someday you have KS problem.
 

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You wonder why companies stop manufacturing important emissions components where you're required to smog.....it makes no sense.......?
yo Brother!
Yep, it a recurring and disturbing issue!
Same prob getting new 4WABS modules or pumps, etc.
 

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Discussion Starter #10
Thanks for the replys. This is for a new 5.0L I'm building for a 1990 F150. The current engine doesn't have one. I bought the truck for next-to-nothing because it had no power. Somewhere along the line someone swapped in a late 70's model 302. The didn't accomodate the KS. I'm pretty well versed in how the sensors work, etc. I just was hoping someone knew how the computer reacted when the knock sensor is missing. I can unplug it on my current 86 with seemingly no problems, but if it is going to be an issue down the road, I'm trying to decide if I should go ahead and convert over the MAF with the mustang ecm. However, I'd rather just find a knock sensor if I could.

I agree with the comments, why manufactures would quite building these, I don't know. There's only millions of these on the road. Thanks again and I welcome some more comments if someone knows how the computer is programmed to act with the sensor missing.
 

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yo,
If KS is removed, the EEC response will be to to change timing; da EEC will retard timing if no knock sensor signal is detected.
if the knock sensor fails, instead of constant knocking, the engine will perform poorly because timing will be retarded all the time.

problems include a lack of power and some hesitation
 

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Discussion Starter #12
yo,
If KS is removed, the EEC response will be to to change timing; da EEC will retard timing if no knock sensor signal is detected.
if the knock sensor fails, instead of constant knocking, the engine will perform poorly because timing will be retarded all the time.

problems include a lack of power and some hesitation
Do you know if once it retards the timing, can I advance the distributor and be back in a good spot, or will it adjust even further, undoing what I just did? Thanks for the help!
 

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yo,
The issue will be under load; so adv a bit as my pal, Sixlitre did;
Tune-Up Info (scroll through pages to view more tips, especially on Page 5); "...Yes, stock timing is 10 degrees, I find optimum timing to be almost exactly 13.5 but you can play around until you notice ping and then back off 2 degrees if you want to, and/or tune by vacuum if you care to. Cheapest Autolites money can buy, nuthin' platinum, nuthin' fancy, just set out to .055 gap..."; miesk5 Note, Vac Cannister info is for vacuum advance distributors
Source: by Sixlitre (Malcolm H, Eddie Bauer) at http://www.fullsizebronco.com/forum/showthread.php?t=63592&highlight=Sixlitre+tuneup&page=3
 

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Discussion Starter #14
yo,
The issue will be under load; so adv a bit as my pal, Sixlitre did;
Tune-Up Info (scroll through pages to view more tips, especially on Page 5); "...Yes, stock timing is 10 degrees, I find optimum timing to be almost exactly 13.5 but you can play around until you notice ping and then back off 2 degrees if you want to, and/or tune by vacuum if you care to. Cheapest Autolites money can buy, nuthin' platinum, nuthin' fancy, just set out to .055 gap..."; miesk5 Note, Vac Cannister info is for vacuum advance distributors
Source: by Sixlitre (Malcolm H, Eddie Bauer) at http://www.fullsizebronco.com/forum/showthread.php?t=63592&highlight=Sixlitre+tuneup&page=3
So if I'm following you right, the computer shouldn't adjust timing anymore once it has adjusted for missing KS? If that is the case, I'm good to go after resetting the timing.

You rock. Thanks.:rockon
 

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You guys may be lifesaver.
Can any of you tell me how to test the sensor itself?

I am getting the code for failure to detect knock on the KOER test and am experiencing hesitation and loss of power under load.

1986 bronco 302ci.

Thanks for your help.
 

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If your Knock Sensor or associated wiring is bad you should get a KOER Code 25 (Knock not sensed during dynamic response test). Likewise, the 3-digit code is 225.

Testing would involve simulating operating conditions by connecting a timing light, starting the engine and tapping the manifold next to the Knock Sensor with a hammer. You should observe the timing retard momentarily. If there is no response, turn the engine off with key on and check the harness connector for 5.0v reference voltage. Check for a wiring short if required.

If you need to replace the Knock Sensor, I believe that OEM is color coded to ensure the correct frequency.
 

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Thanks guys, I should have checked back sooner. I tracked it down via tomco then found it for $37 shipped from rock auto.
I haven't done the tests you mention yet, I saw them elsewhere, but was hoping I could test the thing out of the truck with my meter. I hope I find the ref voltage, cuz I will feel pretty dumb it its just wiring:banghead. I would have a hard time trusting the hammer test.

I am getting the symptoms of a bad one, and the code but no pinging ever. It just stumbles and sputters on heavy throttle or load.

I was so pleased with saving $40+, I hope I haven't jumped the gun.
 

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I should have done the reference voltage test also. I am only showing 2.5+ volts at the KS harness with the key on. Won't start when disconnected either.

Any ideas?
 

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If the engine never knocks, that's probably why the EEC doesn't detect it. A new knock sensor won't make the engine knock.

Did you test fuel pressure, manifold vacuum, compression, timing, plug wire routing, or anything else? Put ALL your truck's details in a signature:

 

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So is it most likely that I have a bad connection on the blk and wht that is the signal return from a variety of sensors? Many of which don't seem to work on my bronco? :barf

Should I test for resistance between the EECV and one of the sensors?

I am kind of lost in the woods here. I have looked at the wiring diagram above and it would seem that my problem should be somewhere between the Blk/ wht signal return wire and or between the knock sensor and eecv.

Thanks to any and all for input.
 
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