knock sensor
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Joined: Mar 2001
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knock sensor
:-X12 I am trying in vane to get my 88 F/I 351W in an F250 to run.I have rebuilt just about everything but made a mistake taking the air/emission components out.I went and asked the wrong people what I could and couldn't live without.I ended up taking my map,egr and o2 sensor off.It refuses to run with any kind of performance.I have those sensors back in place and was wondering about the knock sensor I don't believe I even had in the first place.Looking though the mighty Chiltons I find that some engines have knock sensors and some don't!What gives?Can I live w/o it.Thanks, Ron
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Joined: Jul 2004
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From: Culpeper, VA
I know the 351W doesn't have a knock sensor because I just swapped my 302 out for a 351. (the 302 had it and the 351 doesn't, so i'm just gonna plug it in and tie it up out of the way to prevent error codes)
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Joined: Jan 2004
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From: Belgrade
knock sensor
I rebuilt my 1989 302 over christmas and I had a hell of a time finding the right knock sensor for it. It was located on the back of the block towards the bell housing, on the left hand corner of the engine as you look at it from the front of the truck. It wasn't in the book that I was using to rebuild the motor, so it was a confusing process...but eventually I got er' done! Hope you get it fixed man.
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Just on the topic of knock sensors...
I have an 87' f150, (302) but the engine is out of a 70's mustang (big plug heads and all) so I wouldn't have a spot for a knock sensor would I? (I bought the truck this way so I'm going through it all) I found it today, just kinda hanging around... what should I do with it to prevent error codes? I'm thinking that it might just be some of my computer issues...
I have an 87' f150, (302) but the engine is out of a 70's mustang (big plug heads and all) so I wouldn't have a spot for a knock sensor would I? (I bought the truck this way so I'm going through it all) I found it today, just kinda hanging around... what should I do with it to prevent error codes? I'm thinking that it might just be some of my computer issues...
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Joined: Nov 2002
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From: Concord, NC
It has a knock sensor on the stock 302, yes (probably from 85 on the truck EFI 302's). It shouldn't cause any problems if it is still plugged in electrically but tied securely away from the engine block. What kind of computer problems are you having?
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Fine when its cold but as soon as at gets a little warm... BAM... Surging idle... stalling... poor power... too much fuel seems to be an issue... poor fuel economy(12 MPG at best)
Also I'm getting an error code for all my sensors.
( I checked the ones I could find/test... HEGO - Good, TPS - Good, EGR - Good, MAP - Good, Knock - Just kinda hanging out, ACT - Doesn't appear exist... gotta find one i guess, ECT - seems to be there)
also... my gauges all went screwy as well... first the fuel and oil pressure... then the temp and voltage just a few days ago... ideas? lol the truck's a great truck and i love it but... its got some electrical and computer quirks id really like to fix.
Any ideas?
Also I'm getting an error code for all my sensors.
( I checked the ones I could find/test... HEGO - Good, TPS - Good, EGR - Good, MAP - Good, Knock - Just kinda hanging out, ACT - Doesn't appear exist... gotta find one i guess, ECT - seems to be there)
also... my gauges all went screwy as well... first the fuel and oil pressure... then the temp and voltage just a few days ago... ideas? lol the truck's a great truck and i love it but... its got some electrical and computer quirks id really like to fix.
Any ideas?
Last edited by Flatlanded87; Sep 19, 2006 at 06:11 PM.
Lead Driver
Joined: Nov 2002
Posts: 9,556
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From: Concord, NC
Sounds like a couple of grounding problems. All the sensors you listed use a dedicated computer ground called signal return that goes straight to the computer and is separate from the rest of the vehicle grounds to isolate the sensor signals from noise. The computer grounds through the drivers side fender -- there should be three wires, two with insulation, one just a bare wire all crimped to one ring terminal bolted towards the cab near the hinge mount. Measure the resistance between that point and the negative battery post. Also measure between the engine block and the negative battery post just to make sure there is a good connection there. Also, in diagnosing the sensor problems, test for continuity between the black wire at each sensor plug and also pin 46 on the computer connector (see fordfuelinjection.com for pin location details). I'm thinking that it would be between the sensors and the computer since there is a problem with all the sensors.
I would check the voltage at the battery with the engine running as well to see if anything is unusual with that.
I would check the voltage at the battery with the engine running as well to see if anything is unusual with that.
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I have two wires... the bare one and the covered one thats crimped on the same ring. Checked the resitance between the ground and the battery... its very low... checked continuity for my TPS and my EGR while I had a chance and they both checked out, ill do the others when I have more time.
What is the third wire used for? Could that be my problem?
What is the third wire used for? Could that be my problem?
Lead Driver
Joined: Nov 2002
Posts: 9,556
Likes: 43
From: Concord, NC
You may have all of them there, I couldn't remember for sure. Those wires go to the computer pins 20, 40, and 60 and serve as computer ground. Check continuity between pin 46 and the signal return wire on all the sensors to try to track down a broken wire between the computer and the sensors. If that checks out, test resistance, then test for continuity between the signal return wire and the 5V reference wire and any other power wires that go to injectors, idle speed control, coil, etc. to make sure the ground isn't shorting to power.
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1987 - 1996 F150 & Larger F-Series Trucks
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Mar 22, 2011 08:46 AM