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Knock Sensor Relocation


headpeace
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I relo'd mine to the back of the driver's side head when I had my intake off for something else. There was a hole back there with the right threads, the harness reached, I figured it would make it easier to get to if it had issues down the road.

 

The service manual suggests the 34 code means the circuit is open or shorted (abnormally high or low voltage). EF&EC-99 of the '95 manual has a test procedure that has you check the circuit. Looks like the wiring for it goes through one of the plugs on the passenger's side head, so you don't necessarily have to remove the intake to test the sensor, which is nice.

 

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Yeh I'm thinking I'm getting that code because of the way it is running instead of the knock sensor being the cause of it running so poorly. I've changed the distributor cap and rotor, the coil, the plugs and wires, the air filter, and the fuel filter; cleaned the MAF, cleaned the throttle body, checked the intake boot for cracks/leaks, and ran it with the O2 sensor unplugged and it hasnt remedied the problem. It seems as though it has been a progressive problem instead of an acute problem. It started with me noticing that it was idling a little rough and has progressively gotten worse over the course of a couple of months. I'm not sure what step to take next.

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  • 1 month later...

Okay, when it is cold it runs like dogshiite, very little power. Once it warms up it seems to run fine and idle almost fine. In neutral it idles great, in drive it idles rougher than it did before this problem originated. Anyone know how to unplug the coolant temp sensor? I looked at it but couldn't figure out how to get it unplugged without tearing it up.

Edited by headpeace
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Given what you've done already, I'm not sure what would make sense to do next--though I'd still be suspicious of the temp sensor. When it's running like crap, can you tell it it's running rich? Lean? Misfiring? The plugs might give you an idea of what you're up against and whether it's the whole engine running weird or just one hole. I'm guessing it's got no codes at this point, just to be like that.

 

I'd also check the EGR valve on the off chance it's jammed itself open, or the EGRC solenoid's given up.

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Hmm. Yeah, seems like it would run like ass all the time, though maybe it would be more obvious when cold. You can pull the vac line off the valve and see if the engine runs any different (the valve should close if it's being held open by vacuum), then either apply vacuum with a pump or reach underneath and push the diaphragm (probably best to do that with the engine cold) and see if the engine stumbles when the valve opens, or if it doesn't change from the stumbling it's doing already. The EGR control solenoid was jammed wide open on my dad's '87 F150 and it ran like crap until I tracked it down. On that one I unbolted the valve and put it back with a piece of cardboard in between it and the manifold, sealing off the hole, and when it ran better like that I knew the EGR was at least part of the problem. IIRC it ran a little better when warm, but it never really ran right.

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Any posts that show how to delete the EGR?  I dont have smog so I can just delete it if I knew how. Not real familiar with the EGR.

Edited by headpeace
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Sounds like a sensor issue. The idle air control valve went on mine and it did the same. When you pressed on the throttle it would bog down and come back up but went away as the engine warmed. In the summer if you put the AC on it wouldn’t do it at all. Something with the mixture. 

 

I wouldn't remove the EGR. It helps keep temps down.

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The computer doesn't really need an idle sensor--it's watching engine speed anyway. There is a pressure switch on the power steering and some kind of tie-in from the aircon that tell the computer to raise the idle when those systems are under load, which might explain why Adam's aircon masked his idle issue.

Idle control is done by two valves. The Auxiliary Air Control valve (which the computer controls) is located under the back of the upper intake manifold. The Idle Air Control Valve, which lets air bypass the AAC for a higher idle when the engine is cold, sticks up behind the EGR and works kind of like an electric choke (moves a valve as it heats up, only instead of opening a choke, it closes an air passage). EF&EC-14 of the '95 manual has a picture and description of each. (It also shows the AAC and idle adjustment screw together and calls the pair something else, just to be confusing.)

The IACV is only open when cold, which is when your truck runs its worst, right? The idle control components do one thing, and that's feed air into the manifold, bypassing the throttle body. That air is supposed to come from the intake tube between the MAF and the throttle body, meaning it's gone through the MAF already, so the computer knows it's there (and knows to add fuel accordingly). If the idle control valves are drawing air that hasn't gone through the MAF--air getting into that feed pipe through a crack or a hole where a mouse chewed on it, maybe--the computer isn't seeing that air, and doesn't know to add fuel, so the engine will run lean. It would run leanest when the IACV is open (when it's cold). Once the IACV closes, the engine would idle better, but still a little lean from the lower volume of air going through the AAC valve (low idle). When your foot's on the gas, the AAC should be closed, and the engine should run closer to normal (though perhaps not perfect given that the leak that was supplying unmetered air to the idle controls might also send some the other way to the throttle body). So, yeah, I'd have a look at that air supply pipe.

As for the EGR, I haven't heard of any real benefit to deleting it unless the valve is buggered. Mine works, so I leave it alone, though I did scrape some carbon buildup out of it when I had the intake apart and test it just to see if it was working right.

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Exactly. Mine would have a lean miss when it was cold. Couldn't narrow it down to a cylinder. Checked all vac lines and replace them. I even tore the thing down and did the intake gaskets thinking that was it. I was pretty pissed off when I found the cause! The one you can see by the EGR isn't available after market and I had to find a used one.

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If you end up having to replace the knock sensor. You do not have to pull the intake manifold. You can splice into the wiring harness and remount it on the top of the engine towards the firewall with a longer 10 mm bolt. Or you can remove the transmission support bracket and let the transmission and bellhousing hang down and reach up behind the intake manifold into the valley between the Pistons and pull the knock sensor loose and replace it and remount it on the top of the engine towards the firewall. I watch this procedure done on YouTube.

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