OK...so here's one that has me scratching my head....now remember the, engine isn't original to the truck.

So as I was pulling out the engine earlier this week, I noticed a red wire that was obviously spliced into the wiring harness and not original to the truck. It went to a engine coolant temp low on the block driver's side. Didn't think much of it but thought it was strange. Tonight I'm pulling parts off the old engine and I pulled the ECT sensor on the drivers side head. Once again didn't think much about it, but wondered why there were two. I look in the TSM, and it doesn't show a ECT in the block (unless I missed something).

Wait it gets better...I had noticed when I did my clutch last month that there was a sensor on the back of the block with nothing plugged into it. Engine ran great so realizing it was not the original motor, once again didn't think much of it. Tonight I notice it is the "Knock Sensor". I look on the new engine, and sure enough there is an empty hole where I need to put the knock sensor. I looked very carefully at the engine harness and there is no plug, no wire, or anything left over that isn't already accounted for.

Let me put one more piece into this. The PCM has a sticker on it that lists a re-flash date last year.

Here are my questions.

1. Anyone have any idea why someone would put a second ECT in the block? There is no after market gauges in the truck.

2. Is it possible that for whatever reason the PO took the wire that was designed for the knock sensor, changed it to be the second ECT plug and they flashed the PCM to change the sensor wire purpose? I don't have any idea what I'm talking about when it comes to the PCM. I don't know what can, or can't be done.

3. Since I got this truck for cheap off a lot...does anyone have the location of the PO of my Blazer so I can poke him in the eye?

HELP!

 

1: no idea, usually the blazer has 2 temp sensors, one on the head on drivers side(for the temp gauge), and one near the thermostat (for pcm)

2: not sure if it's possible, but maybe the one by the thermostat was faulty and they didn't bother to replace it... or the year of engine had a different location for it... the knock sensor has a completely different plug... the engine might have been a different year and the knock sensor may have been in the side of the block instead of the back... pictures are worth a thousand words.

3: hire a PI.

 

I used a gear puller on mine it came off easily.Usualy the older 4.3`s has the knock sensor on the side of the block.I beleived they changed that from 96 on up to where it was inside the timing chain cover.Some have a cap that plugs it off which is probaly to compensate for the engines that have it on the block but use the newer style timing chain cover.
Also your 98 shouldnt be any different than my 96 they should be a direct swap.Im thinkingthat the right hand side exaust manifold is from a different year engine.

 

1. Well it looks like what I thought was a second ECT sensor is actually the knock sensor. When I removed it, coolant came out so I assumed it was an ECT.

2. I found on the thermostat housing where a second ECT would go. But there is no sensor. Just a plug (meaning a regular "plug the hole plug". However, the service manual does list a sensor there but then in parenthesis states "If equipped". Apparently, and please correct me if I am wrong, the gauge and the pcm must share the ECT sensor located on the driver's side head.

3. All that being said, what is the sensor noted in the picture? I have nothing unaccounted for from the wiring harness. The strange thing is, the TSM detailed engine blow show that same exact location and shows a plug (plug the hole) labeled as a "Oil Gallery Plug". But inside the hole is just drilled and threaded. There is no oil galleries coming into it or little holes or anything. It's a nice shiny dry hole. That's along with a picture I misread in the manual is what made me think it was knock sensor. Any idea what it is?

 

that's a knock senso for an 03+ blazer... if you want to go to stock you will need to drill and tap that hole for the larger knock sensor.

 

Drat...no wonder the engine ran so nicely...it's not near as old as the truck...if it wasn't for the thrust bearing I wouldn't even be replacing it.

I guess I'll just keep the knock sensor where they had it on the side of the block (see pic)...that's okay....yes? New engine has a 3-year warranty so I can't do any drilling.

Stay with me Cool & Jimmy (and anyone else that is very welcome to weigh in). I can't tell you how helpful this forum is. Even if it is being just a second set of eyes to double check my work. I am sure I will have more questions coming. Anything that doesn't look right to me

 

Well good news for me Cool...the block has the correct sized hole and thread for the stock knock-sensor of my vehicle.

New question: While the engine and the battery is out, I have a badly rusted section just forward of the passenger side rear wheel well. I already found the formed piece at LMC Truck I can weld in. My concern is the PCM. Though I will put the grounding clamp within about 12" of the new panel to be welded in, do I need to be concerned that I could harm the PCM (or any sensors, etc)? The current would not even be heading that direction, and will be very low amperage. Like I have stated before, I am computer stupid when it comes to vehicle computers. Anyone?

 

if you're that concerned you could always just remove the pcm while you're using the welder.. but just disconnecting the battery should be ok... which part is bad? the actual well where it meets the cab or just the metal wheel well insert that the pcm/coolant bottle is attached to?

you're lucky about the knock sensor, I had to drill and tap mine to fit the old knock sensor (03 motor in 00 truck)

 

It's the body in the rocker area just in front of the REAR wheel well.

 

ah.. missed that part