ECT Reads –degrees when starting then never gets over 100 If I disconnect ECT engine runs better, If ECT is connected EGR fails to work (Have a scanner and have monitored under load) also will cause LT fuel to not work, Misfires, and extremely Rich, IF ECT is disconnected everything works and engine runs good no codes being shown (except w/ECT disconnected) I have Ohmed the connections, tried 3 different ECT sensors, 2 EGRs, Harness to ECT bypassed I have tried every Ohm along the 808 black. Every thing from the ECT to the Harness has been replaced, yet still a short persist, one time while jiggling wires to the EGR the Temp on scanner registered properly, I have been unable to reproduce (believe me I tried) When connecting the 808 black in the harness I get ohm readings across 2 of the EGR connecters Pink 1539 & Blk 808 Tried to follow 808 and see the ECT & EGR join at S122 Sec 20, do not know where that is) Any clues, solutions, HELP! Would be great.

Does the temp reading change at all from a cold start?

I'm kinda lost, but EGR operation is disabled until engine temp comes up. Thus inop if temp reading is corrupt low...

Another observation that might lead you somewhere....it should run RICH as hell with corrupt low ECT reading....not lean...

Seems there is more to this than meets the eye....,makes me wonder about the ECM maybe?

Another observation that might lead you somewhere....it should run RICH as hell with corrupt low ECT reading....not lean...

My Bad rich it is!!

Seems there is more to this than meets the eye....,makes me wonder about the ECM maybe?

I poked around on a few mainly on 56 I know very little about voltage ohms etc about 1 step above stupid... but I have a voltage meter so I poke around,

Man I wonder about everything, More updates, Using another ECT just pluged in to harness(not manifold) I unpluged EVERYsensor (TP MAP EGR Coil pack O2 etc) still reads -5 plugged on the scanner, used another harness to the connectors still reads -5. Something that gives me a clue when Ohming off of the Black 808 gnd, and I ohm the pink Ign from the EGR connector wire I get a connection, also using Blk off of the Map I get readings to the pink EGR, Should that be happening?

I'm kinda lost, but EGR operation is disabled until engine temp comes up. Thus inop if temp reading is corrupt low...


Man your lost, I'm stumped :runaround: EGR works fine IF ECT is disconnected and sometimes EGR works with ECT Connected, at Freeway speed all EGR readings work fine (Position, voltage, etc) with ECT connected readings go dead. so all I know is there is a direct correlation between the ECT & the EGR,Yet if I disconnect the EGR it does not make the ECT function properly,
My only clue is the the blk 808 from the ECT,MAP, & EGR will get ohm readings from the pink 1539 Ign on the EGR and MAF connectors, would seem that this should not be, just do not have enough knowledge to figure this out.

Does the temp reading change at all from a cold start?

Yes, will start in the minus (below zero) reading and work its way up to high 90s, will go closed loop at 72 degrees and the ambient Temp is currently in the 70's

Are you reading in celius? Why is it below 0 when started?

Are you certain something is not ungrounded, and the two circuits are interfering trying to steal a ground off one another or something?

I wish I could be more specific, but it sounds like a vaguely familiar scenario

And is there anything else done recently, that would seem totally unrelated?

I once broke a thermostat bolt on a 5.0 Chevy motor with TBI. Buggered it up so bad trying to get the broken bolt out, I had to pull the manifold and have the hole punched and coiled.

Along the line the CTS got cracked, and I replaced it. Then when I put the intake back on, and the distributor in, I liked to never got the damn thing started. Turned out they gave me the wrong sensor, and it was telling the ECM to go full rich, and spraying fuel from the injectors like showerheads...

there's two temp sensors...no chance you're using the wrong one in the wrong position or something? I never noticed if they look the same or anything...never had both out at the same time...

Are you certain something is not ungrounded, and the two circuits are interfering trying to steal a ground off one another or something?

I wish I could be more specific, but it sounds like a vaguely familiar scenario

Thanks At this point I am not sure of anything, but will also try anything, any suggestions?

And is there anything else done recently, that would seem totally unrelated?

I once broke a thermostat bolt on a 5.0 Chevy motor with TBI. Buggered it up so bad trying to get the broken bolt out, I had to pull the manifold and have the hole punched and coiled.

Along the line the CTS got cracked, and I replaced it. Then when I put the intake back on, and the distributor in, I liked to never got the damn thing started. Turned out they gave me the wrong sensor, and it was telling the ECM to go full rich, and spraying fuel from the injectors like showerheads...

there's two temp sensors...no chance you're using the wrong one in the wrong position or something? I never noticed if they look the same or anything...never had both out at the same time...

Well it just up and started after I replaced a rocker, since that time I have removed the heads and installed new gaskets, and replaced the Intake Manifold (stripped a bolt) so same problem with 2 different intakes, I have 2 ECT sensors I have used one at air temp and one plugged into the Intake, same problem with both, plug either one in and get a -5 degree reading give or take a couple of degrees, temp on the scanner will rise with engine but still only half or less of what it should be, its creating a whole bunch of bug a boos, so anything else you can think of, please feel free to let me know (anybody else have an idea?)

Are you reading in celius? Why is it below 0 when started?

Nope all is in F not Celsius, using a EZ6000 scanner, uses American measurements.

Try using a set of jumper cables to supply alternate ground paths and see what happens...chassis to battery, engine to battery, etc. Any ganged grounds that bolted to that intake? (I can't remember)

Most cars will have 3-4 that ground to the upper engine, most times they will use the thermostat bolts but not on ours that I remember, so there must be some elsewhere.

When you see readings that are reacting to changing conditions but out of scale I always suspect weak grounds first. You'd be surprised how many times I provided an alternate ground path and the problem suddenly vanished...and then you find a broken or corroded ground wire, broken strap, etc.

I once read an article in a tech mag that estimated up to 90% of really hard to find electrical faults will ultimately trace back to improper grounds...and stressed the importance of verifying all system grounding before chasing the problem...good advice, saved me a lotta hassle and diagnostic time...

On the real old ones occasionally they be running terrible but when you hooked up a scanner to the diagnostic interface it would suddenly start running fine and show no faults...the problem was a weak ground, and it was drawing just enough ground path through the scanner to make it go away...remove the scanner, and it would go to hell again...

Can you watch the reading at one while you disconnect the other, see if it spikes or drops out?

Would point to a common ground fault involving both...

Try using a set of jumper cables to supply alternate ground paths and see what happens...chassis to battery, engine to battery, etc. Any ganged grounds that bolted to that intake? (I can't remember)

Never thought of that trick, will give it a shot,

Most cars will have 3-4 that ground to the upper engine, most times they will use the thermostat bolts but not on ours that I remember, so there must be some elsewhere.

I have a diagram of the ground points, I have broken/checked one point (G117) early one in my adventure. will try more

When you see readings that are reacting to changing conditions but out of scale I always suspect weak grounds first. You'd be surprised how many times I provided an alternate ground path and the problem suddenly vanished...and then you find a broken or corroded ground wire, broken strap, etc.

I was just probing with a Ohm meter last night, and I was having the pink (839) making conection with blk 808, also with chasis ground, as I was holding one probe to the thermostat housing and then the other probe to pink, on the firewall side of the harness connection, to the MAF & EGR & EVAP these all have the pink (839) running to them. and I figured the Pink is shorting to ground somewhere,

I once read an article in a tech mag that estimated up to 90% of really hard to find electrical faults will ultimately trace back to improper grounds...and stressed the importance of verifying all system grounding before chasing the problem...good advice, saved me a lotta hassle and diagnostic time...

Well I started down that road a few weeks ago, then started chasing my tail for awhile, now I am conviniced that it is a short, just a mater of finding it.

On the real old ones occasionally they be running terrible but when you hooked up a scanner to the diagnostic interface it would suddenly start running fine and show no faults...the problem was a weak ground, and it was drawing just enough ground path through the scanner to make it go away...remove the scanner, and it would go to hell again...

Can you watch the reading at one while you disconnect the other, see if it spikes or drops out?

I have disconnected every sensor, and with the key on, scanner pluged in, not found any change in the faulty ECT readings,

Would point to a common ground fault involving both...

Well I am st the point where I pretty much know what is not causing the problem, just a mater of finding out what it is, You gave me some good pointers, and helped me think, of a different angle of attack, Now if I could just understand these diagrams :smile: If you think of anything else... Thanks

Try using a set of jumper cables to supply alternate ground paths and see what happens...chassis to battery, engine to battery, etc. Any ganged grounds that bolted to that intake? (I can't remember)

Most cars will have 3-4 that ground to the upper engine, most times they will use the thermostat bolts but not on ours that I remember, so there must be some elsewhere.

When you see readings that are reacting to changing conditions but out of scale I always suspect weak grounds first. You'd be surprised how many times I provided an alternate ground path and the problem suddenly vanished...and then you find a broken or corroded ground wire, broken strap, etc.

I once read an article in a tech mag that estimated up to 90% of really hard to find electrical faults will ultimately trace back to improper grounds...and stressed the importance of verifying all system grounding before chasing the problem...good advice, saved me a lotta hassle and diagnostic time...

On the real old ones occasionally they be running terrible but when you hooked up a scanner to the diagnostic interface it would suddenly start running fine and show no faults...the problem was a weak ground, and it was drawing just enough ground path through the scanner to make it go away...remove the scanner, and it would go to hell again...

Can you watch the reading at one while you disconnect the other, see if it spikes or drops out?

Would point to a common ground fault involving both...
Well the latest chapter is that I still have the ECT trouble, but while testing I found that on some hot leads (Pink & White) the car is grounding out when I Ohm a pink or white lead to ground there is a connection, I found that if I disconnect the Ground behind the Starter that breaks the connection, other than that, I Do not know where the short is, I untaped all the wires from the sensor (EGR TP Etc) to the ECM looking for breaks, I pulled both connectors to the ECM and while Disconnected from the ECM Still had the short on Pink & White. Any other suggestions? Also the Ground behind the starter had 2 connections a thick one which I assume is the cable from the battery and a smaller one going into a sheaf, it is this smaller one that breaks the connection.

Update, Still have the grounding issue with the ECT reading at the wrong temp (read pervious posts) but one trick I found is if I short the gnd blk wire (808) to the yellow wire (using a jumper wire) the scanner shows 284 then when unshorting the ECT reads current operating temp, this works until restarting the car.

A side problem is while idling will get misfires and trigger a Misfire on cyl 4, once car is under load purrs like a kitten, I have tried grounding to chasis, but this did not change anything. Still looking for sugestions, ideas, etc

have to ask this... what is an ECT and is it on a 93 3.4L lumina?