Joboo, you nailed it. After unplugging the computer I checked the ECT plug with a test light hooked to positive and it did not light. However, I then checked it with a voltmeter the same way and it DID show a ground. I started tracing the wire under the plenum, around the rear of the engine, up around the coil, and over to the computer without finding anything obvious. BUT, then I checked it again and no ground found. So by moving the harness around I "fixed" the problem. Still don't know why. I plugged in the computer and the ECT plug and started the engine. No engine light, now the engine has a high idle again while cold, and the code reader gives a #11, no problems found. It still runs sluggish and just failed our emission test with a super high hydrocarbon of 1439 out of allowable 220 on the high (2500rpm) idle. CO passed with ease as did the low idle HC with 27 of allowable 220. How could the idle HC be so low and the 2500rpm test be so far out of range?

 

Gov, sounds like that short to ground must be somewhere internal in the harness. Its good you used a meter to check it being sometimes the grounding problem can have enough high resistance to verify via meter but not be able to light a test light bulb. It would still have just enough resistance to pull the voltage down in the circuit and make the pcm think its grounded. Just one of those things where the test light opperates on a much higher amperage than the ect signal circuit to the pcm.

I would guess that somewhere in that harness you may have a single burnt wire that has melted the insulation on a few wires that are close to each other and they are intermittantly shorting together. Either that or some of the insulation has deteriorated away and cracked and wires are touching. Im guessing this being you noted no obvious damage. Moving the harness might have been just enough to get rid of the ground contact.

About your hc count. First, i really think you should fix that ground problem. Even if it entails cutting open that harness to find the failure. If you want to take the easy route, you could allways cut that circuit out and run a redundant wire from the pcm to the ect sensor but i hate going that route being the original problem may be effecting other wiring. The reason i bring this up is, even though the problem seems fixed and a dtc is not setting, there may still be a small high resistance to ground. It would make the pcm think the engine is much colder than it actually is and command a higher pulse width hence more fuel, more hc's. If you happen to have a scanner you would be able to observe the engine temp read by the pcm and see if this is the case or not. I would suggest either using a scanner or volt meeter on that circuit and start bending that harness from the ect to the pcm while watching the voltage. Hopefully you will see a notable fluctuation when you near the effected spot and wont have to cut open the entire harness.

Back to the high hc's issue. I am unsure how this testing is performed in your neck of the woods. It is totally disscontinued down here for all vehicles. Back in the day, at least here in fl, the high speed test under load was only performed if a vehicle failed the idle test. Now your test, the high speed, was this done on a dyno and under load? If so, any missfire that is present could cause this problem. Also a failing fuel pressure regulator that would fail high pressure could cause this. Also, a converter that is clogged or just functioning poorly would cause this problem but i would seriously rule out the original failure of the ect circuit ground before you even start digging further. One last note, regardless if there is a failure or not, prior to taking the vehicle to be inspected, make sure it is extremlyl hot. As hot as you can get it, the hotter the converter is the better it will burn hc's.

Hope that helps. Good luck.

 

I'm running it real hard before I go for the test as I always do with all of my vehicles so it's as hot as it needs to be. Our test is a tailpipe test under No load at all. Just an idle test and then high, approx 2500 rpm no load high idle. I just can't quite comprehend how it could pass the low idle at 27 HC out a possible 220 and then fail miserably at 1439 HC at 2500 rpm. It just doesn't seem possible to be that high at 2500 if it's only 27 at an idle. Our motor vehicle lane just had a "problem" a couple of months ago where they notified hundreds of owners that their vehicles didn't really fail emissions after all due to faulty machines at the motor vehicle inspection lanes so I can't help but wonder if it's them and not me. However, if you have ever dealt with the state on an issue like this their attitude is "we are right and you are wrong" type of attitude. I'm sure it's the original "Y" pipe with the two original converters so they could be bad. However, it passed emissions the last two times with the same two converters and without all of the the other new parts that have been installed.

 

I know when my ECT sensor went bad on my 92 Ford F-150 302EFI 4x4 truck the truck would start flawlessly in the morning when I would start it up the first time of the day, but when I would make stops to the bank or anywhere else the truck would just crank, crank, and crank. I could get the truck to start when I put the gas pedal all the way down to the floor and I guess on fuel injection vehicles this shuts off the fuel injectors so they don't spray fuel into the heads, but it was the only way I could get my truck to start too, but the culprit was a bad engine coolant temperature sensor...