As you know by now from my previous i now have my 96 lt1 on the streets , car runs strong and fairly smooth but a few problems persist, this is a little long winded but i want to make sure i explain clearly,,,

1. problem after running a scan both with the key on and engine not running, is a hard start after it is warmed up, i get a dtc code of po118 which is the engine tempeture control sensor on the bottom of the water pump..it also has a fast idle around 850 900 rpm, now i have done quite a bit of trouble shooting and this code describes my conditions perfectly,idle is off ,,have to push throttle all the way to the floor for it to start, Oh when its cold it start right up just like it should, it also shows a -46 degrees on the sensor which would indicate ,sensor bad, open in wire to ecm, or no grd on black wire, or a bad sensor, i removed the plug from the etc sensor measured black to ground , test good,,,,, key on measured yellow to to voltage , 5 volts so i know the ecm is supplying 5 vlts to the sensor,, removed the sensor did a resistance reading across sensor contacts 2.0 ohms cold and decressed to0.04 when hot ,so i know that is working..i also jumpeerd the sensor plug and that seem to eliminate the hard start. Im know expert but it looks like all the testing i have done show normal, so hope some one can shed the light to this problem,,

2. now this may be directly tied to the above. the cooling fans turn on as soon as the engine starts and stay on...thanks ahead of time for any input,,, Bob

 

I had a weak coil that would start hard when hot. might be a bad connection on the digital temp sensor.

 

My 93 FSM has a procedure to see if the coolant sensor is bad, or a short. It's easy. You will need a real time scanner. Do you have one?

 

my mechanic has one.

 

Black wire should not be grounded. It is sensor low that is supplied by the ECM. When I did my 383 build I removed a lot of things and decided to clean up the wiring. I tied all the grounds and sensor lows to ground. Engine would not idle. Worked for months trying everything. Finally measured sensor ground on the ECM and found that it is NOT GROUND.

 

thank you ed for the reply,,im not sure what the difference between sensor low and grd is, but i do not have a problem with my idle now it is with the "when hot hard start" and "fans running all the time" and service engine soon light. I have jumpered the etc plug and am going to start and warm up the engine this morning and see if this helps in any way to tell me in which direction i should be going, by the way it will shoot out some black smoke on start up when warm which tells me it is to rich. i know the answer is out there.

 

My Car is a 1992 and I know that the ECM is different. I do not have a 96 Manual. On the 92 if the sensor low is tied to ground it causes the sensor voltage which is referenced to ground to be incorrect. It caused a lot more problems other than idle. My engine ran very rich. So rich that the oil was changed three times before I resolved the problem. If you disconnect the connectors from the ECM, you can measure between the ground pin and the sensor low pin on the ECM to see if they are connected. If they are connected (zero resistance) then it would be ok if sensor low is grounded. If they are not connected then sensor low should not be grounded. Hope this helps. I spent a lot of hours chasing a problem that I created.
Ed

 

smell the vacumme line off your fpr and do a leak down pressure test on your fuel to rule out leaky injectors or fpr.might have more that one problem.

 

thanks antfarmer and ed, i have checked my fuel pressure and is normal around 38 to 40 lbs pressure and it does hold, also fpr is dry....If i look at the diagram it shows a direct line of the yellow wire coming from the ect sensor plug to the ecm if i take the ecm connector off and measure the resistance between the ect connector and the open connector on the yellow wire it shows no continuity but if i plug it in and with key on and measure 5v at the etc connector, im confused.

 

Substitute a know good coolant temp sensor and test. I bet that's the problem.

 

i actually took the newly replace heat sensor out and measured it cold as i mentioned b4, it read 2 ohm cold and put it in hot water and watched it go down .04 ohms and let it cool and it went back to 2 ohms so i know that is a working sensor. i also measured it against the old one that i broke the plug off of when i installed the engine and it also was the same.

 

Go to www.alldata and get a 1 year subscription for your car Its $25 and allows you to print pages from it.It is an online copy of the gm service manual.That will give you wiring diagrams so you know what the circuit is doing.Measure you ect sensor from the harness plug for the ecm and see if its the same as the sensor-then you will be checking the ect-connector+ wiring to the ect.I had a 2002 Blazer in my shop last week doing the same thing-the connector at the sensor had streched female pins in it.I checked a gm ect today in my shop and it checked 15kohm cold.

 

That sounds more like it.

2.0 Ohms sounds shorted to me.

 

Thanks for the alldata site , i am now a member ,, great info,,, also as far as the resistance, my bad it was more like 20 ohms at the sensor lead.....NOW.......where are my keys i have some driving to do.

 

Bob-please keep us posted on your results

 

thanks odxr,, so far i have a trouble shooting sheet from alldata, but have not got around to working on the engine,,, i have changed the oil and will put 5 to 6 hundred miles on that then will be going with mobile synthetic 5 30,, car runs strong , i can imagine what it would be like with headers and different heads but for now this will be just fine, after 1k miles i will get a dyno tune..