Need Help With Engine Temp

[RonD]

At idle and at Wide Open Throttle(WOT) the computer ignores O2 sensors, while this is not technically Open Loop, it is similar in that the computer uses long term fuel trim(LTFT) data and the factory tables to set air/fuel mix, regardless of O2 readings, just like when engine is cold.

Idle requires a slightly rich mix
WOT, well computer figures MPG is not your main concern at that moment, lol.

 

[Rearanger]

Idle requires a slightly rich mix

I'm just getting into fuel trims and at basic learning level, but then why are my LTFTs showing in negative territory at idle - shorter injector open times to reduce fuel and lean out the mixture?

 

[JP02XLT]

While Ron is correct in his info, the truck will stay in closed loop even at idle when at normal operating temperature.

If your driving and approach a stop sign once you release the throttle and start to coast towards stopping, it will go into open loop around 25-30 mph with a closed throttle, for a second or so, they do this to keep it from going too lean from shutting the throttle and to give the Idle Air control time to react as well, once all that happens it goes back into closed loop at idle if everything is as it should be with no codes present. Codes present is another situation.

WOT is as he states, an open loop situation with input readings from the MAF & timing to ensure the correct fuel is demanded & delivered from tables in the ECU software according to these inputs. But as soon as your not at 100% throttle its back to closed loop reading off the O2's into the mix as well. One exception is a maxed out or damaged MAF signal, that will jack with what the ECU delivers and why many GM products use a MAP & MAF setup to recognize a low vacuum signal to verify your into the throttle, but this has it's problems as well.

As far as your LTFT's they are a product of the STFT, as the STFT get further out of norm they drag the LTFT's with them accordingly and adjusted injector pulses via corresponding fuel tables in the software.

Have you disconnected the battery and reset the ECU since the new O2's? Might be worth the effort to clear the ram in the ECU. Disconnect battery and pull the headlight switch on and leave it for 10 minutes or so. This should start the ECU into a re-learning procedure for operating fuel tables, and begin the table adjustments based on the new O2 sensor inputs.

JP02XLT

 

[Rearanger]

There was never a problem with the original O2 but it was a lame attempt to up my gradually falling mpg - not the mileage drop I have just experienced in the last 3 months. I didn't have a scanning gauge then so couldn't check any fuel trim data.

Computer should have learned new inputs by now and LTFT should have adjusted STFT to keep it to almost zero balance for proper O2 switching.

The short time idle (closed throttle) fuel trims are in play would not affect my mpg.

 

[JP02XLT]

One other thought, Have you checked to see if a brake may be dragging, ran into that on mine, I had a parking brake cable that was binding just a bit and applying the rear brakes just a bit, only way I found it was I tried to push the truck to re-position it in the garage, it would move forward, but with a little resistance, when I tried to push it backwards it stuck like glue, had to start it and let the truck do the work. Pulled the drums to find a parking cable binding & Rusted and not returning all the way.


JP02XLT

 

[Rearanger]

For sure no brake dragging, I test it from time to time on slow coast to test roll resistance. I use my emerg brake so much that no chance of rust.

Put scanner on O2 sensors and did see how system goes into open loop (O2s turned off at zero) when coasting in gear down hill, no open loop on idle though.

Hope to get oil analysis today, that should tell me a lot.

 

[JP02XLT]

That open loop on idle is a "if" conditions exist & its only for a couple seconds max,

Let me know when you get your oil analysis.

JP02XLT

 

[Rearanger]

Well just got the oil analysis back (wear numbers are fantastic).

No significant amount of fuel detected, but there's only 900 miles on this oil change. Value came back as <.5%, what it's been on all previous analysis reports, except 05 where it was .8% with 9k miles on oil.

There has been a development though. I added a bottle of Lucas fuel treatment to see if it would help clean suspect injectors, no real reason for Lucas, except I can get my money back. Normally don't add anything as there's no way to tell if it works. Have gone through about 1/2 tank with the Lucas and LTFT numbers are better. The idle negatives now show in the -4 to -5 area whereas before they were in the -7 to -8 range. So far no other explanation.

I'll keep posting here on what the numbers are after a full tank and maybe another tank with Lucas. Will also continue to track mpg.

 

[Rearanger]

First tank on Lucas improved mpg but second tank on Lucas went back to 18mpg, so no magic fix with Lucas.

I'm into sending the injectors out for analysis and cleaning.

 

[alwaysFlOoReD]

I'm glad your'e keeping us updated.

 

[stmitch]

I'm into sending the injectors out for analysis and cleaning.

What does something like this cost?

 

[Rearanger]

What does something like this cost?

WitchHunter does it for $22 per injector with parts and before & after report. Cheaper than rebuilt from RockAuto and certainly than new but you need to be without the vehicle for about 12 days as his lead time is now 9 days.

I also get to know if there is a flow problem in the injector(s).

I have also installed a digital temp gauge to replace the temp sender. Both the ECT and temp gauge confirm stat is opening too soon. The stat is an O'Reilly's premium and the last was a Stant SuperStat.

I am going to replace stat with another SuperStat.

I also test drove my graphing software. Much easier to see fuel trim and O2 sensor operation. O2s operating properly.

 

[stmitch]

Thanks for the info. I appreciate your analytical approach to the whole situation.

 

[Rearanger]

Installed new Stant "SuperStat" yesterday.

Test drive shows higher temps than old "SuperStat". I'm now getting from 188.6 to 190.4F (depending on RPM) on ECT. Before I barely got 180F. At about 2k RPM the ECT stays very close to the 188.6, maybe down to 186.8 as stat opens. As well, the digital gauge I replaced the factory sender with is staying from 3 to 5 degrees lower within ECT temp, whereas with old SuperStat it would get up 10 degrees lower difference.

I'm calling this FIXED. Temp readings vary with RPMs and on idle I get the 190.4F with the digital gauge at 189F. These temps are within FSM specs.

The factory temp sender is located on the (I think) heater hose outlet pipe while the ECT is on top of the thermostat casting. More flow appears to go through the heater hose outlet (and maybe heat dissipation) to cause lower digital gauge temp.

There is also the gauge/sender accuracy factor as I am not using calibrated lab sensors. I'm guessing that the coolant is at different temps in different engine locations.

I'm ready to move on to sending the injectors out for test and cleaning to see if my gas mileage (and slightly rough idle) will improve.

In the meantime I have also filled the tank at a different gas station to see if different gas formulation is the problem.

 

[01b3000ds]

Ok, so you've corrected the data path and brought system back to apparent spec, but you've changed one of the "constants". You'll never know if it was sensor data input or fuel formulation messing with your mileage...I guess if it improves it doesn't matter. But what if it doesn't?