Ok, thanks for clarification. Would the coolant temp sensor cause it backfire like that? It didn't do it tonight when I drove to work, didn't let the truck warm up on purpose but it is slightly warmer than it has been lately, but I am still slightly confused, the only thing I did was change the rear ABS sensor because it was bad and nothing else so far. Will have time this weekend to really get in deep and do some diagnostics on it. And yes your right at WOT it is open loop...

Further back story now. Plugged the OBD ii in again today after driving it with no issues from cold start and the p0305 code no longer shows up only the p0455. which may help narrow it down to the plugs or O2 sensor according to the OBD ii diagnostics guide. Any further thoughts?

 

A bad coolant temp sensor will wreak havoc on fuel trims, so yes, it's possible.

To temporarily alleviate the problem, you can turn the key full on but not turn the engine over for about 2 minutes. This will start the heater on the o2 sensor and help get you to closed loop faster.

 

If the PCM doesn't see crank or cam signal, won't it trip the ASD relay though? (and aren't the heaters powered thru that circuit as well?)

 

Ok, so I need to check the coolant temp sensor, IAT sensor, intake gasket, I guess the gas cap and a multitude of other things. THe truck is pushing 200k and I am sure most of this stuff has never been checked/changed (it was inherited when I got married). Going to dig in deep this weekend when I have some extra time and see what I can come up with. I will report back with what I find, any other input is still welcome, and thanks so far.

 

If your scanner will show you data.... check the various sensors before you start the truck, and see if any of them are lying....

 

Yep, you're confused -- and I say that respectfully, please know that. Because the oxygen sensors are heated the PCM will switch into closed loop mode within minutes of start-up except in bitter cold temperatures. From that point forward you're in closed loop unless/until you go WOT (which is an open loop mode). The various modes are discussed in the factory service manual which is available on this site in the 2nd Gen FAQ section. Note that where it says something about normal operating temperature it doesn't mean 195 degrees or even 180, but essentially "somewhere above stone cold".

My own truck switches to closed loop long before the temperature gauge in the dash moves off of the lower pin.

I could be mistaken but IIRC the PCM will shut down the oxygen sensor heaters if it doesn't see crank pulses within something like 20 seconds from key on. OTOH that might just be hearsay that I haven't researched away.

Anyway:

Since the truck was inherited, I'd ask someone who knows if the oxygen sensors have been replaced in the last 80,000 miles or so and change them out if they haven't been. The darn things can be failing long before setting DTC's and set DTC's for months before clearing the CEL threshold. A scan tool will tell whether or not DTC's are being set -- it'd take a DSO and knowledge of oxygen sensor waveforms to go any deeper into proving them good or bad. It's dirt simple once you (have the equipment and) know what to look for, but most folks don't and don't really need to. Just keep in mind that if it starts running crappy right after switching into closed loop and the oxygen sensors have >80k miles, swap 'em out. They're a 100k mile periodic replacement part anyway so you're not really out much if you change them a tad early and it solves nothing.

 

ive seen coolant sensors read -40 with the engine fully warmed up started out reading typical like 50deg and as it warmed to about 100 it started goin backwards .

 

Ok, well I have had the truck since about 130k and from the looks of the sensors if they were ever changed it has been quite some time, I will just go ahead and change them while I am getting in deep on the truck this weekend. Like you said, it can't hurt to change them.

The truck spent its first 7 years in CA, but we moved to upstate NY for about 4 years and the salt and junk really did a number on the truck, so its time to replace as much as I can on the thing and hope it will give me another 200k. It really has been a great truck. In 13 years the only somewhat major issues have been a bad AC compressor and a starter.

 

That sounds like a reasonable plan to me. If you weren't planning it already, dive into the factory service manual and hit all of the 96,000 mile preventive maintenance, especially the automatic transmission fluid/filter/band adjustment. Also seriously consider replacing the timing chain/gears when the weather warms up. Those things ought to go a long way toward getting you the next 200,000 miles on the road.

The automatic transmission is another story... but if you can get 200k miles further for the price of a transmission (and routine maintenance of course) you're in good shape anyway.

Let us know how it works out for you!

 

Ugh, a Cali truck?

Those have 4 O2 sensors and 3 are upstream. You should probably replace all three upstream sensors.