Truck running update

[chev4life]

Hey all, the truck is finally running good (when warm). Turned out to be valves cause Im an idiot and didnt get them right. Well...she is great when warm and stumbles like hell when cold. Takes about 5 min or a few miles to get it running right and after that it seems pretty good...except for me putting a little too much diff fluid in the rear and having come out the vent
So anyway...what could be the cause of the cold running? Like I said in previous posts...almost all is new..coil, rotor, plugs, wires, ignition module, heads, intake manifold.
Thanks again for all the help.

 

[slyguy_22]

Well i have an 89 tbi that i just finished putting head gaskets on. (just have to set the timing quick tonight after work before i leave for the mountains).
Anyhow. those tbi are so damn picky. did you replace the TPS sensor? MAP sensor? the sensor in the intake for the coolent? Think i would start there.
I hate my tbi when it acts up but love in when it runs great.

 

[slyguy_22]

oh did you replace the ignition control module on the dist.?

 

[chev4life]

Yeah, the ignition module on the dist is replaced and the pickup coil ws replaced about 6 weeks or so ago.
The sensors are pretty old, but they worked before I did the heads...could just of went bad though. Hmm...the coolant sensor is the one next to the coolant elbow right? Not sure if I know where the map sensor is and I will check out the TPS.

 

[dyeager535]

Get a scanner. Or borrow one from autozone.

Sounds like the coolant sensor is having issues, although vacuum leak is a possibility. Not likely as that would probably be noticeable hot as well. Wouldn't replace anything without testing. Somewhere, there is a GM service manual page which gives the reistance values for various temps.

 

[chev4life]

I will have to run out to autozone and try to rent/borrow one. So the scanner just plugs in via the OBD port under the dash and spits out voltages, etc...for the sensors? Does it have them listed by type? What exactly should I be looking for?...also...what deems one of these sensors bad?

 

[dyeager535]

In your case, you'll really want to see what happens when it "switches" from running good to running poorly, if possible. (since you will assumedly have to drive the vehicle there)

It should list the sensor being read, and provide the sensor output in a format you will understand. Coolant temp is easy, it should read close to what the thermostat is rated for with the vehicle warmed up.

Should see the O2 sensor voltage bouncing around a bunch, and may or may not switch from open to closed loop while idling.

If O2 sits in one spot, the sensor is dead, or O2 wiring issues, or fueling is wrong for another reason. (bad map, etc)

MAP voltage for certain vacuum readings is also given somewhere, can't recall where I've seen that, probably over on thirdgen.org

 

[Bent77]

Also do yourself a quick over and make sure the engine is grounded both by the battery cable and an alternate ground.

 

[chev4life]

Ok...I think I know what I am suppost to look for. I just drove home from work and its at least consistantly crap when cold. I will get a scanner from autozone tomorrow and check things out. I have a funny feeling its the O2 sensor though.
Funny thing is I have already redone the grounding about a year ago...redid the chassy ground from the engine and the battery ground also.
OH...is there a voltage/ohm that these sensors should be at when good?