hesitates on accel cold please help

[crazykev4x4]

i have a 88K5 350 TBI. I just installed a 98 vortec engine with headers and dal exhaust.i installed a heated o2 and it kind of bogs or heasitates on accel cold u have to baby it or feaTHER THE ACCELerator when cold once its warm it runs good . It did it all the time before i installed the heated o2 but now just when the engine is cold . please help i need this baby runnin good .

Kevin

 

[rjfguitar]

Whats a heated o2 senser?

 

[Confedneck]

heated o2 sensor might not be compatible with the computer, is it the right o2 sensor for the 98?

 

[the professor]

If you wired the HEGO right (Heated O2 sensor), it should start to work almost immediately...
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Also GM, I think, was still using Zirconium Oxide (ithinkispspeltthatrite) O2 sensors, so it should be compatable as far as reading is concerned
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What you did not say is if you kept your stock computer...
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THat is important... The late model computer is designed to run with a HEGO, so it will not go into full "closed-loop", bring the idle down and lean the mixture UNTIL the temp comes up

THe earlier computer, MAY read the O2 sensor and think that the engine is warm enought to go into "closed-loop", causing a problem...

The earlier ECU runs "upstream" A.I.R (air pump) when the enine is cold.. this is added to the exhaust ports, like in earlier no-computer motors, for the sole purpose of heating the O2 sensor, and the Cat... As soon as the ECU sees the O2 sensor "changing" and the temp is past a given setting, the system goes from "open-loop" cold engine to "closed-loop" warm engine, immediately the AIR is directed "downstream" to either the air cleaner or the cat...

If the ECU is getting a "variable" reading off the O2 sensor, it MIGHT read that as a warm engine and lean the mixture etc..

You also may have a problem with the TEMP sensor... make sure you use the one for the ECU, it might have a different calibration...

Hope this helps a little /forums/images/graemlins/thumb.gif /forums/images/graemlins/truck.gif

 

[the professor]

I thought about this some more and re-read your post.. It DID do it befor the engine change...
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I think the problem might possibly be in the "diverter valve"...

As I stated before, Computer Command Control, or CCC or C3 computer systems, on the later systems..both carb and TBI use the A.I.R ( Air Injection Reaction) or AIR pump ONLY when cold in the "up-stream" into the manifold selection, after warm-up, in "closed-loop" they either switch to a dump into the air cleaner or "down-stream" to the Cat... depending on year and clibration...
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IF you are NOT getting "up-stream AIR", as the computer is calibrated to expect with a cold engine, your O2 system will read the exhaust a "rich" and lean it out..causing stumble

. Reason, the "up-stream AIR", mixes with the unburned rich mixture coming out of a cold engine, keeps it burning, lowers Cold emissions and heats the O2 and Cats.. (before computers, this did this all the time..) then, by the time the mixture hits the O2 sensor, is is MUCH leaner that without the AIR.. the ECU expects this, and corrects accordingly...richening the mixture

And, like I say, if no AIR, the computer will read excess rich, lean it..stumbles and stalls..

So anyway, when the engine is cold, the ECU directs the "diverter valve" to direct AIR to the exhaust manifolds (only one on some vans..)

Another very common failure of the diverter valve, is staying in the "up-stream" when warm... this gives a realy lean reading to the O2 sensor, the computer trys to richen up the mixture and the vehicle runs poorly and flunks smog...

Shis is one possiblility.. /forums/images/graemlins/cool.gif /forums/images/graemlins/thumb.gif /forums/images/graemlins/truck.gif

 

[crazykev4x4]

the ecm is stock and it didnt do this before the engine change . i took the air off a long time before i did the engine swap i took the pump off . anyways it only does this cold it did it all the time before i installed the heated o2 sensor but no when its warm it runs good

Kevin