Calling TBI guru's (sbc)

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Dec 13, 2007
68 FJ40, new Summit 350, 92 Suburban 2500 TBI, otherwise all new components, Failed Smog (idle CO @ 5.9% instead of 4.0%).

I was having issues with my Autometer speedo when I smogged, the vss signal pin in the molex connector had pushed out severing contact. Vss goes through speedo and then computer, so no Vss while I smogged.

Hopefully that was the contributing factor, but want to rule anything else out before gambling another $25 on the test.

Another possibility is that I only have 1 CO2 sensor on 1 bank of the dual exhaust. I plan on cutting another one in for the other side but have to replace the pipe first and I'm out of time. Even then, the computer only has the 1 input but at least I could switch them.

Anybody have any other ideas on remedies for my malodies?
I wouldn't bother with an O2 sensor on the other side. Your setup is more common than not for TBI. Have you checked to see if it's in closed loop at idle? The non-heated O2 needs to be close to the manifolds, or change to a 3-wire heated O2 if you haven't already.
My 92 K1500 I use to have ... had 5.7 tbi, one O2 sensor. Do you have a catalytic converter installed on teh exhaust system? Some of the TBI engines had smog pumps (air pumps).
OK, sorry for the lag as I was all oiled up from the rebuild and banned from computer use until after a shower.

I am going to hook up CEL today and the ALDL ckt. See if that gives me any more info. I do not know if I'm running Open or Closed loop yet. So that is a good starting point to figure out.

No catalytic converter requirement in NV for 1968 as they used Leaded gas originally. No smog pump either, just alt/PS w/ electric fan.

Thanks for your replies:)
Agree with the others, the original O2 location for the '92 should have been a single on the drivers side. Not sure which vss you are using (pulse type). Assuming it is correct. Consider by-passing speedo direct to computer. Easy fix for you though - move to California and you wouldn't be smogging a '68, even if it had a blown big block.

Several problems, but I'll cut to the chase.

O2 sensor needs its own reference ground and it's a brown wire located right next to the purple O2.

Winaldl wouldn't work unless I specified ECM 1216488 instead of 7747 which was also a time consuming hiccup. I had to figure that out after making cable.

Whence aldl started working I could not get the O2 sensor to move. I dbl checked all connections and even used a blowtorch on the head and got nothing! I thought for sure my ECM was shot since it came from a junkyard and I never heard it run.

Had it smogged (due today by 5pm) withing an hour of getting the O2 sensor working.


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