Vannin' Home Forums Chevy Troubleshooting UPDATE - SOLVED: O2 Sensor Issue With Headers On A 91 5.0

Well the van project is coming along but have run into an issue with the idling on my 91 (5.0 Automatic). Installed a set of hooker headers (trying to get as much horse power as I can out of the 305 (5.0) V8. Now the original location of the O2 sensor was on the stock driver’s side exhaust manifold (pretty close to the blocks exhaust ports). With the header (which is a “shorty” header) the location of the fitting for the O2 sensor is on the reducer bolted onto the end of the header so it is further away from the engine block. Now before I installed the headers the two times I drove the van the check engine would come on and tests showed the O2 sensor was “dead” (when removed it looked like the original one)…anyway installed the headers and a new O2 sensor along with a set of Dynomax Ultraflow mufflers installed pretty close to the header reducers with no tailpipes at this point). First time out the check engine light came back on ……test proved the new O2 sensor was testing “dead” again so installed a another new one and now no check engine light comes on anymore and a check of trouble codes shows none……now to my idling problem.
The idle seems a bit low and goes up and down when idling in park and has stalled a couple times when at a stop light (with the engine being hot)…with TBI system there is no way to “adjust” the idle….the engine computer does it all…..thoughts are that the exhaust is hot enough at the location of the O2 sensor for it not to activate another trouble code but not hot enough to operate the idle correctly due to free flowing mufflers. Am hoping at this point that once the tailpipes are installed (won’t be until after the van comes back from the body & paint shop at the end of next month) the addition of the two tailpipes will hopefully help the O2 sensor to work correctly with more back pressure and hopefully hotter exhaust gasses at the sensor location. Anyone have any thoughts on this?

Thanks

UPDATE: Well did some checking around and read some posts that classic car, truck and hot rod owners when adding headers install heated 02 sensors.
Did some searching and bought one from Michigan Motor Sports…..easy install; had the correct Weather Jack connector on it plus a ground wire and a hot wire for a connection to a “switched” 12 volt power source. Ran the ground wire to the frame and the “hot” red wire to a switched 12 volt source at the fuse panel. When all connected started up the van let it idle for about 20 minutes to get up to operating tempature, put it in gear and seems to idle correctly now….no surging up and down so guess I have to say the problem is solved.
Don’t you just love it when things go together as planned…LOL

IAC valve?

What Lionhead said.
Also if it's not a "heated" O2 sensor you may need to run a power wire and swap to a heated sensor. You're further from the heat source. Also a heated sensor will give you a more reliable signal. I believe there's some videos about doing this on line or on the squarebody forums.

A heated sensor? Well I searched around for one….They seem to have a different connectors on them….again my stock type is a single wire sensor. Using a heated sensor does make a lot of sense….So how would I go about installing one? Assume the biggest issue would be the connection point. Does anyone make one that maybe has a connector that connects to the stock single wire connector to the computer but has a some sort of adapter on it to connect a power wire?

https://marine-performance-parts.com/gm-tbi-tuning-tips-htm.aspx

Good article on state of tune, fuel pressure and O2 sensor....

Well found a wired adapter to connect a 3 wire O2 sensor to a single wire system. Michigan Motor Sports has one SKU 22300 (18 bucks). Uses a AFS74 type connector. Also found a A/C Delco AfS74 O2 sensor so going to order both and see how to plays out…….comin’ together……