I have searched and read endlessly but still am unsure where to start. I have a 91 RS with a 305-5 spd. Mods from the previous owner include headers, performer intake, open element air cleaner and a Hypertech chip. I installed a new distributor and set the timing at "0". The car runs rich---not to where it hinders performance but so rich that it fumes you out. It's my wife's car and she complains that it gets inside the car when she is in traffic---and she is correct.

Plugs look good---although they are NGK's, injector's have a nice cone to them---the idle will occasionally bounce up 100-200 RPM at times. What are the items I should be looking at? I am rather stumped and I have searched for hours on this board---any help would be appreciated.

 

The best thing to do would be hook up a scanner. If this starts to occur ofter warmup I would suspect you are not going into closed loop due to either a bad o2 sensor or your o2 is not getting to 500/600f to become active and you need to install a heated o2. A bad coolant temperature sensor or sensor reading to the ecm would cause the excessive rich condition or a bad map sensor. You can check for cl operation in field service mode if you don't have a way to connect to the ecm. With the open element air filter did the po install the air temperature sensor ?

 

Not sure but isn't the timing supposed to be at 6 BTDC according to the GM manual?

 

The fsm usually states Set timing according to instructions on Vehicle
Emission Control Information label.

Lb9 and l98 are 6dbtc and the L03 is tdc all with the est disconected.

 

I do not see this sensor installed but I do have a connector/sensor laying on top of the intake manifold which you may have just identified Sorry for my ignorance---I also have a 77 Z-28 and this TBI troubleshooting is all new to me!

These are some excellent suggestions to start with!

 

It called for zero and I set it with the EST wire disconnected.
Thanks

 

does the check engine light work? is the egr valve still good? performer intake with a tbi adaptor? are the gaskets leaking any?

 

As the previous owner of the subject vehicle, I'll shed a little light

1) Gary, FYI the plugs in it are AC Rapid Fires...unless when my uncle's shop changed the plugs, they stole the Rapid Fires I gave them and put NGKs in it! If those plugs really are NGKs, lemme know...I will have a bone to pick with my uncle

2) The sensor near the top of the intake is the IAT. It was close enough to the base of the air cleaner that I did not feel like drilling through the air cleaner base to throw it in there. I had seen enough people on here do it that way, that I figured it was ok. Maybe I am full of it???

3) I wanna say the check engine light comes on when you cycle the key on...never had a check engine issue myself in 6 years of ownership. One advantage of TBI ownership versus TPI! Every TPI car I've owned has given me CEL issues...this car never did.

4) EGR Valve was replaced probably 10k miles ago with a new AC Delco. Car was failing emissions due to the original not working.

5) Performer TBI intake was installed by a local GM shop with whatever came in the box. No spacer or anything was added.

Hope this helps. I told the OP I think the issue could be old injectors potentially dumping too much fuel. About the only parts I didn't touch on this car are the injectors...

 

Thanks Jason---I'm going to do a little more this weekend with all of these suggestions. I probably will download the software and hook up the laptop to see what the ECM is doing---no check engine light right now....just a very rich mixture.
Thanks for the suggestions----you are a great person to buy a car from

 

Make sure the engine is getting up to operating temp, 190-200*
Make sure the ign. timing advances when you rev, if it doesn't, the engine won't be making enough vacuum for the map sensor. The balancer could have slipped on the hub, so timing could be way off.
Check the ecm grounds, most like on the back of the pass. side head, some have them at the t stat bolt.
Do a resistence check on the coolant temp sensor from cold to hot, google for the chart.
Make sure the map sensor is hooked to the proper port, tbi units are know to get clogged w/ carbon, remove tbi & clean ports & replace base gasket.

 

Noxious, eye-watering fumes?

The typical cause is that the engine is too LEAN. Lean misfire throws excess hydrocarbon out the exhaust every time that cylinder doesn't fire. Of course, misfire for any reason does the same thing. Some time on an automotive oscilloscope and an exhaust gas analyzer would do wonders.

If the engine is running rich, the exhaust has excess carbon monoxide, which is colorless and odorless--you won't notice it, and it doesn't make your eyes water.

You'd better find out if the catalytic converter is poisoned.

 

Finally got my diagnostic cable and hooked up a laptop using WinALDL. Under "Flag Data" I have "Closed Loop Flag", "Rich Flag", and "BLM Enable Flag" that pop up intermittently while idling. There are NO error cdes, BLM is 128, INT-132 and O2-.747.

Any ideas what should be jumping out at me? Car is running extremely rich and idles poorly right now.

Thanks

 

What elevation do you live at and what is your map kpa and cts, tps showing at idle. The int is real rich for sure.

 

I am in Florida and only 36 ft above sealevel. At idle--MAP=58-60, KPA=32-36, CTS=108. The TPS shows 1.7 on the "dash" display and 31 on the raw data page.

Thanks for your help!

 

The map Kpa looks good , The cts reading looks good at 226f. The tps if that is a voltage reading it is way to high. IIrc the early tbi tps were adjustable and later years were non adjustable. I can't recall the tps feedback reading for tbi but it should be less than 1v for sure. Back probe with a safety pin the cavity in the connecter on the tps were the blue wire is. With the key on You should be seeing between .55v - .75 I believe not 1.7v

 

Finally got time to get this car back together so I thought I would give an update to close this thread. I ordered a gasket kit and pulled the TBI apart on the bench. I sent the injectors to Southbay (excellent vendor), I cleaned every port and orifice on the TBI. I replaced the TPS and the Idle Air control Sensor---both inexpensive parts. I reinstalled the TBI and it was like brand new....nice cold idle, very little exhaust fumes and ran smooth as can be through the gears.

I think Tuned Performance was correct with the TPS voltage too high but I thought I would take the time to eliminate any other issues with the TBI.

Now on to the next issue....a small voltage drain and time to convert the AC to R134......

Thanks to everyone for the help and suggestions.