I have a 1992 rs 305 tbi all oem with 145,000 miles, the car runs great, doesn't miss at all, but i failed emissions twice b/c it appears that the car is running rich. The engine is always in closed loop for emissions testing, & i keep failing hc, co & nox horribly. Winaldl also shows that the car is running rich, but the car doesn't smoke at all & doesn't burn any oil, & the cooling system is functioning as well. Timing is set @ 0 degrees, i also tried advancing & retarding but same rich issue.

All new spark plugs, wires, 02 sensor, catalytic converter & all other sensors have been replaced (even though they all tested good), the air pump & egr, are functioning as well, the oil was changed & there are no exhaust leaks. I also cleaned out any carbon with the seafoam treatment.

I even replaced the ecm with a salvage one & the car still ran great, but still failed the emissions test.

Both of the injectors spray a fine cone type mists with no drips. The fuel pressure has always been steady @ 12psi, yet the exhaust has always smelled horrible for years. I never thought it was a problem b/c i lived in a county that didn't require emissions testing, but now it has to be tested for emissions.

The only other thing that i can think of is that maybe the injectors are staying open too long & not pulsing off & on as they should be, thus spraying too much fuel all the time. I would also think if this was the case then the engine would flood, but as i stated earlier the car runs as if it were new, if not for this running rich issue.

Is there a way to tell if the injectors are pulsing off & on as they should?

Any ideas?

 

Make sure you have a good 195* stat in it.
Check the timing advance, it should go off the scale when you rev it.
Make sure the vacuum hose to the map sensor is good, hook up a vacuum gauge to that hose (tee into it), vacuum should be 17.5" to 21", steady needle.
Check the ecm grounds, usually at the back of the heads & t-stat area.
Test the coolant temp sensor at hot temp. You can use an ohm meter or scan it.
It might be possiable that someone swapped 350 injectors into it, you can try to lower the fuel pressure all the way to 9 psi, maybe someone made the regulator adjustable.

 

another thing to try that is easy and free. it sounds dumb but give it a try. my car never ran hot either.

remove the radiator cap when the car is cool. unplug the coolant temp sensor on the intake. begin loosening the temp sensor until you can turn it by hand. keep loosening it slowly untill coolant start to come out from around it.

when i had a problem with my car running very rich i was replacing the coolant sensor. upon loosening it(radiator cap still on) i was able to get it all the way out with no coolant coming out. i put the new one in real quick and screwed it down hand tight. removed the radiator cap until coolant leaked around the base for about 3 seconds and then tightened down. my richness went away. the car never ran hot but had an air pocket where the coolant sensor went into the intake. solved my problem.

also check the gasket under the tbi. put a new one on.

 

There are no codes stored by the ecm, but the ecm will flash correctly if i disconnect a sensor, i forgot to mention that i have a new distributor & ignition module, i've also drained & refilled the coolant system recently & purged all of the air from the system at that time. The map sensor vacuum seems good without any leaks, the tbi is all stock & the fpr is internal & has not been made adjustable. The tbi gaskets have all been replaced, & the intake manifold has no leaks at all.

I disconnected the cts & started the car, it ran but the cel lit up & the car shook violently. Reconnected the cts, cleared the code & the car again runs like new. I did the same thing by disconnecting the map sensor & the engine didn't run well, but ran great after i reconnected it.

14 years ago the car had 88,000 miles on it when i bought it, & today it has 145,000 miles & the exhaust fumes today smells the same as it did 14 years ago, which is really bad, yet the car runs great.

Using the service manual for reference, i did check the signals of each wire at both of the connectors at the ecm itself, & all of the grounds at the ecm connector showed to be good, & all of the other ecm signals were good except the o2 signal was always in the upper range of 750-850 mv, although it occassionally dropped to 325-450 mv.

I'll have to buy a vacuum gage to check the engine vacuum, i also thought about the ecm grounds that are on the back of the heads (but i can't reach those nor see those from up above, but i can feel the connected braided strap from the head to the firewall).

Although i can't see nor reach the back of the head to check the ecm grounds, if the grounds all show good at the ecm itself, wouldn't that prove that the ecm grounds at the back of the head are connected & intact?

 

my car to ran the same as you explained. bad with it disconnected and good with it connected. everything seemed great on the sensors. at least try what i explained. my car ran perfect but got really bad gas mileage.

 

hook a wideband up an see how rich it's really running

 

Has anyone ever had to replace the ecm grounds at the back of the heads with the heads still in place?

 

A defective coolant temp sensor will make it run very rich. May be it is tellling the ECYU it is very cold on coolant temp when it is not. I would test that for sure.

 

If it was closed loop the O2 reading should swing back and forth. Staying at .750-.850 mv is rich. Test that again and tap ECM and see if it starts swinging! Also if it has been running rich a long time the O2 sensor will be sooted and need cleaned or replaced to work correctly.

Any exhaust leak before O2 sensor will cause engine to run rich.

Back to CTS, they usually just go bad but occasionally are intermittent. Cheap to replace if it's bad or corroded. If it's reading cold well then the ECM is adding choke, causing rich! Here's a chart to help read CTS sensor.
http://www.gearhead-efi.com/Fuel-Inj...erature+Sensor