TBI Smell

[Kmart2352]

My 87 has a 350 TBI in it and it seems to be running to rich. When I get onto the highway and i get on the throttle some smoke comes out of my exhausts and it when i am at a stop light or just idling it has a smell of to much fuel or something. It gets about 8 miles a gallon when i am staying off the throttle and about 6 when i am on it all the time. I did a full tune up on it last year and this year I installed a throttle body spacer. The truck runs great but it has been smoking and getting that MPG's for a couple of years.

[rfmaster]

Check your coolant temperature sensor CTS - located by thermostat housing. A bad ground lead (black wire) will also casue CTS to report very low temperature back to ECM which will command very rich fuel mixture.

Couple of basics checks you can do without resorting to major expense of replacing CTS. This requires measuring CTS resistance with a DVM at 20C (73F) CTS should read about 3500 to 3600 Ohms. At 80C (~185F) coolant temperature CTS should be around 340 Ohms.
An open ground lead will also result in SES light blinking, but a bad ground (high resistance ) will cause in a sensor reading high resistance (which is equivalent to low temperature). Disconnect CTS connector and measure resistance between black wire terminal and electrical ground - it should be near 0 Ohms.

Additionally, the actual sensor voltage drop can be measured once engine has been fully warmed and idling by measuring voltage, by back probing yellow wire on the CTS connector with respect to ground. With coolant around 80C you should see around 1.25 to 1.5 Vdc.

//RF

[Kmart2352]

Thanks i will check that when i get a chance. Is there anything else that it would be?

[rfmaster]

Well, there are few other things that may cause rich mixture condition:

1)Weak regulator spring in TB fuel pressure regulator. On few occasions I have seen broken springs all together. This will play havoc with fuel pressure and may result in increased fuel being dumped into intake.

2) Poisoned O2 sensor - ECM can not enable close loop operation due to a poisened O2 sensor. O2 sensors are commonly poisoned by painter's silicon sealers or blow by engine oil. Poisoned O2 reads low voltage which corresponds to a lean mixture (high o2 concentration in the exhaust stream). ECM will attempt to add fuel to richen fuel mixture.

3) Exhaust manifold leaks, or if AIR system is dumping air into exhaust when not commanded by ECM. Additional O2 delivered by AIR system (or upstream exhaust leak) is detected by O2 sensor and ECM will command more fuel.


//RF