My son and I have been working on his 89 IROC project. The car runs great, except that it runs really rich, and gets terrible fuel economy (10 mpg). Here's a summary of what we've done/checked so far:

fuel pressure: 13 psi running
coolant temperature sensor: replaced with new
throttle position sensor: 0.8V closed, 4.5V WOT
fuel injectors: replaced with known good from another 5.0 TBI. No change
evap cannister & solenoid valve: replaced with known good from another 5.0 TBI. No change
Oxygen sensor: was reading -3.14V. Replaced. Reads 0.62V now
Manifold Air Pressure sensor: Disconnected, running on stored tune, still smokes
ECM: swapped with known good from another 5.0 TBI. No change.
checked nearly all of the vacuum lines for leaks. None noted.

We did try disconnecting the injectors, and then running the car on starting fluid, then white gas (Coleman lantern fuel), and then gasoline, sprayed directly into the throttle body. No smoke! It ran fine (once I figured out the amount to spray).

Kind of at a loss as to where to look next. Any thoughts???

 

Even though the CTS was replaced, I'd put a scan tool on the ECM to see what it is seeing. With the way the CTS works any resistance in the connector or wiring for it will cause it to report a colder then really is engine temperature.

This will cause the engine to run rich.

RBob.

 

Not having a scan tool, what voltage or resistance values should I expect to see at the ECM input?

 

Chart attached.

RBob.

 

We connected a harness from the CTS directly to the ECM pin C10, and D1. Reading 330 ohms at about 170 degrees, and saw steady decrease in resistance as the engine warmed. The car did not smoke initially at cold start. After maybe 30 seconds or so, he revved it, and it started to smoke. We tried connecting the ohm meter to the ECM and noted that as you change the range on the meter, the engine rpm would change, when connected to the factory harness.

 

Really need a scan tool, even if laptop based, to see what is going on. I'd definitely look at the BLM to see what the ECM is doing for fuel trim.

If you run the fuel pump engine off, does fuel drip from either the FPR or injector pod?

RBob.