1994 C1500 350 cid tbi; poor gas mileage, intermittent stalling & trouble starting
by, 04-18-2012 at 02:58 AM (4891 Views)
A couple of years ago the truck had similar but not quite the same issues. Low power and rough acceleration intermittently. A mechanic replaced the EGR and MAP sensor. Seemed to help for a week or two. Replaced the fuel filter, same deal. It ended up being the fuel pump was pumping about 8 psi. Should be 12-15 psi for a tbi. Thank you, GM for a convenient tap to check this! lol
Recently the truck was hard to start and stuttered and stalled taking off from a stop. Terrible gas mileage. As long as it was moving, it ran ok, but it seemed to have a slight miss. Had to press the gas pedal to the floor when starting cold and black smoke would billow out of the exhaust when it fired up. Error codes 35 bad idle air control and 54 low fuel pump voltage.
Checked the EGR, throttle position sensor, fuel pump relay (& voltage), fuel pressure, tb injectors and vacuum lines. Removed the idle air control and was about to put a new one in, but decided to test the one in the truck after cleaning it up. Plugged it back in and had someone start the truck to see if the pintle moved on the IAC. It worked its' way out and shot out onto the ground. Be careful with the electrical connecting plug as the isolators for each pin connector get brittle over time. By the time I was done messing with it, most of the isolators were busted. Oops! All the tested components seemed to work.
The engine temperature sensor was replaced last year, so I immediately discounted it (and would have been the last thing I checked) until my Dad mentioned it. Sure enough the connectors had rusted to the point of no continuity. It seemes to be a watertight connecting plug, so I can't see how it corroded, unless the pins on the sensor aren't sealed (doubtful). I didnt do the initial installation so I guess we gotta keep an eye on it.