1995 chevy c3500 454. runs rich

[mckenzie913]

i got a 95 c3500 with a 454 in it.. manual trans 196,000 miles. truck runs rich. code 13 and 45. scantool show 1101mv on o2 sensor. fuel pressure is 32. spec is 26-32 for the 454... 350 is 9-13psi. (i looked it up, i thought tbi only need 9-13.. not the 454) i went to napa and bought a fuel pressure regulator kit... spring was very weak compared to the one i took out. only had 18psi with new kit.. truck would stumble... put old spring back in. truck acts up in closed loop.. bogs down as computer is taking the fuel away... obd I. LT fuel is 84. tried new o2 sensor, and computer.. no help... replaced fuel pump due to 38-40 psi... now 32psi... truck runs good when o2 sensor is unpluged, or in open loop. any ideas?... anybody? :hang:

[mckenzie913]

also good spray on injectors, and no dripping. key on, and injectors don't leak down

[GRRRR8]

Check coolant temp sensor. If it looks green on the outside change it. Also when the truck is cold it will usually read - 20 degrees for the ECT.

[mckenzie913]

yeah, already checked that... was reading 198 when hot... i was hoping it would show -40 degrees, meaning open in ect sensor or wiring problem.... thanks.

[GRRRR8]

The MAP sensor vac line is not broken/split? Did you check the TBI base gasket? If fuel is good, ECT is good, now its focus on things that force an engine rich like vac leaks.

[mckenzie913]

on the 454 the map sensor has 1 vacuum line that splits into 2 lines and both of them go to the back of the intake. i sprayed carb cleaner all over the intake hoping to find a vacuum leak.. no luck, no raise in rpms..

[GRRRR8]

Does it chug while its running?

[mckenzie913]

only under a load in closed loop. runs fine then no power, goes from 55-30 then kicks in... the computer takes the fuel away. it can idle in closed loop, smells rich and shows 1101mv on o2 sensor... unplug o2 sensor, still runs rich, but doesn't bog down... i guess because with the o2 sensor unpluged it stays in open loop, and the computer doesn't take fuel away.

[GRRRR8]

See what the engine vac is to make sure it doesnt have a bad cat on it, if it has one. If it doesnt, see what engine vac is hot/cold.

[mckenzie913]

sounds good, i'll put a vacuum gauge on it and get back with you tomorrow.

[mckenzie913]

appx. 18.5 in. of vacuum hot or cold, steady.

[GRRRR8]

When you put it in gear hot does it lose vac with just a little gas and steadily drop?

[mckenzie913]

its a manual transmission. when hot, it has 20in of vacuum just off idle.

[GRRRR8]

Start looking at O2 wiring harness or defective/cheap O2. I have had more Bosch O2s have issues then I can count.

[mckenzie913]

bought a throttle body gasket kit, cleaned all the port of the throttle body. replaced two broken ground straps. r/r cyl head to frame, and to body (just below heater hoses). fixed problem...