1995 Chevy Van Too cold?

BORNLOSER

MEMBER
1995 CHEVROLET VAN
V8
2WD
AUTOMATIC
200,000 MILES

Chevy 350 TBI, gas mileage got real poor. Took it to a dealer, and they said the computer was not going into closed loop because it wasnt getting warm enough but didnt know why. Other than gas mileage, it runs perfectly. No codes or check engine light. Changed O2 sensor and coolant temp sensor. No change. It is a single wire O2 sensor, which reads 375millivolts, at startup and 30 minutes later. No change. BArely changes even as engine is revved. The coolant sensor has 2.5 volts across it when cold (and reads 2k ohms) and after 30 minutes, has 5 volts across it (reads 260 ohms). Any ideas?

5 Replies

RLBSTUCKINHOU

MEMBER
11 POSTS

WHEN YOU FIRST START YOUR VAN AND UNTIL IT WARMS UP THE COMPUTER IS SUPPOSTO BE IN A CLOSED LOOP, IE: NO SENSOR INPUT. ONCE WARMED UP THE SENSORS START COMING ON LINE AND INFORMATION IS SENT BETWEEN THE COMPUTER AND THE SENSOR.
SENCE YOU SAW NO CHANGE IN YOUR O2 SENSOR VALUE AFTER THE WARM UP IT SOUNDS LIKE YOUR COMPUTER IS NOT WORKING AT ALL AND HAS DEFAULTED TO CLOSED LOOP CONFIG THUS THE HIGHER GAS USAGE.
THERE SHOULD BE A FUSE IN YOUR FUSE BOX FOR THE COMUTER IF IT IS GOOD IT IS PROB THE COMPUTER THAT IS BAD. YOU SOUND LIKE YOU ARE PRETTY GOOD WITH A METER SO CK FOR POWER AT THE COMPUTER CONNECTION. I THINK THAT THE COMPUTER IS UNDER THE PAX DASH BEHIND THE KICK PLATE ON THIS YEAR VAN? NOT 100% SURE ON THAT. HOPE THIS HELPS GOOD LUCK.

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Thursday, May 1st, 2008 AT 9:35 AM

BORNLOSER

MEMBER
4 POSTS

The computer is behind the drivers seat in the side panel. It HAS voltage. The computer has been replaced (after this problem occured) but for a DIFFERENT problem. The computer went bad and the transmission went into limp mode, and the transmisiion stayed in first gear. Again, this happened AFTER the gas mileage problem, so its NOT the computer.

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Thursday, May 1st, 2008 AT 10:52 AM

MASTERTECHTIM

MECHANIC
4,749 POSTS

Check the brown or tan ground wires at the thermostat housing. This is a common problem for no o2 activity. Usually the stud loses ground. Remove the stud and clean the threads and replace the eye terminals for the grounds. Hope this helps

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Thursday, May 1st, 2008 AT 11:01 AM

BORNLOSER

MEMBER
4 POSTS

I know the wire you are talking about. If it isnt raining in the morning, I will splice the wire and re-route it to a good ground. I will post back with the results. I am HOPEING your right!
And its a sure bet that if that fixes it you will receive a donation!

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Thursday, May 1st, 2008 AT 5:49 PM

BORNLOSER

MEMBER
4 POSTS

Well, I got a chance to drive it today and check the mileage. I drove it about 120 miles, and no improvement. Still less than 14mpg. I even talked to the former owner, and he confirmed it got over 17mpg. Any other ideas?