5.7 TBI Surging - help the Ol Guy :)
#1
5.7 TBI Surging - help the Ol Guy :)
Hello,
I'm trying to help my old man diagnose a surging problem with his 1992 silverado. It has about 170K miles and a 5.7 engine.
It surges while driving about 35-40 mph, under very little load, and barely any throttle. It does NOT surge at idle. It runs great under acceleration with no surging or loss of power. He's noticed a decrease in fuel economy. The surging is getting worse. It has dual exhaust - I mention this because I'm pretty sure the catalytic converter is gone, i.e. not plugged.
Here's whats been done so far:
1) Fuel pressure on weak side - new fuel pump.
2) New fuel filter
3) New plugs and plug wires
4) New dist. cap and rotor
I was thinking Idle Air Control valve, MAP sensor, vacuum leak, or t-stat sensor/plug?? Any thoughts would be great - thanks.
I'm trying to help my old man diagnose a surging problem with his 1992 silverado. It has about 170K miles and a 5.7 engine.
It surges while driving about 35-40 mph, under very little load, and barely any throttle. It does NOT surge at idle. It runs great under acceleration with no surging or loss of power. He's noticed a decrease in fuel economy. The surging is getting worse. It has dual exhaust - I mention this because I'm pretty sure the catalytic converter is gone, i.e. not plugged.
Here's whats been done so far:
1) Fuel pressure on weak side - new fuel pump.
2) New fuel filter
3) New plugs and plug wires
4) New dist. cap and rotor
I was thinking Idle Air Control valve, MAP sensor, vacuum leak, or t-stat sensor/plug?? Any thoughts would be great - thanks.
#2
CF Senior Member
Join Date: Feb 2011
Location: Middletown DE
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i would check the resistance of the TPS,map sensor and coolant temp sensor, did the fuel pump bing the fuel pressure back in spec? you will need a small hand vacuum pump to check the map sensor at different vacuum levels
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