I unplug my coolant temp sensor and my car runs better than with it unplugged, why?

TyJames
20

Asked by TyJames Jul 05, 2013 at 10:25 PM about the 1993 GMC Vandura G25

Question type: Maintenance & Repair

I've replaced the coolant temp sensor, thermostat, fuel filter, vacuum hoses, checked the fuel pump, replaced the map sensor, idle air control valve, o2 sensor, cleaned the tbi and my car still has a rough idle, dies often times when you first put it into gear, hesitates and jerks when you give it throttle off of stops, has trouble maintaining cruise and sometimes dies at idle. Any ideas as to why my car will run with no problems with the coolant temp sensor unplugged but the symptoms continue when the sensor is plugged back in.  It also often times comes up with a PO44 Error code when running bad which is a lean fuel error code.

8 Answers

therenow
40

Again, vacuum leak. Check ALL hoses and fittings. The reason it runs better unplugged is because the computer throws into a richer mixture. The coolant sensor acts as a choke (in a sense). When cold, it says Throw more fuel. When it's warm, it says Okay,lean me out. There is a connection on the brake booster that could be cracked. What type vehicle is this?

1 out of 1 people think this is helpful.
TyJames
20

I've replaced two vacuum hoses that were leaking and have looked all over the vehicle and I am unable to find any additional leaks. I drive a 1993 GMC G2500 Vandura with a 5.7L V8. Is it normal for the vehicle to run completely fine with the ECT sensor unplugged if there are vacuum leaks?

Js08016
15,955

Before you unplugged the temperature sensor was your "service engine soon" light on? If so, what code(s) did you get?

1 out of 1 people think this is helpful.
TyJames
20

Lean fuel. The exact code was PO44

2 out of 2 people think this is helpful.
Js08016
15,955

That could be a bad oxygen sensor, vacuum leak, weak fuel pump, faulty fuel line, EVAP system problem, bad fuel pressure regulator, faulty fuel injector(s), or even a bad gas cap. HTH. -Jim

TyJames
20

O2 sensor replaced, fuel pump checks out as good, fuel injectors cleaned and some vacuum hoses replaced and I'm unable to find any other vacuum leaks.

Js08016
15,955

Is the intake manifold itself possibly leaking? What about the EVAP system?

Js08016
15,955

An exhaust leak, ahead of the oxygen sensor, will cause a code 44. I believe, if I remember correctly, a faulty MAP (manifold absolute pressure) will also make the system go lean as well. HTH. -Jim

1 out of 1 people think this is helpful.

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