bad engine coolant sensor?

[sholzy]

Long story short...

CEL: 177 (bank 2 rich)
Checked/Cleanded MAF - No change
Changed O2 sensor - No change
Changed MAF - Ran good after about 20 miles
Memory cleared each time after O2 sensor and MAF change.
New wires and plugs recently.
New fuel and air filter recently.
No vacuum leaks.
Fuel pressure not checked, but not suspect either.

Decided to drive truck after engine was cold. CEL again: 177. Same symptoms as before: stumbling/rough running, no power, but not as severe this time.

Could the engine coolant sensor be bad? Is it telling the EEC that the engine is running cold and making it run rich? But wouldn't I get a rich reading on both O2 sensors if that was the case?

I'll check the ECT sensor tonight when I get off work. Anything else I should check?

Thanks in advance for any help on this.

 

[modelageek]

Long story short...

CEL: 177 (bank 2 rich)
Checked/Cleanded MAF - No change
Changed O2 sensor - No change
Changed MAF - Ran good after about 20 miles
Memory cleared each time after O2 sensor and MAF change.
New wires and plugs recently.
New fuel and air filter recently.
No vacuum leaks.
Fuel pressure not checked, but not suspect either.

Decided to drive truck after engine was cold. CEL again: 177. Same symptoms as before: stumbling/rough running, no power, but not as severe this time.

Could the engine coolant sensor be bad? Is it telling the EEC that the engine is running cold and making it run rich? But wouldn't I get a rich reading on both O2 sensors if that was the case?

I'll check the ECT sensor tonight when I get off work. Anything else I should check?

Thanks in advance for any help on this.

check the vacuum line on the fuel prssure regulater. a bad fpr can make the truck run lean or rich.

 

[sholzy]

check the vacuum line on the fuel prssure regulater. a bad fpr can make the truck run lean or rich.

I don't have a vacuum gage or a fuel pressure gage. I did pull the vacuum line off the fpr while the engine was running and the rpm's increased a little. Reattached the line and the rpm's came back down so I assume the fpr is functioning somewhat.

I also checked the ECT sensor and it was in range on the operating temp side of the test. I'll check the cold reading tomorrow before I start the engine.

This morning when starting the engine, it idled rough, almost wanting to die. After driving it for a few miles and the temp starting coming up, it started running better. No roughness, no stumbling. Just like it did before the problems started. 30 miles later coming up to a stop light it started the stumbling, running rough, lack of power again. It was like this off and on for the next 30 miles until just before i got to work and it ran good again. When leaving work, I started it and it idled rough for about 5 minutes then smoothed out and ran fine the 60 miles back home. Not a single problem. It actually felt like it had a little more power than it did before the problems started so I'll attribute that to the new O2 sensors and the new MAF sensor.

After changing out the new sensors and clearing the memory, I guess the EEC needed longer than normal (whatever "normal" is) to "learn" the new readings and make the adjustments? I had probably close to 90 miles on the new sensors before the truck started running good again.

 

[sholzy]

I checked the ECT this morning while the engine was still cold. It was about 27k ohms and should have been 40k ohms as per spec. I bought a new and will change it out tomorrow. I'm looking forward to seeing how the new sensor will improve the performance, if any.

When I started the truck today I had no idle problems like I did the past 2 days. I drove about 150 miles today and never had as much as a hiccup from the engine. It is running much smoother now and feels a little peppier than it was a week ago before I started having the problems. I have noticed my fuel mileage is up to 23 mpg from the 20-21mpg driving the same circuit running about 65-70 mph.

Overall I think the $300 I spent replacing sensors was worth it. Here's to another 200,000 miles.