Ok, please explaine this! 92 305 tbi. I replaced the fan and thermostat (180) to combat Texas heat. Now in town it still gets hot (not near as bad) but on the highway it will cool down enough for the computer to turn on the service engine soon light. On a good hot day on the highway with the ac cranked it will run 220 and not jack with the computer. I don't know the correct this problem. Any help would be great!

Thanks,
Eric

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change the fan switch or CTS...

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Webmaster: www.IROC-Z.org & www.GMPerformance.org

 

Eric, pull the codes from the ECM, running a 180 Tstat should not set off the SES light.

 

Oh, and welcome aboard to www.thirdgen.org, you can find lot's of "how to's" from the main page, look through Tech Central.

 

Thanks for the advice and the compuyer said O2 sencer. Replaced it, took it to races last night. 185 miles round trip to Ennis. The car wants to run at 160 on the open road. You can see the temp guage drop after about 10 miles of open road, and like clockwork the ses light. I also put in a new radiator yesterday (oem). I thought I had a bad tstat so I put another in today. still no help. I'm almost to the point of putting a cardboard box in front of radiator! LOL.

Eric

 

Eric,

The majority of the time, the code indicates that a sensor is not at fault, but that what it is sensing is at fault.

i/e your O2 sensor code could be either rich or lean exhaust, which is more than likely setting a code.

It may be a coincidence that the gauge falls off on the highway at the same time.

The gauge signal has no input to the ECM, the ECM sees the coolant temp from the CTS located at the front of the intake.

What code# appreared?

 

Thanks for taking the time Mike. It was code 45. According to actual gm manuel for the car it is rich exhaust indicated.

 

Hmmn, there's several posibilities for a rich exhaust, most likley too much fuel

So now you need to determine where the excess fuel is coming from and why.

Do you have access to a fuel pressure gauge?

Does the oil smell like fuel?

You might be better off taking the code 45 question to the TBI board as well.

For a quick check, take a sniff in the charcoal cannister and make sure it's not full of raw fuel.

Watch the fuel injectors spray, and make sure one isn't dripping fuel.

Could you have disturbed the MAP sensor connections or tubing during maintenance? How about the CTS plug?

Can you beg, borrow or steal a scantool?

And does it always set the SES light on the highway with the A/C off? And never set the SES light with the A/C on?

Even 160 should not set an SES light, or cause the mixture to go too rich at part throttle, you should be in closed loop, even at 160, with the ECM controlling all fuel functions, might be on the edge for EGR operation though, EGR isn't enabled till like 150+. By a reeeaaal stretch of the imagination, it could be possible that the EGR is not being enabled, or is being disabled at that temp...hence not diluting the fuel mixture, which could result in too high of an F in the A/F ratio, but I'd think it'd only last temporary...Code 45 takes like a minute at being rich to set, I'd think the ECM would be able to adjust by then? Again, just doing some WAG'ing and "what if's".

To verfiy any and all of it, a scan tool would be invaluable.

 

Hang on Mike, let me go give it the sniff test! And no, I'd have to take it to a shop for a scan tool. Don't you sleep???

 

LOL, not while the wifes out and I'm watching the kids Been one of those days...to the pool, to the shop, to the computer...

I did get the 3-wheeler running today though Leats i accomplished something, now I just have to convince my 4YO she too small to ride it by herself...I did catch the 6YO trying to start it though.

And still my IROC sits with the topend in pieces...

 

Good luck w/ the 4yo. I have one that's 3 and she rides my 4 wheeler every where. It's a 425, just a little much for her by herself but she steers and gives it the gas. WFO! Too young for fear. My 9yo won't let me ride with her @ all!

Any way, sniff test is good. The injectors are not dripping. (bet my wife loves that) <grin>. As far as the scan tool I had a revelation. I need to send off a couple of emails regarding the possability of borrowing one. Good Idea!

But it does it when the da** thing cools down. The ac dosen't affect it. I thought that too because it kicks on the electric fan. But, if I can keep the temp up it will stay off. ie. keeping it out of OD and running the r's up now and again. I've been keeping an eye on it the last couple of weeks driving it back and forth to work, approx. 200 miles rt. It will sometimes go out on it's own and I won't have to kill the motor and reset the computer. Driving it in the daytime (over about 90 degrees the ses light will never come on.

 

I found it! It's a iat sensor that took a dump. The computer spit out the code tonight.
That explains the ambient temp symptom.

I will replace in the morning. Thanks for all your help Mike!

 

Cool deal...no pun intended