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90 K1500 SES light & Heater Core Questions


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Posted

Hey guys,

Thanks in advance for any input you all might have on these two issues. I doubt they're related but didn't want to post-spam both issues separately. The vehicle is a 1990 GMC Sierra K1500 Single Cab 5.7L/A4 w/ over 120k on the clock (odometer works intermittently). Recent maintenance includes replacing all plugs/wires this past Saturday, along with the O2 sensor. At the least, the radiator, fan, belts, and most of the hoses were replaced about a year ago when the front end was damaged in an accident. My parents have had it sitting in the yard since that time, rarely driven. Rather than see the vehicle waste away, I've decided to use it as a beater/dailydriver.

 

SES Light

The SES light only appears when driving 10+mi distances at speeds 55mph+. Once the vehicle is turned off and restarted...the SES light is gone. Since the O2 sensor had previously gone out, I assumed this to be the problem again. I replaced the O2 sensor on Saturday and the problem still occurs. The truck smells like it's running a little rich, as the new air filter that was replaced with the oil (3mo/2k mi ago) smells of fuel. Could it be the EGR valve? Any other ideas? I know with my 95 Corvette I can read the codes by shorting out two pins in the OBD-I connector. Is there a similar way to read codes on a 1990 GMC?

 

Heater Core?

Since the accident, the A/C has not worked and the compressor has a white dusty appearance. Not a big deal...I rarely use A/C anyway. However, there is a very oily film on the inside of the windshield and coolant seems to be disappearing. I've noticed no visible leaks, although I've only had the truck for two days. I'll pay attention to that and post back. A couple months ago when borrowing the truck I did hear a huge "slosh" sound in the passenger side of the dash when turning. At that point, I didn't note any residue on the windshield. What's the best step to take next here? Should I replace the heater core? Flush the coolant? Replace the fuel filter? D) All of the above?

 

As an aside...

This is just in case anyone has any input, as I'm very unsure as to this issue. There seems to be just a bit of colorless hazy smoke coming off of the driver's side rear of the engine somewhere around the header. I can't tell exactly what it is or where it's coming from. The truck has been sitting so long that I think a squirrel was living on top of the engine. Perhaps some of his stored food is what is burning off...or perhaps he was still back there. Anyway, that's just a testament to the sad state this truck is in.

 

Thanks in advance for any input! I'll keep the thread updated and check/update for any requested info. I do most of my own regular maintenance (oil/plugs/wires/filters/etc), but I am by no means an expert or even "experienced." I appreciate it!

 

DC

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