Hi all I posted about this before but couldn't find it. I have a 93 4.9 that gets up to temp normally then falls back to about the o on the normal and then throws the check engine light minutes later it goes back up and check engine goes off. The check engine code is an egr closed code. Egr replaced and tested and everything else on it, no vacuum leaks, egr does open as should, thermo replaced twice, coolant temp sensor replaced coolant flushed and replaced and still does this. Any ideas. My next attempt will be throttle position sensor. Ohh yeah fan clutch and water pump are good.

 

My 89 F250 runs at the "N" to "O" on the gauge and its not over cooling.My 95 350 bus runs on the "A" to "L" and its not over heating. These temp gauges are not a exact gauge hence the "NORMAL" range they show.

What is the exact EGR code that pulls up? There are a few EGR codes so you could be replacing parts needlessly.

If there is no code for the TPS(thorttle position sensor) why replace it?

 

Codes are 332 insufficient egr flow and 334 egr closed valve voltage high just started doing this 6 months ago if yours stopped running around that n would you question it, once again it runs at normal temp 2 minutes later it drops close to o and throws cel. Minutes later it goes back up cel goes off. All day long it does this every couple minutes. Something is trying to do something.

 

The EGR position sensor is most likely bad, or bad connection to it. I had the same on a 92 F150, replaced it and corrected the problems. Also check for any vacuum leaks to the EGR solenoid valve, some times a simple vacuum leak will cause issues too.

On the temp gauge, what you are seeing is the thermostat opening and closing. Some temp gauges are sensitive enough to show it. When the tstat opens up, you get a slight cool down with cooler water from the radiator, the tstat senses the cool down and closes stopping water flow to the radiator. The cycle time on my 89 F250 is around 2 to 3 min, on my E350 Bus with a super sized radiator, t-stat cycle time is around 7 to 9 min.

 

Also replaced and tested tomorrow I think I am going to take a better look at that sending unit and ground to it and see what I get. Everything with the egr is replaced and tested cleaned tube manifold ports. I think what I have is the PCM trying to adjust for a bad signal from a sensor just have been able to find which one it is.

 

What you are seeing on your temperature gauge is perfectly normal. The engine temperature raises, until the thermostat opens. At this point a rush of cold water from the radiator causes it to fall. If it's cold enough the temperature can fall to the point where the thermostat closes and the process repeats. It's not as dramatic the second time because the water in the radiator isn't as cold. Eventually everything reaches equilibrium and you don't see it happen anymore.

On a hot summer day you may not see this happen. On a really cold day you may see it happen 3 or 4 times. You're chasing your tail on that.

I'd say you're on the right track with a faulty connection to a sensor somewhere.

 

Faulty ect sending unit replaced and guage sits in the middle where it did 6 months ago no code no cardboard and no moving gauges. I question anyone who says its normal when for 20 years of this vehicle it didn't do it. Come on guys ESP when over and over again I stated it does this all day with a code, thanks for the help regardless.

 

And some of us might would question those who think a throttle position sensor would have anything to do with a temperature "problem" and an EGR code.

Glad you got it fixed to your satisfaction.

 

Maybe PCM is new technology to you I think that maybe the issue here. What was the next thing you were gonna say tape over the light right, it's in my head PCM makes adjustments to readings for the good of the engine I assume they were placed there for gentlemen such as yourself.

 

Waste $$$ shot gunning parts................... I am done here

 

Hell, stick around.. We are getting taught a lesson here!!!!!! Don't be late for class!!!!

 

Yeah he will 412,000 miles on that truck those sensors are 10 15 bucks a piece I owe it to my truck. I spent 18 dollars to diagnose this. 7 for the thermo and 11 for the sender

 

I just wondering WHICH temp sender you replaced... or did you throw both at it "just in case"?

There are two, one for the computer that could throw a DTC and light the check engine light, and another one for the gauge that will not cause a DTC code.

 

Even though the problem was solved I'll tell you this without taking any side, since I understand wanting to have a truck without issues: The "temperature gauge" in these trucks is little more than a sophisticated idiot light. If you want good readings you might need a real temperature gauge, the same goes to the oil pressure gauge btw.

 

Both were so cheap I did them the one on the water outlet looked like crap and the one on the block by the filter was completely soaked in oil from my leaking valve cover ill do that this summer just didn't feel like getting into that manifold job yet so this will motivate me to get to it. Just tackled the 5.4 plugs on the other one so I needed a frustration break.