ECU temp sensor

Discussion in 'Discussion Forum' started by ecohen2, Oct 31, 2018.

  1. ecohen2

    ecohen2 True Classic

    Location:
    Arlington Va
    Does anyone know what the symptoms are when the temperature sensor that sits on the thermostat housing fails? This is for a 1986 Bertone with fuel injection..

    Thanks,
    Ed
     
  2. Waterbury

    Waterbury True Classic

    Location:
    Pennsylvania
    Are you having symptoms that are leading you to believe a bad temp sensor?

    Edit: just doing a quick search I found someone reference it saying it related to the AC system. I have the AC gutted in my 86, can check when I get home to see if they took that out as well.
     
  3. kmead

    kmead True Classic

    Location:
    Michigan
    Indeed, what are the symptoms you are suffering?
     
  4. Dan Sarandrea (Phila)

    Dan Sarandrea (Phila) Waitin' On Parts...

    Location:
    Philadelphia, PA
    If it fails at one extreme, the temp sensor will cause the engine to run very rich all the time, not just at startup/warmup. At the other extreme, it will cause the engine to run very lean all the time. Of the two, lean is a more alarming condition as it could result in overheating, detonation, and engine damage.

    If you have a simple multimeter, follow the test procedure in the FI troubleshooting guide. Don't be tempted to test resistance at the sensor's pigtail---rather, test it at the main harness connection to the Bosch FI control unit per the troubleshooting guide, as doing it that way not only tests the sensor but also tests the wiring to/from the control unit. The ground for the sensor's wiring is one of the two FI harness grounding eyelets on the cam box cover retaining studs.
     
    Cratecruncher likes this.
  5. ecohen2

    ecohen2 True Classic

    Location:
    Arlington Va
    A while back I had my thermostat and temp sensor replaced by a local shop. My thermostat had been stuck open so the engine never warmed up properly, especially in cold weather. Now the engine warms up properly but will run above 190 on the highway even in cold weather.. The gauge on the dash is consistent with the temperature readings on the thermostat housing.

    I do lose power once the engine reaches the higher temps, so I was trying to figure out if the ECU decides to do something when it reaches a certain level...

    Thanks,
    Ed
     
  6. Dan Sarandrea (Phila)

    Dan Sarandrea (Phila) Waitin' On Parts...

    Location:
    Philadelphia, PA
    How confident are you that the shop properly bled your system after replacing the stat? And did they say why they replaced the FI temp sensor in the stat housing? It has nothing to do directly with the cooling system. The sending unit for the dash temp gage is located on the cyl head right above spark plug #2.

    Typical symptoms of air buildup in the cooling system are abnormal temp gage variations once up to operating temp, little/no/intermittent heat from the heater even if the temp slider is on max heat, and late cut-in of the rad cooling fans.
     
  7. lookforjoe

    lookforjoe True Classic

    The temp sender is not interchangeable with newer sensors - I would wonder where they got the sensor & what bosch number it is, assuming it's even an appropriate replacement value sensor. If you are running very lean as a result, that would explain the hot running condition - which is definitely NOT a good thing - it would be unwise to keep driving it as is. It is also possible the higher temps are simply because it's the wrong t/stat, if bleeding makes no difference.
     
  8. carl

    carl True Classic

    Location:
    Virginia
    What does that sensor do, what does it control? Does it override the oxygen sensor once the engine is warmed up?
     
  9. lookforjoe

    lookforjoe True Classic

    It influences fuel delivery at the injectors, along with other parameters. It does not override or replace O2 sensor input, that is continuous once the O2 sensor heats up & is operational.

    I think the correct Bosch # is
    0280130026
     
    Last edited: Nov 1, 2018
  10. ecohen2

    ecohen2 True Classic

    Location:
    Arlington Va
  11. Dan Sarandrea (Phila)

    Dan Sarandrea (Phila) Waitin' On Parts...

    Location:
    Philadelphia, PA
    Several questions:

    1. What was the usual temperature behavior of your car before the stat went bad and stuck open?

    2. Why did the shop replace the FI temp sensor?

    3. Can you be more specific about ""Now the engine warms up properly but will run above 190 on the highway …"? Each hash mark on the temp gage above 190°is 5°, so where above 190° does it sit? Does it pretty much stay at that point or does it swing up and down during steady state highway driving?

    4. As Hussein alluded to, are you confident your shop used the correct thermostat? If they got the stat from local generic sources, they may have used a stat that is rated at 5-10° higher than stock.
     
    Mike Schofield likes this.
  12. ecohen2

    ecohen2 True Classic

    Location:
    Arlington Va
    Dan, all good questions...

    #1. Before the thermostat was stuck open the temperature would hang out about two ticks below 190. If I was in stop and go traffic it would go a couple of ticks above 190 until the cooling fans kicked on or I started moving and then it would return to just below.

    #2. The original reason for replacing the sensor was because during warm up my idle would jump all over the place. I did the usual check for vacuum leaks but couldn't find any. One of the debugging items for the idle issue is to replace that sensor and sure enough it fixed the idle issue. The car now warms up properly and the temp gauge will sit right at 190 for a long time. However, If I go on the highway or have the rpms up above 3500 for a while the temp goes about 4 ticks above 190 and never comes back down.

    #3. I spoke to the shop who does lots of Fiat work and they were positive that the thermostat is correct. They suggested that the gauge was incorrect but it doesn't seem likely that would have broken during the thermostat replacement.

    Additional information...

    * The car has noticeably more power before before the temperature goes above 190. This made me think that the ECU was doing something based on a signal, which is why I asked the original question.

    * I have a new alloy radiator with high flow cooling fans so that should be good.

    * I have NOT replaced the water pump, but I have no reason to believe it is failing... It only has 11,000 miles.. My heater works just fine and the radiator gets appropriately hot..

    Ed
     
  13. carl

    carl True Classic

    Location:
    Virginia
    Ed, you didn't mention that your thermostat was really gunked up with crud and there is a good chance your water pump might be compromised too. Some day, let's have a water pump check party.
     
  14. nichol01

    nichol01 Daily Driver

    Location:
    pennsylvania
    It sounds to me like you might still have air in the system. After my rebuild I had the same issue of temp. Kept creeping up on the highway. I ran it very hard one day with my heater valve open and noticed my temp suddenly dropped. When i got home I burped the system again for probably the 10th time and got alot of air out its been good ever since. Just giving you my experience with my car. It is a large system with alot of places air can hide.
     
    Dan Sarandrea (Phila) likes this.
  15. Dan Sarandrea (Phila)

    Dan Sarandrea (Phila) Waitin' On Parts...

    Location:
    Philadelphia, PA
    +1

    Burp, baby, burp!!
     
    nichol01 likes this.
  16. ecohen2

    ecohen2 True Classic

    Location:
    Arlington Va
    It has been burped, driven hard with the heater on multiple times....

    I think @carl has a sensor and ill give that a try...
     
    nichol01 likes this.
  17. carl

    carl True Classic

    Location:
    Virginia
    I have noted that everytime I have to drain the cooling system on an X I have to burp the radiator at least three or four times to get all the air out.
     
  18. Mike Schofield

    Mike Schofield Daily Driver

    Ok, when you say “burp”....what exactly do you mean. I mean, I crack my bleeder valve and get some coolant dribbling out but have never heard any “air”. Am I not leaving the bleeder valve open long enough?
    What’s the “best” technique in everyone’s opinion?
     
  19. carl

    carl True Classic

    Location:
    Virginia
    That's what I mean, and make sure your heater valve is open to circulate any air that may be trapped in that line.
     
    Mike Schofield likes this.
  20. kmead

    kmead True Classic

    Location:
    Michigan
    I drive my car up a set of ramps to have the nose high to try to draw as much air to the top of the system before opening the bleeder.
     
    Mike Schofield and nichol01 like this.

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