Possible detonation theory?

95mustanggt · 09-26-2001, 03:19 PM

Well I have a theory on my detonation problem in my 95. Please read and tell me if I'm way off base.

Down here in Dallas the temperature has been a lot cooler, in the mid 70's.

My car has been running a lot hotter, but it has been running great, no detonation or anything.

Is it possible (keeping in mind I have no codes on the EEC) that the coolant temp sender is screwed and that it was giving me a low temperature when it was hot causing detonation. But what ever is wrong with the temp sender it does not trip the diagnostics?

I'm reaching here, but this problem is kinda screwy. Does this sound possible?

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1995 Mustang GT

PKRWUD · 09-26-2001, 06:16 PM

If the ECT sensor was sending a signal to the ECM that the engine was colder than it actually was, it would tell you so during KOEO and KOER tests.

Take care
~Chris

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Capri306 · 09-26-2001, 10:21 PM

Um, lemme put in my .02, Chris.

The only way the computer knows what temperature the coolant is at is by the coolant temperature sensor. The only way. Now if that sensor is going bad, but its signal is still within acceptable limits, the computer is going to say, "fine, the engine is at -10 degrees" even though it might be 70 degrees outside. You'll only get a code if the sensor is out of preprogrammed limits, and that's 90% of the time what happens. I think if it IS the CTS, then he's got the last 10% covered.

I had a customer with a similar problem. It'd run like crap when cold, then fine soon as it warmed up. Bad temp sensor.

95mustanggt: I think you're on the right track (possibly an ACT), but you should do some more testing. I'd pick up Charles Probst's book on Ford EFI and dive into it. There's a great section on testing sensors, and it's a tremendous asset to any DIYer or Mustang fanatic. Hope this helps.

------------------
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PKRWUD · 09-27-2001, 04:26 AM

Capri-
If the ECT sensor doesn't tell the ECM that the engine temp is at least 50 degrees during KOEO, or at least 180 degrees during KOER, you will not pass the self test, and a code 21 will come up. In other words, if the KOEO and KOER self tests are performed correctly, the ECM will tell you if the ECT sensor is sending a signal implying the engine temp is colder than it is. This is why you will receive a code 21 if the engine isn't properly warmed up prior to testing. If it is properly warmed up, and you still get a code 21, then the ECT sensor is likely faulty.

Take care
~Chris

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95mustanggt · 09-27-2001, 10:24 AM

Capri306 I see your logic.

PKRWOOD, I was just wondering is say the engine temp was actually at say 210* but the temp sensor read it at say 190*. Then it would pass the KOEO and KOER tests but when the engine was under load, the higher temp (210*) would cause detonation.

Sound possible?

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1995 Mustang GT

PKRWUD · 09-27-2001, 12:27 PM

95mustanggt-
Absolutely. But that would also mean that the engine would have to have been 210 degrees when the KOER test was done. The correct way to perform a KOEO & KOER is to start with the vehicle cold, start the engine and idle at 2000 rpm for 2 minutes. Shut off the engine and do the KOEO test, followed immediately by the KOER test. This way, the engine coolant temp is hot enough to pass the self test, yet cool enough to keep the T-stat closed, maintaining a passing temp. If the engine was at a steady 210 degrees during KOER, the temp gauge would be well above normal. A quick way to check that theory would be to clear all codes, and perform a KOEO self test with the engine cold, and the air temp 65 degrees or warmer. If a code 21 comes up, then the ECT is saying that the coolant temp is below 50 degrees, which wouldn't be true if the air temp is 65 or above, indicating the ECT is reading below actual. This would still trip a code 21 during KOER, though.

What was the engine temp when the KOEO self test was done? What was the engine temp when the KOER self test was done?

Take care
~Chris

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Capri306 · 09-27-2001, 01:39 PM

Exactly. I was just making sure we're on the same wavelength by bringing up the possibility of a 'lying' sensor.

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jimberg · 09-27-2001, 11:30 PM

Okay, I guess I'll throw in two more cents.

There are two coolant temp sensors. One is just for sending the temp to the gauge (The one that 95Mustanggt referred to) and the other is used by the computer (ECT). I'm not sure if there is some confusion about that. The one that PKRWUD and Capri306 are talking about is the one that has a multiwire connector, not the one with a single wire connector on a peg.

An ECT is about $35 so I would just replace it and see what happens.

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351W 89 Mustang GT Convertible

PKRWUD · 09-28-2001, 07:30 AM

Thanks Jim, now I'm totally mixed up. Okay.
95mustanggt-
Are you referring to the temp sensor or the temp sender? The sensor feeds info to the ECM, and the sender operates your temp gauge.

If Jim is correct, and the point I was making wasn't in the ballpark of what you were looking for, let me know. In fact, just ask it again, but a little more specific.

Take care
~Chris

------------------
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MustangNet

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95mustanggt · 09-28-2001, 10:12 AM

I'm sorry, it would be the Sensor that the ECM uses. I would guess that the ECM thinks that the temperature is colder than the car actually is and therefore keeps the timing more advanced that it should be.

Where is the ECM ECT Sensor. The gauge temp sender is just behing the distributor, right?

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1995 Mustang GT

PKRWUD · 09-28-2001, 12:14 PM

behind the t-stat housing.

I don't believe the ECT is at fault, but go ahead and replace it and see. If it's bad, though, you should be getting a code 21 (code 116 or 118 for a '95).

Your first entry in this thread says the engine is running hot, but great, and it's not detonating. So what are we after?

Take care
~Chris

------------------
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95mustanggt · 09-29-2001, 08:57 PM

Quote:

Originally posted by PKRWUD:
behind the t-stat housing.

I don't believe the ECT is at fault, but go ahead and replace it and see. If it's bad, though, you should be getting a code 21 (code 116 or 118 for a '95).

Your first entry in this thread says the engine is running hot, but great, and it's not detonating. So what are we after?

Take care
~Chris

Please check out my post called: Test Results on ECT and EEC-IV: HELP!! and let me know what you think.

Thanks Chris.

09-26-2001, 03:19 PM	#1
95mustanggt Registered Member Join Date: May 2000 Location: Kamloops, BC Posts: 2,875	Possible detonation theory? Well I have a theory on my detonation problem in my 95. Please read and tell me if I'm way off base. Down here in Dallas the temperature has been a lot cooler, in the mid 70's. My car has been running a lot hotter, but it has been running great, no detonation or anything. Is it possible (keeping in mind I have no codes on the EEC) that the coolant temp sender is screwed and that it was giving me a low temperature when it was hot causing detonation. But what ever is wrong with the temp sender it does not trip the diagnostics? I'm reaching here, but this problem is kinda screwy. Does this sound possible? ------------------ 1995 Mustang GT

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09-26-2001, 06:16 PM	#2
PKRWUD Junior Member Join Date: Mar 1999 Location: Ventura, California Posts: 8,981	If the ECT sensor was sending a signal to the ECM that the engine was colder than it actually was, it would tell you so during KOEO and KOER tests. Take care ~Chris ------------------ Retired Moderator MustangNet My site: JimPorterRacing RACECAR spelled backwards is RACECAR HEY !!! Are you ASE Certified ??? If you are, ask me about iATN. The best tool you'll ever have, and it's free !!!

09-26-2001, 10:21 PM	#3
Capri306 Moderator Join Date: Sep 1998 Location: Grand Rapids, Michigan, USA Posts: 1,001	Um, lemme put in my .02, Chris. The only way the computer knows what temperature the coolant is at is by the coolant temperature sensor. The only way. Now if that sensor is going bad, but its signal is still within acceptable limits, the computer is going to say, "fine, the engine is at -10 degrees" even though it might be 70 degrees outside. You'll only get a code if the sensor is out of preprogrammed limits, and that's 90% of the time what happens. I think if it IS the CTS, then he's got the last 10% covered. I had a customer with a similar problem. It'd run like crap when cold, then fine soon as it warmed up. Bad temp sensor. 95mustanggt: I think you're on the right track (possibly an ACT), but you should do some more testing. I'd pick up Charles Probst's book on Ford EFI and dive into it. There's a great section on testing sensors, and it's a tremendous asset to any DIYer or Mustang fanatic. Hope this helps. ------------------ Capri306, Moderator, The Mustang Works Online *"PROUD TO BE AN AMERICAN!!!"*

09-27-2001, 04:26 AM	#4
PKRWUD Junior Member Join Date: Mar 1999 Location: Ventura, California Posts: 8,981	Capri- If the ECT sensor doesn't tell the ECM that the engine temp is at least 50 degrees during KOEO, or at least 180 degrees during KOER, you will not pass the self test, and a code 21 will come up. In other words, if the KOEO and KOER self tests are performed correctly, the ECM will tell you if the ECT sensor is sending a signal implying the engine temp is colder than it is. This is why you will receive a code 21 if the engine isn't properly warmed up prior to testing. If it is properly warmed up, and you still get a code 21, then the ECT sensor is likely faulty. Take care ~Chris ------------------ Retired Moderator MustangNet My site: JimPorterRacing RACECAR spelled backwards is RACECAR HEY !!! Are you ASE Certified ??? If you are, ask me about iATN. The best tool you'll ever have, and it's free !!!

09-27-2001, 10:24 AM	#5
95mustanggt Registered Member Join Date: May 2000 Location: Kamloops, BC Posts: 2,875	Capri306 I see your logic. PKRWOOD, I was just wondering is say the engine temp was actually at say 210* but the temp sensor read it at say 190. Then it would pass the KOEO and KOER tests but when the engine was under load, the higher temp (210) would cause detonation. Sound possible? ------------------ 1995 Mustang GT

09-27-2001, 12:27 PM	#6
PKRWUD Junior Member Join Date: Mar 1999 Location: Ventura, California Posts: 8,981	95mustanggt- Absolutely. But that would also mean that the engine would have to have been 210 degrees when the KOER test was done. The correct way to perform a KOEO & KOER is to start with the vehicle cold, start the engine and idle at 2000 rpm for 2 minutes. Shut off the engine and do the KOEO test, followed immediately by the KOER test. This way, the engine coolant temp is hot enough to pass the self test, yet cool enough to keep the T-stat closed, maintaining a passing temp. If the engine was at a steady 210 degrees during KOER, the temp gauge would be well above normal. A quick way to check that theory would be to clear all codes, and perform a KOEO self test with the engine cold, and the air temp 65 degrees or warmer. If a code 21 comes up, then the ECT is saying that the coolant temp is below 50 degrees, which wouldn't be true if the air temp is 65 or above, indicating the ECT is reading below actual. This would still trip a code 21 during KOER, though. What was the engine temp when the KOEO self test was done? What was the engine temp when the KOER self test was done? Take care ~Chris ------------------ Retired Moderator MustangNet My site: JimPorterRacing RACECAR spelled backwards is RACECAR HEY !!! Are you ASE Certified ??? If you are, ask me about iATN. The best tool you'll ever have, and it's free !!!

09-27-2001, 01:39 PM	#7
Capri306 Moderator Join Date: Sep 1998 Location: Grand Rapids, Michigan, USA Posts: 1,001	Exactly. I was just making sure we're on the same wavelength by bringing up the possibility of a 'lying' sensor. ------------------ Capri306, Moderator, The Mustang Works Online *"PROUD TO BE AN AMERICAN!!!"*

09-27-2001, 11:30 PM	#8
jimberg Registered Member Join Date: Oct 1998 Location: Rogers, MN Posts: 2,089	Okay, I guess I'll throw in two more cents. There are two coolant temp sensors. One is just for sending the temp to the gauge (The one that 95Mustanggt referred to) and the other is used by the computer (ECT). I'm not sure if there is some confusion about that. The one that PKRWUD and Capri306 are talking about is the one that has a multiwire connector, not the one with a single wire connector on a peg. An ECT is about $35 so I would just replace it and see what happens. ------------------ 351W 89 Mustang GT Convertible

09-28-2001, 07:30 AM	#9
PKRWUD Junior Member Join Date: Mar 1999 Location: Ventura, California Posts: 8,981	Thanks Jim, now I'm totally mixed up. Okay. 95mustanggt- Are you referring to the temp sensor or the temp sender? The sensor feeds info to the ECM, and the sender operates your temp gauge. If Jim is correct, and the point I was making wasn't in the ballpark of what you were looking for, let me know. In fact, just ask it again, but a little more specific. Take care ~Chris ------------------ Retired Moderator MustangNet My site: JimPorterRacing RACECAR spelled backwards is RACECAR HEY !!! Are you ASE Certified ??? If you are, ask me about iATN. The best tool you'll ever have, and it's free !!!

09-28-2001, 10:12 AM	#10
95mustanggt Registered Member Join Date: May 2000 Location: Kamloops, BC Posts: 2,875	I'm sorry, it would be the Sensor that the ECM uses. I would guess that the ECM thinks that the temperature is colder than the car actually is and therefore keeps the timing more advanced that it should be. Where is the ECM ECT Sensor. The gauge temp sender is just behing the distributor, right? ------------------ 1995 Mustang GT

09-28-2001, 12:14 PM	#11
PKRWUD Junior Member Join Date: Mar 1999 Location: Ventura, California Posts: 8,981	behind the t-stat housing. I don't believe the ECT is at fault, but go ahead and replace it and see. If it's bad, though, you should be getting a code 21 (code 116 or 118 for a '95). Your first entry in this thread says the engine is running hot, but great, and it's not detonating. So what are we after? Take care ~Chris ------------------ Retired Moderator MustangNet My site: JimPorterRacing RACECAR spelled backwards is RACECAR HEY !!! Are you ASE Certified ??? If you are, ask me about iATN. The best tool you'll ever have, and it's free !!!