Unusual FYI


#1

Thought some of you might be interested in this oddity and make a mental note of it. Go figure.


#2

Darn. I Can’t Do Videos! I Don’t Have The Technology.

Give folks a chance to see it, then somebody’s going to have to let me know what’s going on… please?

CSA


#3

For CSA’s benefit… Taurus DOHC V6, crank but no-start. Crankshaft position sensor shows an output. The scan tool shows 14 degree coolant temp with a 4 volt output during a mild temperature day. Far too low for the conditions. New coolant temp sensor and the car fires right up.

Huh? A LOW temp sensor reading prevents a start? Cars start at 14 degrees coolant temp all winter. Possibly the signal voltage was way out of range? Maybe it compares to the air temp sensor and prevents a start if they are too far apart? Interesting failure mode.

Thanks for the post @ok4450, gotta think on that one some more.


#4

Very good information. This one will definitely go down in my “bag of details”.
Sincerest thanks for the post. This one will help countless people over time.


#5

Interesting, nice easy replacement for the sensor tough. @“common sense answer” would love to get you video, specs on your system? One thought is download helper for firefox that allows you to download videos and convert them to a format you can use.


#6

@“common sense answer” feel free to PM me if you’d like. I bet if you can get to this website, you have the technology required to see videos. Just needs to be tweaked.


#7

@Mustangman
Thanks, that was great. I like your hypothesis. It’s Better than what I’ve got.
CSA


#8

@Barkydog
I know almost nothing about PCs. I’m running Internet Explorer, IBM Think Centre PC, Windows 7 Premium Home, Intel Pentium, 4 GB Ram, 32 Bit…

The big problem, I believe, is speed. I am on a dial-up modem, landline phone connection, currently at 49.2 kbps.

What do you think? Does any of that mean anything? Any hope?

CSA


#9

CSA: No, you need a high speed connection. I get mine via Comcast, at 60 Mbps, as an example.


#10

You should definitely check in to a high speed connection. I’m running a 20Mbs connection for $35 a month. I’ve often run across people who are still on dialup who are paying more than I do for their connection.


#11
You should definitely check in to a high speed connection.

May not have the option. There are areas in this country that your only option is dialup. We have a few towns in NH…where dialup is the ONLY option.


#12

I know - but it should be checked in to anyway. My mother lives wayyy out there, and thought dialup was her only option until I started looking and found a DSL provider that she never knew about.


#13

My theory, the computer thinks the coolant is at 14 degrees, so it is double pulsing the injectors and injecting a lot of gasoline, which is flooding the engine for the actual air and coolant temperature. It won’t start b/c the mixture is way too rich.


#14

What a yo-yo. There’s nothing unusual about this condition. Faulty coolant sensors cause no start conditions on a regular basis. Sensors are nothing but inputs to the controller. Garbage in, garbage out. And the wiggle test he talks about went out in the 1980’s.

He claims there’s no spark yet doesn’t show us or tell us how he came to that conclusion. If I were a betting man (actually, I am), I would lay down $100 that if the tach is showing RPM on an EDIS system, the coil is firing the plugs. Show us the no spark.

The next clue is the temp gauge. It shows an engine at operating temperature. The scan tool data clearly shows that there are 2 DTCs stored, yet he doesn’t read them or address them as part of the diag. He goes on to show a coolant sensor reading 14 degrees when he states that the ambient temperature is 70 degrees. And this is a mystery?

If you can’t explain or understand that with the fuel mapping and spark advance curve on a late model car, inputting a coolant temp of 14 degrees when the engine temp is actually 190 will make the engine not start, you should put away your toys and go home. The fuel injectors are dumping way too much fuel and the spark is coming way too late to have that engine start and run well.

By the way, why the hood is open during most of this video is a mystery. This diagnosis should have been 90% complete from the driver’s seat without even opening the hood or touching anything. The scan tool has all the info you need. The only thing the hood needs to be open for is to backprobe the sensor wiring with a labscope or graphing meter to verify your driver’s seat diagnosis.


#15

A no-start because of a faulty coolant sensor, or even an air temp sensor, is something I’ve never run across or heard of.

I’ve seen both types of sensors in various failure modes and the engine never failed to start although it did illuminate the CEL.

Are you saying that if I go out tomorrow and disconnect one or both sensors on my Lincoln or Chevy (both OBDII) there will be a no-start?


#16

The following comments are the results of my personal experience and opinions and do not represent the views of this station :slight_smile: haha

I’m saying I am not at all surprised to see a Ford coolant sensor fail open circuit or very low resistance and have a crank, no start as a result. I won’t say it happens once a month, but I will say I’ve seen it often enough that I don’t know exactly how many times I’ve seen it.

I will say I have never seen a stand-alone air temp sensor failure cause a no start.

I’m saying if you go out and unplug the ECT sensor (which should result in a coolant temp input of -40*) and the car doesn’t start I would not be surprised. If the car ran poorly then stalled I wouldn’t be surprised. MAF, TPS, ECT, CKP, and maybe CMP and MAP are the primary inputs to get the car started. Mess with any one of these and you’ll get poor or no results.

What really bothered me about the video (other than that) is that the scan tool was the third or fourth thing checked. You never ever start checking or tugging on things under the hood unless you specifically know what you’re after. At least in a shop setting. It’s one thing for a guy who is trying to figure out his own car to do that, but another for a “pro” to be futzing around like that.


#17

“the computer thinks the coolant is at 14 degrees, so it is double pulsing the injectors and injecting a lot of gasoline, which is flooding the engine for the actual air and coolant temperature. It won’t start b/c the mixture is way too rich.”

That is my theory also, George!
Of course, I could be way off-base, but I think that our shared theory is a strong possibility.


#18

I got the impression he did the full diagnostic before he turned on the camera. He already knew what the problem was and wanted to demonstrate it for the camera, so he didn’t have to go through the whole diagnostic routine.


#19

OK writes …

Are you saying that if I go out tomorrow and disconnect one or both sensors on my Lincoln or Chevy (both OBDII) there will be a no-start?

I’d guess both cars would start with the sensor disconnected. My Corolla starts and runs well with the coolant temp sensor disconnected. But a disconnected sensor is different from an inaccurate sensor. The ECM can tell if the sensor is disconnected or has completely failed, and will adjust its algorithm accordingly to assume some mid-range coolant temperature, after turning on the CEL light of course. A better experiment would be to disconnect the sensor, then place a resistor in its place corresponding to 15 degrees and test if the car would start with the ambient at 85 degrees. This would give an excuse for those in the frozen north for a winter trip to Miami too!


#20

it is double pulsing the injectors and injecting a lot of gasoline

I’d think you get at least a wet cough or 2 trying to start on the first couple of turns of the crank if it was over-rich. Maybe not.

I was a bit confused, like @asemaster to see the coolant temp at 192 when he fired it up after swapping sensors. If it didn’t start, how did it get warmed up? I’d guess that may have been a repeat for the video.