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Has run alright, suddenly will crank but not start.

Tiny
FRANKE
  • MEMBER
  • 1996 SATURN SL1
  • 156,000 MILES
Bought the car used 5 months ago. Seems to have been running good other than recently has been idling high and RPMs slow to go down, will stay up at 3k while shifting (manual trans). Drove somewhere and then would crank but not start after being shut off. Going down the list in the Chilton's manual. Replaced fuel filter and gas pressure to fuel rail now much better. Don't know anywhere further along where I could check fuel. Replaced one bad spark plug wire, all wires and both coil packs pass ohm checks, now spark verified at all 4 wires. Possible bad Engine Coolant Temp Sensor. Temp gauge at mid-range as soon as the key is turned on; but that's not new, has been that way since I bought it. Never kept it from running before. Can't find Crankshaft Position Sensor to check. Is it on the backside down under the fuel rail? PCV rattles properly. Check Engine light has not come on since the day I bought the car. It was on and the mechanic said it was an oxygen sensor. He said he replaced it and the light has never come back on, not even while starting. I do not know if he did something to disable it. I hope it is not the PCM itself. What could cause this sudden problem?

Thank you for any help you can provide.

Frank.
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Sunday, December 11th, 2011 AT 12:53 AM

42 Replies

Tiny
SATURNTECH9
  • MECHANIC
  • 30,870 POSTS
You have a bad coolant temp sensor it shouldnt read half way on the gauge when cold. Replaced the sensor and also inspect the connector to it if the terminals are green or blue instead of silver replace the connector as well. Let me know how it runs after you do what I suggested.
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Sunday, December 11th, 2011 AT 12:58 AM
Tiny
FRANKE
  • MEMBER
  • 20 POSTS
I'm not sure I understand. Should I replace the sensor or not? Especially if you say it cannot be causing the symptoms I have. I put one from a junkyard in today, but it did not change anything. The wires are yellow and black.
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Sunday, December 11th, 2011 AT 1:10 AM
Tiny
RASMATAZ
  • MECHANIC
  • 75,992 POSTS
Test the wiring back to the computer
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Sunday, December 11th, 2011 AT 1:14 AM
Tiny
SATURNTECH9
  • MECHANIC
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I never said it wont fix the symptoms?Unplug the sensor and see if the temp gauge reads dead cold with the key in the run position.I wouldnt use a junk yard sensor they go bad all the time.I have owned my 1999 saturn for 5yrs now and have went thru four of those sensors. If the gauges reads dead cold with the sensor unplugged then replacing the sensor should fix it. Also look at the inside of the connector and make sure the terminals are silver and not blue or green. Those sensors leak coolant into the connectors and corrod the terminals. Also inspect the wires coming from sensor make sure there not melted shorted pinched etc together. Let me know what you find.
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Sunday, December 11th, 2011 AT 1:24 AM
Tiny
SATURNTECH9
  • MECHANIC
  • 30,870 POSTS
If the computer doesnt get the correct coolant temp reading then it will cause surging overheating dieing no starts all kinds of different symptoms.
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Sunday, December 11th, 2011 AT 1:27 AM
Tiny
FRANKE
  • MEMBER
  • 20 POSTS
Have the 5 vdc I'm supposed to on the wires to the ECT. I haven't ohm checked the ECT yet, don't want to take it out and lose coolant and can't get the meter probes on it in place. Can this cause it to not start?
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Sunday, December 11th, 2011 AT 1:38 AM
Tiny
FRANKE
  • MEMBER
  • 20 POSTS
I apologize SaturnTech9, I misunderstood. You mean that it would not cause the midrange deflection? The temp gauge still jumps to midrange with the wire disconnected from the ECT. The terminals look ok, I put small wire in there to measure since my meter leads would not fit in. The wires do not look melted or anything.
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Sunday, December 11th, 2011 AT 1:49 AM
Tiny
SATURNTECH9
  • MECHANIC
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Again yes it can cause a no start again those sensors are a piece of junk and wouldnt trust a junk yard sensor a new sensor is only like 11. SO when you unplug the sensor and the key is in the run position what does the gauge read?If the engine is ice cold and the temp reads 1/2 way is this correct?If so that is a problem I would fix first because that very well will cause a no start. Because the computer thinks the engine is much hotter then it is and not giving the engine the fuel it needs. Also it is possible to measure the ohms while the sensor is in place have done it many times.
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Sunday, December 11th, 2011 AT 1:50 AM
Tiny
SATURNTECH9
  • MECHANIC
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Does it read just bellow 1/2 way when its unpluged?Also is that what it reads when the sensor is plugged in?Does the temp gauge ever move when its running and everything is plugged in?
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Sunday, December 11th, 2011 AT 1:55 AM
Tiny
FRANKE
  • MEMBER
  • 20 POSTS
It has been at midrange (I have not noticed any movement) whether hot or cold. Now I have found that it is the same wire on or off. I measured the ECT sensor, (easier to get to than I thought it would be) and it appears to be dead short, 0 ohms.
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Sunday, December 11th, 2011 AT 2:02 AM
Tiny
FRANKE
  • MEMBER
  • 20 POSTS
But the ECT that appears to be a short is the one I got and put in just today, after it will not start. If there was a problem with the ECT, wouldn't the check engine light come on?
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Sunday, December 11th, 2011 AT 2:04 AM
Tiny
SATURNTECH9
  • MECHANIC
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I have seen tons of bad ects not set one code. SO does the temp gauge read a little below half way with it unplugged or hooked to the ect sensor?Really important I get a answer to the questions I ask because this is hard enough trying to help you over the internet. Then having to ask the same question again and again makes it even harder. Also 0ohms doesnt sound right for the coolant temp sensor reading are you sure the leads didnt touch each other when you were testing it?With the key in the run position if you jump those two terminals together for the ect the temp gauge should read pegged hot.
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Sunday, December 11th, 2011 AT 2:18 AM
Tiny
RASMATAZ
  • MECHANIC
  • 75,992 POSTS
He probably fried the computer during the inaccurate testing
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Sunday, December 11th, 2011 AT 2:30 AM
Tiny
FRANKE
  • MEMBER
  • 20 POSTS
I am trying to give you as accurate and complete of answers as possible. The temp gauge is just below midrange (touching the white line that is midrange) while the engine is dead cold. It does not seem to vary whether the wire is connected or not, nor if the engine is hot or cold. I just jumped the terminals going back to the PCM and the gauge went back midrange again. I'm as sure as I can be that I did not short the meter while measuring the ECT sensor.
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Sunday, December 11th, 2011 AT 2:31 AM
Tiny
SATURNTECH9
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Does the ect connector terminals look corroded?I did ask that earlier. ALso does it look like the ect connector has ever been replaced?It sounds like you have a open circuit between the connector and computer.
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Sunday, December 11th, 2011 AT 2:36 AM
Tiny
RASMATAZ
  • MECHANIC
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The coolant temperature sensor voltage drops as the engine warms up-test this
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Sunday, December 11th, 2011 AT 3:00 AM
Tiny
FRANKE
  • MEMBER
  • 20 POSTS
As I told you earlier, they look ok. It does not look like the wires have been replaced to me. The wires are one yellow, one black and they come out of one of those corrugated plastic wire bundles.

Rasmataz, what do you think may have happened to fry the PCM?

Keep in mind, as I said before, this all started suddenly while I was out on errands. It ran fine other than the high idling and staying high when I initially let off the gas, and then it just would not start after it had been shut off. I initially checked all the fuses concerning the the fuel system and PCM I could find. The 5 vdc is getting to the connector that goes onto the ECT from the PCM. I wish I could tell you more about what the guy I bought it from might have done, I suspect he was messing with the check engine light or something enabling it.
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Sunday, December 11th, 2011 AT 3:06 AM
Tiny
SATURNTECH9
  • MECHANIC
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As the coolant temp sensor gets hotter its resistance value gets lower so that would mean the hotter the coolant gets the higher the voltage return to the computer.
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Sunday, December 11th, 2011 AT 3:07 AM
Tiny
FRANKE
  • MEMBER
  • 20 POSTS
Rasmataz, The engine will not start. I do not see how I can test the voltage with the engine warm. And from my reading, it is the resistance of the ECT that decreases as the engine gets hotter. I jumped the terminals on the wire connector as SaturnTech9 suggested and the gauge still went to midrange.
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Sunday, December 11th, 2011 AT 3:09 AM
Tiny
SATURNTECH9
  • MECHANIC
  • 30,870 POSTS
So your ready to replace the pcm without testing the return wire back to the pcm with the ohms meter?
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Sunday, December 11th, 2011 AT 3:10 AM

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