Has run alright, suddenly will crank but not start.

1996 SATURN SL1

156,000 MILES

FRANKE

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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.

Dec 11, 2011 at 12:53 AM

SATURNTECH9

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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.

Dec 11, 2011 at 12:58 AM

FRANKE

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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.

Dec 11, 2011 at 1:10 AM

RASMATAZ

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Test the wiring back to the computer

Images (Click to enlarge)

Dec 11, 2011 at 1:14 AM

SATURNTECH9

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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.

Dec 11, 2011 at 1:24 AM

SATURNTECH9

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If the computer doesnt get the correct coolant temp reading then it will cause surging overheating dieing no starts all kinds of different symptoms.

Dec 11, 2011 at 1:27 AM

FRANKE

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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??

Dec 11, 2011 at 1:38 AM

FRANKE

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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.

Dec 11, 2011 at 1:49 AM

SATURNTECH9

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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.

Dec 11, 2011 at 1:50 AM

SATURNTECH9

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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?

Dec 11, 2011 at 1:55 AM

FRANKE

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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.

Dec 11, 2011 at 2:02 AM

FRANKE

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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??

Dec 11, 2011 at 2:04 AM

SATURNTECH9

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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.

Dec 11, 2011 at 2:18 AM

RASMATAZ

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He probably fried the computer during the inaccurate testing

Dec 11, 2011 at 2:30 AM

FRANKE

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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.

Dec 11, 2011 at 2:31 AM

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.

Dec 11, 2011 at 2:36 AM

RASMATAZ

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The coolant temperature sensor voltage drops as the engine warms up-test this

Dec 11, 2011 at 3:00 AM

FRANKE

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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.

Dec 11, 2011 at 3:06 AM

SATURNTECH9

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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.

Dec 11, 2011 at 3:07 AM

FRANKE

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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.

Dec 11, 2011 at 3:09 AM

SATURNTECH9

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So your ready to replace the pcm without testing the return wire back to the pcm with the ohms meter?

Dec 11, 2011 at 3:10 AM

FRANKE

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Any idea what ohms I might expect across the ECT connector terminals considering it goes through the PCM? I'm not trying to get rude or short with either of you, I only guess that the wire is not open from the PCM to the ECT due to the presence of the expected 5 vdc.

Dec 11, 2011 at 3:17 AM

SATURNTECH9

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You are correct the 5v refrence wire is good it goes thru ect and then back thru the return wire.Depending on the resistance of the ect is how much voltage goes back down the return wire to the pcm.We know the refrence wire is good but the return doesnt look so good.You also connected the refrence to the return and what did the temp gauge read?The same as the ect when its unplugged.I have only worked for saturn repairing these cars for over 16yrs so i think i know a little something about these cars.

Dec 11, 2011 at 3:34 AM

FRANKE

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I already told you that the gauge shows midrange with the connector connected to the ECT (engine hot or cold), with it not connected to the ECT, and with the terminals jumped together (shorted back to the PCM as you suggested). I am glad you were online to help me, I think I got the best possible person, and I am trying to do and answer you the best I can. Is there anything I have not done or answered you? I cannot buy an ECT sensor until tomorrow, though if jumping the terminals makes no difference. do you suspect that replacing the ECT sensor will change anything?

Dec 11, 2011 at 3:43 AM

FRANKE

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Looking at the wiring diagram in my chilton's manual, the PCM appears to be the only active component between the ECT and the temp gauge. I'm afraid the problem is in the PCM. It may have been a problem in the PCM since I bought the car, but something changed drastically yesterday. If it is not the temp circuit what else can I check?

Dec 11, 2011 at 3:49 AM

SATURNTECH9

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If the sensor reads 0 ohms its bad and needs to be repalced replacing it isnt going to fix the incorrect reading back to the computer.Heres what you need to do next unplug the ect then unplug the pcm then measure the ohms reading from the ect connector terminals of the return wire not the 5v one to the return wire at the pcm connector.Let me know what your readings are.

Dec 11, 2011 at 3:52 AM

FRANKE

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Might it be the Crankshaft Position Sensor? If so, where is it physically located? Is it easier to get to from the top or bottom?

Dec 11, 2011 at 3:52 AM

RASMATAZ

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Maybe the temperature gauge is out of calibration-who knows

Dec 11, 2011 at 3:55 AM

SATURNTECH9

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You have spark that means your crank shaft sensor is good and that would have nothing to do with the temp gauge readings.When the ect is unplugged the temp gauge defaults to just below half way on the temp gauge.Please do what i asked you to check and get back to me.

Dec 11, 2011 at 4:03 AM

FRANKE

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So the gauge may be disconnected from the PCM and this may have nothing to do at all with the car not starting? I found the PCM and there are a lot of wires on three connectors. All I know is the wires from the ECTS are black and yellow. I will track them down and post my findings tomorrow. Thank you for the info about the crankshaft sensor, I am learning more by the minute. I hope to hear back from you after I post again.

Dec 11, 2011 at 4:30 AM

SATURNTECH9

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Your not understanding this that ect reads the temp reading for the pcm and the pcm displays the temp on the gauge.The readings of the temp gauge tips off that the pcm is not getting a reading from the ect.If you cant find the correct wires let me know and i will find you some info on them.

Dec 11, 2011 at 4:39 AM

FRANKE

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I do understand that the ECT is the sensor that provides a resistance to the PCM based on the temp of the coolant in the block, then the PCM regulates the other parts accordingly and display the appropriate reading on the temp gauge. I also understand if the PCM is not getting a resistance from the ECT, it will jump to just below mid-range and sit there. I found a pin out of the PCM connectors for a 1993 Saturn, but the wire colors do not correspond, so I'm not sure the pin #'s it says go to the ECT are correct, and I'm not sure which jacks are 1, 2, and 3.. There are two blue connectors side by side and then only one brown connector is used and one empty.

Dec 15, 2011 at 6:26 PM

SATURNTECH9

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Lets do this go to the black wire at the coolant temp sensor connector take your ohms meter at the black wire and tell me what the readings are between the black wire and chassis ground?

Dec 15, 2011 at 9:28 PM

FRANKE

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It is a short..bounes between 2 & 3 ohms..

Dec 15, 2011 at 9:35 PM

SATURNTECH9

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Now unplug the connectors to pcm and check it again and let me know what it reads?

Dec 15, 2011 at 9:41 PM

FRANKE

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With all 3 connectors off and measuring ohms from the black wire of the ECT connector bounces all over the place.. from opent to 4 meg, into the kilo range and back around.. will not sit still..

Dec 15, 2011 at 10:05 PM

FRANKE

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7The wires do not line up with the 1993 PCM diagram I found.. not by color, nor by the wires being used in the connector.. I'm pretty sure this car was originally a throttle body injection (vin 8) and a MFI engine (vin 7) was put in.. I'm sorry I did not say that before..

Dec 15, 2011 at 10:12 PM

SATURNTECH9

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A history lesson on the S model single cam engine from 1991-1994 they had throttle body injection.Then from 1995-2002 they went to multiport injection on the single cam engines.Alright with the pcm unplug measure the voltage across the coolant temp sensor between the yellow wire and black.Let me know what the readings are?

Dec 15, 2011 at 10:43 PM

FRANKE

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Hi SaturnTech,
I took Christmas off of working on the car. I hope your Christmas was good. With all 3 connectors off the PCM, I measured voltage between the black & yellow wires, and from each wire to common and they were all zero. I suspect that is what they should measure with the other end disconnected. I did it with the key on and the key off with no change. I never could find the other end of the ECT wires at the PCM connectors.

FrankE.

Dec 29, 2011 at 6:23 PM

FRANKE

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I can tell you for sure it was a single cam engine originally and it now has a twin cam 16 valve engine. Could a different PCM configuration cause any of these problems? I think I can get a twin cam PCM from a U-pull it yard and see if that changes anything. It may be cheaper than taking it to a shop, which i may have to do after the new year to get this running in time for school to start.

Dec 29, 2011 at 6:32 PM

SATURNTECH9

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Wait a minute did you just say you have a SL1 car that someone put a SL2 twin cam engine in?Because after all this talking with you you failed to mention that fact to me.

Dec 29, 2011 at 6:46 PM