1993 Saturn SL1 hot no-start & battery V issue

CARENTHUSIASTTHANKS

MEMBER
1993 SATURN SL1
208,000 MILES

'93 Saturn SOHC SL-1 TBI (single injector) 5-sp MT 207k miles

When the coolant level on the dash rises above the mid point – engine is hot - and when the car is turned off, and then sits for 22-25 mins, it won't re-start hot. Starts cold every time - though first time cold perhaps with a slight delay followed by a 'let's get this thing going kick.' Runs great (once started)! Starts hot if re-started within 2-5 min.S Starter turns fine (and is new). Solid spark on both coil packs and all 4 wires (all new, including ign mod ground bolts). Fuel pressure is SOLID, UNWAVERING 29.5 PSI at idle (spec is 26-31) - and, again, car runs great! Fuel pressure goes to 28 or 27 as soon as car is turned off. Fuel pressure decays 6 PSI down to 22 or 21 within 5-6 min.S after car is turned off and down to 16 PSI within 15 min.S and down to 14 PSI within 21 min.S BUT, successfully, when putting key into RUN position, the pressure immediately goes back fine to 30 (29.5) for the 3 seconds the Fuel pump runs in RUN. Gas cap new. When hot no-starting, no fuel coming out of the injector. CPS, CTS, IAT, and TPS test fine - cold and hot. Ign switch tests fine (cold) and is new. Fuel pump fuse and fuel pump relay test good - and fuel pump runs each time key put into Run and Start - which also validates ign switch is sending Run and Start signals to ECU and ECU is processing them. No check engine light. No codes - this is the old ALDL connector at the driver's left knee. Check engine light does illuminate during start - which also validates ign switch Start position is getting to the ECU. Ign Mod input V and Bypass mode V (back to ECU) test fine - and ign mod appears to be in Bypass Mode (0 Vs) at start - both cold start and hot start. Ign mod appears to transition to Ign Control Mode (4.81 Vs) once car starts - both cold and hot.

Also, perhaps related, battery V never stays in the 12.6 range once car sits overnight. Solid 14.5x to 14.6x after starting (alternator) and solid 14.10 after trips and charging periods. But, after turned off and sits for several hours and then overnight, battery V falls through 12.7x range, falls through 12.6x range and into 12.5x range and sometimes 12.4x range. Battery, starter, alternator, and alternator-to-starter fusible link cable all new. Checked all fuses electrically for current draw. Found modest draw through chime fuse and radio, but when I disconnected them overnight, the V drop still occurred at the battery. Checked all relays electrically - none stuck on - and none warm to the touch when car off. BUT, I did see a modest 0.06 V on the primary side of the fuel pump relay - on the coil side. When I checked this V through the multi-meter to a ground, the modest V went to 0.00. Fuel pump gives no evidence of running when car is turned off.

Questions - could you please answer each one:

What is 'causing' the hot no-start?

What part(s) need to be replaced - for the hot no-start?

'Why' does car start cold every morning?

What is 'happening' during the 22-25 min.S when the car is turned off hot?

What is happening overnight - that enables the car to start cold the next morning?

Why is the fuel pressure solid at the schrader port right there at the throttle body - just inches from the fuel injector - when back in Run position, but the car then not start?

If it's the fuel pressure regulator leaking, then why does car run great once started? How this can this be? Can you explain this?

How can the injector not be getting or outputting the fuel - it IS clicking -when hot no-start - since the fuel pressure when back in Run position goes right back to 29.5 (spec)?

Could the Fuel filter be the problem by itself - it is 5 years old - but noly 20k miles? If so, can you explain this?

Why is the battery V drop occurring through the 12.6 range into the 12.5 range?

Is the battery V drop related to the hot no-start problem?

Is the modest 0.06 V on the fuel pump relay primary (coil) side a concern - or is this too neglible to affect anything?

Thank you!

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Saturday, October 12th, 2013 AT 7:41 PM

18 Replies

SATURNTECH9

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When it doesn't start it cranks but won't start? How did you test the coolant temp sensor details please?It sounds like a bad coolant temp sensor to be with the symptoms you have of the no start when hot.I have replaced tons of them for that. Try holding the gas pedal all the way to the floor when it won't start while cranking it to start. The coolant temp sensors fail often on those cars.

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Saturday, October 12th, 2013 AT 9:01 PM

SATURNTECH9

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I have seen those sensor read over a hundred degrees off reading too cold versus actual temp. They always read too cold when they fail. You won't see it on the temp gauge because they use a separate temp coolant temp sensor for the gauge. The gauge ones don't go bad often.

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Saturday, October 12th, 2013 AT 9:06 PM

CARENTHUSIASTTHANKS

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Yes, the starter turns fine. It is new. On the CTS details, yes, I tested the CTS several ways and with a new one. Specifically, first, by ohm'ing it, in place on the block - when cold and hot. It was per spec under both cold and hot. I never saw it erroneous, when I felt I was on the pins. Second, I also tested the connector for V. It was per spec. Third, I also disconnected the CTS connector and connected it to a BRAND NEW CTS that came from room temp - and its reading was per spec - and I tried starting the car hot 3 times with this new CTS connected. The first time I held the connected-up new CTS in my fingers and held it against a piece of metal in case the CTS needing ground contact (similar to it sitting in the block). No hot start. Exact same symptom - no hot-start 22-25 mins after car turned off, starter turning, good spark, no fuel out injector. Second time I just laid the connected-up new CTS on a towel to keep it from dangling and still no hot start. Exact same symptom. The third time I left the connected-up CTS in the exact same place on the towel and I walked over to the pass's side and looked down into the throttle and the hot no-start occurred for a brief period during which there was no fuel coming out the injector and the throttle plate was still dry - and then a little bit of fuel finally did come out and the car started and then the injector went to its run-time atomization. Since the connected-up new CTS was showing colder (room temp) than the hot one still in place, I figured that was a great test ruling out the CTS as the culprit. The brand new CTS tested ohms per spec afterwards also. Finally on the CTS, the original CTS was replaced - 5 years ago. On a separate occasion, yes, I did also try pushing the gas pedal all the way to the floor and it did not start. At one point, I tested the TPS and it tested fine - cold and hot - but I replaced it anyway - same no hot-start results original and new TPS. So, again, there is spark on both coil towers (new) and all 4 wires (new) and the F.I. Did click during the hot no-starts on the occasions when I had my stethoscope directly on it. I also connected up a BRAND NEW F.I. (And held it in my hands) and it clicks also. I took both of these F.I. Clicking tests to mean the ECU is trying to get it to open and close (pulse) to let the gas flow through. I took this also to mean the ign mod must be sending the ref high and ref lo and ref 6x signals to the ECU (ign mod new also). Again, the fuel pressure did decay per the data in the original post on the occasions when I measured it, assuming my gauge wasn't the cause.

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Sunday, October 13th, 2013 AT 7:49 AM

SATURNTECH9

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I already explained this to you but hear goes again. Plugging new coolant temp sensor into a hot engine then not screwing the sensor into the head so it reads air temp instead of actually a hot engine temp. Doesn't rule anything out. Say the coolant temp is 200 degrees. Now you unplug the coolant temp sensor and plug in the new one that is reading air temp which is say 90 degrees back to the computer. That's what I was telling you happens whenthe sensors goes bad. They read colder then actual coolant temp. So now the computer thinks the engine is colder then it is and adjusts to give more fuel then a hot engine is given. So you just created a problem with your air temperature reading back to the computer when the engine is hot. When you checked the ohms of the sensor was it installed in the head and the coolant was cold and when the coolant was at about 222 degrees?Also when you measured the ohms of the sensor did you measure the actual coolant temp to compare it to your ohms readings?Also do you have a scan tool that can read live data on the car like coolant temp etc?

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Sunday, October 13th, 2013 AT 1:32 PM

CARENTHUSIASTTHANKS

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I wish we could talk voice-to-voice for just 5 mins. Anyway.

Yes, I completely get your point on the temporarily-connected new CTS registering air temperature when I plugged it in (and just had it laying on the towel). That is why I did that. The intent was to see if the ECU 'would see' the colder temp so it 'would open' the injector more - increase the pulse width - so I could see the fuel coming out of the injector (finally). When it didn't start the first or second tries and then when I walked around to the pass' s side on the third try and looked down into the throttle and it still didn't start at first but then some small amount of fuel did finally begin to come out and then it did start - and ran great, I just figured 'well, it can't be the CTS, after 3 failed tries then, because there was still no fuel and the throttle seemed dry - even when the CTS is saying it is cold and the ECU should be commanding more fuel.' I saw no additonal fuel. In fact, every time I've looked during the hot no-starts, there has been no fuel coming out of the injector and the throttle plate is dry.

Aren't you (also) saying a false colder-than-true CTS reading should result in more fuel coming out? I'm not seeing any on the hot no-starts.

Or, are you saying a false colder-than-true CTS reading 'coupled with' an actual (higher-temp) IAT reading is confusing the ECU causing it to have a table-lookup problem in its parameters that then prevents it from opening the injector?

When it does not start hot, I 'can' hear the injector clicking. And, the test light on the injector at its ECU control pin does show flashing.

So, under these two facts (clicking and flashing), shouldn't there be some fuel coming out?

Also, if the CTS is false signaling (colder temps - or even higher temps), why did the car start up and 'continue' to run when I poured gas in the throttle?

Once the CTS signals bad, would it not have stayed bad just moments later?

On your next question, yes, I checked the ohms while the original CTS was in the head (still is) - and when the car was cold - and when it was hot - and compared with my infrared gun. The ohms cold and hot equalled what the actual coolant temp was.

You asked about 222' specifically also. Well, when hot - right after one of the hot no-starts - the ohms were below 200 ohms - 19xish as I recall - indicating we were over 200' and the coolant was.

At no point did I see CTS ohms go to zero - indicating a short - extra high temp - which I was looking for, figuring then the ECU wouldn't open the injector hardly at all (which, in fact, is what I was seeing down in the throttle body).

At no point did I happen to see a CTS colder than I would have expected.

On your last question, no don't have a scan tool for this older ALDL configuration (I do for the modern OBD-II systems though).

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Sunday, October 13th, 2013 AT 3:12 PM

SATURNTECH9

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I have never looked to see how much fuel was being delivered when the coolant temp sensor was reading a colder temp versus a hotter temp. So I cant say if you could actually see a visible difference.I do know when the sensors go bad they always. Read colder then actual Temp never hotter then actual temp.I have replaced tons of them.

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Sunday, October 13th, 2013 AT 3:37 PM

CARENTHUSIASTTHANKS

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Okay, I am going to replace the CTS tomorrow. I would love - after all this work and on-car electrical testing and checking - for it to be the CTS. If it is, I owe you a cold one. Or a cold six pack.

Is it your experience on these 93 Saturn SOHC SL-1s that when the cars do not start hot - and it is the CTS failing - that there is NO check engine code set?

Any idea why they didn't set a code indicating a delta between what the ECU was seeing CTS-wise and IAT-wise - to at least flag that one of them may have been out-of-sync.

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Sunday, October 13th, 2013 AT 4:05 PM

SATURNTECH9

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Yes I have seen a lot of bad coolant temp sensors cause the engines to not start. Also they usually don't set codes. Sometimes they will set a code 74 if memory serves correct been a while on one that old. It's a ratio error code for the sensor but that's rare it will set. The obd2 cars will set a P0711 code rarely indicating there a ratio error between the coolant tempo and transmission temp. But again that is the exception not the rule. The worse part is you don't have a scan tool to see what the computer is reading when it hot and not starting. Like tps map coolant temp sensor etc. Most of the time if you have fuel pressure and spark with a hot no start its the coolant temp sensor. You are looking at the bottom sensor with two wires going to it with a black wire and yellow wire as the coolant temp sensor correct?I only ask because I have talked to some many people that were mistaking the top sensor for the coolant temp sensor.

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Sunday, October 13th, 2013 AT 4:33 PM

CARENTHUSIASTTHANKS

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Yes, the 2-wire yellow and black. The 1-wire (closer to the radiator) is the dash one. And, the IAT sensor is the same part as the CTS. Both of which I'm sure you're aware of.

Now you say most of the time when there's fuel pressure and spark, it's a failing CTS. But, recall, I'd mentioned the fuel pressure is solid, unwavering at idle (29.5, with spec 26-31), goes to 28 or 27 when turned off, then slowly decays 6 psi within 5 to 6 mins to 22 or 21, then decays to 16 after 15 mins, then decays to 14 around 21 mins. But, then as soon as I go back to Run, the pressure immediately goes back to 30. So, I thought you might have said originally the decay is creating a fuel pullback effect and hence a vacuum vapor lock condition when the engine is hot that might be causing the no fuel at the injector. No question here, just the reminder, just in case the CTS doesn't solve the no fuel at hot start problem, tomorrow.

Will let you know tomorrow on the CTS replacement. Thanks for everything thus far!

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Sunday, October 13th, 2013 AT 5:02 PM

SATURNTECH9

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The fuel pressure decay could just be the fuel pressure regulator bleeding down etc.I have seen some vapor lock very rare on those cars. You could remove the gas cap on a hot no start to rule that out. Actually on that car the air inlet temp sensor coolant temp sensor and transmission temp sensor are all interchangeable.

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Sunday, October 13th, 2013 AT 5:16 PM

CARENTHUSIASTTHANKS

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We're thinking alike again. I had removed the gas cap and the car still did not start hot. And, there was no hiss. Hence, why I replaced the gas cap. Still same result. (My Nissans always hiss and, when I tested their gas caps, their inches of water actually rose from 28 to 38 over a period of minutes. I remove them and let the vacuum release every couple of days, especially when it's hot outside.)

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Sunday, October 13th, 2013 AT 5:26 PM

SATURNTECH9

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Keep me posted looking forward to that six PAC lol.

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Sunday, October 13th, 2013 AT 5:51 PM

CARENTHUSIASTTHANKS

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Installed new CTS. Still no hot-start 22-25 min after previous turn off (after dash coolant level was slightly above 1/2 mark - engine had been hot). Still no fuel coming out at F.I. During the hot no-start. Still can hear fuel pressure with stethoscope on F.I. When key goes to Run. Still can hear F.I. Clicking while key goes to and stays in Start. Starter still turning. Still have spark. Re-verified new CTS ohms right after hot no-start and they still matched infrared gun coolant temp in reservoir (and on head just above CTS and right there in the recess area where CTS sits) (as previous CTS had). Still have same original questions, if you would please re-read the original post. I think the answer lies in one of my questions. Thanks!

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Monday, October 14th, 2013 AT 1:54 PM

SATURNTECH9

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I just read thru all your prevous questions and don't see the answer there. So the car never stalls after its warmed up and doesn't restart?It only has a problem when the engine is warmed up and you turn it off for more then 5mins then it wont start?Till 20-25 mins later till it cools down then it restarts no problem?This is a interesting one for sure I would really like to see some live data from the computer when t wont start. When it wont start do you have a nice blue spark?ALso if you prime the throttle body with a with a little carb spray will it start and run from there?

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Monday, October 14th, 2013 AT 4:57 PM

CARENTHUSIASTTHANKS

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On your first question: Correct - it never stalls. On Q2: I think you're saying what I'm saying. But, just to be sure (to clarify). The car starts cold every time (though with a bit of a momentary delay when it has sat overnight). If recently turned off within 5 minutes or so and still basically cold, then no delay and prompt, good start. Always the car runs great. (No stalling, no hesitation, none of that - never at any time). The car has no issues while its going down the road. Drives and runs great! Once she starts, she's great. The only time there is a problem: after the car has been driven and it has heated up (to the mid-point on the dash gauge - engine hot) and it is then turned off (meaning everything is fine up to that point) and then sits for at least 22-25 minutes, then at the 22-25 minute mark it will not re-start (hot). When it fails to re-start, with the stethoscope placed on top of the F.I. One can hear the fuel pressuring (somewhere in the throttle body or inlet pipe or F.I. Or outlet pipe or some or all of these) when the key is put into Run, then one can hear the F.I. Clicking (still with the stethoscope on top of the F.I. - Same spot) when the key is turned to Start - and throughout the duration of the key in Start, there is spark, and the starter is turning fine. But, no fuel comes out of the F.I. And, then it can't start without the fuel - and doesn't. It also is true when the hot car is turned off and only sits for 5 minutes or so, it will restart. But, let it sit for 22-25 minutes or more up to an hour or more and then she won't re-start. Yes, after a period (presumably cool down period) then she starts again (less hot or cold, as the cases may be). On Q3, yes, there is nice solid spark - I'm color blind so I can't tell you the color. On Q4, yes, when I poured gas down into the throttle, that enabled it to start and it did run from there. I didn't use carb spray per se. I just poured in some gas. It had failed to start hot 5 times in a row prior to the gas being poured in. It had been on the highway for a good run prior to these 5 hot no-starts - and was probably very hot. This 6th time the poured in gas got the engine going and then the F.I. And everything did their things from there.

Now I do want to also clarify the clicking at the F.I. During the hot no-start may not be the same 32nd-note cadence or 64th-note cadence when it's running on its own. But, it IS clicking.

I also should clarify that when the car is cold, the stethoscope sound of the fuel pressuring is different than when it is hot no-start - I would describe it as easier to hear as though it is moving more freely filling in the pipes, filling in the throttle body, going right to the injector - can hear that very nicely, and the return line pressurizes also and even lifts up just a smidge (letting you know the fuel is pressurizing in there). When hot, not quite as easy to hear, but can be heard.

I also should clarify that if you go to Run key position (and hear the pressuring) (fuel pump clearly running) and wait for the full 3 seconds, it does what it should and then stops. Every time. Then if you go to Acc(essories) key position, you can stethoscope-hear a very brief momentary fuel bleed-off. Just a fthhzz. Just an instant. I think that correlates to the solid 30 PSI in Run going to 28 or 27 the instant the car is turned off (out of Run). Then, if you go back to Run, pressuring occurs again. Then, Acc same brief relief. Repeatable.

I also should clarify that on several of the failed hot no-starts, after not starting hot multiple times in fairly rapid succession - say 4 to 5 times within 2 to 3 min.S - I was able to see an eensy bit of fuel finally come out the F.I. (On the last try). Then, it would start - this fuel would catch - and then as you say, it runs from there. And, runs great.

So, with everything you know about the first-gen Saturns, and all of this, whaddaya think is going on?

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Monday, October 14th, 2013 AT 6:50 PM

SATURNTECH9

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It sounds like when its hot it doesn't deliver the fuel shot to start. Since you said it will start hot with a prime and run fine from that point on.I would really like to see the computer inputs when its hot and won'tstart. THats the first thing I would have looked at a long time ago.

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Monday, October 14th, 2013 AT 8:35 PM

CARENTHUSIASTTHANKS

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For others who happen upon this web site and have similar symptoms and similar conditions.

Update approx. 2 weeks later:

The hot no-start problem was vapor lock caused by the throttle body's original fuel pressure regulator leaking.

The original Saturn regulator on the SOHC TBI engines had a ball-in-socket design that enabled the end opposite the socket to pivot over the return hole in the firewall-side of the throttle body. Over time this wore out.

The aftermarket regulators used a different design, just for info.

So, on the '93 Saturn SL-1 SOHC TBI, the hot no-start, with operational starter, with operational ignition - spark, with operational injector - clicking away, with operational CPS, CTS, TPS, and IAT, with no check engine code(s), and with fuel pressure decay, failing regulator-induced vapor lock.

When replacing the regulator, loosen each of the qty 4 T15 torx bolts evenly. Then, when installing the new one, insert the regulator's seal into the groove in the throttle body, align the regulator housing with the inner cap and spring on the new regulator, and push the housing in against the spring while quickly inserting each of the 4 bolts and evenly tightening.

Hope this helps. And, good luck.

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Monday, October 21st, 2013 AT 7:47 PM

SATURNTECH9