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Old 11-12-2018, 11:01 PM   #1
ianh
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1997 SL2
Default Stalling at start up when engine is hot

Hi everyone,

I have a 97 SL2 that has been stalling at start up but only when the engine is already warm. I'm curious to hear if anyone else has seen anything like this before.

When restarting after the engine has been running for a while then left off for a little while (a few minutes to maybe an hour or two), the motor will start, sputter, then die. If I try turning the key another time or two it sputters some more and then starts and runs normally. When it has one of these bad starts the RPM's jump to around 1100 (normal max for warm start up from what I've seen) and then just drop down and die with some sputtering around 300 RPM instead of settling in at idle speed like it should. After a few tries it runs fine. This is only with warm starts. Cold starts are working perfectly fine. The idle is currently fairly steady at just above 800 once it actually gets running. The car has 129k miles. I think the engine has also been shuddering slightly on acceleration lately, though that's hard to measure in any definite way.

I've already done the ECTS and Thermostat. The spark plugs are also recent. I did the rear O2 sensor around a year ago and will be doing the front one soon since it's an easy and inexpensive fix that might help with the stalls. The power steering pump is a noisy refurbished one and isn't doing well, so it could be putting a load on the engine at start up, but that wouldn't explain why it runs perfectly well after trying another time or two. My next best guess is the fuel injectors having leaky seals and flooding the engine, but that's just a wild guess at this point.

Any ideas on what's going on?

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Old 11-13-2018, 01:38 AM   #2
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1997 SL2
Default Re: Stalling at start up when engine is hot

Thats just your fuel pump. The 97s had a faulty fuel pump (pressure regulator specifically I think) Happens to mine and I think everyone else here who also has a 97. An easy fix is turning the key to RUN and listen for the fuel pump. It will be a light hum coming from the back of the car. Once it stops after 4 or 5 seconds, then try starting the car. You could also replace the fuel pump itself for a more permanent solution, but thats a lot more work imo than just waiting a few seconds for the pump to prime.

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Old 11-13-2018, 11:51 AM   #3
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Default Re: Stalling at start up when engine is hot

Right, I had heard about the issues with the 97 fuel pumps and have been giving it a little time for the fuel pump to prime. Priming does help a bit with both cold and hot starts, but it doesn't fix the stalling I'm describing here. This only happens when the engine is already hot. I'll experiment with it some more over the next few days though to double check that I'm actually giving it enough time to pressurize the system.

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Old 11-13-2018, 12:09 PM   #4
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Default Re: Stalling at start up when engine is hot

I would take a look at the IAC/TPS area. Either clogged with carbon stuff, or that the IAC (Idle Air Control) valve is going bad. Not much money and not hard to replace either or both of them.

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Old 11-13-2018, 01:02 PM   #5
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Default Re: Stalling at start up when engine is hot

Automatic fuel pump operation to prime the fuel rail runs for two seconds whether the engine is started or not.

1-Mileage of this car?
2-Fuel filter ever replaced?

A better assessment possible fuel system issues is to connect a fuel pressure gauge and monitor pressures at several points; startup, idling, and when engine starting fails. Autozone and Advance Auto are two places for free loaners.

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Old 11-13-2018, 01:25 PM   #6
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Default Re: Stalling at start up when engine is hot

Mileage is 129000.

The fuel filter was replaced recently (at around 122000, I think).

The throttle body, idle air control valve, and throttle position sensor are, to the best of my knowledge, original, so at the very least some cleaning is in order.

I don't own a gauge for testing, but I'll try a loaner and see what info I can get.

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Old 11-13-2018, 01:36 PM   #7
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Default Re: Stalling at start up when engine is hot

How old (in miles) are the spark plug wires?

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Old 11-13-2018, 02:28 PM   #8
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Default Re: Stalling at start up when engine is hot

Plugs and wires were both replaced around 5000 miles or 1 year ago. For some reason I didn't write down the exact date and mileage, but they definitely have no more than 7000 miles on them.

We did the aluminum valve cover mod around the same time so we used DELPHI XS10256 wires. There had been issues with oil leaking into the plug wells, even with a newly replaced gasket, so we opted to pull an aluminum valve cover off a 93 SW2 at the junk yard instead of fighting with the plastic one any more.

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Old 11-18-2018, 12:12 AM   #9
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Default Re: Stalling at start up when engine is hot

Alright, the last few days have been hectic, so I still have some more diagnosing to do. Thus far I have replaced the front O2 sensor. While that seems to have the car running slightly better generally, it hasn't changed anything with regards to starting.

I double checked that the fuel pump is getting time to prime before starting. It's getting plenty. The sputtering is in spite of that.

The almost stalling issues have started to show up with cold starts as well now though. The engine revs up to around 1100 rpm, then drops down to around 100, then jumps back up to where it should be when the car starts (just above 800 if it's warm, a couple hundred more if it's cold).

Thanks again for the suggestions. I'll keep reporting my progress here.

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Old 11-18-2018, 12:39 AM   #10
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Default Re: Stalling at start up when engine is hot

In addition to replacing the coolant sensor, did you examine the two wire connector for fouling? Leaking coolant from a damaged coolant sensor fouls the tiny connectors, rendering them as troublesome as the faulty sensor by poor electrical connections that simulates a frozen engine with the pcm detecting incorrect signals. It enriches startup to the point of flooding in cold weather as well as run too rich fuel mixtures. Replacing the connector is the only repair. Cleaning with contact cleaner or anything else ruins the tiny connectors. If the connector is clean, move on to other troubleshooting.

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Old 11-18-2018, 01:52 AM   #11
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Default Re: Stalling at start up when engine is hot

This does sound like a rich condition upon starting. Perhaps starting with WOT will help to confirm if it then idles better upon startup.

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Old 11-18-2018, 03:31 PM   #12
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Default Re: Stalling at start up when engine is hot

The ECTS connector is a really good suggestion. It didn't look great when I replaced the ECTS, but the car ran fine afterward so I didn't think much of it.

On a recent cold start I also had the check engine light flick on, then off again almost immediately and then the coolant level/transmission fluid light flick on and then off again almost immediately as well. IIUC, a faulty connection to the ECTS would explain that as well as the weird starting issues.

I'll look at the ECTS and experiment with the full throttle on start as well and report back tomorrow.

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Old 11-18-2018, 04:24 PM   #13
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Default Re: Stalling at start up when engine is hot

One way to see coolant sensor temps is with a reader capable of displaying coolant temps. Plugged into a cold engine, the reader should display ambient temps after an overnight cooling down. The next readings should be right after startup, while driving and after a ful warm-up. Ambient temps from a (cold engine) coolant sensor should be the same as the intake air temperature sensor for comparison purposes. Fully warmed, coolant temps should be between 185F-200F. Erratic temperature swings suggests the connections are faulty.

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Old 11-24-2018, 07:45 PM   #14
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Default Re: Stalling at start up when engine is hot

Okay, I'm back with more data. To me the results seem mostly normal except for the fuel pressure leak.

I've monitored the coolant temperature readings over the last few days and it has been consistently coming back normal. The only significant differences I'm seeing at start up between the intake air temperature and the engine coolant temperature is when the engine has been running some time in the last few hours.

Starting with my foot on the gas does prevent it from dying, but I'd prefer to avoid that as a long term solution since it double-revs the engine before oil really starts circulating.

We also did a fuel pressure and leak down test. The stalling behavior is only intermittent and more pronounced when the engine is hot, so it refused to stall when we ran this test. We took the readings anyway. When the fuel pump primes, the pressure goes to 42 psi. While the car is running it goes to 32 psi. When we disconnect the fuel pressure regulator the pressure jumps back up to 41 psi. Once the regulator is reconnected the pressure goes back to 32 psi. The pressure regulator has no apparent leaks. Slow revving the engine shows no change in pressure. Fast revving the engine shows jumps in pressure which settles back to where it was before.

After turning the key to "run" position and then letting it sit it does lose pressure slowly. When we tested it, the pressure dropped around 10 psi in just 5 minutes.

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Old 11-24-2018, 07:52 PM   #15
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Default Re: Stalling at start up when engine is hot

The symptoms here seem similar to those reported by RatLabGuy and spencerb in http://www.saturnfans.com/forums/showthread.php?t=59497 in that it starts worse while hot and usually will start on the second try. That discussion wasn't very conclusive on what was going on, but supposedly replacing the fuel pump fixed it for spencerb. I'd be thrilled if there were an easier way around the problem though.

Monroe44 also had a similar situation in http://saturnfans3.saturnfans.com/~s...ad.php?t=61762 and the discussion there wasn't conclusive either.

Last edited by ianh; 11-24-2018 at 08:06 PM..

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Old 11-24-2018, 11:44 PM   #16
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Default Re: Stalling at start up when engine is hot

Fuel pressure should be between 40-55 psi. 32 psi is too low. If you can disconnect the pressure regulator and let it run at 42 psi while monitoring pressures, see if the car starts up when hot.

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Old 11-26-2018, 09:11 PM   #17
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Default Re: Stalling at start up when engine is hot

Okay, we tested starting with the engine warm (after having sat about an hour, still letting the fuel pump prime fully before starting) and with the pressure regulator disconnected. It started fine with the regulator disconnected, though it sounded like the engine was being revved. When I reconnected the regulator a moment later while it was still running the engine died immediately.

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Old 11-27-2018, 02:39 PM   #18
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Default Re: Stalling at start up when engine is hot

Replace the pressure regulator.

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Old 11-27-2018, 04:17 PM   #19
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Default Re: Stalling at start up when engine is hot

Sounds good. Best guess at what happened: I had a shop replace the fuel filter semi-recently. They probably used a poor quality part for the filter/regulator combined part. Thanks for the help in tracking the problem!

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Old 11-27-2018, 04:31 PM   #20
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Default Re: Stalling at start up when engine is hot

The 97 and below doesn't use a combined fuel filter and pressure regulator. It's only 98 and up you really have to care about what filter you're getting. I think the fuel pressure regulator is apart of the fuel pump on 97 and below. (Don't quote me on that though)

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