96 Buick - No Hot Start

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1996 Buick Regal, 3.8L NA, ~ 85K Miles
Starts and runs fine until fully warm (approx. 1/4 temp. sweep range), then dies and won't restart despite cranking fast (normal), having spark (at
coil pack secondaries) and fuel sprays at rail bleeder shrader valve when depressed. It will run while using starting fluid, but again stops when that spray is discontinued. It starts and runs fine again when cold. This scenario is fully repeatable everytime it reaches full temp and restarts everytime it's cold. The "service engine" light does not come on (although the bulb works and illuminates normally during the key on test) and an Auto Zone scan doesn't show any stored fault codes. I've not yet checked the fuel pump or its relay but expect those may not be the issue, although I realize the pressure COULD be too low or the relay might be losing its signal/power supply. Other guesses are that the injectors aren't receiving a signal to open or spark is occurring at the wrong time (unlikely as it neither backfires nor cranks too fast or too slow).
Any advice, thoughts, opinions or experience with this type of problem that you may have to share would be greatly appreciated.
Thanx for your time.
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Sounds like a bad control module, or ECM
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On Sun, 17 May 2009 16:33:52 -0700 (PDT), m6onz5a

Could be. A bad ECM on mine killed the engine occasionally, but it restarted every time but once. That time it started ten minutes later. No problems in the winter, but first really warm day of the spring the ECM died completely. Same car would fail to restart when it had been run awhile, until the fuel pump cooled off. Glitched when accelerating too. Mechanic was shocked I had driven it in, as the fuel pressure was so low. Fuel pump fixed that. '88 Celebrity 2.8. Probably not much different than the Buick. The pump is the easy one to eliminate with a gage.
--Vic
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wrote:

Good input, thanx. I'm a former mechanic (haven't wrenched for a living since '79) and still have most all of my hand tools, but no longer own or have easy access to accoutrements such as gauges, carbon pile rheostats, exhaust gas analysers ... ;^( although I still have an old TV repairman's Sencor oscilloscope in storage that I'm considering breaking out to check the injector signals.
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wrote:

around and I don't think I paid more then ten bucks for them.
--Vic
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Both this and your last post (boneyard) are good suggestions, thanx I'll look into them.
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I would not suspect an ECM with the described symptoms. The ECM is not really running much hotter with the engine temp as described by the OP, so I would not suspect it. I'd look more at the fuel delivery system.
--

-Mike-
snipped-for-privacy@windstream.net
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wrote:

Sounds like a bad control module, or ECM --------------------------------------------------
I haven't had an opportunity to return to this issue yet, but I also think that's a possibility. I was surprised by the starting fluid results as my gut feeling had been that the problem was related to spark (thinking that a failing transistor integrated in the Hall effect crank position sensor was failing, that or a bad ICM), but testing revealed that that was obviously not the case.
Btw, should it turn out that the ECM is the cause of the malady, might anyone be aware of a method by which its replacement can be flashed (such as with my own laptop) without having to go the route of providing the aftermarket supplier a 50% surcharge for that service?
Again, my thanx for your feedback/input.
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wrote:

the boneyard and swap them in. Don't think they need to be flashed if they are for the same car. Just do the normal "relearn."
--Vic
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I think this is your first clue..If it will run when being forcefed starter fluid, then you likely have a fuel delivery problem.
I have seen GM ECM's do this, but it may well be something else.
Sounds like you can eliminate ignition, compression, etc.
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I concur, obviously a fuel issue. But yet to be determined is whether it's related to pressure/volume or actual duty cycle/delivery of the injectors.
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Snuckfoe wrote:

Bad fuel pump OR pressure regulator on the fuel rail. More likely the pressure regulator. Use a pressure test gauge, see what you have key ON engine off, then start the engine and see where the pressure sets. Now shut off the key and see if the pressure stays. If the key on engine off pressure is OK (52-59PSI) it probably isn't the pump, but run a    capacity test just to be sure.
--
Steve W.

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Yes, that method is the correct, standard procedure for testing both pressure and volume of the fuel delivery system, even in a carbureted application.
However I think that in this case, evidenced by the sudden and repeatable onset, the issue might also be related to going from the open to a closed loop condition, seems like almost too much of a coincidence otherwise. But given Vic's knowledgeable experience and your sage advice (replete with specific dimensions), the possibility of a low pressure condition really does need to be eliminated as a cause of the fault as well. Thanx for your response.
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Snuckfoe wrote:

One other small test would be to pull the vacuum line off the PR and see if you find liquid fuel or a strong odor of fuel. You shouldn't find either but a blown PR will sometimes show up that way.
But given Vic's knowledgeable experience

--
Steve W.

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Thanx again Steve, more good advice. I'll add that to my list of things to follow up on as soon as I can return to it.

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wrote:

Diagnostic... Take a bottle of cool water (a sports bottle, Poland Springs, or similar).
Get it hot, so it dies. Spray the water on various underhood items, one at a time. If the ECM is underhood spray it too. Spray connectors! Spray wiring harnesses!
If the ECM is underdash, get a spray cooler can at Radio Shack (used to cooler electronic circuits to find temperature related faults) and spray the ECM and try again.
One fo these two will find the heat related component.
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Try removing the fuel filter[s]. If the engine runs ok hot then you have found the problem. Replace the filters and your all set. My 81 Malibu had this exact same problem. A 96 needs to have the filters replaced anyway.
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Thanx for your suggestion but given the symptoms and history, I find a clogged filter, fuel tank sediment, pickup tube or line restriction ... issues considerably less likely than other aforementioned causes, plus the filter was already replaced about 10K miles ago.
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Chilling a suspect circuit board or device is an old electronics repairman's trick to diagnose an overheat related issue (I last utilized the method and discovered a faulty vertical deflection IC in a Sony TV). Freon, or a dielectric like Fluorinert is commonly used. But to employ a dipole like water and willy- nilly soak energized underhood electrics sounds (to me) like a perfectly AWFUL recommendation (no offense intended). I do however appreciate your input and your latter efficacious suggestion, my thanx for your reply as well.
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wrote:

If you were not aware that *all* underhood components are water resistant, you should be. I thought you were reasonably compentent so I made the suggestion. I appologize for doing so.
You should take the vehicle to a qualified mechanic and have it fixed, that is the only solution for your problems. Good luck.

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