Cold nights cause a temperature-dependent max achievable speed

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This had been a problem for a long while, outliving all repairs I have done on the car. Lately I have to drive on a daily basis, and this winter the problem
became a royal pain.
The colder the night was, the lower will be the maximum speed I can get to. At that max threshold speed the car would buck, jerk as if ignition is not happening, and can even stall, if forced.
The oddity is that warming up the engine on idle has little effect, compared to driving under max achievable speed. After about 5 minutes of driving, that maximum speed will start increasing, after 5 more minutes it will gain another +10mph, and in about 30 minutes I can drive fine at any speed until next cold night.
There are no error codes, starting, idling, stopping, accelerating, going at 80mph are all fine, there's no jerking or stalling other than in the situation described. At warmer weather I won't notice the problem, or that max speed would be around 70mph, where it doesn't bother me so much.
This issue survived:
* transmission rebuild * engine change * three MAF sensors change * spark system change (plugs & wires) * ICM change (ignition control module) * O2, camshaft, crankshaft sensors change * new catalytic * new injectors * fuel filters change
Throughout the years it's as solid as my appetite. And it's as disturbing. Imagine how you wake up in the middle of winter, you need to drive to work, and you aren't able to drive above 20mph for good 5 minutes. Now imagine that you're a police officer, sitting in your vehicle, enjoying your morning doughnut, and then a rusty old car crawles right in front of you at a treacherously low speed, and then you see it again and again, as I make several circles around the area trying to get the car to the speed where I could pull on the highway. This picture can make even the most breakfast-minded detective concerned.
I'm looking for any pointers, anything I could try to diagnose what the hell is so profoundly wrong with my otherwise great beast.
It's a 1988 GM with 75K engine, no distributor (coil packs), injection, V6.
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Office Drone wrote:

About the only thing not yet changed out is the fuel pump. Check the pressure at idle when cold.
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Engine pressure is good, but since my oil pump had been noisy for quite some time, and I had a cheap one handy, replaced the pump, fuel filter, checked for restrictions on filter & fuel line. Everything should be fine with fuel delivery now.
Yet the cold temperature/max speed problem persists.
Paul wrote:

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Office Drone wrote:

Doesn't this vehicle have a pump in tank? What is the rail pressure when cold? Does the engine rev high in first and second?

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But did you measure the pressure as the other poster suggested?
On 11 Nov 2004 15:49:26 -0800, snipped-for-privacy@yahoo.com (Office Drone) wrote:

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If it is a 3.8L, You need a new "reluctor" on the camshaft gear. This is a small magnet that is held by a plastic clip that gives the cam sensor its signal. Every time it rotates around past the cam sensor, the sensor changes voltage and thus makes the "pulse". I have found almost identical symptoms in several cars like yours that need this repair. The magnet over time deteriorates and either falls out of the plastic clip or just turns to mush and the sensor no longer picks it up.

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I heard the same suggestion from a dealer a year ago.
But why a weak or deteriorated magnet would be so dependent upon the air temperature?
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Office Drone wrote:

Certain magnets have been known to change their properties when heated or cooled. It's quite possible that the temperature changes in your car are having a similar, and affecting the behavior of the car as a result.
--
E-mail fudged to thwart spammers.
Transpose the c's and a's in my e-mail address to reply.
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For what I'm reading, in such case after cam- or crank- shaft sensor can't read the magnet for 5 seconds, they raise an error code. My car doesn't have relative error codes. However, I was getting CamShaft errors when my ignition module was bad. After I replaced it, everything is clear.
Also, wouldn't a different magnet be inherited with the new engine?
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Would you say that this very interesting problem happens only when overnight temperature is 32 degrees F or below?

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Not really. I would say, the spread of temperatures causing the problem would range between 40F(and below) up to 70F. So the warmer it was, the higher would be the speed at which the car would stuck up.
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OK. That rules out something freezing up then. Can we assume that your machine is not garaged?
Assuming that the vehicle is close to a source of electricity have you thought about positioning a 100W light bulb at various places in the engine compartment overnight to keep specific areas warm. Might be able to narrow down the list of suspects that way.

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Can't get your problem off my mind.
You mentioned that the engine was replaced in your machine. Which components from the original engine were reused on the replacement engine?

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Basically I took everything I replaced for the old engine, and that was expensive: Injectors, Ignition Module, CamShaft sensor, if I'm not mistaken.
Today I unscrewed my ECM, and let it stay indoors overnight - no change. Spoke to another mechanic, who mentioned that it's been pretty common that the persistent problems were getting cured by the replacement or upgrade of the PROM.
Tonight was pretty warm 48F (+7C), so nothing would be freezing inside, and yet I hit the same 20mph with eventual stalling if I was trying to force beyond that speed. After 5-10 minutes it became slightly better.
So ECU is still my primary target.
Silver Surfer wrote:

engine?
when
warmer it

up.
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Office Drone wrote:

Hi...
I'd still love to see the results of swapping the MAT sensor... can't shake the feeling that it's "telling" the engine that it's nice and warmed up even though it's really ice cold...
But, failing that, before you splurge on the big buck items - how about unplugging enough sensors to force it into limp home mode, see how that performs ?
Take care.
Ken
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I like Mr. Weitzel's idea to systematically unplug various sensors to find out if your machine is affected positively. If it runs half way decent with the sensors unplugged then you could plug them in one at a time to find out which one (or ones) is (are) giving you fits.
Don't know for sure, but I'm assuming that the engine will not run at all with the crankshaft position sensor unplugged, and if so, then obviously, it cannot be disconnected for purposes of this test (others more knowledgeable are welcome to correct me if my assumption is off base).
If it is the ECU as you suspect then your recent experiment showed that the ECU itself is not temperature sensitive so perhaps it is mishandling the output from one of the sensors that is temperature dependent. Could it also be possible for the wiring/connectors to a particular sensor to be affected in some bizarre manner by temperature changes? Grounds, opens, looseness, shorts, and the like. Admittedly if would have to be something really off the wall to be so repeatable.
As an aside, I replaced the starter on my daughter's Grand Am three times in very quick succession. After the third one it was time to look further. It turned out that the insulation on two wires in the starter solenoid circuit had rubbed through and the process of replacing the starter disturbed the wires so that the starter worked fine for a short time after each replacement. Long enough for the wires to gradually return to their natural resting position on a metal frame in the engine compartment, after which the machine would not start.
Sure hope you're not dealing with something that weird.
Back to the subject at hand, it seems to me that your problem falls into one of these three general categories:
Reduced/restricted fuel flow Reduced/restricted combustion air flow Restricted exhaust flow
Are there others that are eluding me?
Please keep us informed. Your problem is intriguing.

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Silver Surfer wrote:

I haven't heard anybody say that the exhaust has been unhooked to see if the problem would clear, old mufflers and cats will do a lot of tricks. I've seen engines changed out of frustration only to find out later that loose bafuls were packing up against the back of the muffler. Sometimes you will hear the exhaust hiss when you step on the gas hard.
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ECM & PROM upgrade didn't help. Car is being checked for exhaust problems tomorrow - will post updates later. In the meantime, the weather warmed up, so I'm not hit as badly (or maybe it was an ECM contribution indeed).
Current feeling - that something has to warm up enough inside the car, and it has to happen while driving - idle doesn't seem to have such an effect as 5 minues of trying to break through the cut-off speed.
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noname wrote:

I began to get this same problem with my 1991 3800 series engine, but it began to be very hard starting as well. But today it will not catch at all, I had a spare coil pack and it made no difference, not sure if ICM was ever replaced, nor the crank sensor. So where is the crank sensor located?
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Hi...
Here I go again... not a mechanic, just an old retired electrical guy who loves tinkering with cars, so pay little attention, please. You've been warned :)
Maybe a little advantage in this case... a simpler perspective...
You didn't mention the Intake Air Temperature sensor, nor the Coolant Temperature sensor... they should (I think) set codes, but might it be worth changing them on a whim ? Perhaps you didn't get new ones with the engine change.
I'm particularly thinking this way because I live in real cold Canada... and if I go out and start my car, let it idle 15 minutes while I have yet one more coffee, the car hardly warms at all... air temperature out the vents stays no better than lukewarm. Yet driving it loaded for a couple of blocks has really nice hot air available.
Just a thought...
Take care.
Ken
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