Help me think this one out

[jeffcoslacker]

I have a few ideas...but it would be nice if maybe someone helps me put my finger on it.

My '97 LS (3.1) has 190,000 miles now, still runs like new. Far as ignition and fuel system go, everything is original except the plugs. Only major repair was when I replaced the LIM gaskets and timing chain set a year or two ago.

A couple of months ago, I left the house one morning and found that the motor would cut out violently anywhere above 2000 rpm. It starts hammering and bucking just like it's bouncing off a rev limiter. While this is happening, I can't pull a hill at more than 20 mph or so, and I can slowly work my way up to 55 mph without going over 2000 rpm on flat road. Getting up near 60 puts me in the 2000 rpm threshold so that's not possible.

After driving maybe 10 minutes or so, the problem goes away, and it runs great.

At first I thought I got some crappy gas, I'd been near empty and put a few gallons in from an unknown gas station in the boonies. Thought maybe I got some water in the tank. Filled it up, added HEAT, didn't have any more problem, thought that was solved.

But it's done it several times since...and there is a very distinct set of conditions that precede it every time. Very dense ambient humidity, combined with the car sitting a couple of days. Every time has been after it has been very foggy, drizzly or rained for several days to the point everything was soggy.

Rain itself doesn't seem to be a factor, it's driven fine through many rainstorms, some torrential. It seems it requires that combo of cool-down and sitting for an extensive period while ambient humidity is very high.

Plug wires was my automatic first thought, at 14 years and almost 200,000 miles, it's time anyway....but two things don't seem to support that theory...it's not a misfire, it's the whole motor cutting in and out. And also the computer is not coding for misfire or lighting the CEL, so it's not seeing it as misfire, sequential, random, or otherwise. In fact, there are no codes present at all.

So between the specific conditions required to make it happen, and the lack of recognition of a problem from the self-diagnostic system, I have a few ideas what may be happening.

But I'll keep them to myself for the moment. Have at it.

If it turns out you were right and I was wrong, you win......nothing. Except my gratitude. And possibly an underlying resentment based on jealousy

[WyrTwister]

Originally Posted by jeffcoslacker

I have a few ideas...but it would be nice if maybe someone helps me put my finger on it.

My '97 LS (3.1) has 190,000 miles now, still runs like new. Far as ignition and fuel system go, everything is original except the plugs. Only major repair was when I replaced the LIM gaskets and timing chain set a year or two ago.

A couple of months ago, I left the house one morning and found that the motor would cut out violently anywhere above 2000 rpm. It starts hammering and bucking just like it's bouncing off a rev limiter. While this is happening, I can't pull a hill at more than 20 mph or so, and I can slowly work my way up to 55 mph without going over 2000 rpm on flat road. Getting up near 60 puts me in the 2000 rpm threshold so that's not possible.

After driving maybe 10 minutes or so, the problem goes away, and it runs great.

At first I thought I got some crappy gas, I'd been near empty and put a few gallons in from an unknown gas station in the boonies. Thought maybe I got some water in the tank. Filled it up, added HEAT, didn't have any more problem, thought that was solved.

But it's done it several times since...and there is a very distinct set of conditions that precede it every time. Very dense ambient humidity, combined with the car sitting a couple of days. Every time has been after it has been very foggy, drizzly or rained for several days to the point everything was soggy.

Rain itself doesn't seem to be a factor, it's driven fine through many rainstorms, some torrential. It seems it requires that combo of cool-down and sitting for an extensive period while ambient humidity is very high.

Plug wires was my automatic first thought, at 14 years and almost 200,000 miles, it's time anyway....but two things don't seem to support that theory...it's not a misfire, it's the whole motor cutting in and out. And also the computer is not coding for misfire or lighting the CEL, so it's not seeing it as misfire, sequential, random, or otherwise. In fact, there are no codes present at all.

So between the specific conditions required to make it happen, and the lack of recognition of a problem from the self-diagnostic system, I have a few ideas what may be happening.

But I'll keep them to myself for the moment. Have at it.

If it turns out you were right and I was wrong, you win......nothing. Except my gratitude. And possibly an underlying resentment based on jealousy

Service engine soon lite does not come on ?

I would go ahead and change the plug wires , anyway . Likely easy on the front 3 , not so easy on the back 3 .

Change fuel filter .

Check fuel pressure .

Look for loose , burned , cracked , broken wires and vacuum lines . Same for wiring connectors & vacuum fittings . Same for electrical sensors & vacuum " devices " .

My 96 Lumina 3.1L had a vacuum line going past the battery , that was broke . eaten up . I temporarily plugged it . After researching the issue , found the vacuum resovoir was suspose to be inside the fender , under the battery . Turns out it was not there ? Car runs better now that the vacuum leak is gone .

I have been working on the crank shaft sensors . From what I read , if they are going bad , they can cause all kinds of problems . But , If the check engine lite is not coming on , I do not know about that ?

That should apply to a lot of electrical matters ?

Try to isolate it as to fuel & fuel delivery ? Electrical / control ? Vacuum / control ?

Nothing is over heating ?

It runs OK below 2000 RPM ?

God bless
Wyr

[jeffcoslacker]

Good suggestions...a while back I did my standard verification of connectors and grounds before chasing ghosts...after scuffing grounds and spraying connectors for the IM and ECM with WD-40, the problem has disappeared.

I think perhaps the ECM ground or connector was the issue, as it wasn't seeing any problem despite the profound nature of the misfire/cutting out...lotta times that combo points to the ECM as the cause, otherwise it should see an out of range or missing signal or misfire pattern, and code for it, lighting the CEL....

[j cAT]

remove the plug wires all and check for cracks. also any insulation damage or plastic holders broken. measure the plug wire resistance. all wires should be in the same range with the longer wires a little higher.

when you install the new wires measure the resistance and check for cuts in the insulation .

the problem of cutting out when cold/wet is usually the wires but could be a coil pack. spraying all this wd-40 and it is workings pretty much indicated these issues.

use dielectric grease in the plug wire boot ends.