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shudder under load, sometimes

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In my 99 Monte carlo 3.1L with 133k on it. been occuring for for the last 2 years maybe... this is in Southeast Missouri

symptom: shudders at times, like a cylinder missfired ( best i can describe it at the moment)


- the past winter(2 years ago i think) service engine light came on - went to auto zone, cylinder 4 misfire code, replaced wires at that time , no proof that did much

- misfire code came on again last year during winter (pretty sure) did nothing

- assumed misfire code 2 times in the past month, early month and late month

- trans never serviced to my knowledge,but fluid is still at "full" level, bought second hand (the car) at 100k miles in "03

more conditional things:

- doesn't do it constantly, seems slightly random at times

- sub 50 degree weather usually makes it worse.

- problem almost allways happens under 1500rpms, sometimes in all the gears.

- this is normally more prevalent when not fully warmed up.

- the car can stay in 4th down to about 33mph ~ 1100rpms? even uder about 1/3 throttle, shudder noticeable definatly up to 55mph at least under heavier throttle(no upshifting)

- temp gauge in cold to fair weather, seldom sees what could be something close to 160 - 180 range, more like 140, maybe. but still warms up quickly, like allways

: related?---or other problem---

- i do have a gas gauge that is almost allways full , only sees a resonable reading when left over night at house, on flat area, and started in the morn till i start to back down a hill (driveway) no, noone's putting gas in the thing :lol:

my ideas: any of these crazy?

- crank position sensor, iffy?

- bad injectors? i have used the pour in cleaning stuff, sometimes more than's needed in 1 tank(bottle for 21gallons in a 16ish gallon tank), and tried several brands

- bad coil?

- M.A.S.? mass airflow sensor? new filters seem to do nothing also

-- your part--

recommendations? suggestions?

did you at least like my layout of this post?


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Just going off what you're saying, sounds like you're getting some form of condensation build-up in the spark plug wire boot and that's causing the shudder. Does it only happen when the engine is cold, or when you first crank up, or does it happen all the time? Also, if its been 133,000 miles since you've done any transmission service, get it done soon. Normal service interval for those trannys is 100k. As far as problems, if its a coil, the best thing you can do is swap the coil around to another location and see if the misfire moves. If it does, then its the coil. Mass Air Flow sensor is going to throw a CEL (check engine light) code if it goes haywire. Injectors are pretty easy to pinpoint if they're going screwy, best thing to do with them is make sure that you've got proper voltage goign to them from the harness, and make sure they're functioning (put a screwdriver or stethiscope to them and listen for a faint "click" as they fire).

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well for some reason (nearly warm weather) my car has been running just fine for ~3days

going to get a slow leak fixed in a tire next day or two

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Sounds almost like your getting condensation in a connection somewhere when its cold (happens all the time), and its just taking a little time for it to get thawed out.

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heard something new, any truth to this?.... gm and ford use motorcraft, and other cables not to thier specs can make the engine not run well... a cousin change the wires on his ranger while ago, and runs rough if every gear, worst in overdrive and under hard load... ?

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Actualy, GM uses AC Delco, Ford uses Motorcraft, but they're all, in lthe long run, made by the Prestolite Company, so in a general sense, yes they run the same plug wires, just they stamp a different name on the product when it rolls off the assembly line.

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