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Discussion Starter #1
Hi guys,

as i was describing in my car's thread:

car not running fine, looks like it's missing, it skips and jumps under medium throttle input and won't accelerate hard under heavy throttle input (very down on power). also not precise throttle response.
still no CEL yet, after 250 miles.
i checked the coils and they are fine (i mean sparks are good).
i think maybe a clogged injector , or bad spark plug or wire.
sperk plugs, wires and coils have the same age, which is about 20000 miles.

https://www.youtube....h?v=4wMC0sHzDCs

sorry for my english.
this is a quick video of what happens.
the lower the rpms the more it jumps.
the hotter it is the more it jumps.

it does the issue in all the gears, getting worse with high gears.

any ideas?

1997 pontiac firebird 3.8 5 spd, 180000 miles

thanks
 

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Maybe a bad vacuum leak somewhere, head gasket, or wiring/sensor for the timing is broken (cam or crank sensor, PCM, etc.). Best option is to check compression (a gauge isn't very expensive to try, or borrow).

You can also have someone scan while driving to see what the MAP sensor, Oxygen sensor, timing advance, knock retard, and other numbers are saying. That seems bad enough that a DTC (CEL) might happen soon, but you can hopefully fix it first. If you already have something to scan with, like HP Tuners or something less expensive, that would do the trick.

- Dave
 

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Perhaps try unplugging the MAF sensor once the car is warm enough to run without stalling. This should default to the basemap for A/F. If the bucking stops, use approved MAF sensor cleaner ONLY, test the voltage to the sensor if you have the capability, and if the Hot(12V) or Ground are bad, or the wires are brittle of have cracked insulation, get a new pigtail or make one. Worst case, get a good MAF from the local junkyard...New is pricey, like $175 or so. I've dealt with Pontiac wiring failures both MAF and ABS, and this looks a lot like the MAF wiring problem I fixed. I had to go about 12" into the harness to tie it in, but that was a 2001 GTP, so YMMV....Regards, WPOD
 

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I have used this procedure to rule out the ignition control module and coils, etc. but sounds more likely what dezldave961 suggests. Part 1 -How to Test Ignition Coil Pack -Misfire Troubleshooting Tests (GM 3.8L)

You should verify the lines to the vacuum canister if it has one, and the one-way vacuum check valve at the firewall at that age tends to leak or just fall off. If you are having problems with your climate control diverter it can be a big hint.
 

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Discussion Starter #5
thanks guys,
i appreciate the help.

i'll start working on it in the weekend and i'll keep you updated.
thanks
Tommy
 

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Hi guys,

as i was describing in my car's thread:

car not running fine, looks like it's missing, it skips and jumps under medium throttle input and won't accelerate hard under heavy throttle input (very down on power). also not precise throttle response.
still no CEL yet, after 250 miles.
i checked the coils and they are fine (i mean sparks are good).
i think maybe a clogged injector , or bad spark plug or wire.
spark plugs, wires and coils have the same age, which is about 20000 miles.

https://www.youtube....h?v=4wMC0sHzDCs

sorry for my english.
this is a quick video of what happens.
the lower the rpms the more it jumps.
the hotter it is the more it jumps.

it does the issue in all the gears, getting worse with high gears.

any ideas?

1997 pontiac firebird 3.8 5 spd, 180000 miles

thanks
The way you describe the problem and the way it shakes is very similar to a bad spark plug or a bad plug wire. The best way to isolate this kind of problem is to use a SCANNER to see which cylinders are misfiring. Once you find the weak one or weak ones, check the plugs and wires. Using a scan device is the best way to isolate the culprit. Best of luck mr goodwrench (Jake).
 

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Discussion Starter #7
thanks Jack, i appreciate. yeah i do have a couple of cheacp scanners. i'll see what i can do and i'll report back.
 

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Discussion Starter #8
hi,
yesterday i tried a few "easy" options, but still no solution and no cel. i gave a try to the spark plugs and wires, also cleaned up all 3 coils.
my spark plugs look really bad.
i changed 3 of them (with some leftovers i had laying around), i didn't have any tool to lift the car up so i only changed the ones i could reach with my hands (wires too), but car still making the same problems.
attaching pics
i already ordered a new set of spark plugs and wires though.
i'll try to hook up the scanner hoping to find out the issue.
 

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I should have said, "Unplug the MAF after ruling out plug/wires/coils". The Cam Position Sensor can act up without a CEL. And it Ain't hard to change, but it ain't a picnic to change either--A lift is best, (Belt off before the lift BTW--and the Radiator too), pull the pulley and balancer (It takes an odd length fine pitch metric thread as I recall for the puller bolts), then the cover and there it is. If your Timing Chain is wupped (Which at 180K it is unless someone was there since new), It's a good time to replace that with a name brand name HYVO (Roller chains don't last as long, and you don't need them for less than all-out builds)--And don't buy a cheap sensor either.

All that being said, the best Route is to find a dealer with a Tech-2 scanner which will find "soft codes" that won't trigger a CEL. Also, some independents may have a Snap-on MODIS with a legacy Pontiac card that can do the same.
I prefer to test before doing extra labor, or spending money on parts that may be good. One rare possibility--I've read--is that your PCM may be flaky, but sourcing a spare for testing that has the right flash for your car may be difficult.

Worst problems are sometimes aged brittle wires that intermittently make and break connection as the car vibrates or the amp load increases with throttle--like your MAF or O2 sensor for example--and they require some real detective work! Look for insulation cracks / flexibility, "Bulges" (I've seen wires that were "Green Dirt" inside, but still worked--sorta) and years of oil soak for insulation not meant to live inside the Engine (or trans on an Auto) is also a bad thing. Also, Grease ALL connectors--Batt terminals to everything else!
I don't know if any of this helps, but it's my 2 cent's...FWIW
Regards, Mike
 
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