Bucking under light load Part 2

continuation of my last thread.. it got kinda lengthy so here is where i'm at now. in any gear, under light throttle application, it will start bucking hard. i can usually let off completely and it stops. this occurs almost always when;

trying to accelerate from lights with traffic. light throttle application, slow shifts. right when i get into the next gear and go to accelerate at a traffic moving pace, it starts bucking hard.

so, i found my fpr vac line laying against the firewall this weekend. i reconnected it, and the car drives BETTER. it still does this however, its just a little more manageable now. so this brought up some other questions..

i was told my car operates too cold. it runs at 175* 99% of the time with my 180* t-stat. is this too cold? should i use a 192*?

my map sensor is there and connected. however, the vacuum line is not connected. could this be causing an issue/should it be hooked back up to manifold vacuum?

lots of people tell me the car smells like gas.. i think it might just be the nature of a mustang with o/r exhaust though.

302GTS said:

Had an issue that sounds exactly what your Stang is doing... It ended up being the distributor - threw a new one in and it's been fine ever since. On top of the light throttle bucking, if I went WOT, after around 4k rpms it would sit there and sound like popcorn. Timing was checked multiple times, even taken down a few degrees, thinking it could have been pinging, but that didn't solve it. Threw in a spare dizzy I had lying around, and it fixed it - I'd say dizzy has my vote! Good luck.

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i don't have a miss anywhere except at light throttle.

i also have a surging idle on hot starts. ocassionally at cold(er) operating temps. cannot find a vacuum leak though new o2's, new tps, timing set, checked for vac leaks, cleaned iac, cleaned maf/its new.

HISSIN50 said:

If it's cold up there and you run a balanced (i.e. Mr Gasket, etc) t-stat, your temps are about right on. The balanced stats start to open before their rated temps, so that they are fully open at 180*. If you let it idle in cold ambient temps, the temp should come up (assuming there's no fan running), but like on the highway, it'll run cooler than the rating.

On a MAF car like yours, the MAP sensor functions as a BAP, and it is indeed vented to atmosphere. Sounds like yours is set up properly.

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ok, so i'll check that off the mend list.

what are your thoughts on the vac line falling off situation? it does drive better, but not 100% fixed. i need to get a fuel pressure gauge on it to check that, im also going to replace the fuel filter while im at it.

replaced fuel filter. i had some really dirty fuel leak out of it. so i think it was due for sure. car still does it. seems to be worse when cold vs. warm now. drove it 150 miles round trip to my families christmas party getting 20+ mpg with 4:10s

do i just go for a dyno tune and see if it tunes out at this point?

HISSIN50 said:

The vac line wasn't helping anything but it should not have made a super huge difference. Now that it's reconnected, it will (or did) take the EEC some time to increase the injector PW (since you just basically pulled 5-10 PSI from non-WOT conditions).

It's probably going to be some little issue that's relatively slight and hard to find.

Since replacing the O2's, have you pulled codes again?

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yeah i did jt. the 41 and 91 are gone.

i think somehow it was also connected to that line being off possibly with the lean conditions? either way, new o2's and the line back on and i just get egr codes. which my egr is deleted, so those won't ever go away.

i just scheduled a dyno tune appointment with a very good dyno tuner. i've been putting it off. i explained my driveability issues to him and talked to him for a few.

without ANY hesitation he said don't worry about it, i'll take care of it. so based on his track record and his statements, i expect to gain some hp and leave with a great running car