eternal981

this is going to be kinda long... but i dont want to miss any details... the car is a year 2000, supercharged 4.6L.

alright. i was driving around tonight.... very gently, in fact. everything bad happens when i'm being good. i can rag on the car until heII wont have it, but as soon as i drive normal, something breaks.

anyway, i have a loose wire in the harness for my passenger side headlight. no big deal, but its worth mentioning since this all happened at the same time.

my ABS light started coming on today. its come on eeeeevery once in a while before... once every other week or so. but tonight it came on more frequently. as i'm driving around town, the abs light comes on more and more. i get to one corner, and notice my idle stumbles just a little. by now, the light is coming on and off, on and off. go a little down the road, everything is fine again. i notice the loose wire acting up with my headlight, so i was going to pull into a subdivision and wiggle it real quick so it'd work right until i got home. well as soon as i get in the subdivision, the car starts running weird. i'm going to call it "rough", but it was hardly noticable. you could just tell it wasnt running smooth like usual. i get about 2 blocks up, and its getting rougher. 2 blocks further, and now its running rough. i stop, and tap the gas a little to see whats going on. it wont rev very well, stumbles a little. i take off and turn, make it about 50 feet, and it starts running REAL rough, and then stalls.

this whole time its been running rough, my ABS light is on, and stays on.

so i start it back up, and basically from there on out it ran real rough. stalled one more time on me. i kept my RPM's up between shifts, but i dont know that it mattered. it even ran rough with the RPM's up. so i get it home (which was only about a half mile further). sitting in my driveway, it idled alright. actually by the time i got home, it was back to running just "sorta rough". the catch is, if i hit the gas to rev it a little, my vac/boost gauge shoots right up to 0 as soon as i hit the gas. so when the TB opens, i lose vacuum FAST. although i didnt pay a TON of attention, it seemed like my vac gauge was showing a little less vacuum at idle than normal also.

oh....also.....while i was driving it home, when i'd get on the brakes, i noticed a tapping feeling in the brake pedal. didnt feel like how the pedal feels when the ABS kicks in. it felt like someone was randomly tapping on the back of the brake pedal.

i didn't get to play with it much, it was already midnight, and the car is pretty loud while its running. i'll check things over tomorrow through the day, but in the mean time, do you guys have any ideas?

it sure seems like a vacuum problem to me. i'm hoping maybe it IS a vac problem, and that it's the culprit for my hanging idle thats been going on forever also. THAT would make me happy. but if this isnt a vac problem, what else could it be??

2000GT4.6

No fkin clue.

I can say that I do not see how the vacum problem and the electrical problem could be connected. The ABS should have nothing to do with your vac.

My car bascially goes from vac to 0 as soon as I rev it all the time though, so are you sure this is a problem?

I hope you didn't fuxor your ecu somehow. Did you make sure the loose wire is not touching anything/any other wires?? The "rough" idle almost sounds like a miss, is this how you would describe it?

rw98

check your ideler control valve if it's not that check your vacumelines..... were you working on your car recently, if so you may have left a line loose or off. also you said that it was supercharged check the red vacume lines on top of your motor next to your plenum it may have melted to the plenum. (it happened to me, right where i made a couple of splices in the vacume line,i had to much slack and it melted shut and stuck to my plenum.)

eternal981

when i say that hitting the gas drops my vac to 0, i dont mean trying to rev it hard. i mean what most people call a "blip". enough to get you to MAYBE 1300rpm.

i dont think the headlight issue has anything to do with it either. but i didnt want to leave it out, on some crazy chance that it COULD have something to do with it. the loose wire is actually isolated inside a rubber grommet. it's hard to explain without showing you, but where it's loose, it is absolutely impossible for it to be touching anything.

yeah you could probably describe it as a miss. although the only vehicles i've ever heard missing were very sporadic, so they werent as bad. so i can't say for sure that it's a miss. i've heard of a few people having vac leaks so bad that they hardly run..which is exactly where i'm at. i've also heard of brake warning lights coming on because of vacuum problems on other vehicles. so i can't say for sure mustangs are the same, but it would make sense, as most brake systems i've ever seen are almost identical.

if i DID mess up the ECU, even that wouldn't hurt my feelings too bad. (excuse for a standalone upgrade) but i dont think its that serious. i do think that the ABS light and the running issue are related somehow. i don't believe in too many coincidences. i can't say for sure, because at the time i wasnt paying much attention, but when the light first started coming on, it seems to me that it was coming on and off at certain points in the throttle. for instance, if it was on, and i let off the the gas and hit the clutch, it'd go off. don't quote me on that though. like i said, i wasn't paying attention to it at all. every vehicle i've ever had, has had an ABS light come on every now and then for no reason, so i've trained myself to almost ignore that light..

the more the ABS light came on, the worse it ran. and when it ran the worst, the light never shut off.

eternal981

while i'm thinking about it.... if i was losing vacuum, i should eventually hit a point where my bypass valve would close, and the blower would be blowing into the engine.. wouldnt that cause me to lose even MORE vacuum? or does a centrifugal not spin enough at idle-1500rpm to cause any noticeable changes?

eternal981

its funny you'd mention melting one of the red vac lines...i've actually worried about that a time or 2 myself. the engine compartment gets so hot! (and no it doesnt run hotter than any other mustang on the road, but with longtube headers and the supercharger, there's a lot of heat being produced in the engine compartment). i'll definitely check those lines in particular in the morning.

if it IS one of thse small lines, how do you repair it? i'm sure there's a certain fitting it takes....and i dont feel like relying on autozone to tell me what fitting i need, just to find out they're WAY wrong, again...

i'm 99.99999% positive it has nothing to do with my IAC. although, i HAVE been playing with it lately. but that won't affect the way the car runs at part throttle, and it ran like crap then too.

rw98

is your check engine light on? and does your by-pass valve vacume connect to your egr vacume line? because if you are loosing vac. your egr would probly close also. i would check all the plastic vac. lines on the motor. it sounds like a vac. problem to me. i'm not sure whats going on with the light issue.

rw98

yea, when my iac went i couldn't start the car it would take a while, but when it went it ran like crap. you can repair the line with a 1/4' piece of rubber tubing (small hose) all you do is cut the line that is damaged out with a razer blade, cut your hose to fit the gap between the lines & slip the tubbing over the line (it should fit nice and snug) just make sure that it does not rest on any part of your motor that gets realy hot if you need to use wire tyes to keep them up off the hot spots..........

eternal981

my EGR valve was eliminated a looooong time ago, and nothing with it has ever been tampered with. i'll double check that area too to make sure nothing came loose. i've heard if you dont plug that off, its an INSANE vacuum leak... its been fine forever though, and i haven't touched it. still worth checking. so no, it doesnt connect to the EGR line. i'm actually not sure what line it DOES connect to, i've never really looked too far into it, and a shop installed it. it connects on the passenger side of the compartment, towards the firewall. there have been many thousands of miles put on this car with all the mods though, and no changes whatsoever since then.

which doesnt mean much, other than no new modifications could've caused this.

my CEL light never once came on. i actually found that a little bit odd. no, a LOT odd. if it came on at all, it was while it was idling in my driveway, but i wasnt in the car to see if it was....and since it never was on when i did look, i'm going to say no. i'll hook up my code scanner anyway. isn't there another way you can check for different codes through your odometer?

i'm pretty sure it's a vac problem myself also. i wish i would've had a little more patience, and listened a little harder. although its hard to hear anything over the blower, a vacuum leak that bad would probably be audible.

rw98

hey, good luck. i'm going to bed letme know how you make out. it's always good to get solutions to these types of problems, one can never have enough information. later...