jthorn9

UPDATE!!! NO LOW BOOST!!! Just swapped out my crank pully and put out 10 psi, however I still have the other problems.

OK, here recently my 5.0 has begun drinking gas at an astounding rate. Yesterday I went on a trip and probably got around 10-12 mpg, which is much worse than just a few months ago when I was getting 22ish. My mpg started going down just before the KB install when I started having these weird idel issues. Did the KB, and it got a little better, and now just last week it got much worse. Car starts up fine cold, but once it gets hot it starts acting a little weird, if I sit at a light long enough the idel will drop below 500 RPMs, then bump back up. Then if I turn the car off after running around a bit, and start it back up it starts fine, then when it goes to idel it just stalls, I have to gas it for a few seconds for it to stay running.

It did something very similar to this last year with the IAC, brought it to a shop last week and they ran a full diagnostic and got it do the problem but couldn't pin point the issue as all the sensors checked out. Any ideas?

Also, when I was getting on the interstate yesterday I went to floor it to get around a truck and when I went to WOT the car just tried to stall on the insterstate. Also, when I give it gas after about 45 mph, the boost gauge drops to nearly 0 vacuum as if the S/C is trying to boost, but I know for sure it's not cause it only boost at WOT and I'm just giving it enough gas to speed up.

Here's what I have:
Bad idel
Car stalls when hot
Excessive fuel consumption
No smoke out exhaust
Car lopes a bit at idel as if there is a wicked cam in there (no cam work done)
Had a vacuum check ran, no vacuum leaks
Car tried to stall at WOT yesterday in 3rd gear
Vac/Boos gauge fluctuates between 18 hg, and 10 hg when driving at the same speed when just last week it held steady.
Sensors checked out fine.

393strokervert

""Vac/Boos gauge fluctuates between 18 hg, and 10 hg when driving at the same speed when just last week it held steady.""
""Suffering low boost, 4.5 psi with a 10 psi rated pulley.""
definitely suggest a bad vacuum leak. head or intake gasket ???
what vacuum reading to you get @ idle?
just curious, is you mass air calibrated for your KB,injectors ect......?

jthorn9

Its a pro-m mass air calibrated to 30lb injectors.

At idel it holds steady at around 18-16 hg, its only when under load it goes crazy.

I was thinking head gasket as well, but I have zero head gasket issue symptoms.

393strokervert

good holding vac @ idle, strange.. almost sounds computer related but that wouldn't explain bad vac while cruising. do you still have the egr system? any codes or check engine light?
also, not sure what brand my TB is but it has a vac port on the top that is closed @ idle but opens up while driving. don't know what it is for but it is capped off. might want to check to see if yours has something like that & possibly the cap came off or it is hooked up to something & the line is cracked. not sure what else to say.

malo012000

when we add a s.c the head gaskets get alot more pressure then the would without the s.c. so I Think that you have blown either head gaskets or maybe the intake gasket on the air side so check it out and let us know

jthorn9

Ok, what's a good way to test for a head gasket failure if you're not displaying any normal symptoms like smoke in exhaust, burning fluid, etc?

No, my TB has no extras on it, its a professional products tb.

No check engine light.

Yes I still have my egr.

Also, engine temp is normal if that helps any.

84conversion50

they have the head gasket test kits which test for gasket fragments in oil and water. i personally use sea foam. Any leaks it will smoke out of.

projectresto83

Compression test will tell you if you have a blown head gasket. Maybe you should call KB and see if they can help you at all.

393strokervert, WTF is up with your build? Ported E7's on a 393...does that really run well at all???

94StinkinLincoln

PM sent.

393strokervert

393strokervert, WTF is up with your build? Ported E7's on a 393...does that really run well at all???[/QUOTE]

yea ,I know E7's & the baby cam. all mod's were done by the previous owner. I have only owned it for 2month's & everybody says the same thing you did. after the build it dynoed 310rwhp/383rwtq so it's not too bad & being my 1st fast mustang it's ok for now. the first time I drove it ,it wasn't as fast as I thought it would be with the 393 but for $5,000 it is an awesome car. I,ll probably put a good set of heads,cam & a tune later this year.