More power at 12 psi than 15 psi, why?

[EricF]

I drive a '93 Talon with a Turbo XS MBC, a Holly 255 LPH fuel pump, and an Aeromtive AFPR (set at about 40 psi with the vac disconnected). It has less than 80k miles. Iread on this site that my stock injectors will support 16 psi tops, so i cranked it up to about 15 psi, but the power drops off as the engine raps. My car's way faster at 12-13 psi. For a while I was convinced that my bov was leaking, but i read about about how the 1g is a great bov, so I've been thinking that the car must be pulling the timing back. It's probably important to note that I live about 6000 feet above sea level, but i've traveled to places lower than 3000 and still felt the same effect. Also its usually around -20 degrees when I drive to work right now, and the car is still faster at the lower boost setting. I don't know what conclusion to draw from all of this, hopefully someone more knowledgeable than me can help. Thanks

 

[-DSM2NR-]

You might be leaking boost somewhere. Check for that. People might have told you that it's safe to run 15psi on stock fuel but every car is different so I wouldn't rely on that info. If the car runs better on 12psi leave it at that until you get some bigger injectors, SAFC, and other supporting mods.

 

[oldman]

1. Your fuel pressure should be at 37psi, not 40psi.

2. It's possible that you have boost leaks (or more leaks) at 12+ psi, have you pressure tested?

 

[herovueboi]

I am assuming that you have an aftermarekt boost gauge, so the first thing the came to mind was a leaking BOV. Is there any smoke blowing out of the exhaust that isn't suppose to be there? Like is the turbo in ok condition because it seems that it doesn't make power over 15psi, meaning you could have a leak somewhere. I think you should boost leak test it and try to see if anything is leaking elsewhere at such and such PSI.

 

[EricF]

Thanks for the help! Sorry I forgot to mention, but of course i have an aftermarket boost gauge. The only time i see smoke is when i shift, but i have eliminated my catelytic converter, I'm not sure if that nakes a differance. As far as i know my turbo is in great condition. I have pressure tested, and air did leak out of the dip stick. Honestly, i thought that only leaks in the intake sytem mattered, maybe this is why i'm in the newbie forum.

 

[oldman]

Pressure out of dipstick means intake pressure leaking into the crankcase via turbo seals, valve seals, pcv valve or rings. This is what I just posted in another thread.

1. Pull you licp and check for oil.

2. Compression test both dry and wet.

3. Boost leak test while listen for leaks under the valve cover, this will confirm the conditions of pcv and valve seals/guides.

4. How are you pcv and breather valves routed?

 

[EricF]

Thanks again for the help. I read the other thread that you refered to and I think I gathered that if it was the turbo or valve seals my car would be smoking right? I know that if my rings weren't sealing it would be smoking, so this leaves the pcv valve? I have to tell you i don't know what that is.

 

[oldman]

so this leaves the pcv valve? I have to tell you i don't know what that is.

PCV = Positive Crankcase Ventilation. It's screwed into the passinger/fiewall side of the valve cover, connected to the intake manifold via a rubber hose. PCV is a one way valve which opens when intake is under vacuum to relief pressure in the crankcase and closes when intake is under boost to prevent boost from entering the crankcase.

I read the other thread that you refered to and I think I gathered that if it was the turbo or valve seals my car would be smoking right?

Puff of blue smoke in between shifts are signs of early failure of turbo seal or valve seals.

 

[EricF]

The smoke inbetween shifts seems very white to me, but what is involved in replacing turbo seals? And if it is the valve seals, what can be done short of machining?

 

[Booster-Shot]

I actually had the same problem...until today I always figured my car had a small boost leak because I didnt fully spool until about 4k and that was stock too. Well I upped the boost to about 16psi today and it felt really choppy until I just blew off my intercooler tubing completely (damn rubber hoses!) So now my car runs better than ever!

 

[oldman]

but what is involved in replacing turbo seals?

Depending on the degree of damage and why? A lot of times the leak is temporarily caused by excessive crankcase pressure which reduces the oil return capacity of the turbo forcing oil out of the seals, the turbo could still be ok as long as the cause of crankcase pressure is found and fixed in time. Worst case would require a turbo rebuild or a complete replacement, I doubt this is the case or you would be smoke screening right now.

And if it is the valve seals, what can be done short of machining?

No machining needed. http://www.vfaq.com/mods/Valvespring-seals.html

 

[EricF]

I think my problem is opposite, my car gains hard from about 3000 rpm until 4000, after which point, it doesn't seem to gain any more power ( at 15 psi). And, I hate to make myself sound really stupid, but i'm not sure i know what you mean by "blew off my intercooler tubing completly."
Thanks very much for the input!

 

[EricF]

Thanks for all the help Oldman. What might the causes of crankcase pressure be?

 

[EricF]

Sorry, I just realized that leaks in the PCV valve or valve stem seals are common causes of crankcase pressure, like we already discussed. Thanks

 

[Deadly BlaZe]

Thanks for all the help Oldman. What might the causes of crankcase pressure be?

i'd really like to know an answer for that one too.

i'm not sure i know what you mean by "blew off my intercooler tubing completly."

i think he means the intercooler hose popped off of whatever it was attached to.

 

[rs-t eclipse]

Normaly when your valve seals go bad the car smokes when you first start or when the car has idled to long and the engine is warmed up. normally around after about 5-10 mins of setting still you well notice the car starts to smoke because the seals have expanded allowing oil to seap through. so it smoking between shifts sounds more like a vaccum issue maybe the pvc.

some causes of crankcase pressure is one the pvc valve which is the cheepest to fix or its something internal. bad rings, cracked piston or a blown headgasket. could all be possible causes of crankcase pressure. but normally when its one of these you have heavy smoke when boosting. not just in between shifts.

 

[oldman]

i'd really like to know an answer for that one too.

Post number 6, I thought we went over this in your thread.

 

[Deadly BlaZe]

Post number 6, I thought we went over this in your thread.

your right, i just wanted a little more thorough explanation.

 

[Booster-Shot]

Yeah sorry about the confusion. I guess the guy before me didnt put the clamp for the intercooler piping over the little lip on the side mount. So when I really got on it the hose just poped off the intercooler completely. I took it as a sign to go and buy a fmic

 

[EricF]

Thanks to everyone for the feedback! I am new to DSM's, but I know I could tell if I had a cracked piston or blown head hasket. I can't be 100% positive about the rings, but I have very little oil consumption. The valve stem seals could, quite possibly, be bad. The car does smoke when I first start it, but I've never seen a car that doesn't smoke when you first start it in -20 to -30 degree weather. As for summer, I don't remember noticing a smoke problem. You say the PCV valve is the cheapest to fix, is it a simple case of order a new one and replace it? Thanks very much.

 

[oldman]

You say the PCV valve is the cheapest to fix, is it a simple case of order a new one and replace it? Thanks very much.

Replace with only an OEM pcv as aftermarket ones are pretty much gaurantee to leak. You're welcome.

 

[Deadly BlaZe]

Replace with only an OEM pcv as aftermarket ones are pretty much gaurantee to leak. You're welcome.

oldman, what is the pcv valve consisted of?

 

[oldman]

oldman, what is the pcv valve consisted of?

Post #8.

 

[Deadly BlaZe]

Post #8.

so its just the little metal thing on the side of the valve cover? thats it? there's nothing inside the engine thats part of it?

 

[shadowdrag]

I have been battling this crankcase pressure for months now and still no solution. I've took my car into the dealership for a blow-by and crankcase pressure a week ago. It came out negative, piston rings, turbo, valves seals are all fine. They did leakdown test and found nothing. I spend $89 and hour for this diagnostic and 2 hour of negative results. But when I go to do my boost leak test, I am still getting pressure leak from dipstick.

Maybe we are doing something wrong? I know every time my car its full boost 18psi it gets super rich making my car feel like crap too. The boost is leaking into the crankcase to cause this problem.