Fuel Pressure Issue

[Stigma]

I had a 3.5 maf and translater installed yesterday,the guys at KDK Performance here in Orlando have done the work for me.

They took it for a test drive and noticed that at 14lbs of boost the car breaks up real bad,they noticed that under wot my fuel pressure was dipping instead of holding around 60 it was falling back not sure how low...

They dropped my tank replaced the fuel pump and now they tell me that i have too much fuel pressure?????

They said they will get back on the car first thing monday morning.

Any idea what could be the issue with too much fuel pressure?

I recently purchased the car and that is a new gas tank in there

Also whenever im low on gas and go to fill up the car does not accept gas easily,it clicks constantly as if the tank if full and im trying to top it off.

Any suggestions would be Greatly Appreciated..

[kenmosher]

Sounds like the tank isn't vented properly and/or the charcoal canister purge valve isn't working. Tank might not be baffled correctly either.

Too much fuel pressure indicates the regulator is wrong (is it adjustable? If so, simple turn down the pressure). Otherwise either the regulator is bad OR (and might be related to your filling problems) the return line is kinked or hooked up to the tank wrong.

[Stigma]

Thanks for your input. i recently purchased the f/p regulator from Jack Cotton and im thinking something was installed wrong in the tank myself.

I took my car to KDK because it barely would idle and it would break up as it would boost up...

I was told i had a bad maf/pcm/chip,so i purchased a pcm/chip and 60lb injectors from fullthrottle,and a maf w/translator...now that everything is new,the car Still is breaking up with anymore that 1/2 throttle/14lbs of boost or more..

Then they noticed that my fuel pressure was hitting 63 at wot and then dropping off Quickly.

So they suspected a fuel pump,dropped my tank and installed a new one,and now they say it has too much pressure...

I purchased the car 3 weeks ago and it has been undriveable more than driveable...

What a let down...

I gave up a beautful 99 LS1 trans am that was turn key and a 12 second car plus $5,000 for all these headaches...

[Ts86ttype]

Stigma, Please remember these car are over 20 years old and will take some updating to get them back to good running shape like your 99 LS1... Once you get things ironed out you WILL be very satisfied with your purchase... I'm with Ken on maybe the return line is kinked or installed wrong... If your fuel pressure reg. can't let the fuel bleed off back to the tank to control the pressure where it is set at, then you will have very high pressure... Tom G.

[Stigma]

Thanks Tom for those reassuring words...

You are correct! Once these minor bumps get sorted out i would be much happier...

I had a 87 G/N back in 2003,and it ran very Strong,best et 11.41 @ 117.88 mph.

Ofcourse i had spent alot of money to get it to that point...

This car so far has just been 1 thing after another.

I got the car back today,they guy's at KDK in Orlando installed my MAFT and 60lb injectors and a Full Throttle Chip a Fuel Pressure regulater and Coil and Ignition Module...

The car is running a solid 20lb's of boost and thats with no pressure on the wastegate rod... I need to keep a close eye on engine knock for sure.

I never had a temp gauge in the car and now that i do i see that my car is shooting up to 210 pretty quickly. They suggested a new radiator because it could get out of control real soon.

So im just about there,but got 1 more initial hurdle to jump :-)

Ok thanks again and i will keep you updated

[Keller]

Originally Posted by Stigma

The car is running a solid 20lb's of boost and thats with no pressure on the wastegate rod... I need to keep a close eye on engine knock for sure.

Very. With those engine temps an that much boost (no race gas or alcohol, yet?) your next hurdle might be a set of new head gaskets if you aren't careful...

[Stigma]

pardon my ignorance,but what blows the head gaskets high boost or extreme knock?

because with the alky kits guys are running 22-24lbs of boost and i never hear about them having head gasket issues?

i have a set of 60lb mototron injectors and matching chip from full throttle and and the car is holding 17lbs of boost <i backed out the wastegate rod all the way and it dropped from 20lbs to 17lbs>my scan master shows 760's as high as 773mv and 0.0 knock...

And thats on pump gas,so am i in danger of blowing a head gasket at 17lbs of boost but with no knock?

As always thanks for your input...

Rick-

[kenmosher]

Persistant detonation kills head gaskets, pounds out bearings, pits pistons, cracks rings, etc. It is the quickest way to blow a head gasket (if you're lucky and not the other more severe damage).

That said, there are a variety of failure modes that tune, gas quality, boost levels, mechanical factors, etc. can cause a head gasket to blow ... and it's kind of a domino effect. Many times all of these things combine or cascade to create the "perfect storm".

SO... things that put you at risk:

• Detonation - this can be from a variety of causes. Too much boost, too low octane for the boost level, fuel mixture too lean, carbon deposits, coolant temps too high, hot intake charge. All of these things contribute to detonation events.
• High boost and load. The head can physically "lift" and bend, reducing the bolt clamping loads. The head gasket then becomes unsupported in the area and the pressure uses the gasket as a fuse.
• Lean mixtures with high boost can spike combustion temps to levels that melt the fire ring on the gasket ...if you're lucky ... or ring lands/pistons and rings if you're not.

Basically, combustion pressure spikes (i.e. detonation), mechanical load on the sealing surface, and combustion temp. are all primary factors in head gasket/parts failure. Many things can contribute to those factors and sometimes lead to one or more of them simultaneously (i.e. running 30 psi with 85 octane gas on a hot day with O2s in the 600s ... pretty much guaranteed carnage in all categories).

Each factor can be mitigated by smart tuning and set up.

• Keep the coolant temps low to allow the cooling system to keep combustion temp under control even if it gets a little lean.
• Keep intake charge as cool as possible with a good functioning intercooler and/or alky/water injection to help reduce detonation.
• Run adequate octane for the conditions (and turn the boost down if octane is lacking).
• Run reasonable boost levels for all of the above factors, including the type of headgaskets, head bolts, etc.

[Keller]

I hadn't heard you mention the Scanmaster previously. Great to hear you have a way to monitor knock and O2! Being able to see these numbers is critical.

Given that you are at 760-780 O2 at 17 PSI (you had mentioned 20 PSI, which likely would have been much leaner on pump gas) your tune sounds fine. The TT chip has adjusted parameters that will permit the 17 PSI on pump gas to work without issues. However, understand that that O2 target is about the lower limit. The good news is that as you add airflow improvements (i.e. cold air kit, improved exhaust, downpipe, etc.), you can use the tuning features of the chip to adjust your fueling to match.

Those running more boost with a stock turbo can only do so with race fuel or alcohol. Alcohol cools the charge and changes the O2 target. Race fuel has a higher octane, and is more resistant to detonation. Roughly 20 PSI is generally accepted as the upper limit of the stock turbo. Perhaps a tad more with alcohol due to the cooling it provides. This is due to its design, and its compressor map.

Ken provided a great deal of details above. There are many more in the tech areas (and "recipe" areas) of the website.