Pontiac Grand Prix Forums : Grandprix

alright I know I am a new guy here but I have had this car for my wife for a couple of years and done a lot of stuff to it...

the problem: any kind of positive boost (any thing + on the boost gauge {an AutoMeter boost gauge}) the car acts as it is going VERY lean, you can easy get in to it through the full RPM's but if you try to dip the throttle you get the same results

since I have owned it I have replaced the following:

new long block
ported heads
ported super charger w/ 3.2 pulley
comp cam
pacesetter headers
cat-less back exhaust
new MAF
new Fuel pump
new MAP sensor
new injectors
new 4T65HD trans
ZZPerformance programed ECU
repaired wiring to MAF
new O2 sensor
new ignition control module
the long block came with new:
-----cam and crank sensor
-----crank pulley

and I am sure I am forgetting some things

I know it looks like I have been throwing parts at it but this is not the case, as I have had it I have been making it back to new (my wife and my new born son were riding it it) as I wanted it to be reliable and safe, this problem started before I did the new long block w/ ported heads, ported supercharger, cam, headers and exhaust

I had a previous problem with the MAF and wiring dropping signal sporadicly under boost and cracked three ring lands on the old motor (all though the damn car ran fine like this for over a year after replacing the three plugs with bent electrodes ) this is the reason for the new long block

this problem all started on a long road trip I car was running great (still with the old motor) and I was passing a car on the highway (in it to win it of course) the car kind of stalled and from then on does not want any boost (high load) I am out of ideas and am beating my head against the wall

basically what I am looking for is a brain storming session with anyone putting out idea's I have tried many many things (such as fuel pressure looks good under vacuum and low load, hard to test under boost as the problem) MAF signal looks good

so please please give me your ideas, sorry for the long post

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1999 4dr GTP, new long block, ported heads, comp cam, pacesetter headers, ported super-charger, 3.2 pulley on quick change hub, new 4t65hd trans, CAI, dropped suspension w/ springs and struts, X-drilled rotors with pads and braided lines, full stereo, tinted windows, full cat-less back exhaust

I'd start with a fuel pressure test, and possibly change the fuel pressure regulator. How do you know it goes lean, or is that a guess? Could be ignition related (wires, plugs, or even coils).

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2004 Impala LS - got some mods sold!!!
2009 Subaru Impreza WRX STI

NAIOA moderator Still Imp'n, just in a different Imp.

So when you say acts, do you know for sure if it is? Have any way to monitor the O2 sensor to see what it's reading?

It could be the fuel pressure, but without knowing any readings, it's extremely difficult to diagnose.

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GreenBastardPerformance2000 GTP Coupe (the green bastard)
XP, Pacesetters, LS1 TB & MAF,MSD System, P&P LIM, P&P GenV w/ 3.2, 3.0, 2.8, Devil'sOwn Injected 100% Methanol,PowerTuned, TripleEdge Trans w/3.29's
12.92 @ 105mph

Well your fuel trims could be way off causing your PCM to pull fuel and make you run lean, but only a scan will tell for sure.

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2000 Silvermist Grand Prix GTP Coupe

Mods-Custom Thrasher CAI|Ceramic Coated S&S Headers|3.4" pulley|ZZP S4 Blower|Powrtuner|PRJ 10.4mm wires|HIDs|F-Body brakes|Koni's and Voglant's|

fuel pressure - I want to say it was 48 psi with idle and up to 54 psi as I was accelerating, could not get a reading in boost. this was taken before replacing the engine

has a strong ignition ,new coils, wires, plugs and ignition module

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1999 4dr GTP, new long block, ported heads, comp cam, pacesetter headers, ported super-charger, 3.2 pulley on quick change hub, new 4t65hd trans, CAI, dropped suspension w/ springs and struts, X-drilled rotors with pads and braided lines, full stereo, tinted windows, full cat-less back exhaust

have built and driven several highly modified cars and know how they feel when they run out of fuel, and this feels the same, it does not feel like spark blow out (which I hope would be hard to do at 1 psi of boost)

I have a air/fuel gauge in the car that goes red, I know this is a narrow band sensor though so it is not the most accurate thing in the world (unless around 14.7)

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1999 4dr GTP, new long block, ported heads, comp cam, pacesetter headers, ported super-charger, 3.2 pulley on quick change hub, new 4t65hd trans, CAI, dropped suspension w/ springs and struts, X-drilled rotors with pads and braided lines, full stereo, tinted windows, full cat-less back exhaust

that is what I am leaning to (well that or a fuel line restriction restricting flow, but would think that would restrict pressure somewhat also) but have no idea what idea conditions are for this, with my 3000's I build I have a full stand alone ECU in them I can watch everything and know what it should be doing (as I am the one that had to tell it to do it) with this I have my old trusty Snap-On brick but it is slow and I really don't have anything to base the readings off of

is there software out there that can be used for data logging? tunning?



again thank everyone for their inputs ANY idea are appreciated

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1999 4dr GTP, new long block, ported heads, comp cam, pacesetter headers, ported super-charger, 3.2 pulley on quick change hub, new 4t65hd trans, CAI, dropped suspension w/ springs and struts, X-drilled rotors with pads and braided lines, full stereo, tinted windows, full cat-less back exhaust

The gauge may not be totally accurate according to the PCM though, while it is possible, different O2 sensors read differently unfortunately. While a narrow band isn't very accurate, it is one of the things the PCM looks at for fuel trims

A bad TCC solenoid will also make the car feel like it's starving for fuel. I've been that route. 48-54 psi at idle and under light acceleration is normal, when in PE mode, it should jump to the mid-upper 60's.

If you have any way to look at fuel pressure while the engine is under a load, that may lead to a bad pump or regulator as well.

As much as I hate to point fingers once again, I would highly suggest having someone take a look at that ZZP PCM. I've seen some fuel tables not add nearly enough sometimes with a commanded afr as high as 12.4

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GreenBastardPerformance2000 GTP Coupe (the green bastard)
XP, Pacesetters, LS1 TB & MAF,MSD System, P&P LIM, P&P GenV w/ 3.2, 3.0, 2.8, Devil'sOwn Injected 100% Methanol,PowerTuned, TripleEdge Trans w/3.29's
12.92 @ 105mph

You can pick up a Digital Horsepower Powertuner(pcm interface) for data logging and tuning. Probably have to pick a used one up because they are no longer making them(might still have some new ones in stock). You can also use HPtuners they can be bought new. You'll need a laptop for either one you choose. You can data log and tune with both.

Another handy tool is an Aeroforce gauge, you can display two parameter at a time out of like 20 to choose from. You can also buy them in pairs and then you can display 4 parameters. You can change the parameters you are viewing buy scrolling through them. They have two analog inputs for a wideband etc. They are usually mounted in a pillar pod or a HU pod. I love mine and it's nice to have because I don't always like to hook up my laptop everytime I drive. It can't data log, but it can clear dtc's.

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L26,Xp, zzp trans,3.29's,2700 conv, slp headers/catback, diy ported heads/LIM, 3 angle valve job,.052 MLS hg, outlet ported Gen V, 3.6, N*, LQ4, 4" FWI, agx's, ssc's, f-bodys, gmpp sway's +stb's