Hesitates after 7lbs...

tpunx99GSX · 01-14-2008

I have a friend with a 2g GST.
Mods:
S16g turbo
SAFC
AVCR
550cc injectors
FMIC
Intake
Exhaust

For some reason or another after he spools and around 3500 rpms the car will hesitate and not accelerate any more, then we change gears and it does the same thing.
Its almost as if its hitting a wall at 3500 rpms.
I did a boost leak check and fixed a small leak on the TB, now there are no leaks.
Checked timing and it was perfect at 5 BTDC.
Safc i have set at -8 across the board.
I disconnected the AVCR to make sure that wasnt having any issues, still does it.
Checked the plugs, The tips were white, and the gap backed out to .035 but i wouldnt think that would be a major issue.
Any ideas?

**JET** · 01-14-2008

It is the plugs probably. If you checked the gap, why didn't you close them down? Get them gapped down to .028".

**Shane@DBPerformance** · 01-14-2008

Spark plugs and too rich? Come on. The first thing you should have tried was a new set of spark plugs with them gapped to .028" at the biggest.

brando · 01-14-2008

its a miss for sure. hes hitting fuel cut. DON'T RUN IT ANYMORE. you may need to advance the timing a bit. the car is leaning out not running too rich. if it were running rich they would be black and he would be puffin black smoke

**JET** · 01-15-2008

Quote:

Originally Posted by brando

its a miss for sure. hes hitting fuel cut. DON'T RUN IT ANYMORE. you may need to advance the timing a bit. the car is leaning out not running too rich. if it were running rich they would be black and he would be puffin black smoke

Ignore this guy. He isn't hitting fuel cut at 7 psi. You also have no idea if he is running lean or rich. His SAFC settings would indicate he is pretty rich.

crazy_skier · 01-15-2008

i had this happen.... new spark plug wires will take care of it. Try it

FFPerformance · 01-20-2008

Quote:

Originally Posted by JET

Ignore this guy. He isn't hitting fuel cut at 7 psi. You also have no idea if he is running lean or rich. His SAFC settings would indicate he is pretty rich.

I'd have to disagree with you... spark plug basics 101, reading spark plugs.....

If you pull them and they are wet and black, then you are most likely too rich (possible oil consumption as well)
If you pull them and they are dry and white, then you are most likely too lean (as the original poster stated)
If you pull them and they are a 'toast' or tan color, then you are in the right area for an appropriate afr.

I would double check the wideband sensorys you're usuing to tune the SAFC and make sure that they are in working order. Perhaps cross check the wideband with one from a dyno? I can see how the safc could have been adjusting fuel based on what it thought was a rich reading, and causing a lean condition if the sensors are going out.... sometimes leaded fuel accelerates them wearing out too...

good luck!

$.02

FFPerformance · 01-20-2008

Oh and double check your injectors as well

xveganxcowboyx · 01-20-2008

An SAFC does not adjust fuel on it's own. It's a user input device.

Super Bleeder!! · 01-20-2008

Since when did afcs have sensors?

FFPerformance · 01-20-2008

Quote:

Originally Posted by Super Bleeder!!

Since when did afcs have sensors?

so you just randomly pull or add fuel without knowing the afr then?

Sorry I was making an assumption that a wideband was being used...

crazy_skier · 01-20-2008

try the plug wires.... i'd had this problem happen on my car and on my buddy's stock gst. Both times they were the plug wires and it would just get worse and worse

**Kracka** · 01-20-2008

Like lots of other people have said new, properly gapped, spark plugs will be the best place to start.

xveganxcowboyx · 01-20-2008

For rizzle. Until that's done we can stop speculating.

b00stcreep21 · 01-20-2008

There's a million different things that could be wrong w/ it. You need to be more specific with what's happening. Internet diagnosis usually gets you nowhere, besides giving you around 6 different places to start.. Is it missing at 3500, or does it just stop trying to rev completley like if you turned the key off? Does it ONLY do it at 7psi, or just whenever it's at 3500 like at part throttle too? What do your a/f ratio's do when it's doing the issue?

**JET** · 01-21-2008

Quote:

Originally Posted by FFPerformance

I'd have to disagree with you... spark plug basics 101, reading spark plugs.....

If you pull them and they are wet and black, then you are most likely too rich (possible oil consumption as well)
If you pull them and they are dry and white, then you are most likely too lean (as the original poster stated)
If you pull them and they are a 'toast' or tan color, then you are in the right area for an appropriate afr.

I would double check the wideband sensorys you're usuing to tune the SAFC and make sure that they are in working order. Perhaps cross check the wideband with one from a dyno? I can see how the safc could have been adjusting fuel based on what it thought was a rich reading, and causing a lean condition if the sensors are going out.... sometimes leaded fuel accelerates them wearing out too...

good luck!

$.02

Disagree all you want, it doesn't make you right. Also, it is difficult to really read a plug on a street car. To read a plug you need to shut the engine off immediately after a full throttle pull and then pull the plug, that is not really feasible on a street car. Also, it was never stated that the car had a wideband, so it likely doesn't. If you knew about DSM's, you would know that .035" gap is WAY too big and causes issues just like what was stated. DSM's are picky on the plug gap.

**Shane@DBPerformance** · 01-21-2008

White plugs means they are new plugs, not necessarily lean.

xveganxcowboyx · 01-21-2008

Quote:

Originally Posted by JET

If you knew about DSM's, you would know that .035" gap is WAY too big and causes issues just like what was stated. DSM's are picky on the plug gap.

To add to this, they are also very picky about plugs in general. Make sure they are the OEM plug and not some fancy platinums or anything stupid like that.

Scrmegl · 01-22-2008

My car ran horrible on platinums. Do not use them.

tpunx99GSX · 01-22-2008

Sorry i forgot about this thread.
We tried new plugs gapped at .028, still happens, hes coming over this weekend and we will try some more shit like swapping wires, possible coil pack.

Quote:

its a miss for sure. hes hitting fuel cut. DON'T RUN IT ANYMORE. you may need to advance the timing a bit. the car is leaning out not running too rich. if it were running rich they would be black and he would be puffin black smoke

Hes not hitting fuel cut at 7psi on 550cc injectors and a small 16g. I know what fuel cut feels like.