fuel/air woes

redrider · 10-27-2002, 09:28 AM

I have a sputter and slight popping if I try to drive right away after starting the car. If I let it warm up a few minutes the idle gets settled down and I run smoothly without any popping when slowing down in gear. Even after it's warmed up I get a sputter at the high end of the rpm band under WOT.

My setup is: 347 with T trim Vortech at 12# boost; a racing C4 by PA with 4000 stall and transbrake; an 80 mm blow through mass air with 42 lb injectors; a Kirban adjustable fuel pressure regulator; COBRA intake; Edlebrock 1.90 aluminum heads(ported);BBK 13/4 long tubes; off road h-pipe; dynomax 2 1/2 exhaust.

On the recommend of my mechanic I am getting a Cartech billet fmu to make adjustments at WOT. Do you think that will do the trick or is there something else that is making the car run rough when cold and sputter at WOT?

Hope u can help.

MEDIK418 · 10-28-2002, 01:31 AM

I know this sounds a little strange considering the 42 pound injectors but it sounds like it's leaning out. What fuel pressure are you running? (by the way, I have no idea what it should be, I haven't figured out my own pressure yet) I've seen both of mine do this.Once when the fuel filter started to plug off and when the fuel pump (on a different car) got weak enough to light the "check engine" light which signaled a lean condition on the computer.

redrider · 10-28-2002, 07:42 AM

The pressure on my pillar fuel pressure gauge reads about 34 lbs. My mechanic says the WOT fuel pressure is what counts. He is going to tune the mixture based on fuel air readings on my newly installed fuel/air ratio gauge when he installs the adjustable cartech billet fmu. This unit is supposed to be so adjustable it can even anticipate when WOT is about to occur and increase fuel delivery.

I hope that fixes the problem. All I have to worry about then is when blowby will become excessive because I get a little oil in the breather cap on the valve cover after I nail the gas. Still you have to consider the Coast High short block has over 30k miles of hard motoring.

Thanks for the info

Hozer 88GTConv · 10-28-2002, 11:03 AM

What's your ignition setup and your fuel delivery(i.e. your in-line pump)? I saw that you have a 255 in tank, what do you have in-line? Are you using the stock distributor/TFI module? How old is it? ....
also, I think(?) FMU's generally make you run a little on the rich side. I'll check...

MEDIK418 · 10-30-2002, 01:02 AM

Not knowing squat about blown engines I have to rely on the written word but everything I've been reading on fuel pressure lately says you are in the "zone" at 38. Even so, what you describe is much like the problems we were having prior to installing a new fuel pump on the 89. Rich conditions would generally cause an engine to run really well when cold and get worse as it warmed up. What you are describing gets better after warmup making me think it is running too lean. I'd be real interested to see what cures the problem as the boys are planning blowers for both cars in the next few months.

Hozer 88GTConv · 10-30-2002, 08:55 AM

Have you considered a chip? That is what I am going with in lieu of a FMU. I have been told by everyone worth their salt that a custom chip burned to your specs/setup is the absolute best way to go.
Just my .02.
You live in Fla too so if you want you can call Tony Gonyan at Hocus Pocus motorsports. He is the owner and will help you out.
904-282-7272

10-28-2002, 01:31 AM	#2
MEDIK418 Registered Member Join Date: Mar 1999 Location: Amarillo, Texas, USA Posts: 780	I know this sounds a little strange considering the 42 pound injectors but it sounds like it's leaning out. What fuel pressure are you running? (by the way, I have no idea what it should be, I haven't figured out my own pressure yet) I've seen both of mine do this.Once when the fuel filter started to plug off and when the fuel pump (on a different car) got weak enough to light the "check engine" light which signaled a lean condition on the computer. __________________ 1986 four-eyed LX coupe, 358 Cleveland, Tremec TKO600/centerforce clutch, dish cut Probe forged pistons, comp cams hyd.roller cam, .579/.588@224/230, Edel.performer, 670 holley street avenger, CPR custom built long tubes, ported and polished 4bbl heads, manley valves, beehive springs, MSD peo-billet dist/MSD6AL, fluidamper, 5 lug conv. with 17x8 bullits there's more but it's still not finished yet. Oh, and the oldest boy is turning his 89 GT into a FFR cobra this next summer.

10-28-2002, 07:42 AM	#3
redrider Registered Member Join Date: Apr 1999 Location: seffner, Florida, usa Posts: 95	The pressure on my pillar fuel pressure gauge reads about 34 lbs. My mechanic says the WOT fuel pressure is what counts. He is going to tune the mixture based on fuel air readings on my newly installed fuel/air ratio gauge when he installs the adjustable cartech billet fmu. This unit is supposed to be so adjustable it can even anticipate when WOT is about to occur and increase fuel delivery. I hope that fixes the problem. All I have to worry about then is when blowby will become excessive because I get a little oil in the breather cap on the valve cover after I nail the gas. Still you have to consider the Coast High short block has over 30k miles of hard motoring. Thanks for the info __________________ 88 GT mass air conversion from 90lx, Cobra Intake(ported/polished lower),Edlebrock Aluminum Heads(ported/polished),38# injectors 70 mm BBK TB, 77mm Pro M, Coast High 347 SB, Wolverine custom cam, Vortech T Trim w power pipe(13lbs), fmu & boost retard, 255lb fuel pump (BBK off road H pipe, Dynomax cat back, alum driveshaft w safety loop, Konis,Southside Bars w chromemoly torque boxes,AOD w lentech valve body, B&M MegaShifter, 4.10 with True Track locker, SVO springs, subs, cross drilled rotors, Nitto Drag Radials,MSD A6, black magic fan etc.

10-28-2002, 11:03 AM	#4
Hozer 88GTConv Registered Member Join Date: Feb 2002 Location: Jacksonville, FL Posts: 706	Ignition setup... What's your ignition setup and your fuel delivery(i.e. your in-line pump)? I saw that you have a 255 in tank, what do you have in-line? Are you using the stock distributor/TFI module? How old is it? .... also, I think(?) FMU's generally make you run a little on the rich side. I'll check... __________________ 1988 GT Convertible 331 10:1 TW heads, GT-40 intake, MSD, TRW flattops, B Cam w/ 1.7's, MAC exhaust, 24's, 70 TB, 76 MAF, 3.73's, Pro 5.0, Koni's, Anderson PMS, Wideband 02, yatta, yatta... One week with new motor, two speeding tickets...joy Last edited by Hozer 88GTConv; 10-28-2002 at 11:09 AM..

10-30-2002, 01:02 AM	#5
MEDIK418 Registered Member Join Date: Mar 1999 Location: Amarillo, Texas, USA Posts: 780	Not knowing squat about blown engines I have to rely on the written word but everything I've been reading on fuel pressure lately says you are in the "zone" at 38. Even so, what you describe is much like the problems we were having prior to installing a new fuel pump on the 89. Rich conditions would generally cause an engine to run really well when cold and get worse as it warmed up. What you are describing gets better after warmup making me think it is running too lean. I'd be real interested to see what cures the problem as the boys are planning blowers for both cars in the next few months. __________________ 1986 four-eyed LX coupe, 358 Cleveland, Tremec TKO600/centerforce clutch, dish cut Probe forged pistons, comp cams hyd.roller cam, .579/.588@224/230, Edel.performer, 670 holley street avenger, CPR custom built long tubes, ported and polished 4bbl heads, manley valves, beehive springs, MSD peo-billet dist/MSD6AL, fluidamper, 5 lug conv. with 17x8 bullits there's more but it's still not finished yet. Oh, and the oldest boy is turning his 89 GT into a FFR cobra this next summer.

10-30-2002, 08:55 AM	#6
Hozer 88GTConv Registered Member Join Date: Feb 2002 Location: Jacksonville, FL Posts: 706	chip? Have you considered a chip? That is what I am going with in lieu of a FMU. I have been told by everyone worth their salt that a custom chip burned to your specs/setup is the absolute best way to go. Just my .02. You live in Fla too so if you want you can call Tony Gonyan at Hocus Pocus motorsports. He is the owner and will help you out. 904-282-7272 __________________ 1988 GT Convertible 331 10:1 TW heads, GT-40 intake, MSD, TRW flattops, B Cam w/ 1.7's, MAC exhaust, 24's, 70 TB, 76 MAF, 3.73's, Pro 5.0, Koni's, Anderson PMS, Wideband 02, yatta, yatta... One week with new motor, two speeding tickets...joy

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