Severe bucking at WOT

[gray87GT]

Well, things are definatley different on the street. The car runs sweet when just cruising or under normal acceleration, but when I put her down it bucks like hell. I am really hoping it is a fuel problem, lack of. I haven't installed my 190 fuel pump yet, or the 73mm MAF. I did have my buddy watch my fuel pressure gauge and when I floor it, it goes up to 40 1/2 then down to 37-38 (it is set at 40). Can anybody clue me in on what the problem could be?? Thanks

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87 GT, BBK shorty's, offroad H-pipe, ASP pullies, 70mm T.B., Cobra intake, no smog pump, Windsor Jr irons, Comp cams 1.6 rollers, F303 cam, H.D. export W.P., Tri-Ax, FMS subframes, Battle boxes, SSM liftbars, FMS King Cobra clutch, mass-air conversion, 73mm C&L, 24lb injectors, BBK fuel pressure regulator, 3/8" no EGR spacer, and other piddly sh*t.

[gray87GT]

anybody...please

[slow87GT]

either fuel pump maxed, inj. maxed, or bad TPS

I'm in the same boat, just bought 255 intank and nos external

let me know how you make out

[gray87GT]

I am still trying to figure this out. I have the intake spacer that blocks off my EGR port, but have everything elso hooked up. I do not have any smog stuff either. I am wondering what would make it buck so hard it feels like I am slamming on the breaks.

[Green92LX]

Sounds like you got some detonation on your hands there buddy...

My suggestion is to not floor it again til you upgrade your fuel system unless you want to do those head gaskets again.

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1992 LX:V-1 S-Trim ,Edelbrock 6037 Heads,Cobra Intake,E-303,1.6 Rollers,65MM Holley TB, 75 MM Pro M Mass Air, 190 LPH FP,24 lb injectors,MSD 6A and BTM,BBK equal length shorties,offroad h-pipe,Mac Flowpath Mufflers,Pro 5.0, 3.73's,Motorsport "C" springs,welded subframe connectors,Ponies w/ 225/50 Nitto NT 450's on front,255/50 BFG Drags out back,93 Cobra Spoiler
Daily driver 89 Coupe:BBK shorties,offroad,flowturds with dumps,soon to be cyber green

[gray87GT]

Should I have this big of a big problem with the stock pump and my mods?? Has anyone with similar mods had big problems with the stock fuel pump. I just can't see how it could effect WOT as much as it is. Shouldn't it just bog or just have low power? And can anyone explain how the fuel pressure should be...I have read that it should be around 39 at idle with vacuum unhooked. What should it be at idle with it hooked up, and what it should do under acceleration, and WOT. It should be higher at WOT right? I am sorry for all the posts, I just want to get it straigtened out....and I need some help.

[Green92LX]

It sounds like you are running a severely lean condition due to the stock pump...

I ran my car with the heads and the stock pump, but never floored it, I just started it and drove it around the block to see if everything was OK, then brought it home and threw the pump in (did the injectors during reassembly [duh])

The bucking, in my mind, is detonation...stop running it or else you will suffer severe engine deterioration!!!!!


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1992 LX:V-1 S-Trim ,Edelbrock 6037 Heads,Cobra Intake,E-303,1.6 Rollers,65MM Holley TB, 75 MM Pro M Mass Air, 190 LPH FP,24 lb injectors,MSD 6A and BTM,BBK equal length shorties,offroad h-pipe,Mac Flowpath Mufflers,Pro 5.0, 3.73's,Motorsport "C" springs,welded subframe connectors,Ponies w/ 225/50 Nitto NT 450's on front,255/50 BFG Drags out back,93 Cobra Spoiler
Daily driver 89 Coupe:BBK shorties,offroad,flowturds with dumps,soon to be cyber green

[gray87GT]

Thanks for the replies Green92LX and slow87GT. I have only driven it two times, and only floored it to make sure I heard and felt everything right. It feels great everywhere else but WOT. When the weather decides to get better I will check my fuel pressure and the TPS. And soon after install the pump.

[Skankin]

I'd get a $25 code checker, and start there (even available at Walmart). Have you changed the fuel filter lately? (I make it a yearly thing). Is your fuel pump whinning?

Have you replaced the stock clutch cable? The stock rubber grommet in the firewall could be worn out... allowing the cable to flex, and the clutch to dis-engage... this slippage can cause some bucking (but it doesn't really sound like this).

The EGR only operates while cruising (not at idle or WOT)... shouldn't be a problem.

The EGO sensors adjust the fuel accordingly (when in closed loop). At WOT, the computer only relies on the MAF reading, and uses the stock calibration table (programed in the computer). If the MAF isn't functioning properly, this could be a problem.

Also, when you use a calibrated MAF to fool the computer, you get a little extra timing advance... so make sure your base timing isn't too high... maybe try it back at 10BTDC.

At WOT, you start pulling more vacuum, so the fuel pressure will actually drop (it doesn't need as much pressure to inject the same volume into the low pressure cylinder/intake).

[gray87GT]

Thanks Skankin- I will deffinatly look into everything you mentioned.