engine surging

chickenbot · November 1st, 2007, 07:34 PM

hows everyone doing? ok i have a 1990 5.0 gt with bbk headers, underdrive pully, 3.55 gears and been lowered about 2in. thats all that i know of from the previous owner. lately while im driving i cant stay at a steady speed. it either speeds up or slows down. while its at idle it it surges as well like im gasing it a little and letting off. i thought i may have an intake leak so i replaced the upper intake gasket and the throttle body gasket. i also replace all the hoses under the pletum(sp?) and the pcv valve. now heres the odd part. it only does this while the check engine light is off but when it comes on she drives like a dream. any thoughts?

Speedstang302 · November 1st, 2007, 07:36 PM

Originally Posted by chickenbot

hows everyone doing? ok i have a 1990 5.0 gt with bbk headers, underdrive pully, 3.55 gears and been lowered about 2in. thats all that i know of from the previous owner. lately while im driving i cant stay at a steady speed. it either speeds up or slows down. while its at idle it it surges as well like im gasing it a little and letting off. i thought i may have an intake leak so i replaced the upper intake gasket and the throttle body gasket. i also replace all the hoses under the pletum(sp?) and the pcv valve. now heres the odd part. it only does this while the check engine light is off but when it comes on she drives like a dream. any thoughts?

sounds like a vaccum leak somewhere..

chickenbot · November 1st, 2007, 07:40 PM

where do you recomend to check?

Speedstang302 · November 1st, 2007, 08:04 PM

Originally Posted by chickenbot

where do you recomend to check?

spray carb cleaner on everything, pretty easy way to check, also check all the vaccum ports on upper and lower intake, one may have fallen off

89LX347 · November 1st, 2007, 10:16 PM

map sensor could also be the problem...that happened to me too

78mach1 · November 2nd, 2007, 12:33 AM

i have a 78 mustang with a 302 that i went all out on and i have a similar problem. but its not as bad, its just tiny surges when im at cruising speed and i cant figure it out. (its carburated) if anybody has any ideas please help.

Speedstang302 · November 2nd, 2007, 12:40 AM

Originally Posted by 78mach1

i have a 78 mustang with a 302 that i went all out on and i have a similar problem. but its not as bad, its just tiny surges when im at cruising speed and i cant figure it out. (its carburated) if anybody has any ideas please help.

so does the throttle just stick wide open sometimes? also could be you're timing!!!

jam77 · November 2nd, 2007, 01:23 AM

I had a surging problem and it turned out that my timing was off.

BigBlockFairlane · November 2nd, 2007, 11:44 AM

Originally Posted by 78mach1

i have a 78 mustang with a 302 that i went all out on and i have a similar problem. but its not as bad, its just tiny surges when im at cruising speed and i cant figure it out. (its carburated) if anybody has any ideas please help.

Similar stuff, vacuum leak, ignition sytem, set timing, voltage regulator.

Is it duraspark?

78mach1 · November 3rd, 2007, 02:43 AM

Originally Posted by Speedstang302

Originally Posted by 78mach1

i have a 78 mustang with a 302 that i went all out on and i have a similar problem. but its not as bad, its just tiny surges when im at cruising speed and i cant figure it out. (its carburated) if anybody has any ideas please help.

so does the throttle just stick wide open sometimes? also could be you're timing!!!

no the throttle is completely fine and my timing is set perfect and i have made some adjustments to the timing and it hasnt changed anything.

78mach1 · November 3rd, 2007, 02:49 AM

Originally Posted by BigBlockFairlane

Originally Posted by 78mach1

i have a 78 mustang with a 302 that i went all out on and i have a similar problem. but its not as bad, its just tiny surges when im at cruising speed and i cant figure it out. (its carburated) if anybody has any ideas please help.

Similar stuff, vacuum leak, ignition sytem, set timing, voltage regulator.

Is it duraspark?

ya i was thinking vacum leak to but like i told the other guy, the timing is right where it needs to be, but i was thinking, if i take a propane torch and turn it on so only gas is coming out, and i hold it on all the vacum lines, carb, anything with vacum. do you think it would richen it? so i could find it if it is a vacum leak?...cause i have searched high and low for one and i cant find one. and i am running out of ideas

chickenbot · November 11th, 2007, 11:47 PM

would a maf going out do this too? what is the stock size as well

white93pony · November 11th, 2007, 11:58 PM

use carb cleaner spray all over intake and check all hoses/vaccum lines

78mach1 · November 13th, 2007, 01:31 AM

Originally Posted by white93pony

use carb cleaner spray all over intake and check all hoses/vaccum lines

hey ya i did it with carb cleaner. i had a small leak where the power brake booster hooks to the back of my carb
thank!~

November 1st, 2007, 07:34 PM	#1
chickenbot Enthusiast 1990 mustang gt eventually Join Date: Nov 2007 Location: plano, tx Posts: 938 iTrader: 0 reviews	engine surging hows everyone doing? ok i have a 1990 5.0 gt with bbk headers, underdrive pully, 3.55 gears and been lowered about 2in. thats all that i know of from the previous owner. lately while im driving i cant stay at a steady speed. it either speeds up or slows down. while its at idle it it surges as well like im gasing it a little and letting off. i thought i may have an intake leak so i replaced the upper intake gasket and the throttle body gasket. i also replace all the hoses under the pletum(sp?) and the pcv valve. now heres the odd part. it only does this while the check engine light is off but when it comes on she drives like a dream. any thoughts?

November 1st, 2007, 07:40 PM	#3
chickenbot Enthusiast 1990 mustang gt eventually Join Date: Nov 2007 Location: plano, tx Posts: 938 iTrader: 0 reviews	where do you recomend to check? __________________ 1990 gt 5.0 Mac Performance 76mm straight shot intake 70mm Accufab tb and egr spacer Trick Flow Track Heat u/l intake 3.55 gears MSD distributor, Blaster Coil, and 8.5mm wires

November 1st, 2007, 10:16 PM	#5
89LX347 Hardcore Enthusiast Join Date: Apr 2007 Posts: 1,304 iTrader: 0 reviews	map sensor could also be the problem...that happened to me too __________________ I believe in art when it is not seen. I believe in music when it is not audible. I believe in God when He is silent.

November 2nd, 2007, 01:23 AM	#8
jam77 Enthusiast 1987 Mustang GT Join Date: Apr 2007 Location: IL Posts: 685 iTrader: 0 reviews	engine surging I had a surging problem and it turned out that my timing was off. __________________ 87 GT, typhoon upper and lower,70mm tb, 90mm maf, bbk shorties, bbk x-pipe, flowmaster cat back, 3:73 gear, pro 5.0 shifter, novi blower,afm power pipe, load IO, Trick Flow heads, Anderson B-31 cam, Anderson PMS, 42 lb injectors, t-rex fuel pump.

November 11th, 2007, 11:47 PM	#12
chickenbot Enthusiast 1990 mustang gt eventually Join Date: Nov 2007 Location: plano, tx Posts: 938 iTrader: 0 reviews	would a maf going out do this too? what is the stock size as well __________________ 1990 gt 5.0 Mac Performance 76mm straight shot intake 70mm Accufab tb and egr spacer Trick Flow Track Heat u/l intake 3.55 gears MSD distributor, Blaster Coil, and 8.5mm wires

November 2nd, 2007, 12:33 AM	#6
78mach1 Hardcore Enthusiast Join Date: Oct 2007 Location: utah Posts: 1,365 iTrader: 0 reviews	i have a 78 mustang with a 302 that i went all out on and i have a similar problem. but its not as bad, its just tiny surges when im at cruising speed and i cant figure it out. (its carburated) if anybody has any ideas please help.

November 11th, 2007, 11:58 PM	#13
white93pony Newbie Join Date: Jun 2007 Posts: 14 iTrader: 0 reviews	use carb cleaner spray all over intake and check all hoses/vaccum lines

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