loosing mid/top end power...

Golana · 05-12-2008, 11:12 PM

well, ive been steadily loosing my top end power, but now im starting to loose my mid range power...

my truck has lots of torque and takes off the line like a bat out of hell, but after i shift into 3rd, the power just isnt there anymore... takes me almost twice as long to get up to 100km/h now than it did 2 months ago.

i just did a tune-up: new plugs, cap/rotor, oil change (amsoil synthetic) and i was gunna do wires too, but they were just a bit too much all at once...

any suggestions?

4.3L TBI, custom exhaust, custom cold air intake (i think thats all the performance mods ive done)

Daveman2 · 05-12-2008, 11:22 PM

Quote: Originally Posted by Golana

well, ive been steadily loosing my top end power, but now im starting to loose my mid range power...

my truck has lots of torque and takes off the line like a bat out of hell, but after i shift into 3rd, the power just isnt there anymore... takes me almost twice as long to get up to 100km/h now than it did 2 months ago.

i just did a tune-up: new plugs, cap/rotor, oil change (amsoil synthetic) and i was gunna do wires too, but they were just a bit too much all at once...

any suggestions?

4.3L TBI, custom exhaust, custom cold air intake (i think thats all the performance mods ive done)

seafoam that bitch, then report back

have you check all the sensors, what about fuel pressure, what's the mileage?

Do you know what condition you catalytic convertor is in?

Golana · 05-12-2008, 11:29 PM

i seafoamed it not too long ago... carb cleaned the shit out of it!

249xxx

cat has not been replaced, has screwed up before... bogged me down once before... that would actually make alot of sense... i bet ya its the cat...

how would i go through and check the sensors? which ones should i check?

Daveman2 · 05-12-2008, 11:30 PM

Quote: Originally Posted by Golana

i seafoamed it not too long ago... carb cleaned the shit out of it!

249xxx

cat has not been replaced, has screwed up before... bogged me down once before... that would actually make alot of sense... i bet ya its the cat...

how would i go through and check the sensors? which ones should i check?

02 Sensors/airflow sensors are always good to check, definitely go tap on the cat and see what it sounds like

Daveman2 · 05-12-2008, 11:31 PM

Quote: Originally Posted by Golana

i seafoamed it not too long ago... carb cleaned the shit out of it!

249xxx

cat has not been replaced, has screwed up before... bogged me down once before... that would actually make alot of sense... i bet ya its the cat...

how would i go through and check the sensors? which ones should i check?

02 Sensors/airflow sensors are always good to check, definitely go tap on the cat and see what it sounds like

is it 250,000mi or km? if 250,000 it might just be old, you could get it compression tested to find out how the rings are

Golana · 05-13-2008, 12:06 AM

Quote: Originally Posted by Daveman2

02 Sensors/airflow sensors are always good to check, definitely go tap on the cat and see what it sounds like

is it 250,000mi or km? if 250,000 it might just be old, you could get it compression tested to find out how the rings are

what kinda sound would i be looking for from the cat when i tap on it??
how do i check the 02 and airflow sensors?

its 250,000km so its not that old yet... i might go get it compression tested... thats just pushing air into the cylinders, though the spark plug holes, right? i could build something at work to do that. how many psi would i be looking for the cylinder to hold?

SH-60B · 05-13-2008, 06:49 AM

A compression test is done by cranking the motor with a compression gage in a spark plug hole. With a leak down test you put compressed air in the cylinder through the spark plug hole. IDK how much pressure to use for the leak down test, but what your looking for is how much air leaks past rings / valves in a given time period. But if your truck takes off "like a bat out of hell" I think the compression is good in your motor. You might be able to test the cat by removing the pre-cat O2 sensor and trying that out, it will be loud.

Golana · 05-13-2008, 11:52 AM

i ran my truck without exhaust, just dumping at the cat for a week. THAT was loud!

i could make a compression gauge at work, but as you said, i dont think its my compression, cause i can launch probably harder than ive ever been able to.

i doubt ill be able to get the pre-cat o2 out, its pretty rusted... how would i be able to test it?

Golana · 05-13-2008, 01:07 PM

maybe its not my cat... because my rpm's can get up there, but im just not making power at the higher rpm's anymore...

Daveman2 · 05-13-2008, 01:21 PM

at only 250,000km these motors shouldn't be losing significant power, it's probably a fuel/spark problem

You can't really test an 02 sensor, you just gotta pull em out, and if it's impossible to get out because it's been there so long, then it's probably a good place to start looking for problems.

Is the "custom exhaust" work doing well?

When you tap the cat listen for any loose things rattling around, that will signifiy a broken/clogged cat.

High torque and crappy top-end sounds like exhaust restrictions to me

Doesn't TBI have a MAP sensor? that could be something to check too

kamesama980 · 05-13-2008, 01:31 PM

getting to high rpms without any power is a sign of clogged cat. if you can't get to high rpms at all then you aren't gonna have much anywhere else either.

Golana · 05-13-2008, 02:10 PM

a clogged cat would restrict air flow... high rpm's is pushing out alot of exhaust, i dont think it could be the cat if im reaching higher rpm's...

i might have a MAP sensor... what do they look like?
my custom exhaust work seems to be holding up quite well so far... i dont know what to check for for air restrictions... why would it just do it all of a sudden??

Golana · 05-13-2008, 08:35 PM

could it be timing? cause everything else seems to check out so far...

kamesama980 · 05-13-2008, 11:12 PM

high rpm low throttle is similar airflow to WOT at lower rpm. trust me, you can get to high rpms with a clogged cat they just suck. Had great power off the line and sucked balls over 2500 but still hit the revlimiter: http://s29.photobucket.com/albums/c2...t=DSCF0800.jpg

besides, it's free to check

Golana · 05-13-2008, 11:48 PM

holy crap man... how did you do that?! haha! im just gunna rip my cat off... ive had problems with it before, so fk it. i wanna get a custom pipe built so i can run true duals... im not really into the stock y-pipe...

Golana · 05-17-2008, 01:28 AM

i did a throttle cable mod today...

i stuck a piece of rubber gasket over the throttle cable part just before the throttle body (slid it over the cable, over the black plastic pen-tip thingy, and onto the clip that clips into the metal bracket) it spaced it out about 1/2" taking up all the slack. now, i have a much more responsive throttle, and my truck hauls some serious ass! when i have the pedal to the metal, the throttle body butterfly valves are almost straight up and down hahaa! AWESOME!

i have no problem getting up to and past 140km/h now! i can hit 130 in FOURTH!

ill post some pictures tomorrow after i get my camera some new batteries.

kamesama980 · 05-18-2008, 07:36 PM

I don't know how the cat got like that, I oulled it out like that after I swapped the engine. it's 1st engine blew the head gasket. the second engine (that I got it with) had a thrown rod, I don't know what else went wrong. the curious as hell part of it is that that's the BACK of the cat... away from the engine. the front of the cat was A-OK. the back looked like that and was missing about 3/4 of the material too.

05-12-2008, 11:12 PM	#1
Golana Truck #121616 Age: 21 Join Date: Jan 2007 Posts: 1,221 Location: High River, Alberta User is: Online	loosing mid/top end power... well, ive been steadily loosing my top end power, but now im starting to loose my mid range power... my truck has lots of torque and takes off the line like a bat out of hell, but after i shift into 3rd, the power just isnt there anymore... takes me almost twice as long to get up to 100km/h now than it did 2 months ago. i just did a tune-up: new plugs, cap/rotor, oil change (amsoil synthetic) and i was gunna do wires too, but they were just a bit too much all at once... any suggestions? 4.3L TBI, custom exhaust, custom cold air intake (i think thats all the performance mods ive done)
	[Reply w/Quote]

05-12-2008, 11:22 PM	#2
Daveman2 Road Racing Blazer Age: 21 Join Date: May 2004 Posts: 3,136 Location: Santa Cruz, CA User is: OffLine	Re: loosing mid/top end power... Quote: Originally Posted by Golana well, ive been steadily loosing my top end power, but now im starting to loose my mid range power... my truck has lots of torque and takes off the line like a bat out of hell, but after i shift into 3rd, the power just isnt there anymore... takes me almost twice as long to get up to 100km/h now than it did 2 months ago. i just did a tune-up: new plugs, cap/rotor, oil change (amsoil synthetic) and i was gunna do wires too, but they were just a bit too much all at once... any suggestions? 4.3L TBI, custom exhaust, custom cold air intake (i think thats all the performance mods ive done) seafoam that bitch, then report back have you check all the sensors, what about fuel pressure, what's the mileage? Do you know what condition you catalytic convertor is in?
	[Reply w/Quote]

05-12-2008, 11:29 PM	#3
Golana Truck #121616 Age: 21 Join Date: Jan 2007 Posts: 1,221 Location: High River, Alberta User is: Online	Re: loosing mid/top end power... i seafoamed it not too long ago... carb cleaned the shit out of it! 249xxx cat has not been replaced, has screwed up before... bogged me down once before... that would actually make alot of sense... i bet ya its the cat... how would i go through and check the sensors? which ones should i check?
	[Reply w/Quote]

05-12-2008, 11:30 PM	#4
Daveman2 Road Racing Blazer Age: 21 Join Date: May 2004 Posts: 3,136 Location: Santa Cruz, CA User is: OffLine	Re: loosing mid/top end power... Quote: Originally Posted by Golana i seafoamed it not too long ago... carb cleaned the shit out of it! 249xxx cat has not been replaced, has screwed up before... bogged me down once before... that would actually make alot of sense... i bet ya its the cat... how would i go through and check the sensors? which ones should i check? 02 Sensors/airflow sensors are always good to check, definitely go tap on the cat and see what it sounds like
	[Reply w/Quote]

05-12-2008, 11:31 PM	#5
Daveman2 Road Racing Blazer Age: 21 Join Date: May 2004 Posts: 3,136 Location: Santa Cruz, CA User is: OffLine	Re: loosing mid/top end power... Quote: Originally Posted by Golana i seafoamed it not too long ago... carb cleaned the shit out of it! 249xxx cat has not been replaced, has screwed up before... bogged me down once before... that would actually make alot of sense... i bet ya its the cat... how would i go through and check the sensors? which ones should i check? 02 Sensors/airflow sensors are always good to check, definitely go tap on the cat and see what it sounds like is it 250,000mi or km? if 250,000 it might just be old, you could get it compression tested to find out how the rings are
	[Reply w/Quote]


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05-13-2008, 12:06 AM	#6
Golana Truck #121616 Age: 21 Join Date: Jan 2007 Posts: 1,221 Location: High River, Alberta User is: Online	Re: loosing mid/top end power... Quote: Originally Posted by Daveman2 02 Sensors/airflow sensors are always good to check, definitely go tap on the cat and see what it sounds like is it 250,000mi or km? if 250,000 it might just be old, you could get it compression tested to find out how the rings are what kinda sound would i be looking for from the cat when i tap on it?? how do i check the 02 and airflow sensors? its 250,000km so its not that old yet... i might go get it compression tested... thats just pushing air into the cylinders, though the spark plug holes, right? i could build something at work to do that. how many psi would i be looking for the cylinder to hold?
	[Reply w/Quote]

05-13-2008, 06:49 AM	#7
SH-60B Registered Neanderthal Join Date: Nov 2007 Posts: 830 Location: East Haddam/CT/USA User is: OffLine	Re: loosing mid/top end power... A compression test is done by cranking the motor with a compression gage in a spark plug hole. With a leak down test you put compressed air in the cylinder through the spark plug hole. IDK how much pressure to use for the leak down test, but what your looking for is how much air leaks past rings / valves in a given time period. But if your truck takes off "like a bat out of hell" I think the compression is good in your motor. You might be able to test the cat by removing the pre-cat O2 sensor and trying that out, it will be loud.
	[Reply w/Quote]

05-13-2008, 11:52 AM	#8
Golana Truck #121616 Age: 21 Join Date: Jan 2007 Posts: 1,221 Location: High River, Alberta User is: Online	Re: loosing mid/top end power... i ran my truck without exhaust, just dumping at the cat for a week. THAT was loud! i could make a compression gauge at work, but as you said, i dont think its my compression, cause i can launch probably harder than ive ever been able to. i doubt ill be able to get the pre-cat o2 out, its pretty rusted... how would i be able to test it?
	[Reply w/Quote]

05-13-2008, 01:07 PM	#9
Golana Truck #121616 Age: 21 Join Date: Jan 2007 Posts: 1,221 Location: High River, Alberta User is: Online	Re: loosing mid/top end power... maybe its not my cat... because my rpm's can get up there, but im just not making power at the higher rpm's anymore...
	[Reply w/Quote]

05-13-2008, 01:21 PM	#10
Daveman2 Road Racing Blazer Age: 21 Join Date: May 2004 Posts: 3,136 Location: Santa Cruz, CA User is: OffLine	Re: loosing mid/top end power... at only 250,000km these motors shouldn't be losing significant power, it's probably a fuel/spark problem You can't really test an 02 sensor, you just gotta pull em out, and if it's impossible to get out because it's been there so long, then it's probably a good place to start looking for problems. Is the "custom exhaust" work doing well? When you tap the cat listen for any loose things rattling around, that will signifiy a broken/clogged cat. High torque and crappy top-end sounds like exhaust restrictions to me Doesn't TBI have a MAP sensor? that could be something to check too
	[Reply w/Quote]

05-13-2008, 01:31 PM	#11
kamesama980 The Eye is watching you!! Age: 23 Join Date: Nov 2007 Posts: 715 Location: dekalb, IL, USA User is: OffLine	Re: loosing mid/top end power... getting to high rpms without any power is a sign of clogged cat. if you can't get to high rpms at all then you aren't gonna have much anywhere else either.
	[Reply w/Quote]

05-13-2008, 02:10 PM	#12
Golana Truck #121616 Age: 21 Join Date: Jan 2007 Posts: 1,221 Location: High River, Alberta User is: Online	Re: loosing mid/top end power... a clogged cat would restrict air flow... high rpm's is pushing out alot of exhaust, i dont think it could be the cat if im reaching higher rpm's... i might have a MAP sensor... what do they look like? my custom exhaust work seems to be holding up quite well so far... i dont know what to check for for air restrictions... why would it just do it all of a sudden??
	[Reply w/Quote]

05-13-2008, 08:35 PM	#13
Golana Truck #121616 Age: 21 Join Date: Jan 2007 Posts: 1,221 Location: High River, Alberta User is: Online	Re: loosing mid/top end power... could it be timing? cause everything else seems to check out so far...
	[Reply w/Quote]

05-13-2008, 11:12 PM	#14
kamesama980 The Eye is watching you!! Age: 23 Join Date: Nov 2007 Posts: 715 Location: dekalb, IL, USA User is: OffLine	Re: loosing mid/top end power... high rpm low throttle is similar airflow to WOT at lower rpm. trust me, you can get to high rpms with a clogged cat they just suck. Had great power off the line and sucked balls over 2500 but still hit the revlimiter: http://s29.photobucket.com/albums/c2...t=DSCF0800.jpg besides, it's free to check
	[Reply w/Quote]

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05-13-2008, 11:48 PM	#15
Golana Truck #121616 Age: 21 Join Date: Jan 2007 Posts: 1,221 Location: High River, Alberta User is: Online	Re: loosing mid/top end power... holy crap man... how did you do that?! haha! im just gunna rip my cat off... ive had problems with it before, so fk it. i wanna get a custom pipe built so i can run true duals... im not really into the stock y-pipe...
	[Reply w/Quote]

05-17-2008, 01:28 AM	#16
Golana Truck #121616 Age: 21 Join Date: Jan 2007 Posts: 1,221 Location: High River, Alberta User is: Online	Re: loosing mid/top end power... i did a throttle cable mod today... i stuck a piece of rubber gasket over the throttle cable part just before the throttle body (slid it over the cable, over the black plastic pen-tip thingy, and onto the clip that clips into the metal bracket) it spaced it out about 1/2" taking up all the slack. now, i have a much more responsive throttle, and my truck hauls some serious ass! when i have the pedal to the metal, the throttle body butterfly valves are almost straight up and down hahaa! AWESOME! i have no problem getting up to and past 140km/h now! i can hit 130 in FOURTH! ill post some pictures tomorrow after i get my camera some new batteries.
	[Reply w/Quote]

05-18-2008, 07:36 PM	#17
kamesama980 The Eye is watching you!! Age: 23 Join Date: Nov 2007 Posts: 715 Location: dekalb, IL, USA User is: OffLine	Re: loosing mid/top end power... I don't know how the cat got like that, I oulled it out like that after I swapped the engine. it's 1st engine blew the head gasket. the second engine (that I got it with) had a thrown rod, I don't know what else went wrong. the curious as hell part of it is that that's the BACK of the cat... away from the engine. the front of the cat was A-OK. the back looked like that and was missing about 3/4 of the material too.
	[Reply w/Quote]