Back fire
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Joined: Feb 2001
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From: San Diego, CA
Back fire
I need help from the masters,
I was @ the shop last night getting ready for the race this weekend & was talking with a buddy that has an 90 TPI, headers, no cat, flow masters, 24lb injectors (4 or 5K miles on the injectors), 100k miles on motor, 700R4.
the problem is that when he is decelerating the motor backfires through the exhaust. it reminds me of our old Chevy truck with cherry bombs on it. you are cruising along & let of the gas & as it goes Grrrrrrrrrrrrrrrrrrrrrrrrrrrrr down, it pops through the exhaust.
this is what the decell fuel shut off is supposed to prevent, right?
this has not happened before he changed the injectors, and a few other things that i kind of shrugged of as not important.
I think that this is a leaking injector, any thoughts? & if so, how to prove? he does not have a pressure gauge, but I think that the answer is put a gauge on it. turn the key on. turn the key off. watch the gauge. my car holds pressure for 20 minutes down to 5 psig from 40. if his drops faster than that (& judging from the size of the flames) i am betting that it drops much faster than that.
BW
------------------
Bob Wooten
71 Camaro, 91 EFI
r71chevy@earthlink.net
www.r71camaro.homestead.com
I was @ the shop last night getting ready for the race this weekend & was talking with a buddy that has an 90 TPI, headers, no cat, flow masters, 24lb injectors (4 or 5K miles on the injectors), 100k miles on motor, 700R4.
the problem is that when he is decelerating the motor backfires through the exhaust. it reminds me of our old Chevy truck with cherry bombs on it. you are cruising along & let of the gas & as it goes Grrrrrrrrrrrrrrrrrrrrrrrrrrrrr down, it pops through the exhaust.
this is what the decell fuel shut off is supposed to prevent, right?
this has not happened before he changed the injectors, and a few other things that i kind of shrugged of as not important.
I think that this is a leaking injector, any thoughts? & if so, how to prove? he does not have a pressure gauge, but I think that the answer is put a gauge on it. turn the key on. turn the key off. watch the gauge. my car holds pressure for 20 minutes down to 5 psig from 40. if his drops faster than that (& judging from the size of the flames) i am betting that it drops much faster than that.
BW
------------------
Bob Wooten
71 Camaro, 91 EFI
r71chevy@earthlink.net
www.r71camaro.homestead.com
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iTrader: (1)
Joined: Oct 2000
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From: Pasadena, MD
Car: '87 Camaro IROC-Z
Engine: 385 HSR
Transmission: 700R4
Axle/Gears: 3.42 posi
I'll take a stab at this. 
With no cat, you have less exhaust backpressure, so more of the combustion on decel will take place in the exhaust port and header. It's not much, more like just burning off the rest of the fuel, but it's there. If the DFCO is working, then you are correct that this shouldn't be happening. I don't get any backfires since I know mine is working. Just check to see if the injector pulse widths are dropping to zero to see if the DFCO is actually working...
As far as a leaking injector(s), the fuel might just be draining back through the pump into the tank, or maybe leaking through the fuel pressure regulator and back into the tank. My pressure never holds up after turning the car off, before and with the Walbro in-tank fuel pump, although my injectors do have 130k miles on them now.
------------------
Greg Westphal
'87 IROC 305TPI/A4
With no cat, you have less exhaust backpressure, so more of the combustion on decel will take place in the exhaust port and header. It's not much, more like just burning off the rest of the fuel, but it's there. If the DFCO is working, then you are correct that this shouldn't be happening. I don't get any backfires since I know mine is working. Just check to see if the injector pulse widths are dropping to zero to see if the DFCO is actually working...As far as a leaking injector(s), the fuel might just be draining back through the pump into the tank, or maybe leaking through the fuel pressure regulator and back into the tank. My pressure never holds up after turning the car off, before and with the Walbro in-tank fuel pump, although my injectors do have 130k miles on them now.
------------------
Greg Westphal
'87 IROC 305TPI/A4
Thread Starter
Member
Joined: Feb 2001
Posts: 223
Likes: 0
From: San Diego, CA
Is not the fuel filter supposed to have a reversion valve in it (like the oil filter) so that it can not do that?
thanks for the thoughts, I went stupid on you & did not think to check the Inj Pulse width to see if it was turning off the injectors (or not turning them on).
thanks amigo
BW
------------------
Bob Wooten
71 Camaro, 91 EFI
r71chevy@earthlink.net
www.r71camaro.homestead.com
thanks for the thoughts, I went stupid on you & did not think to check the Inj Pulse width to see if it was turning off the injectors (or not turning them on).
thanks amigo
BW
------------------
Bob Wooten
71 Camaro, 91 EFI
r71chevy@earthlink.net
www.r71camaro.homestead.com
Supreme Member
Joined: Jun 2000
Posts: 7,554
Likes: 1
From: In reality
Car: An Ol Buick
Engine: Vsick
Transmission: Janis Tranny Yank Converter
<font face="Verdana, Arial" size="2">Originally posted by Bob Wooten:
I need help from the masters,
I was @ the shop last night getting ready for the race this weekend & was talking with a buddy that has an 90 TPI, headers, no cat, flow masters, 24lb injectors (4 or 5K miles on the injectors), 100k miles on motor, 700R4.
the problem is that when he is decelerating the motor backfires through the exhaust. it reminds me of our old Chevy truck with cherry bombs on it. you are cruising along & let of the gas & as it goes Grrrrrrrrrrrrrrrrrrrrrrrrrrrrr down, it pops through the exhaust.
this is what the decell fuel shut off is supposed to prevent, right?
Nope.
DFCO is an emissions/mileage thing.
Exhuast leaks can cause it.
Some engines do it when things are right. Keeping the chamber temp up helps with recovery throttle from overrun
this has not happened before he changed the injectors, and a few other things that i kind of shrugged of as not important.
I think that this is a leaking injector, any thoughts? & if so, how to prove? he does not have a pressure gauge, but I think that the answer is put a gauge on it. turn the key on. turn the key off. watch the gauge. my car holds pressure for 20 minutes down to 5 psig from 40. if his drops faster than that (& judging from the size of the flames) i am betting that it drops much faster than that.
BW
</font>
I need help from the masters,
I was @ the shop last night getting ready for the race this weekend & was talking with a buddy that has an 90 TPI, headers, no cat, flow masters, 24lb injectors (4 or 5K miles on the injectors), 100k miles on motor, 700R4.
the problem is that when he is decelerating the motor backfires through the exhaust. it reminds me of our old Chevy truck with cherry bombs on it. you are cruising along & let of the gas & as it goes Grrrrrrrrrrrrrrrrrrrrrrrrrrrrr down, it pops through the exhaust.
this is what the decell fuel shut off is supposed to prevent, right?
Nope.
DFCO is an emissions/mileage thing.
Exhuast leaks can cause it.
Some engines do it when things are right. Keeping the chamber temp up helps with recovery throttle from overrun
this has not happened before he changed the injectors, and a few other things that i kind of shrugged of as not important.
I think that this is a leaking injector, any thoughts? & if so, how to prove? he does not have a pressure gauge, but I think that the answer is put a gauge on it. turn the key on. turn the key off. watch the gauge. my car holds pressure for 20 minutes down to 5 psig from 40. if his drops faster than that (& judging from the size of the flames) i am betting that it drops much faster than that.
BW
</font>
Supreme Member
iTrader: (1)
Joined: Oct 2000
Posts: 1,062
Likes: 0
From: Pasadena, MD
Car: '87 Camaro IROC-Z
Engine: 385 HSR
Transmission: 700R4
Axle/Gears: 3.42 posi
<font face="Verdana, Arial" size="2">Originally posted by Bob Wooten:
Is not the fuel filter supposed to have a reversion valve in it (like the oil filter) so that it can not do that?</font>
Is not the fuel filter supposed to have a reversion valve in it (like the oil filter) so that it can not do that?</font>
<font face="Verdana, Arial" size="2">thanks for the thoughts, I went stupid on you & did not think to check the Inj Pulse width to see if it was turning off the injectors (or not turning them on).</font>
<font face="Verdana, Arial" size="2">thanks amigo</font>
------------------
Greg Westphal
'87 IROC 305TPI/A4
Supreme Member
Joined: Jun 2000
Posts: 1,612
Likes: 0
From: the garage
Car: 84 SVO
Engine: Volvo headed 2.3T
Transmission: WCT5
Axle/Gears: 8.8" 3.73
sounds like you have a bad collector gasket or a leak around a joint, look for sooty deposits on the pipes and the collectors, this typically signs of a leak. my .02 Bob
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