A couple post-coil change questions

[NoDak Ninja]

Hi everyone. I just changed a coil in my Bravada. I have a couple questions I'm hoping someone can answer:

1. Is there any way to delete the Service Engine Soon code without using a code reader? The closest auto-parts store is 40 miles away.

2. While putting everything back together I noticed a hose barb that has no hose hooked up to it. See the picture below for what I am talking about.

View attachment 30136

Thanks for any help you can give me!

 

[The_Roadie]

Welcome!

You should own a code reader. Everybody should.

What was your code? If you solve the underlying problem, then in a few "drive cycles", the light will go off. A drive cycle is a cold start, drive around for a while until it gets warm, then stop and let it cool off foe some number of hours. Could take 2-3 days depending on your driving habits.

That circled nipple is only used on the EXT. Since you don't have an EXT, I bet there is no suction there because it's blocked internally. The OTHER hose end you didn't circle *IS* critical though. It goes to the fuel pressure regulator (FPR) and it belongs on a nipple on the other side of the black intake manifold that I know is making a sucking sound. Go put those together and you will probably start idling at 60o RPM instead of the 900 you might be at now.

 

[NoDak Ninja]

Welcome!

Thanks!

You should own a code reader. Everybody should.

Yeah, I know...It's on my wish list.

What was your code? If you solve the underlying problem, then in a few "drive cycles", the light will go off. A drive cycle is a cold start, drive around for a while until it gets warm, then stop and let it cool off foe some number of hours. Could take 2-3 days depending on your driving habits.

It was a P0300. I ended up having to put in a new coil. I'll be heading to town Monday. So if I haven't gone through enough drive cycles for it to clear itself by then, I'll stop by the parts store.

That circled nipple is only used on the EXT. Since you don't have an EXT, I bet there is no suction there because it's blocked internally. The OTHER hose end you didn't circle *IS* critical though. It goes to the fuel pressure regulator (FPR) and it belongs on a nipple on the other side of the black intake manifold that I know is making a sucking sound. Go put those together and you will probably start idling at 60o RPM instead of the 900 you might be at now.

That other hose (and the vacuum hose on the left) hooks up to the air box that got put back on right after I took the picture.

Thanks for your help!

 

[gmcman]

Hi everyone. I just changed a coil in my Bravada. I have a couple questions I'm hoping someone can answer:

1. Is there any way to delete the Service Engine Soon code without using a code reader? The closest auto-parts store is 40 miles away.

2. While putting everything back together I noticed a hose barb that has no hose hooked up to it. See the picture below for what I am talking about.

View attachment 16902

Thanks for any help you can give me!

I have the SWB (NON-EXT) and that circled port draws manifold vacuum on mine...not sure of the latter years but put your finger over it when it's running....you will tell real quick.

The FPR hose generally hooks to the intake resonator which appears to be missing on yours. The hose is inline pre-TB and I believe draws a vacuum when the air filter gets really clogged....not exactly sure but either case, here's a pic.


Edited to add, you definitely need to plug that vacuum port if it's sucking air.

 

[NoDak Ninja]

I have the SWB (NON-EXT) and that circled port draws manifold vacuum on mine...not sure of the latter years but put your finger over it when it's running....you will tell real quick.

The FPR hose generally hooks to the intake resonator which appears to be missing on yours. The hose is inline pre-TB and I believe draws a vacuum when the air filter gets really clogged....not exactly sure but either case, here's a pic.


Edited to add, you definitely need to plug that vacuum port if it's sucking air.

It seems that I caused some confusion by taking the picture without the resonator on. Yes, the FPR hose hooks to the resonator (couldn't remember what it was called so called it the "air box" in my last post). I had just changed a coil, so I took the pic before putting the resonator back on since the port in question was easier to see.

I did put my finger over the "mystery" port quickly while it was running and didn't feel any vacuum pressure. But, I will double check it tomorrow just to be sure. By the looks of it, it doesn't appear that there was ever a hose on it (or at least not for along time). There definitely wasn't one there when I removed the resonator.

IF there is pressure there, where is it supposed to hook up to? There is no port on the resonator for it to go to. I only got the Bravada about 2 months ago, so I am still learning about it. It's a different beast after only owning cars with V6's for the last 20 years or so!

Thanks for all the help!

 

[gmcman]

IF there is pressure there, where is it supposed to hook up to? There is no port on the resonator for it to go to.

Thanks for all the help!

Just what the Roadie stated.....only applies to EXT or long-wheelbase versions, aka 7-passenger.

 

[The_Roadie]

I have the SWB (NON-EXT) and that circled port draws manifold vacuum on mine...

Now I've got to go look at mine, but isn't there a cap on that to prevent suckage on our SWB?

 

[Mooseman]

This is making me curious. What would need vacuum on an EXT that isn't needed on a SWB? HVAC actuators? Nope, the rear HVAC uses the same crappy electric actuators as the front but that's the only thing I can think of that would be different between the two. Don't remember seeing any vacuum hose in the front or rear HVAC.

 

[gmcman]

Now I've got to go look at mine, but isn't there a cap on that to prevent suckage on our SWB?

Yes, there is a cap on mine. Over the years it tended to crack so I replaced it with a vacuum test hose routed to the front of the resonator.

Pic of factory cap.

 

[The_Roadie]

This is making me curious. What would need vacuum on an EXT that isn't needed on a SWB? HVAC actuators? Nope, the rear HVAC uses the same crappy electric actuators as the front but that's the only thing I can think of that would be different between the two. Don't remember seeing any vacuum hose in the front or rear HVAC.

The EXT has a vacuum powered, electrically controlled, valve on the firewall to block the flow of coolant to the way back if you aren't calling for heat. I think it's a silly design, because it serves only to slow down the flow of coolant when you DO call for heat, but all I can think of is that the plenum design in the way back doesn't allow for total airflow blockage through the heater core when you're in AC mode.

Of course, GM even screwed up that design, and there is insufficient coolant flow to the rear heater core when you DO want heat, so they added a boost pump in later years of the EXT, and offered it for free to customers who complained during the warranty period. Or if you were out of warranty, the boost pump comes as a retrofit kit for $$.

 

[Scavenger]

This place is a gold mine of information. After seeing the above posts and diagrams I went out and looked at my 2002 I6 in the Trailblazer and noticed there is no cap/plug on that vacuum port...........very interesting. If this port was intended to be plugged and isn't, could this be a possible contributing factor to the oil spray/leak mentioned in my "catch can" post?...........thanks

 

[The_Roadie]

Is your port sucking without the cap? I seem to remember looking at one, perhaps on a buddy's 2002, and it had a solid disk molded in. That made me think they had to actively drill it out at the factory for the EXT, not wanting to trust a cap for years and years.

 

[Scavenger]

roadie,

Thanks for the very quick response. Mine does not have any type of plug or disc on it. At this time I have things under the hood torn apart, so it will be several days before I can start it to see if there is any suction from it.............thanks again.

 

[NoDak Ninja]

I double checked mine and there is absolutely no pressure at that port.

 

[gmcman]

Kinda odd I suppose, since I have done nothing to this port except use it for vacuum test purposes..never drilled it, came sucking air from the factory.

 

[bobdec]

Topic got my interest, just checked mine (07 Envoy, SWB) . Pulled cap off , put vacuum gauge on, reading 15 in Hg at idle. removed the gauge (opened up line) when idling and engine lost some RPM, minor stumble and then recovered, but did not seem as smooth (could be my imagination). Apparently, on my engine, w/o a cap the port orifice is large enough to create an engine effecting vacuum leak.