Decelaration Surging

[ndburli]

***UPDATE***

Still looking for some help HOWEVER I did a little further diagnostic today. The truck does in fact surge when I let out of the gas (whether in boost or not). It usually happens around 30-35mph however can happen anytime I let off the gas in that range. It surges/gulps between 1000-1500 rpm. The truck runs smooth with no other issues, no idle issues, no boost issues, no vacuum issues (I have an a/m gauge that reads near 20psi in vacuum). I did not have this issue until I installed the a/m boost gauge which I pulled from the manifold brake booster line. I have check all those hoses/tubes and they are tight.

**One important note-when I turn the blower fan on it subsides**

Thoughts? I need some help. I know someone has seen this before.

Thanks,


I have a question. While driving my Sy (stock with Hood chip) everything runs smooth. No issues at all. Sometimes after getting into the boost a little upon deceleration (going about 10-30mph) without touching the brake or gas the truck starts surging. If I hit the gas or brake the surging subsides. Possible vacuum leak? Anyone have any ideas?

Thanks for the help...I'm a little at a loss.

 

[IGottaSy]

Re: Decelaration Surging

Spray some brake cleaner on the hoses and hose connections. You will notice a change in idle speed when you find vacuum leak. This is better than visual inspection. Actually, spray it anywhere you think the truck is gulping extra air.

 

[ndburli]

Re: Decelaration Surging

Spray some brake cleaner on the hoses and hose connections. You will notice a change in idle speed when you find vacuum leak. This is better than visual inspection. Actually, spray it anywhere you think the truck is gulping extra air.

Do the symptoms Im describing sound like a vacuum leak even though idle is perfect and I have no issues with drivability outside of the minor deceleration surge? I guess if it is gulping ait it must be some type of Vac leak

 

[IGottaSy]

Re: Decelaration Surging

Could be electrical. The brown wire coming out of the distributor doesn't have enough slack. You could try tugging on it while truck idles. I don't see the connection between the blower motor and the engine's ignition system. I simply suggested a different way to find vacuum leaks.

 

[ndburli]

Re: Decelaration Surging

Could be electrical. The brown wire coming out of the distributor doesn't have enough slack. You could try tugging on it while truck idles. I don't see the connection between the blower motor and the engine's ignition system. I simply suggested a different way to find vacuum leaks.

Thanks for your response. I am certainly at a loss. I will try checking the vacuum and brown wire

 

[Quickstop [UK]]

Re: Decelaration Surging

So the issue didn't exist before the gauge install? Can you disconnect it to see if that cures the problem then work it out from there?

 

[ndburli]

Re: Decelaration Surging

So the issue didn't exist before the gauge install? Can you disconnect it to see if that cures the problem then work it out from there?

Yes. My plan is to disconnect and check. The way it gulps for air and stops when I push the brake males me think it is something I did with the gauge install off the booster line

 

[IGottaSy]

Re: Decelaration Surging

You should have plumbed it from the intake. It could be interfering with the signal to boost solenoid (think that's where you connected it to) or if plumbed where the MAP is, might have the same outcome

 

[ndburli]

Re: Decelaration Surging

You should have plumbed it from the intake. It could be interfering with the signal to boost solenoid (think that's where you connected it to) or if plumbed where the MAP is, might have the same outcome

I currently have it plumbed coming off the intake to brake booster line. I also used teflow tape...should I used something else to ensure no leaks?

 

[Don W.]

Teflon tape is fine, taping into the fitting for brake booster is fine. As long as there are no leaks and as long as the brake booster fitting is not restricted in some manner. There has to be no leaks anywhere. IMO taping the brakes or even stepping on them should make virtually no difference in how the motor runs unless the booster is bad. Stepping on the brake provides a momentary "burp" of air then nothing so if there is a difference it should be momentary. If you want to test that, drive with the line pinched off. Just do it on and empty road because you'll have VERY poor breaking. Leave LOTS of stopping distance. Spooky.

Based on what you say, stepping on the brake, it stops the surging then it sounds like it's going rich in "deceleration" mode and the extra bit of air leans it back out. This could indicate a bad MAP sensor. Do you have a wide band?

Since it was fine before, disconnecting the gauge is a good idea. (Already mentioned)

Are you able to log?

Is an "a/m gauge" different than a standard vac/boost gauge?

Caution, small rant...vac isn't measured in PSI, but in InHG (inches of mercury) Yes your ga reads InHG (vacuum) one way and PSI the other.

 

[Don W.]

Teflon tape is fine, taping into the fitting for brake booster is fine. As long as there are no leaks and as long as the brake booster fitting is not restricted in some manner. There has to be no leaks anywhere. IMO taping the brakes or even stepping on them should make virtually no difference in how the motor runs unless the booster is bad. Stepping on the brake provides a momentary "burp" of air then nothing so if there is a difference it should be momentary. If you want to test that, drive with the line pinched off. Just do it on and empty road because you'll have VERY poor breaking. Leave LOTS of stopping distance. Spooky.

Based on what you say, stepping on the brake, it stops the surging then it sounds like it's going rich in "deceleration" mode and the extra bit of air leans it back out. This could indicate a bad MAP sensor. Do you have a wide band?

Since it was fine before, disconnecting the gauge is a good idea. (Already mentioned)

Are you able to log?

Is an "a/m gauge" different than a standard vac/boost gauge?

Caution, small rant...vac isn't measured in PSI, but in InHG (inches of mercury) Yes your ga reads InHG (vacuum) one way and PSI the other.

 

[Don W.]

Teflon tape is fine, taping into the fitting for brake booster is fine. As long as there are no leaks and as long as the brake booster fitting is not restricted in some manner. There has to be no leaks anywhere. IMO taping the brakes or even stepping on them should make virtually no difference in how the motor runs unless the booster is bad. Stepping on the brake provides a momentary "burp" of air then nothing so if there is a difference it should be momentary. If you want to test that, drive with the line pinched off. Just do it on and empty road because you'll have VERY poor breaking. Leave LOTS of stopping distance. Spooky.

Based on what you say, stepping on the brake, it stops the surging then it sounds like it's going rich in "deceleration" mode and the extra bit of air leans it back out. This could indicate a bad MAP sensor. Do you have a wide band?

Since it was fine before, disconnecting the gauge is a good idea. (Already mentioned)

Are you able to log?

Is an "a/m gauge" different than a standard vac/boost gauge?

Caution, small rant...vac isn't measured in PSI, but in InHG (inches of mercury) Yes your ga reads InHG (vacuum) one way and PSI the other.