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Michael Dalke's 1967 Firebird

2020 March
of the Month

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Ok, so my SC belt slips at half or more throttle. I just replaced the belt, of course Gator,  and it still does it.  I was kind of thinking maybe it is the tensioner pulley assembly.  What are your thoughts?

also nothing else is wrong.

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Somewhat of an odd question, but when the S/C belt comes off around mid+ throttle, how are you accelerating to that point - are you slowly applying throttle (i.e. "babying it" to mid+ throttle) or are you accelerating hard (i.e. "punching it")? The first (of a few) line of thinking I have involves engine torquing.

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13 hours ago, gandhi_2006 said:

Ok, so my SC belt slips at half or more throttle. I just replaced the belt, of course Gator,  and it still does it.  I was kind of thinking maybe it is the tensioner pulley assembly.  What are your thoughts?

also nothing else is wrong.

Ok I have to ask this first! What occurs that makes you think you have belt slippage?

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I have an aftermarket boost gauge.  When i slowly apply boost, not flooring it,  the car will stutter, and the boost gauge will bounce.  I have no codes, no misfires,  and all fluids are perfect.  I am running premium 91+ octane. 

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7 minutes ago, gandhi_2006 said:

I have an aftermarket boost gauge.  When i slowly apply boost, not flooring it,  the car will stutter, and the boost gauge will bounce.  I have no codes, no misfires,  and all fluids are perfect.  I am running premium 91+ octane. 

Yah, that’s not belt slippage! If the belt was just slipping the engine would run normal, but not with boosted power! Something else is going on. Maybe fuel injectors, maybe coil, maybe even the blower itself has an issue (doubtful)! Tell us some more of how it performs over all! For instance idle, hard throttle, standing hard  launch, etc.

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It runs great other than that.  Starts and idles like a kitten.  No overheating.  Throttle response is perfect.  I can have boost, just nothing over half throttle, then she will sputter.  I will take the SC belt off and try it. 

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Last Indian is right. There could be other culprits here. This is just a partial list. I recommend starting with the easy/less expensive ones first.

1. Dirty fuel injectors - trying running a take of gas with high quality fuel injector cleaner in it. Seafom, Lucus, 303+, etc.

2. Bad/damaged spark plugs

3. Clogged/dirty fuel filter

4. Bad/damaged fuel pump

5. Vacuum leaks

6. Bad wiring harness / electrical connections

7. Dirty air filter?

8. Partially plugged cat?

9. Dirty throttle body

 

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Hey Frosty, long time no chat lol.  I usually run seafoam about once every three months.  So im thinking that fuel system is ok.  vacuum should be good,  all of the hard plastic GM tubing has been replaced with a higher quality tubing.  I dont have a CAT anymore so thats out lol.  Plugs and wires were just replaced when this started.  didnt fix it.  air filter is good to go.  

 

So i guess fuel pump will be tested.  But first im gonna take off the SC belt and see if it still does it. 

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Fuel filter is probably inline. You might still check it.

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ok, thanks for the heads up guys. 

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Always happy to help a buddy out.

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Posted (edited)
2 hours ago, gandhi_2006 said:

Hey Frosty, long time no chat lol.  I usually run seafoam about once every three months.  So im thinking that fuel system is ok.  vacuum should be good,  all of the hard plastic GM tubing has been replaced with a higher quality tubing.  I dont have a CAT anymore so thats out lol.  Plugs and wires were just replaced when this started.  didnt fix it.  air filter is good to go.  

 

So i guess fuel pump will be tested.  But first im gonna take off the SC belt and see if it still does it. 

 

1 hour ago, Frosty said:

Fuel filter is probably inline. You might still check it.

A couple other possibilities. First one of the first symptoms of an IAT going bad is hesitation/stumble/stutter, so check that. The other real possibility is the fuel pump or regulator. A simple check! Get a pressure gage, get a hose with the correct fittings to connect to the schrader valve on the fuel rail. Make sure that it’s long enough to mount somewhere at the windshield area or inside the cabin, where you can see it. Run the car as you normally would to generate the problem, note the pressure readings. This will tell you if that’s where the problem is. Also the 4t65e & 4t65e-hd can cause this same symptom, under the right conditions, but again, I doubt that to be the problem.

Edited by Last Indian
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Posted (edited)

This may sound crazy...But It is very possible to have weak or starting to get weak valve springs ..Not holding the seat pressure like they should when under boost...Causing one or more of  the valves to not quite close tightly enough to seat properly when under boost but would run normally otherwise..Just something to maybe look at... Especially if they have a lot of miles and the valve  springs have never been changed....

Edited by TWO LANE BLACK TOP

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while i hope not,  im only around 150k miles on an 04.  im the second owner, and never really truly beat on her.  i never roast the tires, 2 reasons, trannys in these cars suck, i have a Stage 1 TEP in mine.  and 2 tires are spendy.  i honestly wouldnt think it would be that, but on a higher mileage car i could see it.

 

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