Violent clank/slap upon power application - 1987 T/A - Third Generation Pontiac Firebird (1982 - 1992) - Firebird Nation

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Violent clank/slap upon power application - 1987 T/A


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#1 blondeau67

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Posted 14 June 2020 - 07:04 PM

Hi all! I'm new here so apologies if this has either been answered or if I've messed up the format or anything. I hope not but you never know. 

 

I bought a 1987 Trans Am coupe with a 305cui and a 5-speed manual only a few days ago and have noticed something pretty odd during my restoration so far.

 

There are two issues:

 

First Issue

7 times out of 10 when I apply the throttle after a shift (only upshifts so far as I am being extra careful on downshifts already) there is a very loud clank like something is smacking against the body repeatedly. It does it between 1-3 times before calming down and letting me continue to drive normally. I was told by a family member who knows his stuff fairly well that it could be the engine mounts being toast and the torque slams something into the side of the bay or causes something to bang loudly. In order for it not to happen I have to let the clutch out extremely slowly (like to stop bucking from a tourqey engine but much slower) and apply the power very carefully.

 

I will try to reply with a video of it happening tomorrow when I do another road test but it is dark where I am now. I have no idea what it is and any suggestions at all would help tremendously - trial and error is likely my best option here. Again, I got it around four days ago so it was happening as soon as I drove the car home.

 

Second issue

My headlights do not pop up. I have read things on this forum giving reasons that I think are correct - that the gears for the headlight assembly motor are stripped - however no one that I have seen has had my exact symptoms. The motors do spin when I push the switch, and the drivers side light will go up if I push with my hand to give it a little help, however the passenger side assembly doesn't move and is pretty stuck. I have tried to manually crank them both up multiple times, both while using my other hand to apply upward force to the assembly and without doing so, and no luck. They will not manually nor electrically move (aside from the driver's side being coaxed into moving). I can also attach a video of this tomorrow if that helps. 

 

Thanks in advance for any advice!



#2 sea dog

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Posted 15 June 2020 - 03:32 AM

On the clank, your family member has the right idea. So check your motor mounts, transmission mount, & the torque arm mount where it goes into trans.

 

On the headlights, try disconnecting the linkage from motor to headlight bucket. See if headlight bucket will move up & down freely. If yes problem is in motor or linkage is binding. If no, then headlight bucket is not moving freely on its mounts.

 

And, welcome to the forum.



#3 blondeau67

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Posted 16 June 2020 - 06:51 AM

On the clank, your family member has the right idea. So check your motor mounts, transmission mount, & the torque arm mount where it goes into trans.

 

On the headlights, try disconnecting the linkage from motor to headlight bucket. See if headlight bucket will move up & down freely. If yes problem is in motor or linkage is binding. If no, then headlight bucket is not moving freely on its mounts.

 

And, welcome to the forum.

It ended up being the transmission mount. I jacked the trans up a little bit and found that the mount was definitely broken. 

 

I am seeing a new problem where, when turning the car off (clutch in/out, neutral, handbrake pulled and not pulled have all been tested) it shudders repeatedly and won't turn off. I can turn the key back to "On" and the engine comes back to life, and when I turn it off again the car finally shuts off. Not sure what could be causing this whatsoever. 

 

Thanks!


Edited by blondeau67, 16 June 2020 - 06:51 AM.


#4 Injuneer

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Posted 16 June 2020 - 07:07 AM

That's called "dieseling".... engine runs on compression.  Low octane fuel, engine running too hot, heavy carbon build-up in cylinders, spark plugs acting like glow plugs, leaking fuel, throttle blades not closing.... etc.  Appears this is a problem you have not experienced before, just started happening?


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#5 blondeau67

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Posted 17 June 2020 - 08:44 AM

No I haven't experienced this issue before. I bought the car recently and otherwise daily drive a Silverado. I bought Spark Plugs but have not had the time to install them yet, and I filled it with 87 octane when I brought it home :/ so maybe that is part of the issue. There is also a vacuum leak between the air intake and the valve cover, and I have heard/seen that it could cause some issues.

 

I have the tuned port injection on the 305. I would add a photo but I'm not sure how. How would I add media to a post here?



#6 sea dog

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Posted 17 June 2020 - 10:41 AM

Make sure the spark plugs are the correct heat range for your car. A hotter plug can cause dieseling because the tip stays hotter and acts like a glow plug.



#7 ZumpTA

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Posted 17 June 2020 - 02:35 PM

In post #4 Injuneer explained several causes of engine run-on and one of them is "throttle blades not closing".  An intake leak such as the one you claim is more or less the same thing.  It is also causing your engine to run lean which isn't the best thing for it. 

 

Replace the intake gasket before anything else and go from there.


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