Author Topic: '79 Trans AM 403 strange hesitation, what could cause it?  (Read 419 times)

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Offline chrislynn5

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'79 Trans AM 403 strange hesitation, what could cause it?
« on: March 26, 2017, 11:48:40 AM »
I finally have all my gauges working and took the car out yesterday. It's a '79, with a 403 olds, and TH350.

The oil pressure starts at around 60-70psi, but once warmed up drops to 35-40, and stays there on idle.

The water pressure goes from 100 to 225 and stays there, I believe I have a 195 deg thermostat, but the temp never goes any higher. I've checked it with an infrared sensor and it says 180-190 degs F.


I drove it about 5 miles. And ate lunch. Then went back out and after about 15 more minutes of normal driving the engine, while gas is pressed, stalled (blogged and hesitated) while the gas was pressed. So I back off the gas and wait and after a couple more hesitations it goes back to normal and continues as if nothing happened. And the gauges didn't move. And A/C not on. And fresh 93 octane gas. (which it has a sticker on it to use unleaded fuel only, but it looks like someone made the hole larger?)


It did this once before after about 30 minutes of driving. Not too hot, outside temp in the 70's.


The air intake is stock. There are headers on it. And I had the carb set via a GMC dealer, and it idles around 900-1000 rpm.


I haven't had it out much since I got it.


Any ideas? I'm new to the Trans AM.

Thanx.


Offline Stringer

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Re: '79 Trans AM 403 strange hesitation, what could cause it?
« Reply #1 on: March 26, 2017, 06:01:37 PM »
Does the vehicle still have a cat? It may sound strange but my 79 did the same thing and it was the catalytic converter.

The car ran great until about 20 minutes into the drive then it would start to hesitate, much like what you stated.  It kept doing this for weeks until eventually it stalled out and would barely run when started.  I had it towed to a shop where they checked it out and said it was the catalytic converter. However, they couldn't remove it  because they are a business and it is illegal.  I got it home and cut it out....sure enough, I couldn't ever see day light through it. The car also ran great.  I have since put dual exhaust on it.

Offline chrislynn5

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Re: '79 Trans AM 403 strange hesitation, what could cause it?
« Reply #2 on: March 26, 2017, 06:50:50 PM »
it was replaced with headers, so there is no cat.