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Topic: 84 3.8L Low on Power (Read 8676 times) previous topic - next topic

84 3.8L Low on Power

I have an 84 Tbird with 3.8L that has weak acceleration.  I replaced the ignition module some time ago after it began cutting out on the highway, and this corrected that issue but still not running correctly, with the weak acceleration.  I replaced the dist cap and rotor, and spent a while playing with the timing, but no improvement.  The car starts and idles fine.  Anyone have suggestions?  The car has 76000 miles, also has newer spark plugs, plug wires.

Thanks a lot!

Russ

84 3.8L Low on Power

Reply #1 –
Plugged fuel filter or catalytic converter?
CoogarXR : 1985 Cougar XR-7

84 3.8L Low on Power

Reply #2 –
Quote from: CoogarXR;459387
Plugged fuel filter or catalytic converter?

Thanks.  I replaced gas filter perhaps 10k miles ago.  Any way I can evaluate for possible restricted cats without just replacing or punching out the catalyst?

84 3.8L Low on Power

Reply #3 –
Try this vacuum gauge test.
https://www.youtube.com/watch?v=d-jp1IIJVVk

If your vacuum gauge is also a pressure gauge, you can remove an O2 sensor and jury rig up your gauge to measure the back-pressure at the O2 sensor hole.

84 3.8L Low on Power

Reply #4 –
How much pressure should be seen at idle at O2 sensor hole?

84 3.8L Low on Power

Reply #5 –
The closer to zero the better. Around 2-3 psi. I'll check to see if the shop manual gives a number.

The Shop  Manual doesn't give a back-pressure number. Only gives the vacuum gauge numbers.
vacuum at idle 16-21 inHg. After revving engine to 2000 RPM, if the vacuum settles to below 16 inHg , you have a blockage.

84 3.8L Low on Power

Reply #6 –
Thanks.  I checked it and found no issue.  I did note that vacuum was 16 inches at idle.  I subsequently found that my static timing was set too retarded, and after advancing a few degrees beyond the factory spec, it ran a great deal better.  Thanks for your help!  The only lingering mystery about this car is that since I bought it, about every year, it begins to run poorly and I reflexively replace the ignition module which fixes the issue.  I have put 3-4 modules on this car in 20K miles.  borg-warner.  Back in the 1990s and had an 84 cougar and 86 tbird with the 3.8L, which I drove each over 100k miles, and replaced the module once on each car, so I dont know what is up with this....any thoughts?
 

84 3.8L Low on Power

Reply #7 –
I don't know about the quality of current replacement TFI modules, but heat has been the traditional killer of the ignition modules. The modules will naturally overheat during normal usage. This is why thermal grease is used between the TFI and the distributor, to conduct the heat away from the TFI.
If the engine is running too hot, the distributor will be hotter and conduct less heat away.
You don't say how retarded the base timing was, but running retarded can cause overheating.

Have you ever run the self tests to see what error codes you may have?

84 3.8L Low on Power

Reply #8 –
Quote from: softtouch;459432
I don't know about the quality of current replacement TFI modules, but heat has been the traditional killer of the ignition modules. The modules will naturally overheat during normal usage. This is why thermal grease is used between the TFI and the distributor, to conduct the heat away from the TFI.
If the engine is running too hot, the distributor will be hotter and conduct less heat away.
You don't say how retarded the base timing was, but running retarded can cause overheating.

Have you ever run the self tests to see what error codes you may have?


I haven't. I have not been excited about counting the flashing light or whatever it is that is needed to pull codes.  Is there a code reader that can be purchased for this system?

84 3.8L Low on Power

Reply #11 –
Do I need this extension cable??

84 3.8L Low on Power

Reply #12 –
Quote from: atengnr;459428
Thanks.  I checked it and found no issue.  I did note that vacuum was 16 inches at idle.
16 inches is still PRETTY low for a stock engine at idle.  At 16 inches on a speed density car, you'll be spraying more fuel.  If you're getting incomplete combustion as a result of this you could be melting down your cat.  Don't rely on a vacuum test for backpressure, check it directly with a gauge.  On WOT snaps, you shouldn't exceed 3 psi.  Obviously lower is better.  You can also compare the temp of the pipe both before and after (with an IR thermometer) the cat to get an idea of the cat's efficiency, though without a downstream HEGO like on an OBD2 car, you're only getting a basic picture of it.

84 3.8L Low on Power

Reply #13 –
Thanks.  Yeah I drove the car tonight and it runs OK but still something isnt quite right.  I took on a 10-15 mile drive, and is still somewhat whimpy on highway entrance acceleration, and hesitates with acceleration occasionally (I know this is a chronic, common problem with these 3.8L motors as I had with my other two cars back in the 90s).

I ordered the scanner.

84 3.8L Low on Power

Reply #14 –
Well, I got the code scanner, and gave me 23, 84 (I have EGR vaccum line plugged), 13, 63.  I ordered a throttle position sensor.  I assume this sensor malfunction could cause the issues that I have had (LOW POWER, hesitation, stall at idle)???  Thanks alot.