My car is a slug, I'm out of ideas

Okay, we know what doesn't happen... what does happen when you rev in 1st and try to break the tires loose?

Does the engine bog? Do you get a lurch then fall flat?

check the timing.

How did you check the timing? You did remove the sprout connector? Does it even have one to begin with? You mentioned you pulled codes and did not find anything. Was this a KOEO and KOER tests? Did you do a cylinder balance test? YOu could have a weak injector and it would not show up in the KOER or KOEO tests. I did this and found one bad injector, replaced it and it really made a huge difference. BTW I did not have a miss I could hear or feel. Check your fuel pressure too.

After the KOER test is completed go in and rev the engine making sure you go to the floor. Just stab the gas pedal once. The ECC will run the Cylinder blance test. Count the number of flashes. 1 = Cylinder 1, 2 = cylinder 2 and so on. a 9 = all OK.

Good luck.

Cylinder balance test:
Warm the car's engine up to normal operating temperature. Use a
jumper wire or paper clip to put the computer into test mode. Start
the engine and let it go through the normal diagnostic tests, then
quickly press the throttle to the floor. The engine RPM should exceed
2500 RPM's for a brief second. The engine RPM's will increase to about
1450-1600 RPM and hold steady. The engine will shut off power to each
injector, one at a time. When it has sequenced through all 8 injectors,
it will flash 9 for everything OK, or the number of the failing cylinder
such as 2 for cylinder #2. Quickly pressing the throttle again up to
2500 RPM’s will cause the test to re-run with smaller qualifying figures.
Do it a third time, and if the same cylinder shows up, the cylinder is
weak and isn’t putting out power like it should. See the Chilton’s Shop
manual for the complete test procedure

Here's the link to dump the computer codes with only a jumper wire
or paper clip and the check engine light, or test light or voltmeter.
I’ve used it for years, and it works great.

See http://www.troublecodes.net/Ford/

IF your car is an 86-88 stang, you'll have to use the test lamp or voltmeter method.
There is no functional check engine light on the 86-88's except possibly the Cali Mass Air cars.



89 through 95 cars have a working Check Engine light. Watch it instead of a test lamp.




Do a compression test on all the cylinders.
Take special note of any cylinder that shows up as weak in the cylinder
balance test. Low compression on one of these cylinders rules out the
injectors as being the most likely cause of the problem. Look at cylinders
that fail the cylinder balance test but have good compression. These
cylinders either have a bad injector, bad spark plug or spark plug wire.
Move the wire and then the spark plug to another cylinder and run the
cylinder balance test again. If it follows the moved wire or spark plug,
you have found the problem. If the same cylinder fails the test again,
the injector is bad. If different cylinders fail the cylinder balance test,
you have ignition problems or wiring problems in the 10 pin black &
white electrical connectors located by the EGR.

How to do a compression test:
Only use a compression tester with a screw in adapter for the spark
plug hole. The other type leaks too much to get an accurate reading.
Your local auto parts store may have a compression tester to rent.
If you do mechanic work on your own car on a regular basis, it would
be a good tool to add to your collection.

With the engine warmed up, remove all spark plugs and prop the
throttle wide open, crank the engine until it the gage reading stops
increasing. On a cold engine, it will be hard to tell what's good &
what's not. Some of the recent posts have numbers ranging from
140-170 psi. If the compression is low, squirt some oil in the cylinder
and do it again – if it comes up, the rings are worn. There should be
no more than 10% difference between cylinders. Use a blow down
leak test (puts compressed air inside cylinders) on cylinders that
have more than 10% difference.

See the link to my site for details on how to build your own blow
down type compression tester.

I think something was up with your old H pipe as well, you definitely should not have been smelling gas that strongly inside the car. I have ran a cat-less H and catless Pro-chamber and never gotten any gas smells like that.

I'm betting the O2's were pretty bad. My 90 was the same way until I changed them out. I wouldn't think an off-road h-pipe would cause anything like the conditions you had. Unless there was a squirrel nesting in the crossover

Also, have you tried advancing the timing a bit more? I only use a timing light to get it close. From there I advance in small increments and test drive after each adjustment to get it set the way I want it.