elementaltoad

I have a 1989 formula 350 with the dual cat option - just recently it started to develope a small miss...oddly enough it seemed to be on one cylinder per side of the engine. I assumed maybe the plugs or dist. etc. were at fault. It still ran like a beast and had no problems under WOT or partial throttle. Now the problem has increased - It seems to run on only 4 cylinders, it has trouble idling, no acceleration, under throttle it acts like it is dragging the whole state of texas behind the bumper.

the good:
43LBS of fuel pressure before the fuel filter change (constant while runing)
Ignition and timing checked and OK'd
MAF checks fine
pulls 16 inches of vacuum at idle (pregressivly more on with throttle - eradic when missfiring)

i replaced the:
ECU
Dist.
plugs
wires
fuel filter

Symptoms:
shakes
no acceleration
rough, hunting idle
puffing airy noise from both sidepipes
poor mileage

any ideas, next step is cutting my god forsaken cats off?

elementaltoad

Could the true dual custom exhaust cause a rich running car to burn or clog old cats? the only exhaust mod is the true dual 2.5" side exit exhaust - cats look original....a hole has been patched on its piping.

IROC-T

I would run a compression test, does it seem to use up coolant lately?

Z28SORR

Running rich is an excellent way to ruin a cat.
How difficult would it be to just drop the exhaust at the headers or manufold and check how it runs.

elementaltoad

well these cars often run rich f untuned, i drilled a 3/4" hole in the right side cat. which is also missing the AIR tube - which as far as i know promotes the combustion of excess fuel, etc. so i went on a hunch and drilled it out...runs and idles fine now. It is still somewhat ragged because of the restricted flow but noticably much better, tomrow they will be cut off and replaced with straight pipe for now. thank you for the responses guys the problem has bugged me for the better part of two months!

elementaltoad

turns out that the cats were fine, it is back to the same routine - missfiring and puffing from the pipes. I CHecked the firing order and it seems to be right on.

New:
plugs (autolite)
wires(MSD Super 8.5mm)
distributor(GM HEI)
ECM

confirmed:
16 inches of vacuum at idle
43 Lbs of fuel pressure consistantly
2.5 LBs of backpressure at the cats.
6* base timing
Injectors balanced
Spark strong at plugs
No codes

elementaltoad

the car still puffs through the pipes as if it has lost compression or is not firing corectly. We hooked it up to the scanner and read the data stream. It seems the O2 sensor sees a lean condition and is trying to dump large quantities of fuel into the cylinders, which is aparently unable to do - it will intermitantly run rich then go lean again causing the IAC to compensate for the lack of air to burn either too much or too little fuel. But as it stands fuel pressure is nominal as well as vacuum and backpressure...only culprit seems to be the fuel entering the cylinders and burning correctly either do to lack of compression or clogged injectors.