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MT2500 is really good for old school vehicles. The fuel sync definitely sounds like the issue. What caused it is now what needs to be narrowed down. The exhaust leak is definitely a contributor. When you have an exhaust leak like that it tends to do a number on the cat and O2 sensor. Whether it ruined them only testing will tell. The O2 is snapped so no testing that especially if it was that rusted it probably was bad/clogged.
If the O2 sensor is pre-cat then there is no way for the engine to know the functionality of the cat. If you do not have to pass emissions in your state so long as the substrate in the cat is intact it does not matter if it is doing its job. Since the there is know way for the ECM to know that as long as there is proper flow through the cat, it will not affect the running of the engine.
If parts of the cat are in the muffler you can definitely shake it back and forth and try to get the pieces out. The Y pipe I am assuming is where the O2 sensor is. I suggest putting a very small amount of anti-seize on the threads of the O2 sensor. You have to watch doing this as it can leak down onto the sensor and burn it up. I suggest the last 2-3 threads you do not leave anti-seize on. Though this is up to you because so long as you install it right you will likely not have to take it back out for some time.
I’m guessing that the previous owner messed with the Dizzy the locking bolt wasn’t all that tight and the plug that block you from changing the idle was removed like someone had to turn it up. It idled way high when I got it.
I’m more concerned about the lies I’ve been told by people I paid to do this for me!
I’m thinking the improvement is also resetting the IAC since the one in there is new when I did the plenum last summer and it was set by the box instructions which means screwing in or unscrewing it so the tip looks to be the same extension as the one I removed!? What if that one is not set right? sheesh. Anyway its good I could reset it. I’m guessing I’ll get even better MPG’s once I get the exhaust fixed.I ordered the Walker Y pipe still looking at CAT’s. I want an exact fit one and it looks like Rock Auto for that too since everyone else has an O2 hole in the Cat pipes they claim are OE and my rig has it on the Y pipe.
My O2 is fine its a practically new Denso. It had thread stuff on it out of box. Pretty sure the CAT is plugged since it started running better when I tapped on it with the rubber mallet. Once I have the CAT and Y pipe in hand I will take it apart from the Manifold back. It seems to be doing OK for now. I hope that stud comes out easy.Hopefully all that is wrong with the cat is it is plugged and you can clean it. I agree adjusting the IAC probably did fix a lot.
I have a feeling once you fix the studs, clean the cat, and replace the y pipe it will probably run like new.
Just dropping by to say I have been busy so I’ve been diving it as is. I have the Y pipe, manifold gaskets and bolts for the Y pipe at the gasket. I have not gotten a CAT yet. I am still wobbling between getting a California one which is what it was OE or a 48 state one. I live in a no test state but I would like it to run as designed so it pollutes less. The price difference is huge..
Lets see oh yea after the MT2500 adjustments the ticking noise came back (probably a lifter or maybe a loose rocker). I got 15mpg’s on the next tank which seemed low. Then the tank after that I got 17+. The only diff being I haven’t been using the AC. That seems like a very big diff for the AC so down the road that may be another project. It got 19+ right after I did the intake plenum, timing chain and replaced all of the sensors in the TB. I have read posters on other sites say they get 23mpg’s so that’s what I am shooting for.
Oh yea there may be a small rad leak when it gets real hot. The overflow tank is losing fluid. That is new since the tranny guy took it overnight to “check” if there was anything wrong.UPDATING
Last week I finally got to it and I replaced the entire exhaust from the Manifold back with the Walker Y pipe and a Walker CAT and Walker exhaust kit About $350 all told plus my labor. The quote I got for just a CAT replacement was over $400! The Walker pipes fit well and I had to cut the end of the CAT and weld the reducer they supply since they only give 3 Ubolt clamps. I still needed another U bolt clamp.
Two exhaust manifold studs were broken and I had to drill them out. I posted about that in Repair Central forum.
It runs a lot better. It shifts smoothly and the ticking I thought may be tappets/lifters is gone. The RPMs go up as they should. I’ve reset the fuel Sync to +1 which is as close to zero as I could get and I have new tires. I got 19mpg’s on a 500+ mile road trip.The exhaust leak and clogged CAT seem to have been the source of a lot of my problems. I wish I would have done this before I paid to rebuild the tranny.
It is not perfect, I want more responsiveness and power but now its at least doing what it was designed to do.
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