What would a bad cat perform like?

[Jimbarrt]

OK, there are a few around who have heard the tales of my poor running truck. Its KBell SC'd, with an M1 4 bbl., RRs 1.7s, mopar headers, Holley TB, mild cam.

The KB install went smooth, and ran fine for about half a year. But I started getting codes for "aps voltage too low" [don't recall the code#] So I changed the TPS, the MAP, the coil, and checked for vacuum leaks. Problems weren't constant, but seemed to occur when it was running hot. [The KBSC throws alot of heat] Water temp was in the normal range, but underhood felt cookin' hot.

The truck would buck, and cough, even if the KB anti knock was 'retarding the timing 10* as it was supposed to. Whether the code was thrown, or clear. It would die, and not restart. 15 or 30 minute later, fine again, for awhile.

There is NO mechanic in my area that has a clue, [on modified vehicles], and I can't afford to keep throwing money at it to try and find a cure.

Somebody suggested a clogged cat could cause the problems I've described. I never considered it, [hi flow cat, installed about 2 yrs. ago], but is it possible?

Or, is there something else to check, I'm missing? I, personally think there is something wrong between the factory computer and the KB add-on thats plugged to it, feeding incorrect readings.

Hoping to be on the road soon, jim

[360 XRT]

First i would get to the basics-inspect cooling system-use thicker oil like 10-40 or 20-50.next take a look at your exhaust.Yeah maybe its the cat,but it also could be a piss poor system choking down the motor.Take a look at your aircleaner,is it dirty or over oiled.In a nut shell your engine is having heat soak issues thats for sure.Just one more thing and i don't think this is it but,years ago i had a big HP smallblock that would literally lock up for a while because it heat soaked.The problem,not ENOUGH timing.Seems the balancer had a flaw that the timing mark moved,so i set the timing 15` retarded.
So if i had to guess(and that is all it is A GUESS ) i think for some reason (maybe low octane or bad crank sensor) you timing is to retarded.

[99dakRT]

I think your crank sensor or cam sensor would definately be worth checking out..
GOOD LUCK PAL!!!

[grapejuice1998]

OK, there are a few around who have heard the tales of my poor running truck. Its KBell SC'd, with an M1 4 bbl., RRs 1.7s, mopar headers, Holley TB, mild cam.

The KB install went smooth, and ran fine for about half a year. But I started getting codes for "aps voltage too low" [don't recall the code#] So I changed the TPS, the MAP, the coil, and checked for vacuum leaks. Problems weren't constant, but seemed to occur when it was running hot. [The KBSC throws alot of heat] Water temp was in the normal range, but underhood felt cookin' hot.

The truck would buck, and cough, even if the KB anti knock was 'retarding the timing 10* as it was supposed to. Whether the code was thrown, or clear. It would die, and not restart. 15 or 30 minute later, fine again, for awhile.

There is NO mechanic in my area that has a clue, [on modified vehicles], and I can't afford to keep throwing money at it to try and find a cure.

Somebody suggested a clogged cat could cause the problems I've described. I never considered it, [hi flow cat, installed about 2 yrs. ago], but is it possible?

Or, is there something else to check, I'm missing? I, personally think there is something wrong between the factory computer and the KB add-on thats plugged to it, feeding incorrect readings.

Hoping to be on the road soon, jim

To address your question instead of the symptoms, I would ask you; has there ever been a rattling sound from the cat when it's first started up?

[Jimbarrt]

I think your crank sensor or cam sensor would definately be worth checking out..
GOOD LUCK PAL!!!

Well, I'll llok at any possibility, how would one go about "checking out" these sensors? I have no diagnostic equiptment. THX

[Jimbarrt]

To address your question instead of the symptoms, I would ask you; has there ever been a rattling sound from the cat when it's first started up?

Well, there is a vibration in the exhaust somewhere, that is noticiable at 1500 rpm, never paid much attention to it. I'll have to crawl under there and see if I can unbolt the exhaust and see how it runs.

Another thought someone had, because the KB is mounted to the side of the manifold rather than over it, it sits pretty close to the fuel rail on the passenger side. Could I be boiling the fuel? I really need a remote thermometer to check the underhood temps. THX, jim

[grapejuice1998]

Well, there is a vibration in the exhaust somewhere, that is noticiable at 1500 rpm, never paid much attention to it. I'll have to crawl under there and see if I can unbolt the exhaust and see how it runs.

Another thought someone had, because the KB is mounted to the side of the manifold rather than over it, it sits pretty close to the fuel rail on the passenger side. Could I be boiling the fuel? I really need a remote thermometer to check the underhood temps. THX, jim

If there is an exhaust rattle, it very well could be the cat.

As for the vapor lock, I suppose it's possible, but it would have to get boiling hot to affect something of the psi and diameter of the fuel rail. You could always try and insulate it.

[bad360rt]

If you've been running rich with the KB, it's very easy to clog a cat. Both of mine clogged within a couple months of putting the blower on. Went from running low 13's to running 15 flat. Gutted the cats and everything was fine.