: exhaust question



dhs
10-04-05, 01:16 AM
I think I may be in for a cat replacement. My 00 dhs seems like it just dosn't want to rev up very high. It runs fine at low rpms, but when I give it a lot of gas it just doesnt respond very well. This is especially evident on the highway, it doesn't have enough passing power. I checked the codes but nothing's showing up. I did a full tune up recently so I'm guessing the cat's at fault.

If I do replace it, I want to go for the high flow one. Does anyone know the diameter of the main pipe? (not the two connected to the mufflers, but the one going down the center of the car) I was thinking of gutting the cat it has on now, but won't that wreck havock on the computer?

davesdeville
10-04-05, 03:06 AM
There's an O2 sensor after the cat. I believe these cars have a code for poor catalytic converter performance, but mine's OBDI so I dunno for sure. Anyway if that code exists and you gut the cat it will show it. I believe the stock pipe there is 2.5", at least that's what it is in my car.

mcowden
10-04-05, 10:04 AM
There's an O2 sensor after the cat. I believe these cars have a code for poor catalytic converter performance, but mine's OBDI so I dunno for sure. Anyway if that code exists and you gut the cat it will show it. I believe the stock pipe there is 2.5", at least that's what it is in my car.

All OBD-II cars have a sensor after the cat to determine its efficiency. If you gut the cat, you won't get rid of the SES light or the code, and you'll never pass an emissions inspection without pulling off some funky electronic stuff to fool the computer.

Does the car have any other symptoms other than a reluctance to rev up?

dhs
10-04-05, 12:49 PM
I forgot to mention that a couple times it has stalled on me once it came to a stop. The weird thing is that theres no codes showing up that could be related to this, the only thing I found is some network code and "temperature 3 range/performance". Wouldn't it sense too high pressure because of a clogged cat? What would that code say?

mcowden
10-04-05, 02:02 PM
I forgot to mention that a couple times it has stalled on me once it came to a stop. The weird thing is that theres no codes showing up that could be related to this, the only thing I found is some network code and "temperature 3 range/performance". Wouldn't it sense too high pressure because of a clogged cat? What would that code say?

Post the exact codes and let's see what we can figure out. I assume one was a Uxxxx code and the other a Pxxxx. There is no sensor for high exhaust pressure, hence no code for a plugged cat. The O2 sensor after the cat is Bank 1 sensor 3, so if you're getting a code for "sensor 3 performance," it could mean the converter is not doing its job for one reason or another. Again, just post the raw codes and we'll help you sort it out.

dhs
10-04-05, 08:28 PM
It showed me these,
B0429 - Temperature Control #3 Rear Circuit Range/Performance
U1064
U1016
I don't think the network codes mean much but I didn't know that there was a temp sensor in back of the cat. If it's an O2 sensor how can it measure temperature? Or does it assume an out of range temperature based on bad O2 concentration? There arent any sensors connected directly to the cat?

Kev
10-04-05, 08:38 PM
Another train of thought on a possible cause to your problem;

My '88 5.0 Mustang developed a problem similar to yours. It would only rev to about 4000 rpm and then crap out or level off. I'm thinking; "This engine should rev till it blows if someone were foolish enough..." Long story short, it turned out to be the fuel pump. It was weak (on it's way out) so it ran OK under low load but couldn't supply volume above 4000 rpm.

You might want to throw a pressure gage on your fuel rail to see if your pump is still up to snuff before swapping out cats and O2 sensors.

Just a thought...

mcowden
10-04-05, 10:27 PM
It showed me these,
B0429 - Temperature Control #3 Rear Circuit Range/Performance
U1064
U1016
I don't think the network codes mean much but I didn't know that there was a temp sensor in back of the cat. If it's an O2 sensor how can it measure temperature? Or does it assume an out of range temperature based on bad O2 concentration? There arent any sensors connected directly to the cat?

Well, none of those are engine or O2 sensor codes. The B0429 is not related to catalyst performance at all, I have no idea exactly what that one means. The U1064 I have seen before on other cars and it turned out to be a bad body control module. That may not be your issue, though, and I would check wiring to the BCM first. U016 means loss of communications with the PCM. That may also be a wiring or failing module problem. Hopefully someone else will chime in about what you should look for next. The Uxxxx codes are mostly beyond my grasp.

It might be worth the fuel pressure check as Kev suggested. I'm not sure what else would cause it to bog down. Maybe a "flat spot" in the TPS?

eldorado1
10-04-05, 11:05 PM
2000 stalls with no codes.... hmm... I would be suspicious of the crank sensors, especially if they haven't been replaced by the new updated ones.

mcowden
10-04-05, 11:14 PM
2000 stalls with no codes.... hmm... I would be suspicious of the crank sensors, especially if they haven't been replaced by the new updated ones.

Yeah, definitely with ya on that one. Replace those crank sensors, STAT!

dhs
10-04-05, 11:34 PM
But that still doesn't explain the sluggish acceleration. There was a period where it would stall from time to time but it seems to have passed. I don't want to jinx it, but it hasn't stalled for some time. It also used to show an abs and no traction light everytime I hit a bump, but that seemed to fix itself when I reset the codes so I'm not sure what's going on. Are the crank sensors an expensive job? I would rather have a high flow cat I don't need then crank sensors.

By the way what is the specific code it would show if it detected a bad cat? One more reason I suspect the cat is that when I had some work done on the car the mechanic said something about having to replace the cat soon, but I havent seen him again.

mcowden
10-05-05, 11:09 AM
But that still doesn't explain the sluggish acceleration. There was a period where it would stall from time to time but it seems to have passed. I don't want to jinx it, but it hasn't stalled for some time. It also used to show an abs and no traction light everytime I hit a bump, but that seemed to fix itself when I reset the codes so I'm not sure what's going on. Are the crank sensors an expensive job? I would rather have a high flow cat I don't need then crank sensors.

By the way what is the specific code it would show if it detected a bad cat? One more reason I suspect the cat is that when I had some work done on the car the mechanic said something about having to replace the cat soon, but I havent seen him again.

There is a P0420 code for "Catalyst System Low Efficiency," which is the one I would expect to see if your cat was not performing well. You risk getting that code non-stop by going with a "high flow" cat. Others may have done it successfully, I don't really know for sure, but if it was me, I'd just get the direct fit replacement converter and be done with it.

If you want to reduce back pressure, do a complete cat-back system. Plenty of folks have done that here. I don't know what converter they use in the process, but if you use the Search feature above, you can probably find what you want to know about it.

The crank sensors on 2000 model year cars are a known weak point. They were prone to failure. One respected expert who used to frequent this board indicated it would be best to just replace them and be done with it, especially if you were having stalling issues.

Kev
10-05-05, 11:39 AM
Check your fuel pressure before you start spending money replacing parts that may be working just fine. Eliminate low fuel pressure/flow as a problem (relatively inexpensive task) first.

Just my two cents.

eldorado1
10-05-05, 12:33 PM
But that still doesn't explain the sluggish acceleration.

Sure it does. The crank sensors tell the PCM how fast the engine is running. If they are having intermittant problems, the PCM will see the engine stuttering, and running slower than it actually is. If the PCM sees the engine is running at 1000rpm, but the engine is actually running at 3000rpm, it's only going to give you fuel and spark for 1000rpm. It'll probably be misfiring like mad, because it will only be firing the spark plugs 1/3 the time it would need to be running at 3000rpm. This is an extreme example, but you see the idea.

I would also recommend trying to diagnose the problem first, but the problem is most people don't have a fuel pressure gauge, or volt meter, or ...... so by the time they bought all that, they could have taken it to a shop.

Shotgunning parts is a good way to spend money. In cases with no codes though, it might be the only alternative to bringing it to the dealer or buying (necessary) tools.

zonie77
10-05-05, 12:59 PM
Did you replace the fuel filter on that tune up? Plug wires?

I'd replace that filter ( it would be interesting to check fuel pressure at higher RPM before and after). The fuel pressure test is definitely in order.

Eldo1, you're right that most people don't have the tools, but for the price of that visit to the shop you can buy a lot of them. Not everyone wants to do all their work but for those who do it's poor economizing to scrimp on tools. You made a great point on shotgunning parts.

dhs
10-05-05, 01:30 PM
I replaced the fuel filter along with the plugs and wires once it hit 70k.

I assume only the dealer can change the crank sensors? I heard that the computer has to be reset afterwards, and independent shops don't have the equipment. I really hate going to the dealer for anything, not only are they extremely slow, but charge 3x what a job should cost. Allthough that's not really a suprise to anyone.

I do have a bunch of tools I use to work on my motorcycle, like a volt meter and compression gauge. My neighbor's a mechanic, so I think he would have a fuel pressure gauge.

eldorado1
10-05-05, 06:36 PM
There shouldn't be any need to reset the computer. Basically you just unbolt them, pop the old ones out, pop the new ones in, and bolt em in. Now one thing to note here, is that IF the crank sensors are intermittantly going in and out, the dealer isn't going to be any better suited at finding the problem then you are. The sensors are $32 ea from rockauto.com, you need an upper and a lower one. That's not too bad, and will eliminate the most likely cause of your problems. Feel free to search for "crank sensor" and pull up some past info on it.

The great part about these caddies is they monitor everything and the service manual can literally break down the sequence for diagnosing and fixing what's wrong. But in the case where you don't have any codes........ you're kinda SOL, and forced to suspect everything.

Make sure you get ACDelco parts if you do replace the sensors. The aftermarket parts may not have the updated components.

edit: http://cadillacforums.com/forums/showthread.php?t=34044

Kev
10-05-05, 06:49 PM
Obtaining a fuel pressure gage is not that hard. One little gage, 48" of rubber fuel line, one fitting for the schrader valve and two hose clamps?!! :)

Oh yeah, a little duct tape too.

dhs
10-05-05, 08:16 PM
That's good, I was expecting a couple of hundred bucks for the sensors alone. I searched around the posts here and it looks like I might even be able to try it myself. But the posts mention that the car has to be reflashed after replacing the crank sensors. Is this really necessary? Could I (or some independant mechanic) put the sensors in and then take it to the dealer for a reflashing?