Cascade Crew

alloy · Posted: Sat Jul 24, 2004 8:16 am Post subject: Test pipe

Has anyone here had problems after they pulled their cats off? I installed one of those "test pipes" yesterday and immediately have a mis type of problem.

The car runs ok til it goes into closed loop, then has intermitent bucking-missing. The tach needle drops/jumps. Kinda like I'm turning the ignition off-on. My cat was completely empty from 18 years of use, and I installed the test pipe to get better flow. I don't really believe in coincedences, but this problem occuring right after I put the test pipe on is too much of a coincedence to ignore. It's dificult for me to believe that a change in the exhaust caused this problem. I didn't have any problems like this when I installed the headers, but again it's hard to ignore that the problem started right after I put the pipe on.

I've checked all the normal stuff, loose wires, connectors ect. Anyone have any thoughts?

Dewey316 · Posted: Sat Jul 24, 2004 7:18 pm Post subject:

it only does it in closed loop? at part throttle?

alloy · Posted: Sat Jul 24, 2004 8:52 pm Post subject:

Well as far as I can tell, yes only in closed loop, but is now getting much worse. My instincts tell me it's an ignition prob cutting out like that and the tach dropping, but there is still the undeniable coincedence of putting on the test pipe and the problem showing up. I just can get by this fact in my thinking process.

I hate to put the old "empty" cat back on just to see if it cures it. The headers should have made a much larger difference in the exhaust flow and what the computer sees as far as sensor input, but they didn't give me any drivability problems at all.

Dewey316 · Posted: Sat Jul 24, 2004 10:02 pm Post subject:

the computer should be correcting for it at part throttle in closed loop. it does sound an awful lot like ignition to me. or funky o2 readings, causing the computer to do wacky things with the fueling. which is in turn causeing the miss.

92RS shearn · Member Joined: 01 Jul 2004 Posts: 55 Location: Seatac, WA

Alloy, I have running my car without a cat for 3 years now and have had no problems at all. I don't know why putting a strait pipe on would give you any adverse effects. Maybe just double check your O2 and other sensors.

alloy · Posted: Mon Jul 26, 2004 7:54 am Post subject:

Well I'll probably pick up an 02 today. They are only $22 and with my discount about $18. The 02 in there now isn't that old, maybe 2 years, but easy and cheap to replace and one more thing to cross off my list of possible problems.

I drove the car last night and it was better, but still did it when driving, even at idle. But park the car and lif the hood and try to catch it doing it........well heck no.

I did some reading on TGO about this type of problem, and it seems like there can be many things causing this type of malfunction. I've read 02 sensors, bad alternator (low voltage), bad cap/rotor/plug wires, and EGR valve.

I have new cap and rotor, really good (but old) jacobs wires, the EGR is maybe 2 years old along with the CTS, TPS, and 02. The alternator is putting out plenty of voltage. And new pickup coil and module just a few weeks ago. The wiring harness to the distributor seems to be in perfect shape, and the weather pack plugs are in tight and the connectors are not corroded. The ground strap from the engine to body seems to have a good connection also.

So I'll try the 02 first, then may try unplugging the vac line to the EGR.

alloy · Posted: Tue Jul 27, 2004 8:03 pm Post subject:

Ok, update.

Isn't 02, and isn't ignition module. Also disconnected and plugged the vac line to the EGR and no difference.

It's getting worse now, even does it's "cutting out" right when I start it before it goes into closed loop. Does if for 10 or so seconds, then clears up for a little while. and repeats.

I'm sure it's ignition. When it cuts out and catches again there is a small backfire where the unburned fuel seems to be ignited in the exhaust system.
So, back to square one for now.

Dewey316 · Posted: Tue Jul 27, 2004 8:29 pm Post subject:

have you pulled a plug to at least look at the condition of them?

alloy · Posted: Wed Jul 28, 2004 8:32 am Post subject:

Plugs look really good. One of the first things I checked. Just didn't think to mention them.

Have done some more trouble shooting. I swapped out the coil for an old one I had, and disconnected the MAF sensor lead. No change.

I have an Auto X-Ray and have done some scans. I can do a monitor type of thing for 14 seconds, then hit the button and monitor when the problem occurs. So 28 seconds of data is stored. I have a scan like this, but not sure what I'm looking for in the data it collected. I can't see and glaring difference between normal run data and when the problem starts.

And, forgot to mention, fuel pressure is good at 42 psi.

Dewey316 · Posted: Wed Jul 28, 2004 8:43 am Post subject:

any way you could post that data?

alloy · Posted: Wed Jul 28, 2004 10:11 am Post subject:

yes, will take awile but here goes.

Prom ID 891
coolant temp 130.1
start up coolant temp 73.4
throttle sensor .60 volts throughout the scan (scan taken idling)
engine rpm from a low of 390 to a high of 1482
veh. speed 0
o2 sensor volts from 308 mvoltts to 0 back up to 638 (New sensor yesterday)
02 cross counts from 0 to 50
block learn 133
block learn cell 0
intergrator 127 to 131
idle air motor pos 120 steps to a low of 53
desired idle 750
engine load 38 to 91
man. air temp 69.8F
EGR dutry cycle 0 all through the scan
CCP duty cycle 0
bat volts from a low of 10 to 13.4
fuel pump volts 13.4
spark advance 24.5 to 31.1
knock sensor 15
knock retard 0
inject pulse 1.4 ms to 2.0 ms
MAP sensor volts 1.13 to 1.15 volts
mass air flow from 6 gr/sec to 14 gr/sec
o2 sensor ready
CCP purge off
air divert solenoid off
air switch soleniod off
learn control enabled
rich/lean flaf from laen to rich several times
loop status: closed

I've omitted things like shift light, AC not commanded and so on that are not relevant.

Dewey316 · Posted: Wed Jul 28, 2004 10:40 am Post subject:

alloy · Posted: Wed Jul 28, 2004 10:51 am Post subject:

Well both the new and old 02 had readings like that. And, the 0 reading ocured when the engine was running good, and when the problem occured. The 02 readings all across the scan are almost identical with the old 02 I pulled out Confused

Does the computer take 02 readings in open loop mode? This problem occurs in both open and closed loop modes. I thought the computer only read the 02 in closed loop?

Gota go to work now, but will will be thinking of what to try next.

Dewey316 · Posted: Wed Jul 28, 2004 10:53 am Post subject:

the computer only uses the o2 reading in closed loop, in open loop you can view the sensor readings, but they should be consistant around 450mv, the won't start swinging around until closed loop startes.

alloy · Posted: Thu Jul 29, 2004 2:40 pm Post subject:

Ok, well found one critical problem and hopefully I caught is before it did any damage. Alternator was charging at 16.65 volts. Not good.

Replaced the alternater and am now getting proper voltage everywhere. I found this while checking for voltage at the coil power lead. But this didn't seem to cure the problem. I happened to catch the the engine running bad whith my DVM hooked to the coil wire, and no voltage drop to speak or. Just .2 volts less that the voltage measured at the battery.

I did try unhooking the EGR sensor lead and (crosses fingers) it may have solved the problem. But it's so intermittent I won't know til I drive it for awhile

Now, next question. What problems awill occur running the engine with the EGR sensor lead disconnected? The EGR and sensor are only 2 years old, and are real GM parts, not copies.

I also ran a scan wih the X-Ray unit and the EGR duty cycle is from 0 to 99.4 to 18.7 to 24.9. I'd think with the sensor lead disconnected this wouldn't register.

Anyway the jury is still out as to whether or not this fixed the problem. Time will tell I guess.

Any thoughts on the sensor being disconnected?

alloy · Posted: Tue Aug 03, 2004 5:50 pm Post subject:

Well it's official, disconnecting the EGR temp sensor wire cured the problem completely.

Now, what problems will this cause running with the temp sensor disconnected?