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Discussion Starter #1
Hey all, I'm new here.

I bought a 99' 3.8 with a missfire. I've already did some searching and cleaned the MAF sensor and replaced the fuel pressure regulator. I checked spark plugs, they were about .065 so I regapped to .055.

When I first got the car it had rich codes that went away after cleaning the MAF sensor. It was REALLy dirty, the worst I've ever seen and I've seen a few. After doing some research it was suggested that I replace the fuel pressure regulator so I did. I was already in there fixing a coolant leak the turned out to be the plastic elbo under the intake.

The car idles fine and will go through the revs just fine(5 speed) is I don't put much load on it. Before I replaced the fuel pressure regulator it would only miss in the low RPMs under high load. Now it seems like it take more load to make it miss but it misses more in the higher RPMs. Do you think it's a bad new fuel pressure regulator? What else is common on these engines that I should check out?

Thanks.
 

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If the ignition system can't take a heavy load, ie, WOT, usually a bad coil(s).
When regapping the plugs, any of them dark? Meaning no spark to the plug?

Welcome to the Club, Daniel.
 

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Discussion Starter #3
If the ignition system can't take a heavy load, ie, WOT, usually a bad coil(s).
When regapping the plugs, any of them dark? Meaning no spark to the plug?

Welcome to the Club, Daniel.
No, there was no fouling of any sort, clean electrodes that were a little worn which is why I regapped them.

I was thinking maybe a coil, my other car, a Lincoln LS is known for coil failures and acts similar fashion. I'm thinking maybe I should test my spark plugs wires before I replace any coils. How much resistance should I be looking for? I also noticed that the center coil pack looks newish like it's been replaced, maybe the wrong one was replaced?

I wanted opinion of experienced people with this car but sounds like a generic diagnosis will suffice.

Oh a side note, I just popped a code P0420, are rear O2 sensors known to go bad on these or is it more likely my cat went? Is there an easy test to see if it's my sensor without just buying a new one and putting it in?

Thanks
 

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Discussion Starter #4
Fixed the miss. Had a loose spark plug wire on one of the posts of the coils. I might have fixed the O2 sensor code too, but we'll find out if the light goes out.
 

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Cool! Good job.
After several starts, 50?, if fault is no more, light goes out.
Visit an Advance store and use the code reader to reset/erase the code(s).
 

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After several starts, 50?, if fault is no more, light goes out.
Visit an Advance store and use the code reader to reset/erase the code(s).
Yea, I've been reading that it's crazy high for it to self clear. I have a scanner that I can remove the codes with. I just hate doing clearing them because it restarts all the monitors because I'm trying to get the car smogged and every time I reset it takes at least 3 days to get enough running again to pass smog.
 

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Discussion Starter #7
Being as I already have this started I'll post this here.

I keep getting the codes P0420, cat efficiency low. I got this after one drive after resetting the computer. I looked though the monitors and this is what I found:

"Monitors are ready.
Misfire Ok
Fuel System Ok
Comp Com Ok
Catalyst Ok
Heated Cat N/A
EVAP System No
2nd Air system N/A
A/C N/A
O2 Sensor Ok
O2S Heater No
EGR system Ok"

I'm confused, it says "Catalyst Ok" but pops a P0420 code, but says no to EVAP and O2S. Does a "No" mean the monitor is not ready or it failed? Does N/A mean it's not ready or it doesn't have it or....?

I'm trying to learn something here so don't flame me for asking. I'm also open to suggesting on how to fix/what do do next. Cats are expensive so I'm saving that for last.

Thanks.
 

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N/A = not available, as in not equipped. O2 sensor may be working good, as Cat is Ok, but sensor may be slow in getting to operating temp, as in no heater,
Check O2 sensors, GM's, or most of them, have one wire from them, no heater.
If more than one wire, then it has a heater within the sensor to heat the tip. The heater may not be power as in a bad relay, no relay control to turn on the relay, or a broken fusible link/blown fuse or a bad sensor internally. But since the report reads Cat OK, PCM is reading the O2 sensors, pre- & post- and comparing the info collected.
 

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N/A = not available, as in not equipped. O2 sensor may be working good, as Cat is Ok, but sensor may be slow in getting to operating temp, as in no heater,
Check O2 sensors, GM's, or most of them, have one wire from them, no heater.
If more than one wire, then it has a heater within the sensor to heat the tip. The heater may not be power as in a bad relay, no relay control to turn on the relay, or a broken fusible link/blown fuse or a bad sensor internally. But since the report reads Cat OK, PCM is reading the O2 sensors, pre- & post- and comparing the info collected.
It has a four wire setup, at least the post cat one is.

"But since the report reads Cat OK, PCM is reading the O2 sensors, pre- & post- and comparing the info collected"

Does this mean that the sensors are good and my cat is bad?
 
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