Hello

I'm fairly new to working on C4's. Its running very rough after warming up (open loop => closed loop). It hesitates and wants to die when letting the clutch out, and starts popping when doing anything more than very lite acceleration.

For that and other reasons I suspect the O2 sensors need to be replaced. I've replaced O2's on other cars, but before I buy the parts, haul out the ramps, jack stands and tools --- can someone tell me if they're reasonable to get to? Any tips on getting to them? Or is it one of those things that's best left to a shop?

Any other advice?

Thanks in advance for your help! Dave

Update: forgot to mention that its a '92 LT1

 

Different year C-4's have different number of O-2 sensors. My 96' has four. One in front of each cat and one downstream the cats. The way to find which one is the problem, pull the code. The code will nail down which one is the problem.

 

Hi Dave, and welcome to joys of the C4! I didn't see what year C4 you're referring to. Early models have one 02 sensor per side and I believe '94 on has two per side. As for changing them, I guess it's luck of the draw. It could be a cakewalk, or you could be in for a long day. I just had both of them changed by my mechanic, primarily because I don't own a jack or stands, and I'm just not comfortable crawling around underneath a car. I was glad I farmed this out too, as when I picked the car up, my mechanic told me they had a heck of a time getting the right one out and actually had to remove the catalytic converter and part of the exhaust in order to wrench that sucker out of there. I believe that some 02 sensors also require the use a specific wrench as well.

By chance, are you getting a "Service Engine Soon" light on in your car? While the problems that you're describing can certainly be attributed to faulty 02 sensors, there are still a host of other things that could cause it as well.

 

runner140* & screamin_conure -- thanks for the info. Its a '92 LT1, & I updated the original post.

I'm not seeing a code, but haven't had it scanned either.

Anyone know if '92s have 2 or 4 O2 sensors?

 

A '92 LT1 would have two 02 sensors, one for each exhaust bank, located in the exhaust forward of the catalytic converters.

 

You might want to try a local auto parts store (Pep Boys, Autozone, etc.) and see if they can run a basic code scan on your car. The '92 uses the OBDI interface standard (which is older than the current OBDII), but they should still have the proper cable available, and in most cases they do this for free. If you come back with any particular codes, post them here and I'm sure you'll get lots of feedback on how to proceed.

Good luck!

Ron

 

I had one that ran like a bear cold and skipped and set misfire codes when it warmed up. Bad spark plug.

 

What code did you get? I'm getting a code "16" now, which is "Ignition low resolution pulse not detected". Not sure what that is or if its even related to this. The battery had gotten low and had to be charged up. Wondered if the "16" could be related to that.

I just drove it, and pretty much blew the "open loop => closed loop" theory. It ran great for ~15 min and was very warm. I came to a stop, it started idling rough, and started driving rough again -- wanting to die as I let the clutch out with some exhaust popping. The popping was more like thuds. One other thing. I was told that unplugging the MAP sensor would force it into open loop. I unplugged it today to see if that would help but it didn't make any difference. Either unplugging the MAP sensor doesn't affect open/closed loop like described, or my problem may not be sensors.

The display (LCD) has had a history of going blank in the past -- long before this problem started. It was a coincidence today that the display went out right at the same time it started running rough. That same sequence of events hasn't happened in the past that I noticed. A company you read about on the Forum, SIA Electronics, had refurbished the ECM 3 times. Thinking there could be some correlation between it running rough and the ECM.

Can anyone confirm that unplugging the MAP sensor forces it into open loop? If that's really true, then I'm more suspect of the ECM.

Any other thoughts?

 

oops, a 16 is opti spark.
Time to buy a waterpump and an opti.

Probably best option is get a venter cap and a stock replacement.
The third party stuff these days does not seem to have a good rep.

 

I did some reading and found that if my car is showing code 16, it will not start.

I am able to start the car, hammer it up to 5000 RPM without a hiccup. So there is no way that the Opti is dead.

So why would my car show code 16 but not actually have the problem?

I am leaning towards the ECM having problems for a few reasons. First, the ECM has had problems in the past where car would randomly die, would not start, and would run sort of rough immediatly upon starting. When I sent the ECM into SIA Electronics, they discovered that when the ECM was heated up, it started to show errors. Second, when I was driving today, this is how the car reacted ---

*Starts perfectly fine and drove fine during open loop(fully charged battery)
*It ran fine for a little while during closed loop
*The car was able to go up to 5000 RPM without a problem
*Eventually the car started to run rough, and when that happened, the LCD display went out(I am not sure if the two problems are linked)

Third, I followed the instruction to unplug my MAP sensor to force the car into open loop. I unplugged it after the car was fully warmed up. When I unplugged it, the car ran exactly the same as it did in closed loop. That should techinically rule out all sensors causing this problem.

Whats left? ECM?