[RESOLVED] Weird CEL Issue, No Codes

[jeremylee_7]

Hello my CEL came on today and last thurs on my 92 laser awd (dsmlink, gm maf, agp turbo with supporting mods), but when i check with dsmlink there is no codes. Also the CEL does not stay on consistantly, it flickers on and off half the time; there was even a short time frame where it would come in when i pressed in the clutch, and off when started driving agian.

Now i did install an audiovox cruise control module last week, although today i never turned the unit on. The two wires taped into that are linked to the ecu are the vss and the tach wire.

I have went ahead and unpluged the harness from the cruise servo, but since the car ran with no CELs for 4 days after the last time, it will be hard to tell.

Any ideas as to why the cel would come on, but yet not have any dtc codes, or be so fidgity?
(ohh and the owner who installed the dsmlink had the caps replaced on the ecu).

 

[lacroixdp]

I've had my ECU do this for two things - a bad O2 sensor and bad caps. Since you have new caps, you might want to take a look at your O2 sensor.

 

[EagleTSIawd]

That sounds like dsmlink flashing the CEL as a warning from engine knock, I have mine flash when It knocks above 3 counts.

 

[jeremylee_7]

originaly i thought knock, but a) the CEL is on even at idle b) the boost gauges (which is set to knock on dsmlink) doesnt move when the CEL is on, also i have it set to not show knock bellow 2500ish rpms and/or 30% throttle

When i hooked up laptop to try to pull the cel codes with dsmlink, the o2 volts was all over the place at idle, .1 to .8 volts almost like a sine wave.

 

[lacroixdp]

That's exactly what mine was doing when my CEL was coming on - I replaced the O2 with a Denso unit from oxygensensors.com and it fixed it right up.

 

[Ceddy]

When i hooked up laptop to try to pull the cel codes with dsmlink, the o2 volts was all over the place at idle, .1 to .8 volts almost like a sine wave.

That is exactly what the oxygen sensor is suppose to do when in closed loop mode.

The O2 sensor is giving feedback on how much fuel to add.
.1v = add fuel
.8v = subtract fuel
Thats how it maintains 14.7 A/F ratio at idle.

 

[lacroixdp]

That is exactly what the oxygen sensor is suppose to do when in closed loop mode.

The O2 sensor is giving feedback on how much fuel to add.
.1v = add fuel
.8v = subtract fuel
Thats how it maintains 14.7 A/F ratio at idle.

Is it suppose to oscillate this much at WOT however? Mine was doing the same thing as his while I was at WOT, which would periodically trip a CEL light. After I replaced my O2 sensor, the oscillation isn't as wild and the CEL no longer lights up. I think if he were to do a log while at WOT he would get the same thing. Of course, I could be off my rocker

 

[turbosax2]

Dsmlink will also turn the CEL on for high coolant temps. Check your coolant temps on the laptop when the CEL comes on and compare to your setting for the temperature it's supposed to come on at. It doesn't sound like this is your problem but it's easy to rule out.

 

[jeremylee_7]

Temp gauge never went past half point while I was having the CEL problems but if it does it agian I will check it with dsmlink to rule that out.
(dsmlink is set for CEL on 3 counts knock, 225 degrees coolant, and boost gauge is knock count)

So it is normal for the 02 volts to be oscillating like that in closed loop?

Here is a quick picture of the o2 volts at idle in dsmlink (green line)
<img src="http://www.1stgendsm.com/Images/dsmlink.jpg">

 

[daren_p]

Yes, that is normal operation for a NB O2 sensor to oscillate like that, under closed loop conditions.

 

[jeremylee_7]

You were right turbosax, it was because the coolant temp was tripping the CEL. DSMlink is set at 225 degrees for tripping the CEL, is 225 degrees a little high for city driving in 95-100 degree weather or is that fairly normal?

Unless 225 is abnormally high temp for my driving conditions, I will just set dsmlink to 240 instead of 225, and probably get some water wetter before it gets to the worst of the summer

 

[turbosax2]

That's hotter than I would prefer to be at. Have you verified that your fans turn on and function properly?

 

[jeremylee_7]

No I was going to do that latter tonight, doing oil change/plugs/rear brakes tonight . Good news is if i do have a bad fan i have my old fans from my last dsm!

UPDATE: Fans work just fine, will go ahead and change out thermostat for good measure.