CEL activation?

[quick72toy]

Does the CEL actually have to come on when you have a code?
I had to fix some stuff, and put a scanner on the car to pull the codes. There were two there, but my CEL never lit. (When I have the key on engine off, the check engine light lights up ok.) but has never lit up to indicate a code problem. I did an test, and cleared the codes without doing any fixes, and after a while the codes came back, but no CEL? What gives? What has to happen to get it to light?

 

[Stickman]

Did you ever figure out the answer to this. Not getting any CEL's but car runs terrible until warm.

 

[CheeseHelmet]

Depending on the DTC, the CEL might not come on. Generally the CEL will come on for emissions-related stuff. For example, if your VTCS solenoid fails the CEL will light up, but if the VICS solenoid fails the CEL won't light up. Each of those solenoids control a set of butterfly valves in the intake manifold, the only difference is that VTCS helps with emissions and VICS helps with performance at high-RPM.

Stickman, I doubt a hidden CEL would help diagnose your problem. Could you describe what you mean when you say that it "runs terrible"?

 

[MS3_KIDD]

The dtcs your referring to are pending. The vehicle needs to see the same fault under the same conditions in 2 consecutive run cycles to set the light. It could see a fault once and in a blue moon and store the code as pending and never see it 2 times consecutively and won't set the light

 

[CheeseHelmet]

The dtcs your referring to are pending. The vehicle needs to see the same fault under the same conditions in 2 consecutive run cycles to set the light. It could see a fault once and in a blue moon and store the code as pending and never see it 2 times consecutively and won't set the light

That's true, but there are also some DTCs which do not turn on the CEL. Have a look at P0660 in the service manual, you'll notice that it doesn't say that the CEL illuminates.

 

[Stickman]

Cheese,

Cold Idle Problem after engine swap,
Upon initial start, after idle comes down to norm (800 - 1000), it won't hold at 800.
Keeps dropping, chokes, tries to increase, revs up to 2000, dies back down, can't hold idle, and stops running. Restarting produces same results.

I have to start, rev it myself to 2000 RPM, let out clutch, then go. It will kill if I accel;erate too hard. Acts like I'm short a cyl.

After a few minutes of driving, all is fine, idles 800 at stop lights, etc.

Let car sit a bit and same problem, just not as long to get it running normal.

No CELs. For CEL test , disconnected one coil and ran. No CEL. CEL light not burned out as it shows w/ rest of lights at starting.

Sure can use some help. Thanks.

 

[CheeseHelmet]

Sounds like the symptoms of a stuck-open EGR valve, but normally it's not that bad. How much of the engine got changed (ie. just the longblock or longblock+manifolds, etc)?

It's weird that your CEL won't come on. Here's one way it'll come on for sure: unplug the upstream O2 sensor with the engine off, start the engine and let it run for a few seconds, turn it off and then turn it on again. A little bit after the second start you should get a CEL.

 

[FLIPOTTAWA]

Its wierd im having the same issue with my car except you are lucky enough to be driving yours. Im in the middle of putting the car back together and been trying to get the car running fine. (NOT EVEN CLOSE YET)

Here is my typical start up.

Turn the car over revs to 1500 rpm then drops and stalls out.
Start car over again give it some gas...idles from 800-1500 rpm. I let it run a couple of minutes and it bounces around a little. Never steady at one rpm.
Give it gas and it responds like it should. Give it too much gas and rev to high and it drops down to 800 then dies again.

Couple of mods ive done so far.
Split second AFC v2
O2 CEL eliminator
Supercharger
Vaccumm block
HKPRO stock sc map tune
Innovate wide band
Colder spark plugs
Butterfly removal

Im going to recheck the tune make sure its there.
i was throwing two engine codes P106 Manifold Absolute Press and p122 Throttle Position sensor. Since i adjusted though no codes just terrible idling.

So im hoping some of the solutions they find for you will help me out.

Oh the car had been sitting for a couple months but i put in fresh gas 94 octance and at least it starts now

 

[Stickman]

Cheese, Longblock only. IAC, MAF, cleaned by mechanic. EGR is original.
I'll try the o2 upstream sensor. Where is it?
Thanks.


Flip,
I've been told that timing belt being off one tooth can create wierd problems. Don't think that's my problem as it runs fine warm. Can't hurt to check.

 

[CheeseHelmet]

Cheese, Longblock only. IAC, MAF, cleaned by mechanic. EGR is original.
I'll try the o2 upstream sensor. Where is it?

You'll see it if you remove the front airbox (the big flat thing that's secured with 2 10mm nuts). The sensor sticks out of the exhaust manifold, just follow the wire to the connector (less than 15cm away).

 

[FLIPOTTAWA]

Just did my timing belt and everything lined up fine. Actually did it three times till i figured out i had a CAM SEAL LEAK. But lined everything up as per the service manual. I went to a junkyard this morning picked up a new Throttle body with sensor, MAF sensor changed those and still having problems.

Ill start the car, it turns over no problem revs up to about 1000 then dies right away. If i keep my foot on the gas and keep it at 2000 rpm it stays and idles a bit off but soon as i let go drops and dies.
Maybe fuel?
Im going to be checking the tune later on this evening...

Also i have an INNOVATE wide band and when the car is in NA mode the gauge doesnt move but soon as i put it into boost it goes from 14.7 to 22.1 any ideas ?

 

[Stickman]

Cheese,
Didn't have to check further, it finally lit a CEL. Air intake was loose. Must have taken the computer 200 miles to catch up, reset.

Cheese, Flip,
As to cold engine running poor. All of a sudden, it's OK.
I'm thinking either
deteriorated gas from sitting a few weeks before engine swap,
or computer had to catch up w/ different engine,
or midnight alien visit,
or .............

Flip, did you get yours back to running normal?

Thanks guys.