CEL only at WOT? "lean"

[tim281]

I have been getting code 41 & 91 at WOT since I installed a GT40 intake, BBK TB, and C&L inlet tube. The funny thing is the code only appears when the pedal is mashed all the way to the floor regardless of RPM. I was thinking this maybe a fuel pressure issue or delivery volume issue, but I doubt that it would be showing up at the lower RPMs. I am going to swap out the FP and reg anyways since they are probably originals so maybe that will help a bit. I am going to also try clocking the C&L mass air a few times and see if that helps. One last thing, I currently have platinum plugs in the car and will be swapping in some copper motorcrafts....I know, I know...don't run the platinums but I didn't know any better.
I was just checking to see if anyone else has dealt with an issue like this and may have some pointers. The Check engine light appears only when the pedal is all the way down....once you lift the light goes out. Seems to be regardless of RPM.
I probably do need to ensure my timing is set properly after the intake swap as I just marked the distributor when the timing mark was at 0 and re-stabbed after the intake install. Doesn't seem to ping, but I got a backfire through the intake once which is probably associated with a lean WOT condition.
Thanks for any tips.

 

[NotchAbove]

If you did not pull the cam here is what you should do.

Pull #1 spark plug, put thumb over spark plug hole, turn engine over until you feel air pushing your thumb out. This is the compression stroke and where you want to be. Once you feel this look at your harmonic balancer and turn the engine over until the pointer is at -0-. This is TDC.

Now looking at your distributor, take the cap off, and see where the rotor is pointing. It should be in the area of the #1 spark plug terminal (it will not be right on since the car should have advanced timing, if your timing was zero, it would and should line up 100%).

If its not even close, then you need to pull out the distributor at this point, line it up with #1, and then turn it very very slightly clockwise. This will give you some base timing. Then put all back together and hit it with a timing lite.

 

[tim281]

Thanks. I didn't pull the cam, but I did mark line up the distributor to #1 plug before I pulled it. I am not sure if it was TDC of #1, but I know the distributor was pointing to #1...so I think this is the same thing?
I rotated the engine to 0 degrees and marked the distributor casing with a marker to see where it lined up with the gear assembly at the base and I also marked the spot at #1 where pointer was located. All in all, I can't think how I could have gotten anything off since nothing moved during the assembly. I really should get myself a timing light and check it out.
I may have to pick up a harbor frieght special timing light....unless someone knows they are total crap.?

 

[tim281]

I got a timing light, removed the spout and checked the base timing.
It read exactly at 16 degrees?
What timing should I be running for 92 Octane gas???
Thanks,
T

 

[tim281]

I did some searches in the archives and it looks like 16* might be a bit much for timing for 92 octane....and also timing settings can vary from car to car. The stock OEM timing is set at 10*.

I am wondering if I really have a timing issue since the CEL light comes on and reads lean at WOT because I dont' think I hear any pinging? I did get a backfire through the intake once. Would running too much timing lean out your O2 readings?

 

[HISSIN50]

If you can, have a passenger check your pressure when it's at WOT and the CEL comes on (have the FP gauge stuck under the passenger wiper blade, etc).

Also check your TPS to make sure you dont have a dead spot near the end of the scale (as you approach WOT). This could cause leanness when the TPS takes a dump

 

[phutch11]

You may just also have a miss fire at high load conditions. I had a bad plug that was causing a code 41 and it took me forwver to figure it out.

Get rid of those platinums immediately and check and double check all your wires.

My money is on a ignition based missfire.

Good luck....
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[tim281]

Good point about the ignition...I think that could be the ticket since it happens at any RPM. I will ditch the platinums this weekend or sooner and go out for some WOT runs. I just clocked the C&L to 1 o'clock and I will see if that has any effect.
If I switch the plugs and it still has the CEL, then I will back the timing down to 14, then 12 to see if that fixes it. These are all pretty easy and quick things to try.

 

[PJC Racing]

The base timing is a little high, but what you are describing sounds like a WOT lean condition. I went through this couple of month ago with my D/D. Are you using the stock in jectors with a million miles on them? There may be your root cause, it was in my case and I had the exact same symptoms you are describing.

 

[tim281]

I just removed all the injectors and had them ultrasonically cleaned on an ANSU flow bench so that is why I was questioning the fuel pressure regulator and fuel pump. I am going to try and get a fuel pressure gauge I can put on the rail while I hit the throttle and verfiy pressures at HISSIN suggested. Since it happens at lower RPM, even 2.5K to 3K I was thinking the plugs maybe having something to do with it.
I will double check for vacuum leaks again. If nothing else, I can always dyno tune the car and richen the fuel to fix the issue but I think it should be fixable with the current set up.

 

[93 LX]

when was the last time you change O2 Sensors?

 

[PJC Racing]

I am going to try and get a fuel pressure gauge I can put on the rail while I hit the throttle and verfiy pressures at HISSIN suggested.

Agreed, you NEED to do this.

I was thinking the plugs maybe having something to do with it.

Read the plugs.

I will double check for vacuum leaks again.

Good idea.

If nothing else, I can always dyno tune the car and richen the fuel to fix the issue but I think it should be fixable with the current set up.

Not really good idea. This would be a band-aid, not affix. You need to find the cause. Do you know what your injector duty cycle is?

 

[tim281]

Installed ford copper plugs and reset timing to 12*, but still had the lean condition. I did test fuel pressure at idle and it seemed stable. FP no vacuum was 44 psi. With vacuum ~35 psi.
I did a compression test also since I was switching the plugs and the lowest cylinder was 110psi and the highest was about 128 psi. About 103k miles on the engine. Tried to read the plugs but they seemed fine, there was a very slight bit of white haze on the electrode stem...that is probably from a being a bit lean (my guess). The plugs were only in there for about 2k miles and overall, they look great.
I recently put in 2 new bosch O2 sensors. TPS is new with BBK TB.
My guess is that the fuel pump maybe lowering at load?

 

[jrichker]

EFI engines will always show lean plug readings when you drive and then shut down normally. The computer always chooses the leanest mixture for normal driving. The only way to get an accurate reading of the spark plugs is to drive the car at full throttle, take it out of gear and turn off the ignition. Pull over to the side of the road and pull the plugs. Do it any other way and the computer will go back to the lean/best economy setting. That will hide any evidence of anything out of the ordinary happening.

 

[ImportSlayer347]

I had the exact same problem. I found the orange ground wire strapped to the back of the driver side cylinder head had come loose when I was working behind the intake. I reattached and no more codes.