LC-1 Wide Band and DB Guage issue

[Rock2610d]

So, my wide band is acting funny.....or maybe its my engine.

Everyday normal driving the A/F ratios are pretty good...14.3 to 14.9.

Issue is when I get on it a little and boost goes above 10 psi, my wide band shows about 10.5 to 11.5...pretty normal. But if I let off the air pedal just a little and continue driving without boost the A/F ratio will be 11.5 to 12.5 and will stay in that range even while engine is in vacuum.

However, if I let all the way off the air pedal and push the a/f ratio up to 21 or so and then push gas again the a/f ratio will go back to 14.3 to 14.9.

Why after a 10 psi or higher boost do I have to completely let off the gas pedal to get a/f ratios back to 14.3 to 14.9?

 

[gsexxx]

I had the exact same issue with a MTX-L in my gsx. It ended up being a huge boost leak. EGR valve was stuck open thus allowing air to exit through the #4 exhaust port. Where is your wb sensor located in the exhaust?

 

[Rock2610d]

its about 8 inches below the oem unit, between NB o2 sensor and flex pipe.

 

[gsexxx]

I am assuming you calibrated the wb correctly? If so, I would check for boost leaks.

 

[Rock2610d]

yup, calibrated correctly, and there are no external boost leaks as I do a boost leak check at least once a month sometimes more when I do work on it....like when I removed the down pipe to install the wide band bung. BUT:


Car will not hold 20 psi...never has since rebuild, I assume its leaking out one of the valves as I do not know where the piston/valve relationship has all valves closed.

I have used soap and water, listened and even used starting fluid all around while running and no "external" boost leaks detected.

I did find one internal a couple months ago....OEM BOV leaked so Now I have a EVO 9 BOV. BUT I cannot rule out a internal leak, but air does not sound like its passing thru turbo/exhaust. Car idles great and kicks hard....especially for a T-25. I have 6 to 8 psi boost at 2000 rpm in 3rd gear. 4 or 5 psi in 4th at 1800 rpm with throttle at 100%.

I can get and hold 15 psi on a T-25 all day long and A/F ratio is around 10.2 at 15 psi in a 3rd gear pull.

Do you think I could have a leak somewhere else? Never read of a EVAP valve sticking open causing issue like I have.

Please note I am at 7800 feet of elevation.

 

[stunt2]

if there aren't any boost leaks, I would suggest to make cylinder head leak down test. that will reveal faulty valve or piston rings
but can't say if any of the above can cause symptoms you described

 

[gsexxx]

Well my egr valve was still on the car with the lines deleted. I could still hit 17lbs with a t-25. Do you have the emissions lines deleted with the egr still on the car? If so, just throw on a egr block off plate. On my spyder I had the same situation but much more severe. The valve had a lot of carbon build up which caused the valve to always be stuck open and it wouldn't even hold 2lbs during a blt. I wouldn't rule it out since it is such an easy fix.

If it can't hold 20psi then it's definitley leaking somewhere which would cause you wb to act like that (from my experience anyway). Have you done a compression test?

 

[Rock2610d]

My main question is:
Why would a/f ratio act as if its in closed loop after a 10 psi + boost? Until I let up completely on the accelerator?

Oh just seen your post, I will put a new egr on and see if that helps. Thanks

Have not done a leak down! Engine only has 1800 miles on rebuild. Want to wait another couple thousand for ring to seat good.

I could do a compression test but not sure what numbers I should get at 7800 ft and 9:1 compression.

One other thing: the air fuel ratio will drop from 14s to high 11s when I hear a clicking from one of the solinoids on fire wall. When clicking stops, the a/f ratio goes back to 14s.

 

[gsexxx]

If you have the lines deleted just throw on a block off plate for $15. You don't want to have the egr on the car with the lines deleted, even if you block off the nipples the egr will still leak. Like I said, it's worth checking out because it's such an easy fix. When I bought my spyder I got $2000 shaved off the final price because it wouldn't hold boost. Threw on a $15 block off plate and am now holding 30psi no prob

 

[Rock2610d]

No, all vacuum lines are still on car and are new. EGR is 18 yrs old.

 

[gsexxx]

If it is that old it could very well have enough carbon build up to eventually cause the valve to not function properly. I would either clean yours or just buy a new one to rule that out. I would do a compression test as well. Good luck and keep us updated!

 

[Rock2610d]

I will update, but would like to know how much vacuum it takes to open EGR. I am at 7800 ft an my standard idle vacuum is 14 in HG. It seems like my EGR needs at least that to open back up.