Why is my 3.2 only lean on the left side?

[cgarr]

Been messing with this for over a year now. First thought it may have been a vacuum leak so its got all new intake seals, everything etc. Now I just swapped out the injectors, did all the checks on the fuel pressure. Everything is perfect except at idle I cant adjust the fuel AFR's, its hanging around 16.0, the right side will adjust anywhere from 12.9 to 16, I have the right side at 14.6 and the left side is 16. I have B&B headers with a split muffler so each side has its own outlet and I am not running the o2 sensor. Now I did unplug the left side fuel pressure regular vacuum line so it would increase the fuel pressure and it did help the lean condition on that side but it also made the right side real rich.

Now the engine is not stock, its now a 3.4 10.5/1 twin plugged.

Any Ideas? I also get a slight pop out the left side when shifting at high RPM's which most likely is because of the lean condition.

[rusnak]

You should see a jump in the AFR when you open the oil cap.

Usually, within a few seconds the mixture would return to normal, as the dme adjusts the fuel pulses to compensate. But you disconnected the O2 sensor. That would make it run in open loop, which would not let the dme do anything except run the default map. Are you adjusting the mixture at the air bypass screw in the AFM?

Disconnecting the fuel pressure reg. vacuum line is the rich stop test. You would see the mixture jump very rich, then return to normal. This tests the dme/O2 response and ability to compensate for rich conditions.

The lean stop test is opening the oil cap, creating a false or unmetered air leak.

Since your left side is so lean, why don't you reconnect the O2 sensor and see what happens? Also re-connect the fuel pressure regulator, basically run it as it was designed.

[BGCarrera32]

Slight pop is it leaning out, I wouldn't worry about it between shifts. The real question is what are the AFR numbers under load.

1st thing, how many turns out is the bleed screw under the AFM (3mm hex)?

2nd thing, at full throttle under load, what is your AFR reading? Are you seeing 13.0-12.7?

My first thought was an imbalance in fuel pressure from left to right- not sure what the allowable tolerance is or how sensitive the injectors will be to +/- say 2-3 psi from one side to the next, and if that will create your imbalance in AFRs. Have you ever replaced the pressure regulator or damper at the back of each rail? If the pressure is correct on the left bank (drivers side) that would lead me to think maybe the damper is slightly off on the right bank.

One side being rich could, and this is just a thought, be weaker spark/ignition on that bank but seems even more unlikely with twin plug. Certainly would not want one bank sitting at 16 and the other at 12 at idle- have you looked at the plugs?

Sending you a PM.

BG

[cgarr]

I did try it with the O2 sensor connected. The left side would come into spec pretty close but then the right side was real rich. The sensor is only on the left header. Normally I would unplug the sensor and get the AFM's close with the bypass screw then plug it back in and it would close loop.

[BGCarrera32]

Other thing you'll have to figure out how to do is get the factory o2 sensor to read the exhaust average across the whole motor. And you can't do that on just one header bank. (O.k. well you can certainly put it there but the DME will just be making adjustments based on that bank, not all 6 cylinders as an average).

I think if you place the factory o2 on the lean bank and it enriches the mixture slightly, it will take the already rich right bank and make it worse.

[BGCarrera32]

LOL you posted as I was typing my last response...

[rusnak]

I wonder if it's possible that fuel pressures are different for the left and right sides? We know from doing the rich stop test that the injectors are affected quite a bit by fuel pressure.

You would notice it missing so that rules out a bad injector on the left side.

And you probably did the starter fluid trick on the intake manifold gaskets.

[BGCarrera32]

They would be different not by design but by regulation being slightly off I'd think (which is what I believe you are saying). I'd like to see part and full throttle AFRs for each side, my thinking is that at full throttle vacuum should be nil so that is quite different than lots of vacuum applied to the regulator and damper at idle. Might be that at 2,000 rpm or something the AFRs balance out and this an idle-only problem he is chasing. I'm not sure. Obviously, what we don't want is 15 and 16 numbers on one bank when you've got foot to the wood. This all assumes what I've described is fuel related.

[rusnak]

An LM-1 would be able to give part and full throttle numbers, as well as load mixture.

I think pulling the plugs and looking at them as a group couldn'd hurt either.

[BGCarrera32]

Yup. I've been doing a lot of work lately with my wideband...I converted a 3.2 into a 3.4 and for whatever reason the old 3.2 ran really well, albeit tired, and the new 3.4 just hated the mixture adjustments with the same control system. I was able to hit 14.5-14.7 at idle, however, I was seeing as low as 11.5 at full throttle. Basically, the 3.4 was gagging on its own barf at full throttle. After 2 years of dabbling, I finally figured out some lunatic had tampered with the Air Flow Meter before I got the car 8 years ago. I ended up tightening the helical clock spring on the flapper door up about 6 clicks, and then resetting base idle mixture. The difference in throttle response went from muddy to more of an "immediate vigor"...

Moral of the story, AFR readings at idle is only one part of the puzzle.

[aigel]

Cam timing?

George

[cgarr]

WOT on the right side is 3.35 the left side WOT is 13.47

The cams we checked this winter and it was dead on for both sides.

[cgarr]

More testing! I swapped out the air meter box (flapper box) with my spare and there was no change. unplugged the alt switch, no change. Ran it separate on upper and lower plugs and there was no change. I changed my rotary switch on the dme 2 clicks to give me 6% more fuel and the left side came in around 14.9 and the right side is 13.0 and this is with the air bypass screw all the way in. Next is a compression check on the left side.

[BGCarrera32]

I think the answer is your pressure damper on your right side if the WOT numbers are so close. I am almost positive n8 never changed it or messed with it when he had it, I think they're like $90. Other thought would be to figure out how to get a pressure gauge on the right side rail.

Swapping the air box, alt meter, etc. won't resolve an imbalance from the left side to the right side.

?

This whole thing however makes me want to go dual channel on my LM2 and check my own setup out.

Do call me when you have a chance. I have some other related but unrelated questions...

[cgarr]

I may put a port on the right rail to check fuel pressure! The left side is perfect, 30 running 39 when I pull the vacuum to the regulator and it holds pressure forever. I pinch off the return line and it jumps to 60, all check out as it should but I am going to make something to check the right side.

Compression checks dead on, with the dme reset to rich, now I got the left side to 14.6 and right is 13.2

I only checked the left side fuel regulator, I guess if the right side was bad and the pressure was high it could also screw up things?

[rusnak]

I don't think changing thd fuel quality switch should be a long term fix.
If you go back to baseline, then the left side fuel pressure is good, the left cylinders are lean and the right side cylinders are perfect 1.0 lambda at idle and slightly rich at wot.
I would start to suspect the dme at this point because the fp is correct but the left side is lean and you have to alter the injection pulses artificially to make the left side come into spec. The only problem is now the right side is too rich, but it is doing what it should be doing.
Can you try putting the stock chip back in or borrow a dme?

[dshepp806]

I'd look for another DME for immediate rule out.

Doyle

[cgarr]

I guess I could swap in the stock chip, the new chip is timed for my twin plug setup but just running it at idle may not hurt just to see what happens.

[cgarr]

I can get a change in AFR's by pulling the vacuum line on the pressure regulator as you should because the pressure then jumps up to 40psi but when I pull the vacuum line on the fuel pressure damper which is on the right side I get nothing, no change in AFR's or anything? Should I be seeing a change?

[cgarr]

May have the problem solved! Checked all compression and #6 is weak and the plugs are oily so its not that the left side is lean but the right side is showing rich. Have planned to pull it all apart this winter anyhow.