cylinders 2 and 5 lean

[T77911S]

i have seen this mentioned here quite a bit about cylinders 2 and 5 running lean compared to the others. is there any conclusion on this?

my head is at flowtech right now, should i have 2 and 5 richened?
i am going to call larry today about it but i was just curious what others had to say.

[RarlyL8]

Larry can ballpark it but you have to adjust on a running engine if you want it perfect.

[Miguel Antonett]

How do you adjust/isolate 2 & 5 from the rest?

[JFairman]

It may be that 2 and 5 just run a little hotter than the others because they have cylinders on each side of them.
I think you could have Larry adjust the fuel head to give 2 and 5 a little more fuel than the others while it's on his flow bench. That would probably be close enough for CIS

[JFairman]

Originally Posted by Miguel Antonett

How do you adjust/isolate 2 & 5 from the rest?

By turning the little 3mm allen head spring tension adjusters under the 4mm button head screws next to the injector line banjo fittings on the top of the fuel head a tiny bit.
Trying to do it yourself could easily screw it up so have Larry do it on his flowbench.

Ask him if he uses different o-rings in the fuel head made of viton or something that can survive in E10 or E15 fuel.
I wonder if you could have the aluminum fuel heads rebuilt with different o-rings and adjusted way richer to run E85 fuel with correct air fuel ratios.

[PcarPhil]

Originally Posted by RarlyL8

Larry can ballpark it but you have to adjust on a running engine if you want it perfect.

X2.

Originally Posted by JFairman

By turning the little 3mm allen head spring tension adjusters under the 4mm button head screws next to the injector line banjo fittings on the top of the fuel head a tiny bit.
Trying to do it yourself could easily screw it up so have Larry do it on his flowbench.

IMO a somewhat safe way of doing it yourself is to:

- Take baseline 'readings' by taking pictures of the inside of your header tubes and spark plugs. Note any variance between cylinders. Most likely 2 & 5 will be leaner/hotter than the other cylinders.
- Richen 2 & 5 by turning the adjusters a few degrees in the proper direction. You can search my username for additional info on this.
- Drive the car for 100 miles with no/minimal boost, then re-check header tubes and spark plugs. Try to avoid excessive idling during this 100 miles. Ideally you will have less variance between cylinders.
- Fine tune as necessary. I found once I got 2 & 5 close to 'ideal' I had to also fine tune the other cylinders, although nowhere near as much as 2 & 5.

By doing the above I was able to get my header tubes and spark plugs to look almost identical. The engine runs smoother and seems to have more power as well.

A few notes on this adjustment:

- I feel you can make a pretty accurate adjustment by reading the spark plugs alone. This is assuming you know how to read spark plugs.
- IIRC if you have the later Lambda fuel head (like my '87) you can rich/lean adjust as necessary. If you have an early non-Lamda cast iron fuel head then this is a one shot deal - you can richen but not necessarily lean it back out as the internal diaphragm is different. So if you richen too much you may have to replace the fuel head diaphragm in order to lean it back out.
- I have seen conflicting info on how much adjustment is 'ok' and not 'excessive'. YMMV. Like most CIS adjustments a little goes a long way however keep making adjustments until you get the readings where you want them. I have a feeling that the amount of overall adjustment needed between Lambda and non-Lambda fuel heads is different (non-Lambda needing less overall adjustment).
- Changing any part of the intake/exhaust path can cause this balance to change. When I went from B&B headers to RarlyL8 equal length headers I had to make another round of adjustments.
- I'm assuming you have a WB02 meter installed. If so it's neat to see the AFR changes when adjusting the cylinders. I richened up the individual cylinders as needed, then leaned the overall warm mixture with the WUR to get the overall AFR back to my target.

Good luck. It is well worth it to get the cylinder AFRs more closely matched, at least more-so than the factory variances. Do this adjustment correctly and your engine will thank you. Do it wrong and your engine could go BOOM!

[Miguel Antonett]

What's your opinion (lean/OK/rich) on the shot below? It was taken after a very spirited drive...

[PcarPhil]

Originally Posted by Miguel Antonett

What's your opinion (lean/OK/rich) on the shot below? It was taken after a very spirited drive...

I would need more info on your setup to give you a good answer. After saying that - the variance between cylinders looks minimal. I wouldn't try to adjust between cylinders.

[T77911S]

dont get larry started on ethenol gas, ive been down that road.

His website has a page on gas

[T77911S]

for those that have actually looked at the AFR of each cyl, how lean are 2 and 5 compared to the others.
are they also lean on boost?

as long as thye are rich enough on boost does it really hurt anything to be lean at cruise? after all, my car was running in the 16's at cruise when i got it due to air leaks.

when 2 and 5 are adjusted richer, how is the idle? any difference?

[PcarPhil]

Originally Posted by T77911S

when 2 and 5 are adjusted richer, how is the idle? any difference?

My idle became smoother after adjusting 2&5, although my idle wasn't bad to begin with. Also slightly more power after I reset my overall AFR.

Do you have a pic available of what the insides of your header tubes look like? Like Miguel's pic?

My cylinders 2 & 5 were noticeably leaner/hotter than the other cylinders before I made the adjustment. In comparison Miguel's look very consistent between all cylinders.

[T77911S]

no, my car has been VERY rich, like in the 12's.

[fredmeister]

This is a good question but to do it with any degree of accuracy my opinion you would need to install an O2 sensor at the individual exhaust ports or in the pipe well before it merges in the collector on each bank. otherwise I am not sure reading plugs or looking at subtle changes in color in the pipes would give you enuff accuracy to do any meaningful calibration to within +/-0.5 AF ratio between cylinders.

Plus taking the headers off between runs while you make adjustments would be a huge PITA to me.

If you could weld sensor bungs to the individual header pipes and plug the ones you are not using at any particular time you could get by using one wide band O2 sensor and keep swapping it around between cylinders while making runs under boost or cruise while dialing in the fuel head.

Let us know what Larry says though after you talk to him.

thanks,
Fredmeister

[RarlyL8]

The factory fuel settings were rich which compensates for the assymetric air distribution of the intake, among other things. The AFR reading at the tailpipe is an average of all 6 cyl of course so you want to leave it a little fat if manually adjusting the WUR.

[T77911S]

i talked with larry and i decided to just have the head set to spec. if its a little lean at cruise thats ok, as long as boost is good. i run it on the rich side so i dnot think it will be a problem, after all, its lasted this long when it was leaner.

[Lapkritis]

Modern approach is individual o2 and egt sensor for each cylinder. Eyeballing isn't worth spit compared to the cheap and plentiful modern instruments.