Fresh Build: 2 cylinders running rich...
 

Quick info:

Full rebuild on my Motec EFI 3.2 to 3.4 :

• Brand new Mahle 98mm pistons and cylinders, rings etc.
• Heads completely rebuilt and assembled by Competition Eng
• Brad Penn 30W break in oil
• Miles so far: only 150

Have done about half dozen break in drives, RPMs up to about 5K, followed the routines as I understand them:

• first drive: 20 minutes, 2000-4500 rpm, varying load, engine braking.
• second drive: 1 hour, 1,500-5000 rpm, varying loads, engine braking
• oil and filter change.
• Rebalanced TB linkages at 2,000 RPM after 60 miles.

Drives terrific with no change needed to my EFI mapping to drive quite well. Without looking at each bank's AFRs, you wouldn't know anything is off. No smoke, little smell, oil pressure and temp all good.

Concern:
AFRs on second bank are noticeably low: for any given RPM, AFRs are 1-2.0 pts low, as low as 10.7. E.g, can be running at 12.4 AFR on bank 1, Bank 2 at 10.7.
Most noticeable under load at 20-50% constant throttle.
New Bosch 4.2 wideband sensors: did 2 different fresh air calibrations, swapped sides as well.

Pulled the plugs at 60 miles:
#1-3, #6: light toasty color, almost as new.
#4: surprisingly sooty black color. Does not seem oily, more like baked on soot.
#5: somewhat black

#1 (2,3,6 similar):
http://forums.pelicanparts.com/uploa...1664804676.jpg

#4:
http://forums.pelicanparts.com/uploa...1664804676.jpg

#5:
http://forums.pelicanparts.com/uploa...1664804676.jpg

Given how few miles, went out for more driving to see if #4 and #5 rings need to be seated. Next few drives about 1-2 hours each, again medium aggressive load, hills, engine braking, varying rpm. Up to 150 miles or so now.

AFRs still much lower on bank 2.

With the MOTEC, I tested trimming fuel on #4 and #5 just to be sure the plugs were telling the story. This brought the AFRs on bank 2 much closer to bank 1, using about 20% trim on #4 and 10% on #5. Trimming #4 alone mostly brought the AFRs up closer, so that cylinder seems to be the big issue.

Swapped entire fuel rails and injectors between Bank 1 <-> Bank 2 to make sure the injectors are working and not leaking on #4 and #5. No change. Bank 2 still rich.

I realize rings can take more than 150 miles to seat, but according to Mahle and most folks, modern rings should be 80-90% seated within the first 100 miles. The radius and napier rings from Mahle should be mostly seated by now from my understanding.

Not panicking, but asking what to look for or thoughtful advice: drive more and harder I assume? Going to do leakdown and compression tests to get more info, and put a scope down the bores. It's not running crazy rich (hardly under 11 on the bank), but the disparity between the cylinders seems pretty abnormal. Considering trimming #4 and #5 for a while in case the running rich is preventing the rings from seating and vice versa.

Thx

update: 250 miles in.
Still running great but sensors report bank 2 is still richer than bank 1.

Have swapped fuel rails/injectors, plugs, coils and sensors from bank 2 to 1 and vice versa without a change in AFRs.

Compression (and Leakdown) numbers:

#1: 152 PSI (9%)
#2: 161 (6%)
#3: 170 (5%)

#4: 183 (6%)
#5: 181 (6%)
#6: 181 (6%)

Any thoughts or theories? Wondering if focusing on bank 2 is not the right approach. At the moment just continuing to enjoy the break-in driving.

I would think spark is the first problem I would chase ,
The leak down numbers seem high.
Ian

Thanks for the suggestion. I swapped everything from bank to bank including coils and plugs with no change.

I experimented with bank fuel trims and a 10% trim on the right bank brings it into AFRs very close to the left bank, in fact maybe leaner. It seems very sensitive to small changes in fuel. I will try 5%.

The leakdown numbers may be misleading since as I approach 90-95 PSI the tester o-ring may be starting to leak, and my tester has limits on how tight I can get the tester to seat. It sounded like it may have been coming from the plug hole. I doubt it was coming from the valves, and I could here a slight hiss in the oil tank from the left bank cylinders which is consistent with the lower compression numbers.

Drives very strong at all RPMs (have not gone over 5000), idles perfectly, etc.

I am starting to think things are still breaking in and I am over analyzing it.

Hi,
Just a thought but have you checked for air leaks below the butterflys? You could be perfectly balanced at the inputs but air is leaking in on some which is bringing their AFR up.
Also what are you using to balance the ITBs?
Cheers Neven

I will check but i'm not sure where it would be leaking with newly finished heads, new gaskets and spacers, and the problem side (with dark plugs) indicates rich not lean.

Balancing done using synchronometer at 2000 RPM per specs, but per talking to Ian seems a good idea to check 3,000 to see what I learn.

that's true but if your air leak is making some cylinders run correctly, the ones that don't leak will be rich

I agree with your logic, though this would mean that I have 4 leaking intakes across 2 banks (1-3 and #6). Not impossible, but not that likely. I will keep in mind as I investigate.

PS. This idea gave me some thoughts on tests I can do. Thx

I had a maximum of 2 valves leaking in 2 wheels at the same time 4 it is very hard not possible

I am finding that the mixture is extremely sensitive to very fine ITB/linkage balancing. I balanced at 3,000 RPM (thanks Ian for the suggestion) and it made a very big difference in closing the AFR gap between banks. The balance significantly changed since I balanced at 60 miles and I was out of balance by a lot.

I think as things wear in I need to keep revisiting the balance. I suspect I am now not far off.

I assume you are balancing at low/no load? It might be worthwhile investing in some dyno time and balancing at load though you will still likely have an issue if the load based balancing varies far from no load (throttle shaft air leaks for example?)

I'm a little late to the party....but my 1st thought was air-flow balancing......and/or linkage setup....I.E. one bank getting more/less air than the other.

regards,
al

To close the loop, my problem was cam timing.

I am not sure how since I checked it like 4 times, but...my right bank cam timing was set about 1.7mm too high. I mystified by how I messed that up and why that amount.

The good news is I had double checked the piston to valve clearances before ever firing up.

I adjusted all valves and retimed the 4-5-6 cam and I am no longer running rich relative to the left bank.

Thanks to those who offered advice.

Will, that is great news and proper diagnostics . Not being afraid to look at everything !
I am happy for your progress.
Ian