Diagnosis? Why two cylinders lean to detonation & the rest are good?

[CDMBill]

So, in addition to blowing out the head gasket between #6 and #7 and fire slotting the head in the same space I have two beat to death rod bearings, #1 and #2 which are the first and second on the passenger side bank for those not familiar with BB Ford's. They are consistent with detonation and the #1 piston has lifted the top ring land as well.

The AFR's seemed OK although I couldn't datalog them just watching the FAST unit at different speeds at Irwindale's 8th mile where all this fun happened December 13th. I did get it very hot when the electric fan failed at Infineon for PINKS All Out in staging in September with just a little street driving after, and that is what we attributed the head gasket failure to at Irwindale on the third pass of the day and now I'm not so sure.

I changed plugs in the morning at Irwindale and the old ones were uniform if showing slightly rich. These were plugs that had been in the motor for several thousand miles including a trip to Famoso much earlier in the year as well as the hot day at Infineon.

The new ones came out looking mostly oil fouled after the head gasket incident with #6 & #7 covered with grey stuff, molten aluminum from the gasket failure and subsequent fire slot caused by the combustion in one chamber at TDC burning into the adjacent cylinder which is at BDC. All that is except for #1 which looked clean as new, or lean in my book. #2 was slightly oil fouled compared to the others and the manifold was pretty wet with oil film.

So the question is, what caused two cylinders to lean out and pound the bearings into the copper at the top of the bearing inside the rod while all the other six rod bearings look brand new even those on the same two crank throws?

[JeffMcKC]

Re: Diagnosis? Why two cylinders lean to detonation & the rest are good?

sounds like spark cross over from one cylinder to the other, plug wires should cross at a 90 * angle lots of small block Fords do this

[dieselgeek]

Re: Diagnosis? Why two cylinders lean to detonation & the rest are good?

yikes.

I 'm betting that it's less likely to be fuel mixture, and more likely either a little too much timing (although I didn't think we were "pushing it" that much, unless the distributor was adjusted a little too far advanced during a later teardown perhaps?)... or electrical problems causing timing error.

Jeff makes a good point, I have seen that before. But I know you run the proper wires...

Do you have any datalogs that show tach spikes or dropouts? the tach signal line would have a missing section, or a spike to some unrealistic RPM - but the fact that you have a distributor would keep the comptuer form being able to throw out some wild timing. but I'm a little concerned that maybe there's an electrical issue, only because BOTH problems you have can be caused by random spark events... even if you only have a "cruising" datalog, you would likely see the issue I'm talking about. Let us know...

and, sorry for the headache!

-scott

[dieselgeek]

Re: Diagnosis? Why two cylinders lean to detonation & the rest are good?

One other thing to check: I am pretty sure those two cylidners are wired up on different injector channels (there are two injector channels on Bill's EMS). But they might share a common power wire, which would be worth a quick check.

-scott

[JeffMcKC]

Re: Diagnosis? Why two cylinders lean to detonation & the rest are good?

Lost a few Big block chevy head gaskets this way with good wires also, never run wires parallel for a very long lenght or time


See the following TSB, Your local Ford dealer can print a copy for you



LIGHT TRUCK: 1987-1994 BRONCO, E-150, E-250, F-150, F-250


ISSUE:
Engine miss, spark knock, buck/jerk, surge and other driveability concerns may be caused by induction crossfire. This occurs because of improperly routed spark plug wires.

ACTION:
If spark plug replacement is performed, the correct firing order and spark plug wire routing is essential to prevent the possibility of induction crossfire between cylinders. Refer to the following procedures for inspection of the spark plug wire routing and firing order. Properly reroute the spark plug wires if required.

FIRING ORDER

The firing order for 1987-1993 vehicles is 1-5-4-2-6-3-7-8. If #7 and #8, or #2 and #4 spark plug wires are routed next to each other at the separation bracket, an induction crossfire condition can occur.
The firing order for 1994 vehicles is 1-3-7-2-6-5-4-8. On these vehicles the #1 and #3, or #5 and #6 spark plug wires must be separated to eliminate the possibility of an induction crossfire.
To eliminate the possibility of the coil wire becoming disconnected, route the coil wire under the spark plug wires at the distributor cap.
1987-1993 VEHICLES

Inspect the routing of the spark plug wires. Refer to Figures 1 and 2.


Figure 1 - Article 94-4-10




Figure 2 - Article 94-4-10


Make any spark plug wiring corrections as required.
1994 VEHICLES

BRONCO OR F-SERIES

Inspect the routing of the spark plug wires. Refer to Figures 3 and 4.


Figure 3 - Article 94-4-10




Figure 4 - Article 94-4-10


Make any spark plug wiring corrections as required.
E-SERIES

Inspect the routing of the spark plug wires. Refer to Figures 5 and 6.


Figure 5 - Article 94-4-10




Figure 6 - Article 94-4-10


Make any spark plug wiring corrections as required.

[dieselgeek]

Re: Diagnosis? Why two cylinders lean to detonation & the rest are good?

this TSB has a point, doesn't it?

The wires for the busted cylinders run right next to each other. Bill, you're not running solid core or "race" wires maybe?


Also, I looked at Bill's data logs today (thanks for taking them, and sending!) and there are no tach input interruptions. THere are occasional voltage drops and spikes, indicating ignition noise is getting into the grounds, but it's not affecting his computer. His tach signal is surprisingly smooth for a distributor input. Long story short, his problem isn't being "commanded" by the EFI computer. It's something mechanical, or electrical, downstream of the computer itself. Crossfiring sure sounds like a possibility...?

Bill, what did the engine guy say? Any signs of detonation in any other cylinders? I am quite sure we weren't running any lean cylinders. His tune was not "ragged edge" by any stretch. In fact, very conservative,

-scott

[BBR]

Re: Diagnosis? Why two cylinders lean to detonation & the rest are good?

Have we ruled out trash in a fuel line or partially plugged injectors? How are the fuel rails plumbed?

just throwing out ideas.

[JeffMcKC]

Re: Diagnosis? Why two cylinders lean to detonation & the rest are good?

Bill did you spray it? That will do this too.

[CDMBill]

Re: Diagnosis? Why two cylinders lean to detonation & the rest are good?

Hmmm, no spray, and I am anal about plug wire routing, I use the big black MSD 8.5 wires and separators and the adjacent firing cylinders are physically separated and cross at an angle.

I have worried about distributor phasing after I changed the cam and stabbed the distributor back in. I had of course marked the location and the new cam was timed at the same 109 as the previous one though it did have one more degree of LSA, 112 vs. the former 111. I checked the timing light indicated idle speed advance on the balancer vs. the that indicated by the EMS and they were the same 22 BTDC at 1100 rpm, and as well as at 3000 rpm unloaded. The spark table has a number of various points for light load, cruise etc.

You may recall my post about cam gear phasing from cam shaft to cam shaft and I am still not sure if it matters but I checked everything I can think of when I degreed in the cam and resent the mechanical timing. The distributor was not quite at the same mark as it was before the cam change, maybe 1 - 2 degrees less BTDC

The two cylinders with obvious detonation 1 & 2 and the two where the head gasket died 6 & 7 are not the ones firing in sequence, see Jeff's post re the 15426378 firing order as mine uses. Care examination of the plugs I took out of the car in staging before the engines final three passes show glazed porcelain on 1 & 2 consistent with the later problem in those cylinders. The others look to be on the edge given how far down the on the porcelain the carbon ring starts.

I have checked for debris in the #1 & 2 96 lb. injectors but they they appear clean and identical to #3 & 4 and would have to be pretty clogged as they run at 55% duty cycle at WOT (saving room for dry N2O). The rails are .5" supplied with #8 lines form a #10 supply fed by an Aeromotive pump and then from the rails to an Aeromotive regulator then back by #10 to the tank. I run an 100 micro filter before the pump and 10 micron after and filters are new last August.

I suspect that with the cold weather at Iwindale December 13th (OK, cold for Cali) I was on the lean line at WOT AFR due to the slightly bigger cam, I hadn't adjusted the fuel map. This didn't show at idle and cruise when I could read the AFR's directly from the FAST meter for that bank. The other bank reading has a glitch which I had from this meter at DW 07 as well and it was supposedly fixed. It wouldn't give me a good datalog on the FAST as a result. Oh well.

Perhaps I still had a bit too much actual WOT timing and that and the lean condition did me in for the two cylinders that were over the line. I'll check the plug wires but I don't think I'll see anything obvious like a burned wire. I don't think an inductive spark cross fire would do that in any event. Time to get the AFR meter working correctly and datalog the FAST and the EMS. Staging will be even busier.

[JeffMcKC]

Re: Diagnosis? Why two cylinders lean to detonation & the rest are good?

log EGT maybe

Bill what does the timing make on the ground starp look like how far back is it burned?

[dieselgeek]

Re: Diagnosis? Why two cylinders lean to detonation & the rest are good?

I didnt' realize there was a cam profile change earlier on. Guess I missed that. If it flows more air at WOT, the speed density setup on his EMS is going to need a bump in fuel at WOT. The fact that his AFR meter has been flaky, so we can't log WOT AFR, is a pain in the butt likely covering a lean condition at WOT.

We'll retune it after he puts it back together and get the AFR logging problems corrected.

[CDMBill]

Re: Diagnosis? Why two cylinders lean to detonation & the rest are good?

I think I had a perfect storm issue, on the edge of lean tune, really good air, just a bit more cam e.g. airflow, not my usual fuel (stupid Winter mix in Cali at different gas station), and two cylinders that just happen to get the most air next to one another, which is odd.

Out of this I've learned a lot more about plug reading, my EMS-Pro amazing capabilities and how to ensure that the tune I want is the tune I have. With great flexibility and complexity comes great responsibility to know what the hell I'm doing.

[JeffMcKC]

Re: Diagnosis? Why two cylinders lean to detonation & the rest are good?

LOL I hear ya, Lean hurts parts, but is fast, a razors edge is sharp.