Nothing in the search..what can make an MFI REAL rich on one side and not the other?

[Zeke]

Not much else needs to be said. Black sooty plugs on one side and perfect plugs of the other. Other systems good.

[Grady Clay]

Milt,

First question: Are you sure of the cam timing L-R?

Can you borrow a pair of individual mufflers/megaphones and to a tail pipe sniff L & R? Is the rich mixture at idle, part throttle or full power on the cam? If at idle and part throttle, do all the butterflies come off the stops simultaneously? I recall your disaster with the plaiting; did the new linkage get back in correlation? With the linkage disconnected is the air flow equal to all cylinders?

Is this a change due to the great spin-out?

Best,
Grady

[ewave]

There are only two circuits in the DME for the injectors. One for the left, on for the right. Perhaps there is a problem with the DME, the ground path for the injectors, or a bad connector?

[Zeke]

Grady, thanks for the questions. Let me shed some light. Actually, I spent a good hour reading over the many threads you and others have contributed to last night, some before I posted and some after. I even found some places where people were having some problems at specific cylinders. The threads went dead before any definative answer came to bear.

Yes, this is more recent and corresponds to my tracking of the car. I think I have the throttle plates and linkage as good as I can get it. I will readily admit, my injection needs some professional attention. Unfortunately, it is rather worn out in the usual places. I don't ever expect to tune this perfectly in this condition, that would be impossible.

But, recognizing the deficiencys allows me to "work" with the things I have to work with. I just am absolutely flabbergasted that I could have black, dry, sooty plugs on one bank and nice brown plugs on the other.

So, the first thing I went after is the side to side correlation and coming off idle at exactly the same point. Seems OK. I have to have everything slightly preloaded to have it all at rest where I want it, so due to slop in the lnikages and added together, there is some error. However, at dead rest idle, I'm seeing a LOT of black unburned fuel from the right bank. I can't expect perfection with the conditions, but this is so radical and so unbalanced that I wondered if there was some peculiar situation that would allow this to occur. I almost can't drive the car, but if I keep the revs up, aviod traffic and keep it cleaned out, I can manage.

The track spin did knock the main linkage piece off. The one from the bell crank at the front of the motor to the cross bar. It was slightly bent as a resut. Weird things happen when you slide over 5-6 inch rocks which is the norm for Willow Springs in an off track excursion.

Knowing that all recent changes can have an affect, I'm looking at the linkage and not seeing what I need to see. AFA cam timing, this is not something I have monkeyed around with, so I'm putting that at the bottom of the list.

No DME on my car. I wish, that would mean I'd have a 3.2.

[ewave]

Zeke... OOOPSSSS! I don't know WHY I always assume everyone has a 3.2 LOL!

[Grady Clay]

Milt,

OK, It is possible but VERY unlikely it is something to do with the pump but it wouldn’t hurt to check the pump timing. That leaves us with only air flow differences L-R, engine pumping difference L-R, or ignition difference L-R.

It is very unlikely there is a difference L-R with ignition – it fires alternately left and right. I suppose the plug wires could be off by one cylinder on the right; 4 on 6, 6 on 5, and 5 on 4 or some such nonsense. I’ve never tried that, I wonder what happens?

If you can see the throttle plates all come off the stops simultaneously that is an indication there isn’t more of a linkage problem.

When a 911 is doing acrobatics, it is possible for it to get grip in just the wrong attitude and turn the engine backwards. Chains aren’t good pushers. It is possible the right cam jumped a tooth.

I assume you have (or have access to) an air flow gauge for setting the stacks. With the engine at just off idle and at 1200 RPM using the hand throttle, check the air flow L-R.

Next test; pull all the plugs and check cranking compression.

Best,
Grady

[john walker's workshop]

i had one like that recently. 5 and 6 sooted up, and the rest were fine. after spending a couple of hours on it getting a feel, and swapping the injectors, a pump swap fixed it.

[Zeke]

I think I will go out a nd pull an upper valve cover right now. This is on the 4,5,6 side, not too hard to get to.

And, yes, I have all the tools except the protractors. I have been setting the pump/throttle body correlation by having the 2 push rods start the opening of the throttle plates when the pump comes off it's rest and having them both arrive at WOT at the same time. What else can you do? The percent of opening of each in relation to each other can only change with a change in push rod length and one of the other of the parameters would be off, correct?

[jluetjen]

Zeke;
Did you pull the plugs after the car had been idling or was it a "Hot shutdown"? I wonder if it would be possible to eliminate some suspects by comparing a "Hot shutdown" to how the plugs look after idling? If the problem is an idle problem, I could picture it being related to the throttle butterflies, syncronization, etc. If it is a WOT problem, I'd be looking at the pump, valve timing and adjustment and stuff like that since such things as synchronization and idle screws and the like just don't matter at that level of air flow.

[Zeke]

Dial indicator in place on no 4. Can I do this w/o a degreewheel? What reference can I use? I mean one tooth is all I'm looking for right now. Cam chain cover is on, it's not coming off today. If I have to go that route, I'm pulling the motor first.

[jluetjen]

Zeke. I've measured cams without a degree wheel. Just count the number of teeth and divide into 360 (but I'm sure that you already figured that out). If you want to be more precise, you can even use teeth and hollows. As far as I can tell it's good enough.

[Grady Clay]

Milt,

No broken rockers? You can look down at the exhaust rockers where they contact the cam and see if there is dramatic clearance. Valve clearance everywhere?

Start with the crank at OT and the rotor pointing to #4 plug wire on the cap.
Make sure you have valve clearance.
Set the dial indicator so it can extend ~10 mm when the cam depresses the valve.
Set the indicator dial to zero.
Rotate the engine CW a full 360 degrees (now OT #1).
Measure how much the valve moved.
Confirm the dial indicator still is in contact with the valve retainer.
Repeat several times, always turning the engine CW
The S spec is 5.0 – 5.4 mm (0.197 – 0.213”) with the ideal at 5.2 mm (0.205”).

There are 27 teeth on the cam sprocket. A jumped tooth is 13 1/3 camshaft degrees, 26 2/3 crankshaft degrees – a lot.

Here is a link that Warren posted the other day:
http://members.rennlist.org/911pcars/camtiming-1.htm

If everything measures OK, put the cover back on and report.

Best,
Grady

[Zeke]

.205 pretty much every time depending on my "interpetation" of the Z1 mark alignment. I'll go button it up and wait for the next idea. Glad that worked out. Thanks. I mean it. That's a load off my mind.

[Grady Clay]

Milt,

You are absolutely sure no broken exhaust rockers?

Just stick the cover on with a couple of nuts.

Let’s do a cranking compression test.

Best,
Grady

[Zeke]

Stand by. That might take a few minutes and it will be a "cold reading." No, I admit I didn't take off the exhaust rocker cover because of the oil. Currently , I have the car up on stands and can't tilt it. I will crank it and check the compression.

You know, I drove it home and it runs fine. It really does as long as it doesn't have to idle much. More than a minute of idling brings about the rough running and dying from too rich. the 4,5,6 plugs show that rich, but it's not a deep deposit. It washes off with carb cleaner to reveal a nice brown plug.

Results: 3 revolutions, # 4 = 100 lbs., # 5 = 100 lbs, # 6 = ZERO. What now?

More: #1 = 100, # 3 = 50.

[john walker's workshop]

did you open the throttle when you did that? makes a huge difference, although the 0 and 50 readings are annoying.

[Grady Clay]

Milt,

So … no broken rockers.

Cranking compression:
#1 – 100 psi
#2 - ?
#3 – 50 psi

#4 – 100 psi
#5 – 100 psi
#6 – 0 psi

I would repeat the compression test again in firing order sequence. Just to make sure.

Let’s measure (not set) the valve clearance. You can do that with your dial indicator. I expect we will find some with excessive clearance (almost certainly #6). This is probably from a bent valve where it is sitting on the valve seat at an angle, opening up the clearance.

Next a cylinder leak test. This will define the problem.



The reason for the cam check, rockers, compression, cylinder leak are to insure the basics. I can’t tell you how many times I have seen people (and professional mechanics) going in circles because “It runs just fine driving.” A 911 will drive remarkably well on three cylinders.

I will speculate that there is enough leakage of both combustion gasses and unburned mixture past #6 intake to cause #4 & #5 to start misfiring also. This could account for the #4-5-6 cylinders all appearing rich at low flow. At more throttle the proper running other cylinders masked the less-than-perfect #6.

Keep at it, don’t loose heart. This is all easily fixable. You wanted to touch up the valves anyway – didn’t you? I’m sure glad you stopped driving to look for the problem. A dropped valve would be disastrous.

Best,
Grady

[Zeke]

Originally posted by john walker's workshop
did you open the throttle when you did that? makes a huge difference, although the 0 and 50 readings are annoying.

You know what, JW? I didn't and I know better. But, I wasn't going for an accurate reading doing it cold, just an indication of a BIG problem, which I have. I re-did no. 6 enough times to know this is the real deal. Motor is coming out ASAP and I have a tranny to install anyway. So, I'll just ship the heads off to Olllies, EMS or EBS and have things sorted out. Meanwhile, I'll take a look at the P/C's as best I can w/o disturbing the ring seal to check for broken rings.

I have a 2.4 that I wanted to spend the money on, so I have a decision: Stop gap repairs to the 2.2, or full blown rebuild and scrap the 2.4 high comp E idea with the small stacks that Warren mentions often. I have a BRAND NEW E MFI pump that I was going to put with the T stacks and 2.2 E pistons with the 2.4 crank. I might have the T stacks opened up a bit.

I'll keep the numbers matching 2.2 for the car and it's posterity.

BTW, Grady, I don't think I bent a valve at Willow. I knew that no 6 was wet earlier this year when I pulled the exhaust. I just didn't want to know how bad. At the extreme conditions at the track, I may have worsened a very leaky valve and seat. I won't be driving the car much, but I hope to make it to Dana Point next weekend. If I lunch it, I lunch it. It was coming out anyway.

Well, I have digressed. I started this thread because there were a few dead end MFI threads that covered a lot of issues but not this particular situation. So, now you know. One whole side can go extremely rich due to valve or otherwise no compression issues. Add that to the archives.

As always, I much appreciate your help. Grady, JW and others. This is the place, eh? I mean on a holiday weekend Sunday and I've got friends. Very nice indeed.

[CliffBrown]

Milt

If you don't intend to do a complete teardown of the P & C, it might give you a little peace of mind to do a leakdown test now to determine if any piston rings are leaking badly. Something you can't do very well by eyeball or after the heads are removed.

It'll also provide a good point of reference if you end up just doing a valve job.

[Jay Auskin]

I quickly scanned the posts, and there's one thing I didn't see (in my quick review). What if the injectors on that bank are bad. Can they be dribbling fuel in instead of spraying it??? Of course dribble vs. spray is exaggerated, but could this be a possibility. A fairly cheap check is to have your injectors ultrasonically cleaned, and tested, then re-install.

Again, sorry if this was covered. I'm in the process of moving so I'm being lazy