RS MFI - Strange Combustion Problem

Jandrews · 06:09 PM

Hello,

I have been chasing a power loss problem for over two years now. Some of you may remember my saga, which began with a missed shift and an overrev. You can go back and review a lot of the history here:

Elusive RS Vibration

Long story short, after completing a top-end rebuild and finding the problem still present, I recently began teardown number two. Since the power loss problem felt like a vibration / miss combination, I thought maybe a bent rod, intermediate shaft or crank. In any case, I had come to grips with the fact that I was going into the bottom end this time to see if something was evident. I should mention that I only put about 300 miles on the car since the top-end job, as it ran EXACTLY the same afterwards. I should also mention that Pacific Fuel Injection rebuilt my MFI pump at the same time, which also offered no improvement.

When I started taking it apart, I noticed something odd. The exhaust ports on the numbers 1,2,3 cylinder heads were still showing a lot of the clean, blasted metal surface from the machine shop, with just a trickle of carbon on the bottom of the port. However, the 4,5,6 cylinder heads were carboned fully as I would expect from this engine.

I have talked to Gus, and will be sending him my pump again for further inspection, but I am really wondering what could cause this uniformly lean condition on just the left side. Just for an FYI... I have replaced distributor, cap, rotor, wires, fuel filter, fuel hoses, and flow tested the electric fuel pump and spray tested the injectors.

Any thoughts would be appreciated.

Here are a couple of pics.

Cylinder number 2 closeup:

Cylinders number 1,2,3 as a bank:

And the "normal" cylinder number 5 closeup:

Jandrews · 02-17-2004, 07:04 PM

Anyone ever seen a problem like this before?

Thanks,

JA

Tyson Schmidt · 02-17-2004, 07:13 PM

Couldn't help but notice that the adjuster screws on the exhaust valves are backed all the way out. Are your exhaust valves even opening?

Jandrews · 02-17-2004, 07:24 PM

Thanks Tyson,

No, I just loosened them all as a precautionary measure to provide maximum clearance when removing the cam nuts. Cam timing and valve adjustment were done and re-done multiple times during this saga, but thanks for noticing.

JA

tobluforu · tobluforu's Garage

Were the cams properly timed? Just a guess because I f'd this up when I rebuilt my motor. The cam on bank 4. 5 and 6 was way off causing my car to run like crap (no power). I guess I had the dial indicator not positioned right the first time.
Good luck.

Tyson Schmidt · 02-17-2004, 08:16 PM

O.K., just making sure.

Well, your exhaust ports definitely look like the mixture is very lean on that bank.

I would have to guess that either the steel fuel lines on the left side are plugged, or the cam timing is off on the left bank. I don't see how the fuel lines would have coincidentally become plugged when the valves were bent. But I could see how the cam on one side could be timed 180 degrees out, and made the car run just like it did before when the valves were bent.

Is it possible that the cams are timed on the same stroke? In other words, both set to TDC of #1, instead of one at TDC #1 and the other TDC #4?

Jandrews · 02-18-2004, 05:48 AM

Thanks for your thoughts Tyson.

Well, I can say that I have also almost completely dismissed the small possibility of the three hard lines or three injectors or three anything going bad all at the same time. I have been a tad skeptical of the MFI pump, and will be sending it to Gus for re-verification, but not confident in that diagnosis either.

Which ultimately leads us almost exclusively to Tyson's suggestion around the cams. I will say that I am getting a bit of a sick pit in my stomach at that suggestion, but I am questioning how the cams could be timed wrong 3 times in a row by different people. The first set of fingers on the cam timing were from an incompetent local mechanic. Could he have done it wrong on one side? Absolutely! In fact, probably! But after getting the car back from him and having it run poorly, I took it to another, possibly more reputable shop here in town and had them check it. They supposedly changed it slightly, as apparently one side was out of spec, but as I recall only in the 5.44 mm range, not 180 out. Next, came a friend of mine here who is the technical advisor for the local PCA who helped me do it when we re-assembled the completely torn down top end. If I recall, we got both sides close to 5.2mm, right near the center of spec.

Anyway, this is the history of cam timing changes since the initial problem. I would think it unlikely for three different people to all do it wrong, but I am beginning to wonder.

In any case, I appreciate Tyson's simple approach to eliminating possible causes and boiling this down to the few items that could realistically be contributing. Any other thoughts or opinions would be appreciated as I continue digging.

JA

69911e · 02-18-2004, 08:18 AM

If the cam was 180 deg out of phase, you would have nothing on 3 cylinders. Your first statement was about power loss. Is the car only running on 3 cylinders or running on all cylinders but poorly?

Early_S_Man · 02-18-2004, 09:39 AM

John,

Sorry to hear more of the ongoing problem saga!

Were the hard injector lines ever left open to atmospheric moist air for any extended period of time during the repair for the over-rev?

Before sending the MFI pump off to Gus again ... I suggest a bench test of the pump, hard lines, and injectors ... fully assembled in what I call the 'Butterfly Configuration' with fuel replaced by B-12 Chemtool via 4-foot temporary lines and a pint or quart can, suspended as an IV-bag is in a hospital. If all is well with pump, lines and injector ... you should get a sequential 'squeeking' and conical spray patterns from the injectors ... after all air has bled out -- could take five minutes of turning over pump by hand. After you have bled out all air ... you could suspend/fasten test tubes over each injector and test delivered fuel quantity over, say, 10 turns of the pump ... that could possibly point you towards some specific problem, or away from pump, lines, and injectors. If your injectors are still original, they should be hand-engraved with a 'set' number and cylinder number ... so any variations could be tested further by swapping injector locations, and you would still know the original cylinder number! If replacement injectors ... I suggest engraving with a cylinder number with a carbide etching tool, just to keep track of their location during testing.

Good luck!

Peterfrans · 02-18-2004, 09:52 AM

Did you rule out the possibility that whole cam is wrong (out of a T or a E).

Another possibilty is that the throttle bodies flow different amounts of air (basic setting wrong or even different types). Have you checked the correlation?

The search is for some part that is the same for all cilinders in the left cilinder bank. This does not apply to:
The MFI pump, these have six separate pistons in them. I could believe that one broke, but not three on the same side (lets savely rule out any mistakes made in the pump rebuild).
This also applies to the ignition, fuel lines and injectors; why only the left bank and not for instance 1 4 and 6. Seems to much of a coincidence.

69911e · 02-18-2004, 10:07 AM

How about misadjusted throttle linkage? This would mess up the whole bank.

Jandrews · 02-18-2004, 07:18 PM

Hello,

Certainly some good suggestions here, including the MFI pump, cam timing, cam part numbers and throttle correlation / linkage. All of these things have been checked to some degree, and I would say the throttle bodies and linkage have been checked sufficiently to eliminate as a possible culprit. In my mind, we are looking at either the MFI pump or something around the cams. I will bench test the pump as Warren suggested, but let me ask a question about the cams.

From what it looks like there was SOME amount of combustion going on in all six cylinders. As an aside, for those of you who know Stephen Kaspar (Imagine Auto) wizard, I had him drive it and he thought it felt "weak, but not exactly a full miss". Based on looking at the plugs and the ports, it appears either a trickle of gas or a trickle of air or a trickle of both were getting through. Obviously this could be caused by cam timing or a fuel delivery problem.

Can someone describe how the valvetrain would operate on one side with a camshaft timed 180 degrees out? Does this basically imply that the valves were open when the piston was on it's firing stroke and they were closed when it was on it's intake and exhaust stroke? Would this cause interference with the pistons? Would this not fail a compression test in a big way on that side of the engine?

I am highly suspicious that three different people could do this wrong three times in a row on the same side of the engine, but if what I describe above is correct, this sounds hauntingly descriptive of my symptoms. I think between this and the MFI pump we are slowly getting to the bottom of this long running problem.

Thanks,

JA

Tyson Schmidt · 02-18-2004, 09:12 PM

If it runs on all six, but just lacks power, then you don't have a cam that's 180 out. We can rule that out.

I strongly agree that you should carefully check throttle linkage correlation. Maybe you have a bent cross-arm, incorrect rod lengths, etc. This could throw off one bank.

And here's a stupid question. Is the exhaust plugged on the left side?

speeder · speeder's Garage

FWIW, if a cam was 180deg. off, it would not cause interference problems. (I don't think). The pistons would always be where they are supposed to be in relation to the cams/valves, just the spark and fuel delivery would be at the wrong time. A 911 motor running on 3 w/ 3 dragging would be beyond weak, you would be losing races to pedal rickshaws, if the car ran at all.

Tyson is on the right track; you need to look at everything, not just the things that you think of or someone suggests. When a problem such as this makes me pull my hair out, I always think of the famous Vince Lombardi half-time speech when the Packers were getting their asses kicked off:

"Gentlemen, this is a football."

(Start w/ the basics).

KobaltBlau · 06-03-2004, 05:17 PM

Any update on this, Jandrews?

Jandrews · 06-03-2004, 05:38 PM

Hello fellas,

Thanks for asking KBlau. I do have a few updates, but no conclusions yet. I sent Gus the MFI pump and injectors, and they all came back clear. Gus tested pressure, volume and spray pattern at varying ranges up to and including 6,000 rpms, and gave the whole system a clean bill of health.

I also came down with a little bit of "while I am in there syndrome", and sent various pieces off to Ollies. In fact, I just got those parts back last week. Specifically, I had them boattail my mains, mooncut the cylinders, knife-edge the crank, and magnaflux and recondition the rods. Again, these pieces all came back clear.

So, I plan on beginning re-assembly next week, but have not found anything that would point to the strange combustion pattern outlined in my above post. I guess I am kind of going with "the basics", putting everything together very carefully. I will spend extra time on the ignition and fuel delivery this time, since I now have the benefit of observing the suspect ports. This should allow me to narrow things down a little better than I was able to during my previous troubleshooting.

I really don't have any answers. I will just have to methodically check, double-check, and triple-check everything from the tank, through the lines, through the filter console, and into the pump. I will also have to track my voltage and ignition all the way through, but I am sort of coming up blank on what could cause incomplete combustion on just one bank of cylinders.

Thanks for reviving the thread. Any new perspective is always welcome.

JA

KobaltBlau · 06-03-2004, 07:12 PM

Did you ever check the throttle linkage when the engine was together? I don't remember reading a response about that.

Jandrews · 06-04-2004, 07:17 AM

KBlau,

Yes, I did check the throttle linkage when the motor was together and running (poorly). I verified full wide-open throttle was occuring on each bank when the pedal was at the floor. All butterflies were perfectly aligned and wide open.

At this point, I am wondering about some strange obstruction in the hard fuel lines, similar to a post that was written here a few weeks ago. Even then, why affect only one side of the engine? Is it possible that in a low fuel situation, one bank takes preference in scavenging whatever fuel is available?

JA

KobaltBlau · 06-04-2004, 07:51 AM

seems unlikely that all 3 hard lines on one side would be blocked in a similar way, since they go directly to the pump. Since the pump broke that piece you posted earlier, I would believe 1 hard line plugged, but not 3 equally.

Jandrews · 06-04-2004, 10:45 AM

Agreed. I was actually referring to the hard fuel lines in the tunnel and between the tank and the filter console. The MFI hard lines have been blown out with compressed air and tested fine. I am comparing this to the thread where there was some goop found in the return line between the MFI and the fuel tank. The rubber hoses are new all around, but I did nothing with the hard lines in the tunnel.

Any other thoughts?

JA