Diagnose Spark Plugs Please (Photo)

[Jandrews]

Hello,

These are out of my '73 2.7 RS Spec MFI motor. I have been having trouble with a vibration and power loss, and I am curious about these spark plug results. A little background:

o Rebuilt top end including heads, valves, seals
o Rebuilt MFI pump by Pacific Fuel Injection
o Flow tested electric fuel pump
o New fuel filters
o New Plug Wires
o Bench tested Injectors
o Two different distributors tried

The lean one is from cylinder number 3, and the rich one from cylinder number 6. I have moved injectors and plugs around to see if the problem seems to move and it does not.

Does the lean one look overheated from running too lean? With MFI, how can one cylinder run lean and one run rich, assuming the injectors are eliminated as a cause?

Any thoughts would be appreciated.


JA

[jeff m]

Compression test - to check work that was done
Check air flow on stacks
Valve adj, I assume is ok, do you have beru connecters on your plugs, they can break down. Although if you have I expect you have already swapped them around.
Jeff

[JSDSKI]

What Jeff M said and some ideas... Check, Measure, Adjust - you are certain the valves are properly adjusted and compression is within spec?

If the spark is fat on each cylinder, and the problem stays in the same cylinder (assuming valves and compression is ok) when you swap plugs and/or wires then it must be mixture...

You didn't mention whether or not the stacks were rebuilt... so, make sure the air jet and vacuum ports are clean (Berrryman's B12). Reset butterfly's (using Bob Spidel or Lee Rice's method on the MFI tech articles on Pelican) and check air flow on each stack with a synchrometer or Unisyn.

RE: different fuel to injectors - is it possible a hard line between the pump and injector is clogged or crimped? Also, I remember from a previous post that this pump was rebuilt when a tappet broke.... I wonder if the cylinder the MFI piston was inside was scored and is changing the mixture ... this is just a wild ass guess

[Early_S_Man]

John,

The yellowish plug looks normal to me, not lean! What do the other four plugs look like?

[Ceder2.4S]

Hi John

I have the same problem on my 2.4 S. In my case it is uneven worn thottlebody butterfly (is that the correct name in english???) bushings. If these bushings are worn, false air will be drawn through them, making the mixture to lean in the low to middle power area. You can't adjust for it. A worn butterfly bushing sounds like a loose valve. You can also feel if it's worn by putting a finger on the end of the butterfly shaft, while the engine is idling. Sometimes you can even see the movement. There should be no movement at all. I don't think there is any other way than to get the TB's rebuild, if you want your Porsche to run proberly.

I'm in the middle of making new bushings for my TB's. If I lived in the US I would send my TB's to Eurometrix right away.

http://www.eurometrix.ws/

Hope this will help you.

Carsten

[Jandrews]

Thanks for the replies, guys.

A few responses to your suggestions:

o Compression test is good. Ted Robinson at German Precision did the head work and I trust it is right.

o I have not double-checked the valve adjustment yet, but this motor has less than 300 miles on it and I did the valve adjustment on it while it was out. I will check it again, next.

o Plug wires are new, so assuming the Beru's on new wires are ok, that should be fine as well. To double check, I checked the resistance on each of them using a digital multimeter.

o My throttle bodies are indeed VERY worn. A couple of them hammer fairly loudly and you can see the movement. However, it is my understanding that at part- or wide-open that this would not be a factor, only at idle, which is not really all that bad.

o Warren, as for the other plugs, cylinders 1,2, and 4 look just like the number 3 in the picture. Cylinder 5 is a little darker like number 6, but not at bad.

o The broken tappet in the MFI pump occurred in cylinder number three. Seems to be unrelated based on the looks of the plug in that cylinder.

o Regarding my air correction screws, they appear to make very little difference due to the worn throttle bodies. I am sure they are out of adjustment, but airflow is similar in all stacks as measures with a Synchronometer. Again, it is my understanding that the air correction screws only affect idle.

o Stacks were not rebuilt, but while I had the motor out, I took every piece off and cleaned and oiled it, including the enrichment ports. Same with the throttle bodies, including the vacuum ports.


How can I check for quality of spark? Just pull the wire and ground the plug with it running? That seems like just an eyeball test as compared to the other cylinders. Would that be conclusive, or should I find a shop with an ignition scope?

At this point, as you might imagine, I am really getting to a loss with this vibration and power loss. This has been incredibly elusive. Most of the ideas on this board suggest that it is a dead/weak hole, and not something internal. I think I now agree with that, but I am really having a hard time finding the problem. I thought the black plug in number six might be a hint, but I am not sure. Would a very weak spark in that cylinder cause this condition? If so, how would I find out the cause, given what I have already done?


Thanks,

JA

[Ceder2.4S]

John,

I have been through exactly the same things and thoughts as you have. But I have come to the conclusion (In my case anyway) that worn TB-bushings must be the problem. It must affect the mixture to at least 3000 rpm or 9° throttle valve angel (where Porsche specify to adjust the idle screws). That also explains why you have to set the MFI so rich to get it to run properly.

Carsten

[Ceder2.4S]

ups, bummer. Not the "idle screws" but the "air correction screws"...

[UTKarmann_Ghia]

John, what kindof digital camera are you using? On my Canon there's a "macro" mode which will bring those closeups in focus for you. If it's still not in focus enuf, then get it to focus pretty close and then zoom, this will help out on future photos

[Jandrews]

Thanks for the photo tips, Ghia. I use a Sony and I must admit I am not an expert at it.

Regarding the air correction screws, last night I turned them all closed, and there was no change in anything. I think that indicates that the TB's are leaking air in and keeping it idling, but again I don't think this would affect part- or wide-open throttle.

And furthermore, this appears to be an over-rich condition, but maybe on just one (or maybe two) cylinders. I think the other four are looking nice and clean. I do not want to richen the mixture on the rack any further at this point, until I can resolve what is fouling number six.

Any other thoughts? Again, I switched injectors between cylinder number one and cylinder number six and six still fouled. That eliminates the injector I think. I also switched plugs, so I don't know what to think.


JA

[Superman]

Yeah, the one plug looks pretty normal. You wanna see a lean plug...look at any K-Lambda CIS plug from a car that is adjusted to emission spec! They look like they're sugar-coated.

[Early_S_Man]

John,

I don't think it is a lean/rich issue ... your black plug doesn't seem to be firing at all, or at least not when warmed up, which is a classic indication of an open Beru connector! Beru connectors can fail or be bad when new, and a 'static' bench test with a multimeter is only a test for a 'hard' fault! I suggest a 'shake' test of your #5 and #6 connectors ... affix test leads securely with alligator clips and hold Beru connector (and test lead clips) at both ends (after unscrewing from wire) ... and shake the connector strongly, laterally without hitting anything! An analog meter works best, unless your digital multimeter has an audible continuity test function. An assistant to watch the meter would be useful so you can watch the Beru and make sure it doesn't come loose from the test clips or hit anything!

I first suggested this test more than two years ago online while talking to a fellow Pelicanhead on ICQ about a myterious miss ... and sure enough, a relatively new Beru connector that had the proper, nominal 3000 Ohm resistance sitting on the bench ... showed an intermittent open when shaken slightly!!!

[Jandrews]

Warren,

I will try the "shake test" tonight!!

Thanks, and I am glad to hear you don't think it is firing at all. That would certainly explain the power loss.


JA

[Ceder2.4S]

I’ve been down that route. Checked all my Beru connectors, shifted them around, measured while shaking them etc just like Warren recommends. Freshly rebuild engine, exchanged the distributor, sparkplug wires, sparkplugs, injectors and so on. I still have a very fouled nr. 1 plug and a way to lean nr. 3. The others seem to be ok. I changed my TB’s 8 month ago, because I thought the “new” ones would be better. Had no problems with 1 and 3 before. The bushings for nr. 3 is so badly worn, you can see the shaft moving. Nr. 1 doesn’t have any movement at all and seems to be fine. As for the other 4, they are all a little bit worn. If you adjust the mixture with worn bushings, you will reach an average for all 6 cylinders where the engine runs at its best (not necessarily good). If the TB-bushings on one cylinder are worn beyond the average of the rest, it will run lean. If another cylinder has bushings not as worn as average (as my nr. 1) it will run rich. You can’t adjust for this on the air correction screws with a syncrometer. I have tried to adjust the air correction screws bye looking at the colour of the sparkplugs. Helps a little bit, but not much. If I drive around with full throttle, the engine seems to run better after a while. Fine on a raceway, but on the street….

I will return to tell if rebuilding my TB’s has helped. I hope to get it done bye the end of this month.

Carsten

[Jandrews]

Carsten,

Thanks for the thoughtful reply. Sounds like you have gone the distance on this mixture issue and throttle body problem. I will be interested in your results.

My situation, while very very similar, may be a bit different, but I'm really not sure. I have this vibration and power loss, and I am trying to isolate whether it is a combustion problem in one or more cylinders, or whether there is some internal damage in the engine (bottom end).

Last night I tried the "shake test" on my Beru's, and they passed. However, I switched in a new Beru on number six, just as a last resort. It seemed to help, as the plug seemed to start firing and lighten up in color a little. It was late so I didn't get to drive it much. Since I didn't have another Beru, I was not able to do the same with number 5, but I think it is in a similar situation. The vibration is still there, and the power is not full strength, but the exhaust note seemed to improve, indicating that I was affecting something!!

I am now wondering if the motor was running on 4 1/2 cylinders before (1 weak spark), and now it is running on 5 cylinders at full strength??

These wires will make a real monkey out of you. As Warren indicates, they can pass a bench test, and then fail when shaken. Or even pass when shaken, and seem to still not be good. And I am talking about brand new Beru brand wires!!

So, bottom line, I still don't know for sure whether the wires are making any difference. I need to get to a point where the number 5 and 6 plugs are lightened up indicating good combustion, and then re-assess the vibration and power situation. I'll keep this post updated with the results of the spark plugs.

Since I am going to need to buy some new wires, does everyone here still recommend the OEM Beru's? I actually built a set with some bulk Beldon wire from my friend John Walker, but I am suspect of the Beru connectors (actually both ends)!! In fact, last night when I was checking with my multimeter, it seemed that either end could cause an open situation. Is that possible?


Thanks,

JA

[ruf-porsche]

Disn't have any problem with the existing Beru wires that came with the car but decided to change to Magnecor.

[jmohn]

Originally posted by Jandrews
Carsten,

suspect of the Beru connectors (actually both ends)!! In fact, last night when I was checking with my multimeter, it seemed that either end could cause an open situation. Is that possible?


Thanks,

JA

Yes. Either end can fail. If I were buying all new ignition wires, it's unlikely I would buy Beru (or OE), I think there are others on the market that are more than adequate.

Jerry M
'78 SC

[Ceder2.4S]

JA,

I'm not that happy about the Beru's either. Maybe they are ok when cold and missing when getting hot. Only way to find out is to switch them around. If it is one Beru causing the problem, the problem will follow the Beru from one cyl to another. I have tried switching my Beru's around, with no result at all.

A good deal of the horses in my 2.4S seems to be on summer grass as well. But luckily I have experienced moments where it turned into a little rocket, when hitting the perfect mixture. I can also feel some vibrations, when my engine runs at its worst (less than 6 cyl). I have spent hours and hours checking and adjusting the MFI, the ignition, valves…. If it’s not the worn TB’s in my case, I don’t know what else. Could be nice if Pelican could sell a TB rebuild set, with 6 fresh 8mm butterfly shafts, 12 new screws and 12 bushings made of oil sintered bronze, so we never had to worry about that again.

Carsten

[Bones]

I haven't had any problem with my stock Beru set up but when I do change it will be Magnecors. The resistor in the Beru is a bad idea in such a hot place IMHO.

[JSDSKI]

Replaced Beru's with Magnecors and points with Ignitor a few months ago - car runs MUCH smoother....