Bizarre troubleshooting and firing order

[ohbugger]

Hello again,

For anyone who wants to chime in, here is my story after messing around with the motor in my first Pcar over the past week.

When I bought the car, it had a backfire around 3,000 RPM. Messed with the timing, got new Bosh ignition rotor, points, and distributor cap. Reset timing and dwell, seemed to make the car run better overall and after we got the timing/dwell dialed in, nearly eliminated the backfire.

To top it all off I bought new Beru plug wires and NGK plugs. In the meantime, while waiting for these to arrive, I was poking around the engine bay to psyche myself into the task ahead. It was only then that I noticed that the last two wires were switched on the distributor cap (3 & 5). While I had swapped caps the week before, I only replaced one wire at a time; so this was in fact the way they had been hooked up before.

Thinking that this could have clearly contributed to the problem, when I got the new plugs/wires and put them on today I connected everything as it “should” be, as per the Zündfolge (I love that word) sticker: 1-6-2-4-3-5. Well, after all this the car ran worse than before, and was actually quite similar to how it was when I bought it with the backfiring around 3,000. Tried to dial in the timing with no good results. So as my friend and I stood and scratched our heads, I had the crazy thought to swap the last two connections on the cap to how they were before. We did so, fired it up, and stared at each other in amazement as the car purred like a kitten throughout the rev range. Dialed in the timing, because now it backfired a little on throttle-off, but soon this was remedied.

Are we crazy? Is this a valid solution? What in the world?

TL;DR: Engine running rough and backfiring around 3 grand, new ignition parts, tweaking of timing/dwell, and keeping plug wires 3 & 5 swapped on the distributor (going against the normal firing order) seems to have solved it.

[Flat6pac]

Things are still wrong. The firing order is in the bottom of the engine. You have the distributor layed out the wrong way in the set up or youre rotation is wrong. the rotor on a 75 turns clockwise and #1 is to the left of the clip next to the fan. The rotor should point to the mark on the edge of the distributor when you are on TDC, Z1, your dwell should be 38 +/-3. If you have to pull the distributor to get the rotor right do it, there is 12 teeth on the bottom of the distributor.
There is some basic youre overlooking.
Bruce

[ohbugger]

Thank you for the response. I will definitely check the rotor direction at TDC. As for the wire layout... do you mean start with #1 here



or here?

[equality72521]

First picture.

[ohbugger]

Wow... you can probably guess which location they had been starting from. Thank you both very much!

[Gogar]

Pull the cap off and turn the engine with a wrench on the pulley nut. When you hit the notch on the pulley marked "Z1", your rotor will be pointing at #1 or #4.

[James Brown]

Some one could have removed and installed the distributor off by a notch or two double check what Gogar stated and if it's off pull the dist. out and re index it. (for the next guy). But it sounds like it's in there right.

[ohbugger]

Well, the distributor is in correctly... I found TDC and the rotor points to the line corresponding to plug #1. Turns out I did have the spark plugs installed correctly (with the exception of 3 & 5.) Tried re-timing and even took the distributor out and went a tooth in each direction and no better adjustment could be made.

In short, the only way the car runs well and doesn't backfire is with plug wires 3 & 5 switched on the distributor cap. Could someone who worked on the car before I got here be masking a problem that lies deeper? Where should I look next?

[James Brown]

Hummm, that does sound funny. valve lash and valve timing is/are correct? On you cis motor, also check the injectors to see if there squirting correctly.

[jstobo]

Are you sure you are numbering the cylinders correctly. 1-2-3 on the drivers side and 4-5-6 on the passenger side starting at the rear of the engine counting toward the front of the car. It's not a Chevy.

[ohbugger]

I'll have to do some searching on valve lash/valve timing & how to check the injectors.

And by having no previous experience with the cylinder numbering schemes of other cars, I am in fact numbering them correctly as Porsche's arrangement seems "normal" to me.

This is weird because if I try to time it correctly, with a timing light, the engine misses and stutters as I rev it up. if I power-time it, I can get it to run smoother but it still doesn't sound right and has that awful cackling and popping noise around 3 grand.

Back to searching the archives...

[ossiblue]

ohbugger,

After looking closely at the pictures, I noticed a pen mark on the distributor cap which, I assume, marks the notch on the distributor body. I checked my distributors (for a 76, and 77 T) and the notch is, in fact, to the right of the mounting spring (looking from the top). In short, #1 wire should be in the position shown in your second picture. Do a double check--remove the cap and look straight down on the distributor. Note the spring clip and the location of the notch. The information posted by Bruce is also correct (to the left of the clip) if you are looking at the notch from the outside of the distributor. Both locations put the wire in the position shown in picture 2.

[Walter_Middie]

At what RPM are you setting the timing at? If you are only checking idle, you should check both idle and high RPM to see if the distributor is working correctly.

[ohbugger]

ossiblue,

Correct. Thanks for the clarification. After some more poking around, I realized that the second picture was the correct way to go (and the way I had it originally). The wire for plug #1 lines up with the notch this way, and I go clockwise from there: 1-6-2-4-3-5.

Walter_Middie,

I have been checking it at idle with the Z1 and 5 after marks, and noticed as I rev the motor it does go toward 30 and 35. But I haven't disconnected the vacuum advance hose and had it up to 6,000. When it starts popping around 3,000-3,500 I back off because it seems that something just isn't right and I don't want to go any further.

[ossiblue]

You may want to try this: Connect your timing light to different wires as your rev to 6K--not to measure timing, but to observe the strobe (ignition) for each plug wire. Start with the suspects, #3 and #5. Slowly increase rpm and see if you notice irregular flashing and at what rpm they occur. Switch the wires and repeat. Let us know what you find, if you choose to run this test.

[ohbugger]

Ok... I'm back for an update. Over the past couple weeks I checked the cam timing, which was spot on. Performed a valve adjustment (for the most part the clearances were tight when I got there; I could not fit the feeler gauge in most of the gaps at first so I adjusted them to where the feeler was just able to get in snugly). Today I buttoned everything back up, filled it with oil, and started it up. Timed it to 5 degrees ATDC, and we still had it popping and backfiring around 3 grand. Then I pulled the injectors, and squirted fluid from each one into jars. They all squirted, but one and three were a little low. Three was about 17% lower in volume than the norm, while one was just about 10% down. I wouldn't think that would be cause for alarm, and especially not have anything to do with my backfiring issue; right? Also while I had the airbox off, I had my helper watch to make sure that it wasn't the pop-off valve that was making some of the popping noise, which it was not.

While I appreciate all I am learning by doing this troubleshooting (and it is a lot!), it's frustrating to not find anything clearly "wrong" yet. I'm beginning to think it might have a burned valve...

[James Brown]

Try swapping the injectors around and see if that makes a difference. Do a leak-down and a compression check next.

[Flat6pac]

The easiest way to check is a bottle of Windex and spray it on the exhaust at the head to see which exhaust tubes are cool or cooler than the rest. You can do this after running for a few minutes so the piper are hot enough to fizz the hot cylinders.
Compression test will show a defect on the cylinder compression as a burned valve will leak by the pressure.
Bruce

[ohbugger]

Ok... latest update. Finally ran a compression test! Was relieved to find that all cylinders were around 145-150, even #3 and #5. They also all all held the pressure well. Anyway, when I pulled the spark plugs out, #3 looked like it had never fired. I did the exhaust spray test and found that cylinder #3 was significantly cooler than the rest and the windex did not sizzle on it.

[ohbugger]

Oh, and tomorrow I'm going to try swapping injectors (probably 2 and 3) and check the exhaust temps again. I'm wondering if the #3 injector could be mis-spraying a bit and drenching the plug?