Rear Shaking and Poppin

[JINKATIN]

Hello everyone.

This past weekend I replaced the cap, rotor, wires, oil, oil filter, fuel filter, lower valve cover gaskets, oil pressure relief spring, installed M&K premuffler on my 86 Carrera. Now my rear shakes as I accelerate and back fires when I shift. I noticed the old oil pressure relief spring was longer than the new one as you can see in the photo. Could it be the oil pressure relief spring causing this or the premuffler or both?

Thank you

[JP911]

I would start by double-checking that you have all of the plug wires routed correctly, the rotor is fully seated, and the cap is secure.

[Flieger]

One spring works with the oil bypass mod, the other is for non-bypass mod cases. DO NOT mix the two. Do you have the oil bypass modification? It requires machining the case. The symptoms of something wrong would be very high or very low oil pressure. It should not effect backfires.

[JINKATIN]

JP911, the cap, rotor, and wires checked and okay.

Flieger, I do not believe I have the oil bypass modification that I am aware of. How can I find out if I do?

Thanks you

[JP911]

I agree with Flieger that an oil bypass mod would not cause bucking and backfiring. Has to be something with the ignition or with the cat bypass. Any issues with the oxygen sensor when you removed it from the cat? Possible that a wire in the sensor connection was damaged?

[Flieger]

Originally Posted by JINKATIN

JP911, the cap, rotor, and wires checked and okay.

Flieger, I do not believe I have the oil bypass modification that I am aware of. How can I find out if I do?

Thanks you

Well, I believe that Carreras had it from the factory, since it came in with a change in oil pump with smaller scavenge and larger pressure side.

You need to make sure you have the right spring.

Have you checked distributor timing?

[JINKATIN]

I don't believe I damaged the o2 sensor, but I can't be certain. I will check the o2 sensor connection. Last night I checked to see if the cap, rotor wires and plugs were on right. Which they were. Thats why I was thinking maybe the spring or the premuffler.

Thanks guys

[Flieger]

1976 the factory used the oil bypass mod.

You must have the piston without the holes.

Here is information regarding the spring lengths, and the fact that new ones are longer: Question on pressure relief springs

[JINKATIN]

Flieger, I purchased 901-107-531-01-M260 oil pressure relief spring from our host. It states it is the one for my car. I have not checked the distributor timing; I really do not know how to do that. I will look into how to do that.

Thank you

[Zeke]

Backfire on shift is exhaust leakage. Your gaskets are not sealing properly. A lot of times they don't and that's why I use this: Pelican Parts - Product Information: WRTH-100045

[JINKATIN]

Thanks Milt. question though, do I apply this with or without the gaskets? Sorry about the stupid question. I will order today.

Thanks again

[Zeke]

Coat both sides of the gasket and bolt up. Gaskets bolted up once have crushed and are not easy to seal, but it you keep track of the orientation, sometimes they can be reused with the Wurth.

[JINKATIN]

Thanks Milt

[JINKATIN]

Update, I tighened the nut & bolts on the exhaust which relieved the popping sound when shifting (Thanks Milt). I rechecked the cap, rotor, and wires. Only one was not sitting properly. I'm still having some shaking but not as much as before, could this just be how the car reacts to having a premuffler instead of the cat?

Thank you

[gtc]

I don't think so. It sounds like something is still amiss (ha!). My car did not show these kind of symptoms when I removed the cat.

[al lkosmal]

This still really sounds like you have the spark plug wires connected incorrectly and/or the distributor is off a tooth...some kind of ignition/timing issue. No matter how many times you work on these things, it's still one of the most common errors. I know that I've often checked this stuff 2-3 times and have sworn everything is ok, only to find a cable routed wrong....on the 4th check. Also, check your timing and while you have the timing light out, connect the inductive clamp to each plug wire, one by one , to verify that all plugs are sparking., and...........Show us pix of everything.

Good luck,

Al

Al

[JINKATIN]

Al, I do that tonight and post the pics.

Thank you

[steve911T]

I am sure you already have done this, but make real sure that the plug wires are real tight on the spark plugs. Sometimes they take quite a bit of pressure to get them to snap on. I made that mistake on my 89 Carrera. Hope it is that simple. Steve

[JINKATIN]

I took pictures of the cap, rotor, wires, and coil. I unplugged each wire and reconnected them, then I noticed the wire going to the coil looked like it was not on right. It was the only wire I had overlooked, I thought it was on right but apparently it wasn't. As you can see in the photo the coil wire connector is different than the maganecor wire I was used to using. I also cleaned the inside of the distributor as you can see it needed it. Now my baby is running great, no more shaking and poppin.

Thanks for all the help and support,

I love you guys
sorry, just got a little emotional

[4sd911]

The oil pressure releif spring has nothing to do with the popping. But if you removed a short spring this must be the safety valve and not the pressure releif valve. The long spring needs a guide tube in it so it doesn't rub wall of the hole. Check this post for a picture of the spring locations, post #4.
Oil relief setup for a 2.7 engine