CIS Backfiring Issue, Need Help, Electrical Short?

[mercury26]

I have 1982 SC that was running fine a few weeks ago when I parked it in the garage. During the time that it was parked, I did the following work:

* Installed Odyssey Battery PC-680
* Headlight Relay Kit
* Replaced Door Speakers
* Replaced Door Stops/re-enforcement kit
* Fixed flag mirrors (wires were all cut)
* Removed Whale Tail, installed grille

I decided to drive the car to work today, since we are supposed to get a break from all the rain. I fire up the car and the idle starts high, sounds good. Then all of a sudden drops down to about 800 RPMs. Kind of weird, but not totally out of the ordinary as I am fighting some idle wandering issues.

I go to hit the gas and the engine totally starts backfiring out of the intake pop-off valve (thank goodness we recently installed this). The more gas that I give it, the more the car backfires. As the car is running the idle seems to go lower to about 500 RPMs.

I turn the car off and try again, same issue. I take the intake cover and air filter out, I can see the pop-off valve blowing open as I try to get it throttle by hand. The more throttle, the more the engine bogs down. I am running late for work, so decide to get to work and check with other Pelican members (hence the thread).

My guy feeling tells me this is an ignition issue. I had one small flub while installing the battery. When I was connecting the positive terminal, the wrench slipped and cross-connected positive to negative terminals on the battery (some sparks flew, yikes). Ground was NOT connected to the body at the time. I am wondering if I shorted out the CDI Unit on the car. A previous owner had installed a Perma-Tune unit on the car.

Up until I parked the car and did the work, everything ran fine. I am at a loss of what the issue could be. Is possible that I shorted out the control unit under the passenger seat? And/or CDI Unit?

Thanks,

Chuck

[MotoSook]

I doubt the short you had across the battery is causing your trouble. The fact that the car sat for a "few weeks" might have more to do with it if the fuel wasn't the best quality (due to a number of things). Since it ran fine before you parked it, I would let it run to heat up or drive it if you can to heat up to normal operating temperature and report back.

If it drives well at temperature, go drive it like you just got a Dear John letter and your dog dies while you were reading it and a tree fell through your front window....that may get the system back into normal sync.

[mercury26]

Originally Posted by Soukus

I doubt the short you had across the battery is causing your trouble. The fact that the car sat for a "few weeks" might have more to do with it if the fuel wasn't the best quality (due to a number of things). Since it ran fine before you parked it, I would let it run to heat up or drive it if you can to heat up to normal operating temperature and report back.

If it drives well at temperature, go drive it like you just got a Dear John letter and your dog dies while you were reading it and a tree fell through your front window....that may get the system back into normal sync.

Not sure, I can drive it. As I hit the throttle, the engine completely bogs down. I can try to let it warm up and then drive it. Is it safe to drive with all the backfiring? Am I going to do more harm? I did put Shell Premium, so I do use good gas (though not to say their are not other contaminants in it)

Thanks,

Chuck

[MotoSook]

Chuck,

Let it idle for 10 minutes and see if you can coax the engine to run higher RPM with the throttle. If you're getting michine gun noises from the POV popping, I wouldn't recommend it, but a pop now and then isn't going to hurt it. Just check that it seats well when you part it.

Did it pop on initial start up after it sat?

Will it idle without popping?

Do ou know how to check idle mixture using the field method to determine rich or lean condition?

[mercury26]

Originally Posted by Soukus

Chuck,

Let it idle for 10 minutes and see if you can coax the engine to run higher RPM with the throttle. If you're getting michine gun noises from the POV popping, I wouldn't recommend it, but a pop now and then isn't going to hurt it. Just check that it seats well when you part it.

More throttle that I gave it the more it popped, not rapid fire but frequently.

Originally Posted by Soukus

Did it pop on initial start up after it sat?

No, only backfired when I attempted to give it throttle. The more throttle I give it, the more the car bogs down to almost stalling. Giving throttle causes the backfire and bogging. More throttle, more backfiring.

Originally Posted by Soukus

Will it idle without popping?

Yes, but idle is quite low. Low but won't stall.

Originally Posted by Soukus

Do ou know how to check idle mixture using the field method to determine rich or lean condition?

No, I do not. Does this require monitoring the O2 sensor voltage?

[Targalid]

Backfiring is due to a lean fuel mixture, improper valve timing or ignition timing. What might have changed while it was parked and you worked on it? if an intake valve is not seating properly, ignition could be taking place in a cylinder and communicating with the intake manifold. Spark occurring before the intake valve closes all the way will give similar backfiring. Lean mixture could result from the CIS getting out of adjustment These are the places to look. When was your last valve adjustment? Check ignition timing? Did you accidentally pull a vacuum hose from the distributor?

[mercury26]

Originally Posted by Targalid

Backfiring is due to a lean fuel mixture, improper valve timing or ignition timing. What might have changed while it was parked and you worked on it? if an intake valve is not seating properly, ignition could be taking place in a cylinder and communicating with the intake manifold. Spark occurring before the intake valve closes all the way will give similar backfiring. Lean mixture could result from the CIS getting out of adjustment These are the places to look. When was your last valve adjustment? Check ignition timing? Did you accidentally pull a vacuum hose from the distributor?

I had complete tune-up completed about a month or so ago. It was part of my Post-Purchase Inspection (PPI). I had the Pop-Off Valve installed at the same time. Valve adjustment, new spark plugs, fuel filter, etc. I had it done at a reputable Porsche shop. Also, they checked all the fuel pressure, etc and everything came out OK (at cold and warm). I did not make any changes to the engine at all.

I can check the advance vacuum hose on the distributor, but I did not mess with anything on the engine.

Thank,s

CHuck

[MotoSook]

Lets keep it simple first before we go thinking internal is wrong with the engine.


I see now that the POV was newly installed. If the car started fine as per your original post and then settle to 800, its not a bad thing. The moment you went to apply throttle, it can pop as some CIS systems will, but given your POV was newly installed, check it over. Make sure it is seated correctly, a little bit of grease on the o-ring is good to have but don't goop it on. Check around the POV to makes sure the epoxy the shop used hasn't cracked or freed itself from the airbox.


Start simple.....

[tirwin]

Chuck,

When I bought my '83 back in February it exhibited similar behavior although yours sounds worse.

I found that right after starting, I had to give gas and keep the RPMs at 2k for about 30s to a minute until the engine had warmed up. If I didn't give it gas quickly enough the engine would cough, sputter, wheeze, backfire at low RPMs until it eventually died. And as you said, it seemed like the more throttle I gave it, the worse it would get. Getting the RPMs above 2k was like it was clearing it's throat.

I tested the CIS pressures. All good. Most people on here suggested I have a vac leak. I think I still do -- I'm taking it to a shop with a smoke machine soon to see if we can track it down. But the thing that made the biggest improvement was changing the plugs, plug wires, dis cap, rotor and doing a valve adjustment. I suspect that better spark improved my situation, so maybe there is something to your thinking. Especially if this was a sudden change in behavior as you say and not a gradual worsening over time.

Still, check everything methodically before rushing to judgment. Good luck and keep us posted.

[mercury26]

Originally Posted by Soukus

I see now that the POV was newly installed. If the car started fine as per your original post and then settle to 800, its not a bad thing. The moment you went to apply throttle, it can pop as some CIS systems will, but given your POV was newly installed, check it over. Make sure it is seated correctly, a little bit of grease on the o-ring is good to have but don't goop it on. Check around the POV to makes sure the epoxy the shop used hasn't cracked or freed itself from the airbox.

POV seems fine, I checked the epoxy and looks good. I also give it a bit of a tug to see if things moved at all. No movement on the POV. The shop that installed the POV checked it also and felt that it was sealing OK. The used a slow curing epoxy, since they felt that it provided a better seal.

I can put a little big of CV grease around the rubber portion of the POV seal.

What would be the next step, check or try? Should I throw a couple of gallons of fresh gas into the the tank?

I never had any backfiring issue before the work done and letting the car sit. Though I have only had the car for a couple months and this is the longest that I have let it sit.

Thanks,

Chuck

[MotoSook]

Chuck,

Get it running to temp and report back....internet guessing can cost you a lot of money and time.

In the meantime (wasting time at the office) read these threads:

It's that time of the year AGAIN! (CIS)

CIS Idle Speed and Mixture Setting Without an Analyzer

[T77911S]

if the car runs, the CD unit is good.

try the sensor plate. with the key on, try to raise the sensor plate. you should be able to push it up and you should hear the fuel system "squeal". the control pressure should also push it back down. (checks for sticking plunger).

plugged or clogged inlet screen to the WUR raising the FP, thus making it run lean. also plugged return line to tank. you could check pressures. (DO NOT make any adjustments to the mixture until you have checked the pressures). (this could make it run lean)

ignition not advancing. check it with a timing light

air leak. make sure the seal around the POV is good and that the flapper is properly seated.(lean)

fuse 18. make sure it is good.

check the relay under the seat

make sure the frquency valve is working. should be buzzing.

this will keep you busy.

[mercury26]

**FIXED**

Fuse 18 was blown. I guess that it is a fairly important fuse.

[boyt911sc]

Originally Posted by mercury26

**FIXED**

Fuse 18 was blown. I guess that it is a fairly important fuse.

Mercury,

If you did a FP test for fuel pressures check, the FV should be buzzing at the same time while FP was running . If it (FV) did not, you already located the problem. FV is controlled by a relay getting power from fuse #18.

I'm glad you did not touch your mixture setting. This mixture setting does not change at all even if you wrecked your car (figure of speech) . The fuel mixture changed due to 2 predominant factors like change in fuel supply and air ratio. I'm surprised that in spite of the numerous discussions in this forum people tinker their mixture without realizing the effect of their actions.

Sometimes it is good to be lucky but you cannot depend on luck most of the time specially for (technical) problem solving.

Tony