Just found this site. Wow. Great info. I have had my 72 914 for 30 yrs. Restored it 10 yrs ago. Still all original--fuel injected. Since then, it has been driven very little (unfortunately). In the last year, I have started getting a popping or backfire on decceleration. It is getting worse and worse. The car drives great and strong other than this annoying habbit. I heard about the exhuast leak possibility and put my had under the car while it was running. I can feel airflow under each heat-exchanger to head connection! Is this normal? I don't understand how ALL could be leaking. I used the copper rings when I connected them 10 yrs ago. Could they be going bad?? I need an expert!!

ExPeRT!? NO! YOU NEED A COMPETE IDIOT!

Never fear, I am certified.

You have GOT TO FIX THAT NOW, they work themselves out, and the heat causes MAJOR HEAD DAMAGE. You MUST tighten them constantly to spec, you don't want them to use the free play to YANK the threads out of the heads..

It may have already happened, and I say that because you said they were all leaking.

That detonation thing you talk about is a Porsche killer, be affraid, be warned, fix it.





M

backfire on decel is "a" sign of exhaust leaks. If the car hasn't been fired in a year. I would do the old valve adjustment, check dwell and timing. Also, Check the exhaust bolts for tightness, but be easy, they can snap off when old. Try loosening them a little first. If they loosen easily, then try to tighten, but just a little past snug.

I wish I had found you guys sooner! I did get under there to check if the connections were loose, and they didn't seem to be. I tried tightening, and sure enough, one of them snapped off! Damn it! I think I can cut the heat-exchanger hole down so the bolt will screw back on. In any case, they seem to be on there solid--no movement. But I can still feel hot air comming from somewhere in that vicintiy. I shouldn't feel any air there, right?? Could the seals just be bad or not a smooth fit?? Not sure where to go from here.

The air you feel could also be coming from the heat exchangers, control valves, joints, connections, and hoses. They are all in that area. Bad habit, but a little smoke in that direction should give a clue. Look for leaks in other areas of the exhaust as well. If the felt air is definitely coming from the head to header connection, then gaskets should be relaced as well as bolts. soak the bolts in a good penetrate overnight before attempting to remove(you already broke one). Might be time to remove motor and fix it right.

best of luck, and welcome to the forum

The air you feel is the cylinder cooling air.

You guys have all been a great help! I will search some other reasons why it might be backfiring before I rip out the exhaust system. It does seem to lessen as the car dirves and warms up. Does anyone recommend the stainless steel heat-exchangers? The ones I have are the original heavy steel type.

I have found a 914 home!

Don't waste your time. The exhaust is the most likely culprit and you know that you already have a problem (broken stud) so start there.

First off, get a can of PB Blaster and soak any and all of the bolts that you will encounter in the exhaust system. Then, start working from the back of the car forward (you really need to do it this way anyway).

Remove the muffler and exhaust from the heat exchangers. This involves six bolts and is pretty easy to do. After you drop these items check them very carefully for rust and holes. Holes even this far back in the system can cause a backfire problem. If you find any problems here, come back and tell us. We can then have a week-long discussion about what muffler you should buy. Even if everything is good, you will need to buy two muffler gaskets for reassembly. I would also recommend that you buy new bolts and washers.

Even if you found a problem at the rear, we are not done yet. You mention that these are the original heat exchangers. I would put these at the top of the list of suspects. You live in the Northeast and on the ocean, so I would think that your 32 year-old HEs might have a problem. You are going to have to go in and drop the heat exchangers. There are two things that will make this job a little easier, a torch and a stud puller. Use the torch to apply heat to the bolts that are still there. Use the torch and stud puller to remove the one that is already broken. Drop the HEs and inspect for rust and holes. Replace as necessary. Don't forget that you are going to need new copper gaskets. Those shouldn't be reused. You should also get 8 new exhaust nuts.

If you need to replace them, I would definitely go with stainless steel heat exchangers. I think that you will need to find a good used set for your car.

Now, as far as replacing that broken stud, I'll let other chime in as to what is best.

Assembly is the reverse of disassembly.

One issue hasn't been raised: overly rich combustion. This will produce backfire! It might be just a matter of CO adjustment, but faulty fuel pressure, dirty injectors, or worn distributor contacts can also play a role.

I would at first use a fuel injector cleaner. Consider ultrasonic cleaning of the injectors; it did wonders for my engine!

Sorry to hear you snapped off a bolt.

Definitely go for SS HE; I have them since 5 years; no rust only some discoloration.

My advice on old HE's is that when re-installing them to carefully flat file the gasket mating surface. The oem steel ones tend to warp as they get old and never seat right.
If you look around you can find the stainless steel ones used and install those. They are worth every penny cuz they actually provide heat to the car unlike the feeble oem ones. They also are sealed so exhaust fumes don't stink up the heated air when you do turn on the heat.

90% of the time, the backfire is a exhaust leak.

Let's see some pics of the car over the years!

Geoff

I know for a fact that new SS heat exchangers exist.

ASK LOUDLY, if you want some.

Wow--I appreciate all the world class advice. The car is actually a CA car and has been in CA, AZ, and CO primarily. I just moved to the Northeast last July, so it is still pretty much rust free. (Military life) I am shopping for used heat exchangers now. I can do all the work except for the new stud. I am clueless there. Would a machine shop handle it or a standard mechanic?? It broke right under the exhaust nut, so most of it is still there. I am considering just cuting the hole on the heat exchangers so I have enough left to put a new nut on. Any opinions? This is great.

Here is a set for sale on Ebay. The ad says he is sure they are for a 2.0 but they look like 1.7-1.8 to me.

Heat exchangers on Ebay

i was told that having a leaky exhaust (which causes pops and backfires during hi-rev closed throttle) wouldn't do any engine damage.

is this correct? or do i need to get some new heat exchangers on asap?

n

Once again:

Detonation is a killer, deal-ender, show stopper, the last hurrah, the prelude to taps, the next-last thing that happens before you are driving your grandmother's volvo..

More analogy?



M

Just bought used S/S heat exchangers on ebay. Also new nuts and copper seals. I am going to replace my old heat exchangers to try and eliminate the backfiring on decel. Does anyone have advice on what to do about the broken stud? Should I pay to have it replaced, or cut the exchanger mount down to allow enough of the stud to poke thru?? Not sure how complicated a task it is to replace a stud.

Thanks in advance for the help.

Examine the "ears" on the SSI's when you get them. People tend to overtighten them and bend/break the ears.

Also make damn sure you remove the old copper gaskets from the heads. Be prepared for a fight. I use a dental tool with a "90" in the end and pick them out.

When reassembling ... use hight temp orange silicon on the copper gaskets.. only the side that goes to the head. This will help hold them in the head while you place the heat exchanger in place (otherwise they can fall out as you start getting close to the head with the HE).

I'm betting your exhaust leak is in or around the muffler... look for black soot around the muffler flanges.

B

Oh.. welcome to the site.

I can easily say we have THE smartest 914 owners on this board. If they are on any other board.. they are'nt too smart...LOL


B

Brad didn't answer your question.

Don't cut the "ear" on your new heat exchanger to make a broken stud work. You have to get the stud out. Soak it w/ penetrating oil over night. If there is enough thread left you can double nut it. Otherwise, you will have to use vice-grips or a stud removal tool. If you have a torch, heat will help.

I didnt read his whole question..

B << I'm the dumb one.


Actually it has been years since I have broken one.. I have a "feel" for when they are about to break..


B

to be safe, give them about 3 days soaking with repeated sprays of blaster or another GOOD fluid. if you can clean the rust off the exposed bit of studs do that as well. haste can be your enemy.

kevin

They are a different length.

Your cylinders are offset.


B

They are 1.7/1.8 HE's... NOT 2.0


B

I would like to echo all the "SMART 914 owners" dressing up the ends of the pipes is essential to a good seal. Copper SILICONE sealer works great to stick the NEW gasket to te head. I also put some sealer on both sides of the NEW copper gaskets. (worked for me).

My SSI exchangers had been "over tweeked" "over torqued" BENT EAR syndrome. had a good welder friend bend them back and TIG up the ripped tube and reinforce all the welds. This was at least a year ago and so far has worked for me.

You can seal both sides.. nothing wrong with that at all. Every time I try it... I make a mess. So I stick to one side..lol

The guy who sold the HE's must be fairly new to the 914 market.. he didnt know who made them..LOL


B

I have a '76 that backfires.

After a recent tune-up, the mechanic told me that the pollution control air pump is the case of the backfire.

He said he could disconnect it, and the backfire should disappear.

Does this sound like good advice?

My car has an aftermarket muffler. Other than that, it is completely original, and I wiant to keep it that way.

Any ideas???

Thanks.

Definitely some smart 914 folks on this site! I have been going though all the tech questions. Learned more in several days than the last 10yrs!

Question--once I get the broken stud out--where do I find a new one? Is it a Porsche/VW part or just a generic replacement I need to find? Are there any tricks to getting a good seal this time around--or is filing the ends down smooth all I can do?

Thanks for putting up with a "newbie".

(And welcome Boston914--I can't say enough about this site. When is a Mass 914 get together planned? I will be there.)

I just bought exhaust studs for my 914/6 from my FLAPS. Take in your measurements, and they should be able to hook you up.

Don't know what a FLAPS is? Go here: 914 Rennlist FAQ

-Rusty

Got it! I will let you all know if I can make this work and fix my backfire problem.

Boston,

First off let me welcome you to the BBS

He could be correct. The 75-6 smog system has a "maze" of tubes that fresh air moves thru and into each exhaust port.

If you have a leak in ANY of the tubes or pump... you will have an exhaust leak sound coming from the engine compartment and it will cause backfiring just lilke we are talking about in this thread.

He would have to plug all 4 air injection ports to rid you of this leak. Just disconnecting the pump wont do it (unless he blocks off the main line coming into the pump with a hand fabbed block off plate).

B

Hey Brad,

Is that anything like the '68 912 heads? Those were pretty crappy heads.