engine and drivetrain Ignition/fuel problem? Definite misfires...

[Tooly]

I don't really know what was wrong with the old distributor. The inside of the cap was covered with dust when I removed it. I rebuilt the engine, but decided to reuse the distributor that was on the car when I bought it. It may have been the original for all I know. I just figured if I had compression and fuel, it must be the spark.

[Tooly]

I forgot to mention, I was getting spark to the #4 wire before I replaced the dizzy. Bottom line, do the compression check and work from there..

[rtheriaque]

According to C.D's compression test 101, I have either a burned valve or severely burned head gasket- the compression test went up incrementally (actually using his example of 30-60-90-120). The others were borderline rebuild time (150-160).

I couldn't locate anything for a leakdown test. I did hook up my compressor directly to the cylinder to see if I could hear a leak. I had to drop the output off the compressor to about 25 PSI before it stopped simply pushing the piston enough to crack open one valve or the other even in 4th gear). At 25 PSI, I could barely hear anything, but something was making a slight whistle. It definitely wasn't the intake. It may have been the exhaust, though the noise from the exhaust was considerably different when the exhaust valve was fully open. The noise didn't change at all when opening the oil fill or the dipstick, nor could I get any pressure buildup when plugging them.

Does all of this add up? Would a slightly burned exhaust valve cause no reaction at all from the car when the spark plug is pulled? Wouldn't I hear some sort of combustion noise or get smoke? Part of me wants to lean toward head gasket- there's just no evidence in the exhaust or intake of combustion making it past the cylinder- shouldn't there be some sort of smoke or sound from the exhaust or intake?

Any input is certainly appreciated!

[Guest Anonymous]

"Since I bought the car it's had an intermittent hesitation- never bad, just a little nag."

1-Most likely the carb, accel pump weak output or a little clogging of the passages, jets.

2-Timing advance not working properly.

[rtheriaque]

I have a rebuild kit, gasket set, and CD prescription on the way, but there's definitely a problem with cyl 4.

You know, something JUST occurred to me...

The vacuum line attached to the brake booster is DEEP on the intake track for cylinder 4 (and cyl 4 only)... That cylinder couldn't be running lean, could it...?

[rtheriaque]

I have a rebuild kit, gasket set, and CD prescription on the way, but there's definitely a problem with cyl 4.

You know, something JUST occurred to me...

The vacuum line attached to the brake booster is DEEP on the intake track for cylinder 4 (and cyl 4 only)... That cylinder couldn't be running lean, could it...?

Well, let me preface this... I've been working in the sun all day AND I just had a good (both in quality and size) glass of scotch.

Please take a look at the attached routing.jpg. See the fabric/braided hose from the brake booster to the cylinder 4 intake track?

I took that off the intake and plugged it with my thumb. When I pull the plug from any one cylinder at that point, they all act the same! Either that line is allowing a huge vacuum leak causing a lean condition (and probably a hot one that has at least partially burned a valve) or my brake booster is dead.

Hooray? I think? Anybody got a brake booster?

I'm going to have the wife drive me down to Autozone after dinner to grab some breather line. What is the fitting in-line there? I can probably rip it off the '76 if it's necessary...

[rtheriaque]

Okay... Getting there, but I made a new problem.

I ran a new hose from the intake manifold to the brake booster (with the old check valve in place). Same situation. I cut the hose and plugged both ends (isolating the brake booster). The engine now acts as one would expect when any one plug wire is pulled. So, the brake booster is bad and causing a vacuum leak. Fine- I have one in the parts car I can try. But...

The tach is now ALL over the place and the car is now clearly misfiring. At first I thought it might induction current from the rat's nest I made of the wires (both plug and smaller ignition stuff). I cleaned it up and the situation got no better. There isn't any real play in the distributor shaft (other than what can be attributed to the mechanical advance).

So, I have a randomly jumping tach (though sometimes it does twitch in time to misfires) and definite misfiring. I checked the timing and the dot is solidly in the window, even with the misfiring.

What's next? Do I recrimp all of the wiring in the system? I don't think the Pertronix itself could be at fault... The ballast resistor isn't case ground, is it? I'd think it would be isolated from the body intentionally. It seems to move a bit in its mount now (where it didn't before).

Thanks for all the help so far... Almost there (I hope!)...

[scottt]

You've got us hooked.

[rtheriaque]

The hesitation doesn't seem to be there when the vacuum line is connected to the brake booster, but that makes cyl 4 run too lean. I must be too rich without the vacuum reference to the brake booster.

Can I get vacuum from somewhere else for the brake booster? I have a mechanical distributor- can I take the vacuum from the port on the carb instead? I want to try to "distribute" the vacuum throughout the manifold rather than put the burden on one cylinder. Maybe that will lean things out enough to run again...

[ahlem]

Well in rural America people just run a hose from the brake booster in through the passenger window. A couple seconds before you need to apply the brakes you yell "Now Marge". As long as Marge isn't on the cell phone you will be OK.

[rtheriaque]

Won't work for me, unfortunately. I don't know a Marge.

I drove the car around the block yesterday- I can live with manual brakes for a bit until I can swap boosters.

The hesitation, however...

I hope I haven't used up my quota of help!

I dug around a bit more this morning. The misfire is present in any vacuum configuration (contrary to my previous assertion). So, that's out. We're back to what I'm assuming is an ignition issue.

To recap, I'm running a relatively new Pertronix and a black coil with a ballast resistor. Rechecking everything this morning, I believe the pertronix lead was on the wrong side of the ballast resistor. I think I made a bad assumption when installing that I should just use the free spade on the resistor. Electrically, it was on the same side as the coil. Oops.

So, I wonder if I damaged a component of the ignition system. I have an aftermarket coil I can try. I suppose I could throw the points/condenser back in, too (that would make me a sad panda).

Questions:

Can a Pertronix be partially bad? As a Hall-effect sensor, I wouldn't think so, but the question seems worth asking.

What would your next steps be? The tach is fluctuating far more wildly than the misfire seems to indicate (especially at higher RPM), which has me thinking this is an electrical issue.

Any help is greatly appreciated... I'd be more than happy to gift a spare or a nice BMW t-shirt to whoever hits on the answer!

[rtheriaque]

Won't work for me, unfortunately. I don't know a Marge.

I drove the car around the block yesterday- I can live with manual brakes for a bit until I can swap boosters.

The hesitation, however...

I hope I haven't used up my quota of help!

I dug around a bit more this morning. The misfire is present in any vacuum configuration (contrary to my previous assertion). So, that's out. We're back to what I'm assuming is an ignition issue.

To recap, I'm running a relatively new Pertronix and a black coil with a ballast resistor. Rechecking everything this morning, I believe the pertronix lead was on the wrong side of the ballast resistor. I think I made a bad assumption when installing that I should just use the free spade on the resistor. Electrically, it was on the same side as the coil. Oops.

So, I wonder if I damaged a component of the ignition system. I have an aftermarket coil I can try. I suppose I could throw the points/condenser back in, too (that would make me a sad panda).

Questions:

Can a Pertronix be partially bad? As a Hall-effect sensor, I wouldn't think so, but the question seems worth asking.

What would your next steps be? The tach is fluctuating far more wildly than the misfire seems to indicate (especially at higher RPM), which has me thinking this is an electrical issue.

Any help is greatly appreciated... I'd be more than happy to gift a spare or a nice BMW t-shirt to whoever hits on the answer!

[rtheriaque]

I had some help from an American muscle type guy and he was stumped. He felt it was more of a fuel delivery issue, but I haven't messed with the fuel system.

I threw a coil in from the other car. It didn't need a ballast resistor, so I bypassed. Same symptoms. I tried to adjust the timing, but with the misfire the mark was jumping all over the place. I put the timing light on each wire to verify that each cylinder is indeed misfiring.

As the car warmed up, it got so bad I could barely keep it running and I couldn't find a distributor alignment to keep the car running.

The only other thing I can mention is this IS a new tank of gas. Maybe I got a bad tank? I filled my S4 up just a little while before from the same pump with the same grade and I'm not having problems.

If anybody in the area can help, I'd really appreciate it. I pay in whatever your beverage of choice is and all the BBQ you can eat!

Any internet suggestions would be greatly appreciated as well...

[rtheriaque]

She officially won't start at all. I've never seen a problem get progressively worse like this!

It turns over, fires, and sometimes catches. I need to give it skinny pedal to keep it running. I had my wife hold the gas while I turned the distributor to see if I could find an alignment: no luck.

Does bad gas make sense at this point? I filled up, drove home, started to notice the hesitation after a few miles. I started tinkering with the car running, did a number of tests, and went through more and more gas. Now I'm here...

Any ideas?

[Guest Anonymous]

I tried to read through your posts and I am confused more by what you have tried than what you have eliminated as a potential cause.

First, you are not clear as to what is going on with compression in each cylinder. You posted some readings, and if they were accurate, you have a snowball's chance in hell of getting the engine to run acceptably. The fact that you MAY have discovered a vacuum leak at the vacuum booster may certainly affect the engine's running even with perfect high compression readings. It will not negate or correct the very low compression reading even in one cylinder.

If you are implying that your compression readings were erroneous and you have 100+ lbs./in2 in each cylinder, then I would consider going back to basics. First, dump the petronix, you can always reinstall it later. Insure that you are getting a spark at each cylinder. If you are not I would not be surprised to learn that you have a problem as simple as a bad rotor or even a bad rotor and cap. Do not take these mundane items for granted. If they are not the right part or carbon tracked, they can be the difference between a good running engine and one that doesn't.

Make sure your cam timing is correct too. Set engine to TDC and make sure the mark on the cam points in the correct direction. If this is foreign to you obtain a Haynes manual and READ.

If the carb has problems, be they floats or jets or disconnected idle solenoid, as you originally suspected, you can still get the engine to start (not well) with starting fluid or even a few teaspoons of petrol down the carb's mouth.

But, if you do not have compression, give up now and figure out how to get some.

Post an update either here or in a new post so we can follow your progress. You are not alone. There are plenty of yahoos that have been in the same situation probably more than once. And there are plenty of experienced/knowledgeable folks who would like to help you.