The basics...
'76 2.0 mostly stock in a '73. ERG and air injection is removed. 1.7/1.8 exhaust with 4-1 collector and glass pack muffler. Yeah, it's a bit loud.

It was running pretty well after warm-up. I swapped out the "trigger points" for a spare I have, to see if it would help the warm up roughness. It did not. The timing is off a touch from removing and reinstalling the dizzy. I did replace it very close to where it was with the intention of resetting the timing.

This is where it started popping out the exhaust. Not terrible, but still.

I replaced the original Trigger points and it's still doing it. I don't remember it doing this before, even with the timing a bit off.

I would like to fix it before sustaining 3500 RPM while setting the timing correctly. As I up the revs it gets worse. I don't like the sound of it.

So... What did I mess up while I was at it?

Thanks,
Bob

firing order, 1432

Vacuum leak?

Check all FI connectors.

You can set the timing staticly, without the engine running. Then set the points gap again.

If that doesn't help it's something else.

Thanks guys,

Rich: Dist. cap and wires were not messed with. 1432 confirmed

MBlizzard: I will recheck.

Ripper911: Timing points were not touched, just the FI trigger points. Dwell should not have changed BUT... stranger things have happened. I will recheck

Ah... I always forget about the F.I. trigger points.

I like carbs.

OK. I confirmed dwell angle, checked the vacuum lines and spark plug wires.
It starts as usual and runs OK.

Still popping!

Should I just deal with it while setting the timing and hope it goes away?

Racer Chris taught me that "popping" is usually a lean condition. Second the check for vacuum leaks. Can you tell if it's exhaust or somewhere in the intake? Right or left? Valve lash adjusted recently?

I can't think of anything I did to create a lean condition. Nothing has been adjusted.
I rechecked dwell angle. Spot on. The spark timing must be off a little from pulling the dizzy.

I did check the vac hoses. One to the decel valve was off. I replaced it. No change.
the popping is coming out the exhaust.

On rare occasion I hear a metallic knock When warming up which sounds like it is coming from the intake plenum/air cleaner. This is a different thing.

Valves were set about 2-300 miles ago. I checked 3&4 at the same time I tried the other trigger points because they sounded a bit clackity. They were fine, no changes made.

Check the plug that goes into the trigger points may be damaged causing misfire? I cracked one using pliers to get it out. Didnt produce this problem though, just irritation.

Too advanced. Retard the dizzy abit (clockwise)

Hello again, I finally had time to play with it. I got the timing set (engine warm) It wasn't far off.

I checked everything I could see. Nothing seemed "off" or loose.

It is still popping, just less. Still out the tailpipe.

Now the idle is low and the air bleed screw doesn't do much. Had this issue before and don't know how I fixed it.

I did notice the timing mark was not rock solid at 3600 RPM. it was shifting slightly in the notch. I can wiggle the dizzy shaft very slightly front to back relative to the car. it can also be moved up and down a bit, not just the rotor. I'm sure this could cause my problem, but it wasn't until I messed with the trigger points.

So can I rebuild the dizzy or do I need a new(er) one?
Should I get a new TPS board while I'm at it?
Anything else I should check before spending $?

Remember, it was running nicely once it warmed up?

Why did I mess with it again?

How old are your spark plug wires? It is possible that #1 spark plug wire is damaged. Whatever you do do one thing at a time and recheck

A good thought!

I never liked that the wires can just pull out of the end connectors. They don't feel securely held together. Just a light friction fit.

Are there better connectors that can be used? I have Behr now, But they are older.

The idle air screw is a controlled vacuum leak.
If you have another vacuum leak, like you really do, really....the idle air screw no longer effects the system because you already have a leak.


Leaks can be in many places.
First look at all the vacuum lines, and make sure they are tight, including the vacuum advance line to the distributor.

Vacuum leaks can also be at the injectors which you may have moved while working on the car.

Vacuum leaks could be the decel valve which has one small one and one big line, both could have been touched while you worked.

Vacuum leak could present itself as the Aux Air valve that opens during cold start, but over time may not close all the way. this valve could also have come unplugged while you removed and installed the Fi trigger points.

Lean popping could also be on injector not firing properly due to wires being wiggled loose, grounds being pulled off ( pulled when you unplugged and plugged in the FI points)

The ambient air temp sensor is also over in that area, so that may have become unplugged.


If it did not do this before you touched the car, chances are you did something to course this condition, so you need to check everything you touched.

I just recently made my own plug wires from MSD "red" wire.

So have a spare set of almost brand new Bosch wires (stock 914) I would get rid of and I have two distributors that would replace yours. Both have zero play in the shaft.

Check your gaskets on the muffler. When I had a similar problem with my old 1.8 that fixed the problem.

I am constantly rechecking the torque at the heads to keep them tight. The other connections are good.

I have read about this a lot. If there was a leak, would the popping come out the tailpipe or where leak was?

If you have an exhaust leak, sometimes the leak will suck in air instead of blow out exhaust.

Then when the engine runs rich, the remaining fuel will combust in the exhaust causing a backfire.

I think some of us were confused at first.
Typically when you say "popping" we think out the intakes and "backfiring" as out the exhaust.

Thanks for the clarity on popping vs. backfiring. I was trying to describe the sound of it. I had v8 that was backfiring due to a Cracked dist. cap and the sound was much more of a bang, blew out my muffler.

After some more checking connections it is running much better. I think an injector plug was loose. I don't know how I fixed the vacuum leak, again. I went for a ride and it goes better than ever (since I have it).


It is still backfiring. My fuel pressure is at about 31.
I'll report back when I try 29psi.


Stugray, what are you looking for on the dizzy/wires? P.M. me about it.

Thanks again y'all.

One more thing. I was just reading a thread about gas and remembered that I put some in the car right before I started playing with it. I put 87 octane in. I had been using premium.

I know lower octane can cause pre-ignition but would it cause backfiring?
It seem reasonable but I'm not sure.

Please tell me that's the problem!!