Guess we are trying too hard

[Justin71]

OK, car generally runs good, no problems, but needs some engine cosmetic work. So we sprung for some awesome new valve covers, and replaced the spark plug wires with some beautiful red custom hi$ stuff.

New PCV valve, new PCV hose, and cleaned up alot. Spent alot of time trying to get the plug wire routing looking nice.

NOW, however, engine starts and runs ok, seems to run good at hi-rpm, but as soon as I release the throttle, a lot of back-firing, popping, and general unpleasantness.

So, we have double, triple, quadruple checked the wires go to right cylinder (we replaced them one at a time anyway), I'm virtually certain the distributor didn't rotate during the replacement - seems firmly in place now. But - sure sounds like a timing issue.

Help? What could we have screwed up? Thoughts?

Was: looks bad, runs good

is: looks good, runs bad

Not exactly the change I was looking for.

Jay

 

[Jeff73Mach1]

First make sure the distributor cap is fully and properly seated.

Run it at night, hood up, lights off in a dark area and I bet you'll see a wire (more likely wires) arcing to ground.

Check that each wire is fully seated. Often new wires will need to have the boot pushed back a bit to allow the connector to seat fully in the distributor or on the plug. In double and triple checking if you pulled a wire off a plug, you may have pulled the wire apart internally if you didn't use a boot puller.

If you used fancy wire seperators, someone else posed recently with the same issue and their seperators cut the wire.

 

[will e]

Yeah, sounds like wires are cross firing or grounding. What kind of wires did you get? Did you have to cut them yourself? Did you use the right tools? And you are sure you have the firing order correct, the rotation correct and all?

 

[Wolverine]

Check the vacuum advance on your timing:

Shut off car.

Remove Distributor Vacuum Hose

Start car.

Take a look at the timing.

Plug in hose

Look at timing again.

If you have dual vacuum to the distributor, do each hose. One hose(closest to distributor) retards timing(ATD), other advances.(BTD). Typically the timing marks that go to 10 are the ATD, the marks that go up to 30 are BTD.

Additionally, there is a throttle pod on the carburetor that should prevent a sudden closing of the throttle...basically it slows the closing.

Other things to check:

-Lean condition (especially when the throttle blades snap shut)

-Exhaust header gasket leak (failed exhaust gasket allows additional air into cylinder during the camshaft's overlap period)

-Retarded ignition timing (use a vacuum advance distributor or adjust for more lower RPM timing - lighter centrifugal springs.

-Vacuum leak (which may only leak when decelerating - a high vacuum condition)

And, most importantly, please post a LARGER PICTURE of your car.

 

[Don65Stang]

Are the new wires the correct type of wire? Some wire types work great on our cars other types cause all kinds of trouble. There was a post on here recently about plug wires that explains it pretty well.

 

[Justin71]

First off- This is some good help guys- thanks so much.

So, we had the car out today. Went to a little car show nearby, and while it starts and runs, the backfiring/popping etc is really bad when coming off fast rpms. So, something has got to be screwed up. My son & I looked this over multiple times on making sure wires were to correct cylinders, and unless we am using a screwed up reference, it still looks right to me. In any case, I took as good a picture of the plug routing as I could get, and I have attached it. You can basically see the routing to each cylinder in the pic.

That pic shows the condition we drove them in today. I am a little concerned about the wire going to #4 as it wraps closely to the fuel inlet, but we did go lights out in the garage and run the engine, and there is no sign of spark anywhere visually.

We bought the ACCEL™ super stock spiral wire from autozone - a $60 8mm set. Yes I did crimp them myself, and I did not have a tool, but I took care to ensure as good crimp as I could get. The boots were extremely tight, and we used a little water with some dawn dishwashing soap to get them to slide on.

I don't know - I am not seeing the problem here....

And, most importantly, please post a LARGER PICTURE of your car.

Hey Wolverine- you can see larger pics of the 71 here:

http://www.7173mustangs.com/ezgallery.php?action=myimages&u=1372

 

[Jeff73Mach1]

15426378 is a (302 firing order) If your distributor #1 is pointing at

You need to remove the distributor cap, if you used the wrong position for #1, you may be 1 terminal off all around (I doubt it, it shouldn't run but. . . )

To find TDC (and see where the rotor is pointing) Remove the #1 Spark plug Cover the hole with a finger to create a seal and have someone turn the engine over by hand with a 1/2 ratchet and socket on the crank bolt. Watch the timing marker on the harmonic balancer. You will feel pressure as it approaches TDC on the correct stroke. When you feel pressure have your assistant bring the engine slowly around until the timing marker lines up with appx 10Degrees after you pass the TDC mark (there are numbers coming up to the 0 then more numbers as you keep going. Unfortunately balancers slip so you need to manually verify top dead center. No big whoop here, just use a straw or the equivalent to insert into the spark plug hole and you should feel the top of the piston.

Now with the distributor cap off, look at where the rotor is pointing. That is #1 regardless of what the cap might have marked on it. You can pull the distributor to correct a cap number, but there is no reason to do so, and you can have trouble aligning the oil pump drive rod so I recommend you avoid that for now. Correct wires if they are in the wrong position reinstall your #1 spark plug and coil wire and you should be good to go.

 

[Justin71]

No, Sorry for not being clear, but I DO have a 302 V8.

 

[Jeff73Mach1]

Yeah I looked again and was editing the post to make it specific to your car. It looks like the 2:00 position is what you used for for the # 1 cylinder and your order looks right, but without seeing the rotor position at appx 10 degrees after TDC I don't know if you started in the right spot.

 

[marks73]

You can use your timing light to verify if you're gettig spark to the plug. Just connect it as close to the plug boot as you can and see if the light works. But sounds as though you're 1 tooth off on the gear.

 

[will e]

you say it pops when you take your foot off the gas? Do you get any back fire when you REALLY get on it?

You replaced them wire for wire right? I think I read that earlier in the thread.

 

[Justin71]

It DOES pop when I let off the gas. But, it feels and sounds quite healthy when I romp on it. It's just a stock 302, so it's not a dragster, but it feels strong, and there is no backfire at all when accelerating.

I did replace the wires one for one. We located one mistake in the process, had 2 plugs off at once for just a moment, and sure enough got those reversed, but we fixed that.

As far as I can tell it is not missing, but I don't have a trained ear for this. In fact, it's been more than decade since I drove a naturally aspirated engine (it is good to be back) so I am not a pro at this. I did run it for about 4 guys in the mustang club, and a "friend expert", and none of them believe it is missing. Best theory at this point is a carb that has some leaky gaskets, allowing drips of gasoline into the intake which ignite at incorrect times when they get to cylinders. Before we acquired the car in March, it had sat for 4 yrs straight (not running). So, theory is that gaskets dried up and now could be leaking.

PO gave it a holley 2V carb, so I am hunting a rebuild kit at the moment for that.

Will keep everyone posted. I'm not in a huge rush to find the issue as we don't drive it too much (20-30mi/wk) - but I don't want to drive around with a cylinder not firing, or something that is hard on the equipment.

 

[mustbrad]

cross fire under the cap goto a wide cap with a pertronix it should go away mine did

 

[will e]

If it doesn't back fire on hard acceleration my experience is you don't have a firing/cross firing issue. The bad carb is probably a good guess. Holley's don't do well sitting unusued for long periods of time. Normally the carb is the last thing I blame but in this case it sounds very possible.

 

[Justin71]

Thanks guys. I am now trying to locate a carb rebuilt for the Holley carb I've got. I'm having a little rouble figuring out which model I have. If anyone has a tip for how to ID a Holley carb, let me know.

Thanks again.

Jay

 

[mustbrad]

mine would not even idle properly till I changed the cap ,even with MSD wires ( they were a little swollen in some areas and were also replaced)