Hello,

My car has been acting strangely lately. The engine I am running is a 350, Vortec heads, RPM intake, XE268 cam, Eddy 600 carb, and Hooker headers.

About 3 weeks ago I warmed the car up and it was running nicely. I decided to take my g/f for a spin around the block (on the tires I currently have I don't want to go much further) and no sooner than I had reached the corner (about 200 feet) the car started running badly: backfiring in the exhaust, sputtering, etc. It was acting like the timing was suddenly way off.

So I came up to the stop sign in my neighborhood, and just to see what would happen, I gave it some gas. Of course, it sputtered, backfired through the carb, and almost stalled out. Which I expected. What I did not expect was that a few seconds later, it started running nicely again, and did so for the remainder of the drive, which turned out to be about 45 minutes because of all my little cousins who wanted rides in the "mean machine".

Well, over the weekend I replaced the power steering pump, and I was running the engine to bleed the system. Again the car was running nicely. I ran it for about 10-15 minutes to get it warm, cycled through the pump bleeding process, and then shut it down. (phone call). After the call was done, which was about another 10 minutes later, I started the car up again. It ran fine for a few minutes, but it suddenly started running badly again, showing the same symptoms as before.

What would cause this to happen? Theories I have gotten so far range from bad gas in the tank to something wrong with the distributor.

The vacuum advance is currently hooked up to the driver's side port of the carburetor. Would it be better suited to manifold vacuum?

Anyway any insights would be appreciated. Thanks in advance!

Brian

I would suspect maybe a vacuum problem. Maybe something with the vacuum advance. Could also be crud in the carburetor. Maybe you have worn mechanical advance bushings. Difficult to say.

I would go through everything. I might even start by hooking up a vacuum gauge to see what happens when it does this.

Do you still have the TVS (thermal vacuum switches) on there? They're those little valves on top of the water neck. If so, those could be giving you problems.

For the record, I have my vac. advance hooked up to full manifold vac. and I think it runs better this way. Idle is smooth, quiet, and most of the fuel it burnt.

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Gordon

1979 Camaro Berlinetta

[This message has been edited by MacDaddy (edited April 25, 2005).]

Sounds like its running out of gas or loading up from trash in the fuel system maybe rusted gas tank inside out, look at your fuel filter, Next time it happens look at the carb for fuel overflowing from vet tubes. The sputtering is probrably something else, timming or accel pump

Have you touched your timing?

Sounds like a typical HEI problem, get a new module, could be that, doubt its vacuum, cuz it prolly do it all the time instead of intermitently.

Hard prob to pin point really. It can be just about anything, but i'll give my opinion on things I would check 1st.

1) trash in fuel system.. Take fuel line off carb, re move fuel filter, un hook line at rear close to tank and blow through with compressed air, change fuel filter, take carb top off (very easy to do on your eddy carb) and look to see if theres any trash floating around in there.

If there is, then it's a good time to pull carb off and take each little pc. apart and clean, then reinstall. Eddys have little wire mesh sock filters under the floats in the needle seats, they will have alot of trash in them if you see any specs in the bowls

2).. HEI dist. giving probs.. As far as common "go bad" items in them.. In order theres 3
module
coil
pick up.
Theres no reason to give you why the module will do strange stuff like that, but they just do, now on the coil or pick up, they could have a broke wire, and sometimes it touchs, other times it may touch, not touch, touch and cause that prob

Starting to backfire and miss after it warms up certainly sounds like an ignition problem, most likely the module is getting heat soaked.

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79 Z28 Bought new, honeymoon ride, same wife, same car.

MWilson, I can't get a really accurate timing setting as I have discovered that I have a mismatched timing tab and balancer. I set it just by ear, and it was running really well for awhile. I could slam the throttle, and other than the typcial Eddy carb hesitation, it would rev right up no problem.

It ran great for awhile, and then this weird problem arose. I am going out of town this weekend, but I will pull the module out when I get a chance. I know they test them at auto parts stores, but I don't know if it will choose to act up there.

Thanks for the advice, everyone. I'll try all your suggestions and post results!

Okay, finally got around to doing something.

I started it this morning, and it was the same as it was last time I ran it, still running badly.

I replaced the fuel filter, and since I can't do much about the gas tank right now, I just poured a LOT more gas in it, hoping to get enough in it so that it wouldn't be scooping sludge off the bottom.

I started it again, and it ran better, but it was running with a miss. I did a cold tube test and noticed that #5 wasn't firing.

Let it cool off (almost all day, as I had to help my g/f move some things into my house. This should prove interesting, no?). I pulled out plug #5, cleaned it off (it was pretty black), put it back in and started it.

Ran MUCH better. Took it for a drive, and it still didn't feel right. Still felt off, so I parked it again and played with the timing a little bit and I think it's as close as I can get it now. Unfortunatly, I can't take it for a drive tonight as I promised I'd take my girl out for dinner.

So, it looks like the fuel theory was correct. I know I can't do this forever, eventually i have to replace the tank, but I really appreciate your help guys.

So, what do you do about having a mismatched balancer and timing tab?

Well, that didn't totally fix it. Was running badly this morning, so I pulled the control module out and had it tested. It failed, so I bought a new one and installed it.

Runs, but still with a miss. In fact, cylinder # 5 is the one missing. The spark plug wire has spark, I tested it with a little testing tool. I swapped the plug out for one in my father's race car (he has the same plugs I do) and still a miss. (did the cold tube test on the header)

I also pulled the valve cover and had looked at the valves as I turned the engine over, paying special attention to the two valves for the number 5 cylinder. All the valves moved up and down normally.

So, what would cause the cylinder to not fire, if spark is reaching it and the valves are opening properly? The only thing I can think of is the plug itself, and since I swapped it with another one....maybe I just had two bad ones? Or is there something I could have overlooked?

Check the number 5 terminal on the inside of the distributor cap it may have broke fell apart or is VERY dirty.

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All Throttle no bottle!! 1981 Z28 Stroked, world product S/R heads 4:10 th350 3500 art carr converter
12.34 @ 109mph
Made in Canada.

Even if a spark tester shows a wire good, that don't mean it is.

Firing the plug, and the air fuel mix is alot harder to do than firing a tester, so the wire could be bad, or like Led said, the term for #5 in/on the cap

This just gets weirder and weirder. Thanks for the info, Led-Z and Night Rider. I pulled the spark plug out, and with the wire attached,held it against a bracket and had my g/f crank the engine. The spark plug sparked; I just wanted to see that the spark plug would fire too.

So, I tried something to test the wire.....I swapped wires number 5 and 7. I swapped the ENTIRE wire, both ends of them, just so you don't think I screwed my timing up. (I say that because the last person I explained this to thought I had only switched one end of the wires.)

Well, the wire that had previously been on cylinder 5 was now on cylinder #7. Well, cylinder 7 was still firing, and cylinder #5 was still not. Despite having switched the wires. On a side note, I also noticed that cylinder #8 is also missing. D'oh!

But here is where it gets really interesting. I revved the engine up, and did the cold tube test with it revved up....and it appeared that #5 was firing. So I let it idle for a bit (badly) and tried it again, and it appeared that #5 was NOT firing. Confused, I revved it up again, and once again it appeared #5 was firing again.

So, it appears that once the engine is moving faster, that particular cylinder hits. It still has a miss revved up, and I can only deduce that #8 is missing regardless. I couldn't check #8 as my arms aren't long enough to reach the throttle linkage from the passenger side and my g/f had left by then.

This is new to me, I haven't come across a problem like this before. What would cause this.

Also, to any of you who have kept up this this post, I sincerely appreciate everything you have done so far.

As per Led's earlier suggestion.....how does the distributor cap and rotor look? New ones aren't very expensive and should be changed with every tune up anyway so you won't be wasting money in putting on new stuff.

Most gearheads have an old HEI or two laying around, maybe you can borrow one from a friend for a few minutes to help isolate the problem.

[This message has been edited by MikeM79 (edited May 09, 2005).]

Forgot to mention, although I haven't looked for sure yet (I forgot to today) the cap isn't more than 2 months old, and it is an Accel cap. But if I get the chance I will do that tomorrow.

Dumb response since I'm not a huge troubleshooting guys, but do you possibly have #5 and #7 spark plug wires backwards?? They do fire right next to each other. The car will seem normal and run but not be right obviously.