engine misfire?

[72WiscSub]

1972 Suburban - 350 engine, auto tranny. I did a tune up the other day, replaced plugs, wires, distributor cap, rotor, coil, condenser. The engine ran a bit rough before so I wanted to tune up because I was not sure what the PO had done. Some of the spark plug wires were pretty rough.

After installing all parts the engine started fine, and ran smoother. That was two days ago. This morning I take the Burb out and it runs fine. Went to do some errands, and was cruising around for 1/2 an hour with no problems. I did notice just a little hitch in the idle once and a while buy nothing to noticeable. Well tonight the wife and I went out for dinner (16th anniversary) and on the way to the restaurant no problems. When I got in to come home and pulled out of the parking lot the Burb all of a sudden it seems like the engine is misfiring, it hesitates on acceleration and it has a slight popping noise. When at cruising (30-35 mph) it seems fine, but when I take off from a start it hesitates again and pops. Funny thing is it is not all the time.

Also, before tune up the engine started great, turn the key and bam, starts right up. Since tune up the engine cranks a few times and starts then quits. Pump peddle a few times and starts but I get a little puff of smoke from the exhaust.

I am pretty new to this engine stuff and wondering if anyone has any ideas what is causing this. Is it the new Dist. cap or rotor?

Just frustrating that it ran better with no problems besides a bit of a rough idle, before tune up.

Look forward to your feedback.

Thanks

[67ss&99ss]

Have you checked the timing? If it is a stock 350, the timing should be around 6-8* BTDC.

[72WiscSub]

Would the timing change with replacing the parts I replaced? It didn't have the problem with the old parts.

Again, this is pretty new stuff for me.

[67ss&99ss]

It would if the distributor was slightly loose when you changed parts. Moving it a little can cause a big change how it runs.

[72WiscSub]

Looks like I will be buying a timing light tomorrow. I guess I will learn how to check timing!!!!!

[72WiscSub]

If it was the timing, wouldn't it have done this from the start? I mean it ran fine this morning and then at night it started. I guess I should check to make sure everything is bolted down tight. I'll still check the timing.

[67ss&99ss]

To check the timing, hook up the light to your battery and put the wire clip on the # one plug wire. Disconnect the vacuum advance and point the timing light to the timing mark on the balancer. You can see it on the drivers side of the engine, directly above the balancer. Before your start, I recommend finding the mark on the balancer and painting it with white out. This will make it easier to see when setting the timing.

[El Jay]

I didn't see anything about points; if you changed the points, you changed the timing. Even if you just adjust the points, you'll change the timing.
Did you change the fuel filter(s)?

I'm watching a ball game. If I think of more as the game progresses, I'll repost.

[72WiscSub]

Did not change points. Fuel filter is good, it's new.

What is a decent timing light go for. I don't need some top of the line light do I?

[fastwillie 696969]

check your spark plug wires again i bet you got wire in the wrong fire order
18436572
http://www.boxwrench.net/specs/chevy_sb.htm

[Longhorn Man]

inspect the plug wires, see if here's one siting on the exhaust manifold.
It sounds to me like one got burned through.
If I am right, you can repair the wire with a dab of sillicone RTV, then you'll want to make 100% sure there aren't any more on or real close to the exhaust manifolds.

[69GMCLonghorn]

I'm guessing the distributor is not tight. So maybe it's "walking around" a little bit. The timing might be ok at certain times, then either retard or advance too much and cause to run all funky.

The other thing is that maybe the points are burned and need to be replaced. If they are burned, they may work at certain temps, and cause a backfire/hesitation at other temps.

I can stop over and help you if you want. If I leave in the morning, I should be there by... Thursday??

[72WiscSub]

Thanks for all the tips. I will check all the wires, check the points, see if the dist. is loose and check the timing.

Still seems odd that it ran fine this morning, and then all of a sudden it has a problem later in the day.

Again, thanks. It's nice to have a great place like this for us beginners. If anyone is every in east central Wisconsin, let me know. It would be great to sit around, grill some good food and talk trucks!

I'll keep you all posted.

[prostreetC-10]

Originally Posted by 72WiscSub

Still seems odd that it ran fine this morning, and then all of a sudden it has a problem later in the day.

.

Hmmm...you are right. Not sure it's timing if you drove it that much and it was fine. I'd tend to lean towards Longhorn's suggestion. I can't read the post while replying so I'm not sure if you changed the wires or not but they could be resting on the edge of the manifold.

If you just changed the timing when you did the tune, the idle would immediately be either faster or slower depending on how much the initial timing change but it would still run consistent and not jump around.

Did you do anything to the carb? Did you bump or vibrate a vac line off somewhere? How much did you drink during your anniversary dinner??

just kidding and happy anniversary!!!

[tim21391]

get a dwell meeter. check to see if your dwell is set right.. when i had points that was why my truck mis fired and ran so bad.. dwell should be around 15.. that was what it was on my truck anyway.. switch to hei and its so much better

[72WiscSub]

Yeah HEI sounds like a plan. Just have to get the confidence up to do the change over. I don't want to make things worse.

Thanks

[prostreetC-10]

These are small issues here. Can be worked out on the board. If you were trying to rebuild an auto trans....that's another story.

[72WiscSub]

Well I think I found the problem. Remember when I said I am kinda new to this stuff, well you all have permission to call me dumb a**!

I went out his morning and started to check to see if the plug wires had any damage from manifold heat. I thought that was the easiest place to start. As I was checking to make sure the wires were not sitting on the manifold, I got to the passenger side and as I was feeling the wires, next thing you know the 6th cylinder wire fell off!!!

Yep, I must not have push it all the way on and as I drove around it came loose. I snapped it back on and made sure it was seated on the way on the plug.

I think this explains why I had a small bump in the idle and also why it drove fine in the morning. Must have been on just good enough to get some spark, but as I drove it later the wire must have pull off more and created the misfire.

I am glad it was something simple, but disappointed that I didn't double check all the wires to make sure they were install correctly. I guess you live and learn.

I still think I am going to upgrade to the HEI soon.

Thanks for all the feedback. I think today I will keep it simple and install the new factory style steering wheel that came in the mail yesterday.

[prostreetC-10]

yes....an 8 cylinder running on 7 will give you a not so smooth idle and performace!

[El Jay]

Yup.
Going "back to the basics" and starting fresh will normally solve a ton of problems, especially in the ignition department.

I'm doing that right now on a problem that is giving me fits.

[1970 Bowtie]

I dont think that anyone on here would call you dumb.All of us were new at this at one time,I started messin with cars when I was about 14yrs old.I made alot of mistakes,some were small others were not(but we wont talk about them)but thats how I learned.Just last week I did a tune up on my 70,something I have done a hundred times on new and old vehicles.Did plugs,wires,cap rotor,etc.Took it for a drive and it was missing bad,scratch my head and messed with the timing for almost 30 minutes.Ended up being two plug wires crossed,simple mistake.There is alot of good info here,and alot of good people more than willing to help out.Remember the man who claims he knows everything,thats the dumb a##!

[72WiscSub]

Well said 1970 Bowtie.

Even when things don't go so well, it beats not having a truck to work on at all.

Again, thanks to everyone here for the support. Being new here it is refreshing to see so many willing to help and offer good advice to others, even when it turns out to be a simple fix.

[tim21391]

hei isnt bad.. i did mine for the first time this past thursday.. if i can do it you can do it..

[Longhorn Man]

even people who do this all day long will make that kind of mistake on ocasion.
Now if you WANT us to callyou names...
Its all good man, you are back out in your classic.