Engine cuts out on higher RPMs

Hey Guys,
The small block in my truck has been cutting out in the 3K rpm and higher, unless I throttle it real slow.Plus the power snaps right back if I let off the gas peddle, or even slightly letting off.
I've been doing some tests, and found that it only does this when under load from the trans (automatic).

It will not do this if I just rev the engine in park/neutral. To best describe the symptom is that is like a surging type miss? The truck doesn't do the jerk motion, just looses some power, with a slight stumble with a popping sound out the muffler.

I've tore the 1-2 year old Holley 600cfm (w/ va***m secondaries) apart, replacing the secondary valve spring, I ended up putting the stock one back in, which it ran the best with.

I checked the float levels, fuel mixture screw settings, engine timing, lifters, points sparkplugs, sp wires, all wires to engine, and even made sure the oils were fine/topped off.

The only thing left I haven't done was check for an air leak at the base of the carb, maybe a leak in the va***m from the intake to the va***m modulator.

I've also heard something about that sometimes when air enters the top of the carb, the air flow can pull out the fuel being sprayed into the carb out causing the engine to misfire.

Also the engine timing is currently set at 16 advanced, AC Delco plugs set at .045, points in distributor set at .016, edelbrock performer intake, holley 600cfm, blockhugger headers, crane cam power range 2K- 5,500rpms(works perfect with the low rear gears).

What do you guys think?
TIA,
David

 

fuel filter? fuel pump? cracked fuel line? replace the condenser?

 

if i was a betting man, my guess is that you're starving for fuel. check all that go along with that.... fuel lines, fuel filters, contaminants, fuel pump, etc...

let us know what it is when you figure it out.

-scott noteboom

 

If I wasn't going through something very similar I'd say carb, BUT my issue is spark, turns out the ballast resistor was bad making the coupe run like **** @ higher RPM, same symptoms as you had, try that, your points, condensor, cap, rotor, plugs, wires, & coil and you'll be where I was!

 

I'm with Notebooms, but spark could also be a problem. I've had a dud coil that ended up being the problem (one of those u-beaut 40,000 volt things). Swapped in an old stocker for a blast round the block and bingo, that was it.

 

Not enough fuel. Check inline filters plus the filter in the carb where the fuel line screws into the carb. Be gentle, its aluminum and very unforgiving.

 

My impala did the same thing a few years ago and it was the distributer. I had jump started a girl at the gas station (i wont jump start a car with my car running anymore )and right after that it would cut out. I got a new dizzy and it worked great.

 

Thanks for the relpies everyone.
I'll post back with what I find.
Many thanks,
David

 

While I wouldn't rule out spark my guess is with the guys thinking it's fuel related - lack of fuel that is. Winging the throttle to 3k in neutral DOES NOT use as much fuel as it would when driving at 3k - a motor UNDER LOAD uses more fuel - your letting off the throttle supports this - since yuo are basically reducing the load and are definitely reducing the amount of AIR which makes your LEAN condition BETTER.

I'd check your SPARK first - just cause it's easy and it'd be nice to rule out -if it looked good - I'd then focus on the fuel side of things - clogged fuel filter - pickup in the tank - weak fuel pump - etc.

 

Bad vacuum can on the dist? Maybe bad capacitor in dist?
Where is the dist vacuum hose connected on the carb? If this is a SBC it should be connected below the throttle plate.

 

Who was it that said " 99% of your fuel problems are ELECTRIC" ?

BB

 

I'am fiighting the same thing on the race car. let us know what you find
dad always said check everything twice be fore you go to the carb!

 

I had the same issues with my T once. It had one of those twist dial pressure regulators in the fuel line that was clogged slightly and at speed it would stumble but sitting still was fine.

 

Thanks for the replies guys.
Yesterday I messed with the truck for over 12 hours. I replaced alot of the electrical components, and it still does it.

Now it's down to the carb, fuel line, fuel pump. Since the new exhuast was put on saturday, I can hear real crisp pops sounds backfiring out the mufflers like it's kind of loading up?

I did forget to check the va***m, and recheck for any vac*** leaks. The only thing I did not touch or replace in the dizzy is the wieghts & spirngs, could the springs be wore out, and opening to soon?

This is a early 350 sbc, was hoping it to be a 327 because it had a 327 harmonic balancer on it when I brought it home.

I've got a good used Mallory distributor I could use, but it is missing the points. Should I try swapping out the stock distributor unit if the carb, and fuel related items check out?
TIA,
David

 

Put A stock HEI in it and see what happens...


Thats my .02..

S****s

 

Thanks S****s.
I'll try that first.
Many thanks,
David

 

My first thought when I read your original post was EGR or coil or the advancing mechanism in the distributor is bad.

you dont still have an intake with the EGR on it do you?

 

One more thing. How are your lifters set? Popping in the exhaust could be valves floating or holding open as the RPM increases.

overspray

 

what kind of fuel pump are you using? is it electric? where is it located.

i just went through a similar problem on my poncho

 

Check all your fuel lines. Especially around any rubber to metal line connections. You may be ****ing air into your fuel line, and it won't drip when the car is sitting. If you have checked the fuel filter and it's not that I would try putting another carb on it, if you have another that you know works well. If nothing changes then you are back to electrical / ignition.
If that is not an option, or it runs better with the second carb, I would check the power valve in the Holley. They can go out, it's allways been a problem with Holleys.

Some other easy checks, Pressure guage on fuel system, should be 6lb ish.

Hook up a vacuum guage in the cab and watch it when you drive. If it drops too much it could be a vacuum leak at the Intake manifold, common on sbc's.

How clean is you'r fuel tank? Is there a filter on the end of the pickup tube?
I think an S-10 has a sock type filter that can be made to work on old G.M. stuff.

I really think it'll turn out to be something simple. And not a mechanical problem. My best bet would be on the fuel.

 

Hi Guys,
The intake is an edelbrock performer, and no smog stuff on the engine.
I drove the truck 8 miles 1 way this morning with the popping out the mufflers with power loss (when mashing gas peddle only).

Once I was at the mall (where I was headed), I tinkered a little on the engine, and noticed that the coil terminal wwas way to close to the air breather. I took off the airbreather to see if there was a difference in performance on the way home.

On the way home, it ran at higher rpm with ease, a little faster, but still had the popping going. Later this eveing i'll check the valve settings, and try some new springs & weights in teh distributor.
Many thanks,
David

 

Has this engine run properly with this intake manifold?

It is rare but I have heard of the exhaust crossover having an eclusion into the intake causing exhaust g***es to get in.

The popping thing is the clue here. Any number of things, incorrect fireing order, bad valve springs, hung valve, flat cam, rocker arms too tight and yes lean popping. As others suggested, you could be fighting a fuel starvation problem.

 

Hi ELpolacko,
Yes, the engine has been running flawless since end of last june when I broke the engine in. Just recently it started acting up.

Tonight my Dad came over to help me, I had the rotor off the distributor when he showed up, I found that the wieghts were sticking slightly. I cleaned the old grease off, cleaned up all the moving parts, and re***embled it.

Then I had to retime the engine, it was off by 8 degrees. I retimed the engine with the va***m line disconnected. I then took the truck for a quick spin, it still did it, but alot less. He did point out that the timing mark was jumping every few seconds the mark would jump almost to the next notch, and go right back to the where I had set the timing.

My Dad also suggested try running the truck around the block without the va***m line hooked to the distributor, so I did, still the same with no changes. I asked him what's the differnece supposed to be, he said exactly, you distributor is bad. So I use a va***m guage on the va***m port on the distrbutor for a leak down, it moves so slightly releasing the pressure.

So it looks like it might be the whole distrbiutor itself, i'm going to be replacing it with a Mallory double point dizzy without va*** advance, and see what happens. I'lll report back with what happens.
Many thanks,
David

 

Try using a dwellmeter and set the points dwell. might help. more acurate than feeler guage.

 

I would try replacing the small black wire that goes from the points to the coil. Sometimes it has a break that only shows up when the timing is fully advanced because that is the only time the wire is fully stretched. Sometimes the wire will be open (engine would probably stop) or it has a break in the insulation that allows it to ground when fully advanced.

 

I found are problem on the race car we replaced the hole ign. system including wires from the switch still did it got to talking to the cam guys and we had valve springs with not enough spring psi. and the hydrulic lifters are acting like shock absorbers and losing contact with the cam surface bumped up the spring psi runs great know.
with this in mind could you have a broken or weak valve spring ?when cheking the valves look at the inner spring ?
just a thought
I know i have alot less hair on top know

 

Thanks Guys,
I did swap out the original (stock) points distributor for a Mallory dual point distributor, and it did change the way the engine ran. Since the vac***m was'nt working on the distributor plus it beinge excessively worn, it needed tossed.

Now it runs more consistant at idle, and on the gas, but itnstead of missing out around 3500 rpm's, now it does it in the 4,500-4,800 rpm's. I also had to lean the carb out some, which did make it run alot better, but still had the popping.

I'm thinking it might be the carb, cause the va***m diaphram on the dizzy was fine, but it was not getting much va***m. Plus even with the carb leaned out, the exhaust fumes smells strong of running to rich. It might be the power valve, I got an extra one for the carb I could try.

The worse thing last saturday I was driving the truck in a car parade, and the temp was in the 235-245 range doing 5-10mph for a good 25-30 minute cruise/parade. Shortly afterwards, I pulled over, and killed the engine, about 5 -10 minutes later I went to start the engine, the temp guage was pegged at 255-260 degrees, but dropped down automatically to 230 when I started the engine.

Since last saturday, the engine "pings" under accelloration, very slightly you can hear the diesel ping sound, and a few times it will diesel when shutting the engine off. I'm about to shoot this truck/engine. lol Daytime it will run around (now) 210-220, at night time 190-200 degrees. Now I got the cooling system to fix to. lol

I'll pull the valve covers, and check for any bad valve springs, and for fully opening valves, if not, i'll check to see if if they need adjusting, a wiped lobe, etc.
Many thanks everyone, I really appreciate your help.
David

 

Hi Guys,
the last few nights i've been messing witht he truck, saturday night I got shocked big time through my left knuckle up my arm, and down my left side. This was when I was setting the timing on the dual point distributor on the 350 inthe dark.

I did notice that there was some spark coming from the wires on the p***enger side, I thought it was the wires from the engine harness. But after a good look tonight, there is a blue/grey fire type spark at all 8 cylinders between the sparkplug boots & the base of the sparkplugs. I replaced all the sparkplug wires saturday, same day I tried to timed the engine.

How do I get rid of the sparking at the spark plug boots? My Dad said try to tighten the metal clips some, but what about the porcelin(sp) on the sparkplugs, shouldn't I clean these too? Is there any type of grease, or substance I can put on the sparkplugs to?
TIA,
David

 

Hey man, I had the same thing happen to me, but with an edelbrock 650 cfm. It would stumble and surge when I was cruising at street speeds (35 moh let's say). And it didn't do much better whenyou mashed it. It ran great before this.

I replaced the fuel filter, air filter, jets, rods, checked my vaccuum advance (HEI), and got nowhere with it. I looked for exhaust leaks and loose manifold bolts thinking that there was an imbalance in the exhaust pressure from side to side (dual exhaust). I even tried shouting "Be Heal-duh! You shall be heal-duh!" bbut to no avail.

So then one day I'm on the expressway doing about 80 and and she starts to die like she's out of gas. Then there's a loud BANG! I put it in N and start coasting off the e-way on an off ramp. I put it back in gear at the top of the hill and nursed it around the corner. And you know what? It ran great.

There must have been some **** lodged in the guts of the carb from sitting for a couple of months. I haven't had trouble since.

Good luck.

 

I was gonna suggest you look at the plug wires, I just had a similar problem with my SBC with blockhugger headers.

replaced the old ones with new Taylor 8mm wires, no problem since.

good luck.

Vance