Breaking Up at WOT

[74bigblock]

So I thought my gremlins were solved, but after my drag strip excursion, I was wrong. First run was great... after that it was horrible. She was breaking up almost right out of the hole... and got worse as RPM's increased. I'm thinking its the plug wires... 8.8mm 300+ race wires for HEI. The wires are a bit long, and having trouble routing them apart from each other and leaning on other metal items like the steering box. I'm just not sure where to start at this point. The other issue is that my choke flap was sticking closed.

yes, I used tape to hold it open... so what?

 

[wishuwerehere82]

May be plug wires, might be fouled plugs.
You did say that your choke was stuck closed for the first few runs and all the way to the track. That would foul the plugs up pretty well.
Might be a lifter sticking or a valve backlash adjustment.

 

[Ken]

Tough to diagnose without more info, Dave. First off, you'll have to better define the terminology "breaking up"; is it definitely a misfire, or is it more like it's going "soft" on you, like the timing isn't advancing enough?

If the carburetor's choke is sticking, that leads me to believe there may be more trouble lurking there; what condition is the rest of the carb in?

Many questions.

 

[6 Shooter]

What about using a little tape?

Later . . . . . .
6 Shooter

 

[74bigblock]

I will try to describe better.


When I mash the gas it sounded and felt like she went down at least a cyl or 2; Bogging out due to lack of gas or spark. Lack of power... motor almost sounded as if it was shut off. Then it would kick back in, fade out, back in. If I got out of the gas she would recover a bit, but as soon as I put my foot in it, back to the above.

At idle she was rough... it would stutter or skip a beat.. fluttering. Like there was an intermittent miss.

 

[magoo]

Missfire or "breaking up" under load is usually a secondary ignition problem such as ign. wires, cracked dist. cap, coil wire, plugs. Bogging down under heavy fuel demand like WOT and fading in and out as you describe would normally be a blocked fuel filter, sometimes pickup screen in fuel tank and maybe fuel pump. You prolly knew this already but hope it helps.

Save the wave.
Mike

 

[Hib Halverson]

Because this problem is occuring in all gears and at idle, I'd, first, be looking at ignition...plugs, wires, cap, rotor, module, etc.

If you find nothing there, hen I'd run a leakage test, looking for burned valves.

Outside chance you have a broken valve spring.

 

[74bigblock]

Missfire or "breaking up" under load is usually a secondary ignition problem such as ign. wires, cracked dist. cap, coil wire, plugs. Bogging down under heavy fuel demand like WOT and fading in and out as you describe would normally be a blocked fuel filter, sometimes pickup screen in fuel tank and maybe fuel pump. You prolly knew this already but hope it helps.

Save the wave.
Mike

Yep. And since I don't run a fuel filter and the tank is brand new along with sending unit and pump... Ibeen in since last spring with no probs so I know it's not that!

The plugs and wires are also new, but the problem occured shortly after this swap. The Disty went in mid summer and has been great. It's the manual tach drive HEI from Mid America.

I gotta think its the plug wires. #1 plug wire boot was burnt crispy and crumbling.

 

[74bigblock]

Because this problem is occuring in all gears and at idle, I'd, first, be looking at ignition...plugs, wires, cap, rotor, module, etc.

If you find nothing there, hen I'd run a leakage test, looking for burned valves.

Outside chance you have a broken valve spring.

Hib.. I agree. I will assume that it is electrical because the problem is intermittant. If it was a burnt valve/s, I would expect it to be a constant and increasing condition.

I am going to pull the valve covers and re-torque the heads anyway.... so I will check the visible valve train then.

Thanks for the input! -Dave

 

[MMM]

My GUESS is a fuel flow problem. Reason is the way the power comes and goes. Sounds like the carb is running out of fuel then as the demand drops (because of fuel starvation) a little fuel builds up in the carb and it power on again until it that supply runs out.
If you are not running a filter and unless you otherwise filter the fuel before it goes into the tank, it is possible to get some trash into the system. The most minute trash will clog the float valve (needle and seat), thus a restriction. A partially clogged float valve will also create rough idle situation.
It could be the wires and if I had to suspect any it would be the coil wire. But you mentioned you have HEI, so unless you have an external coil conversion, you won't have a coil wire.

Mike

 

[74bigblock]

Well,


I just got back from my mechanic's shop. I picked up some Taylor wire (uncut) and a loom kit. I'm gonna pull the plugs and check them to make sure they aren't fouled, take off the valve covers ... take a peek under there, then put everything back together and see how she runs.

Unfortunately, it's supposed to start thunderstorming here in a few hours. Nice out now though... took the Trans Am down and romped on her! Nothing like reliable power!

 

[Ken]

... since I don't run a fuel filter

WHAT??!!?? :eek

By all means, install a good filter.

 

[74bigblock]

WHAT??!!?? :eek

By all means, install a good filter.

I've got one.. I just don't have it in I will install wen I put everything back together.

 

[74bigblock]

Well... a half a nights work and I have the passenger side all wrapped up. I checked all 4 plugs on that side... they all looked perfect. Everything under the valve cover on the Passsenger side looks good. I checked the gaps on the plugs, put on my new looms, cut my wires, crimped, installed. Tomorrow I'll get to the drivers side. I'll keep you all informed.

Thanks!
Dave

 

[74bigblock]

Well.... after a late night and early morning... I have both sides buttoned up. Valve train looked fine on drivers side as well... plugs were fine too. I am positive it was the plug wires. The wires I bought were a "custom" BBC length. They were Accel 300+ Racing wire for HEI. Well.... they were so long that they had to be grounding out on all sorts of things... like steering box and linkage. The plug boots were so fat that a few of them were pressing right on the headers. One of them burned through.

The replacement wires are fantastic. I got the Taylor 8mm unfinished wire and a loom kit. The wire kit came with both regular anbd HEI style boots and fittings. I measured twice, cut once, stripped, crimped, cussed at getting the dang fitting through the boots and stabbed my thumb with a screw driver twice... but it was all worth it. The wires are all the perfect length... the run right where I want them to. NONE of the wires touch each other or any metal object.

I ran her, and it was good as new. There was no stumble at idle, and no breaking up at any RPM or in any gear, WOT or regular driving.

If you are going to replace your wires.... do yourself a favor... GET THE CUT TO LENGTH ONES!!!

-Dave

 

[69396Chevy]

A friend had the same thing happen to his 6.6 T/A, but his was fine at idle or low end but when he mashed it . . . fell flat on its face. He swore up and down his wires were fine until I told him pull the car in the garage with the lights out and start it up and rev it . . . . it looked like a fireworks show!! New wires solved his problem