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Popping under load - Sometimes


snomobeelr

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Starts runs and drives. Rev's up in park and neutral without any issue. Have had intermintent issue with it popping when on the gas hard. Then another time out driving she is fine , I hammer on her and she tach's up no problem. I am wondering it it could be electrical. I also have an issue when starting her sometimes.  I go to start it and I hear the Solinoid click but dosent turn over.  I do it about 4 to 7 times and she finally turns over. It dosent appear to be a fuel or timing issue. 

 

 

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There is no popping from the carb. I hear the popping from the exhaust. It is not a loud popping but I can hear it, faintly almost like a miss. I mainly feel it and hear it when hammering on her. When I am  exelarting normally and driving it you don't feel it or hear it.  

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It is not that. It is defintly popping / misfire under load. I verified the timing and float settings on carb. Nothing has changed since she was running good. Only change besides the popping is when I go to start her sometimes it clicks. After about 5 times she turns over and starts. 

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I had the same thing happen to mine a few years back. What I did was undid the exhaust to rule out something in the exhaust like a leak letting O2 into the hot exhaust (not a wise choice when sitting in a garage). My out come was something in the exhaust was causing the popping. I ended up swapping my mufflers at the time they were over 10 years old. The mufflers were starting to rust out from the inside and the plates that were welded to the case had broken lose. I changed mufflers and the popping stopped all together.

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Tell us about the engine. Small block big block? High miles? Souped up or stock? Electronic or points ignition? Stock fuel pump?

 

Could be cam, ignition, valve springs, poor compression, valves, fuel.......

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Everything is pretty new  3600 Miles on Engine and Exhaust,  Car on road last 2.5 Summers. I pasted the Engine Build  Below.  Have been running 93 Octane. Sometimes adding 4 to 5 gallons of 100 octane to smooth it out. I did run the Lucas Gas Treatment a coupe times. Just  cleaned /changed Plugs.  It is not just noise, I can also feel it in the engine/car when I hear it.

 

 

 

MSD HEI Distributor
Carburator:    850 cfm
Engine Cubic Inches:    468
Compression Ratio:      10.1
Intake Manifold Brand:  Edlbrock AIR GAP RPM
Header full Patriot     1 7/8"
3 inch Exhaust
....................................................................
Cylinder Head Type:     Brodix race rite oval port
Broddix Race Rite :     119cc Chamber, 270cc Intake Runner
Intake Valve Diameter:    2.250 in.
Exhaust Valve Diameter: 1.880 in
...................................................................
Type of Camshaft:       Hyrdaulic Roller Lifters
Camshaft - Intake Duration @.050:       232
Camshaft - Exhaust Duration @.050:      244
Camshaft - Intake Lift at Valve:        595
Camshaft - Exhaust Lift at Valve:       581
Lobe Separation:        107
....................................................................
 
The Spark Plugs are NGK V-Power  R5671A-7  Gap is .45
................................................................................
Federal Mogual Forged      :   .095 Dome Pistons
Felpro 1027 Head gasket    :   .039 thickness
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Start with the usual suspect, the ignition. Inspect the cap & rotor. Remove the rotor and see if there's any burn marks on the bottom side under the pickup tab. Any tracking marks or cracking in the cap?

 

Run the engine at night, in the dark. Rev it up, look for glowing or arcing around the ignition wires. Stare at the cap and coil also.

 

Pull and inspect every spark plug.

 

Standard Motors Blue Streak cap & rotor are great quality, I'd use them before MSD. An external oil filled coil always outperforms the HEI in-cap coil, mount it vertically. MSD wires are very good and relatively low resistance. I've actually had better luck with ACDelco spark plugs than others.

 

If all this checks out, we'll move onto other things.

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I checked the cap and Rotor that seems fine as do the Wires. I had changed the plugs out and issue was still there. I took it out yesterday still doing it. But it is cold here about 40 and my temp only made it to about 160/170. But again it does not do this when I am in park. Only when driving.   Thank You 

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Old story, around 1970 my dad's 66 Olds 98 425 4BBL was missing under load. We misted some water on the cap and plug wires. After it was wet My brother in-law got in, shifted into drive and brake torqued the engine some. I think each wire light up with sparks where ever it was close to metal. It was like a Christmas display, so cool. Changed the wires and it stopped missing.

My 71 was missing and I found the charging system was not working.

After that was repaired, the miss went away.

Low battery??

It did start fine, no slow cranking like a weak battery.

Good luck!

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Under load (like brake torque) is way different than a free rev in park.

Have you tried it?

My engine missing problem only happened when the trans was close (1-2 shift) to shifting, under full or almost full throttle.

Bruce

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Silly question, do you have a MSD 6al or the likes with a chip or rev limiter? I had a few cars in the past that had the same issue and that’s what it wound up being. Bouncing off the rev limiter or “chip/pill”. Hope this helps.

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I have the MSD - HEI. I think it is Part #8365 with the Rev-Limiter. I never set the Rev-Limiter tough. I have replaced the coil  already. I was thinking it might be the distributor and thought about getting the "DUI" distriputor but hate to buy it and it not be that. .  

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There are a lot of HEI modules on the market but I'm not convinced they're not all the same two or three parts with different maker's stickers on them. Nor do I believe every body's claims that they're is "better". I've never thought cramming so much stuff in one tiny module was a great idea.

 

If you determine the cause of the popping to be the ignition, I'd suggest you use the HEI distributor as a pick up and use an external box-there are kits for this. And an external oil filled coil with a HEI external coil adapter cap.

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You guys were right. I finally ran the car in the garage In the dark. There was no arching. But at as I was looking I saw a glow. At first I thought it was my eyes adjusting to the darkness Two of the plug Wires, 5 & 7 I could see the spark traveling through the wires, they were glowing. None of the other wires were doing this. I grabbed them and moved them around , did not get shocked or see any arching. I also pulled number 5 while she was running and did not there was no effect on the way she was running. I had an old set of wires and changed those two wires out. There is not anything glowing now. Unfortunately it has been really crappy weather so I have not been able to take her out to test it.

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Just think of the sparks you would have seen if you misted a bit of water on the wires and cap! (Sounds like a good YouTube video!)

 

I would pull the plugs and take a look at them also.

Have you eve run a compression test?

Good time is when the plugs are already out.

Open the throttle plates some so you get enough air into the cylinders.

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Ha  Ha , I would have probably freaked with the sparks. I was supposed to have an outpatient surgery yesterday that was cancelled. Since it was a beautiful sunny day in the 40's I took her out to check. No more miss/popping.. Now unfortunately it is time to fog and put her away for the winter. But I am happy that was resolved before putting her away. Now for some suspension upgrades while away.  I will be getting new wires and cap and rotor for next season. Ones on there now only have 3700 miles.  Oh well.   Thanks again guys , I really appreciate it

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