Re: Help!! Engine Miss
 

have you tried a different carb?

Re: Help!! Engine Miss
 

Ben,
I built a new engine for a customer and it missed and popped from the very first time we started it. Took it out of the car and put it on the dyno and all was fine. Changed everything in the car we could think of. The last thing we changed was the master cut off switch. We should have changed it first.

Re: Help!! Engine Miss
 

Now that you mention it, I've heard of that happening before.

Re: Help!! Engine Miss
 

Thanks to all for your input so far.

I've already got a #10 ground strap to one head, and I'm down to bare metal at both contact points. I'll add a second ground strap to the other head, just to be safe. Please keep the experiences and thoughts coming. It gives me places to look, things to check, and God-willing, the possibility of narrowing down the problem.

-Ben

Re: Help!! Engine Miss
 

Did anyone mention a firewall feed thru for the coil wire, ?

Re: Help!! Engine Miss
 

Flat lobe on exh would cause popping out carb.

If it's a miss while reving in neutral I would of closed off the choke and check the result.
Also look down the throat while reving and see if it's a smooth pattern of fuel or blobs of fuel from the emulsion tubes on both sides. If it makes no difference, rev it and move the dist around(advance/retard) and listen for a difference.

I'd also close the gap on the plugs to about .030 just to test.

Another dist wired directly to batt and another carb will prove if it's external. Your saying you've switched dist and carb so next is;

Comp check and leak down

Valves are adj right.....you didn't leave the break-in valvesprings on did you???
vacuum leak, p/brake hose cracked or carb gasket etc?


And the "out there ones"
Same oil pan as the dyno? thinking oil pump sucking the pan because of lack of clearance and the resulting vibration/cavitation acting on the dist causing spark scatter.

How did you lift the engine to install it? undo an intake bolt or remove carb and use lift plate? Check those area's for warp/vac leak

Re: Help!! Engine Miss
 

67camaroracer,
-coil is mounted on the firewall. No feed-through. Already replaced the coil and wires.

goinbroke2,
- car starts right up and fuel flow is smooth out of the squirters. Fuel pressure gauge is rock steady.
- oil pan is the same as dyno, and oil pressure is good.
- lifted the engine in the car via a carb-plate
- break-in springs were changed on the dyno
- while I haven't hooked up a vacuum gauge yet, I've checked for leaks visually. The engine is running rich as opposed to lean, so I don't suspect a vacuum leak. The unburned fuel brings tears to my eyes when it's running, and the plugs are all over the map, but mostly dark.

-Ben

Re: Help!! Engine Miss
 

Ben, can the miss be isolated to one or two cylinders, or is it just a miss that moves from cylinder to cylinder?

With a completely different ignition system and carburetor having been tried, if I read correctly, you're starting to move toward a mechanical problem, as much as that is something you do not want to hear. I'd do a compression test, check the lash, check the lobe lift, hook an undampened vacuum gauge to a manifold vacuum source, and check the valve springs.

You might try a fresh set of slightly (1-2 steps) hotter plugs, with a gap in the 0.026" range.

Have you hooked a volt meter to the various 12 volt positive inputs to the ignition system? You might look for a voltage drop when the miss is happening.

Re: Help!! Engine Miss
 

Alan said: "hook an undampened vacuum gauge to a manifold vacuum source, and check the valve springs."

Exactly what I was thinking. Found a lot of miss-fires other shops didn't seem to be able to find on my big old Sun Engine Analyzer bu using it's big, un-dampened vacuum gauge.
Invaluable tool if you learn how to use it. You can even isolate the offending cylinder with it. Just put a short piece of vacuum hose between each plug wire and the cap. Using a long screw driver with a jumper wire grounding it to a good ground, touch the short pieces of vacuum hose to ground the spark for each cylinder. If it's a cam or valve or spring problem the gauge will smooth out a lot when you ground the offending cylinder. It will deflect some for any miss-fire, but much more with a leaky valve.

Re: Help!! Engine Miss
 

Ben when I tried everything I could think on mine a few years ago I just gave up and had Mike Bush completely rewire my entire car. Hope you solve this. trust me it will be something small when you find it. Ed

Re: Help!! Engine Miss
 

Is it really running rich or is the ignition system so weak it isn't lighting off the mixture correctly? How is the carbon tip in the dist cap?

Re: Help!! Engine Miss
 

Alan,

I was moving toward a possible mechanical issue because I thought that I had eliminated any electrical possibilities, but it sounds like there could still be a gremlin lurking somewhere affecting the ignition. As bad as the miss is, particularly under load, I would expect that if it were a mechanical issue, it would show itself more readily. Maybe I'm wrong.

Regarding whether or not the miss can be isolated to one or two cylinders: I've pulled the plugs a number of times and I don't see anything that screams out as being an offending cylinder.

I like the idea of hooking up a voltmeter to the 12 V sources. I'll add that to my list. Thanks again for your input.

Ed,

I'll be honest, I can't quite envision what you're suggesting. I don't have an undampened vacuum gauge, but I'd consider getting one if it could help me isolate the issue. Is there somewhere I can go to see this setup in action? Thanks for the tip.

Adger,

I was suggesting exactly what you stated, that it's running rich due to an unburned mixture. Maybe I'm wrong, but I assume that if my problem was purely a vacuum leak, then I'd actually be running a bit lean as opposed to rich? The carbon tip on the distributor cap looks brand new. Thanks.


-Ben

Re: Help!! Engine Miss
 

Ben,
Please don't take this the wrong way, but "Looking good and being good" are two entirely different things. There may be a problem there. I would "Check it" with a Volt /OH Meter to see if it has high resistance. Some of them are spring loaded and can burn the spring out. I've also seen the path from inside the cap to the brass contact broken by being burned out , yet it "looks good" on both sides, resulting in Open circuit or high resistance. I think you need to go over the eletrical system with a fine tooth comb. get friendly with your V/O meter and check the system, loaded, not static. "Load it" by running the engine. It could be a switch that "looks good" but has high resistance when a load is put on it. I would even put another battery in it. I've seen batterys in some dirt cars look fine and load check fine, but when you load them with "G" forces the plates bounce around and arc internally and kill the ignition. Start taking loads off the battery and you might want to put a dedicated one for just the ignition. Have you tried moving the plug gap down a little to see if the miss leaves? I've had that happen and it could indicate several things. Not "enough" coil output to jump the spark at the plug is usually the fix for that. The acting like it is running rich and your carb guy says the carb is healthy makes me think the electrical system is suspect. As the "Engine Guy" I usually end up figuring out what the problem my customer has because it is always "My Engine" at fault. I've got a long list of "silly things" it always turns out to be. Don't get tooooo frustrated. Problems like this can make you ... well, you understand.. :~) Good luck.

Re: Help!! Engine Miss
 

Look at the ground, it will be the problem. You may have to ground it in several places, and also, put a timing light on the motor in the car, rev it up to peak, and see if the timing moves. If it does, it is a ground.

Re: Help!! Engine Miss
 

timing on a engine with a chain drive will tend to retard as the engine increases in rpm and advance when the rpm decreases if you time it by reving it up its the chain stretching ever so slightly or taking up the slack that causes this movement---try timing it at a steady rpm of say 5000 rpm see what it does if its moving around or not---I'm gonna bet tht you have a bad wire somewhere either broken or bad connector maybe even a bad sparkplug try swapping out plugs one at a time see if it helps I've seen bad ones from the factory not often but it does happen---works and then kinda works depending on the load and other things---- -- maybe go so far as to take the engine back out of the car and run it on the dyno again see if the problem persists or goes away---if it persists its the engine if it goes away its some thing in the car---if its in the car then you'll hafta start looking at the entire electricla/ignition system----Comp

Re: Help!! Engine Miss
 

I've been reading this post and there has been alot of good suggestions mentioned here. Two things that grab my attention are the 3000 ish RPM limit and new switches being installed. The RPM the problem occurs almost seems to be a clue, I've encountered these issues due to several different things, low battery voltage, improper triggering of the ign. controller along with obvious things like loose or ommited grounds. I noticed Pat Collins had asked you to check the wire colors from the Dist. to the MSD, very good idea as it takes a short amount of time to actually look and be absolutely sure they are correct, I've caused myself many head aches by assuming things. My self I believe the first thing I would do is put my trusty MSD tester on the car and spin her up to make certain the box and coil are up to the task. If it sparks all the way up we can say the control box and coil are OK. During this test may be a good time to put the DVOM on the Batt. Pos. as well as the switched pos. ( small red wire) to make sure we have sufficient voltage. Is it possible your new switches have an issue such as a large voltage drop thru them, testing in this way will tell you. As with any problem we need to break it down into smaller units and test the units that we can, by eliminating one unit we can concentrate on the next one and so on. No testing the carb. thats another story, as others have mentioned it may be easier to swap one out and see if you get the same result. Belive me I understand your frustration trying to isolate this concern, I deal with these kind of issues every day, unfortunately no o9ne can give you the magic fix via the net however I'm sure by properly testing the things you can test you'll resolve this problem. Good luck Joe

Re: Help!! Engine Miss
 

Adger,

I've tried 3 different distributors,each with their own new cap and rotor, so I believe I've eliminated that possibility. I've also replaced the coil, plug wires, plugs, MSD box, battery, and rerouted and insulated the MSD connectors, double-checking the polarity of each. I appreciate the encouragement and continued support.

Randy,

Thank you for your input.

FED 387,

Thanks for your input. Pulling the engine is the last resort, but I've been considering it.

buzzinhalfdozen,

I believe that I've eliminated the "insufficient voltage to the ignition system" by installing the HEI with a single wire direct to the battery. However, this does still leave the door open to a possible ground issue elsewhere in the vehicle. I've also tried a second carb, eliminating that possibility. The new switches are definitely on my list of things to eliminate. Perhaps I'll disconnect them, and hardwire the components one by one. Thank you for your input.

-Ben

C

Re: Help!! Engine Miss
 

Ben, is the battery for this vehicle in the trunk or under hood ? If in the trunk how is it grounded ? If it's in the trunk and grounded somewhere in the trunk area do you have a dedicated ground wire to the front of vehicle? Also you stated that you "hard wired" an HEI unit direct to the battery with the same results which would nearly eliminate the switch as being the issue as you have bypassed it alltogether, we still have the question of sufficent voltage. From rereading your posts I'm starting to believe you have a mechanical problem assuming your voltage is sufficent to operate the vehicle. Have you performed any mechanical diagnostics, compression test, leak down, checked spring pressures, checked valve action while rotating engine with valve cover off? just some thoughts. Joe

Re: Help!! Engine Miss
 

Ive had a broken valve spring cause a similar problem

Re: Help!! Engine Miss
 

Joe,

The battery is in the factory location behind the driver's seat ('71 Corvette), and the negative cable goes through the floor and grounds directly to the frame. I've got an additional ground wire from the cylinder head to the front of the frame.

I haven't performed any mechanical tests yet. I've had the valve covers off, and reset the valves, but it's worth a second look.

-Ben

Re: Help!! Engine Miss
 

This is what I would check

Re: Help!! Engine Miss
 

I've been watching this for a while, scratchin my head. Here's my guess:

Water in the fuel would start and idle fine, and it would struggle to rev up. I see you drained the fuel and replaced it in October 2011, but does the fuel cell have foam in it? If so, moisture could be retained in there, which would blend with new fuel instantly.

You mentioned that you " ..pulled the plugs a number of times and I don't see anything that screams out as being an offending cylinder". Does this mean you tried pulling the plug wires off at the cap one at a time, with the engine running, to listen for one that doesn't cause the engine to drop off?

Re: Help!! Engine Miss
 

Tony,

I'm running the factory gas tank, and had it drained well. I was even able to get a rag in there and soak up any residual, and peek in with a flashlight to double check.

I haven't pulled the plug wires off one by one as you're suggesting. Thanks for your input.

I guess I'll be visually inspecting the valve springs soon. Thanks.

-Ben

Re: Help!! Engine Miss
 

While you are on the fuel tank give the sock (fine wire, plastic in some, mesh) that is on the pickup tube some attention. Leave the gas cap off and go to your fuel line upstream from the tank pickup and blow(blast) compressed air, at least 150 lbs back through the fuel line. If the sock is varnished up or clogged it will usually dislodge whatever is there or blow the sock off. That just eliminates a restriction in the fuel system. Be sure to not have your fuel pump in line or the cap on the tank when applying the air pressure. Another way to give the pick up attention is by removing the tank and remove the fuel line/sender access and remove the pickup screen.

Re: Help!! Engine Miss
 

Ben,You might want to check the ground at the frame. We have had problems with the connector on the end of the cable inside the rubber cover.Good Luck with your problem. Phil

Re: Help!! Engine Miss
 

It sounds like you've isolated everything external to the engine- after 67 posts it's hard to take it all in.

As you said, the valve train is your next suspect. You've had the valve covers off- did you run the engine while they were off? This is a quick way to see if a lobe is flattened, a pushrod bent, a stud pulled out of its threads, or a broken valve spring. You'd probably be able to spot these things even if you just cranked it with the covers off. Any of these will make a popping sound in a consistent rhythm.

An overtight valve just sounds like crap, hard to describe, but a valve is not closing, so it's just weak and shakey.

One more thing I remember chasing long ago- a head gasket that is blown between two cylinders. Spits out the exhaust and intake of the two affected cylinders.

All of the above have a distinctive sound. If it was possible to post an audio file, many here would probably recognize it.

Hope you solve it soon, and hope you'll post it when you do.

Re: Help!! Engine Miss
 

Adger,

I can see the fuel sender and sock very easily looking through the filler neck. I didn't blow it out, but it looks very clean. I'll consider this.

Tony,

I was just talking with my dad about mocking up a set of see-through valve covers to watch the valve train. I couldn't run the engine with the valve covers off - I'm too much of a neat freak. I spun it with the covers off, and didn't see anything, but again, it's worth a second look.

I'm running MLS head gaskets, so I'd be really surprised (and disappointed) to find something wrong with them. I leave it open as a possibility though.

I will certainly post whenever I find the source of my frustration. If I have any money left, I may even throw a party.

-Ben

Re: Help!! Engine Miss
 

Ben,
Back a number of years ago I had a similar problem where the motor on Brenda's car would skip (miss) when I would set the timing, or accelerate at a normal (non-dragstrip pace). However, the car would go like a scalded dog down the track. I was pulling my hair out over this. Then at a Nat Event, I asked Mike Walter to come take a look/listen. After 30 seconds he said there is no problem...its a race carb...set up to run at idle, OR wide open throttle, and nowhere in between. He further explained the secondaries are set up with such a light tip in for reaction off the line, so they flutter on slow acceleration.

Not saying...just relaying something to think about.

Bill

Re: Help!! Engine Miss
 

Ben several years ago i had a 396 that had almost the same problem. It was a ground i checked everything like you have . I found it when i pulled on each ground,one of them pulled apart. Just another thought. Jim

Re: Help!! Engine Miss
 

I fought the same problem for six months engine would miss around 3 grand are under a load. I changed out every thing over 3 thousands dollars in parts, the only thing that was not changed out by me was that stupid disconect switch at the back. I orderd a 175 amp switch and problem was solved. Switch was corroded inside and not supplying enough amps to the msd.

Re: Help!! Engine Miss
 

Jim, Herbie,

Thanks for the input. I don't have a main shut off switch, but my battery cables will definitely be an area of interest, along with all of the grounds.

Bill,

Your issue is very interesting, Thank you for sharing.

-Ben

Re: Help!! Engine Miss
 

Ben... Any compression or leak down test results yet?

Re: Help!! Engine Miss
 

ben... what type of lifters > solid or hyd > hyd shubeck/limited or reg hyd ???
i had an issue years ago when over winter a lifter went south, would occasionnally try to pump up and cause the miss... at idle & low rpm was good enough to run...b4shubecks

jack

or you could trade it in on a cj or dragpak... dealers love trade ins :)

Re: Help!! Engine Miss
 

Maurice,

Compression test and leakdown test are on the list once it warms up a bit.

Jack,

I'm running Smith limited travel Hydraulic lifters, with about .002" lash.

-Ben

Re: Help!! Engine Miss
 

Ben,

When you get it running have someone shoot the headers with a temp gun to see if one cylinder is hotter or colder then the others. start checking right away at start up

also check your wire size on the new switches, perhaps they are incorrect size or wired in a way that they steal voltage via a shorted wire.

one thing you can try, see if the car has a electrical draw...........shut off all the accessories..........does the battery spark when you hook the cables up? if so pull fuses one at a time until you find the circuit that is causing the draw.
next check the draw with your new switches turned on one at a time. see if any spark more than others? actually wiring an old door buzzer up with clips on it does wonders for performing these tests, and safer too.....
Did you install any relays with the new switches?

Re: Help!! Engine Miss
 

Kirk,

No new relays installed with the new switches, only what was already there for the fuel pump, electric fan, and water pump. I've never heard of your method for checking for a draw. Thanks for sharing.

-Ben

Re: Help!! Engine Miss
 

Hey Ben, ever get your miss figured out?

Re: Help!! Engine Miss
 

Junior,

I just finally fired up the car last weekend after making a number of positive changes to the ground circuits including isolating and adding grounds along the way. I also replaced the negative battery cable, just to be sure, as well as the water pump and electric fan relays, just because. I also performed a lot of continuity and resistance checks along the way, as well as checking voltage to all areas. I've been reevaluating and checking every aspect of the vehicles wiring, and I haven't found any smoking gun. Everything checks out ok. Needless to say, problem persists.

I plan on performing a leakdown test next weekend (after I buy a leakdown tester). If that checks out OK, I'm not sure what my next move will be. My dad and I have been tossing around the idea of installing another engine that he's got, to know for certain if it's the car or not. Of course, that's a big task, and free time's been hard to come by lately.

As always, I'm open to thoughts and suggestions. Thanks for checking in.

-Ben

Re: Help!! Engine Miss
 

had a gremlin we chased for 1/2 a season--we solved ours this way-----look into the distributor itself any wires in there??? we insulated/shielded them by wrapping them with alum foil--- it worked in our situation --not saying it will in yours but it seems we were picking up signals?? or interference?? of some sort when we got to higher RPMs from electrical wiring passing in the area of the distributor--look into it might just be it---Comp

Re: Help!! Engine Miss
 

Ben, check the gear on the distributor. Had a situation where the edges of the gear were worn almost razor sharp which was causing a miss. Replaced the gear and problem solved. Hope you find the problem.