Engine misfiring and stumbling

Leecbr · #1 (**permalink**) 10-08-2011, 11:46 PM

Hey guys, I know this is not a new topic. I appologise in advance if this is redundant.

I have a 351 windsor with a 4 barrel holley carb. Msd distributor, Msd box, and Msd wires. Also new Holley blue fuel pump ( electtric ). New Starter was installed this year. My spark plugs are clean too.

So here is my situation. My car ran perfect all year no problems. I had it dynoed and tuned last year.
I added lucas gas treatment stuff to it last friday ( september 30 ) and filled the gas. It was rainy all this past week until this past friday ( october 7th ) when I started it and drove it with no issues. After sitting a week due to rainy weather.

It ran perfect until saturday ( october 8th ) morning when I started it. It had a really rough start and idle...Even with the manual choke... I figured maybe colder temps and humidity...

When I started driving, it was stumbling and started to misfire alot. Dunno how this could of happened overnight. I had an old Mallory ignition coil so I changed it out for a msd 3 blaster coil. It ran better but still stumbled a bit and had random misfire mostly in second gear. 3rd and 4th gear ran horrible also.

Could my Msd 6 multispark box be going too. I am somewhat mechanicaly inclined but electrical isn't my thing. Is the Msd distributor bad and possibly threw out the timing.

The cobra was built in 1994 so these parts may very well have been on it since then. I don't know for sure. It only has 28,000 miles on it.

Will the car crap out overnight like this if these items are starting to fail? Or does it not start at all when they begin to fail.

I'm new at this and learning along the way. Any advice will be greatly appreciated.

Thanks,

Lee

RICK LAKE · #2 (**permalink**) 10-09-2011, 01:31 AM

Lee Start with cap and rotor, check to see if contact is still in cap and touching rotor spring. This should be replaced any way with an MSD system. They eat the center contact if carbon base. if the car still acts up, pull cap and see if rotor is spinning and you have oil pressure. This checks pin on distributor for not being broken. If this checks out, mark locations of rotor to housing and housing to block of car. Pull housing and check gear on distributor for all the gear being complete and in good shape, Ifd they are shaved, need new gear. Will also need to check canshaft gear too. Some MSD distributor come with bronze gear and wear out. Timing goes nuts. Start here and report back. Make sure you pull the coil wire before doing testing and power is off. If everything checks out, we are looking at coil, Is coil mounted on motor and which way, vertical or horizontial. Coil burnt out if laying on there sides over time. MSD box or module in distributor check next. Other thing is to make sure all contections are clean and tight. Battery has full charge and reads about 12.3-12.6 volts. Ground wires from frame to motor, battery to motor ( ground) battery to frame. Clean contections. This is a good start. Rick L. Ps pass this point may want to goto a garage if you are unsure about your abilities working on the car. If gears are chewed, Pull pan, cut open oil filter, oil change and alot of cleaning.

Good luck, wait for report Rick L.

Gaz64 · #3 (**permalink**) 10-09-2011, 01:34 AM

I'd say fuel.

Dwight · #4 (**permalink**) 10-09-2011, 07:48 AM

several of our guys had the same problem

winter blend of fuel or ethanol crap fuel.
carbs do not like ethanol fuel.
clean the fuel out of the carb, replace with ethanol free gas and try it.

Dwight

BT SNAKE · #5 (**permalink**) 10-09-2011, 07:57 AM

If it's stabling but running most likely it's a fuel problem.
Do you smell gas while it's running? If so, then I think you popped
A power valve. Check your vacuum at idle then buy the appropriate valve for the recommended application. Go tO the holly site for more info.

Hersh

jhv48 · #6 (**permalink**) 10-09-2011, 08:56 AM

Start simple first.

Pull all the plugs and compare them. Let us know what you see.

Got to be either ignition or fuel. Might be as simple as a stuck float. Do a quick float level check.

Could also be condensation inside the distributor cap. A shot of WD-40 will quickly cure that.

Leecbr · #7 (**permalink**) 10-09-2011, 09:13 AM

Thanks for all of the suggestions.

Rick,
I went through and cleaned all of the connections..Checked the grounds and cleaned them. Checked the distributor connections and cleaned them too. My blaster coil is mounted in front of the engine ( driver side) in a vertical position. Checked and cleaned the spark plug connections to the msd wires. I also sprayed the carb with some carb cleaner.

As for the distributor it's a bit out of my league. I fully understand the function behind it but I don't have enough knowledge to tinker with it.

Once I rule out the other possible solutions then I will have to take it to a garage. I have a great mechanic here that deals with hotrods. He's done all of the major work on my car. Maybe it's time to replace the distributor due to the fact I don't know how new or old it is..

Gary and Dwight,
Should I add some staybil to the gas and fill it up..I figured the Lucus oil gas additive I put in it would of helped with the water or ethanol while the car sat.

Hersh,
It didn't smell any different than usual. The one thing I noticed was that it only backfired from the driver side.

Jim,

I will try the plugs too..I will check for condensation..I'll check the floats..

I have quite a bit to do..

..might be a bit before I update you guys..stay tuned..

Thanks again guys,

I'll keep you updated on what I find out.

Lee

jhv48 · #8 (**permalink**) 10-09-2011, 09:19 AM

"The one thing I noticed was that it only backfired from the driver side."

There's your first clue. Not fuel related if only one side is backfiring. Has to be ignition. Pull the dizzy cap and check for corrosion on one of the terminals to that side of the engine. Got to be a little condensation got in.

Tommy · #9 (**permalink**) 10-09-2011, 10:24 AM

Expand on your description of "backfire." Has it ever blown back through the carburetor? If so, Hersh's idea about the power valve may be right on target. If you mean it sounds like it is missing on one or more of the cylinders on one side of the engine only, then I agree it is likely ignition related. ... After my last engine rebuild, it was running spark plugs that were too cold and they would foul out much sooner than expected. That caused the engine to sound like it was running very badly. Replacing the plugs is relatively easy to do to rule out that as a cause.

Rick Parker · #10 (**permalink**) 10-09-2011, 10:25 AM

Spray some carb cleaner in the air bleeds of the carburetor. Could also be fuel filter.
Generally you can differentiate between fuel and electrical.
Fuel will cause the car to gently "nose" over, electrical will cause an abrupt or intermittent shutdown, causing the loss of spark to the plugs. Think it through.
I think it is too soon for formulation changes of fuel at the pumps, it has to get colder, even in Utah.

Leecbr · #11 (**permalink**) 10-09-2011, 11:57 AM

I changed the fuel filter just in case..

Tommy,

The back fire is from the driver side exhaust. I hear it right next to me. The stumble is more of a loss of power when I give it some throttle..more like sputtering and then it hooks up some..then runs rough/labored...

The floats check out fine. The center of the distributor (internal on top) has a circular brass node that has some wear. The points under the distributor cap looks good. here are some pics..

Spark plugs next to check out. The cleaning of the wires and grounds, changing the fuel filter, cleaning the carb with some spray and new blaster coil helped it run and idle a little better. Power valve might be my thoughts. Maybe timing?

Power valve will probably have to be a shop visit..

Rick

I cleaned the air bleeds when the problems started..The car doesn't nose forward but just sputters along and stumbles..then hooks up some and if not will backfire then stummble..It runs really weak, has that feeling like it's has built up pressure or something is clogged..

TN Shelby Cobra · #12 (**permalink**) 10-09-2011, 02:43 PM

Lee, Same thing happened to mine this week. It was the MSD master blaster coil. It was just one year old. Mark

Leecbr · #13 (**permalink**) 10-09-2011, 03:00 PM

Mark,

after you replaced the blaster, then your car was fine?

I replaced mine too. The car was only slightly better but still far from the same car... I'm going to try and take to the carb shop and see what is going on with it..I love these cars but somedays I feel like it's one repair away from selling it..

My wife is cool with all of the parts and shop time but I can tell she is starting to wonder about my hobby.

Maybe time to pick up a side job to fund my cobra..

Hersh and Tommy,

Where would the Power Valve reside...Sorry if it's a dumb question..I figure it's got to be the only thing. I have tracked down everything that I could do.

I'll let you guys know what the shop finds out this week. I need to call monday morning and see if they can get me in right away.

Thanks,

Lee

Leecbr · #14 (**permalink**) 10-09-2011, 03:07 PM

Found out where the power valve is..gotta love the internet.

Carburetor Power Valves Video - Holley Carb Tuning DVD - YouTube

Hopefully it's just the gasket on the power valve that blew..I'll need to check the vaccume or follow some of the tips from the video to see if it's the valve that went out. Then I've gotta get into the carb to see the Valve size etc anyhow..another learning experience.

Thanks guys,

Have a good day..

Lee

TN Shelby Cobra · #15 (**permalink**) 10-09-2011, 05:52 PM

Lee, I replaced my wires first than the dist cap and rotor and plugs. I than changed the fuel filter. My dist. is a MSD prop billet and it was corroded and rusted bad inside. I bought and installed a new one. I have an extra MSD box so i changed it. Still ran bad. It was about to drive me crazy. I had been working on it for a few weeks cause I wanted to run at a nostalgia race saturday. Didn't make it. I was about ready to torch the sucker!!! I knew the carb was OK cause its a new 750 Holley I installed a few months ago. I changed the coil out today and it's running great!! Mark

Tommy · #16 (**permalink**) 10-09-2011, 07:21 PM

Leecbr,
If it turns out that your coil is the cause of your problem, don't just chalk it up to bad manufacturing. Take a good look at where and how it is mounted. Coils fail more quickly when subjected to vibration and intense heat. Some also fail if not mounted right-side up. .. Good luck with your search for the cause.

YerDugliness · #17 (**permalink**) 10-09-2011, 08:21 PM

Quote:

Originally Posted by Leecbr

Found out where the power valve is..gotta love the internet.

Carburetor Power Valves Video - Holley Carb Tuning DVD - YouTube

Hopefully it's just the gasket on the power valve that blew..
Lee

Lee, I'd suggest you check the power valve every time that your engine backfires or "burps" out the carb in any manner. That blows the PV almost every time.

Hoping it's just your coil.....that's gonna be an easy fix.

Cheers, Dugly

Barnsnake · #18 (**permalink**) 10-09-2011, 08:29 PM

The disabled mechanical advance in the distributor should make for some serious tuning challenges. Do you have trick MSD box that provides an advance curve?

RICK LAKE · #19 (**permalink**) 10-10-2011, 03:49 AM

Leecbr Lee Picture #1 show 2 black marks in the cap at 1 oclock and 3 oclock. Is this a shadow? It looks like a carbon track going into the cap. This will cause missfires. You have the cap upside down so I don't know what 2 cylinders those terminals are. You said the missfires are coming out of 1 bank. This cap looks shot. The spring on the rotor is pitted also.
Next I know you might not know but like others have said, why is the advance wired off. You don't have an FI system. MSD system give you 15 degrees of spark, but rumor has it that this only last to about 3,500 rpms and then stops because the compasitors cann't recharge that fast. That advance should not be wired off with out weights and springs on there.
Before you go crazy with power valves and fuel system checks, lets finish with this distributor. By the way there are no points in this one. I know you didn't know. It's all good. With over 10 years on this, IMO I would order a new one complete, Shop around for the best price, Jegs, PAW, Summit, Pep Boys, Reilleys, Autozone, and other places. i have learned over the years, lets replace 1 part at a time, this stops alot of misstakes and buying extra parts. Any one locate that you could use their as a tester?? this would really help off a know good running motor?? Good luck Lee. Rick L.

mr0077 · #20 (**permalink**) 10-10-2011, 08:11 AM

When it happened to me the first time it was plug wires. The second time, I changed the plug wires first thing and again it fixed the problem. Also had a problem once with the MSD cap.