Weird intermittent problem with my '66
 

Yesterday as I was leaving the Kirkland Concours d'Elegance my car died. I started it up, drove out of the Porsche area (it's running great at this point), and about 30 seconds into the trip up the road it started popping and backfiring. It eventually got so bad it wouldn't even run, and died. I ran the battery down trying to restart it. That resulted in this embarrassing moment.
http://granitehead.smugmug.com/photo...40_529Sc-L.jpg

It's been doing this for a couple of weeks. It pops, backfires, loses power, and then seems to get over whatever is going on and runs fine. It only does this on a cold start...never when it's warmed up. It lasts for about a minute.

I charged the battery today and it started right up. I let it idle in the driveway until it started backfiring and checked the fuel pressure, it was a steady 3.5. I took it out for a run around the block and for about 30 seconds it ran bad - a minute later, it ran great.

Any ideas? It's hard to troubleshoot a problem that goes away in a minute. I know a minute doesn't sound like much, but on the road, it's endless. And now that it's stranded me, I gotta fix this. The car is a '66 with a 2.2T motor with Webers, an MSD ignition, and a sport muffler.

Since you asked for ideas, this is only a wild guess. You might try checking out the MSD. The symptoms seem so short-lived and only at start up that the MSD sprang to mind. Just a thought.

Rich,
Fuel blockage ?
Go through the fuel system from the tank(rust specks?),clean the tank filter,blow the fuel lines,check the motor fuel filter(if you have one) and the carbs for dirt.
I had grief several times in mine with very similar symptoms and it took my mechanic several goes to fix it properly.
Not a confidence building feeling to be flat bedded home ! :(
Alternately,maybe a bad tank of gas ?

Cheers,
Dennis. :)

Rich,

I recommend doing some more diagnostics before you tear into anything.

A few questions: Does the tach ‘act up’ when the problem exists? That can be dirty or incorrectly set ignition points.

Temporarily plumb your fuel pressure gauge to the cockpit. Note the fuel pressure while the problem is happening. I’ll second Dennis’ (Pelican gulf908) fuel observation. These can be symptoms of a restricted fuel screen filter at the outlet fitting in the fuel tank. At the transition from working to blocked it is intermittent and load sensitive. Turning the car off for a few minutes makes it work again for a bit (particularly if it has had a trip on a flatbead).

Another test is to wire an analog voltmeter to the 12V power wire to the CDI. You are looking for ‘flickering’ indication of the voltage. Poor connections at the battery, fuse block or ignition switch are common culprits.

You want to find the actual problem and know that it is fixed – not just have it go away and return later.

Best,
Grady

be wary of your fuel pump running dry lest you need to purchase another.

once this 'acting up' is done can you drive the car with no further problems?

nice picture btw!

Possibly just running off what is in the bowls of the carbs.....

i seem to recall that fuel pressure does not necessarily indicate adequate fuel volume.


cold start only certainly gets you thinking about empty float bowls ie inadequate fuel supply.

check the coil. i had a permatune, did the same thing, installed an MSD and it ran great for a year, then started doing it again. changed coil ( to an MSD ) and its been fine ever since. some say not to mount the coils up-side down, which my last one was. oh, the old one was a permatune coil and CD setup.

Thanks for the replies!

L.J. - I was checking the MSD web site last night and they have a troubleshooting guide. I'll work on that tonight.

Dennis - Fuel blockage is what I'm thinking too. I've got a Mahle filter on each carb and they don't appear to have any crap in them. When the car is running, both filters look like they're flowing gas and the level in the filter didn't drop any when the car started running poorly. It's done this through 2 tank fulls, so I think bad gas would be an amazing coincidence.

Grady - My tach is always acting up...even with the MSD tach adapter installed. I was able to briefly replicate the problem in the driveway last night and while the car was popping and backfiring, the fuel pressure was rock steady 3.5. I'll check the line of filters tonight. I've never looked at the one in the pump before. Maybe I'll luck out and not have to drain a full tank of gas. I'll do the voltage check too - good idea...my MSD box 12V is wired into the switched fuel pump circuit. You're right about needing to fix this permanently.

berettafan - yes, that would suck to run the pump dry and thanks, I had to document that.

911quest - that would explain why it always happens for the same length of time...hmmm

T77911S - I've got an MSD Blaster 2 on there now...and it's mounted upside down. I'll try flipping it.

Lots of stuff to check tonight...thanks guys.

Just another thought.

Where is the fuel pressure gauge plumbed? After the in-line filter?

There are also four little screen filters at the banjo bolts in the carb tops. It may have been decades since they were cleaned. Old fuel hoses can come apart internally, restricting flow. This is where checking the float level is useful.

Best,
Grady

Grady,

The filters are plumbed between the junction block/pressure gauge and the carbs. When I replaced the engine, I rebuilt the carbs and had John Walker set them up. All the fuel lines are new from the tank back.

I'll check the voltage at the MSD power source, but I fear this is going to be a clogged filter on the tank outlet. I cleaned them out when I painted the tank during the suspension pan replacement and I did notice some rust in the tank. Having the tank cleaned out & sealed is on my winter project list...that may move up to the fall project list. Did I mention I just filled it up?

Update: I finally got some time to work on the car yesterday and more weirdness and a question.

I thought I'd start with the easiest thing, the fuel pump. I took it apart, cleaned up the inside and the screen, and put it back on. There was a tiny amount of very fine gunk in there. Now, instead of a steady 3.5psi, I'm getting a steady 4.75psi...and the car seems to run fine. I'm pretty sure I put the pump back together the same way it came apart. What would cause the pressure to change? The only other change was to replace the 10" long fuel line from the outlet to the pump. The line was less than a year old, but I had to cut it off when I removed the pump.

Take out your idle jets on both carbs. See how they look. These won't make your engine not run unless they are terribly dirty but they could add to running problems. They have O-rings on them so if they look terrible also replace the O-rings but if you are careful and OIL them when replacing the jets they shouldn't break. I just put on the tiniest bit of lube just on the ring so it wouldn't bind when tightening and then cause the jet to fall out later on.

UPDATE:

Well, it happened again this morning on the way to work (at four freakin thirty in the morning) - popping, banging, and dying. I had to push the car about 300 yds to the end of the driveway, leave it there, and take another car to work. It was the perfect start to a day that sucked all the way around.

So I call my buddy Skip today to share my misery and he, and others on this thread, said to look at the ignition system. I was convinced that the intermittent-ness of the problem pointed to a fuel issue, probably blockage in the tank outlet filter.

This afternoon, after jump-starting the car and getting it back into the garage, I decided to look at ignition system. I started at the end and was going to work my way forward. All the plug wires were seated in both the plugs and the cap. The cap inside contacts looked pretty black and the end of the rotor didn't look too happy either, so I took them off and Dremmel wire brushed the cap contacts and replaced the rotor. Before I put them on I checked the points and they were black too. I checked the point gap and there wasn't any...nada. It looks like the plastic piece of the points that rides on the distributor shaft had worn down so far the points weren't opening at all. I took the points off, gave 'em a sanding, put them back in, and gapped them and...it runs like a fricken champ. I guess you have to lube the distributor shaft more than once...when you put the engine in the car. Fortunately, I have a lifetime supply of distributor lube (one tube).

I really hope this is the end of this problem. Anybody know the suggested distributor shaft lube interval?

One more thing...my loopy tach quit bouncing around and reads steady RPM's now...something to do with points not opening? That alone made up for the crappy day I had.

a bit late i know but wanted to point out that you NEED to reset your timing after resetting points gap.

just reset mine after stalling at idle and a tach acting up. it too had zero clearance. after resetting the gap my timing was WAAAY advanced.

Thanks for the tip!

By the way, since I replaced the cap, rotor, & points, the problem has completely gone away.