Intermittent power loss

Tony Radford · #1 (**permalink**) 04-03-2010, 05:28 AM

I've got one of those pesky intermittent problems I need to fix, but I don't know where to start. 99% of the time, everything works great under any accelleration condition. But after I've been sitting in stop and go traffic, the engine will stall for about half a second, usually when I'm shifting between first and second gears. I can't tell if it's fuel or spark related. I'm running an MSD 6A and double pump mechanical carb. I've considered vapor lock, but the water and oil temps are well within spec. For the first time, It did it while leaving a restaurant last night after sitting for a couple of hours. During a "spirited" exit from the parking lot, it felt as though someone turned off the key when I clutched at the end of first gear. It was only for a split second, so it recovers with a lurch into second gear. I have an aluminum flywheel, so the problem is particularly obvious.

I can't see it being a fuel filter since it runs great at high speed for hours at a time. The braided fuel line doesnt seem to be getting hot. The MSD box is located on the firewall, but it's been that way for the past 30K miles. This anomaly has only existed for a relatively brief period of time.

I know it's not much to go on, but I'd like to see some comments before I start ripping stuff out.

Ron61 · #2 (**permalink**) 04-03-2010, 06:38 AM

That could be a hard one to really pin down. But you are pulling harder between 1st and 2nd than when you are running at high speed. If it were heat related I wouldn't think it would have happened after setting that long in the restaurant parking lot. Having went through a somewhat similar problem a few years ago and spending a couple of months trying to track it down, I found that my problem was fuel related except the car would completely shut then engine of and then it would start right back up and run well for a long time before it would do it again. Then one day by accident while the car was up on the rack down at my friends garage and it was just idling, it shut off and we noticed that a short, about 6", piece of rubber fuel line which we had already taken off and checked twice seemed to move. It would some times just suck completely closed. We replaced it and then cut the old one open and it looked great and there was no soft spots in it before we cut it open. But I have never since had a single problem like that. I would be more likely to suspect that yours has to do with the electric system as it only happens when you are under heavy load at that 1/2 shift. Hope that you find it son as something like that can be really annoying and frustrating.

Ron

RedBarchetta · #3 (**permalink**) 04-03-2010, 08:36 AM

Check all ground connections to your ignition/MSD. Doesn't take much to cause a cutting out situation.

Ron61 · #4 (**permalink**) 04-03-2010, 08:48 AM

Also one more thing that you might check, though in this situation I really don't see how it would only affect you in the 1/2 shifting. If you have an MSD Distributor pull the cap and see if there is any carbon or signs of arcing inside the cap.

Ron

Excaliber · #5 (**permalink**) 04-03-2010, 09:51 AM

I think it's simple, the plugs are "loading up" and it takes a few cycles for them to clean out and fire proper again. It's running temporarily rich, could be due to hot fuel over boiling a bit from the carbs when you first take off with a hot engine thats been sitting OR turning a corner or in some cases just sitting at a long light with a lumpy idle.

I don't know of any good solution for this, check float level and set it as low as possible is all I can think of.

OK, not so simple, but thats my 2 cents.

Maurice Butler · #6 (**permalink**) 04-04-2010, 01:58 AM

have thought of using a oxygen sensor to log the mixture, may give a clue

Tony Radford · #7 (**permalink**) 04-04-2010, 05:43 AM

Thanks guys. When I neared the end of my long ride home on Friday afternoon - and after half an hour of heavy stop and go traffic, it started to get much worse than it ever has in the past. But after traffic thins out and I can do a litle sustained driving, the problem goes away. If the cause is temporary fuel starvation, or even saturated plugs, would the hesitation be compete among all cylinders? It acts like I'm turning the key off, like a complete power outage, lurch and immediate return to excellent performance. And it will idle all day. It accellerates through first gear (even if I wind it up) and then stumbles typically one good time after the RPMs bottom out inbetween first and second. I have seen on occasion that it will die WHILE accellerating, which is what led me to think it was vapor lock. The lurch Friday night did throw me a curve as I was ready to blame it all on thermals. Hopefully whatever it is will completely crap out as I'm coasting into my driveway (yea right). My plastic clear fuel filter does touch the timing cover, so I think I'll replace it and adjust the hard line so that it's suspended in open air. At least that's cheap and non intrusive. After that, I'm stumped.

ekrupa2 · #8 (**permalink**) 04-04-2010, 06:42 AM

Start simple. Had a similar issue and my terminal going to my MSD Blaster coil broke. Had similar drivability issues (very intermittant). Then completely died on me one day. Coasted to a stop wiggled the wire an behold it was broke. The tension of the wire made it looked fine but the terminal was still on the coil and the wire in my hand. Emergency repair, came home and crimped on new terminals, then heat shrink wrapped. Based upon your description it does seem electrical related versus fuel. I would trace yoour whole ignition circuit. One loose wire can break the chain.

Tony Radford · #9 (**permalink**) 04-04-2010, 07:28 AM

Anyone experienced similar symptoms due to a decaying MSD Blaster coil? Mine looks ok (connections are good). Does it make sense that it could be affected when the engine bay temp gets to a certain level? What's typically tougher, the coil or 6A box? My distributor is much newer than the coil or box. I still think it's heat related.

Mister · #10 (**permalink**) 04-04-2010, 07:49 AM

I have had the occasional hard start and miss in the Spring and Fall after the car has been run and then stopped for a bit. After some puzzling, I have attributed it to winter gas and underhood heat. It seems winter gas is "more gaseous" than summer gas and, in my car, seems to result in vapor lock occasionally. I have never had this occur with summer gas. A smaller diameter non-drop base air filter has helped.
Mike

smallblockhead · #11 (**permalink**) 04-04-2010, 05:08 PM

I agree with Mike, sounds like a winter gas/engine compartment heat is causing vapor lock. I just yesterday experienced exactly the same symptoms. I don't know when they switch to the summer formulation, but I hope it's soon. (The other alternative...for the weather to get cold again, is not an option I wish to contemplate!)

Gary

Tony Radford · #12 (**permalink**) 04-05-2010, 01:17 PM

I rolled my car off the Kwiklift this morning for a ride into work only to find that she's now officially "dead in the water". I didn't have time to mess with her this morning, but I now feel like I have a failure somewhere in the ignition system. The fuel fliter is filled with fuel, but I didn't get anything close to a spark. So now what is it - distributor, Ignition Box or coil? Let the troubleshooting begin!

ekrupa2 · #13 (**permalink**) 04-05-2010, 03:37 PM

MSD troubleshooting here....http://www.msdignition.com/page.aspx?id=3206.

Another possibility....ignition switch.

Tony Radford · #14 (**permalink**) 04-05-2010, 04:55 PM

This is starting to bum me out. I got home and tried to start it with no success. I pulled the coil wire at the coil and got my wife to turn the key. Now I know what Ben Franklin thought when he did the kite and key thing. Ouch! Well, looks like there's spark. I pulled the air filter, gave the throttle a twist and just as you'd expect - fuel galore. Then I turned the key and it started right up. I took a brief jaunt down to the end of my street and though it still runs well under load, it doesn't idle very well. It cut off on me while turning around. I guess I'm back to the fuel filter replacement. Damn!

snakebittexan · #15 (**permalink**) 04-08-2010, 08:21 AM

I'm reading with great interest because mine is doing the same thing and as you said, I've never had this issue before. Last Saturday she stalled after a long light and making a u-turn while winding it out in first, clutch in, changed to second and no problem. Started it up a few hours later after sitting for an hour, drove fifty feet, quit as if it were fuel starved, let her sit for a minute then started as if nothing ever happend. I'll check the fuel filter tonight and give you an update--good luck with yours.

Ron61 · #16 (**permalink**) 04-08-2010, 08:39 AM

Just for kicks try changing the coil wire. When you moved it you may have closed an open inside the insulation on it. Also if it seems fuel starved on turns or any time, make sure that you don't have varnish on the needle valves. I had that happen once and spent a day trying to figure out why it wouldn't start at times and then would kind of sputter at times. Once I looked at one of the valves it took about 10 minutes to clean everything up and I had no more problems.

If you are still having starting problems and most of your posts would seem to indicate that the first problems were under heavy load, use a remote starter when it won't start and try pulling a spark plug boot to see if any fire is getting there. If not work your way back, not moving the wires any more than necessary and check the output of the coil wire at the distributor end. If you have fire there, take the distributor cap off and look at the rotor and inside terminals.

I hope that you find the problem soon and I will be watching for what it was to file away in my weird troubles book.

Ron

Tony Radford · #17 (**permalink**) 04-08-2010, 09:01 AM

Ron, I've inadvertently created a divergence in this thread by creating the "MSD battery drain" thread. Due to a series of events, I've gone from the fuel filter (replaced) to the MSD (seems to be OK) to the ignition switch. Yesterday, while my car was parked outside my office for 8 hours or so, the battery was completely drained despite nothing being left on. I jumped it from another car and it immediately started and made the 30 minute ride back to the house with a full charge (I did experience the dreaded "momentary power outtage during acceleration" about half way home). It always idles great and accellerates perfectly throughout the RPM range. The ignition switch intermittency prognosis was offered a couple of times. Now I'm listening.

DON BEVERS · #18 (**permalink**) 04-08-2010, 09:21 AM

Winter time fuel in our area contains "up to" 10% ethanol. This considerably lowers the boiling point of the fuel. The fuel is most prone to boil in the emulsion well of a carburator rather than the bowl as that is where it is thinned out and the air is added. Hot fuel due to heat sink combined with hot air under the hood, (the scoop doesn't begin to cool the air until you are well under way) can be a real problem with a carburated engine. Dead-head type fuel pressure regulators do not allow the fuel to circulate as a fuel injection system does. There are by-pass type regulators available for carb systems and they do help. A heat shield under the carb and insulated fuel lines can also help. Mandated ethanol use is tough on carb systems and it will only get worse as ethanol use grows, new laws are on the way.
On the electrical side, if you are using the black 2-wire plug that comes with all MSD kits, to possibly hook-up your distributor, they are notorious for going intermittant. On the race car, we always replace that with a 2-wire GM weather-pack unit. Completely reliable and easy to get apart for maintance.

Tony Radford · #19 (**permalink**) 05-19-2010, 02:50 PM

Well, at this point I'm inclined to agree with everyone who suspects the fuel. I filled up with my usual BP and took off for Gadsden last week (a little under three hours), which I drove non-stop and included some dead-stop traffic on the interstate. I drove back later in the day and was stuck in heavy stop and go traffic for at least an hour during the heat of the day. I experienced no issues during the trip. I suppose it's reasonable to assume I was using summer gas for this trip.

tbracker · #20 (**permalink**) 05-24-2010, 12:55 PM

Wow, I could have written this one myself. I have been having a nearly identical problem, and it is frustratingly intermittent. The hesitation almost always happens after sitting at a light for a couple of minutes. Some rapid acceleration and it will choke momentarily in 1st or 2nd, recover and then its OK.
I posted the problem last year and the best I could come up with was fuel issues. I found a small leak where air seamed to be being drawn into the small clear filter I have just before the carb. That didn't seem to fix it. I pulled the big filter I have back between the tank and pump and found some grit. I cleaned the filter and it worked better. Could it have been a fresh tank of 'summer' gas. I don't know, but it has been doing it again and we're coming out of winter. Hummm. I checked the filter and again some dirt was found. I'm replacing the element this time. Two years and about 10k miles.
One person suggested that my filter was too restrictive. I looked it up and the 10 micron element is intended for carbs. Anyway I don't know where to find a less restrictive element for my Summit Racing SUM-G1501 filter.