High Speed Intermittent Miss

[Bob Chadwick]

Funny you should mention that. MSD just happens to sell a shielded wire. $14 at Summit. I ordered it and have the polarity information from MSD. I'll take a go at these issues this weekend and see if this makes it go away. If not, I'm off to play with the carb.

 

[tlong]

Bob,

I seem to remember in the good old days before OBD we'd take the car to a shop with an 'analyzer'. It would read advance, timing, total spark electricals under load on rollers. I think it would isolate the fuel/spark problem. Does anybody have those around here anymore? It could be a fuel thing with a simple obstruction somewhere. You'll get it.

Tim

 

[wishuwerehere82]

Bobchad,

Any progress yet?

 

[Bob Chadwick]

Got the shielded cable in from MSD and have it in place. I need to pull the cap off the distributor and check the polarity based on the info they gave me. Hopefully this weekend. The holidays have been very busy.

If not then, I'm off for two weeks.

Thanks for asking.

 

[lone73]

I haven't read this whole thread (encyclopedia) but have you checked engine compression with a compression guage and valve lift with a dial indicator? I posted earlier that I had the same prob and I came to the conclusion after I tried literally EVERYTHING else that that was probably my prob (ground cam that is) but I'll admit I never went to buy a dial indicator to check cam lobe lift - got in a hurry and just stabbed a new motor in it. The new ZZ4 worked fine with the same carb that was on the old motor and same type of distributor. Further evidence that there was an internal problem. it may not be your situation but if you've tried everything else I believe a dial indicator wouldn't be a bad investment.

good luck with it
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[Bob Chadwick]

Lone73,

That is setting in the back of my mind but it was a "not there one day, there the next" situation. I suspect a cam would be a more gradual deterioration leading up to this type of symptom.

bob

 

[Jack]

it may not be your situation but if you've tried everything else I believe a dial indicator wouldn't be a bad investment..

An inexpensive dial indicator w/magnetic base IS a wise investment for anyone who is gonna do most of the work on their car/truck/bike. It is required to measure runout on hubs/rotors, to degree-in a cam (or check for lobe wear/collapsed lifter), to measure runout in distributor shaft. A decent china-made DI w/ mag base can be had new for $25-$50. Same goes for having a decent dial or digital caliper w/ at least 6" or 8" range ... I got a new decent chinese 6" digital caliper at traveling tool show for $15 and decent chinese combo with 6" dial caliper & 1" mike for $20. Keep em dry and don't abuse em ... they'll outlast you.
JACK:gap

 

[Bob Chadwick]

I helped Heidi's (78SilvAnniv) husband a little when he was rebuilding the motor in his car. He had a set. They were pretty nice. Set them on a metal piece with a magnet, zero them in and you were off and running.

 

[lone73]

Bob,
Yeah, I remember reading that in the beginning of the thread but if I remember correctly mine did that as well. Just one day started missing at speed. Some days it would do it a lot worse than others. One time it started cutting out so bad I thought it was gonna' leave me on the side of the road. Then it smoothed out and ran decent 'till I got home. Again, I didn't check my cam either but I know for sure it had some kind of internal problem and compression was good. I had even put a new timing chain set on the front, new valve springs, adjusted valves a few times, messed with the timing curve, I was trying out all kinds of ideas to fix it. Nothing even made a difference.

Just as sure as I talk you into buying a dial indicator you'll find out it's not the prob, but as Jack posted it's usefull for rotor run out and a lot of other stuff and at least you'd know the condition of your cam.
It's just another idea to try...
good luck
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[Bob Chadwick]

Well I don't know if the problem has gone away but I have done no harm. I replaced the trigger wires running from the MSD box in the front of the car to the distributor with shielded cable from MSD. The run was slightly over 10 feet so I bought two of the insulated cables, which I discovered clip right together, cut the end of one and, after checking with MSD on the correct polarity (which I had) I added the correct connectors and the car started right up.

I also took a close look at the distributor wire spacing and it appears ok.

Next weekend I will need to get the car out on the freeway for a half hour or so and see if the fuel filter, vacuum and electrical changes I made had any impact.

If not, the next step will be to replace the rotor and cap, which has the original coil in it, to see if the problem is in one of these three items. After that check the fuel pressure, the float to make sure that it is adjusted correctly and take a look at the fuel metering.

The carb on the car is not the original Q'jet so it is possible that it was replaced incorrectly. Whether or not that could lead to fuel starvation issue is something the experts will have to tell me. Isn't there a number on the carb that could tell me whether or not this is a correct carb?

I've bought Doug Roe's book and after one reading I'm not so sure I want to open the carb up and may take it to a shop.

 

[Bob Chadwick]

Well the first thing I have found out is that the carb that was placed on the car is for a 1976 Chevy C10. The carb appears to be a little richer than the stock carb.

Stay tuned.

 

[69MyWay]

I think the ignition control module is faulty. When you hit a magic temp while cruising at a certain speed, there is an open spot in the circuit that is jumping and causing it to cut out.

A lean carb will BACK FIRE, not just cut out. Bad ignition will cut out like you are flipping a switch on and off.

I am not sure how your aftermarket system is set up, but if this were a stock HEI, I would simply yank the control module and replace it for about $25 at the local parts store. I also always make sure that I put plenty of die electric grease between the module and the distributor body.

Otherwise, I think it is a faulty MSD unit.

 

[Bob Chadwick]

Chris,

By ignition control module I think you are referring to the module inside the distributor. The problem developed when I put the new distributor in with this new module. However, when I added the MSD 6AL unit this unit is pulled with the MSD unit controlling the function formally controlled by the module. There was no change when I did this.

Is there another ignition module that you are talking about?

Thanks for the input.

Bob

 

[Bob Chadwick]

The saga continues. Took it out from my house and made it roughly the same distance that I made it the last two time before I got the "sound". Pulled off the freeway and was able to get around the car before it stopped. Does not appear to be coming out of the tail pipes, which to me suggests that is in not backfiring. In addition, after messing with the vacuum, electrical connections, etc. over the course of the last several weeks, it seemed to be much smoother and I can't say for certain that it is running rough while this is occurring, or if it is, it is very slight. Opened the hood and you could definitely hear a "knocking" sound that went away after idling for about a minute.

I pulled the vacuum line from the distributor, not really expecting any difference, but wanting to rule out any possibility of advance. Continued on the way down the road to a friends house, had lunch and drove back. Had the same problem so I hooked the vacuum back up. Was able to hear the noise again.

The sound seems to be coming from the back of the motor block in the middle or perhaps more so on the passenger side.

It happened 3 times on this trip that I noticed. The last time had some fluttering upward of the oil pressure gauge from around 40 - 60 psi if I gave it gas. It was making the sound as well. This oil pressure has been another intermittent problem since I bought the car four years ago so this may or may not be related.

Probably going to put the old distributor back in and see if the problem goes away. I'm not optimistic and suspect that this was all coincidental. Also going to check the tightness of the exhaust manifolds though the sound did not appear to come from this area.

I'm going to get a pair of those automotive stethescopes from NAPA and bring it with me on the next run to see if I can pin down more specifically where the sound is coming from.

Does this sound like a sticking lifter(s) or valves that are out of adjustment to anyone?

I'm to the point where it's going to the mechanic to have them diagnose and fix the problem.

 

[wishuwerehere82]

Yeah Bob, it does sound like a sticky lifter, or your distributor isn't meshing properly with the cam gear. Boy, 60 PSI sounds a little high for oil pressure. Maybe one of your oil passages to the lifters is clogged with something, and one of your lifters is starving for oil and collapsing. If it was a lifter sticking up, your cam would be smacking it. I'm betting it's something with the distributor gear. Is it still breaking up like it was before? Or it just the noise now?

 

[wishuwerehere82]

Wait a minute! If it happens roughly at the same point that you get to on the freeway, it could be a heat problem. How is your cooling system and water pump doing? It sounds like a temperature related problem could be causing your lifters to stick. Is your coolant temp. normal when this happens? Your heater core return line is right in that area and could be clogged, causing a hot spot in the back of the block. Maybe the hose is pinched?

 

[Bob Chadwick]

Cooling system us rock solid at 190 degrees. I don't think there is any miss at this point.

Heater core is working fine so there shouldn't be a heat issue with that.

The 60 PSI is just a top end fluctuation. Think of the movement as batting your eye lids rapidly. Normal oil pressure is 40 psi when hot.

I was wondering if my oil pump could be the problem?

Could this be a timing belt issue with the belt messing up under power and settling down at idle.

The distributor is sitting all the way down so I don't know how it could be a meshing issue. And the intermittent nature has me. Never the less it's coming out this week and we'll see what happens.

What confuses me the most is that it happened three times driving cold from my house to the same stretch of road.

 

[wishuwerehere82]

I guess it could be the plastic shaft coupling on the oil pump has cracked and is causing the noise. Possibly one of the gear teeth on the oil pump is missing. The timing chain is up front, but could be getting sloppy, I suppose.

What the heck, swap the distributor back out. Since that was the point that your problem started.

 

[GerryLP]

...Does this sound like a sticking lifter(s) or valves that are out of adjustment to anyone?

Bob,

A sticking lifter would very often have a mechanical-type sound. It is caused by the rapid bleed-down or the slow expansion of the lifter. The culprit is often sludge build-up. It could be a broken spring, but its very unlikely. A weak spring should be more noticeable at higher RPM. The rate of sound would increase as the engine rpm increases. IMHO, I find it doubtful that it is a lifter, but then again, I am not there to hear it.

I would ask you to check for the lash on the cam (and MSD does suggests the same), by adjusting the rockers.

The very abreviated procedure is set #1 piston @TDC, Back off the rocker nut for the intake (I) side until you feel the rod turn, tighten until you can't turn the rod with your fingers, and then turn nut one additional full turn (this will be hard to do on a collapsed lifter). Repeat for #2, 5, 7 I valves. With the #1 still at TDC one can adjust for #1 exhaust (E), and #3, 4, and 8 E valves.

Next, place the #6 cylinder at TDC (rotate crankshaft 360 degrees) and adjust in the same manner #2, 5, 6, 7 E valves and #3, 4, 6, 8 I valves.

One positive outcome of one checking all these suggestions is that one will be more secure of the condition of the engine. On the negative side, it takes a lot of time to accomplish.

GerryLP:cool

 

[Bob Chadwick]

Pete and Gerry,

Keep motivating me on.

I all but pulled the distributor tonight. My 10 year old was helping me so I am to the point where I need to pull the new out of the engine and put the old back in. With all the fun I had last time lining up the oil pump I deciding to spare him the colorful language. I'll probably do it tomorrow and then on Saturday take another freeway run. You have to do it on the weekends here in Atlanta or you can't go the speed limit.

If it is still there I'll be taking a look at the valves. It it still makes the noise, I'll probably pull the pan and take a look at the oil pump. While I have it apart, I'll likely tackle that rear seal.

Bob