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-   -   Odd Miss (http://www.clubcobra.com/forums/ignition/134714-odd-miss.html)

Detroit Bill 09-23-2015 07:47 AM
Odd Miss
 
I am not sure where I should post this because it could be fuel or ignition.

The last two times I drove the car I experience this. A miss/stumble after a shift. I never experienced this before.

One odd thing I noticed (that you can see in the first video) is that the tachometer takes off at higher RPM. I had never seen that before. I also don't believe the tach. That was not a 6K shift, it may be my imagination but I feel power is down. The second video was after I filled up the gas tank. The engine does have a ground strap it is mounted to a bell housing bolt. I am going to add a second, probably to the block. I have the parts to do that.

Early on I had a similar miss and I upped the rev limiter to 7,000. I assumed the dial MSD was inaccurate and I had "fixed it" I was going to start dialing it back until I hit the limit and bump it up again.

[ame="https://www.youtube.com/watch?v=M4Ko88GMqzY&feature=youtu.be"]https://www.youtube.com/watch?v=M4Ko88GMqzY&feature=youtu.be[/ame]

patrickt 09-23-2015 01:40 PM
Yep, that's definitely a miss alright....:cool: Turn your rev limiter completely off either by pulling the little chip out if that's what you have or turn the dials so that it's off. Make sure the MSD lines to the coil are on the opposite side of the block from the distributor pick up lines, so that they are not interfering with one another. Then pull all your plug wires, inspect them, and put them back on making sure none are loose, broken, munged, etc. Then take it out for a run and see if it still does it.

Detroit Bill 09-28-2015 07:47 AM
Still missing
 
I still have the miss. I checked the plug wires. I turned the limiter up to 8,000.
I checked the Distributor and Coil wires they are separated. Pulled the cap and inspected it.

I want to check add a second ground strap and check the timing. I am afraid the MSD box is to blame. I may swap it out to a Crane box if I can't diagnose the problem.

patrickt 09-28-2015 08:17 AM
Quote:
Originally Posted by Detroit Bill (Post 1364723)
I still have the miss. I checked the plug wires. I turned the limiter up to 8,000.
I checked the Distributor and Coil wires they are separated. Pulled the cap and inspected it.

I want to check add a second ground strap and check the timing. I am afraid the MSD box is to blame. I may swap it out to a Crane box if I can't diagnose the problem.
It's not the ground strap, but go ahead and add one. When you put a timing light on your marks and rev the engine up to 3500 RPM are you moving smoothly up to around 35 or whatever Barry says that engine likes? Does your distributor have a vacuum advance on it?

Detroit Bill 09-28-2015 08:26 AM
Quote:
Originally Posted by patrickt (Post 1364730)
It's not the ground strap, but go ahead and add one. When you put a timing light on your marks and rev the engine up to 3500 RPM are you moving smoothly up to around 35 or whatever Barry says that engine likes? Does your distributor have a vacuum advance on it?
I did have a timing light on it and it did move smoothly up the RPM range. I was not able to see the numbers so I marked the balancer. I ran out of time so I was not able to check the actual timing.

It is not a vac advance dist.

patrickt 09-28-2015 08:31 AM
Quote:
Originally Posted by Detroit Bill (Post 1364732)
I did have a timing light on it and it did move smoothly up the RPM range. I was not able to see the numbers so I marked the balancer. I ran out of time so I was not able to check the actual timing.

It is not a vac advance dist.
OK, first things first then. With aluminum heads, mark 35 degrees on your balancer using some of your wife's finger nail polish. Confirm that your total timing at 3500RPM is right about that mark, give or take a degree, or whatever Barry spec'd you at.

Detroit Bill 09-28-2015 08:32 AM
Already done, I will check it tonight.

Thx.

patrickt 09-28-2015 08:35 AM
Quote:
Originally Posted by Detroit Bill (Post 1364735)
Already done, I will check it tonight.

Thx.
Put the bottle back on her dresser carefully, so she doesn't know you used it on your engine.;)

Bernica 09-28-2015 02:50 PM
Sounds like the box. Where is it mounted? Under dash or in engine bay?
Also just for kicks, check the condition and separation of your plug wires between #7 and #8. ;)

Tim7139 09-28-2015 02:56 PM
You should resistance test the individual plug wires, you'd be surprised how often they break internaly down near the plug boot. Last year I found 3 that tested weak.........cheap fix.
Even though it's a new motor, I would'nt rule it out.

Gaz64 09-28-2015 04:19 PM
Seems more like a complete cut of the engine rather than a misfire.

MSD is not what it used to be.

Get a Mallory.

blykins 09-28-2015 05:09 PM
Just do it on hard acceleration? What's your fuel pressure doing at that point?

slider701 09-28-2015 06:42 PM
Are you sure the clutch is not slipping and its bouncing off rev limiter? Take off medium throttle in 1st and then at about 5k shift into 4th and get on it hard. If the clutch is starting to slip this will confirm as it will slip really bad doing this and you'll see it on tach and hear it. If clutch is healthy it will not allow eng to rev freely.

A98Coupe 09-29-2015 05:55 AM
Check the connections onto your ignition switch. I had the same issue once. Turned out to be a loose connection.

Detroit Bill 09-29-2015 06:47 AM
Checked a few things
 
Quote:
Originally Posted by patrickt (Post 1364736)
Put the bottle back on her dresser carefully, so she doesn't know you used it on your engine.;)
I checked the timing last night, it advanced to 36 like it was set on the dyno.

I tried nail polish but I couldn't get a good line. I ended up using a sharpie.

Detroit Bill 09-29-2015 06:51 AM
Quote:
Originally Posted by Bernica (Post 1364779)
Sounds like the box. Where is it mounted? Under dash or in engine bay?
Also just for kicks, check the condition and separation of your plug wires between #7 and #8. ;)
MSD 6AL2 is mounted under the dash.
Wires 7 and 8 were separated already, I inspected and separated more.

Detroit Bill 09-29-2015 06:53 AM
Quote:
Originally Posted by Tim7139 (Post 1364780)
You should resistance test the individual plug wires, you'd be surprised how often they break internaly down near the plug boot. Last year I found 3 that tested weak.........cheap fix.
Even though it's a new motor, I would'nt rule it out.
That test is Ohm meter looking for 0?

DanEC 09-29-2015 06:54 AM
Pretty clear on the video that it happens momentarily "after" shifting when revs have fallen back and starting to build again. Doubt it's a fuel issue if it's running clean before the shift at higher rpm - but could be a lean issue during that shift transition. But sounds more like the entire engine is cutting out rather than just leaning out or an individual cylinder misfiring. Don't know what goes on in one of those electronic mystery boxes for MSD that would cause this but I would be suspicious of it.

Detroit Bill 09-29-2015 06:54 AM
Quote:
Originally Posted by blykins (Post 1364789)
Just do it on hard acceleration? What's your fuel pressure doing at that point?
Yes it just does it on hard acceleration and I have to be high in the RPM. Lower down and it does not do it. I do not know what the fuel pressure is. I have a mechanical pump.

Detroit Bill 09-29-2015 06:56 AM
Quote:
Originally Posted by slider701 (Post 1364792)
Are you sure the clutch is not slipping and its bouncing off rev limiter? Take off medium throttle in 1st and then at about 5k shift into 4th and get on it hard. If the clutch is starting to slip this will confirm as it will slip really bad doing this and you'll see it on tach and hear it. If clutch is healthy it will not allow eng to rev freely.
I'll try that. I don't think it is that I would smell it. I also have the rev limiter set at 8K and I am not hitting 8K. My rear main is leaking. I plan to fix that when it gets colder.


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