What's new
CK5
Register an account today to become a member! Once signed in, you'll be able to participate on this site by adding your own topics and posts, as well as connect with other members.

Light throttle miss help...

Keitha

Keitha

1/2 ton status
 Premium
Joined
Oct 13, 2008
Posts
1,027
Reaction score
75
Location
Costa Mesa, CA
Any suggestions are appreciated:
I am having a hard time tracking down a light throttle/cruize miss. It is very noticable in the following examples:
1) slow cruizing around a parking lot - just off idle
2) cruizing slowly (20 mph) in 2nd gear
3 highway speeds with TCC locked up, Trany in OD

Under higher load I never notice any missing

383 with just a few thousand miles on it.
Motor runs great otherwise, but the missing makes it tough to tune better.
I just put in a new distributor and module but it did the same thing with the older one. Plug wires are new-ish MSD 8.5mm wires. Plugs are good.
 
I had a set of Accel wires do similar to me. I went through the entire fuel/ignition thing on my truck. Pulled the distributor, thoroughly cleaned it all, replaced the vac advance mech, unstuck the mechanical weights (gunk/grease/goop made them sticky) new plugs, fiddled with the carb, new iggy module, new cap, rotor...

In the end I was stumped and still had this damn miss. I went wheeling and my battery tray busted loose sending my batt into the alt fan and soaking the wires in acid. I was ticked off cuz it cost me a battery, and wires that were only 6 months old. I bought a new batt and new wires and the miss went away. I'm certain it wasn't the battery...so it had to be sh!tty wires straight out of the box.

Dunno if that helps, but that's my experience with a similar miss. Once I did get new wires on it (that weren't crap) it ran better than it ever did. I did notice it ran slightly better with each fix i threw at it, and once the real prob was found it ran like a friggen dream!

Rene
 
1991 Suburban? Is it still fuel injected? If so how much bigger did you go with the camshaft in the 383?

Reason I ask is I did a Comp Cam in my 87 K5 and just off idle under very light load the motor would have a slight surge that I thought was a miss. It was ever so slightly too much cam for the computer at that particular throttle position even though it was specific for the TBI motor.

I could actually duplicate it by having the tranny in drive, holding the brakes and giving the motor light throttle. Just a thought.

You can also test your MSD wires with an ohm meter before you spend the coin on a new set. The wires should read 40-50 ohms of resistance per foot of wire. ie: if you have a two foot wire resistance should be about 100 ohms.

You might try getting the truck in a dark spot and loading the motor as described above and have someone check for arcing. Obviously you will want to use extreme care when doing this since the truck will be in gear. I'd check it at in park to begin with for safety reasons.

Last but not least. If you do check it at night you may see a blue "halo" on the cylinder head by the plug. This is not a problem and in fact is perfectly normal with a wire that has such low resistance.

-Phil
MSD Ignition
 
Thanks Phil. Yes, my 1991 is still TBI. I will check it out this evening. Cam size is just an LT1 spec cam. I have been working on tuning my PROM, but I just could not tune around this issue.

It is great to see a product rep on these boards!

On another note:
I sent my 6AL in last week - Hopefully your guys can bring it back from the dead!

Best regards,
 
Phil,
I only have time to test the odd cylinder tonight but My #7 wire (2' long) measured +400ohms while #1,3, & 5 were all around 40ohms/ft. Could having a wire that far out of spec cause the missing?

My wires are only about 7 months old. Does MSD have a replacement policy for a faulty wire (I really do not want to buy a whole new set)?

thanks,
Keith
 
Considering most wires can be 600 - 900 ohms per foot 400 total is still pretty low, although high for super conductors. Super conductors are some of the best plug wires there are available in my opinion at only 40 ohms per foot while still providing EMI suppression. Anyway, I guess my point is, although that wire sounds abnormal, unless you can wiggle it and cause it to be open that's probably not your miss if at most it has 400 ohms. To me it sounds like you miss is a lean spot at light throttle and medium load that maybe you can't tune out with your cam and TBI. With that said I would still look into getting that wire fixed, replaced.
 
Keith,

I'll send you a replacement wire no problem. Check the rest out to make sure we only need one sent; if I need to send two or so I'd rather make them and send them together.

400 ohms of resistance on a two foot MSD Super Conductor wire is deffinately too high and may very well be your miss. I'll get you squared away. Give me a call at work when you get a chance. My direct line is (915) 856-2739. If I don't answer leave me a voicemail and I'll yell back at you as soon as I can.

-Phil
MSD Ignition
 
Philly87 said:
Keith,

I'll send you a replacement wire no problem. Check the rest out to make sure we only need one sent; if I need to send two or so I'd rather make them and send them together.

400 ohms of resistance on a two foot MSD Super Conductor wire is deffinately too high and may very well be your miss. I'll get you squared away. Give me a call at work when you get a chance. My direct line is (915) 856-2739. If I don't answer leave me a voicemail and I'll yell back at you as soon as I can.

-Phil
MSD Ignition
Click to expand...

Phil,
I appreciate your offer to send me replacement wire(s). I will measure resistance on the even # cylinders this evening and call you tomorrow.
Product support like this will keep me as a MSD customer for life.

Thanks much,
Keith
 
Thats what we like to hear!!!

When you call me have the lengths of the wire(s) and what boot ends you need and I'll shoot them out. I know how every little bit helps and if I can help out CK5'ers and continue the MSD reputation at the same time it's a win win combo...

-Phil
MSD Ignition
 
Phil,
It was good to talk with you and thanks again for helping with the spark plug wires (and the 6AL?). The fact that you pro-actively offered to help with a replacement wire speaks volumes about your pride in MSD and the support a company like MSD offers to it's bread and butter customers. I can not think of many other companies that would stand behind their products like this.
Like I said, I am a customer for life. This give the confidence to continue to purchase your products knowing that the company, and employees like you, stands behind them.
 
Keith,

Glad to help. Looks like the 6AL shipped out no charge as well...

Enjoy!

-Phil
MSD Ignition
 
You must log in or register to reply here.

Latest Posts

Top Bottom