Help!! Engine Miss

[Bob Pagano]

no he dose not, its a Stocker

[Vic Santos]

Ben, I've been anxiously waiting for the solution to be posted (it hasn't yet). It made me go back to your original posting. You said you changed switches and added a ground terminal because your old switches didn't need a ground. Unless your all your circuits were changed to relays (and your switches switch to gound to turn on the relay) your switches should not need a ground. Most switches have a 12v supply and switch the 12v to the component that needs it and the component is grounded. I'm confused why a switch would need a ground.
Vic Santos

[njk53]

Have you tried removing all of the switches, gages, etc. from the vehicle loop and try running the engine with the minimal amount of items needed to start the engine and run? What I am trying to say is it would be like runing the motor on a homemade dyno in the car. Bare minimum of items necessary to start and evaluate the motor to see if the miss is still present. This will help you to zero in on the engine components that are left or if the miss goes away, the fault is in the vehicle electrical system, gages, connectors.

[Ben Kallies]

Vic,

The new switches require a ground because they are lighted. My old ones were not. They stll function without a ground, they just don't light up.

njk53,

I have wired the old switches back in and disconnected the accessories that I don't need to start the car. With the exception of my tach, all of my guages are mechanical.

Thanks for the input. I'm currently looking for a good chassis dyno in the area with the right diagnostic equipment to help me figure this out. I'll keep everyone posted.

-Ben

[Gary Wiegand]

Hi Ben,

The reson I had asked if your engine has a carb. spacer plate is because an engine miss I once had behaved strangely like what you're describing. In any case don't overlook a small vacuum leak which can show up more pronounced under load, and may not even be noticable at idle or when reving the engine. My situation involed an "Extreme Poly" 1" spacer plate which became deformed after a number of races one summer evening. (Dyno time heat could possibly cause a similar situation?) I didn't notice the miss until the next weekend at the track when the engine would misfire under load. Seemed like a lean misfire, but plugs were good and I hadn't changed anything in the carb. lately so I initally thought it was electrically related. The plate had apparenly heat soaked possibly from the cast cast iron heads which were on the car at the time. After chasing down every conceivable electrical problem I could think of and finding nothing, I accidentally found that the bottom of the spacer plate had become deformed. It was only after cracking the carb. base plate after having removed the carb. for the third time for cleaning and inspection, that I removed the spacer plate and found the problem. I was curious as to why the carb. plate would crack if it was level on the manifold with normal tightening procedure, and not "strong arming" it. I replaced it with a Moroso unit and haven't had a problem since. Anyway, maybe you have a small vacuum leak somewhere, don't overlook manifold bolt threads and things like that. Just a suggestion - at this point I'd sure like to know what you find out. This sure has been dragging on for a long time. Good luck finding the problem!

[Dan Bennett]

I've seen this situation three times. The first time was insufficient grounding, the second was a bad two step switch, and the third was a bad MSD rpm chip.

I think the original poster mentioned that the car is a Corvette; remember that these are wired differently from the factory as there are no natural body grounds with fiberglass. In the midyear cars even the radio antenna had to have a separate wire to the frame for it to work. That can sometimes also cause problems with RF interference to/from the MSD box as the fiberglass isn't any sort of shield. Again, in the stock versions a metal cage surrounded the ignition wires so the radio would work.

With the battery in the stock location behind the seat, the negative cable is very short as the frame is right there. I'd still check it carefully to make sure it's still internally sound enough to do its job.

Ben has done a remarkable job of running down all those little things that could cause the problem. Unfortunately, I've often had the experience that the longer you thrash on a problem, the farther you get away from what is really causing it.

I've seen some of the best minds in racing here in this thread, and it's amazing we still don't have a fix. Hang in there, Ben.

[Ben Kallies]

Gary,

I appreciate your input. A vacuum leak has crossed my mind a number of times, but the car seems to be running rich, as opposed to lean, as I would expect with a vacuum leak. I'm certainly open to the possibility however, that I'm misinterpreting something. What's the best way (ie: effective and safe) to check for a vacuum leak? Anyone?

Dan,

You're spot on with your Corvette thoughts. They are a slightly different animal. Just to reiterate, and speak to the items you mentioned, my negative battery cable was fairly new, but I just replaced it last month, to be sure. At the same time, I payed a great deal of attention to all of the ground circuits on the car, and made some nice improvements along the way. I've already unplugged the two-step and removed and replace the RPM modules, with no change. Thank you for your words of encouragement.

-Ben

[Alan Roehrich]

Ben,

Consider getting a known good basic Holley 3310 or similar carburetor, and bolting it on with an adapter.

[Gary Wiegand]

It's probably an electrical problem - but I do like the idea of trying a carb. that you know is good. That's a really good way of eliminating a lot of potential problems. As far as vacuum testing is concerned, it helps to know where your engine ran when it was running well. In any case, you can find LOTS of info. on-line concerning vacuum testing. Check out:
http://www.atlanticz.ca/zclub/techtips/vacuum/
Looks like some good info. there.

[dartman]

At the Lucas Oil in late May at Reading I had something in the screen of my fuel pump inlet which cause cavitation in the fuel(by not allowing a good amount fuel to get to the pump).It rev free in neutral.but going down the track miss like a pig.the fuel coming out of line was not clear,it look milky.there still lot of flow but it was full of air.maybe some thing look at.