small hesitation/miss after installing ignition box.

[Foxfan88]

i had this problem before when i first installed my box. its a summit street/strip box. first time i put it on it made the car miss so bad i could hardly drive it bucked around so much.

i am guessing it was a problem that was there and the box amplified it.

well i have tinkered around, the coil was replaced as so was the ignition module. i got around to putting the box back on and it runs alot better. the start up and idle smoother and WOT is excellent i actually noticed a slight difference in power.

but the only bad thing is around 2500-3000 it will get a slighty stumble to it, its spark related i am pretty sure. and its only when just driving, give it some gas and it will clear up easily. its not near as bad as it was when i first installed the ignition box the first time. its alot better than it was and can actually drive the car good.

i am just confused why the idle and WOT are great but the part thottle driving will stumble a bit just in that small rpm range.

could be something in the dizzy? like the pick-up?

any ideas or suggestions.

 

[ratrapp2]

i have the same exact problem.i had a msd6a installed for a year problem free.i woke up on a sunday morning and the car started to run and miss like crap.i thought a plug wire had went bad so i put new ones on but it had the same miss.i unhooked msd box and car ran great.i left it unplugged for about 3 months with no problem.i recently bought a mallory 6a box and now the car has aslight surge at in town driving speed(20-40mh).i also feel like it's simply amplifying an existing problem that i really haven't had time to track down.

 

[Daggar]

Fox Fan...

Are you running a bypass valve?
Have you done anything to change the EEC (i.e. are you still running closed loop)?


I agree that your issue is likely spark related but also suspect that the trouble you're having probably coincides with your boost transition when the EEC is in closed loop.

I had a similar problem and fixed it by changing the load scale (actually the tuner did) point where the EEC changed from closed loop to the WOT throttle table. The change was taking place at the same moment that my bypass valve was closing.

Look at your vac/boost gauge and see of your stumble occurs at or very near 0 psi. and is consistent.

Something else you can try is to move your base timing down 2 degrees from present then up 2 degrees from present to see if there is a change.

The condition of your wires and other ignition components can also contribute to a problem like this (of course).

 

[ratrapp2]

my car is a natural aspirated 5.0 so i can't blame my problem on that.maybe foxfan can look there but not me.

 

[Foxfan88]

Fox Fan...

Are you running a bypass valve?
Have you done anything to change the EEC (i.e. are you still running closed loop)?


I agree that your issue is likely spark related but also suspect that the trouble you're having probably coincides with your boost transition when the EEC is in closed loop.

I had a similar problem and fixed it by changing the load scale (actually the tuner did) point where the EEC changed from closed loop to the WOT throttle table. The change was taking place at the same moment that my bypass valve was closing.

Look at your vac/boost gauge and see of your stumble occurs at or very near 0 psi. and is consistent.

Something else you can try is to move your base timing down 2 degrees from present then up 2 degrees from present to see if there is a change.

The condition of your wires and other ignition components can also contribute to a problem like this (of course).

i am running a bosch bypass valve just the basic plastic one. i think with the 14 lb spring.

i havent done anything to the EEC just yet. I am planning to get a tweecer rt here in a month or so once i stop messing with the car for the winter and try to tune on it some.

the coil is new the plug wires are fairly new and the igniton module is new.

i hadnt really though about it being blower related. i will look at it next time i drive and if its related to boost pressure or not. but it does run great at WOT and i cant feel anything at all.

i'll keep you posted.

 

[Daggar]

Ok... Yeah, mine ran great at cruise and WOT as well. It was only during that transition when the bypass valve closed. It was like a very small spot where it was lean. It was really bad when in a higher gear with the cruise control on and transitioning for a small hill climb or something.

 

[Foxfan88]

mines a bit different. its running great at idle and WOT but will start bucking and missing a tad bit at cruising speed. its nothing horrible like i stated before but its enough to take initiative to get rid of it.

 

[RYC CUKR]

Damn,

You're still fighting that miss. I finally found out what caused mine. I had a plug that had been dropped or something and I must have dropped it and just picked it up and installed it without really looking at it. I was probably in a hurry. Anyways the strap on the plug got bent down to the point where there was practically no gap at all. It ran fine at idle and at WOT but had a nasty miss at any part throttle condition. I fixed that and it runs much better now.

 

[Foxfan88]

i was driving mine around last night, it ONLY happens with a very light load and under engine vacuum. i happens pretty much when i have very light pressure on the throttle to keep the car at cruising speed. it doesnt really seem to do it with the foot off the gas. get the pedal more pressure and the car will accelerate and wont miss. JUST when i have LIGHT pedal pressure trying to keep a constant speed.

i am going to try timing and see if it changes it any. its set at 12* base at idle.
i will also check the plugs, do you think opening up the gap may help. with a more powerful spark i could run a wider gap. but i didnt think a small gap would cause a miss?

i dont have any vacuum leaks i am pretty sure.

 

[Daggar]

So your gauge reading is still well withing the Vacuum side (that the way I read it in your last post)).

You get a hesitation (bucking/choking) at cruise when feathering the pedal down very lightly.

Let me go over a couple of other things that you said:

Opening up the gap will not give you a more powerful spark. It will give you a larger spark surface area but the spark itself will be less intense. Since your running a blower car, you should be running plugs that are at least one heat range cooler than stock. Those plugs should be gapped to .035 if you're running the stock ignition system.

I remember you saying something about swapping your wires out in the near future. It may be time. Look over your current set really good. Shine a flashlight into the boots. If you see ANY corrosion, take them apart, wire brush the terminals, and polish them with a dremel drill and q-tip end soaked in chrome polish (sounds stupid but this works great!!!). The same can be done with your cap and rotor terminals (don't forget to do UNDER the rotor as well). Ensure that all polishing compound is wiped clean/removed prior to installation.

I would also take a look at the terminals for the TFI and the plug terminals for the wire harness going into the distributor. Wire brush them all and fill the cavities in with some dielectric grease. Do the same with the TPS connector.

Finally, the TPS sensor. Make sure that the screws are snug bot not over tightened. Use a little blue thread-lock on the screws if you have some. Often there is a little bit of play in the screw holes. Hold the sensor one way or the other so that it's tight against the screws before tightening. DO NOT drill the screw holes out. Clean out the TB with some carb cleaner if you see any build up.

I had similar issues to what you're having when I got the new motor in and boosted it. I can't count the number of times that folks told me that the stock ignition system just wasn't up the task. It was the CONDITION of the related components that was the cause of a lot of it. All the boost did was make the issues more apparent.

Swapping over to a brand new set of cut to fit Taylor plug wires made a WORLD of difference in my combo. It would probably have made zero improvement, had I not "spruced up" the other components first.


Unrelated to your current problem:

If you think you're going to be sticking with the stock ignition system for a while, you might want to consider a boost-a-spark at some point. I consider these to be invaluable REGARDLESS of what ignition system you run. Even with the dial rotated to zero, they regulate the voltage going to the coil and keep it CONSTANT whereas normal voltage to the coil varies considerably.

 

[Foxfan88]

vacuum wise it always seem to have read a little low personally. i never had a gauge before the blow so i have no idea what it was before. but at a good idle (around 750-900rpm) it will make 8-12 inches and revving it up quickly will snap it to zero and as rpms fall the vac goes to 15-20 inches then back down to idle. but half the time at idle it makes like 5-8 inches.which definatly doesnt seem right. i have replaced all the vac lines recently and i get no results from spring ether on the engine. so i am baffled. the vacuum readings are smooth and steady never fluctuating around they just seem low, maybe a internal leak??

in gear it will run steady and vary according to engine load... letting off the throttle in gear it will pull 20 consistantly. never more never less.
the numbers seemed a little low especially at idle. some say its the cam and the blower causing this... but the b-cam doesnt have all that much overlap, it only has a 112* LSA. i could see the blower causing a vacuum loss. it constantly pushes extra air even at idle, enough to where the engine can still consume it all without it causing a pressure build-up in the manifold, which would seem like it would lower vacuum... let me know if my reasoning is wrong... and if my vac readings seem off.

when you mean "stock ignition" daggar? do you mean with no ignition box??

i have the summit digital ignition box. its the cheapie with no rev limiter.

before i added box yesterday it ran perfect no miss at all. and drive perfectly fine.

after the box it has a miss and stumble only under light light throttle and usually cruising speed where a light throttle is maintained for a while.

today i was coming home in the stang and was going about 65-70 in 5th gear. at these speeds there is wind resistance pushing against the car, so i had to press the gas pedal a tad more to keep it going a constant speed. at this speed the gas pedal was far enough down that it didnt miss at all. it ran smooth as silk. once i had to slow down to 45-55 i didnt have to press the gas as much to maintain the slower speeds so it started missing.

do you think a colder plug could cure this? i am currently running regular non-plat motorcrafts with a .033 gap

and the parts are fairly new. the plug wires are FRPP wires and i put them on maybe 5 months ago. the cap and rotor are maybe 2 months old. the TFI module is also 2 months ago. coil isnt even a month old. plugs were installed with the blower.

its just strange to me how it had no miss at all and then after adding the ignition box it starts missing. like some small imperfection was amplified is what it seems like.
the only other thing ignition related i can think of that i havent replaced would be the pickup in the dizzy. could this cause a problem??

i will try some of the things you said daggar. i'll post back if i find something.

 

[Foxfan88]

i replaced the pickup in the dizzy and it seemed to help some. it still has a popping sort of miss but not near as bad and its alot more driveable. i verfied again that it runs fine without the box. i unplugged it and it runs super smooth not a miss in sight but with the both it will miss a bit around 2500-3000 rpm.

i'm starting to think it may be something in the box? could there be something wrong with the box or would it just not work if something was wrong???


or could it be my wiring??? i had to extend the wires and i used the little wire crimpers. the manual says to solder all connections could this be my problem???

 

[Foxfan88]

today i messed with it some. adding a little FP seems to help the problem.

i ususally ran it at 35 i cranked it up to 40 more like stock and it seemed to help the problem. maybe the more effiecient spark burning the mixture better. so it could use some more fuel??