Missing at idle RPMs

[manhattanmustang131]

I have a terrible missfire that shakes the car at idle RPMs and the engine, overall, is lacking in power.

1994 5.0, bolt-ons, supercharger and brand new equipment to support it....

That's where I'm really stumped; all new plugs, wires, injects, fuel pressure regulator, MAF, spot-on tune. The car ran PERFECT for months leading up to this.

I checked for vacuum leaks and loose cables at lunch, to no avail.

What do you guys think?

 

[MaximumRisk]

-check timing
-check spark plugs
-check spark plugs cables/boots (for arcing)
-check coil
-are you running an ignition box (like MSD)??
-distributor cap
-make sure MAF is not dirty

How many miles since tune? Was/Is it running rich?

 

[manhattanmustang131]

heres the thing: I just recently had my supercharger installed at Sansone Ford this past November; not more than 500 miles ago.

All of the systems mentioned above seem to be in good shape and were in perfect order before this started. And I am running a 6AL in this setup.

There is also a vibration in the cabin that comes with the erratic idle, which seems to disapear with an increase in the RPMs.

 

[MaximumRisk]

you should pull a plug and see what it looks like. You can also try bypassing the MSD to see if the problem is with the box. Does the car backfire during acceleration/deceleration?

 

[manhattanmustang131]

the car basically chokes when I try to accelerate; when I started getting that I grandpa'd my way home.

I'm thinking fuel or ignition, leaning towards components that could just kick out rather than slowly get worse and worse.

 

[manhattanmustang131]

I'm going to try the MSD bypass when I get home, check out a few other things that could have just gone up and sh** the bed.

I was wondering if anyone else encountered a bastard like this before.

 

[manhattanmustang131]

UPDATE: so everything is basically mulled over and I have it pegged to something occurring after initial warm up.

When I start the car it runs like it normally does; Perfect. After about a minute, after reaching "post start-up/operating temperature" she turns into a pig.

The engine idles erratically, rough enough to shake the car.

What's your guys take?

 

[MaximumRisk]

Have you replaced the fuel filter? What pump are you running? how old is it? Like you said, it could be either a fuel or ignition problem. Do you have a fuel pressure gauge?

 

[MaximumRisk]

UPDATE: so everything is basically mulled over and I have it pegged to something occurring after initial warm up.

When I start the car it runs like it normally does; Perfect. After about a minute, after reaching "post start-up/operating temperature" she turns into a pig.

The engine idles erratically, rough enough to shake the car.

What's your guys take?

just saw this post.

What are you using for tuning? Any engine codes? The change in temperature may also be affecting the tune (MAYBE). When the car starts to stumble does the exhaust smell rich?

 

[manhattanmustang131]

For tuning, its basically a piggy-back chip that the guys from Sansone used to tune the car.

As far as I can tell I'm not throwing a CEL, but I have to get the handheld from work to check if I'm throwing any other codes.

It was pretty cool this morning when the change occurred. I ran the car yesterday when it was hot like hell and she ran like a champ.

I have to give the exhaust a smell next time I get out there, but normally when she runs correctly the exhaust is perfect.

 

[manhattanmustang131]

Just came back from a ride, and I'm feeling like my MSD 6AL might have cooked my coil

The car runs, but hesitates under load. The smell of the exhaust is richer than it should be, but nothing like an untuned car or POS.

I'm also considering the IAC with some reservation, since we're talking about start-up changes when the car goes into closed loop.

 

[03SONIC]

I owuld lean toward the MSD they are know to have issues. Also pull plugs as posted and read them to see what is going on. It sounds like something pretty simple.

 

[92BIGREDBEAST]

I had a MSD coil go bad after only 1000 miles. Car wouldnt start at all tho. Sounds like fuel pressure issue rather then spark. Make sure your MAF is clean. I think the computer does adjustments under open loop, so maybe when you warm up and switch to closed loop the EEC is reading bad MAF signals throwing your air fuel out of wack. Just my 2 cents.. GL

 

[manhattanmustang131]

All right guys, heres the scoop; you're going to like this one:

Long story short my dad told me to just go outside last night to check for arcing. Bingo.

Three spark plug wires sit very close to my shorty headers, and one boot basically rested on the passenger side. Luckily, the guys at Sansone saw that this might be a problem, so they wrapped the few boots with the protective cloth.

But I went out for a cruise on the 4th, a prettt hot day (90*), and really got on the car to test its warm weather performance. Everyone knows it ran like a charm, but I probably got those headers too warm for the wrap that protected the 3 spark plug boots.

My solution is to get a hold of a set of super high temp protective covers to the plug wires and keep my sharp right eye on all the components that could be susceptible to high heat corrosion.

I want to just say thanks to everyone for taking a look at this thread, proving help and I hope this helps out anyone in the future.

 

[MaximumRisk]

glad you figured it out! are you running equal length shorties by any chance?

 

[manhattanmustang131]

+1 to Maximumrisk for suggestion arcing yesterday afternoon

 

[manhattanmustang131]

yes equal length shorties; they're a real bitch when it comes to anything spark related like getting the plugs out, wires, etc.

 

[MaximumRisk]

yeah, they are notorious for burning boots!, I dont know what your setup looks like but In my car I am running custom cables that have a short, 90degree boot at the plug (instead of a 45) which give me a little more header clearance. You could try that if you like. I don't think the spark plug cover are going to help (being there). I have never tried them, but you can also look into the Accel cables that comes with ceramic boots or just go to unequal length headers (that's what I ended up doing) :-D