Banging and bogging under boost...

[txstang84]

Hey guys, I posted a similar thread in the power adder section, but they don't seem to get much attention in there-and yes, I've already done a search...but, couldn't really find what I was seeking.

Most of my setup is in my sig, the 42lb'ers and 77mm MAF are now installed, no FMU, 255lph in tank pump. Currently I'm running autolite 103 plugs gapped at 0.035". So far, the most boost I've hit was 8psi.

Here's the problem, about two weeks or so ago, my car decided it didn't want to run worth a crap under boost. It bogs heavily, and pops alot. A friend followed me home the other day and said that with the exhaust popping came some black and gray smoke. The part I don't understand about this is that up until that time, the car ran great with boost-screamed! But, now I have to stay out of it. If I exceed about 2psi, it falls on its face, and bangs out.

The only thing we could figure out is that I'm blowing out the spark...my ignition consists of a stock dizzy, and module, FRPP wires (ohm'd good yesterday, but they are kinda old), and a Crane PS 91 E-core coil. I did do a plug swap prompted by the crappy performance. I swapped from 104's gapped at about 0.033". Obviously no fix. I tested my coil @ 0.8 ohms primary resistance, and 3.5K ohms secondary resistance. My timing is 10* initial, and my AFM PMS is set for 2* @ 1psi, and 20* @ 20psi, so basically 1*/psi timing retard.

So, exactly what does it feel like when the spark blows out? This is a phenomenon I've never personally experienced...only heard about. I don't personally know too many people with power adders, and I was not around for any faults they ran into. My friend suggested I try running it with the belt off to see if it runs good WOT without the boost. I haven't been able to floor it since this crap started.

So, in a nutshell:

Could I be blowing out my spark under boost (and only 2 psi??)?
What else could be wrong?

Any help you guys could give would be greatly appreciated...

 

[Daggar]

Is this a problem that cropped up out of the blue or is it something that started after some modification that you made?

I'll assume that you've not made any recent changes via the PMS recently (or you'd already be looking down that path).

What comes to mind (on what info you've provided) is a weak ignition (of course). I'd be looking at the charging system and replacing the normal tune-up components: Cap, rotor, wires, TFI. Run the car for a bit... drive it around town and stay out of the boost. IMMEDIATELY after shutting down, record the battery voltage. Check it again in another hour. You're looking for a voltage drop to indicate either a short (however small) or an incomplete charge of the batter (to indicate a problem with the charging system). You symptoms stink of a bad or weak alternator. You might also check battery voltage at idle with everything off, then again with all of your accessories on to try and get an idea of how well the alternator is keeping up.

Charging aside, it's back to the ignition system. After doing the tune-up then you might want to consider swapping in a known good coil to rule it out. I've not had much success at determining that a coil was good by just running an ohms check on it.

My only other thought would be that you may have a corrupt tune in the PMS. For that, you're on your own my friend. hehe I've never had the opportunity to play with one.

 

[txstang84]

Thanks for the reply, and yea, the problem pretty much cropped up out of the blue.

I check the charging system, basically, on a day to day basis. That possibility had crossed my mind once before. At idle, hot or cold, my voltage rarely dips below 13.8-14.0v unless it's cold, dark, and wet outside. Even then it's never below 13.2v @ idle.

I inspected my cap and rotor, they have minimal amounts of deposits. I've foregone cap and rotor replacements in the past with no ill effects, but then again, that was prior to addition of boost. The only peculiar thing I noticed was from the coil. After performing a primary and secondary winding check, the tolerance based on what is in my haynes manual was WAY out of spec for secondary. The manual specs out 8k-11.5k ohms for secondary, and I just checked it again with a known multimeter and it's even lower today @ 2.78k ohms. Based on basic electrical principle would that not insinuate that the coil windings are fried, and not providing enough voltage or energy to fire off the plugs under boost?

Again, thanks for the reply

edit: The PMS tune has not been messed with since addition of a 3-bar MAP sensor (prior to crap performance), and I've run through all the cells with no finding of different numbers...wierd?

 

[Daggar]

I think you may be onto something with that coil. Even with that said, I'd STILL replace any aging ignition components you have. Boost will show-off any weakness in the ignition system.

It also occurs to me that your wires and/or cap and rotor may be arching someplace. Plug wires can ohm good but still leak.

 

[txstang84]

Hey thanks alot Daggar, I'd have already been to the parts store and back, but global warming apparently took a break in west Texas and decided to drop some snow on us...

I'll be R2'ing the cap, rotor, coil and wires-the plugs are still less than 200 miles, so I think I'll leave them in for the time being and just ck the gap...

 

[Daggar]

Reset the gap to .035 if you're going to take them out anyway. A little more spark surface won't hurt you and and the extra .002 shouldn't give you any trouble either.

 

[txstang84]

coolio, will do

 

[txstang84]

For those of you that are running blower, do you use just an intank pump, or intank + booster pump?

 

[txstang84]

IT'S FIXED!!! ....and I'm an idiot

So, I changed out the coil, wires, cap, rotor, all to no avail. Then on a whim, I ordered a couple of new elements for my fuel filter. As soon as I opened it up-dead giveaway. Initially I didn't think about checking it, as it had only been in there for about 5,000 miles...but, see for yourselves...it's disgusting

 

[tylerrocks]

going lean huh? always nice to find the problem. I am from Big Spring BTW

 

[txstang84]

No kidding...I'm immensely relieved that it runs like a bat outta hell again, but man...I should've checked that first.

You ever make it out to Abilene?