'94 MAF Problem??

94 LT1/9C1 Caprice., 350. New distributor and fuel pump. Flaming out of tailpipe and blowback out of cold air intake. Major backfiring. Major drivability problems. Is my MAF fried, and is my K&N oil filter doing the damage?? Take off MAF unit and not too bad. Put it back on, damn. Thanks. Sean

It sounds like somethings messed up with your new distributor. What kind of cold air intake are you using?

sounds like the opti spark distributer, but it could be any number of things, knock sensor, maf sensor, etc... any check engine lights if so whats the code???

OPTI and Spark Test

The opti has two functions in the spark process. The first thing that happens is as the cam turns, the optical section of the optispark picks up the signals by the rotation of the shutter wheel. The pulses are sent to the pcm via the optispark electrical harness. The pcm processes the signals along with other sensor input and determines the proper time for the coil to fire. The pcm sends a signal to the Ignition Coil Module (ICM) and it, in turn, causes the coil to fire. The spark from the coil travels through the coil wire back to the secondary ignition section of the optispark (cap and rotor), to be distributed to the proper cylinder.

If the opti is never sending the signal to the pcm, the pcm will never send a signal to fire the coil.

Here is some testing you can do. Refer to this diagram.
http://shbox.com/1/95_ign_system_schematic.jpg

Disconnect the ICM connector. Leave coil connected.
Turn key to ON.
Check for dc voltage with a digital meter at harness terminal "A" to ground and and also "D" to ground. Note: Use a high impedance meter (at least 10 megohm) when dealing with the pcm.
Result should be 10v dc or more on both terminals. If you get no voltage, use the diagram and chase back toward the coil and the ignition fuse. Power for the ICM comes from the ignition fuse and through the coil, so any of that could be bad.
If you have good voltage, switch the meter to ac scale and connect test leads to terminal "B" and to ground. Observe meter while cranking the engine. You should see between 1 and 4 volts ac (those are the pulses that trigger the coil to fire).

If you don't see the proper ac voltage the problem could be the optispark, the harness to the optispark, the PCM or any of the wiring in between. Visually inspect all the connections you can get to for poor contact or corrosion.

K&N cold air intake. It's been cleaned and recleaned and works fine. I know about the problems with this intake and the MAF sensors.

So far my mechanic has gone through EVERYTHING, and I mean everything. Last week thought it might be the ignition coil amplifier. I'm printing off the posts and will show to him. He doesn't think it's related to the new opti distributor or sensor, MAF, crank sensor, etc. Thinks it's electrical. Not getting check engine lights.

Thanks for the responses. I'll keep you posted!

I can't help but think that a couple of plug wires are reversed...

I've done it myself, not hard to do!

guys, it turns out the cop mechanic took out the PCV and put in a "blank" free flow elbow valve. running way too rich. I had to jimmy rig the right vave in, but I did. World of difference, believe it or not. Keep you posted in this wild wacky world of a '94 LT1 9C1 motor...

If you're talking about the one on the valve cover, the cop mechanic didn't do that, the factory did. That's supposed to be a "blank" elbow.

twdz28:
I am having a similar problem with my 94 LT1. Thanks for some good info, and the diagram. My problem is a little different, but one common issue - no Check engine light or codes, although the thing nearly dies when it has its problem. My situation is this:
Car has 148k on the clock. At about 70k, I had a serious mis-fire. Dealer diagnosed bad #8 plug wire. Ii figured, replace 'em all. (I looked and decided pretty quick I didn't want to try. Its tighter than my 'vette in there!) During plug wire replacement, dealer also replaced opti-spark (and water pump). For the last two weeks the car has been having an intermittant problem. When it happens, it has a serious mis-fire, and backfiring. When it runs smoother (usually when engine cold), it will run up in 1st or 2nd, but mis-fires at high rpm. (Plugs replaced at 100k w/ac plats.) The #8 plug was fouled. Cleaned it, and it was better for a few days, but problem is back. This only occurs after engine warms to operating temp.
I love this car and engine, when it runs right. But, when it doesn't...
Any additional thoughts?

sounds like the opti spark distributer, but it could be any number of things, knock sensor, maf sensor, etc... any check engine lights if so whats the code???

OPTI and Spark Test

The opti has two functions in the spark process. The first thing that happens is as the cam turns, the optical section of the optispark picks up the signals by the rotation of the shutter wheel. The pulses are sent to the pcm via the optispark electrical harness. The pcm processes the signals along with other sensor input and determines the proper time for the coil to fire. The pcm sends a signal to the Ignition Coil Module (ICM) and it, in turn, causes the coil to fire. The spark from the coil travels through the coil wire back to the secondary ignition section of the optispark (cap and rotor), to be distributed to the proper cylinder.

If the opti is never sending the signal to the pcm, the pcm will never send a signal to fire the coil.

Here is some testing you can do. Refer to this diagram.
http://shbox.com/1/95_ign_system_schematic.jpg

Disconnect the ICM connector. Leave coil connected.
Turn key to ON.
Check for dc voltage with a digital meter at harness terminal "A" to ground and and also "D" to ground. Note: Use a high impedance meter (at least 10 megohm) when dealing with the pcm.
Result should be 10v dc or more on both terminals. If you get no voltage, use the diagram and chase back toward the coil and the ignition fuse. Power for the ICM comes from the ignition fuse and through the coil, so any of that could be bad.
If you have good voltage, switch the meter to ac scale and connect test leads to terminal "B" and to ground. Observe meter while cranking the engine. You should see between 1 and 4 volts ac (those are the pulses that trigger the coil to fire).

If you don't see the proper ac voltage the problem could be the optispark, the harness to the optispark, the PCM or any of the wiring in between. Visually inspect all the connections you can get to for poor contact or corrosion.

The wire from the coil to the opti can get pretty bad, and cause high RPM misfires. My friend Tony's car did the very same thing a few weeks back. If replacing the wire, be sure to clean up the lug on the coil too, as they seem to get nasty as well as the wire. A bit of steel wool seems to do the trick.

If you're talking about the one on the valve cover, the cop mechanic didn't do that, the factory did. That's supposed to be a "blank" elbow.

Why would they do that? Wouldn't that make it run too rich? Thx.

No, not really. Think of the vavle cover hole as a crankcase vent. In fact, a lot of guys remove that line from the car all together, and put a small filter in the valve cover, and cap off the port on the TB. If you look at your emissions hose routing diagram, you'll notice the PCV valve is located on the driver's side of the intake manifold. Perhaps the your PCV in the manifold is bad, causing it to run rich, and you're compensating for it by PCVing the valve cover vent hole.(?)

No, not really. Think of the vavle cover hole as a crankcase vent. In fact, a lot of guys remove that line from the car all together, and put a small filter in the valve cover, and cap off the port on the TB. If you look at your emissions hose routing diagram, you'll notice the PCV valve is located on the driver's side of the intake manifold. Perhaps the your PCV in the manifold is bad, causing it to run rich, and you're compensating for it by PCVing the valve cover vent hole.(?)

1. What is value of filtering the valve cover and capping off the TB port; and;
2. Where the hell is the PCV? I can't find it and I don't have the emissions hose routing diagram. I thought I WAS dealing with the PCV, LOL. Do you have the diagram you can post, or a link?

"Driving" me nuts! I thought that hollow valve WAS the PCV location! Thanks!

Pardon my inexperience, but I don't know how to post any pics, but here's a description:

It's RIGHT in the center of the left side of the intake manifold. The PCV has a metal tube running from the front of the intake, and is fitted into a rubber grommet in the manifold.


Hope this helps.