4WD Noise + Ignition Problem

[stanger42]

'94 rodeo
3.2L
4WD
~140350 miles

Recently I learned that if you have 4wd, you should drive the vehicle approx. 10 miles a month in 4wd to keep everything in good order. I tried driving (on normal city streets) in 4wd. The only problem I noticed was a slight whine that increased with vehicle speed. No pulling or wandering or anything, just the whine. I pulled over, put it back in 2H, backed up approx 3 meters, then went on my way, no more noise. Can this be caused by improper fluid level? Anything else that can cause this? 99% of my driving is in 2wd, normal city driving.

Also, I was able to hook my car up to one of my school's Sun Scopes. My ignition patterns for cylinders 2 and 5 are all jacked up. The firing line is very low, there is no spark line, and no coil oscillations. I swapped out the coil with the one next to it and nothing changed. I then swapped the spark plug in cylinders 2 and 5 with known good ones. Still no effect. On all cylinders, at idle, the dwell jumps all the way to the end of the coil oscillations then moves back to where they should normally be and they do this all together. What's the story behind that? Tomorrow I'm going to swap out the control module and see if that doesn't fix anything.

Thanks for your time.

Nick

[swingline]

as for your 4wd concerns the noise is most likely normal, of course i don't know how loud of a whine you are talking about. it wouldn't hurt to change the fluid or at least check it.

as for the spark problem, did you try known good wires? i am going out on a limb here, but I would guess it's a wastespark system and cylinders two and five are companion cylinders.

if the wires are good the only thing i can think of is high cylinder pressure causing high resistance between the electrodes, now remember in a wastespark system the spark has to bridge the gap of two sparkplugs, the one on the firing cylinder and that of it's companion. you said that the dwell on all cylinders is the same so that tells me the coil is attempting to fire but can't. or there is no gap so it takes little voltage to push the electrons through the circuit.

[stanger42]

The noise in 4wd was barely audible over regular road noise on the freeway, a little more noticable on the streets.

I'd be more apt to think it was the wires if the resistances are high. The wires don't have cracked insulation and aren't grounding before the plug. It is definately a wastespark system. You're right in that the same coil has to fire the two companion cylinders at once but because of the polarity of the coil it actually 'pulls' one towards the coil while it 'pushes' the other towards the spark plug. The plugs I got are some crappy platinums. Guy at AutoZone said they were the stock plugs for my car, boy was he wrong. Platinums and irridums are horrible for cars. Anyways, what I meant by that is the gap is okay but can't be adjusted.

Some time this week I'm going to do a cylinder leakage test, both dry and wet on the thing and see if I can fingure anything out.

My instructor was surprised that a misfire in two cylinders wasn't causing the engine to idle worse, but as it stands, there are only minor signs of a misfire at idle that do not get worse under load or at higher RPMs.

So this week I plan on doing the CLT, swapping out the control module (apparently they are very susceptable to heat and the fact that they sit right on top of the engine probably doesn't help much), and checking the resistance on the wires. Anything else I might want to look into? I have access to a full shop with scan tools, oscilloscopes and everything else a good shop should have so, barring any manufactorer specific tools, I'm pretty much set in that department.

[swingline]

do you know if cylinders 2 and 5 are companion cylinders?

it seems to me it must be something from the coil to plug. i think a compression test should come before the leak test. the compression test tells you if the cylinder leaks, the leak test tells you where.

good luck

[stanger42]

2 and 5 are definately companion cylinders and the CLT I'll be doing is a combination compression test/leakage test.

I'm going to change the control module today and I'll lket you know if that makes any difference. Also going to test the wires and will let you know what I find. My current instructor is leaning heavily towards bad control module and that's easy enough to replace.

[stanger42]

so controle module didn't fix anything. One thing I did notice is that by cylinders 2 and 5 there are grounding straps. what are these for?

[directory]

Originally Posted by stanger42

so controle module didn't fix anything. One thing I did notice is that by cylinders 2 and 5 there are grounding straps. what are these for?

grounding the engine..duuuh

just kidding.

i don't really know...

[swingline]

they are just to ground the engine to the chassis to complete the ground side circuits.
i don't really think they would cause your problem.

look real close at the wire boots for something called carbon tracing. a little black line on the inside of the boot from the terminal to the edge of the boot. current will follow carbon tracks to the block, bypassing the spark plugs. i'm really thinking it's the wires.