A Fun Ride Home: Please Help

[granit_silber]

Hey Guys,

Today on my way home I noticed that something funny was going on.
When I stepped on the accelerator, the car felt a little rough. As it's only 87 or so here, I had the windows down and also noticed that when the engine was rough I heard a clunk sound in the read-end.

I started thinking Guibo (that was after the "Oh Crap!). However, after a little further down the road the clunk wasn't a clunk it was a puff; and rather than the rear end it was coming out of the tailpipe!
The puff happens only under decent acceleration (pedal pushed 1/2 or further). When the car is crusing it's okay and under slow (read grandpa) acceleration it's okay.

Now the noise isn't a pop or backfire, just a puff. I haven't changed the fuel filter(it's due and I've ordered one). I did change the spark plugs earlier this year.

My thought is that I am having a no spark situation in one of the cylinders.

So here's my question...
How do I check to see if my diagnosis is correct and which cylinder the problem is? I don't own a multi-meter, timing light, etc...
I do own basic tools and sockets and live 2 miles from a Harbor Freight store.

Thanks!
-ashley

[DanDombrowski]

I always thought a no-spark would throw a check engine light, but I may have spent too much time working on the newer mitsubishi engines that do that, ours might not.

[granit_silber]

I always thought a no-spark would throw a check engine light, but I may have spent too much time working on the newer mitsubishi engines that do that, ours might not.

okay, so now i'm getting nervous. No check engine light.
-ashley

[Kalevera]

The diagnosis makes a lot of sense, but it's probably just a dead plug, coil pack or lead. Or a combination thereof if the valve cover gasket is letting oil leak past and into the plug wells.

Ash...I'd pull the coil packs and inspect them for leaks, also visually inspect the rest of that area. It really sounds like a misfire.

best, whit

[granit_silber]

The diagnosis makes a lot of sense, but it's probably just a dead plug, coil pack or lead. Or a combination thereof if the valve cover gasket is letting oil leak past and into the plug wells.

Ash...I'd pull the coil packs and inspect them for leaks, also visually inspect the rest of that area. It really sounds like a misfire.

best, whit

Thanks Whit!

I did notice that when I changed my plugs that one of the wells had a small amount of oil in there. By small amount I mean like 2-3 drops worth.

What does all this entail? I can pull the coils, wires, and plugs but how do I check to see which one is the problem. Once I pull a plug must I replace it with a new one? How difficult will the valve cover gasket be to pull and replace? Can I do it with basic tools (sockets, etc...) or do I need special stuff?

Again, thanks for the info Whit!
-ashley

[Kalevera]

Surely.

Well, there really shouldn't be any oil in there. I'm in the middle of a 540 nikasil block replacement at work. The car had been sitting in it's "unstartable" state for a few months, sometimes with the hood unlatched. I pulled the nicky and removed the coil pack covers to discover water, oil....you name it, it was in there :) But yes, it should be dry as a bone. Oil kills the leads.

It's not that much work, all in all. The plugs and leads are routine stuff. So is the valve cover gasket, if it needs to be replaced. I finally learned a thing or two about coil packs. Previously, I'd seen them DIE when they oozed the "candy" insulation. Caused misfiring, all sorts of junk like that. Bentley should have the specific procedure for testing them. Then, I started seeing (and hearing about) instances wherein they still worked fine yet were oozing. The coil pack (or ignition coil for us M20 and M30 people) should be replaced if any candy is visible: the lack of insulation/burnt insulation can fry the ignition stage in the DME, it's happened to people in my shop.

best, whit