Okay guys, so I've been gone all summer preparing for med school, and I finally got around to replacing my plugs and wires. First off, that's one hell of a job. Took five hours, so I figure that wasn't too bad for 8.5mm MSDs. Here's what happened:

Got done changing the plugs and wires (including coil wire), fired her up, and the engine shake was still there (both in neutral and in gear). So now I need to move onto something else. Help me out here guys, am I on the right path?

1. Check fuel injectors
2. Check knock sensor/module?
3. Change out Optiplex.

Are these three relevant and could actually cause my continued engine shake? It's so obnoxious, but not that I changed the wires, it is worse, presumably because now the other cylinders are firing well while another is not firing, exaggerating the problem. Does this sound right? I haven't for codes because I'm a 95, so I can't borrow one and get a scan. Stupid year..... Help!

 

Look for the dead cylinder by pulling the injector clips one at time. Once you have that, it's easy from there.

 

Could it simply be a mechanical vibration?
My car vibrated in neutral/park so it couldnt have been the driveshaft or anything. Turned out there was a slight bind in the transmission mount or something, loosening it and tightening it back up fixed it.

 

I wish....Doesn't matter whether it's in gear or not, the engine itself is actually shaking. I suspect a misfire.

Speedy, thanks a lot. I will do that. If it's not a FI though, then what? The opti? Dam they are expensive.

 

Pulling the fuel injector clip to find the dead cylinder does not give you just fuel injector issues. It tells you which cylinders are dead for ANY reason. If you remove a clip and nothing changes, you simply found the dead cylinder. Then you have to figure out WHY.

 

You're a genius! Now, how do you test fuel injectors? Let's say the cylinder is dead, but I suspect the injector. Can I test it somehow?

 

You can take a DVM and set it to ohms (greek omega letter). This checks the resistance. I believe it should be around 12-13 ohms(I think closer to 13), but I would check all of them and they should all be pretty close to the same readings.

You can also take a screwdriver or a stethoscope, (I assume you have possibly since your going to med school)while the car is running, put it on the base of the injector, and check to see if they are clicking consistently and uniformly. I also believe there is a way to check and see if the computer is sending a signal to the injectors. You may need an o-scope for this, but not entirely sure. I'm sure there are people on here that can give you more in-depth procedure. I am fairly new so take what I say with a grain of salt. This is what I did to check mine though.

 

Alright, thanks!

I also suppose that if I replace one injector all the others have to be replaced to in an ideal situation?

 

I don't know on these cars........I have replaced just a single injector on 4.3 s-10's before and haven't had a problem. Plus it a lot cheaper......I wouldn't swear to it either way though.....You absolutely need someone with more knowledge than me on that one. Hope I help some atleast though.....

 

First things first. Check your oil (by the dipstick) to see if it smells of gas. If it does, change your oil immediately. See below for an explanation.

NOW Find any dead cylinders. That is the whole goal of this.

To actually answer the question you asked:
If you want to investigate fuel injectors, you simply lift the fuel rails up. Then have someone crank it over while you inspect the "squirt pattern" of the suspected injector compared to the adjacent good injectors.

Incidentally, measuring the resistance of the injector may show the windings in the injector are good, but it still does NOT mean it is working. Nor does checking the pulses from the PCM with a noid light.
BUT, my money is on a spark issue. Spark issues are far and away more common than injector problems.

My common sense suggestion is find the dead cylinder(s) then remove at least the spark plug from that cylinder. If not all of them which is what I recommend.

If the plug in the suspect cylinder is black velvety looking, you know it is either getting the proper amount of fuel and has a spark issue. Or it is getting too much fuel which is less likely.

When trouble shooting an unknown, you sometimes follow the path of more common failures. Then if they are not the cause, move to the ones that are less likely.

Don't mistake removing an injector clip to show only fuel problems though. Understand that it takes 3 things to fire a cylinder. Fuel, spark and compression. By you removing one those 3, and the running characteristic of the engine does NOT change. You have merely identified the cylinder that was not working before you removed it. At that point, you don't know which of the 3 was lost to the cylinder that caused it to stop in the first place.

Now a note of caution: If the cylinder is down because of loss of spark, which is likely. You have a potential for serious damage. While the engine is rotating, the injectors are squirting fuel. If there is loss of spark, the fuel continues to build up in the cylinder(s) and can eventually get to the point where it "soups" the cylinder. In that, it washes off the oil film that is supposed to be on the cylinder walls. Then the rings start "galling" the cylinder wall. Now you have a big BIG can of worms.
The fuel smell could be a leaking injector which is totally flooding the cylinder making it too rich to fire but this cause although possible, is much less likely.

Get the dead cylinder(s) found before something like this happens. Oh yeah one last thing. Through experience I have found that a SBC will not run if it has 3 or more dead cylinders. So I feel confident in saying you won't have more than 2 dead cylinders. Hope this info helps you.

Dave

 

8-| Okaaaay.... Helps a lot, but I have been driving this car for a while with the misfire because I heard it doesn't hurt for short trips. I did just change the oil and it was normal, though. I also just changes the plugs and wires over to MSD and NGK TR55s. If the problem is spark, it's going to be the opti or coil. As far as the dead cylinder goes, I'll check the injectors and see what's up.

 

Oh yes, sorry for the double post, but also, since changing the plugs n wires, the ABS INOP light is on. Any clues?

 

A very common cause is your plug wires are too close to the ABS wiring. But the big question is when you changed the plugs and wires, how did the plugs look?

 

Two were fairly grungy looking, but not horrible. I've seen worse from other engines. I am sure one or both are involved in the misfire, but will know for sure after injector test later today.