HELP Missfiring

Ok so I just got my 95 z going and it's running real rough. It feels like a consistant miss and the car doesnt have the power it should, expecially at low rpms. And at idle the car shakes horribly. I already put new plugs in and double checked that at all the wires are right and everything is good. Then I was thinking it's injectors, so I pulled the wires off of each one, one at a time to see which ones run worse or dont cange anything. Turns out that when I pull the wires off the # 3,7,8 cylinders it runs the exact same (from when they are all on) and there is a noticable differance (worse) when I pull any of the others off. So does this confirm that the injectors are bad? I already put injector cleaner in the gas and am running it through right now but I'm wondering if I just need a new set? Can anybody help me? Is there anything else I can test or try? Thanks.

my best guess, would be a failed optispark distributor, they are notorious for causing similar problems to what you are describing. they are placed below the water pump and on the lower front of the engine, so they get wet very easily and cause corrosion inside the housing causing misfires. the dealer price on one of these is over 600 dollars, i reccomend www.gmpartsdirect.com, i think the last time i went there it was under 300 bucks.

i'm not sure what the injector values are suppose to be, but you can check them yourself. they should be fairly close to each other resistance wise, but still doesn't rule out a bad injector. do 95's have a mass air flow sensor? or i'm with IROC bout the optispark. do the basics first tho, check fuel pressure and engine vacuum.

I would be more worried about it being an ignition problem except for when I changed the plugs I checked and everything had good spark, plus it is very consistant, regular miss. It does have a mass air flow sensor by the may. I dont know for sure what else would cause just the 3 cylinders to stop firing. It also heats up fast to about 190 (at least thats what the gauge reads) but it smells like its getting hotter. It stays at that temp though so I dont think it's over heating, but just running hot. What should it be running at?

optispark, its the very first thing i would look at. at the very least, i reccomend you pull it, and take it apart on a bench, and look for signs of corrosion or rust. dont bother trying to clean it and put it back in, just get a new one. it is a bit of a bother, you have to pull the harmonic balancer and the water pump to get it off. if you get to that point ill walk ya through it.

not to disagree w/you IROC about it being the optispark, but thats a hell a price to pay if it doesn't fix the problem. if i was gonna spend $350 and up for that thing, i wanna know it's gonna fix the problem.

you can get a spark tester, it's usually a pen that you hold next to ur plug wires so you can watch em spark. i'd start with the plugs and move backwards. find the cylinders that are mis-firing then test the plugs, wires then move to the optispark

Check and see if it is fuel related. Grab a can of carb clean and pull off a vacuum hose and spray some in. Should smooth out if its not getting fuel from those injectors.

lol, by all means disagree with me, it would be a boring forum if ya didnt ;) good advice by the way on both fronts, but if you have already traced the problem to three cylenders, missing on a regular basis, i find it hard to beleive unless you got a tank of crappy gas that three injectors simoultaniously gave out. more likely its some sort of optispark failure, just speakin from experience, its almost textbook.

check the wires again! It is VERY easy to get them mixed up. The opti cap is labeled with which wire is which. I have seen people switch stuff out and run wires down the opti on the drivers side in 1,3,5,7 order. I had 2 wires crossed when I put my motor in and the car was idling poorly, it would drive okay above 3k, but at WOT it felt like it was pushing a tractor trailer. I checked the wires a few times and kept looking over it somehow.

I'll double check the wires again to see if they are mixed up but i thought i was careful about keeping them straight. And when I was switching the plugs I tested for spark and they all were good. I did just buy the car and it had a blown head gasket which I fixed but the guy did say it had been sitting for a while and it looked like even longer. I did notice a differance once I got good gas in it and I dont know how it was running before either. I haven't worked with injector at all really, could someone tell me how to get them off and test them? Thanks

how did you test the plugs? pulling them out and watching them spark isn't the right way to do it. just because they spark outside the block doesn't mean they will spark under compression.

i'm not sure how you get the injector wires off on the LT1's, but on the tpi you remove a wire clip then pull the connector off. testing injectors is kinda like testing cylinder compression. use an ohm meter and test the resistance on each injector and write each value down. then compare all the values, none should vary more than 3-5ohms i wouldn't think.

OK, I tried some more things. I checked to make sure everything was on and on in the right place. I checked for spark with a timeing light while it was running (is that an ok way to check?). I cleaned the injectors and then switched a couple of the ones that I thought were bad with ones I know are good and that didnt change anything. So I dont think its the injectors them self and I dont think its spark. All cylinders have good compression but #'s 3, 7, and 8 arent fireing, at least that's what I think from how I said I tested that before. Does this still sound like it could be the optispark? 4onFloor could you or anyone explain to me again how to test that the injectors are injecting. Where do you check the resistance? From where to where? Someone suggested to spray carb cleaner into a vacuum line, is there a certain hose I should use? Cause I would like to try this to see what it does. And also if anyone has any other ideas for me to check, let me know. Thanks

not to sound like a broken record, but yeah, still sounds like optispark to me. however i will say that you could have a PCM problem, or a wire rubthough on those injectors, however those are VERY unlikely senarios. i would say its optispark. at the very least, i would pull it and check the internals for any corrotion or rust.