wrenchin

workin on this 93 z28 for a friend, its all stock. he just bought it and i did usual tune up, fuel filter, plugs, wires, cap and rotor, since it had a little hesitation and sometimes some poppin through the exhaust under 2k rpm. ran a little better for 2 weeks and then it quit on him goin down the road. the car will start and run now while its cold. once it gets warm it dies, then while cranking the tach jumps all over and the car refuses to start. since it doesnt have a crank position sensor the only rpm sig comes out of the opti right? ive got the car on my lift right now with the opti torn off so i guess its too late to be wrong, he wanted an msd billet dist anyway. so am i on the right track?

bingo

Check the ICM and coil as well.

wrenchin

yep, he was on his way to get a new coil when it died. but the coil wont cause the tach to go spikey will it? after a lot o searchin i found that the icm can screw up the tach sig too. i can tell the opti got really wet though its got water marks on the slotted wheel. i can see where the water was flung out from the center. if it does end up bein the icm then we just jumped the gun a little on the 135k mile opti. prob wouldnt have too much left in it anywho. ill post up what happened monday when the part comes in.

Dave89IROC

I have seen coils effect the tach reading, no idea how, but it did it

wrenchin

the coil can do that too? good ol GM engineerin' huh. I noticed that the optical sensor inside the old opti had the mitsubishi diamond star stamped on it. did gm outsource that sensor to mitsu or is this an aftermarket piece?

bingo

I have taken apart 4 optis and they all had Mitsubishi parts inside. I had a coil go out on my car. It wouldn't get above 2500RPMs and the tach would go crazy. I was sure it was the opti. On a whim, I tried another coil I had. Started right up and ran perfect. I bought a new coil and haven't thought about it again.

wrenchin

Doh! shouldn't have let myself get rushed into a diagnosis, if it were my car and money i would def have taken more time to test and research this. good thing i'm the only guy in the world who loves to do extra/needless work maybe I'll get lucky on the old parts swappin/guessin technique. we'll know tomorrow!

wrenchin

the opti fixed the dyin and no start. still had the hesitation that he bought the car with, though it does start easier now. replaced the coil with msd and the icm with gm since both parts were some parts store crap. still got some hesitation up until about 2k. the fuel pressure is about 38 at idle with vac and 45 without vac, so its good. maybe fuel injectors? the car does have 135k on it, maybe the injectors need replaced/rebuilt. its hard for me to diagnose this since i cant scan obd1 cars.

bingo

Have you considered a fuel filter?

wrenchin

did that first thing, check my first post.

bingo

My bad.

Dave89IROC

have you cleaned the MAF?

2000GTP

An injector flush may be a good start, also, I would make sure you have good, clean connections everywhere.

wrenchin

there's no maf on a 93, its speed density. i need to take a look at them injectors though.

fbodyboy

injectors are a good probablity. on my first transam i had, it had a hesitation and stumble at idle. first thought it might be opti but decided to try an injector flush because it needed one do to mileage. cleared the problem right up and even increased milage a noticable amount.