spark, fuel, compression still wont start
12-04-2010, 06:55 PM
#1
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spark, fuel, compression still wont start was at the track last night. on my second run i did my burnout rolled up to the line, waited for the other car, start to rev up to launch and my car dies. turn it back on 3-4 times and it would only run for about 5 seconds idling at ~2-300 rpms.
pushed it off to the side, then it wouldn't start at all. towed it home. now it's in my driveway and still wont start. did a compression test and got:
1 - 130........2 - 140
3 - 80 .........4 - 140
5 - 130........6 - 140
7 - 130........8 - 115
i know it's not good, but all i care about right now is getting it running which it should do with those numbers.
i pulled the fuel rail and every injector is working. have 40psi with key on.
pulled the coil wire and i'm getting good spark from the coil. pull a wire off a plug and getting good spark there too.
now i'm stumped, have compression, have fuel, have spark. what am i missing? i have code 41 for Electric spark timing (EST) open circuit. idk if that came on when i unplugged the icm to do the compression test?
car info:
1995 z28 automatic
turbo'ed @ ~8-9psi
motor is just the completely stock 145k mile lt1
pushed it off to the side, then it wouldn't start at all. towed it home. now it's in my driveway and still wont start. did a compression test and got:
1 - 130........2 - 140
3 - 80 .........4 - 140
5 - 130........6 - 140
7 - 130........8 - 115
i know it's not good, but all i care about right now is getting it running which it should do with those numbers.
i pulled the fuel rail and every injector is working. have 40psi with key on.
pulled the coil wire and i'm getting good spark from the coil. pull a wire off a plug and getting good spark there too.
now i'm stumped, have compression, have fuel, have spark. what am i missing? i have code 41 for Electric spark timing (EST) open circuit. idk if that came on when i unplugged the icm to do the compression test?
car info:
1995 z28 automatic
turbo'ed @ ~8-9psi
motor is just the completely stock 145k mile lt1
12-04-2010, 11:31 PM
#3
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how is that not enough compression for it to run? i've driven cars with much worse compression than those numbers. a couple weeks before i was trapping 113-114mph with the same motor
12-05-2010, 12:06 AM
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Even if there is spark from a plug wire it doesn't necessarily mean it's sparking at the right time. Aside from your compression readings, it is possible the rotor screws have backed out causing the rotor to spin freely and send spark to random cylinders. I would check your opti before getting too involved in what looks to be an engine rebuild.
12-05-2010, 09:56 AM
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Even if there is spark from a plug wire it doesn't necessarily mean it's sparking at the right time. Aside from your compression readings, it is possible the rotor screws have backed out causing the rotor to spin freely and send spark to random cylinders. I would check your opti before getting too involved in what looks to be an engine rebuild.
i'm assuming the only way to tell is to pull the opti off and take it apart? should it throw a high/low res failure code or no?
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12-05-2010, 10:06 AM
#8
I had a very similar problem recently. After changing the opti I found that my msd coil wasn't letting the pigtails plug in snug enough and wasn't giving strong enough spark. I switched to a stock coil and it fixed it
Id check into the coil and icm before I'd pull the opti.
Id check into the coil and icm before I'd pull the opti.
12-05-2010, 10:55 AM
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if the icm was bad i wouldn't be getting spark tho right? all the wires are getting spark. i did get this code before when i had an aftermarket coil and it went away when i went back to the stock coil, i'm still using the stock coil now though. i have a spare opti laying around (as all lt1 owners should 
) so i'll throw that in and see what it does. i sprayed some starting fluid in the throttle body and it back fired a little bit. hopefully the opti is just throwing the timing off or the rotor came off
) so i'll throw that in and see what it does. i sprayed some starting fluid in the throttle body and it back fired a little bit. hopefully the opti is just throwing the timing off or the rotor came off 
12-05-2010, 09:05 PM
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Anyway, I agree the OP's numbers are not looking good with that #3 cylinder being down. For N/A I have always shot for somewhere between 185 and 200.
12-05-2010, 09:42 PM
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Is that a GM opti? I hope wherever you got it you will raise hell for a refund.
That does seem just a tad high. Like "WTF" high. When I had a LPE 211/219 pulling 19" of vacuum it was giving 200 to 210psi of compression.
Are you sure about those numbers? I'm not saying you are wrong, but that seems extremely high for a pump gas engine especially since you have a stock short block. It seems like you would have to have very thin head gaskets, heads milled alot, AND have a camshaft with tiny duration and overlap numbers to come up with that high cranking compression.
Last edited by SS RRR; 12-05-2010 at 09:48 PM.
12-06-2010, 02:01 AM
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sorry guys cant afford a rebuild. really wish i could but until it literally blows up it's staying low on compression
and yes it's a gm opti. has a one year warranty and it's only 10 months old (didn't realize it was that old when i posted before) so hopefully i'll be getting a new one tomorrow
and yes it's a gm opti. has a one year warranty and it's only 10 months old (didn't realize it was that old when i posted before) so hopefully i'll be getting a new one tomorrow
12-06-2010, 12:59 PM
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You might be on the verge of that very thing happening. As a rule of thumb if you have more than a 10% drop in your compression numbers between cylinders - not good things are already happening.
12-07-2010, 12:48 PM
#19
Nice opti destruction!
It really doesn't cost all that much for a rebuild. You could probably get away with a hone and re-ring for cheap, especially if you do everything yourself (provided the rings are the problem). Grab some wrenches and get that thing rebuilt!
Seriously, you're already on thin ice boosting a stock bottom end to 9 psi.
It really doesn't cost all that much for a rebuild. You could probably get away with a hone and re-ring for cheap, especially if you do everything yourself (provided the rings are the problem). Grab some wrenches and get that thing rebuilt!
Seriously, you're already on thin ice boosting a stock bottom end to 9 psi.
