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Discussion Starter · #1 ·
Hello guys please excuse me im so excited that i can't even write properly....

I was out for a sunday ride 1 hour ago fueled the car up and drove around a little bit. I formerly had issues with the car that it takes 10 miles till it runs properly when the night was a little bit cold and there must be dew in the optispark. The car feels powerless and sometimes there are very small and silent detonations, like the clicking of a relay. Today this problem was even worse it took nearly half an hour till the Optispark was dry and the car had full power so everthing fine till i nearly reached my house.

A huge BANG appeared it really scared me even when the windows were closed and the car felt like it ran on only 2 cylinders or so. At first i thought a piston or rod broke and i looked all over the engine or looked at the tail when it ran... nothing no smoke no oil no fume...

But huge missfiring when you hit the gas. The pre owner said that they never touched the optispark so it must have 150000 miles on it (summer only car).

I purchased an ALDL cable 1 week ago but it takes a while till it arrives in europe/austria that i can make a readout. But the SES light or something else didnt come up nothing only that loud ongoing misfire.

Yesterday i drove 50 miles and when the car warmed up everything was fine it appeared from one second to another and now the engine shakes, rattles and has no power. I'm glad i made it to my parking lot where the car sits when I have to go to work etc.

maybe you have a tip for me but everything seems to me that the optispark is dead...

Im very sad because i bought the car and since that i only drove mayme 1000 miles :(

Kidn regards from Vienna :) Marvin
 

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When my opti was bad that thing backfired so loud me and my wife and i'm sure everyone else around thought we were going to die....lol

But mine never acted funny at first then got better, it was always the opposite. Once the car warmed up I couldn't drive it until it cooled down.
 

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Discussion Starter · #4 ·
I will check shbox.com's tutorial and measure all ICM module voltages and so on next week, then i will readout the pcm with my hopefully soon arriving aldl cable. then i should know more.

i am very happy that you also had this backfiring thing. it was just so damn loud that was cruel.....

thx for your reply
 

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Discussion Starter · #6 ·
I have contact to all pre owners except the first one who owned the car till 130k miles now it has 160k and no one of them said they swapped the opti. i think it is gone due to mileage :)

but damn can missfiring be THAT loud? it really scared me it sounded like a extremely loud new years eve explosive detonated under my car :)
 

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....i know the opti is very easy to blame....but i have driven my lt1 in flooding rain, got the opti wet, dried the next day and ran just fine. it was a GENUINE GM opti though...as with all my GM parts. but stumbles bangs and "miss fires" are very broad. start with air fuel and spark. check vacuum leaks, intake leaks. check fuel pressure, if its that original i'm sure that fuel pump is getting ready to go six feet under. and of course spark. wires, plugs, spark leak, loose plugs, loose/broken wire. i just like to K.I.S.S. things first... "Keep It Simple Stupid"
 

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Discussion Starter · #9 ·
Hello there, spark plugs and cables are barely 5k miles old, the pre owner replaced all that.

That issues with the optispark appeared during 100miles of driving when i got the car i had to warm it up a little bit then it ran perfectly and very strong (compared to my friend ls1 camaro). but it got worse from day to day the car sit over night and yesterday it was worst and now it is not even driveable.

When this problem appeared at first the car was still good driveable during the warmup phase only at WOT it made misfiring. but then the misfirrings got louder and louder it rattled the first 10 minutes like a bearing is broken. when the engine reached its normal operating temp the rattle started to get more and more silent and suddenly it was gone and the car had full power and gas response.

Yesterday the same drove 30 minutes with rattle - rattle gone- drove 1 hour with full power and suddenly after a hard takeoff from a traffic light this huge bang and then the car ran very very poor with lots of detonations an misfirring.

maybe my mistake was to wash the underbody slightly from back to front with a high pressure foam lance. i didn't really aim at the optispark but maybe a few drops are enough to knock it out.
Is the MSD for 94,95 which is then also vented water resistant? i think it should be because it doesn't have the holes on the bottom like the unvented one am i right?

kind regards :) Marvin
 

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Discussion Starter · #10 ·
Hello, tonight I questioned myself that if i do the voltage tests and there are 1-4V ac an the optispark, it doesn't automatically mean that the optical section is in perfect working order right?
Because even with a true rms meter thats just a mean value for a voltage.

For correct measurement i have to connect an oscolloscope right?

which signal should I see at this 1 pin of the opti? the high or low res pulses?

If the optical stuff is ok it should be fine again with just replacing cap right?

regards
 

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Hello, tonight I questioned myself that if i do the voltage tests and there are 1-4V ac an the optispark, it doesn't automatically mean that the optical section is in perfect working order right?
Because even with a true rms meter thats just a mean value for a voltage.

For correct measurement i have to connect an oscolloscope right?

which signal should I see at this 1 pin of the opti? the high or low res pulses?

If the optical stuff is ok it should be fine again with just replacing cap right?

regards
You don't look for the 1-4vac at the opti. It is done at the ICM connector, because the PCM generates that signal. That test is fine for determining if the firing pulse is getting there. If you want to look for high and low res signal wave forms, you would look at the opti pigtail. The wiring diagram shows which are high and low res.

A cap and rotor issue is not going to come and go. Yours sounds like an electronics issue that is affected by temperature. So, unless you can test signals under all temperature conditions you may be fooled into thinking that a part is ok, when it might not be under all conditions.
 

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Discussion Starter · #12 ·
Hello, received my aldl cable this friday, connected it everything fne with the 94-95 reading tool here from the forum guy.

No engine or transmission error codes only code 62 from SIR, it means redundant circuit code or so says the diagnosis tool. dont know whats worng the sir is a little bit strange the aribag light is on and after driving around for about 10 minutes and start the car again its off. what menas the code 62? the airbags cant deploy everything on the car is fine absolutely no accidents.


but no other error codes, which also means a faulty optispark. the car is misfiring the whole time in idle but it throws no error. shouldnt it throw a knock error or something like that? will check the opti circuit in 1 week only have time on sunday :)

kind regards
 

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Hello there, spark plugs and cables are barely 5k miles old, the pre owner replaced all that.
that's a warning sign to me... it's very easy to mis-route plug wires.. you should confirm none of them are burned
 
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