Corsica misfiring after rain (nowadays problem with IAC valve)

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Re: Corsica misfiring after rain

Postby Bapsu » Mon Feb 05, 2018 11:07 pm

No its 12v afaik



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Re: Corsica misfiring after rain

Postby 3X00-Modified » Wed Feb 07, 2018 9:08 am

It is 12-14v, but I would not just smack them to battery... IIRC the best thing to do is get a tool that will pulse them as they are designed to operate.



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Re: Corsica misfiring after rain

Postby ifixalot » Wed Feb 07, 2018 5:46 pm

Wasn't sure about the voltage but I didn't think it proper to just apply battery voltage to test.
I didn't want to read he now needs new injectors.
There is info out there that says to test with a 9v battery to avoid too much current to the injector and thus damage it.
Still another site says to test with 5 volts.



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Re: Corsica misfiring after rain

Postby Bapsu » Wed Feb 07, 2018 10:04 pm

Hm. I already thought im gonna give max 1 second pulses to them with wires, to prevent overheat or sth.

Maybe I'll hook up 9v battery also.



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Re: Corsica misfiring after rain

Postby Rettax3 » Thu Feb 08, 2018 11:49 pm

Definitely be careful. Back in the day, I toasted both injectors on a TBI Police Special 5.7 Caprice detective car by pulsing them too long (multiple 1/4-1/2 second bursts). They were mechanically sticking and thus bad anyway, but it was still a bad way for their coils to go. One second is a HUGE duty-cycle for any injector -I wouldn't recommend it. Ohm-test them -specs are available on here somewhere. If you still have suspicions that they are clogged, sticking, etc, failing in some mechanical aspect that would not show up on the electrical-side test, then leave them attached to the fuel-rail, place small jars (baby-food jars are perfect) under each injector, KEEP A FIRE-EXTINGUISHER HANDY, and have someone crank your car while you watch them operate. This is a good way to check them for flow-matching too, making sure you not only have good atomization but similar volume output. Good luck.


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Re: Corsica misfiring after rain

Postby Bapsu » Fri Feb 09, 2018 3:55 pm

Hmm, ok. I'll check it out and give really short pulses. Its safe to run start motor while injectors are pulled out?

Also, where is fuel pump relay and how to bypass it? To get pump run constantly?

Do you guys think lamda would be the culprit for hard start while hot?



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Re: Corsica misfiring after rain

Postby Rettax3 » Sat Feb 10, 2018 12:35 am

-Safe? Atomized fuel spraying anywhere can be dangerous... If contained properly, with safeguards (like extinguisher) and common-sense, should be okay. Be careful not to let ANYTHING down the injector holes (or intake ducts, for that matter) in the manifold too, especially while cranking. Otherwise, it won't hurt the engine to crank it without the injectors.
-The relay should be near the right-side strut tower, but I am not 100% certain on a '93.
-Try unplugging the O2 sensor when it is misbehaving -the ECU will throw a code, and default to a richer condition, but it won't be getting bad sensor readings tripping itself up... I doubt that is your problem though.


1989 SuperCharged 3800 Srs-II (First)Six-Speed GTU
1990 Turbo 3.4 5-Speed T-Type
1990 4.0L 4-Cam 32-Valve V-8 5-Speed Indy GTi (Project)
1990 Stock(!) 3.1 MPFI Auto Indy
1995 LA1/L82 4T60E Z-26
1995 3.4 DOHC Turbo 5-Speed Z-26

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Re: Corsica misfiring after rain

Postby Bapsu » Sat Feb 10, 2018 12:38 pm

Nah, dont worry about it. Of course I put jars under injectors. Its also -5 to -10 here in Finland so nothing burns nearby.

Gotta take look for the relay...

I actually am coming to conclusion that its still something with iac valve. The engine started quite fine with broken iac (stuck), after i put working iac in i got hard starts again... my friends fleetside had broken iac, erratic idle + had to crank 5-10sec to get it start.

Since even working iac wont help and idle is still bit low (600rpm), erratic and i still got hard starts, I think there is something work with computer controlling the IAC... and yes, I have performed idle relearn few times, without success.



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Re: Corsica misfiring after rain (nowadays problem with IAC valve)

Postby Bapsu » Wed Feb 14, 2018 10:03 pm

Ok,

Injectors tested. No leaks. Put power on while all injectors were connected. When you put power on with key, each injector sprays one load of gas. I think this is supposed to happen?

Made two leak tests: First on, i disconnected each injector wires, and put full pressure on the line. None of the injectors dropped anything. So all ok here.

After first leak test, i took each injector and gave it short pulses with 9v battery. Each one sprayed beautifully, and none had leaks after spray stopped.

Also ohmed out each injectors: all were 11.9-12.1 ohms. So I think my problem isnt here.



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Re: Corsica misfiring after rain (nowadays problem with IAC valve)

Postby Bapsu » Wed Feb 14, 2018 10:06 pm

Moving to next suspect: IAC valve operation. Seems like also my current IAC (stolen from another Corsica) is also stuck. Cant move the pintle with my fingers? If i remember it right, I could move my previous IAC pintle easily with fingers when I cleaned it up.

I also managed to find out from internet, that at least with gm 3.4 have had IAC problems, which caused hard start. Reason why this happens, is because the pintle is stuck too far, blocking the air coming in. Is there any way I could check if the ECU is directing IAC in a right way? Meaning in example how can I know which position should the valve be in different situations?

Any help is appreciated... This car starts being bit too much for my little brains. :D



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Re: Corsica misfiring after rain (nowadays problem with IAC valve)

Postby Rettax3 » Fri Feb 16, 2018 1:42 pm

The IAC should not be movable by hand -a TINY bit of wiggle is fine, but if you can move it freely in and out, it is broken. A Noid light (typically used for injector testing) can be used to verify ECM signal to the IAC valve -it operates on short pulses of 12V, forward of backward (two circuits, hence four wires), and the Noid lights operate fast enough to register the pulse, just like the injectors. So, if you can get your hands on one of those, we can help you figure out which two wires to hook together to test forward (closed, lowering idle) and reverse (open, increasing idle).
I am concerned though, that you may have damaged or jammed the 'new' IAC when you installed it -if it was extended too far and bottomed-out (either from carbon/debris build-up in the housing, or a lack of proper gasket, or over-crushed old gasket), it could be malfunctioning now. Also, have you checked for vacuum leaks? CAREFULLY use a spray, like carb-cleaner if available to you, around the intake, throttle-body, any/all vacuum lines you can find, while the engine is running. If the RPM fluctuates while you spray at something, there is a leak. If you do find one, keep looking, make sure it isn't the only one...


1989 SuperCharged 3800 Srs-II (First)Six-Speed GTU
1990 Turbo 3.4 5-Speed T-Type
1990 4.0L 4-Cam 32-Valve V-8 5-Speed Indy GTi (Project)
1990 Stock(!) 3.1 MPFI Auto Indy
1995 LA1/L82 4T60E Z-26
1995 3.4 DOHC Turbo 5-Speed Z-26

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Re: Corsica misfiring after rain (nowadays problem with IAC valve)

Postby Bapsu » Fri Feb 16, 2018 9:40 pm

My idle is quite fine, though its sometimes quite low, around 600rpm. Only real problem is starting, where IAC seem to have effect on, since with the old, broken one the car started just fine (in most situations).

I actually took picture of the iacs four wires, but is there somewhere pinout so I could know what wire to inspect for voltages. There are 4 pins, I guess 2 are for reversing mode (pulling pintle in) and other 2 for push mode (pushing pintle out).

Here is picture of wires: https://imgur.com/8L6E36Y

Intresting side is that this another corsica, with broken IAC is starting just fine... at least for few times I have tried starting it. Since my injectors arent leaking and I got steady fuel pressure, I am next focusing to ecu, if I find out that theres something weird with IAC cmds/ fuel delivery during start up.



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Re: Corsica misfiring after rain (nowadays problem with IAC valve)

Postby Bapsu » Sun Mar 11, 2018 8:08 pm

Running soon to dead end here. Iac seem to act ok. Even though i unplug i when car is running warm, i check its not stuck closed, I still have to crank to get it started.

New notice: if i crank in short (i.e 1 second) cycles, after few cycles (around 5) it starts right up. Still fuel pressure? Pressure lost only when engine is warm? And when i cold start, fuel pressure is being hold?

I checked injectors only when it was dead cold...

Another notice:

I start the engine dead cold (starts great), run 10 seconds and turn off. Then when i try starting it again, i need to slightly crank. Not much, but still more than i should need to.



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Re: Corsica misfiring after rain (nowadays problem with IAC valve)

Postby Bapsu » Sun May 13, 2018 7:58 pm

Well well, time to post little update here.

Good news first: Corsica is now my daily driver and in great shape. :) Turned out, that hard start with warm engine was caused by failed ecu, swapped another one in and no problems since that. Also had to order new upper water hose and right after installing that realized that radiators upper hose mounting point was cracked and leaking. %) Both replaced now, car holds coolants in and runs & pulls & starts like a beast. Changed transfluids and coolants also along the other repairs.

Since its summer soon here in finland also (bit early lol, +30 degrees at May is quite warm...) I'll keep driving this thing. Gotta already say I enjoy that torque and sound... also AC is cooling quite well. Gotta post some pics here when i got time to take some. :beer:



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Re: Corsica misfiring after rain (nowadays problem with IAC valve)

Postby GT_Indy » Tue May 15, 2018 11:35 am

Wow. I wonder how many of these computer boxes will be avaliable in another 20 years. lol
I had 3 fail a few years ago. Usually the car just stopped working all together. Only one box made it run rough but it died a minute later.


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