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| mikee | 92 corvette wont idle, must pump gas when starting | ||
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Guru Newb
 
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I realy need some help here. engine wont idle and wont start unless you pump gas while cranking. have 40 lbs fuel pressure. have replaced optispark distributer, fuel pressure regulator, temp sensor and 2 weak fuel injectors (all injectors ohm out at 12.2 ohms) used noid lamp to check injector pulse (all flashing), pulled egr valve and cleaned (egr working ok), checked all electrical connections and vaccuum lines. im realy hope one of you gurus can help me outwith some answers
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Posted on: 2011/10/8 21:25
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| bogus | Re: 92 corvette wont idle, must pump gas when starting | ||
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Grand Imperial Pooh-Bah
 
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Sounds like a bad IAC - Idle Air Controller.
I would check it and the harness to it. Any codes? Oopsie, almost forgot: WELCOME!  |
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Posted on: 2011/10/8 22:47
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| mikee | Re: 92 corvette wont idle, must pump gas when starting | ||
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Guru Newb
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originaly had right o2 lean, prom failure and fuel enable failure. changed prom out with stage 2 prom I have with engine management only (no vats) made no differance so I reinstalled old prom (I could be wrong but I think the fuel enable failure pertains to the vats). cleared the codes and they never came up again. Is there any way to check out the IAC to see if its bad, it gets exspensive changing out sensors. thanks for your imput
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Posted on: 2011/10/9 3:40
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| bogus | Re: 92 corvette wont idle, must pump gas when starting | ||
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Grand Imperial Pooh-Bah
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These should about do it.
Attach file:  IAC Page 1.jpg (269.89 KB) IAC Page 2.jpg (162.84 KB) |
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Posted on: 2011/10/9 4:30
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| tjpreul | Re: 92 corvette wont idle, must pump gas when starting | ||
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Elite Guru
 
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I would also check the fuel pressure while cranking.
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Posted on: 2011/10/9 13:37
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Vegas wasn't built on winners. '92 auto, MSD, Banski, Taylor wires, SS lines, C5 rims, 3.07 gears, white gauges, seats from a '96. Motor: Forged rotating assy, Probe pistons, CC valvetrain, AFR heads, Procharger P1SC |
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| BillH | Re: 92 corvette wont idle, must pump gas when starting | ||
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The Stig Moderator
 
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Quote:
Mike, welcome. I agree with Andy & Tyler on checking the IAC. The fuel enable is part of VATS but all that is is a signal to the ECM to close the circuit to the fuel pump relay. The fuel pump relay still needs to be working correctly (even with VATS removed). Upon initial starting, the FPR energizes the pump for 2 seconds to provide pressure for starting. Injector pulses are different during start than thay are during run. There is a secondary way that the FP gets energized during start, if the FP is not energized when the key is turned on (problem with the FP relay or circuit), the fuel pump will be energized thru the oil pressure switch. If the FP relay is not working correctly, when the oil pressure reaches 28 psi during cranking, that signal is sent to the ECM and the FP gets energized (that bypasses the FP relay, I think). This can be a cause for long crank times. The idle thing does sound like the IAC. You may have 2 separate problems. Have you ever disconnected the IAC electrical connector while the engine was running? And did you change both 02 sensors? |
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Posted on: 2011/10/9 14:41
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| mikee | Re: 92 corvette wont idle, must pump gas when starting | ||
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Guru Newb
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the fuel pump energizes when key is turned on and I have 40 lbs pressure when running. have not changed o2s, I know they will give you idle problems but its having to pump the gas thats got me confused. car ran good until I started it up one day and it ran like crap, every one said it had to be the optispark so I changed that and it made no differance. I keep throwing money at it and not getting results. whish I had a computer to swap out just to eliminate that. thanks again you guys have been great
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Posted on: 2011/10/9 15:08
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| BillH | Re: 92 corvette wont idle, must pump gas when starting | ||
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The Stig Moderator
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Have you tried starting it with 1/4-1/2 throttle instead of pumping? Yea, the O2's have zero to do with starting, just idle. They are not even in the system in open loop. |
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Posted on: 2011/10/9 15:56
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| mikee | Re: 92 corvette wont idle, must pump gas when starting | ||
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ok I started the car with gas pedal part way down and it started right up with out pumping gas. now I have a deffinant miss in engine. It had a low rpm miss that cleared up at higher rpm now its ther all the time. has new plugs and good spark
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Posted on: 2011/10/9 16:37
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| mikee | Re: 92 corvette wont idle, must pump gas when starting | ||
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Guru Newb
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I think im going to change out IAC. I unpluged it and it did not change a thing. it does start right up holding gas pedal down part way, could the throttle position sensor have any thing to do with it or would IAC cause all of this?
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Posted on: 2011/10/9 17:27
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| bogus | Re: 92 corvette wont idle, must pump gas when starting | ||
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Grand Imperial Pooh-Bah
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IAC would be more of a cause here. TPS would set off all sorts of cascading codes...
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Posted on: 2011/10/9 23:31
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| Matatk | Re: 92 corvette wont idle, must pump gas when starting | ||
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Webmaster
 
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You can try cleaning the IAC and throttle body passages before replacing it.
matthew |
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Posted on: 2011/10/10 0:00
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2002 EBM convertible, Magnusson supercharger, cam, headers, etc. 1989 Corvette...RIP |
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| mikee | Re: 92 corvette wont idle, must pump gas when starting | ||
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Guru Newb
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I removed the IAC, looked a a little black but not bad, the air passages are pretty good size and they looked open. I put the IAC back in but I did not turn it all the way in and now it idles. ran out of time today but tomarrow im going tighten the IAC and see if it changes the idle. It either started working or its getting more air with it being out a turn, will let you know. thanks again
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Posted on: 2011/10/10 7:40
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| Matatk | Re: 92 corvette wont idle, must pump gas when starting | ||
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Webmaster
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The passages will get all gunked up with carbon deposits. You should really disassemble it and clean with an old toothbrush, pipe cleaners, etc, or at least remove the IAC motor and blast a ton of carb cleaner through the throttle body while it's removed. |
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Posted on: 2011/10/10 12:15
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2002 EBM convertible, Magnusson supercharger, cam, headers, etc. 1989 Corvette...RIP |
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| BillH | Re: 92 corvette wont idle, must pump gas when starting | ||
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The Stig Moderator
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Mike, did you unplug the IAC with the car running or shut off?
If running, there's a reset procedure. |
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Posted on: 2011/10/10 12:34
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| BillH | Re: 92 corvette wont idle, must pump gas when starting | ||
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The Stig Moderator
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BTW, if you clean the IAC, don't move the pintal in or out.
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Posted on: 2011/10/10 12:51
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| RickAnthony | Re: 92 corvette wont idle, must pump gas when starting | ||
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ASE Master Certified
 
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How was it running last time you shut it down after driving it? I wonder if you have a chunk of carbon holding te EGR part way open, you'll find when this happens they can be hard to start and Idle rough once running.. you usually have to hold the gas pedal part throttle if the EGR is stuck open enough..
just an idea.. as the IAC if shut all the way would cause a hard start and low idle.. but it shouldn't cause a miss fire.. |
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Posted on: 2011/10/10 18:07
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| mikee | Re: 92 corvette wont idle, must pump gas when starting | ||
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Guru Newb
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I was totally unaware of any reset procedures on IAC. just installed new one and seems to functioning ok. woud like to know procedure for future referance though.
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Posted on: 2011/10/11 2:02
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| bogus | Re: 92 corvette wont idle, must pump gas when starting | ||
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Grand Imperial Pooh-Bah
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reset is rather easy...
1. turn off engine if running. 2. depress gas slightly. 3. start and run engine for 5 seconds. 4. turn off ignition for 10 seconds. 5. restart engine and make sure all is ok. |
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Posted on: 2011/10/11 3:33
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The single biggest problem with communication is the illusion that it has taken place. - George Bernard Shaw Education is the best tool to overcome irrational fear. - me |
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| mikee | Re: 92 corvette wont idle, must pump gas when starting | ||
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Guru Newb
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I want to thank every one who came to my rescue and sharing your knowledge and expertise, your a great bunch of guys. when you have multible problems like I started out with ( leaking fuel pressure reg,worn out optispark dist, 2 bad injectors and a bad IAC) and nothing you do seems to make it better it kind of makes you brain stop funtioning.
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Posted on: 2011/10/11 5:57
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| bogus | Re: 92 corvette wont idle, must pump gas when starting | ||
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Grand Imperial Pooh-Bah
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It can get heavy... I will say that.
Glad we could help! As for the injectors, you have had 2 bad ones, I would consider contacting our sponsor, FIC, and get a set of 8 new, matched injectors. I think you will be really happy with the results. |
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Posted on: 2011/10/11 16:58
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_________________
The single biggest problem with communication is the illusion that it has taken place. - George Bernard Shaw Education is the best tool to overcome irrational fear. - me |
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