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RPMs disappear upon throttle

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Old Dec 30, 2010 | 10:51 AM
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Default RPMs Drop to Zero on Open Throttle

My car barely started this morning. And when it did, the idle was extremely low. Then when I give it gas the RPM guage drops to zero - even though the engine is revving. Albeit, the engine is not revving like normal. It is extremely bogged down and sputters. Also, my exhaust is like smoke now.

I thought it may have been my primary O2 sensors (been having other related issues for the past several months that point to bad primary O2 sensors), so I changed them.

NO DICE! Car still barely starts, and continues with the same symptoms as before.

What's going on here? Bad IAC valve, maybe???

Thanks in advance for the good word. Gotta get whatever part(s) I need before the shop closes for New Year, so I can get back to work come Monday.

Last edited by SuperCoupe400; Dec 31, 2010 at 07:04 AM.
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Old Dec 31, 2010 | 11:00 AM
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No One?

Nobody's had this happen?

Just to clarify, the tachometer doesn't drop tozero until RPMs reach 1,000. Power is muted (can feel it). And the exhaust is thick smoke. It all just started overnight. The day before, I had driven 60+ miles. Then the next morning the engine started this odd behavior.

I've changed my primary O2 sensors and cleaned my IAC valve.

Could it be my secondary O2 sensors?

Anyone?.....Anyone?....... (I gotta hit the parts store before they close in the next 3 hours, otherwise I'm not going to make it to work on Monday)

Last edited by SuperCoupe400; Dec 31, 2010 at 11:11 AM.
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Old Jan 3, 2011 | 08:24 AM
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could be alot of things so its hard to diagnose over the internet. its definately not your o2 sensors if its happening upon engine start, it takes a while for the o2 sensors to even read anything on our cars. I would check the fuel system/fuel pump ecu, or even the engine ecu.
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Old Jan 3, 2011 | 08:43 AM
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Well, I've already performed the 12v mod and gotten the same rersults, so it's not the fuel pump ECU. I'll have my mechanic pull the codes.
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Old Jan 3, 2011 | 09:46 AM
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crazy electrical problems are usually some type of sensor or ecu. There have been quite a few reported sc400 engine ecu's with bad caps lately.might be worth your time to test out another sc400 ecu or crack yours open and look for signs of damage.
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Old Jan 3, 2011 | 10:04 AM
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Just spoke with the service supervisor for my local dealer, whose been working there since '91. He recommended a fuel pressure check. If it's not there, then he says there are two other likely causes: bad (black) lead wire going into my left bank coil, or a bad ignitor.

I'll report back when I know which of those turns up positive.

He also gave me a method of checking codes myself (without a diagnostic device). I'm sure people here already know about it. Basically you insert a jumper between a couple of the pins in the diagnotic panel. I' don't remember which ones off-hand. I'd have to look at the pins to jogg my memory. Anyway, you jump the pins, then turn the ignition halfway and read the number of times the engine light flashes.
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Old Jan 3, 2011 | 10:17 AM
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te1 and e1 i believe are the pins.
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Old Jan 3, 2011 | 10:20 AM
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thanks inDementeD
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Old Jan 7, 2011 | 03:59 AM
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It was a bad coil pack. Stealership wanted $410 to replace just that one. I told them no thanks. Picked up two Borg Warner coils for $49ea and swapped them out myself in 20 minutes flat.

Mannnnn... I don't know about you people, but I sure am glad I'm not one of the millions of lemmings that get helplessly led to the slaughter by the stealership evertime they need something done to their car out of warranty.
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