Runs super-rich after sitting overnight
06-09-2008, 03:14 PM
#1
Race Car
Thread Starter
Runs super-rich after sitting overnight [solved]
Ok, so this morning is the second time this has happened. Car has driven great for months, no problems. Park it in the evening, go to sleep. Wake up in the morning to go to work, try and start it catches then immediately dies. Hmm? So I try to start again and it catches and runs super rough and coulds of black smoke out the tail pipe. Eventually it dies and will no longer catch while starting, but I smell an intense gas smell. In fact, if I look at the tail pipe after about 30 seconds of running the starter, I can literally see fuel vapors flowing out. Running so rich that it won't start. So I pull the fuel pump fuse and try to start and sure enough, it starts and runs pretty well for 5 seconds or so then dies as it exhausts all the fuel dumped into the cylinders. Replace fuel pump fuse and try to start and it's super rough/rich again with coulds of smoke. So I play with the accelerator to try and keep it alive for 1 to 2 minutes, and it clears itself up and runs and idles fine. So, I got spark and compression, but too much fuel.
So... what would cause the car to run very rich until (I assume) the O2 sensor heats up enough to begin correcting the mixture? The car has the Andy K. supercharger kit. Mind you, this has only happened twice; the car has started fine over a hundred times in the morning without issue. It can't be injectors leaking overnight because it would have started running fine after pulling, starting, then replacing the fuel pump fuse. Throttle position sensor, MAF or LH or ...?
Dan
'91 928GT S/C
So... what would cause the car to run very rich until (I assume) the O2 sensor heats up enough to begin correcting the mixture? The car has the Andy K. supercharger kit. Mind you, this has only happened twice; the car has started fine over a hundred times in the morning without issue. It can't be injectors leaking overnight because it would have started running fine after pulling, starting, then replacing the fuel pump fuse. Throttle position sensor, MAF or LH or ...?
Dan
'91 928GT S/C
Last edited by dprantl; 07-03-2008 at 12:40 PM.
06-09-2008, 03:25 PM
#2
Rennlist Member
Leaking injector(s), regulaor and dampers are possibilities. Check for fuel in regulator and damper vacuum hoses.Edit was busy at work and didnt read all of post and just read end of last paragraph.
06-09-2008, 03:28 PM
#3
Under the Lift
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I had a couple of oddball instances like this as well after installing the Supermodel SC. Conditions weren't exactly the same, but the car ran as you describe. I could fix it temporarily by briefly disconnecting the battery. In the end I decided it was a poor ground for the LH harness. When you relocate the MAF and throttle as part of the Supermodel SC installation, the harness grounds are "extended". Pull off the back of the SC intake and look at those grounds. Check the wiring to the MAF. Also, unplug and re-seat it.
As a side note, rather than extend those ground wires, I just relocated them from their stock locations on the block to a spot on the manifold. They did not like that much at all. Most of the time things were OK, but occasionally the fuel injection system went bonkers. So, I ran wires back down to the stock ground points and the problems went away.
As a side note, rather than extend those ground wires, I just relocated them from their stock locations on the block to a spot on the manifold. They did not like that much at all. Most of the time things were OK, but occasionally the fuel injection system went bonkers. So, I ran wires back down to the stock ground points and the problems went away.
Last edited by Bill Ball; 06-09-2008 at 11:24 PM.
06-09-2008, 04:18 PM
#4
Supercharged
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+1 on the grounds especially the ones at the back of the valley.
Other possibilities...
Bad MAF/MAF connection. Check the MAF & wiring and make sure everything is happy here. Try disconnecting and see if that helps.
Pending LH Failure - if your LH has not been rebuilt, it might be time.
Bad O2 - A faulty O2 sensor might cause this. You could try disconnecting it and see if it runs better, but I beleive it runs in closed loop mode anyway when cold, so probably not it.
Other possibilities...
Bad MAF/MAF connection. Check the MAF & wiring and make sure everything is happy here. Try disconnecting and see if that helps.
Pending LH Failure - if your LH has not been rebuilt, it might be time.
Bad O2 - A faulty O2 sensor might cause this. You could try disconnecting it and see if it runs better, but I beleive it runs in closed loop mode anyway when cold, so probably not it.
06-10-2008, 11:56 AM
#6
Race Car
Thread Starter
How can I find out if my MAF is actually a Super-MAF? I see a sticker that the MAF was rebuilt by JDSPorsche. Is there any way to tell?
Dan
'91 928GT S/C
Dan
'91 928GT S/C
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06-10-2008, 01:10 PM
#8
Official Bay Area Patriot
Fuse 24 Assassin
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Fuse 24 Assassin
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This is a stupid question, but where are the grounds located for the LH? (If there are other ones besides the ones at the back of the engine Andrew is talking about.) I don't have a WSM in front of me right now.
06-10-2008, 01:36 PM
#10
Race Car
Thread Starter
06-10-2008, 04:24 PM
#11
Rennlist Member
The SMAF has a "SMAF" label on it, so easy to spot...... Cameron used a stock MAF when he SharkTuned his car. A clone of those chips also went into Sab's car.
Do you now own Sab's car ?
Do you now own Sab's car ?
06-10-2008, 04:29 PM
#12
Race Car
Thread Starter
Dan
'91 928GT S/C
07-03-2008, 12:41 PM
#13
Race Car
Thread Starter
So my problem was the temp II sensor. Replaced it and the problem has not reoccured. It must have been reading wrong when fully cold.
Dan
'91 928GT S/C
Dan
'91 928GT S/C
