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No start, sputtering start, rich at startup, erratic

 
Old 03-24-2010, 02:38 PM
  #1  
Brett Jenkins
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Default No start, sputtering start, rich at startup, erratic

I'm flying through my to-do list of things for my S4 and I've come around to the one I dread digging into. Here are the symptoms.

Sometimes, the car will crank, fire, and then sputter and die, like it's not getting enough fuel to run. The exhaust smells very rich. I can crank it again and it will fire again and run a little longer, but will die unless I feather the gas a little. Cranking it again usually starts it up and it runs but runs very rough for a short time and then smooths out.

Sometimes, it will not start unless I go unplug the temp II sensor near the front of the intake. It will then start up first crank and run fine. After I drive it for a bit and turn it off and it sits for a while, it will not start unless I plug the temp II sensor back in. I can almost always get it to start by holding the pedal down like the engine is flooded. Leaky injectors maybe?

The exhaust always smells very rich. I think I'm pulling some of the exhaust into the cabin, because I can smell the rich exhaust on my clothes all day.

The 02 sensor is fairly new and I replaced the temp II sensor when the issue first came up. I've swapped the old 02 sensor back in before with no difference.

Another, maybe related symptom, when the fuel tank is low and he car is idling low, like from a stop-start, it sometimes wants to die or runs like it's on 4-cylinders. Being an 88, it doesn't have the limp mode does it?

Any suggestions on where to begin troubleshooting? I'm replacing the EZK, LH, ignition, and fuel pump relays this weekend. I pulled the fuel pump to flush it and will replace the fuel filter this weekend as well. The check valve is fairly new as well, replaced with the fuel filter < 1 year ago. Plugs and plug wires are fairly new as well.

Thanks in advance for any and all help.
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Old 03-26-2010, 06:04 PM
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It might not be your biggest suspect, but have you checked for leaky injectors? I replaced mine and that fixed (so far!) a hard starting problem.
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Old 03-26-2010, 08:52 PM
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On the list of things to buy in the next month, 24lb FOTE from 928srus, along with coils, and probably the stuff to do an intake refresh, including knock and hall sensors, etc.

Pulled fuel pump to flush/reverse flush and replacing fuel filter and check valve tomorrow. Got new fuel pump relay, LH relay, ignition relay, and ezk relay today. I might put the fuel pressure gauge i've had for a while on the fuel rail and check fuel pressure while i'm at it.
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Old 03-27-2010, 02:10 AM
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MAF.
Unplug it and see if the symtoms change
Then send it off to John
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Old 03-27-2010, 11:20 AM
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MAF or LH. Leaking fpr.
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Old 03-27-2010, 05:51 PM
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Brett,

You are welcome to borrow my MAF to test. I should be free most of tomorrow morning/afternoon if you want a hand.

Hans
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Old 03-27-2010, 07:03 PM
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Well, I'll have to take you up on that at a later date. I'm not at a point where the car will be running yet. Too many side projects going. :-)
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Old 04-03-2010, 01:00 AM
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After removing the fuel pump and flushing it, replacing the fuel filter, and replacing the LH relay, fuel pump relay, EZK relay, and ignition relay, the car starts up immediately every time and seems to be idling much smoother now and not running as rich. I also pulled the cats and "cleaned them out". While the cats were off, I noticed that the O2 sensor was threaded in at an angle, was loose and wasn't completely sealing, so that may have contributed to my overall issue too.
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Old 04-03-2010, 01:03 AM
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+ 3 on the MAF.
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Old 04-03-2010, 01:23 AM
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I am surprised that no one has mentioned the MAF...

We had exactly the same symptoms last year with the GT, and guess what...

Until the engine warms up, the LH is running open-loop and depends entirely on the MAF for fuel mixture. (and the temp-II sensor to tell it how warmed up it is). If the MAF is reading high, then the LH will over-estimate the fuel and the engine will run too rich. Once it warms up the LH goes closed-loop and compensates, if it can-- but if the MAF is way off then it may still be too rich.

Swap the MAF with another, only takes a minute.

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Old 04-03-2010, 06:23 AM
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The reason it sometimes started when unplugging temp 2 is that when you do that, the LH defaults to the 80degC fuelling i.e weaker than you would normally have when starting a cold car.

If an S4 doesn't fire quickly, then it will easily flood.

Check out the igntion leads, rotors, anf caps.

If you need a rebuilt MAF, Louie Ott stocks my rebuilds.
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Old 04-05-2010, 10:42 AM
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Well, it acted up again this morning, first time since replacing the above-mentioned items.

The symptoms are that it will crank but not fire at all until I unplug the temp II sensor. It will then fire up immediately, but run rough for 30 seconds or so. Is the temp II telling something to not supply fuel?
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Old 04-05-2010, 11:10 AM
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See post 11. Unplugging temp 2 will weaken the mixture. It is possible your temp 2 connection is intermittant - goes infinite resistance. That will make the mixture much too rich for temperate conditions.
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Old 04-05-2010, 11:45 AM
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I meant to check the wiring to the temp II connection, I'll do that next.

If the temp II and/or MAF are acting up, forcing the car to be too rich, it should at least fire right? It almost seems like at that point, there is either no fuel or no spark.

The next time it does it, I will check for fuel and spark to determine which isn't present and go from there.
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Old 04-05-2010, 11:54 AM
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If it's flooding, you'll generally get a cough, then nothing but gas fumes for about a minute of cranking. Then a sputtering startup. Full throttle when cranking may help, as some (most? all?) FI ECU's recognize that you're trying to clear a flood and shut off fuel under these circumstances... at least, it seems to help in my car.
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