Running way too rich, hard start, tough to idle

Tiny
JENNAS CAR
  • MEMBER
  • 1993 NISSAN AXXESS
  • 107,000 MILES
Going through fuel like a drunk with a bottle. 107000 miles, running rough about a week, replaced plugs/wires, added engine treatment to fuel. Drove 125 miles, muffler shop diagnoses plugged catalytic converter. Round trip 50 miles, hard start, stalls at low rpm, really rough, barely make it back to town to Minute Muffler.

After cat conv cut open, still runs rough, shop checks plugs, all plugs fouled, remove cat-replace with straight piece of pipe, replace plugs, 02 sensor good, mass air flow sensor slightly out of range, but within normal parameters, still runs badly. 40 mile round trip, remove/inspect fuel filter, OK, replace it, find plugs blackened, cleaned up, re-gapped, cap/rotor OK, still poor performance, can't sort it.

On to Nissan, tell them all that has transpired. 3-hr diagnostic, mass air flow sensor, intake systems, vacuum lines, fuel sensor, pressure in combustion chamber, fuel pressure to fuel rail, spark plugs, plug wires, cap and rotor, cylinder compression--All no faults, systems are in specs. NO faults OR solution discovered.

I'm told that they have to keep disassembling to find problem, next would be to remove and inspect fuel injectors, who knows where it will end. I call time-out, and am told to run engine treatment and premium fuel (runs hotter) to see if that will help. Wish they had told me to eliminate that possibility BEFORE 3-hr diagnostic.
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Tuesday, October 22nd, 2013 AT 8:31 PM

5 Replies

Tiny
MADMIKE1735
  • EXPERT
Your upstream o2 is most likely bad also. The cat was clogged, they dont go bad by themselves. How did they verify the o2s are good? This is what ultimately tells your engine if its getting to much fuel or not. It reads exaust gasses. I dont think this is the cause of your problem, but keep in mind it should be adressed. Your complaining of this running rich. If you have any vacuum, or air leaks, it will cause the engine to run lean. In return, your 02 sensor will catch this, and tell the engine to dump more fuel in to make up for the false reading it is recieving. Does this make sense? It is possible that a fuel injector is stuck open. I will agree with that. But the fuel rail needs to be removed in order to verify. A stuck injector will spray with the key on, engine off. It shouldnt! And running premium fuel is a waste! It doesnt burn hotter. It burns longer. I can get into a whole theory and operation of it, but I wont. (I run race fuel in my drag motorcycle because I need it with 12:1 compression) your engine is fine with 87 octane.
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Tuesday, October 22nd, 2013 AT 8:48 PM
Tiny
JENNAS CAR
  • MEMBER
Hi Mike, thanks for your reply.

Minute Muffler examined the 02 sensor(s). They cut the catalytic converter off, I'm guessing that's when they verified the condition of the 02. Where is the 'upstream' 02 sensor located? Is it on the exhaust between the engine and the cat? Also, is there one after the cat, between it and the tail pipes? I will call the muffler shop tomorrow about the 02 sensors.

The fuel rails were removed by Nissan in an attempt to further diagnose this, but, they didn't remove any injectors. They said that would take another 3 hours, and my wallet is bleeding already ! I will call them about this tomorrow to ask about the injectors spraying with the key on and engine off.

Yes, the 'false reading causing a dump of fuel' makes sense. Also, thanks for the tip on premium. Nissan told me that it would run hotter, and clean the system out better.
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Tuesday, October 22nd, 2013 AT 9:17 PM
Tiny
MADMIKE1735
  • EXPERT
Your upstream o2 sensors are located before the cat. They read the air/fuel ratio prior to entering the cat. The downstream o2s are located past the cat, and read the air/fuel after the cat. Hope this helps, sorry for the late reply.
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Friday, October 25th, 2013 AT 3:34 PM
Tiny
JENNAS CAR
  • MEMBER
Hi Mike I spoke with the technician at the muffler shop (Steve) and filled him in with all that had transpired at Nissan. Steve is convinced that the problem is electronic, something controlling the fuel. Does this still make you think it's my injectors? This issue is burning out ALL of my spark plugs, not just one or two. And, apparently there was only one 02 on my car.

Steve has had an 02 test OK, but, replacing it solved a similar problem. Also, my mass air flow sensor was slightly out, but still within normal parameters. He said that either this or the 02 can be far enough gone to cause this issue, and the only way to really find out, unfortunately, is to start replacing parts.

So, yesterday he replaced the cheapest part, the 02. And yes, the car is running better. Steve isn't totally happy yet, but, told me to monitor it. My car started at about a 1000 rpm idle today, and steadied at about 1250 as the car warmed up. It runs fine at highway speed and has acceleration again. The problem isn't 100% solved, but, I'm hopefully optimistic.

Steve said that my car was so badly flooded yesterday that it was difficult to get it into the bay. I had only driven about 40 miles round trip to get it back to the shop, and I only drove it the 20 miles home yesterday. I've only driven it about 5 miles today. I didn't have a chance to check the plugs today, but, I will do that tomorrow. And, if they're at all fouled, I will clean them and check the gap.
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Friday, October 25th, 2013 AT 7:13 PM
Tiny
MADMIKE1735
  • EXPERT
Well ultimately, your computer will control fuel based upon the upstream O2 sensor. If it was replaced, and still running rich, then something is still malfunctioning. If you have an vacuum leak anywhere after the mass air flow sensor, your system will read lean, and dump in extra fuel. What are the fuel trims? They need to read this on a scan tool. It will help point out where to go next. If the trim is negative at idle, around 1-3, thats normal. If its reading positive, this indicates an unmetered air leak.
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Friday, October 25th, 2013 AT 7:49 PM

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