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The old misfire at idle problem some have never solved

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Old 01-16-11, 10:31 AM   #1
92LS400LIV
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Default The old misfire at idle problem some have never solved

We have a 92 LS400 since new.It has 116,000 miles It developed a misfire at idle(whole car shook when put in gear)and missed when revving the motor up till about 2500rpm where it seemed to clear up but still lacks power.When put in gear it used to accelerate like a slow four cylinder missing while accelerating and after reaching speed.Very poor drivability and the car has been sitting for almost two months.I have spent many hours researching this problem online and still have not solved it,with one owner practicaly wanting to give hers away after spending over 3k without fixing it.I have all necessary tools and performed the following repairs:CHECKED COMPUTER CODES 25+26,lean and rich codes,New FUEL PUMP and FILTER 8K miles back,just performed THROTTLE BODY CARBON CLEANING,IAC IDLE AIR CONTROL MOTOR CARBON CLEANING and electricaly tested it to see it step back and forth,CHECKED BOTH COILS RESISTANCE,CLEANED FUEL INJECTORS by directly injecting two cans of NAPA fuel injection cleaner with my 3M hose kit that allows you to tap directly into the fuel rail removing the fuel pump relay or fuse and running motor off straight injector cleaner(like shops do for over $100) and the problem improved but still there.Replaced BOTH CAPS,ROTORS.(LEXUS)and NGK PLATINUM PLUGS AND WIRES,next I put the gauge on and did FUEL PRESSURE TEST,at idle it was 39psi and when revved it jumped to 48-49 and when the FUEL PRESSURE REGULATOR vacuum hose was disconnected,it jumped to 45psi.I ran a third can of 3M fuel injection cleaner through it and the misfire almost totally disappeared,but you can barely feel it at idle and barely see the motor shake however now when you put it in gear it is so powerless it will barely accelerate and fells like some swapped a lawnmower motor under the hood,and yet can,t feel misfire anymore.How could a can of injection cleaner cause these strange results?Feels like the timing is set after top dead center but I know the computer controls timing so that seems impossible.Can someone please help me as I'm really frustrated and the work I've already done would have cost over $1000.My parents have long since retired and can't afford to pay for the troubleshooting I've done.Anybody have a clue to determine if it's an injector and which one?THANKS Duane I forgot to mention pressure gage drops to almost zero overnight.
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Old 01-16-11, 11:06 AM   #2
etex
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This may sound totally unrelated, but have you ever changed your coolant temperature sensor?
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Old 01-16-11, 01:28 PM   #3
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Hi,
Measuring the coil resistance may have given you the correct resistance reading but these things break down under load i.e working conditions. When you have around 20,000 volts on the coil output it could be breaking down.
The most common one is the passenger side coil and for $30.00 it would be worth replacing it just to be sure.
Another sign of a failed coil is glowing cats due to un-burnt fuel
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Old 01-16-11, 01:34 PM   #4
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I agree with Steve's call...I had a "stumble" at idle that wasn't as bad as what the OP describes that occurred after I put in new coils. I took a guess at the passenger side coil (the easy one on top), swapped it from a $10 coil from pick-n-pull, and it fixed the problem. The "bad" coil never tested bad; ie both primary and secondary resistances were within spec. Secondary is difficult to measure correctly anyway iirc.
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Old 01-16-11, 03:16 PM   #5
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i had the same issue and it was the coils
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Old 01-16-11, 03:39 PM   #6
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The NGK plugs & wires can be trouble. The Lexus wants Denso Iridium plugs and OEM wires would be best. But if you had the problem before and after instaling them then forget my comment. Just that replaced NGK plugs & wires on my Caravan and it began missing immediately. Turns out it wanted Champion platinum plugs only. Swapped plugs and problem fixed. NGK wires gave out shortly after
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Old 01-17-11, 04:46 AM   #7
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platnium plugs will spark better then iridium, and copper sparks better still. iridium plugs are for people that are too lazy to change their plugs when the scheduled maint says too. Platnium plugs is what came in it stock.

anyhow, if the power is that weak, get a spark tester. the adjustable ones that let you change the gap. hook up a plug wire to one and adjust the gap to the stock spec and look at the spark. is it blue? or red? do this for a wire on each coil. should let you know which one is bad. blue is good, red is weak.
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Old 01-17-11, 04:54 AM   #8
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Quote:
Originally Posted by williamb82 View Post
platnium plugs will spark better then iridium, and copper sparks better still. iridium plugs are for people that are too lazy to change their plugs when the scheduled maint says too. Platnium plugs is what came in it stock.

anyhow, if the power is that weak, get a spark tester. the adjustable ones that let you change the gap. hook up a plug wire to one and adjust the gap to the stock spec and look at the spark. is it blue? or red? do this for a wire on each coil. should let you know which one is bad. blue is good, red is weak.
Really? I got OEM plugs here in my hand in the Toyota box from Lexus Denso PK20R11 iridium plugs. All other websites I've searched show that iridium came in the car. But mine's a '93 maybe '92 is different
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Old 01-17-11, 06:05 AM   #9
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mines a 93, i dont even think they had iridium plugs till like 2000+. first time i even heard them offered for anything at an auto parts store was ~2001. mine came with denso platinums. theres a part number in some of the paper work that came with the car of them when they were replaced by a lexus dealer. for some reason, people think iridium sparks better because it costs more. when in fact it isnt the case. they just last longer as the electrode is harder. as i said, they are for lazy people. the dealer will tell you that you have to have iridiums because they cost more and they make more of a profit on them. if you go to autozone, they will tell you your 1970's pinto requires iridium so they can boost their sales margin. either way, he has new plugs already so that shouldnt be the issue. he can do a spark test as i mentioned to see if the spark is sufficient or not.
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Old 01-17-11, 07:43 AM   #10
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Quote:
Originally Posted by StevieA View Post
The NGK plugs & wires can be trouble. The Lexus wants Denso Iridium plugs and OEM wires would be best. But if you had the problem before and after instaling them then forget my comment. Just that replaced NGK plugs & wires on my Caravan and it began missing immediately. Turns out it wanted Champion platinum plugs only. Swapped plugs and problem fixed. NGK wires gave out shortly after
chrysler products are tempramental,ngk plugs are some of the best plugs out there...dont get the 2 confused and think just because ur caravan had issues with the plugs that they arent any good...put bosch plugs in a ford and watch what happens.
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Old 01-17-11, 09:18 AM   #11
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Quote:
Originally Posted by python View Post
chrysler products are tempramental,ngk plugs are some of the best plugs out there...dont get the 2 confused and think just because ur caravan had issues with the plugs that they arent any good...put bosch plugs in a ford and watch what happens.
agree and GM wants AC-Delco, Chryslers like Champions, my Honda dirtbike wanted NGK's, as did my snowmobiles, and my Uncle's 440 Mod sled needed Bosch plugs........

But NGK does make some cheap wires
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Old 02-01-11, 02:07 PM   #12
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Quote:
Originally Posted by StevieA View Post
Really? I got OEM plugs here in my hand in the Toyota box from Lexus Denso PK20R11 iridium plugs. All other websites I've searched show that iridium came in the car. But mine's a '93 maybe '92 is different
Most LS400 come with iridium but they aren't really better except they should last longer. Who in their right mind would leave plugs in for 100K anyway? 60 K is plenty.
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Old 03-12-11, 09:45 AM   #13
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My sc3 throwing same codes slightly different symtoms been replacing stuff that hardley helps too .... Sigh
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Old 03-12-11, 08:16 PM   #14
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If you suspect an injector, here's an old mechanic's trick to isolate the problem cylinder: when the car's misfiring, disconnect and reconnect the plug wires one at a time. If one of them doesn't make the misfire worse, you've found the problem cylinder. Then you just have to determine if it's an injector, plug, wire, or valve. The easiest place to disconnect would probably be at the cap. Don't zap yourself.
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Old 03-13-11, 11:30 AM   #15
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park in a dark garage and take a spray bottle and mist water on the plug wires, coils and plugs. if you you see any blue lightning it is a voltage leak through insulation. the fact that it clears up with rpm makes me think it is that. i had one on my camry from the coil wire in the rubber insulated wire bracket. odd place for a crack ion the rubber but $60 for a wire set because no one sells coil wire only.
and again, pulling plug wires will id the offending cylinder if it is isolated to one. if the injector is firing correctly you will smell the unburned gasoline in the exhaust.
old mechanic's expression"you only need three things to make it run; air, gas and spark and it's always electrical."
my $.02

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Old 03-13-11, 11:30 AM
 
 
 
 
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1970, 1992, 7mgte, c10, caravan, chevy, coil, cylinder, dead, firing, idle, lexus, makes, mis, misfire, misfiring, ms2, supra

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