Miss firing need help
10-21-23, 11:43 AM
#1
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Miss firing need help
Hello sort of new here been lurking and gathering information for a while but this problem has seem to stump me dead in my tracks,my 95 ls400 started acting weird coming home a few weeks ago and I didn't pay much attention till it started miss firing and throwing codes,the codes that came up were for miss fires on cyl 8 and 2. Changed the plugs,no change. Changed the wires,still didn't fix it. Changed the cap and rotors,still no dice. Changed the throttle position sensor because previous owner put in some cheap China after market one and still no change. I've done the whole fuel pump resistor bypass and still no change. The only I haven't done is check the fuel pressure and I have no clue how you check it on this. Even tried swapping ecus from my buddies ls400(same model year) and still running absolutely horrible. Same codes came back with the different ecu. Checked timing with my scanner and everything seems normal,the only thing I can see is the bank one sensor two is a bit bellow threshold but no by much.
10-21-23, 11:59 AM
#2
I'm far from an expert on these things - my blind guess would be test for vacuum leak. But I'd imagine that would cause a miss on more than just the same two cylinders.
Also, did you clean out air mix passages? Perhaps they are clogged with carbon which is interfering with the atomization of the fuel by the injectors.
https://www.clublexus.com/forums/ls-...ttle-body.html
I'm sure some other folks will have far better ideas than this as well. Best of luck.
Also, did you clean out air mix passages? Perhaps they are clogged with carbon which is interfering with the atomization of the fuel by the injectors.
https://www.clublexus.com/forums/ls-...ttle-body.html
I'm sure some other folks will have far better ideas than this as well. Best of luck.
10-21-23, 12:55 PM
#3
If the plugs, wires, distributor, AND ECU were swapped, but you're still getting misfires only on cylinders 2 and 8, I'd put my money on the fuel injectors. Could be that they're failing, got clogged, or have wiring issues
Last edited by GoldStar; 10-21-23 at 12:59 PM.
10-21-23, 01:19 PM
#5
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10-21-23, 01:21 PM
#6
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Originally Posted by Jsutafurr;[url=tel:11599475
11599475]for cyl 2 and 8 they were black like those two are running really rich,doesn't smell like it's burning oil
10-21-23, 01:21 PM
#7
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I'll take them out and swap them with my buddies,thankfully the doesn't drive his ls that much and he gave me permission to use his parts for diag
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10-21-23, 01:23 PM
#8
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10-21-23, 01:26 PM
#9
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Thread Starter
Hello sort of new here been lurking and gathering information for a while but this problem has seem to stump me dead in my tracks,my 95 ls400 started acting weird coming home a few weeks ago and I didn't pay much attention till it started miss firing and throwing codes,the codes that came up were for miss fires on cyl 8 and 2. Changed the plugs,no change. Changed the wires,still didn't fix it. Changed the cap and rotors,still no dice. Changed the throttle position sensor because previous owner put in some cheap China after market one and still no change. I've done the whole fuel pump resistor bypass and still no change. The only I haven't done is check the fuel pressure and I have no clue how you check it on this. Even tried swapping ecus from my buddies ls400(same model year) and still running absolutely horrible. Same codes came back with the different ecu. Checked timing with my scanner and everything seems normal,the only thing I can see is the bank one sensor two is a bit bellow threshold but no by much.
10-22-23, 07:13 PM
#10
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Thread Starter
Possible lead
Used my buddies good scanner to see all values of all the senors and everything seems fine but the downstream o2 sensors,they are reading .662 for bank 1 senor 2 and .750 for bank 2 senor 2. I've been reading everywhere and I can't come up with if that is normal or not,anyone here know?
10-22-23, 07:14 PM
#11
Raw values for O2 sensors mean nothing. What matters is the pattern they display. for example, the upstream o2 sensors should oscillate between 0.1v and 0.9v. And downstream sensors should report a steady value and should not oscillate.
There are a million videos on Youtube showing what you should see.
The downstream O2 sensors are really only there to make sure the cat is working and are unrelated to your symptoms.
There are a million videos on Youtube showing what you should see.
The downstream O2 sensors are really only there to make sure the cat is working and are unrelated to your symptoms.
Last edited by 400fanboy; 10-22-23 at 07:19 PM.
10-23-23, 12:54 PM
#12
Rookie
Thread Starter
Raw values for O2 sensors mean nothing. What matters is the pattern they display. for example, the upstream o2 sensors should oscillate between 0.1v and 0.9v. And downstream sensors should report a steady value and should not oscillate.
There are a million videos on Youtube showing what you should see.
The downstream O2 sensors are really only there to make sure the cat is working and are unrelated to your symptoms.
There are a million videos on Youtube showing what you should see.
The downstream O2 sensors are really only there to make sure the cat is working and are unrelated to your symptoms.
10-23-23, 05:42 PM
#15
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Thread Starter
compression test came back OK ish,bank 1 (cyl 1,3,5,7) they are all at 180,bank 2 (2,4,6,8) they are low from the other bank at 150-160. I have the original service manuals the big dealer books and it says 145 is the min and 190 is on the higher end. So they are still with in spec. Talked to a local toyota/lexus mechanic and he said it could be excess carbon build up so there's only one way to find out. But so far it's still not wanting to run right. (Yes I did the compression tests dry and wet made no difference)