1995 SC400 Problem
10-22-19, 08:49 AM
#1
Pit Crew
Thread Starter
1995 SC400 Problem
Hello CL Members,
So a couple of days ago I was installing a lip on my front end of my SC. (A little garage door seal from home depot) Everything was running fine previously for a couple of months since my last maitententance (timing belt).
Suddenly as soon as I finish, I'm sitting in my car looking at pics of the finished project when I hear my car slightly jerk, and think of it as nothing and pull away. On my way home I notice the jerking starting to happen more frequently and the tachometer is not smoothly rising as I accelerate. It starts to rise then halts / slight jerk then continues, almost as if it was hiccuping. Later the CEL pops up and I call it a night.
The following morning I'm on my way to work (only a mile away) and as I'm accelerating up a hill (not flooring it or anything) I hear a loud pop in the cabin (felt like it came from my left side) It sounded like I blew a tire but sharper and more loud. I arrive at work and check my tires and everything checks out ok. I'm still unsure what it was, backfire maybe? Then again I wouldnt think backfire would be that loud, I mean I had my windows up.
Things to note are it doesnt tend to hiccup / rough idle / rough acc when the engine is cold in the morning. I noticed that today. I researched more than several threads and came down to these conclusions:
A. It could simply be my MAF
B. Distributor Coils.
C. Spark Plugs .
D. Timing belt may have misaligned. (Although I think is unlikely because the timing was done in AUG)
E. Clogged Cats
Also I checked the CEL and it read back a 13. (RPM Signal) I believe.
E: I meant to mention that I'll be starting with cleaning the MAF, but if anyone has had any experience with this first hand and may have some clue to finding the issue dont hesitate to reply lol. Doing more research
So a couple of days ago I was installing a lip on my front end of my SC. (A little garage door seal from home depot) Everything was running fine previously for a couple of months since my last maitententance (timing belt).
Suddenly as soon as I finish, I'm sitting in my car looking at pics of the finished project when I hear my car slightly jerk, and think of it as nothing and pull away. On my way home I notice the jerking starting to happen more frequently and the tachometer is not smoothly rising as I accelerate. It starts to rise then halts / slight jerk then continues, almost as if it was hiccuping. Later the CEL pops up and I call it a night.
The following morning I'm on my way to work (only a mile away) and as I'm accelerating up a hill (not flooring it or anything) I hear a loud pop in the cabin (felt like it came from my left side) It sounded like I blew a tire but sharper and more loud. I arrive at work and check my tires and everything checks out ok. I'm still unsure what it was, backfire maybe? Then again I wouldnt think backfire would be that loud, I mean I had my windows up.
Things to note are it doesnt tend to hiccup / rough idle / rough acc when the engine is cold in the morning. I noticed that today. I researched more than several threads and came down to these conclusions:
A. It could simply be my MAF
B. Distributor Coils.
C. Spark Plugs .
D. Timing belt may have misaligned. (Although I think is unlikely because the timing was done in AUG)
E. Clogged Cats
Also I checked the CEL and it read back a 13. (RPM Signal) I believe.
E: I meant to mention that I'll be starting with cleaning the MAF, but if anyone has had any experience with this first hand and may have some clue to finding the issue dont hesitate to reply lol. Doing more research
Last edited by Slackful; 10-22-19 at 10:39 AM.
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KahnBB6 (10-23-19)
10-23-19, 08:42 AM
#4
Pit Crew
Thread Starter
Thanks for replying, yes I havent touched the actual MAF Sensor but I undid the whole air intake tubing with box for the first time to get familiar with it. I looked inside my TPS and saw it wasnt really dirty. Today I'm going after spark plugs, coils, and maybe leads. I'll have to buy and multimeter though to test the leads. If that brings no success I will try the IACV I think and clean that. I'll also be trying cleaning the throttle body see if that helps hopefully it's not as sensitive as the MAF.
10-23-19, 08:50 AM
#5
Those are all worthwhile maintenance things, but I don't see the IAC or TB as being likely culprits. The TB would have to be majorly gunked up to affect driveability like that, and the IAC mostly does its thing at idle, allowing a small amount of air to bypass the throttle plate.
In my experience, coils will test fine even when they're problematic. If you suspect them, just get replacements.
In my experience, coils will test fine even when they're problematic. If you suspect them, just get replacements.
10-23-19, 08:57 AM
#6
Pit Crew
Thread Starter
Those are all worthwhile maintenance things, but I don't see the IAC or TB as being likely culprits. The TB would have to be majorly gunked up to affect driveability like that, and the IAC mostly does its thing at idle, allowing a small amount of air to bypass the throttle plate.
In my experience, coils will test fine even when they're problematic. If you suspect them, just get replacements.
In my experience, coils will test fine even when they're problematic. If you suspect them, just get replacements.
10-24-19, 08:27 AM
#7
If it isn't acting up when cold, that means it isn't one of the sensors/components used during open loop operation. That right away dismisses ignition components...unless it's an oddball issue where the component is fine when cold, but developes a problem when it gets hot, which is possible.
A back fire certainly can be loud, I wouldn't dismiss that as being the pop you heard on volume, alone.
You can not see the condition of a TPS by looking at it. The functional parts of it are sealed inside and they are prone to failure. They can be tested with a digital multimeter.
I would look up to see what sensors the engine uses in open loop vs closed loop. I can't fully recall right now to give you that info. I'm fairly certain the O2 sensors are not used in open loop, and the ECU only uses their data once the car reaches a certain temp and it goes in to closed loop...so, that, to me, is one place I'd look.
A quick theory based on the limited info and not being in front of the car...
Faulty O2 sensor
Not effecting drivability when cold because of open loop operation
Effecting drivability when warm because of closed loop operation
Symptoms are fuel mixture richness causing back fires and drivability problems
Do you see an unusual amount of black soot on the tail pipes?
How do the spark plugs look when you pull them? Are the electrodes black, white, brownish...
Of course, there could be a myriad of other possibilities.
When you say your tach fluctuates, does it do it really abruptly, or slowish? If really abruptly, that would contradict what I said above and point to ignition and/or electrical. ECU is also a possibility, as they're known to fail and cause a ton of odd problems.
Your fault code points to cam and crank sensors.
A back fire certainly can be loud, I wouldn't dismiss that as being the pop you heard on volume, alone.
You can not see the condition of a TPS by looking at it. The functional parts of it are sealed inside and they are prone to failure. They can be tested with a digital multimeter.
I would look up to see what sensors the engine uses in open loop vs closed loop. I can't fully recall right now to give you that info. I'm fairly certain the O2 sensors are not used in open loop, and the ECU only uses their data once the car reaches a certain temp and it goes in to closed loop...so, that, to me, is one place I'd look.
A quick theory based on the limited info and not being in front of the car...
Faulty O2 sensor
Not effecting drivability when cold because of open loop operation
Effecting drivability when warm because of closed loop operation
Symptoms are fuel mixture richness causing back fires and drivability problems
Do you see an unusual amount of black soot on the tail pipes?
How do the spark plugs look when you pull them? Are the electrodes black, white, brownish...
Of course, there could be a myriad of other possibilities.
When you say your tach fluctuates, does it do it really abruptly, or slowish? If really abruptly, that would contradict what I said above and point to ignition and/or electrical. ECU is also a possibility, as they're known to fail and cause a ton of odd problems.
Your fault code points to cam and crank sensors.
Last edited by emLEX; 10-24-19 at 09:05 AM.
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10-24-19, 09:21 AM
#8
Pit Crew
Thread Starter
If it isn't acting up when cold, that means it isn't one of the sensors/components used during open loop operation. That right away dismisses ignition components...unless it's an oddball issue where the component is fine when cold, but developes a problem when it gets hot, which is possible.
A back fire certainly can be loud, I wouldn't dismiss that as being the pop you heard on volume, alone.
You can not see the condition of a TPS by looking at it. The functional parts of it are sealed inside and they are prone to failure. They can be tested with a digital multimeter.
I would look up to see what sensors the engine uses in open loop vs closed loop. I can't fully recall right now to give you that info. I'm fairly certain the O2 sensors are not used in open loop, and the ECU only uses their data once the car reaches a certain temp and it goes in to closed loop...so, that, to me, is one place I'd look.
A quick theory based on the limited info and not being in front of the car...
Faulty O2 sensor
Not effecting drivability when cold because of open loop operation
Effecting drivability when warm because of closed loop operation
Symptoms are fuel mixture richness causing back fires and drivability problems
Do you see an unusual amount of black soot on the tail pipes?
How do the spark plugs look when you pull them? Are the electrodes black, white, brownish...
Of course, there could be a myriad of other possibilities.
When you say your tach fluctuates, does it do it really abruptly, or slowish? If really abruptly, that would contradict what I said above and point to ignition and/or electrical. ECU is also a possibility, as they're known to fail and cause a ton of odd problems.
Your fault code points to cam and crank sensors.
A back fire certainly can be loud, I wouldn't dismiss that as being the pop you heard on volume, alone.
You can not see the condition of a TPS by looking at it. The functional parts of it are sealed inside and they are prone to failure. They can be tested with a digital multimeter.
I would look up to see what sensors the engine uses in open loop vs closed loop. I can't fully recall right now to give you that info. I'm fairly certain the O2 sensors are not used in open loop, and the ECU only uses their data once the car reaches a certain temp and it goes in to closed loop...so, that, to me, is one place I'd look.
A quick theory based on the limited info and not being in front of the car...
Faulty O2 sensor
Not effecting drivability when cold because of open loop operation
Effecting drivability when warm because of closed loop operation
Symptoms are fuel mixture richness causing back fires and drivability problems
Do you see an unusual amount of black soot on the tail pipes?
How do the spark plugs look when you pull them? Are the electrodes black, white, brownish...
Of course, there could be a myriad of other possibilities.
When you say your tach fluctuates, does it do it really abruptly, or slowish? If really abruptly, that would contradict what I said above and point to ignition and/or electrical. ECU is also a possibility, as they're known to fail and cause a ton of odd problems.
Your fault code points to cam and crank sensors.
So I attached a photo of the only spark plug I managed to get out before it started raining. I guess it looks bad. I'll try my best to finish the rest today. And the tachometer it fluctuates pretty quickly. To be more specific whenever I try to floor it almost feels like the car is kicking back and jerking. Imagine having bad lag in a online game where you are running but it pulls you back a few steps every couple of seconds. Also TRAC turns off whenever I drove it and the CEL came on (so they came on simultaneously).
I'll get back to you with a picture of the tailpipes as well. If you would like I can PM you my number and I can send videos of how it runs.
Another small thing to note is there is a sound like compressed air or kind of a light fart sound is coming from the middle underbody of the car (possibly where the Cats are) when in idle. The sound is in sync (it happens at the same time) with tachometer drops.
That's about it for now. After work I will rush to finish the rest of the plugs before it gets too late. Thank you for your input.
10-24-19, 10:14 AM
#9
That plug doesn't look too bad. Pull at least one from the opposite bank since the 2 banks are being ignited from 2 different coils...if it was me, I would pull them all to inspect.
The noise you're hearing from under the car when it acts up is an issue. The car should never do that, so I'd definitely be looking in that direction. Seems as something may have been blocked and back pressure caused a burst, which might have been the pop you heard in your OP. Cats can clog, or crack in the housing and block exhaust gases from exiting the engine.
The noise you're hearing from under the car when it acts up is an issue. The car should never do that, so I'd definitely be looking in that direction. Seems as something may have been blocked and back pressure caused a burst, which might have been the pop you heard in your OP. Cats can clog, or crack in the housing and block exhaust gases from exiting the engine.
11-19-19, 11:16 AM
#10
Pit Crew
Thread Starter
So unfortunately after I replaced my plugs (NGK) and leads (NGK) I started her up again for only the misfire to continue. Although the plugs werent that bad just crusted brown a bit from normal wear. Although, when replacing the leads one of the conductor clips that connect to the tip of the plug had actually ripped from the lead itself. I figured that might be the cause of the misfire. Regardless I figured the symptoms would slowly wear away and it did.. but I believe it was only because of the weather being colder (snowing, freezing) etc. Like mentioned before the misfire doesnt happen immediately after a cold start but I'd say 10 minutes or so after when its warmed up. That's when the misfire, stalls, and the tachometer jumps from 800 through the 300 range going up and down etc. There also is a good presence of gas or some type of smell I should mention. I initially didnt state this because I thought that was normal for the car but I feel the smell has been getting a little stronger. I'm not sure exactly what this can be but I'm moving to checking the O2 sensors and the catalytic converters. If anyone has any idea on what this might be I would greatly appreciate it! Thanks <3
11-19-19, 12:16 PM
#11
When I was chasing down a misfire on my sc400 I found the problem to be the distributor it wasn't fully seated so one of the contacts wasn't getting proper spark. Also I would look into the ECU see if you blew a cap its like 20 min procedure.
11-19-19, 12:31 PM
#12
Pit Crew
Thread Starter
Thanks for the information, I'll definitely look into that afterwards. I appreciate the thought.
11-19-19, 01:30 PM
#13
Disconnect the battery negative over night to hopefully reset/clear any codes.
Next morning, reconnect battery and check codes before starting and driving the car.
Then drive the car and re-check codes again.
Code 13 is usually for a faulty cam sensor(there are 2, one for each cam), but it could also be pointing towards the timing belt skipping a tooth.
Next morning, reconnect battery and check codes before starting and driving the car.
Then drive the car and re-check codes again.
Code 13 is usually for a faulty cam sensor(there are 2, one for each cam), but it could also be pointing towards the timing belt skipping a tooth.
11-19-19, 01:47 PM
#14
Pit Crew
Thread Starter
Disconnect the battery negative over night to hopefully reset/clear any codes.
Next morning, reconnect battery and check codes before starting and driving the car.
Then drive the car and re-check codes again.
Code 13 is usually for a faulty cam sensor(there are 2, one for each cam), but it could also be pointing towards the timing belt skipping a tooth.
Next morning, reconnect battery and check codes before starting and driving the car.
Then drive the car and re-check codes again.
Code 13 is usually for a faulty cam sensor(there are 2, one for each cam), but it could also be pointing towards the timing belt skipping a tooth.
Also if it was a belt system issue wouldnt the it be present even during a cold start?
P.S. I'll also add cam sensors on things I need to research.
11-19-19, 02:08 PM
#15
Both cams have to be in time with the crank. You have to check it when piston #1 is at TDC(Top Dead Center) on the combustion stroke. Only then will the marks align.
And I probably should've worded it differently, I wasn't suggesting your t-belt skipped. If the code comes back after clearing them, then start checking the sensors and the wiring to them.
And I probably should've worded it differently, I wasn't suggesting your t-belt skipped. If the code comes back after clearing them, then start checking the sensors and the wiring to them.