HELP! Constant misfire getting worse daily...

Bradleybnc

Bradleybnc

Registered Member
Joined
11 October 2011
Messages
21
Location
Deer Park Tx
95 NSX-T 130,000 miles.

When I bought the car it had a slight misfire and surging idle. It had a service engine light that said bad O2 sensors. I replaced all of them with factory sensors from SOS. Service engine disappeared for 15mins came back showing 3 misfires. Several minutes later CEL started blinking again I checked it and it was showing misfire on every cylinder.

List of mods:
DC Headers
Test pipes
Comptech Muffler.

List of parts replaced trying to fix problem...
O2's
Spark plugs
Coil packs
Fuel filter
Adjusted valves
Took slack out of timing belt.
Installed Fuel Pressure gauge and it reads 40psi with vacuum and 50 psi without.

The misfire has only gotten worse and now the car dies every time I stop and is hard to restart. The idle surge is drastically increased as well. It steadily misfires at Idle with the CEL blinking. It starting dying yesterday but has been missing for months.

Anyone with a similar issue that fixed it?
​
 
Have you done a compression check and/or leakdown?

The FIRST thing to be sure of is that the engine is mechanically healthy.

Regards,
LarryB
 
I'll try the ICM. I was told that the problem wasnt consistent with ICM so I haven't replaced it yet.

Haven't done a compression check yet.

The light blinks while car is running at idle while misfiring. I have a scanner to check the CEL.


Oh I forgot to mention it runs fine under WOT. Or seems to anyway.
 
Hi,

i had the same symptoms: rough idle (misfires) and it seemed as fine at WOT.

damage: 4 burnt valves - Low compression on 1 cylinder... 40% of what it should be.

cause: water came into the sparks pit and corroded the underside of the coilpack, which caused bad ignition, which lead to all 4 valves on that cylinder being burnt.

Solution: 4 new valves, 3 new rear coilpacks, everything water isolated and never happened again (it happened when i had about 135000kms, now i have 211000kms)

Nuno
 
Bradleybnc said:
I'll try the ICM. I was told that the problem wasnt consistent with ICM so I haven't replaced it yet.

Haven't done a compression check yet.

The light blinks while car is running at idle while misfiring. I have a scanner to check the CEL.


Oh I forgot to mention it runs fine under WOT. Or seems to anyway.
Click to expand...

Reading the ECU failure could give more detailed information then is available with most code readers. I know actron doesn't list NSX specific codes.

Mike
 
The only codes I've been getting since new coils is 1201 1203 and 1300. Which just say Misfire on Cylinder 1&3 and random misfire. It did throw a lean code once and after I cleared it, it hasn't came back.

It runs horrible if I clear the codes but as soon as the CEL comes on the car does run better, but still gradually has gotten worse. I haven't driven it at all since its been acting up this bad. I will do a compression test to see if I do have a problem like that. I really hope not...

Thanks guys.

I ordered that used ICM it should be here Monday or Tuesday. I figured try $20 before I spend $250.

How do I read the ECU Failure?
 
Start on page 11-16 of the service manual which is available in the wiki at the top of this page.

The ECU has a backup system that will engauge when the system has certain failures and that is probably why it starts running better when the CEL comes on.

Mike
 
Thanks for the info guys. I'm hoping mine isn't near that serious. I checked all grounds and they look tight and connected. I'm tired of throwing money at it and coming up with nothing though. I moved it out of the way today and it will not idle at all anymore just from sitting one day. After the ICM comes in i may have the injectors cleaned?
 
I had similar codes. I checked all the same things you did in the end, it was a sticky fuel injector.
With the motor running listen to each injector to see if it is clicking. If not, could be clogged. See this post http://www.nsxprime.com/forum/showthread.php?t=147397 number 15.
I listened to the injectors with a home built stethescope. To un-stick the injector I used a long handled screwdriver with the end on the injector and "tapped" lightly on the other end of the screwdriver.
 
larry bastanza knows his shit. You don't have a lot of posts, so i don't know how familiar you are with the users here. He is one of the most technically proficient NSX techs around.
 
I changed The ICM and no difference at all. Something I forgot to mention previously was the gas mileage is crap. Like 12 in town and at best 19-20 on the freeway. Driving normal you can watch the gas gauge move. It runs very rich as well. So I'm wondering if maybe it has stuck injectors. I'll check them next and do a compression check. Anything else anyone can think of would be great all help is greatly appreciated.
 
Running that rich you can build up carbon and jack a ring. 02 sensor related but I'm not Larry B. Do what he says.
 
Thanks for the info. I will check that as well. Something I've been thinking about though... The car has always had a misfire since I bought it. The timing belt was supposedly changed at 90k. That's what the previous owner told the owner before me. When I pulled the covers to adjust valves I saw the timing belt was loose. I set the engine at tdc and put bolts through the cam covers into the cams. All 4 lined up. I loosed the tensioner bolt and pulled the slack one at a time on the cams removing the bolts on the cams I tightened. There was a ton of slack by the time I got to the back cam. I didn't Check the markers on the back of the cams after I removed slack. Now that I've done this my problem increased quite a bit. So I'm thinking the rear exhaust cam is off a tooth and causing my misfire issue. I'll be pulling it back apart to check this now...
 
Dave is awesome. I talk to him quite often actually. He has been very helpful with everything I've needed. I just can't afford to say, here... Fix it.
 
This post is like Ray Charles skeet shooting:).

I will try this one more time:

1. Do a compression test/leakdown first, post results

2. While they are out, read the spark plugs

3. Do a fuel pressure test and post results

Regards,
LarryB
 
Do you have a shop manual? I believe there is one online here.

I just checked mine and the first thing that shows up is a caution not to adjust the tension anytime other than when the belt is replaced.

You need to check pages 6-22 thru 25 and figure out if your cam timing is correct.

I don't know from your description if you've changed the cam timing, but I hope you don't have a bunch of bent valves.

As far as I recall, having the rear cam off by one tooth just makes the car low on power, not misfire.

Sulley
 
Ok last night I got the time to do a Compression test.
#1 185
#2 205
#3 210
#4 200
#5 205
#6 215

plugs 123 were black and wet.(Cylinders that misfire).

plugs 456 were perfect.

While I was doing the work I pulled the throttle body and cleaned the vacuum ports, throttle body, and as much of the inside of the intake I could reach. I looked at the screws in the vvis and they all appear tight as well. Reassembled everything and tightened the loose ground on tb and the car idles perfect. No more surge but still has a little studder. I will drive it tonight and let you all know how it does.

Thanks

Bradley
 
Went for a drive and it drives so much better. CEL came on showing misfires on 1,2,3 but is still way better than before. I've heard that the headers can hairline crack and cause the o2 to read lean and richen the car up too much. Is this a possibility?
 

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