'96 LSi - Cylinder 3 Misfire

[dizzan]

Hi all... been a while since I last posted. Last I was here, I had just got one of the original PWR rad's installed, then some jack**s rear-ended me and totalled my '92 LS-L!

I finally found a new SVX recently, a 96 LSi, about 115k miles. It's been treating me well for the most part, but recently (2-3 months ago) there was a smallish exhaust leak right before the main catalytic, caused by the flange gasket deteriorating. I attempted to repair it but couldn't find the exact part (locally) at the time. It was better, but not perfect. Slowly, it's been getting worse again.

While getting ready to replace the gasket and associated pieces to get the exhaust sealed up, I started getting a check engine light. OBDII reader shows me P0303 - Cylinder 3 misfire. I found conflicting information on which is cylinder 3, so I checked the middle plug on both sides of the engine. Both are getting spark. The plugs were recently replaced with Bosch platinum 2's and are still almost brand new looking, though I swapped them out just to be on the safe side. Cleared codes, and P0303 came back again after letting the car idle for a few minutes.

The symptoms of what's happening are as follows:
- Motor shakes pretty bad below ~800rpm, but runs much smoother > 1000 and even > 2000.
- While driving, you can hear what sounds like misfiring especially at low rpm.
- There is a distinct and severe lack of power as opposed to when it was running correctly.

My question is, could the misfire be caused by the lack of compression due to the exhaust leak, or would you think there may be something else causing it?

I'm planning on repairing the exhaust in the next week or so once I get the parts needed. I hope that clears everything up, but in the mean time I was wondering if anyone had any suggestions on what else to check to narrow down the problem.

Thanks!
Dan

[Chiketkd]

Originally Posted by dizzan

Hi all... been a while since I last posted. Last I was here, I had just got one of the original PWR rad's installed, then some jack**s rear-ended me and totalled my '92 LS-L!

I finally found a new SVX recently, a 96 LSi, about 115k miles. It's been treating me well for the most part, but recently (2-3 months ago) there was a smallish exhaust leak right before the main catalytic, caused by the flange gasket deteriorating. I attempted to repair it but couldn't find the exact part (locally) at the time. It was better, but not perfect. Slowly, it's been getting worse again.

While getting ready to replace the gasket and associated pieces to get the exhaust sealed up, I started getting a check engine light. ODBII reader shows me P0303 - Cylinder 3 misfire. I found conflicting information on which is cylinder 3, so I checked the middle plug on both sides of the engine. Both are getting spark. The plugs were recently replaced with Bosch platinum 2's and are still almost brand new looking, though I swapped them out just to be on the safe side. Cleared codes, and P0303 came back again after letting the car idle for a few minutes.

The symptoms of what's happening are as follows:
- Motor shakes pretty bad below ~800rpm, but runs much smoother > 1000 and even > 2000.
- While driving, you can hear what sounds like misfiring especially at low rpm.
- There is a distinct and severe lack of power as opposed to when it was running correctly.

My question is, could the misfire be caused by the lack of compression due to the exhaust leak, or would you think there may be something else causing it?

I'm planning on repairing the exhaust in the next week or so once I get the parts needed. I hope that clears everything up, but in the mean time I was wondering if anyone had any suggestions on what else to check to narrow down the problem.

Thanks!
Dan

As the the '96 has 115K miles, my advice would be to change all six spark plugs and replace the two knock sensors and go from there...

-Chike

[dizzan]

Originally Posted by Chiketkd

As the the '96 has 115K miles, my advice would be to change all six spark plugs and replace the knock sensors and go from there...

Yes, I did just change all 6 plugs < 3000 miles ago. Upon getting the misfire code, I RE-changed the 2 middle plugs just to be safe, even though they appared to be sparking fine (just from looking at them). They're Bosch platinum 2's all around. As for the knock sensor, wouldn't that throw it's own OBD code?
Thanks

[Chiketkd]

Okay, I re-read your post and have a few questions:

1) Are the Bosch Platinum 2 plugs OE replacments for the SVX? If they don't have the same heat range as the OE plugs it could cause a misfire.

2) Have you checked the fuel injector for the number 3 cylinder? When facing the engine from the front of the car, the cylinders are numbered:

5-6
3-4
1-2

Bad/incorrect plugs and a clogged fuel injector are the most likely causes of your problem. Either way, I'm pretty sure it wouldn't be from an exhaust leak by the main cat...

-Chike

[dizzan]

As for the plugs, I've used the platinum2's in my '92, and now in this '96 for a couple thousand miles before any of these issues came up. Bosch lists the 8303 model platinum2's as replacements for OEM. I think I still have the previous plugs that I took out when I purchased the '96, so perhaps I'll try swapping them in.
I'll also check on the injectors. What's the best way to check them?

I'm thinking about redoing the whole exhaust while I'm at it and getting rid of some of these "extra" cats I saw your setup while looking through some threads... I was just wondering if you'd mind sharing what you paid for the whole setup?
Thanks again,
Dan

[Chiketkd]

Originally Posted by dizzan

I think I still have the previous plugs that I took out when I purchased the '96, so perhaps I'll try swapping them in.

If the plugs that were in the car before don't throw a code, then you know it's the Bosch plugs you bought. Personally, I only go with the OE NGK plugs from my dealer.

Originally Posted by dizzan

I'll also check on the injectors. What's the best way to check them?

No need to check the injectors, just the injector for the #3 cylinder. To remove, you'll need to unscrew a metal cap (that's held in place by two screws) and unclip the electrical connector going to the injector. Getting the injector out of the fuel rail can be a bit tricky though as they are known to get stuck in there with age. The injector should come up and out with a light tug.

Here's a pic Svxfiles took of an SVX injector:



-Chike

[RedHotSVX]

Originally Posted by dizzan

Yes, I did just change all 6 plugs < 3000 miles ago. Upon getting the misfire code, I RE-changed the 2 middle plugs just to be safe, even though they appared to be sparking fine (just from looking at them). They're Bosch platinum 2's all around. As for the knock sensor, wouldn't that throw it's own OBD code?
Thanks

I bought my SVX with a misfire from the dealer I work at,cleared the code,came back about 1 1/2 months later.I cleared it yet again,came back on.I replaced the spark plugs with NGK Iridium plug's from Motorsport's.It's now been an additional 12 month's,the only time the light came back on was for a knock sensor,which I replaced.But no misfire's...

[RedHotSVX]

Originally Posted by RedHotSVX

I bought my SVX with a misfire from the dealer I work at,cleared the code,came back about 1 1/2 months later.I cleared it yet again,came back on.I replaced the spark plugs with NGK Iridium plug's from Motorsport's.It's now been an additional 12 month's,the only time the light came back on was for a knock sensor,which I replaced.But no misfire's...

My misfire was also a #3....Hmmmmmm..

[dizzan]

Originally Posted by RedHotSVX

I bought my SVX with a misfire from the dealer I work at,cleared the code,came back about 1 1/2 months later.I cleared it yet again,came back on.I replaced the spark plugs with NGK Iridium plug's from Motorsport's.It's now been an additional 12 month's,the only time the light came back on was for a knock sensor,which I replaced.But no misfire's...

I wish mine lasted a month! I drove it around the block and the code was back

[Chiketkd]

Originally Posted by RedHotSVX

I bought my SVX with a misfire from the dealer I work at,cleared the code,came back about 1 1/2 months later.I cleared it yet again,came back on.I replaced the spark plugs with NGK Iridium plug's from Motorsport's.It's now been an additional 12 month's,the only time the light came back on was for a knock sensor,which I replaced.But no misfire's...

The stock NGK plugs are two steps colder than what most NA cars use. The SVX uses: NGK pfr6b-11

Which means is has a heat range of +6. Most n/a cars use spark plugs with a heat range of +4.

What's the part # for the Bosch Platinum 2 plugs you purchased?

-Chike

[dizzan]

Originally Posted by Chiketkd

The stock NGK plugs are two steps colder than what most NA cars use. The SVX uses: NGK pfr6b-11

Which means is has a heat range of +6. Most n/a cars use spark plugs with a heat range of +4.

What's the part # for the Bosch Platinum 2 plugs you purchased?

-Chike

Sorry, it's the 4303 Platinum2's (not 8303 as I typed before)
http://www.boschusa.com/AutoParts/Pa...e=H6+3.3+8+GAS

[Chiketkd]

Originally Posted by dizzan

Sorry, it's the 4303 Platinum2's (not 8303 as I typed before)
http://www.boschusa.com/AutoParts/Pa...e=H6+3.3+8+GAS

The part # isn't very descriptive, but they also fit 993 and 996 Porsche's and after searching the Renntech forums, it seems like they have a heat range of either +2 or +4. If that's the case, you really need to pick up a set of OE plugs.

www.langstonspeed.com sells them at a great price!

-Chike

[dizzan]

Originally Posted by Chiketkd

The part # isn't very descriptive, but they also fit 993 and 996 Porsche's and after searching the Renntech forums, it seems like they have a heat range of only +2. If that's the case, you really need to pick up a set of OE plugs.

www.langstonspeed.com sells them at a great price!

-Chike

I'll have to see if my local dealer has them... but wouldn't other cylinders be misfiring as well, not just #3, if this were caused by the plugs?

[Chiketkd]

Originally Posted by dizzan

I'll have to see if my local dealer has them... but wouldn't other cylinders be misfiring as well, not just #3, if this were caused by the plugs?

It all depends. Deposits on injectors or valves build up at different rates. Your #3 cylinder is running lean for some reason...

Btw, SVXers have run Bosch plugs with a heat rating of +4 with no issues. I suspect a well-maintained engine will not have any problems with these plugs.

-Chike

[lhopp77]

Have you checked the coil pack on #3? I would cause it to miss---not necesarily a misfire by most definitions.

Lee