[96_LS_4dr]

Ok, I'm going to start off by saying I'm definitely a noob on here, so I apologize in advance if this has been answered, but I DID try looking around first. I searched far and wide with no avail... *sigh*

So, I've got a '96 LS auto with a misfire. A pretty bad one. It's low RPMs only. Seems to be just fine in the mid-high range, but as soon as I'm just above idle, it misfires pretty bad. Not to the point of stalling, but it makes the engine rock 4 inches front to back. (Yes, my mounts are fine). Engine codes galore, but deciphering anything they tell me at autozone is pretty futile...

I replaced the distributor, wires, plugs, sea foamed the crap out of it (valve train, intake, and fuel system), adjusted the distributor to the point that it would idle nice when warm, and replaced the PCV valve.

I did notice that when the A/C button is engaged, the engine bogs down big time and shakes badly. This is a randomly occurring thing. Sometimes it does, sometimes it won't... ?? The compressor is fine. Bearings are good, holds pressure, and the A/C system pumps out nice cold air.

It is a random misfire code that was read at autozone, and it is very clear and audible when it happens. It almost sounds like the engine "stutters" every 10 seconds or less.

I looked for vacuum leaks, and nothing. Everything is good in the vacuum department. However, there is the sensor on top of the intake manifold that's right by the throttle body. I guess it's the evaporative emissions purge control solenoid (EVAP solenoid)? I unplugged it momentarily while the engine was idling and nothing happened to the idle. Could this be the sign of a faulty sensor? Or does it do darn near nothing (aside from it's intended purpose of allowing gasses to be released)? I did some research on that solenoid, and supposedly it affects the A/C system? I have no clue, but that's why i'm here asking. lol

If anyone has any tips and/or suggestions, I would be very grateful.

Thanks all!

 

[dpaton]

Heavy bogging when the A/C is on points to the IACV, but not always.

Misfires can be caused by a lot of things. We need the entire list of codes.

 

[96_LS_4dr]

Heavy bogging when the A/C is on points to the IACV, but not always.

Misfires can be caused by a lot of things. We need the entire list of codes.

Allright, I will run to autozone and get my grocery list of codes again. lol

Thanks for the pointer, but I guess if it's something as broad as this, I'd need to put up the code list to get any for-sure answers, huh?

I'll be back with the codes. Thanks again!

 

[MorningZ]

Thanks for the pointer, but I guess if it's something as broad as this, I'd need to put up the code list to get any for-sure answers, huh?

No codes = broad, could be anything

Knowing the codes = point in the right direction to fix your issue.. your car knows what it wrong and will lead you in the right direction

 

[96_LS_4dr]

No codes = broad, could be anything

Knowing the codes = point in the right direction to fix your issue.. your car knows what it wrong and will lead you in the right direction

Ok, I have returned with some codes.

And just for reference, the car does smoke a bit. Guessing valve seals because it puff a good cloud on a cold start up, but dies out when warm.

Anywho... Codes are: P1399, P0301, P0302, P0303, P0304, P1300

So, if anyone could point me in a "for-sure" direction, I'd be VERY grateful.

My assumption originally was that the valves would need adjusting. Engine has 200,000 miles on it. I would assume that valve seals are pretty much gone, but are the valves in a B18B1 adjustable?? I would probably make that my next plan of attack.

Thanks again all! Really appreciate it!

 

[gsrider004]

I think your timing belt may be off by 1 tooth or more. Check your timing and if that isn't it, I would check spark plugs, plug wires, ignitor, icm, firing order, and valve lash. Sounds like you have checked or replaced most of those items, but this is what I would be looking at.

 

[macura2001]

Sadly my 2001 LS with 150,000 is having the same issue now. I get the P1399 pending code and after driving for 150 miles or so I finally get a P0300, P0301, P0302, P0303, P0304.

So far I have put in new plugs and swapped wires from known good car. I cannot tell it is misfiring though. It runs and drives perfectly fine. It does burn oil. It seems to set the P1399 code only when its cold started. I also did a valve adjustment and nothing changed.

Plan is to swap dizzys with a 2000 LS I own this weekend and go from there. Also to add to the mix, under hard load and uphill acceleration in 5th, the CEL started flashing until I let off the gas. leading me to think it is the coil being weak. I don't want to a parts changer though.

Also SAD is that all the great TI articles got lost when the sever changed. used to be a good Ignition Trouble shooting article that is missing. Anyone have any info on that?

Thanks,
MAC

EDIT:

found it .... Advanced Ignition Troubleshooting

 

[jjkz24]

Sadly my 2001 LS with 150,000 is having the same issue now. I get the P1399 pending code and after driving for 150 miles or so I finally get a P0300, P0301, P0302, P0303, P0304.

So far I have put in new plugs and swapped wires from known good car. I cannot tell it is misfiring though. It runs and drives perfectly fine. It does burn oil. It seems to set the P1399 code only when its cold started. I also did a valve adjustment and nothing changed.

Plan is to swap dizzys with a 2000 LS I own this weekend and go from there. Also to add to the mix, under hard load and uphill acceleration in 5th, the CEL started flashing until I let off the gas. leading me to think it is the coil being weak. I don't want to a parts changer though.

Also SAD is that all the great TI articles got lost when the sever changed. used to be a good Ignition Trouble shooting article that is missing. Anyone have any info on that?

Thanks,
MAC

EDIT:

found it .... Advanced Ignition Troubleshooting

Have you performed a compression test on the motor yet just to rule out a mechanical issue?

 

[macura2001]

No compression check yet. I could do that easy enough after work on Saturday.

 

[macura2001]

cylinder 1 dry- 200 wet- 210
cylinder 2 dry- 160 wet- 170
cylinder 3 dry- 125 wet- 130
cylinder 4 dry- 160 wet- 170

definitely burning oil on 3. spark plug was very ashed up before I replaced them with new. The interval between setting the hard code for P0300, 301, 302, 303, 304 is becoming less miles.

I wonder maybe if the cylinder 'power' imbalance is causing the random misfire.

 

[jjkz24]

Any time where compression is low, it'll cause misfiring. There should never be more than a 10% difference between your highest reading cylinder, and lowest. From your numbers above, you're at 37% between cyl #1 and #3.

Likewise, you're 20% between cyl #1 and #2&3.

If your compression increases with oil in the cylinders (wet), then your culprit is rings.

But, it's the low compression causing the mis-fire that you're having.

 

[macura2001]

Any time where compression is low, it'll cause misfiring. There should never be more than a 10% difference between your highest reading cylinder, and lowest. From your numbers above, you're at 37% between cyl #1 and #3.

Likewise, you're 20% between cyl #1 and #2&3.

If your compression increases with oil in the cylinders (wet), then your culprit is rings.

But, it's the low compression causing the mis-fire that you're having.

So it will set a code for every cylinder for misfire even if that cylinder is not misfiring? I guess the fluctuation in crank speed is throwing the codes