Well I thought I'd get at least 6 months out of this car before trouble comes to town, but here we are

I was driving in to work this morning (stop-go traffic) and the car suddenly starts misfiring really badly. After a few seconds I get the Check Engine Light. This light will flash every few minutes before staying steady-lit again (keeps sending a code?).

The misfire seemed to get slightly worse and then remained the same - a steady misfire that's worse when accelerating at low speeds. Misfire continues at idle. I think it gets slightly worse as the temps rise, but that could be just coincidental.

There is also a fairly loud ticking noise at idle I've never heard before coming from somewhere around the exhaust on the passenger side - somewhere near the cats.

I just took it to Autozone and used their OBDII reader, which looked like a really cheap model. I get the code P0300 - 'multi-cylinder misfire'

So I'm really looking for where to start with this problem. I don't get any bad fuel smells and a visual inspection of the engine bay with torch doesn't reveal anything obvious. I'm thinking it's electronic. I don't have a better code reader.

More info: the water pump and opti were both replaced May last year. It also has had plugs and plug wires replaced recently (one of the reasons I picked this car was all the recent maintenance).
It is my DD and I do 50 miles a day in LA traffic - a mix of fairly fast freeway and stop-go crawling traffic. Temps go the full range, from 220 to 192, with quite a bit of time spent in the 200s every day.

I've not had any other problems. However the last time I drove it was Friday night and I had a very weird engine surge while I was decelerating in 2nd gear. THe engine was just warming up and I was using engine breaking to slow in 3rd. Revs seemed unusually high so I changed down to 2nd, still foot off gas. suddenly it was like someone stamped on the accelerator pedal and the car surged. I had to hit the brake pretty quick! It didn't do anything else unusual and we were very close to home. The car has never done anything like this since I got it in October - prelude to this misfire problem maybe?

thanks!

 

Here's a bump for you....

 

Start with the IAC (idle air control valve), EGR (exhaust gas recirculator), and TPS (throttle position sensor). Then on to the expensive stuff like a bad injector(s).
I'd put my money on the EGR.
Hope this helps.

 

thanks!
Didn't they do away with the EGR on 96 models?
How would I test these things?

I'm going to be putting an order in for a FSM as soon as I get home!

 

The LT4 doesn't have an EGR.

I don't think its any of those things. Do your temperature guages (both mechanical and electrical) read correctly and somewhat close to in number to each other?

Sounds like you have an exhaust leak. Where exactly is the ticking noise coming from?

If you think its coming from the exhaust take it to your local frendly exhaust guy and he should be able to tell you exactly where its coming from, and fix it for cheap. It might also be your cats have gone bad, but I don't know a whole lot about that so someone else who has experienced hopefully will chime in.

Have you checked your plug wires to make sure they are all ok and not touching the headers? At night start the car and open the hood and see if you see any sparks from around the spark plug wires and especially where the spark plug wires meet with the spark plugs. If you see any flashes of light, little arcs, then you need to (first turn the engine off of course) and after she cools a bit check to make sure your spark plug wires are on fully. If they are, then you probably need new plug wires.

 

on the LT4 they did, but not on the LT1.

 

thanks Cold_B

Temp gauges seem ok - I have been watching them really closely the last 2 weeks because I thought I noticed it running a bit hotter since I reset the Hypertech programmer back to stock settings. I may have had the fans come on at a lower temp before, hence the higher readings. THe analogue gauge is hard to read but generally follows what it says on the dig display as far as trends go. Cooling appears normal at speeds above 30mph, ie around 192/ 194, and in traffic climbs slowly to around 220/ 225 before going down again when the fans come back on or I get moving again. Oil temp gauge will generally follow the water temps up to a stable temp of about 215. highest I've seen it go is 219

I already had a cursory look with a torch at the leads but didnt see anything - I'll check for visible arcing in a bit when I leave work (its dark now). I just heard from an experienced LT1 mechanic (who wont go near them anymore) that he thinks its probably leads too and I could spray a bit of water on them as this will make it easier to see.

The ticking noise tho, that bothers me and it started at exactly the same time as the misfire. It sounds like its coming from around the passenger side cat - would this kind of exhaust leak cause the whole engine to misfire? o2 sensor? Maybe its just a rattle thats caused by the uneven firing...

 

Well you should be good to go on the temp thing. I was just wanting to check to make sure they were fairly close as the computer uses the temp sensor to help it figure out the amount of fuel needed. I know some people here on the forum have had trouble when the temp sensor went south.

I'm pretty sure an exhaust leak could a misfire, I know when I have had an exhaust leak the car drove alot worse, even when the leak wasn't that bad. I had an leak at my resonator and the car drove pretty bad even thought the leak was that far back.

I highly suggest you take it to an exhaust shop tomorrow and they will be able to tell you if you have one, and quickly and cheaply fix it.

If the noise is down by the pass cat, then I would really think it would be a leak.

Check for arching to, it sure could be a bad plug wire.

If its not either of those, then it would be time to start looking at other parts.

 

Thanks again B - good to know. Will let you know

 

This sounds similar to a problem I had not to long ago. Mine turned out to be a cracked spark plug...the clicking sound on mine was the arc jumping of the plug to the header. If its a cracked plug and you look for it at night it will light up like a fireworks show near the plug. When I first found it I could not see the crack on the plug until i actually took it out. Anyway hope its something minor for you.

 

Sounds like a problem I had a couple of years ago. At night or in a dark garage, start your engine and open your hood and with the engine running, look for a spark gap/flash/arc etc. Sometimes a plug wire touches or grounds on a part.

If you see that type of light show, turn off the engine and use a zip tie to move the plug wire from the ground.

The above worked for me over two years ago. My 1996 also threw that code.