Here's what I've got.. I have a 99 em1 with 177000 miles... Having a very strange misfire, I always run premium unleaded fuel from Shell religously and recently its misfiring badly and getting horrible mileage. The other day I slacked and couldn't make it to shell and went to exxon... Being sick and sleep deprived I accidentally pumped 87 low grade gas into my car and proceeded to work... The miss was still there but was hardly noticeable compared to before... I check often for codes and there are none, any ideas what could cause this strange behavior? Any positive help is greatly appreciated seeing as this has been an on going problem... Thanks!

 

bring it to my shop. We can hook it to the MODIS, and see exactly where your misfire is.

 

Where are u located and how hard is that going to hit me in the wallet? Lol

 

Oh and I forgot to mention, I used to get 400 miles to a tank, I'm now getting around 250 under normal driving...MSD pro billet dizzy about 1 year old with coil and coil driver, "performance" wires also about 1 year old, and Denso irridium plugs 1 year old as well.

 

Your aftermarket ignition system may be having some fun with you.

Otherwise, check the ignition timing with a timing gun.

 

Would that make it vary with the gas? Maybe the gas didn't really do it and it just happened to straighten itself out temporarily...will check ignition timing, thanks ron

 

If the ignition timing is way off, check whether the mechanical timing is off by a tooth.

 

What is the best/ easiest way to check that? I know just by looking at the cam gears its hard to tell one tooth

 

Remove the valve cover and then the upper timing belt cover. Put the front end on stands, and turn the crank pulley ONLY counterclockwise until the cams are perfectly positioned at TDC1. Then look to see whether the crank pulley is also positioned precisely at TDC1. If not, the timing belt slipped.

 

And tdc on the crank is the white mark correct?

 

Yes. See diagram.

 

Lol sorry, I'm on my blackberry and pics aren't the greatest.... Thanks a lot ron!

 

Staunton, VA

I do all scans for free, any diagnostics is $65/hour

 

Thanks but ill have to pass on the shitty gas mileage all the way up there and can't really afford 65/hour right now, tryin to get a house and married and money is tight! Thanks tho I appreciate it

 

i completely understand. if you can get to a decent scan tool, you can try and read misfires, and try to trace it. fuel filter recently?

 

New fuel filter, however, on the way to work today the crank pulley bolt backed itself out and threw the alt and PS belts and dropped the small 6 dollar crank key...got new belts and new key and bolted the crank pulley back on and reassembled everything in the parking lot that I luckily made it to, fired it up and it sounded like it had a beast *** cam in it...timing jumped somehow so I'm thinking that is what it couldve been and just gradually getting worse... Car has been towed and by a friend who owns a garage and is a reputable mechanic who is going to set the timing back since I'm sick of F'in with it. If the misfire still occurs when I get it back tomorrow then ill repost yet again lol. Thanks for the help thus far