Bad Gas and Cyl #4 misfire

[Subarunation 713]

It has been a while since I have posted. I have made great use of the search on my last few issues and didn't have to bother the group.

 

This one however has the mechanic and me a little perplexed. My wife's 96 OBW 2.2 5 speed 152K miles had a CEL come on. It ran fine but had a little hesitation occasionally. I made an appointment with our mechanic but since the car wasn't dead with it's tongue hanging out we kept driving it as we need 2 cars. The light was still on hesitating occasionally and sometimes the CEL would blink.

 

Just to make sure the mechanic got the codes pertinent to our current problem I disconnected the battery to clear al the codes. The CEL came back on and we dropped it off at the mechanic. He checked the code and it was a cyl 4 misfire and that was it. He checked injector resistance, pulled the plug and it was as clean as could be (only had 4,000 miles on the plugs, air filter, PCV, and fuel filter). He cleared the code and let it idle waiting for it to come back on. He let it idle for 2 hours and it never came back on.

 

Frustrated he told me to pick the car up and see if it would come back on again. Seeing that the plug wires were original I stopped at the stealership and picked up new plug wires, what the heck it was beyond time anyway.

 

The car ran fine for about a day and the CEL came back on. Same code. That was Saturday so we drove it for a couple of days. Just for giggles I put a bottle and a half of isopropyl gas line antifreeze in the tank and topped it off. (As a habit I put a bottle of isopropyl gas line antifreeze in the tank about every 2 to 3 weeks year around).

 

I told my wife I wanted to drive her car and see what was going on myself. I drove to work Monday and the car ran rough and the ECL light blinked as I drove it. After about 20 minutes it smoothed out and has been fine ever since. The ECL turned itself off after 3 cold starts and has been the smooth running machine it always has been.

 

Now, the $64,000 question. Why only the #4 cylinder misfire code? Obviously it was bad gas. The mechanic asked that early in the problem but I had told him no, it happened before the previous fill up. I was wrong (not the first time)! Why not #1, #2 or #3 cylinder misfire? Why always #4?

 

The important thing...the car is now running great!

 

Thanks for any input,

Greg

[SevenSisters]

This may not answer your question, but it has to do with the use of gas line antifreeze. A long time ago, with a carburated vehicle, I added a bottle of gas line antifreeze in August to "get it off my garage shelf". Well, I fought fuel line vapor lock and misfires until the tank of gas was used up. Even in the summer, Michigan (except for the UP) isn't cold enough to run ipr-oh in your gas.

 

With the pressurized FI we have now, vapor lock may not be a problem, but I would hold off on adding anthing except FI cleaner and see if it helps.

Good Luck.

[robm]

Many years ago, a friend of mine experienced vapour lock on his injected Supra, while using a commercial gas/ethanol mix. My carbed 510 ran the same stuff with no trouble at all. So the pressure may not always help. Fuel rail location is part of the equation here - how close to a heat source?

[Subarunation 713]

As far as the antifreeze, I have been doing it for years. A 12 oz bottle of isopropyl in a 13 gallon tank of gas should not produce vapor lock. If it does, I will take the car out back and shoot it!

 

Still can't figure out the #4 cylinder code and nothing else.

 

Greg