rrs1619

Hey guys,

This is not a thread asking for questions. This is a thread for the diagnosis of my 1995 ES300 given the following conditions. It stumped me to the point where I spent about $600-800 to replace a $80 part.

Long story Short:
-Symptoms:
--No power below 3000rpm
--Engine Missfire
--CEL On
--Low Fuel rail pressure
-Solution
--Bad O2 sensor.

Long story Long:
Out of nowhere over the summer, my car becoming limp. It would develop a misfire, and speeds above 35mph and the CEL was on(obviously). And the car developed almost no power. However, once the car passed around 3000-3500rpm it would start developing it normal power/torque at that rpm so it would take off like a rocket.
When we plugged the computer into the car, and let it idle the car would not throw any misfire codes. It was only when the car was power-braked up to around 3000 rpm where the misfire codes would develop on the front bank of cylinders(the easy ones).

Naturally, we thought it was either the spark plugs or the distributor caps. The spark plugs where swapped two years prior, so they were inspected. For two year old spark plugs, nothing was wrong with them. So, we went straight to the distributor caps. Luckily, I knew the parts manager at a local Toyota, so he was able to get me the distributor caps almost at cost. I needed to get my rear valve cover gasket replaced, so we decided that while the rear bank of cylinders was easily accessible. We would place the new distributors on the rear bank of cylinders and the old rear on the front.

After the swap, things seemed to work fine. Except now the car would develop a missfire at a slightly higher rpm/mph. Weird. Next up, we thought the fuel injectors were the culprit now that the computer would throw low/sporatic fuel rail pressure. We ended up running the car on some high-end fuel injector cleaner to really wipe them clean. It was a cheaper fix than getting the fuel injectors replaced as well.

After that, the new top speed on the car was about 50mph before the misfire developed. The car was still not developing ANY power below 3000rpm. After I went back to the shop, we decided we would unplug the O2 sensor for ****s and giggles. After that, the car ran PERFECTLY! So, we ordered a new O2 sensor and the car ran fine.

The good news to take away from all this is, now my when my distributors go, it will be the ones up front and not the ones in the rear.

Hope this helps!

2013FSport

iTrader: (2)

The Coil Over Plugs (COP) you replaced likely only failed under load while warm. Their failure in combination with fuel cleaners could have taken out out the aged O2 sensor(s).

Point the COPs were bad causing a misfire. If the O2 sensor is also determined to be bad the engine will run default fuel trims for STFT and LTFT. This is going to be richer than the the ideal AFR of 14.7:1 stoichiometric burn the O2 sensors try to maintain. P030X misfires mostly happen when warm and under load hence why you can't duplicate them in the driveway until you power brake the vehicle. Speculate it needed everything...
rockauto is a good source for most items and a fraction of the cost of dealership wholesale....

Oro

What this helps is, I hope, to prove that throwing parts at a problem is not the solution.

Lots of users on this forum donate their time freely and generously to try to keep folks from doing just this. And I hope that helps!

rrs1619

Forgot to mention that the engine was still misfiring after I swapped them with good ones. It was only after the O2 sensor was replaced that the Engine Misfire issue went away.
Rockauto is a good source, but that didn't come to mind. That and I was getting the COP's at cost through my parts manager friend. Even if they weren't bad, it's now an issue I do not have to deal with anymore!