This morning on the way to work my C320 coupe check engine light came on and it started running rough after it warmed up, about 6 miles of driving. It would not go over 45-50 miles per hour and accelerated slowly. I took the car to Auto Zone to have them check OBD II and there were several error codes P 0300, P 0301, P 0303 etc, as well as a P 0715 and
P 0445. The local mechanic wants to change the spark plugs and go from there. He says the P0715 is now gone and only the engine missfire codes are there. My car has over 115K miles. I am sure a tune up won't hurt but I do not think it is the problem. Could it be the crank shaft sensor, or is the P0715 code the culprit, which according to the mechanic is not showing up on his reader like it did at autozone.

I was reading some threads about a limp mode, if my car is in limp mode will it miss fire on all cylinders?

Could it be the MAF even though there is no error code?

Could it be the Crank Sensor even though there is no specific code for it?

 

P0445 = Evaporative Emission Control System Purge Control
Valve Circuit Shorted

P0715 = Input/Turbine Speed Sensor Circuit Malfunction (transmission)

The 715 has nothing to do with this condition. The 445 could well be causing misfires on multiple cylinders if the purge valve is stuck open & causing a vacuum leak.

Check purge valve & circuit.
Check Plugs, coil packs & plug wires.

This is the purge valve - is it clicking? listen to valve with a screwdriver against your ear

 

Thanks Glyn,

Yes, the purge solenoid is ticking every second.

How do I check the coil packs?

Also cylinders 1, 2, and 3 are the misfire. Are these the ones on the passenger or drivers side?

 

OK, I replaced the spark plugs, they were really old and the electrodes worn down to almost nothing. still I am getting error codes 0300 0301 0302 and 0303, missfire cylinders 1, 2, and 3. I pulled the connector one at a time of the six coils and restarted car each time, it idled rough with each cylinder disonnected but idled ok when they are connected.

In park the engine will hit 4000 rpm and stop then slowly rise over 10 seconds or longer to close tp 5000 rpm.

when driving it the car will run fine as long as I do not try to accelerate hard. when i try to accelerate it will not go over 3000 or so rpm and then start missing. it will keep missing until i turn the engine off then on again.

could the three coils be breakking down under load?

Could it be clogged cats, especially on the 1, 2, 3 cylinder side?

Could it be a common wiring problem to the 1, 2, 3 cyllinders?

I am lost.

 

The ECU controls how far you can rev an unloaded engine. Cylinder numbers are stamped on the heads.

Move coils around & see if misfires change cylinder. Only DIY way to check them. Mark them so you don't get confused.

Your car is around the mileage that plug wires start giving trouble. Replace them

It's possible that you have a clogged Cat on one side but unlikely. It would wheeze through the exhaust.

 

The car runs OK, no errror or check engine light, until you try to press pedal hard to accelerate, sounds like it is being choked, then the rough idle starts. Error codes are p0301, p0302, and p0303.

I started the car with drivers side coils disconnected as a sanity check and it gave 0304, 0305, and 0306 missfire errors. Indicates that I am working on the correct side of the engine and the errors popped up quickly while idling.

I swapped all the coils one at a time from passenger side to drivers side. Still got 0301, 0302, and 0303, cylinders 1, 2, 3 missfire. All passenger side cylinders. Replaced wire set, pricey for 12 short wires. Still same. Replaced for and aft O2 sensors on passenger side, still same problem.

By the way the car was indeed well over due for a tune up, the plugs had a huge gap, especially on the passenger side where the error code indicated. Though they had a huge gap there was no fouling, or carbon build uo. They looked like the had been a little hot, dry and reddish colored, no carbon.

I thinking it is the passenger side cat. I do not have a pressure gauge to test the exhaust pressure for and aft of the cat, so my plan is to take it to muffler shop tomorrow.

A couple of more symptoms that say cat, a couple of months ago the exhaust sarted making a rattling noise, like rock in tin can. A cat with busted up ceramic? About a month ago the fan for the radiator started turning on soon after starting the engine, i attributed it to the texas 100 degree weather biut now I think a clogged cat was causing excess heat build up in engine.

Is there anything I may have missed that would casue these symtoms? That is missfire on one side of v6 engine.

 

Sorry - I did not know you had an exhaust rattle. Sounds like a piece of honeycomb broke off the monolith & is stuck post cat.

 

OK, i found a place that replaced the two rear cats for $500. The car is running great now that it has had a tune up and the new cats. The ratttle was the rear cats, it is now gone. It looks like when the ceramic fell apart inside the cat it must have turned sideways and blocked the flow. Oh and the fan for the radiator is not running full blast anymore. Looks like the failing cat was causing a bunch of problems, excessive heat, loss of power, and that horrible rattling noise.

Same shop that changed the Cats said they will replace my lower control arrms and align the car for $530. Best quote I have had yet. Also said I can buy parts and they will install and align car for $150. it is nice to find and independent shop that treats you right and prices right. The place was packed, 8 bays full and several cars waiting to be picked up or checked out. There were a bunch of repeat customers there that they new by name and the customers new their names. Great garage

Next I need to flush the cooling system and refill, 114K miles on original coolant.

 

Good news!. Stay away from speed bumps etc when your Cats are incandescent.

 

Glynn, tnks for the help