PO305 Cylinder 5 - misfire (solved)

Truck started running rough Monday. Code was PO305 cylinder 5 misfire.

• I swapped coil packs around and misfire remained on cylinder 5.
• Plugs look good, but swapped the one from 3 to 5. Still misfire on 5
• No sign of coolant in the oil, and no sign of loosing coolant (but that would be harder to tell)
• Plugs and wires are only a couple years old. I'm thinking maybe injectors.

Sometimes it runs just fine, other times very rough like it's running on 5 cylinders. Seems to be worst when I drive a while, park it for 5 or 10 minutes, and drive again. It initially started acting up about 20 or 30 miles after I had fueled up. I normally use the ethanol blend stuff, but this time put premium/ no ethanol in it. The fuel might not be related, but seems like quite a coincidence if it's not.

Any suggestions?

 

why would losing coolant be harder to tell?

 

Motorwest Denso injectors. Use the SuperLube supplied with them in place of the gas/fuel as described in the FSM.

 

Check the coil boots and plug wires really good for signs of arcing

Listen at each injector with a metal tipped stethoscope and compare #5 to the others when the problem happens. They should all be ticking away with roughly the same sound. Or get down to the connectors and ohm each one out

Does it run better if you feed alternative fuel into it?

 

Cyl 5 injector is accessible right? So if you have a DMM check injector resistance. I suggest checking cold and hot. I had a similar issue and finally isolated to a weak injector. The resistance on mine was only out of spec when hot - FSM does not distinguish between hot and cold AFIK so I don't think it should change much but in any case mine was obviously bad.

I think this is a rare failure type (electrical failure) but easy to check. Injector could still be bad if its mechanical issue.

 

It's not leaking coolant, that would be easy to tell. I was refering to burning it, as in bad head gasket or cracked head. There isn't any obvious steam coming from the exhaust, but with how hot and dry it is right now it might not be visible.

 

A chemical block tester kit would detect a coolant leak into a cyl

 

Well anything is accessible if you take enough parts off.

Wouldn't it be easier to just switch two of the injectors and see if the misfire moves with it?

 

I'm not familiar with that process. Is this a kit I can buy at an autoparts store, and do the test myself?

 

If a coil boot was bad wouldn't the misfire move when I put it on a different cylinder? Also, wouldn't bad wires only effect the cylinders on the other side?

Might have to pick one up. I have a medical stethoscope, but not one made for automotive uses.

 

For all the work it takes to get to the injectors, it's FAR easier to just replace them all while you are there. The Denso injectors (from Motorwest) are very affordable. If you're still on your stock injectors, it's time to change them out. Same is true for the valve cover gaskets. If you haven't done those- just do them while you have all the intake manifolds off. I did both (as well as replace all the vacuum lines) easily within a weekend.

 

Looks like they are out of stock. Plus I'd kind of like to make sure they are bad before spending $300

I changed the valve cover gaskets, plugs and plug wires two years ago. Vacuum hoses a year ago.

 

or you could simply look at the tank and see some missing. Mine and a lot of other people that seems to be where cracks form. Mine Only put steam out first few seconds while engine was cold

Yes easiest way to knock that off the list and not taking anything apart.

https://209yota1.com/product-category/engine/fuel-systems-components/fuel-injectors/

 

Yes you can get one at Napa

It's just some common things to check for

 

Long screwdriver will do the same.

 

It would have to loose a fair bit to notice a drop in the coolant level. How much does it loose with a bad head gasket? If it's only like a cup or two per 100 miles it wouldn't be very easy to track.

 

Best way to check for a slow loss of coolant is to look under the rad cap every morning before you turn the engine on.

If there's space to add coolant, fill it up and check the next morning. Over time you'll see if it's disappearing

 

I would check the cranking pressure on that cylinder and compare it to the others. I bet you get interesting numbers.

 

I'm thinking about siphoning all this fuel out of the tank and filling up with the ethanol stuff I have been using. That would be a fairly easy potential cause to cross off the list.

 

Doubt that you getting misfire on only cylinder 5 bc ther isn’t any ethanol in your premium gas.