Spark plug wire resistance

On 4/2021 when I did the timing belt on my 97 4Runner, I also replaced the spark plugs (Denso) and the three plug wires (NGK). Although I had measured the resistance of the new wires before installation, I had not recorded them (lesson learned for future).

A couple of weeks ago my son who drives the car reported that he is sporadically seeing the check engine light come on. OBD scan showed that to be a P0306 code - missing cylinder 6. Checked the car, spark plug is good and the three NGK plug wires tested at 8-10 k-ohms. I even swapped the coils and the P0306 code kept reappearing. Last Fri I replaced the NGK wires with Denso and since then the issue has gone away. The Denso wires have resistance in the range of 1.8-2 k-ohms. Toyota's spec says that wire resistance should be below 25 k-ohms but perhaps my coils are not as good as they used to be and a lower resistance wire is needed. I should have taken the time and measured the resistance across the coil terminals as well but did not. Anyway wanted to through this out in case someone else has experienced this. I was also wondering what is the preferred brand of spark plug wire.

 

Thanks. Glad it was easy for you to sort it out.

Preferred brand of wires? OEM. OEM OEM OEM.

 

Well after a week of no issues the check engine light came on and the OBD scan showed it to be a P0306 code. I am baffled now as to what the cause may be. Like last time the miss occurred during the drive on a relatively hot day (90F).

 

Swap the injector with another one. See if the miss moves.

 

Sumitomo!

 

Injectors were all refurbished 10K miles ago ~ (4/2021). I hate to think that one or more of them may have gone bad given the amount of work involved in pulling them out. I can really use a break with everything that is demanding my attention now.

 

Well, if spark is ruled out, which I think it is, you're down to a few things:

Bad head gasket.
Bad injector
Bad compression.

How were the injectors refurbished? Flow rated?

Pull the plug on that cylinder and how does it look?

Where are you getting your parts? There are so many fakes out there now I pretty much have to get stuff from a discount online TOYOTA dealer. Amazon and ebay are just a dumpster fire anymore.

 

I sent all six injectors for refurbishment to an outfit in California. They were flow-tested (before & after). I think two were weak so I ended up getting two refurbished ones plus my six that I had sent them.
The plug looks good. Thus far the issue has happened every time it is has been hot outside > 90F
The parts that I put into that car last year (timing belt, water pump, .., etc) were procured from McGeorge Toyota. I think I got the NGK Spark plug wire set from Rock Auto.

 

Sounds like you're doing everything right. I'd maybe do a test on exhaust gases in the coolant to see if there is a head gasket issue. Otherwise maybe a compression test (wet and dry) is in order to see what the health of the cylinders are.

 

^^^ THIS! Verifying these two items would likely eliminate or confirm the worst-case scenario.

 

Just an update ...
The intermittent miss became a constant miss last week. This made it easier to diagnose the problem. Connecting and disconnecting the #6 plug wire did not affect the engine RPM so this meant no fuel. Earlier this evening I removed the components to have access to the injectors. Resistance across the #6 injector's terminals is 640 ohms vs. the other two at 14.3 ohms. Spec says they should be around 13.8 ohms at 60F. Injector 6 has definitely gone bad and I'll be replacing it once my parts arrive. Hopefully this is the only thing that has gone bad and everything else is OK.

 

So Injector 6 was flow tested but still went bad?

 

The short answer is yes. I had sent all 6 injectors to be tested (& cleaned) 16 months ago. Afterwards 4 were good and the remaining two were out of spec. They gave me two replacement (refurbished) injectors. After roughly 10000 miles injector 6 has gone bad. I should have marked the ones that they gave me so I do know whether the one that has failed was mine to begin with or not.