Misfiring Issue, Cant Figure it Out

Got a 2000 3.4 L V6 with 285 k, only 30k on a swapped used motor.

Getting codes for cylinder 5 misfire. My mechanic got all new plugs, wires, coils, switched injectors, then got a brand new injector for cylinder 5. Code will not go away. Was also compression tested and said it was fine. He thinks it could be the computer.

Recently replaced MAF, Fuel Filter.

Ive seen many other threads with exact same issues but inconclusive results.

 

Isn’t cyl 5 and 6 prone to head cracks on that engine? Hopefully not the case but...

 

Is it still misfiring?

 

@RedManRocket Still Misfiring. After getting it back from the mechanic I just drove it around town and seems to run fine but code won't go away.

 

Injector I bet.

 

Pull the spark plug and take it look in side to the cylinder. This happen to me on the 3rd cylinder I had water in there.

 

With all of the things that were done we are assuming that the motor is mechanically OK.
Can you feel the misfire? Try putting a vacuum gauge on it and see if it is steady or if there is a vacuum fluctuation. If there is a rythmic vacuum fluctuation then there is a mechanical "issue". If there isnt then there is something non mechanical.

As to the non mechanical, the only things I can suggest is that you are going to have to find a tech that has a lab scope that knows how to read the ignition primary coil patterns and the injector voltage patterns. There could be an issue where the driver for that fuel injector is damaged. A set of NOID lights

https://www.oreillyauto.com/shop/b/...s--electrical---diagnostic-19165/81e7e5a1e58e

might help... https://dannysengineportal.com/noid-light-testing/

 

I can't feel any misfire, just a slightly jumpy idle at stop lights. I'll try these out, but what might be a "mechanical issue" causing this?

 

Tonight the truck just stalled on me at a stop sign for the first time ever.

 

Any new codes?

 

I do not read where a scanner was used for diagnostic purposes other than the P0305 code. Fuel trims, pending codes, live data can all be used to help figure out if this is a mechanical issue or something else.

The mechanical issue could be almost anything but the fact that it is isolated to cylinder #5 really narrows the search. Have the valve clearances been checked latley. A slightly out of spec valve clearance, one or two thousanths too loose or thight, wont cause and issue but one with only one or two thousanths clearance will. A broken valve spring will cause an issue too as the valve wont seat perfectly every time. Is there any oil in the bottom of the spark plug well for #5? Take a look at the engine harness where it travels from injector to injector really close and poke, prod, wiggle all along the harness to see if anything changes. Wires get old, connectors get flaky.

 

Now getting P0300 and am still getting P0171.

Guess I'm gonna take it to another shop for a diagnostic test to figure it out.

 

first I have read about a P0171 and a P0300. Both of these point to a problem that effects ALL cylinders not just #5. These are usually related to a vacuum leak or a bad MAF, something that effects ALL cylinders. The most overlooked vacuum leak is the brake vacuum booster.

 

UPDATE: After another mechanic, compression test results are

When hot:

1:188

3:190

5:152


when cold:

1: 185

3: 183

5: 138


There was a 25% cylinder leakage on Cyl #5 around intake valve. Valves need to be repaired. They tried to add shims but no luck.


I think that when they swapped the motor a year ago, they kept the original valves??


So its time to sell unfortunately. Thanks for all responses.

 

Awww, suck. Where you/truck located? Might get lucky and find someone that likes the truck and will do their own labor on the tear down. That's a lot of money on new parts that your mechanic had you buy and pay him to install that had nothing to do with your bad valves/heads..... If you get my drift.

 

How much do you into the truck ?

That's what I was thinking and the first (mechanic) said compression tested good .

 

Yeah it sucks. I hate when this crap happens to people. People always looking for a first gen Tacoma. Quite possibly the easiest truck to sell in the history of the automobile

 

Yeah a bummer, Im in LA so hopefully I can get a a couple thousand?