2.7 random misfire and start up issues, no codes.

Bought this truck recently from my friends coworker. He had told me he had some start up issues and didn't want to sell it to me til he fixed them. When I bought the truck he told me he changed one of the injectors (haven't actually confirmed) and the fuel regulator, it explained why the systems were reset, and that it was running better and he hasn't had any start up issues since.

Well fast forward a week and sounds like its misfiring under load randomly, then its back to perfect. Then one time it doesn't start. Cranks but no start. I unplugged/plugged the relays for the fuel system and lines from the regulator, sit 5 minutes and it cranks up first try no problem. Then take the car to my smog guy and he says his system is out service because the state tech has to come inspect something, but since it has known issues he just do a pre test and tell me if it will pass. He notices a small hiccup at around 25 but says it will pass no problem. Go back today that he's allowed to test again, and no pass, says the hyrdocarbons are significantly higher and the misfire is more noticeable this time. Start driving home and I can feel the shift from roughness back to normal.

The part that is stumping me is that no codes are coming up. In the past w/ other cars and trucks even if it misfires once the code comes on. Am I wrong to think this is a misfiring cylinder? any ideas based on the symptoms?

My plan is to put some injector cleaner in the tank, then plugs, the plug wires, and go down the list from to cheap to expensive until the problem goes away for good. Although if some one can point in the right direction and save me some money I'd appreciate it.

Thanks in advance, David.

 

Sounds eerily similar to how my son's Tacoma was acting. He had intermittent codes and sometimes none at all, but sometimes it ran; always ran when 100 percent cold.

Random stumble issue, easy to replicate | Tacoma World

Mark

 

Thanks Mark. I was hopeful it would lead to an easy fix but it looks like I'll have to start replacing things as well.

I went to autozone to buy some seafoam, drove ok, spent 5 minutes in the store came out and it drove perfect on the way home. Even thought to myself okay I'm not crazy this is definitely how it's suppose to feel. Start reading your thread and it had been about 10-15 minutes since I had got home. Went outside to test. Crank crank, no start, waited about 30 seconds and it started right up. Drove around the block, a little rough but not as bad as usual. Sat in the truck for exactly 5 minutes, started it up and it started but it struggled more than it does when 100% cold. Let it idle and the roughness kicked in. Weird thing is still no codes, so I should be able to pass smog if I can take it when it's running right.

I now remember the guy was offering to include a radiator for an extra 150 but it doesn't seem like it's overheating at all. I will probably start with the ECT sensor and start replacing everything until I can have it 100% perfect 100% of the time. Thanks for the input.

 

Start with the easy and free. I don't know your skill level or toolset, but I'd check vacuum lines, sparkplugs, coil boots and contact springs. Then use a scanner to see fuel trims to see if they change much with RPM / temperature. The engine computer uses the ECT sensor and MAF to adjust fuel trims, so you may be cutting right to the chase with the ECT. Lastly, vacuum leaks (injector seal leaks are a vacuum leaks) can sometimes be tricky, so don't neglect looking for them. They're also inexpensive and easy to fix (once you find them).

Mark

 

to answer your question about no CEL. It really depends on what is the cause for the PCM to trigger the CEL. For a misfire there has to be certain number of misfires occur before that code is set. Each code has different code setting criteria. If you scan tool can check for pending codes, ill bet that there is/are pending codes. Some codes require 2 drive cycles to set, others are instantaneous.

 

Yeah I cut right to the chase and it’s not the ECT sensor. Pulled it out and the resistance matches the graph in the FSM. Also changed the spark plugs back to oem style(had iridium ones gapped at .41). No changes.

LT Fuel trim was -13%. And I have no clue what that actually means. I will try and learn about this and see how it helps.

Also, I have a new issue now, trying to refill the coolant after messing with the ECT and I can’t get heat in the cabin anymore. I have a coolant funnel and it’s just not bubbling. When I used it the past the coolant in the funnel gets so hot that it’s steaming but this time it’s a cold as when I put it in. So I imagine it’s not circling for some reason. The drained coolant was a lot chunkier than typical as well so maybe that has something to do with it. I can’t imagine it’s the thermostat because it all worked fine before I drained it.

Also I discovered that when I turn the lights on the roughness significantly increases.I’m sure that’s just the low idle struggling to keep up with the extra alternator load but I’m not sure if that’s normal.

Lastly, I can recreate the no start 100% of the time. If I run the car and let it warm up, I can turn it off and turn it back on, if I let it sit 5-10 minutes it will not start on first crank. I have to crank it then stop, then crank again while stepping on the pedal. If I let sit for longer it starts first try.

Unfortunately no pending codes either.

 

Just update my own post, it was none of the above, was head gasket needs engine replaced.

 

Oh man. Sorry to hear that. Best of luck to you

 

Headgasket doesnt mean you need an engine replaced, unless you burned it down to shit