Random stumble issue, easy to replicate

My son brought his 2003 Tacoma Prerunner 2.7l over to the house because it's having a peculiar issue(s).

Here's the symptom(s)

1. Starts from cold and drives (seemingly forever) just fine.
2. Turn off the vehicle, wait 5-10 minutes
3. On re-start, no codes...but rough idle and seemingly not firing on RANDOM cylinders. If I drive it a mile or so the codes will eventually pop up (random cylinder each time)
4. Park it a few hours and I can drive anywhere....until I have to shut it down and restart it.

What I did to troubleshoot:

--pulled, checked and reinstalled EACH vacuum line (all were good). No change
--inspected and tested the brake-check valve (it was good)
--changed all plugs, plug boots and springs on the coils
--used a known good ignition coil on each random code misfire. No change
--cleaned MAF sensor, and also swapped in a KNOWN GOOD sensor to double-check. No change
--Replaced 10-year-old upstream O2 sensor with new OEM O2 sensor. No change
--found ONE injector that was bad (vehicle ran the same when it was unplugged) and replaced it (now it works as well as the rest when cold). No Change

My though process is that power is great (until restart), so fuel pump, valves, compression and filter must be OK. Checked intake manifold gasket for leak with starting fluid and nothing happened.

Started it cold this morning, and I went 30 miles on the backroads including stop signs and had to pass a farm tractor (got it up from 40-60MPH). Not a single issue, so i stopped for a cup of coffee and a burrito at a local gas station. Got back in and when it started....it was stumbling. I got random (different each time) misfire codes again.

I'm stumped...

Anyone with an idea of what to look at next? I'm thinking the Computer?

Mark

 

simple things first, as a test I would locate the evap purge line and disconnect that and plug the line where it leads into the intake. if is still misses, smell the exhaust for faint traces of coolant on first startup cold.

 

Good thinking. I disconnected the evap purge line, and plugged it at the manifold, which triggered an Evap code (no inspection here, so don't care), and took it for a spin. When I started it (cold), I also smelled the exhaust....and it smelled rich, with no white or blue smoke visible. Still no change as far as how it ran though.

Mark

 

My money is on the ECM. I just spent months troubleshooting misfires/ weird hesitation and poor acceleration. It was my ECM

 

I'm leaning that way too. I was watching Timmy The Toolman's vid, and he was trying to solve the same issue. His turned out to be crankshaft play. Not feeling that it's likely with the 2.7L though. That's why I'm still thinking ECM

Mark

 

OEM PARTS ONLY

 

Are all the computers the same for the 2.7L 2002-2004 Tacoma automatics? My truck is a 2004 and my son's is a 2003. Both trucks are PreRunner Ext cab 2.7l Automatics. Was thinking about swapping mine to his truck. If it works, I'll buy an ECM, if not...back to work trying to figure this out. It's nippy out there, and I don't want to spend any more time out in the cold than is necessary.

Mark

 

One more, does it happen when after that first drive from cold and then shut the engine down and then restart it immediately (no burrito brake)? Or is it only after "cooling down" for 5 minutes or so?

If so, maybe a leaky injector(s)? My thinking, maybe after shutting down it collects extra fuel in the intake and till all it gone, the engine will run rough. Just a wild guess.

 

Good line of thinking. It's ONLY after a shut-down and wait...but if I wait until it's fully cold....it starts and runs fine.

I'm thinking that as the fuel air control goes from open loop to closed loop, something isn't translating. When I restart in closed loop, it gets confused?

I just pulled the 2003 computer, and am headed out into the cold to pull the one from the 2004. If the part numbers match, we'll have a relatively (30 minutes) quick answer

Mark

 

OK, they're not the same, 89661-04B30 for the 2.7l 2004 Prerunner Auto, and 89661-0y080 for the 2003 2.7l PreRunner Auto.

I guess it's now a matter of finding a 89661-0y080 one that's not going to break the bank at this time of year....

Mark

 

A voice in my head told me to replace the ECT before throwing any more money at this. I just remembered that with my volvo S40, that the same codes used to pop up if either the thermostat or ECT wasting within spec.

I'll update once my lazy-ass sone swaps that out.

Mark

 

Good thing to check. I've seen this with a failing ECT (the one with two wires). The ECT didn't recognize the engines was warm and sent too much fuel to a warm engine causing a mild case of flooding.

 

Before you replace this one why don't you test it first

 

Change the spark plugs if you haven't already. Might be that simple.

 

Awesome! Thanks! The part's cheap, but my time isn't. I tell my son that time is cheap and money is expensive when you're young, but when you're older, money is cheap, and time is expensive. Since I'm doing most of the work, time is worth gold to me!!!

Mark

 

So I tested the Engine Coolant temp sensor (not easy to get at if you have large hands) and it was bad, so I replaced it, reset the computer and went on a 45-mile, back road adventure. I stopped once for fuel, again for a Slim Jim and a bag of chips. I also stopped and waited for 3 Led Zeppelin tunes to play though when parked and ignition off. Not one issue

I get home...nervously awaiting any issue, drink a beer and waited 15 minutes and.....random misfire. At his point all that's left are the other three injectors and the computer. I've already officially replaced every sensor in the engine compartment and the upstream O2 sensor. I only have the vacuum from the fuel pressure regulator, and the brake booster. All other vacuum lines are capped.

Any good places to buy a set of injectors? I found a known good computer, so might as well grab that this week.

Mark

 

Unfortunately injectors are not cheap. I mean you can buy cheap stuff but they are not good injectors, just a china crap not even worth a test.

Do you have EGR? Maybe this is getting stuck. I really can't think of a good testing procedure. The ECM does not tell you much and because of the nature of the fault it is not simple to replicate. Maybe plug in the ODBII monitoring will shine some light. ECM in 1st gen does not show to much in live data, but maybe one of these parameters would stand out. Guessing at this point.

 

Yeah, around 200 dollars for injectors at reputable shops is the norm. That's totally OK by me, because I have better things to do with my time than dick around with this issue. EGR COULD cause these symptoms, but I deleted the EGR in 2013 when it went bad.

I'm ordering injectors, a fuel pressure regulator, fuel pump and fuel filter. I pick up the known good computer this week, and once installed, everything relevant to fuel, intake, ignition, controls and exhaust will have been replaced. The only thing left is the wiring harness and long-block, which runs GREAT when it runs.

Mark

 

SO I got it running fine! Thought I'd circle back and list the diagnosis and outcome.

It was a virtually perfect storm of smaller issues of neglect that built up to failure:

1. Bad plugs (gap was HUUUUGE)
2. Bad plug contact wires
3. Bad plug boots
4. bad Engine coolant temp sensor
5. Vacuum leak from Evap hose to intake
6. Three dried out injector lower-seals
7. One bad injector (partially clogged)
8. Upstream O2 sensor not reading correctly (tested with known good swap)
9. Dirty MAF sensor (NASTY, son uses oiled paper-cone filter)

In addition to the parts above, I ended up buying MotorWest injectors to have a matched set instead of mix-and-match 250,000 mile units.

Truck runs GREAT! better fuel economy, more power and smoother running. Pain in the ass to diagnose, so I thought that I'd share in case someone else has similar issues.

Mark