Intermittent loss of power

My son has an 08 6 cylinder TRD. The truck has times of an intermittent loss of power, slow acceleration, runs rough, and the CEL light flashes. If you turn the truck off and immediately turn it back on, the check engine light is gone and the truck runs smoothly. It can run for quite a while with no issues or have multiple issues in a day. The first time I checked the code it stated cylinder misfire 2 & 5. We changed both of those coil packs, as well as new ngk plugs, and mass air flow sensor. The next time it occurred the OBD said random cylinder misfire but then listed all cylinders. We then replaced all coil packs to no avail. We then took it to Dealer #1 and explained the situation, all they did was swap the coil packs around and said the problem did not return, but again, if you turn the truck off and turn it on, it resets and runs fine
Since that time we've also checked all electrical connections to which we could get access and sprayed them with electrical cleaner as well as checked all fuses. There is no rhyme nor apparent cause as this occurs very intermittently. Recently, we waited for the engine light to flash and loss of power to occur and immediately took it to Dealer #2. Gave them the history of all that was done and asked for a diagnostic of the ecu. They obviously found the random cylinder misfire and stated we needed to change the coil packs with OEM Toyota and stated the ECU seems healthy but, they did not run the ECU diagnostic, given the codes. I've talked with 5 mechanics and one computer tech and they all concur that it is either an electrical or an ECU issue. Looking for anyone who has experienced the same issue. Obviously dealers are of no use. Thanks

 

How many miles? I'm guessing your fuel pump is failing. Killing it and restarting the engine is just giving it time to catch up. I'd check fuel pressure first and see. If that looks good, I've seen O2 sensor go bad but never throw a code, but it's rare.

 

It has 125k. There has never been an issue with it starting. Thanks

 

Welcome to TW, it sounds like an electrical issue to me, possibly an intermittent short circuit. I had a 2008 Tundra that would run great and then suddenly lose power and die, damn near all of the lights on the dash would flash, I would turn the key to off and then restart and it would run fine again. Never found out what was wrong with it, only did it 3 times in 5 years.

 

We are suspecting an electrical or an ECU issue. Three times in five years isn't bad No other signs of electrical as radio, lights etc. are not affected? Thanks

 

I don’t remember any other symptoms. I sold the Tundra over a year ago.

 

That age and those miles, to complement your comment, that fuel filter is saturated.


Also check all vacuum hoses for split ends and leaks.

 

Are there bubbles in the radiator over flow container while idling or revving?

 

Sounds like a bad ground whip out your scope on a rope and chase it down.

 

Can't comment on the ECU, but 125k seems too low for that to go bad already.

You might want to keep a log of conditions when the erratic problems return. Log anything that you.feel might contribite to the error comdition.

Things like himidity, temperature can affect electric connections, and clear up as the weather, humidity changes.
Other thoughts: how the engine or orther systems were running prior to trouble, road conditions, was Aunt Bertha aleays sitting in the right rear seat, etc....

Look at all of your grounds (again) for corrosion, wiggle these, or better yer, disconnect, scuff to bare metal, put a dab of corrosion inhibitor, and reconnect. Pull your relays and check for corrosion, cracks, or other tell-tale signs (discolored, dried water spots).

Electric issues can manifest in a lot of not so obvious ways, and can bevery difficult to track down. Eventually, you might find a pattern that may lead you dpwn the.path to the resolution.

Good luck, can't wait to hear what the cause was.

 

I just like to rule out the easy stuff on these intermittent problems so that it doesn't come back and bite me. Not that it ever has... It may start fine with a failing fuel pump, but not able to provide the needed pressure/flow for the injectors while accelerating and under a load.

I wouldn't rule out O2 sensors. If they are cheap enough, I would replace the primary's, the secondary's shouldn't matter. With 125K they really need to be changed anyway.

It could be a bad connection, but bad grounds and connections generally don't go away with a key cycle.

ECU's are generally reliable but, if they are bad, they are a pain to diagnose. You will not get the dealer to say you need an ECU, because they are hard to nail down as the problem and are expensive. It's easier to tell the customer that they don't know what your problem is, than "here's a $2500 bill with an ECU that didn't fix your problem".
I have replace 5 ECUs in construction equipment over the last 8-9 years, not one of them would the manufacture admit that the problem could be in the ECU even after hours of trouble shooting.

This.

 

We've had the same mechanic for a number of years and I've always found him to be very honest and very reliable. In a recent conversation he told me he went over the truck with a "fine tooth comb" and, the only sensor that has not been replaced is the crankshaft sensor and he has never seen one present these problems and reset when an engine is turned off and back on again. He also said he checked fuel pressure and the fuel pump. Since my last post I've had a conversation with the dealership Service Manager who was consulting with his tech. He said they are 100% sure the ECU is fine as they were able to communicate with the ECU and get the random cylinder misfire without the CEL on and the problem occurring. He stated if there was a problem with the ECU they would not be able to do that nor communicate with it? They are adamant it is the coil packs as he said when they swapped the coil packs it followed the same two packs. My mechanic said that when he initially swapped two coil packs that were kicking the cylinder misfire code, the same thing occurred and he replaced them. When the problem persisted we then replaced all the coil packs. I have been told there could be a fault in a specific driver of the ECU which could cause an intermittent issue. I've also been told that if it were a bad coil pack(s), it or they would not reset by turning the ignition off and on. Thanks

 

Like I said, the dealer will never admit that the ECU may be bad. And no, just because you can plug into it and communicate with it, doesn't mean it's good to go. ECU are complex with circuitry, diode, resistors, capacitors, etc. One hairline crack in the board can cause shorts, sometimes they work great cold but as it gets hotter, it will start failing. They can also have software glitches as well, just like a computer.

I worked on a brand spanking new 65ft man lift this year that had a bad ECU. Would sometimes lockup on startup and wouldn't responded to anything. Only way to reset it, is to disconnect the battery for 30 seconds. After that it would work for the rest of the day, as long as you didn't shut it off. After 15+ hours of troubleshooting, everything pointed to the ECU. The manufacture had me replace $2500 worth of wiring harness's, sensors and update the software with no luck. I told them it was the ECU, but they would not admit it or authorize it. My boss told them to come fix it, if they wouldn't authorize the purchasing of an ECU. Can you guess what they did to fix it?

If your misfire is following the same coils, it is your coils. But sounds like your mechanic is giving you a different story than the dealer. Also, you said you had a code for random misfires on all cylinders. Without seeing a wiring schematic, it could possibly be in the wiring from the coils to the ECU. Finding a used wire harness at a junkyard may be worth a try. If you think that you and your mechanic has exhausted all the possibilities. I'd start calling around to your local junkyards and try to find an ECU that matches your year, engine, and trim model. I'm not sure if it is plug and play though, so I'd make sure that they will allow for returns.

Let us know how it turns out. Best of luck!

Andrew.

 

Yeah, a good friend who taught auto mechanics said the same thing about ECU & computer issues as did a buddy who is a computer guru and tinkers with cars. At this point going back to the dealer to have them run a diagnostic on the computer, at least I'll know one way or the other. If that's it and it can be reflashed or replaced great, if not we'll follow some of the words of wisdom others have shared. While I am not mechanical, I can and do think logically so...Anymore thoughts are appreciated. Thanks