3.4 unplugged

Hey people. I just joined this forum. I have a great '96 4x4 Tacoma 3.4 that I've had for about 9 years. It just passed 300,000 miles, and is usually a reliable workhorse. It has an issue that it temporarily had over a year ago, somehow stopped misbehaving, then just came back today. After driving on the highway at moderate speed (65 or so), for about an hour, it shuts down. Period. It just shuts down like someone unplugged it. After resting for five minutes or so, it starts up fine and runs for a while longer before repeating the offense. Once the issue starts, it'll do it even at lower speeds on back roads. It does eventually get me home (I live in the mountains in Colorado), but it's a major inconvenience, especially if I go to a bigger town like Pueblo, where it does the same thing in traffic. I get no dashboard malfunction light at all, not even a cylinder malfunction (like the typical cylinder 3 malfunction code when that coil goes bad). I'm thinking it might be a vacuum issue, especially because I go up and down elevations over a thousand feet on a regular basis, so relative pressure changes. I looked at all of the hoses during one of the rest periods today, and everything appears to be in place. I will add that I changed the air filter today before the problem recurred. It hasn't done it in a long while, including while going over La Veta pass and back every day for three weeks strait earlier this year. It seems like it was happier with a dirty air filter, so running lean. Any ideas? Most of these wacky glitches are odd but pretty simple once someone figures out the problem (like the vacuum "ticking" issue which has nothing to do with lifters or valves). As an added bit of evidence, today was the first time I tried to notice any specific pattern to it's behavior, other than being concerned with the possibility of a long walk, since it started on the dirt roads up the mountain towards home (so not concerned with fast traffic flying past me). As long as I didn't throttle up over 1,000rpm, it wouldn't completely shut down. If I tried to drive it even at low speed, it bogs down at the least bit of throttle. Anyway, that's a detailed description of what it's doing. Any suggestions or ideas will be appreciated. I'll throw in my experiences and help in return (like the easy alternator replacement I put together from a couple of other video tutorials). Thanks in advance for any suggestions.

 

Check the fuel system. Make sure your Open Circuit Relay is in good condition (there are multiple threads on how to test relays) the OCR relay powers your fuel pump. The fuel pump itself could also be faulty. Also see if you suspect the fuel filter hasn't been changed in a while (or ever) you can change that out too. May be clogged and is poorly delivering fuel to your engine. Fuel injectors can also clog and cause engines to shut off. An ignition switch can also be to blame for fuel system issues as well.

It could also be your spark plugs/coils, check those out.

Check the MAF sensor.

Check the alternator and its connections.

Lastly, rent out a compression test kit from Autozone or Pepboys. And run a test. It's really easy to do and there are plenty of videos on YouTube to show you how to run compression tests. The engine is really old so it could be losing a lot of compression

 

Do you lose all electrical power, headlights, dash lights, etc? Or is it just the engine dying?

It sounds like you could have a bad cable connection at the battery. Corrosion or clamp not tight. Or a bad ground. Check the ground from negative battery to fender and the ground from engine to firewall.

 

Adding to what G59 said, since the Mass Air Flow (MAF) is near the air filter, and you recently changed the air filter, maybe some debris found its way onto the MAF. You could try the MAF cleaner. You might also be able to find another toyota/lexus for a temproary MAF swap (my '99 es300 had the same part number as my 2000 tacoma). Worth noting, if the MAF was the issue I would think you would get a code.

 

Thanks for the replies. I'll try the suggestions. One thought I had was it might be on the fuel supply side. Does the gas filler cap vent to atmosphere? I can't tell be visually inspecting it, but there's no pressure or vacuum release when I open it during these episodes. We live on dirt roads 7 miles to pavement, so filters get replaced often, but there could be a clog somewhere. I replaced the fuel filter and fuel pump about a year and a half ago. The coils, plugs, and wires are about a year old (I got the check engine light and code for cylinder three then replaced them all). Battery terminals are clean, and battery less than two years old. Ground wires are in place. I replaced the main fuse when changing the alternator last fall. Even when it's not acting up (as I mentioned, the problem hasn't happened in over a year), there is sometimes a slight gasoline smell when I stop which I can't locate. Opening the hood to inspect never reveals gasoline or the smell. It has no obvious leak that I have been able to locate under the truck, but fumes do sometimes escape. It could be between the pump and engine compartment, but nothing is ever wet. The roads (and vehicles) up here are really dusty, so anything wet (fuel or whatever) would be obvious. Anyway, I'll do more diagnostics this morning and keep the group posted. ...a friend up here has both a '96 4Runner and '99 Tacoma with the 3.4, so might let me borrow his MAF, but there hasn't been a code alert at all, which is part of the mystery. ....I haven't tested compression, but it's not as new with over 3000,000 miles. Renting the tester is a good idea, but I wonder if low compression would display the problem more than intermittently. It's worth looking into.

 

Something about this just screams fuel issue. You can actually test your injectors too to see if theyre running properly. Also, consider that when engines heat up they expand. So its possible while your engine is still climbing up to operating temp a possible gap between the block and head(s) may only expand and open one the engine is fully heated up and cause compression loss

 

I looked into Open Circuit Relay for this series of trucks on youtube, and one video has the guy checking/replacing the EFI relay, which caused a similar issue. He swapped the EFI relay with the identical tail light relay and his fuel supply issue stopped (and had intermittent issues with his tail lights, evidence to the relay being on it's way out). Later, he tried replacing the Toyota OEM relays with Denso units, but it didn't work... testing the original good relay, the primary tested 90 ohms, and the Denso ones 110. On my truck, someone replaced both relays with Bosch units, with both reading 78 ohms right now. I'm still looking for what the main reading should be for the Circuit Opening relay. I don't see it in my Haynes manual. The manual does show it's location under the dash. Another post on this forum was a person who couldn't locate the relay. You have to take the lower dash panel off to access it, but it's there. In the meantime, I have one ordered from O'Reilly Auto parts that will be in the closest real town (Alamosa, CO) tomorrow... I'm going to replace the fuel filter again for good measure, although it's less than two years old old. As a heads up for anyone who might be having similar issues, the circuit opening relay is about $80, and the EFI relay is around $30. I'll keep reporting what I find.

 

when you check for codes is a P1000 reported and / or are the readiness monitors reset. If they are you are loosing power to the PCM, both switched and constant. I would start with a cleaning of the battery terminals and cables... keep it simple.

 

Please do! I'm curious as to what ends up being the problem

 

@G59, Wife had to go to Alamosa today anyway, so she's picking up the relays, filter, and MAF cleaner. I'll let you know how things turn out. @Glamisman, I don't get any error codes, and the battery terminals were clean (negative is removed at the moment for the service) and battery a year old/checks good. Thanks for the reminders.

 

....picking up the parts isn't around the corner... Alamosa is an hour away.

 

The new relays are installed, and I cleaned the MAF sensor. I haven't yet replaced the fuel filter (although the new replacement is in hand), since it's only a year and a half old. I did the test drive down to town and the liquor store, 20 minutes each way, and the truck ran great. The disclaimer I'm adding is that the issue has been intermittent (and not appearing at all for over a year) other than stalling more often a couple of days ago. I'll give it an hour plus run tomorrow to see how it's reacting. Replaced parts: the EFI relay, and the COR (relays impacting the fuel system), plus cleaning of the MAF sensor with dedicated MAF sensor spray. I cleaned and lubed the battery posts as good measure, since the negative post was disconnected anyway. As a "DUH!" expose', while I'm not a mechanic, and didn't know what a Mass Air Flow sensor was a couple of days ago, I was prepared to purchase a new one a couple of days ago. Research following a reply here (thank you!!!), the sensor can and should be cleaned somewhat regularly, especially in dusty dirty driving conditions. Our situation is exactly that., since we're 7 miles to pavement. Tomorrow's longer drive hopefully will be event free.

 

Awesome dude im glad to hear its running smoothly so far. Update again tomorrow after that long drive! And its all good, after regular maintenance and little repairs like this you learn a lot. I didnt know what a MAF sensor was when I first bought my truck 3 years ago and now im doing major suspension upgrades and heavy maintenance all by myself in my garage haha

 

300K ? Might be time for these.....
https://www.amazon.com/Ignition-1996-02-1995-1998-1995-2004-2000-2004/dp/B07CNJX3WV

 

So far, so good. Since it has been an intermittent problem, I'll post if it stalls again. @Frito, I replaced the coils, plugs and wires not terribly long ago- at about 285,000 miles. When the coil on cylinder 3 malfunctions (that's the one that usually fails, as the best mechanic I know told me even before he put his reader on it) , the engine misfires, does not die, the "check engine" light comes on, and you get a code. As I mentioned, I've never gotten a code with this issue. But thanks for the thought. Thanks everyone who made suggestions.

 

....as another "Duh" thing, the Bosch relays ARE Toyota original parts. Toyota is stamped on the side of them, not on the top with Bosch and the pin diagram. Denso supplies some electrical parts, but not in this case. I learned something new yesterday.

 

Here is a cheap OEM MAF sensor, probably worth having one on hand. I always keep a new one in the garage for troubleshooting. I also clean mine every oil change, keeps the throttle responsive.

https://www.ebay.com/ulk/itm/264206881320

 

Yeah I thought the same thing when I looked at my relays a while back. Was wondering why they all got replaced by Bosch ones lol

 

After a longer drive with no problems, it did it again yesterday. I'll change the fuel filter since I have it in hand then report ....the fuel smell was the gas cap. A good one has two gaskets, and one on them on mine was badly split.